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The Origin of Species
I?
Charles Darwin
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THE HARVARD CLASSICS
KDITBD BY CHARLES W ELIOT LLD
THE ORIGIN OF SPECIES
BY
CHARLES DARWIN
WITH INTRODUCTIONS. NOTES
AND ILLUSTRATIONS
P F COLLIER & SON
NEW YORK
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By P. F. Colli SK & Son
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'^ut with regard to the material world, we can at
least go 8o far as this — ^we can perceive that events are
brought about not by insulated interpositions of Divine
power, exerted in each particular case, but by the estab-
lishment of general laws/'
Whewell: Bridgewater Treatise.
"The only distinct meaning of the word 'natural' is
stated, fixed or settled; since what is natural as much
requires and presupposes an intelligent agent to render
it so, i.e., to effect it continually or at stated times, as
what is supernatural or miraculous does to effect it for
once."
BuTLEB: Analogy of Revealed Religion.
"To conclude, therefore, let no man out of a weak con-
ceit of sobriety, or an ill-applied moderation, think or
maintain, that a man can search too far or be too well
studied in the book of God's word, or in the book of
God's works; divinity or philosophy; but rather let men
endeavour an endless progress or proficienoe in both."
Bacx)N: Advancement of Learning.
Doum, Beckenham, Kent,
First Edition, November 2ith, 1859.
Siath Edition, January, 1872.
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CONTENTS
PAGE
EDITOR'S INTRODUCTION 5
AN HISTORICAL SKETCH
Op thb PRO6RBS8 OP Opinion on thb Origin op Spbcibb 9
INTRODUCTION 3X
CHAPTER I
Variation undbr Domestication 25
CHAPTER II
Variation xtnder Naturb 58
CHAPTER III
Struggle por Existence 76
CHAPTER IV
Natural Sblbction; or the Survival op the Fittest 93
CHAPTER V
Laws op Variation 145
CHAPTER VI
Dippicultibs op thb Thbory 178
3
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4 CONTENTS
CHAPTER VII PAoi
Miscellaneous Objections to the Theory op Natuilal
Selection 2x9
CHAPTER VIII
Instinct 26a
CHAPTER IX
Hybridism 298
CHAPTER X
On the Imperfection op the Geological Rbcord . 333
CHAPTER XI
On the Geological Succession op Organic Bbinqs . 364
CHAPTER XII
Geographical Distribution 395
CHAPTER XIII
Geographical Distribution — continued .... 427
CHAPTER XIV
Mutual Affinities op Organic Beings: Morphology:
Embryology: Rudimsntary Organs . . ' . . 450
CHAPTER XV
Recapitulation and Conclusion 499
GLOSSARY 531
INDEX 541
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INTRODUCTORY NOTE
Charles Robekt Darwin, horn at Shrewsbury, England, on
February 12, 1809, came of a family of remarkable intellectual
distinction which is still sustained in the present generation. His
father was a successful physician with remarkable powers of
observation, and his grandfather was Erasmus Darwin, the well-
known author of "The Botanic Garden." He went to school at
Shrewsbury, where he failed to profit from the strict classical
curriculum there in force; nor did the regular professional
courses at Edinburgh University, where he spent two years study-
ing medicine, succeed in rousing his interest. In 1827 he was
entered at Christ's College, Cambridge, to study for the B. A.
degree, preparatory to entering the Church; but while there
his friendship with Henslow, the professor of botany, led to his
enlarging his general scientific knowledge and finally to his
joining the expedition of the "Beagle*' in the capacity of natural-
ist. From this Darwin returned after a voyage of five years
with a vast first-hand knowledge of geology and Moology, a
reputation as a successful collector, and, most important of all,
with the germinal ideas of his theory of evolution. The next
few years were spent in working up the materials he had col-
lected; but his health gave signs of breaking, and for the rest
of h*s life he suffered constantly, but without complaint. With
extraordinary courage and endurance he took up a life of
seclusion and methodical regularity, and accomplished his colossal
results in spite of the most severe physical handicap. He had
married in 1839, and three years later he withdrew from London
to the little village of Down, about sixteen miles out, where he
spent the rest of his life. His custom, which was almost a
method, was to work till he was on the verge of complete collapse,
and then to take a holiday fust sufficient to restore him to working
condition.
As early as 1842 Darwin had thrown into rough form the out-
lines of his theory of evolution, but the enormous extent of the
investigations he engaged in for the purpose of testing it led
to a constant postponing of publication. Finally in June, 1858,
A- R, Wallace sent him a manuscript containing a statement
of an identical theory of the origin of species, which had been
5
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6 INTRODUCTORY NOTE
arrived at entirely independently. On the advice of Lyell, the
geologist, and Hooker, the botanist, Wallace's paper and a letter
of Darwin's of the previous year, in which he had outlined his
theory to Asa Gray, were read together on July i, 1858, and
published by the Linnaan Society, In November of the follow-
ing year "The Origin of Species" was published, and the great
battle was begun between the old science and the new. This
work was followed in 1868 by his "Variation of Animals and
Plants under Domestication/* that in turn by the "Descent of
Man*' in 1871, and that again by "The Expression of the Emo-
tions in Man and Animals/* Each of these books was the elabo-
ration or complement of a section of its predecessor. The later
years of Darwin's life were chieHy devoted to botanical research,
and resulted in a series of treatises of the highest scientific value.
He died at Down on April ig, 1882, and is buried in Westminster
Abbey,
The idea of the evolution of organisms, so far from origincUing
with Darwin, is a very old one. Glimpses of it appear in the
ancient Greek philosophers, especially Empedocles and Aristotle;
modern philosophy from Bacon onward shows an increasing
definiteness in its grasp of the conception; and in the age pre-
ceding Darwin's, BuWon, Erasmus Darwin, and Lamarck had
given it a fairly concrete expression. As we approach the date
of the publication of "The Origin of Species^* adherence to the
doctrine not only by naturalists but by poets, such as Godhe,
becomes comparatively frequent; and in the six yeats before the
joint announcement of Darwin and Wallace, Herbert Spencer
had been supporting and applying it vigorously in the field of
psychology.
To these partial anticipations, however, Darwin owed little.
When he became interested in the problem, the doctrine of the
fixity of species was still generally held; and his solution occurred
to him mainly as the result of his own observation and thinking.
Speaking of the voyage of the "Beagle,** he says, "On my return
home in the autumn of 1836 I immediately began to prepare my
journal for publication, and then saw how many facts indicated
the common descent of species. ... In July (1837) I opened
my first note-book for facts in relation to the Origin of Species,
about which I had long reflected, and never ceased working for
the next twentv years. . . . Had been greatly struck from about
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INTRODUCTORY NOTB 7
the month of previous March on character of South American
fossils, and species on Galapagos Archipelago, These facts
(especially latter) origin of all my views/' Again, "In October
(1838), that is fifteen months after I had begun my systematic
inquiry, I happened to read for amusement 'Malthus on Popu-
lation/ and being well prepared to appreciate the struggle for
existence which everywhere goes on from long-continued ob-
servation of the habits of animals and plants, it at once struck me
that under these circumstances favorable variations would tend
to be preserved, and unfavorable ones to be destroyed. The
result of this would be the formation of new species. Here
then I had at last got a theory by which to work."
From these statements by Darwin himself we can see how far
it is from being the case that he merely gathered the ripe fruit
of the labors of his predecessors. All progress is continuous,
and Darwin, like other men, built on the foundations laid by
others; but to say this is not to deny him originality in the only
vital sense of that word. .And the importance of his contribution
— in verifying the doctrine of descent, in interpreting and apply-
ing it, and in revealing its bearings on all departments of the
investigation of nature — is proved by the fact that his work
opened a new epoch in science and philosophy. As Huxley said,
"Whatever be the ultimate verdict of posterity upon this or that
opinion which Mr. Darwin has propounded; whatever adumbra-
tions or anticipations of his doctrines may be found in the writ-
ings of his predecessors; the broad fact remains that, since the
publication and by reason of the publication of 'The Origin of
Species' the fundamental conceptions and the aims of the students
of living Nature have been completely changed."
The present year (1909) has seen the celebration of the hun-
dredth anniversary of Darwin's birth and the fiftieth anniversary
of the publication of his great work. Among the numerous ex-
pressions of honor and gratitude which the world of science has
poured upon his memory, none is more significant than the vol-
ume on "Darwin and Modern Science" which has been issued by
the press of his old University of Cambridge. In this are col-
lected nearly thirty papers by the leaders of modem science
dealing with the influence of Darwin upon various fields of
thought and research, and with the later developments and modi-
fications of his conclusions. Biology, in many different depart-
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8 INTRODUCTORY NOTE
ments. Anthropology, Geology, Psychology, Philosophy, Soci-
ology, Religion, Language, History, and Astronomy are all repre-
sented, and the mere enumeration suggests the colossal nature
of his achievement and its results.
Yet the spirit of the man was almc^t as wonderful as his work.
His disintereistedness, his modesty, and his absolute fairness
were not only beautiful in themselves, but remain as a proof of
the importance of character in intellectual labor. Here is his
own frank and candid summing up of his abilities: "My success as
a man of science, whatever this may have amounted to, has been
determined, as far as I can judge, by complex and diversified
mental qualities and conditions. Of these, the most important
have been — the love of science — unbounded patience in long re-
flecting over any subject— industry in observing and collecting
facts—and a fair share of invention as well as of common sense.
With such moderate abilities as J possess, it is truly surprising
that I should have influenced to a considerable extent the belief
of scientific men on some important points,'*
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AN HISTORICAL SKETCH
OF THE PROGRESS OF OPINION ON
THE ORIGIN OF SPECIES
PREVIOUSLY TO THE PUBLICATION OF
THE FIRST EDITION OF THIS WORK
I WILL here give a brief sketch of the progress of opinion oh
the Origin of Species. Until recently the great majority of
naturalists believed that species were immutable productions,
and had been separately created. This view has been ably
maintained by many authors. Some few naturalists, on the
other hand, have believed that species undergo modification,
and that the existing forms of life are the descendants by
true generation of pre-existing forms. Passing over allu-
sions to the subject in the classical writers,* the first author
who in modern times has treated it in a scientific spirit was
Buffon. But as his opinions fluctuated greatly at different
periods, and as he does not enter on the causes or means of
the transformation of species, I need not here enter on
details.
*Ari8totl«| in his ' Physics Autcultationes ' (lib. 2, cap. 8, s. 9), after
remarking that rain does not fall in order to make the corn grow, any more
than it tails to spoil the farmer's corn when threshed out of doors^ applies
the same argument to organisation; and adds (as translated by Mr. Clair
Grece, who first pointed out the passage to me), "So what hinders the dif-
ferent parts [of the body] from having this merely accidental relation in
nature? as the teeth, for example, srow by necessity, the front ones sharp,
adapted for dividing, and the grinaers flat, and serviceable for masticating
the food; since they were not made for the sake of this, but it was the
result of accident. And in like manner as to the other parts in which there
appears to exist an adaptation to an end. Wheresoever, therefore, all things
together (that is all the parts of one whole) happened like as if they were
made for the sake of something, these were preserved, having been appro-
priately constituted by an internal spontaneitv: and whatsoever things were
not thus constituted, perished, and still perish.*' We here see the principle
of natural selection uiadowed forth, but how little Aristotle fully compre-
hended the principle, is shown by his remarks on the formation of the teeth.
9
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10 HISTORICAL SKETCH
Lamarck was the first man whose conclusions on the
subject excited much attention. This justly-celebrated nat-
uralist first published his views in 1801 ; he much enlarged
them in 1809 in his Thilosophie Zoologique/ and subse-
quently, in 1815, in the Introduction to his 'Hist. Nat. des
Animaux sans Vertebres.' In these works he upholds the
doctrine that species, including man, are descended from
other species. He first did the eminent service of arousing at-
tention to the probability of all change in the organic, as well
as in the inorganic world, being the result of law, and not of
miraculous interposition. Lamarck seems to have been chiefly
led to his conclusion on the gradual change of species, by the
difficulty of distinguishing species and varieties, by the almost
perfect gradation of forms in certain groups, and by the
analogy of domestic productions. With respect to the means
of modification, he attributed something to the direct action
of the physical conditions of life, something to the crossing of
already existing forms, and much to use and disuse, that is,
to the effects of habit. To this latter agency he seems to
attribute all the beautiful adaptations in nature ; — such as the
long neck of the giraffe for browsing on the branches of
trees. But he likewise believed in a law of progressive de-
velopment; and as all the forms of life thus tend to progress,
in order to account for the existence at the present day of
simple productions, he maintains that such forms are now
spontaneously generated.*
Geoffroy Saint-Hilaire, as is stated in his 'Life,' written
by his son, suspected, as early as 1795, that what we call
species are various degenerations of the same type. It was
* I have taken the date of the first jpublication of Lamarck from laid.
Geoffroy Saint-Hilaire's (* Hist. Nat. Ginirale,' torn, ii, p. 405, 1859)
excellent history of opinion on this subject. In this work a full account is
given of Buffon's conclusions on the same subject. It is curious how largely
my grandfather, Dr. Erasmus Darwin, anticipated the views and erroneous
grounds of opinion of Lamarck in his ' Zoonomia ' (vol. i. pp. 500-510), pub-
shed in 1794. According to Isid. Geoffroy there is no doubt that Goethe
was an extreme partisan of similar views, as shown in the Introduction to a
work written in 1794 and 1795, but not published till long afterwards: he
has pointedly remarked (' Goethe als Naturforscher,* von Dr. Karl Meding,
s. 34) that the future question for naturalists will be bow, for instance,
cattle got their horns, and not for what they are used. It is rather a singu-
lar instance of the manner in which similar views arise at about the same
time^ that Goethe in Germany, Dr. Darwin in England, and Geoffroy Saint-
Hilaire (as we shall immediately see) in France, came to the same conclu-
sion on the orij^n of species, in the years 1794-5.
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HISTORICAL SKETCH 11
not until 1828 that he published his conviction that the same
forms have not been perpetuated since the origin of all
things. Geoffroy seems to have relied chiefly on the condi-
tion of life, or the "monde ambiant" as the cause of change.
He was cautious in drawing conclusions, and did not believe
that existing species are now undergoing modification; and,
as his son adds, "C'est done un probleme a reserver
entierement 4 Tavenir, suppos6 meme que Tavenir doive avoir
prise sur lui."
In 1813, Dr. W. C. Wells read before the Royal Society
'An Account of a White female, part of whose skin re-
sembles that of a Negro'; but his paper was not published
until his famous ' Two Essays upon Dew and Single Vision'
appeared in 1818. In this paper he distinctly recognises the
principle of natural selection, and this is the first recognition
which has been indicated ; but he applies it only to the races of
man, and to certain characters alone. After remarking that
negroes and mulattoes enjoy an immunity from certain trop-
ical diseases, he observes, firstly, that all animals tend to vary
in some degree, and, secondly, that agriculturists improve
their domesticated animals by selection; and then, he adds,
but what is done in this latter case "by art, seems to be done
with equal efficacy, though more slowly, by nature, in the
formation of varieties of mankind, fitted for the country
which they inhabit Of the accidental varieties of man,
which would occur among the first few and scattered inhab-
itants of the middle regions of Africa, some one would be
better fitted than the others to bear the diseases of the coun-
try. This race would consequently multiply, while the others
would decrease; not only from their inability to sustain the
attacks of disease, but from their incapacity of contending
with their more vigorous neighbours. The colour of this
vigorous race I take for granted, from what has been already
said, would be dark. But the same disposition to form varie-
ties still existing, a darker and a darker race would in the
course of time occur: and as the darkest would be the best
fitted for the climate, this would at length become the most
prevalent, if not the only race, in the particular country in
which it had originated." He then extends these same views
to the white inhabitants of colder climates. I am indebted
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12 HISTORICAL SKETCH
to Mr. Rowley, of the United States, for having called my
attention, through Mr. Brace, to the above passage in Dr.
Wells' work.
The Hon. and Rev. W. Herbert, afterwards Dean of Man-
chester, in the fourth volume of the 'Horticultural Trans-
actions,' 1822, and in his work of the 'Amaryllidaceae'
(1^37* PP- i9> 339) » declares that "horticultural experiments
have established, beyond the possibility of refutation, that
botanical species are only a higher and more permanent class
of varieties," He extends the same view to animals. The
Dean believes that single species of each genus were created
in an originally highly plastic condition, and that these have
produced, chiefly by intercrossing, but likewise by variation,
all our existing species.
In 1826 Professor Grant, in the concluding paragraph in
his well-known paper ('Edinburgh Philosophical Journal,*
vol. xiv. p. 283) on the Spongilla, clearly declares his belief
that species are descended from other species, and that they
become improved in the course of modification. This same
view was given in his 55th Lecture, published in the ' Lancet '
in 1834.
In 1831 Mr. Patrick Matthew published his work on 'Naval
Timber and Arboriculture,' in which he gives precisely the
same view on the origin of species as that (presently to be
alluded to) propounded by Mr. Wallace and myself in the
'Linnean Journal,' and as that enlarged in the present volume.
Unfortunately the view was given by Mr. Matthew very brief-
ly in scattered passages in an Appendix to a work on a differ-
ent subject, so that it remained unnoticed until Mr. Matthew
himself drew attention to it in the 'Gardener's Chronicle,* on
April 7th, i860. The differences of Mr. Matthew's view from
mine are not of much importance : he seems to consider that
the world was nearly depopulated at successive periods, and
then re-stocked; and he gives as an alternative, that new
forms may be generated " without the presence of any mould
or germ of former aggregates." I am not sure that I under-
stand some passages; but* it seems that he attributes much
influence to the direct action of the conditions of life. He
clearly saw, however, the full force of the principle of natural
selection.
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HISTORICAL SKETCH 13
The celebrated geologist and naturalist, Von Buch, fai his
excellent 'Description Physique des Isles Canaries' (1836,
p. 147), clearly expresses his belief that varieties slowly be^
come changed into permanent species^ which are no longer
capable of intercrossing.
Rafinesque, in his 'New Flora of North America,' pub«
lished in 1836, wrote (p. 6) as follows : — " All species might
have been varieties once, and many varieties are gradually
becoming species by assuming ccHistant and peculiar charac-
ters;" but farther on (p. 18) he adds, "except the original
types or ancestors of the gemts."
In 1843-44 Professor Haldeman (' Boston Journal of Nat.
Hist. U. States,' vol. iv. p. 468) has ably given the arguments
for and against the hypothesis of the development and modi-
fication of species: he seems to lean towards the side of
change.
The 'Vestiges of Creation' ai^ared in 1844. In the tenth
and much improved edition (1853) the anonymous author
says (p. 155) : — ''The proposition determined on after much
consideration is, that the several series of animated beings,
from the simplest and oldest up to the highest and most re-
cent, are, under the providence of God, the results, first, of an
impulse which has been imparted to the forms of life, ad-
vancing them, in definite times, by generation, through grades
of organisation terminating in the highest dicotyledons and
vertebrata, these grades being few in number, and generally
marked by intervals of organic character, which we find to
be a practical difficulty in ascertaining affinities; second, of
another impulse connected with the vital forces, tending, in
the course of generations, to modify organic structures in
accordance with external circumstances, as food, the nature
of the habitat, and the meteoric agencies, these being the
'adaptations' of the natural theologian." The author ap-
parently believes that organisation progresses by sudden
leaps, but that the effects produced by the conditions of life
are gradual. He argues with much force on general grounds
that species are not immutable productions. But I cannot see
how the two supposed "impulses" account in a scientific
sense for the numerous and beautiful co-adaptations which
we see throughout nature; I cannot see that we thus gain
A— HCXI
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14 HISTORICAL SKETCH
any insight how, for instance, a woodpecker has become
adapted to its peculiar habits of life. The work, from its
powerful and brilliant style, though displaying in the earlier
editions little accurate knowledge and a great want of
scientific caution, immediately had a very wide circulation.
In my opinion it has done excellent service in this country in
calling attention to the subject, in removing prejudice, and
in thus preparing the ground for the reception of analogous
views.
In 1846 the veteran geologist M. J. d'Omalius d'Halloy
published in an excellent though short paper (' Bulletins de
I'Acad. Roy. Bruxell6s,' tom. xiii. p. 581) his opinion that
it is more probable that new species have been produced by
descent with modification than that they have been separately
created: the author first promulgated this opinion in 1831.
Professor Owen, in 1849 (* Nature of limbs,' p. 86),
wrote as follows: — "The archetypal idea was manifested in
the flesh under diverse such modifications, upon this planet,
long prior to the existence of those animal species that
actually exemplify it. To what natural laws or secondary
causes the orderly succession and progression of such organic
phenomena may have been committed, we, as yet, are igno-
rant." In his Address to the British Association, in 1858,
he speaks (p. li.) of "the axiom of the continuous operation
of creative power, or of the ordained becoming of living
things." Farther on (p. xc), after referring to geographical
distribution, he adds, "These phenomena shake our confi-
dence in the conclusion that the Apteryx of New Zealand
and the Red Grouse of England were distinct creations in and
for those islands respectively. Always, also, it may be well
to bear in mind that by the word 'creation' the zoologist
means 'a process he knows not what*" He amplifies this
idea by adding that when such cases as that of the Red
Grouse are " enumerated by the zoologist as evidence of dis-
tinct creation of the bird in and for such islands, he chiefly
expresses that he knows not how the Red Grouse came to be
there, and there exclusively ; signifying also, by this mode of
expressing such ignorance, his belief that both the bird and
the islands owed their origin to a great first Creative Cause."
If we interpret these sentences given in the same Address,
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HISTORICAL SKETCH 15
one by the other, it appears that this eminent philosopher fdt
in 1858 his confidence shaken that the Apteryx and the Red
Grouse first appeared in their respective homes, "he knew
not how," or by some process "he knew not what"
This Address was delivered after the papers by Mr. Wal-
lace and myself on the Origin of Species, presently to be
referred to, had been read before the Linnean Society. When
the first edition of this work was published, I was so com-
pletely deceived, as were many others^ by such expressions as
" the continuous operation of creative power," that I included
Professor Owen with other palaeontologists as being firmly
convinced of the immutability of species; but it appears
(* Anat. of Vertebrates,' vol. iii. p. 796) that this was on my
part a preposterous error. In the last edition of this work
I inferred, and the inference still seems to me perfectly just,
from a passage beginning with the words " no doubt the type-
form," &c. (Ibid. vol. i. p. XXXV.), that Professor Owen
admitted that natural selection may have done something in
the formation of a new species; but this it appears (Ibid. vol.
iii. p. 798) is inaccurate and without evidence. I also gave
some extracts from a correspondence between Professor
Owen and the Editor of the * London Review,' from which it
appeared manifest to the Editor as well as to myself, that
Professor Owen claimed to have promulgated the theory of
natural selection before I had done so; and I expressed my
surprise and satisfaction at this announcement; but as far
as it is possible to understand certain recently published pas-
sages (Ibid. vol. iii. p. 798) I have either partially or wholly
again fallen into error. It is consolatory to me that others
find Professor Owen's controversial writings as difficult to
understand and to reconcile with each other, as I do. As far
as the mere enunciation of the principle of natural selection
is concerned, it is quite immaterial whether or not Professor
Owen preceded me, for both of us, as shown in this historical
sketch, were long ago preceded by Dr. Wells and Mr.
Matthews.
M. Isidore Geoffroy Saint-Hilaire, in his lectures delivered
in 1850 (of which a Rcsum6 appeared in the 'Revue et Mag.
de Zoolog.,' Jan. 1851), briefly gives his reason for believing
that specific characters " sont fix6s, pour chaque espece, tant
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16 HISTORICAL SKETCH
qu'elle se perpetue ou milieu des memes circonstances : ils se
modifient, si les circonstances ambiantes viennent a changer."
"£n resume, I'observaHon des animaux sauvages demontre
d6j4 la variability linUtie des especes. Les experiences sur
les animaux sauvages devenus domestiques, et sur les ani-
maux domestiques redevenus sauvages, la demontrent plus
clairement encore. Ces memes experiences prouvent, de
plus, que les differences produites peuvent etre de valeur
genMque," In his 'Hist. Nat. Generale' (tom ii. p. 340,
1859) he amplifies analogous conclusions.
From a circular lately issued it appears that Dr. Freke, in
1851 ('Dublin Medical Press/ p. 322), propounded the doc-
trine that all organic beings have descended from one pri-
mordial form. His grounds of belief and treatment of the
subject are wholly different from mine; but as Dr. Freke
has now (1861) published his Essay on the 'Origin of Spe-
cies by means of Organic Affinity/ the difficult attempt to
give any idea of his views would be superfluous on my part.
Mr. Herbert Spencer, in an Essay (originally published in
the 'Leader/ March, 1852, and republished in his 'Essays,' in
1858), has contrasted the theories of the Creation and the
Development of organic beings with remarkable skill and
force. He argues from the analogy of domestic productions,
from the changes which the embryos of many species under-
go, from the difficulty of distinguishing species and varie-
ties, and from the principle of general gradation, that species
have been modified; and he attributes the modification to
the change of circumstances. The author (1855) has also
treated Psychology on the principle of the necessary acquire-
ment of each mental power and capacity by gradation.
In 1852 M. Naudin, a distinguished botanist, expressly
stated, in an admirable paper on the Origin of Species
('Revue Horticole,' p. 102; since partly republished in the
'Nouvelles Archives du Museum,' tom. i. p. 171), his belief
that species are formed in an analogous manner as varieties
are under cultivation; and the latter process he attributes to
man's power of selection. But he does not show how selec-
tion acts under nature. He believes, like Dean Herbert, that
species, when nascent, were more plastic than at present.
He lays weight on what he calls the principle of finality;
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HISTORICAL SKETCH 17
''puissance mysteriuse, indeterminee ; fatalite pour les uns;
pour les autres, volonte providentidlle, dont Taction inces-
sante sur les etres vivants determine, a toutes les ^poques de
Texistence du monde, la forme, le volume, et la dur^e de
chacun d'eux, en raison de sa destinee dans Torde de choses
dont il fait partie. C'est cette puissance qui harmonise
chaque membre k Tensemble, en I'appropriant i la fonction
qu'il doit remplir dans I'organisme general de la nature, fonc-
tion qui est pour lui sa raison d'etre."*
In 1853 a celebrated geologist. Count Keyserling ('Bulletin
de la Soc. Geolog.,' 2nd Ser., tom. x. p. 357), suggested that
as new diseases, supposed to have been caused by some
miasma, have arisen and spread over the world, so at certain
periods the germs of existing species may have been chem-
ically affected by circumambient molecules of a particular
nature, and thus have given rise to new forms.
In this same year, 1853, Dr. Schaaffhausen published an
excellent pamphlet ('Verhand. des Naturhist Vereins der
Preuss. Rheinlands,' &c), in which he maintains the devel-
opment of organic forms on the earth. He infers that many
species have kept true for long periods, whereas a few have
become modified. The distinction of species he explains by
the destruction of intermediate graduated forms. 'Thus
living plants and animals are not separated from the extinct
by new creations, but are to be regarded as their descendants
through continued reproduction."
A well-known French botanist, M. Lecoq, writes in 1854
('Etudes sur Geograph. Bot.,' tom. i. p. 250), "On voit que
nos recherches sur la fixite ou la variation de I'esp^ce, nous
conduisent directement aux idees 6mises, par deux hommes
justement cel^bres, Geoffroy Saint-Hilaire et Gcethe." Some
•From references in Bronn's * Untersuchungen uber die Entwickelungs-
lesetze,' it appears that tlie celebrated botanist and pabeontolonst Ungcr
. ublisbed, in 186S, his belief that species undergo development and modifica-
tion. Dtelton, likewise, in Pander and Dalton's work on Fossil Sloths, ex-
pressed, in 1821, a similar belief. Similar views have, as is well known,
been maintained by Oken in his mystical ' Natnr-Philosophie.' From other
references in Godron's work ' Sur rEsp^e,' it seems that Bory St Vincent,
Burdach, Poiret, and Fries, hsve all admitted that new species are con-
tinually being produced.
I mav add, that of the thirty-four authors named in this Historical Sketch*
who believe in the modification of species, or at least disbelieve in separate
acts of creation, twenty-seven have written on special branches of natural
history or geology.
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18 HISTORICAL SKETCH
other passages scattered through M. Lecoq's large work,
make it a little doubtful how far he extends his views on the
modification of species.
The 'Philosophy of Creation' has been treated in a mas-
terly manner by the Rev. Baden Powell, in his 'Essays on the
Unity of Worlds/ 1855. Nothing can be more striking than
the manner in which he shows that the introduction of new
species is "a regular, not a casual phenomenon," or, as Sir
John Herschel expresses it, "a natural in contradistinction to
a miraculous process."
The third volume of the 'Journal of the Linnean Society*
contains papers, read July ist, 1858, by Mr. Wallace and my-
self, in which, as stated in the introductory remarks to this
volume, the theory of Natural Selection is prcxnulgated by
Mr. Wallace with admirable force and clearness.
Von Baer, towards whom all zoologists feel so profound a
respect, expressed about the year 1859 (see Prof. Rudolph
Wagner, 'Zoologisch-Anthropologische Untersuchungen,'
1861, s. 51) his conviction, chiefly grounded on the laws of
geographical distribution, that forms now perfectly distinct
have descended from a single parent-form.
In June, 1859, Professor Huxley gave a lecture before the
Royal Institution on the 'Persistent Types of Animal Life.'
Referring to such cases, he remarks, 'It is difficult to com-
prehend the meaning of such facts as these, if we suppose
that each species of animal and plant, or each great type of
organisation, was formed and placed upon the surface of the
globe at long intervals by a distinct act of creative power;
and it is well to recollect that such an assumption is as un-
supported by tradition or revelation as it is opposed to the
general analogy of nature. If, on the other hand, we view
'Persistent Types' in relation to that hypothesis which sup-
poses the species living at any time to be the result of the
gradual modification of pre-existing species a hypothesis
which, though unproven, and sadly damaged by some of its
supporters, is yet the only one to which physiology lends any
countenance; their existence would seem to show that the
amount of modification which living beings have undergone
during geological time is but very small in relation to the
whole series of changes which they have suffered."
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HISTORICAL SKETCH 19
In December, 1859, Dr. Hooker published his 'Introduction
to the Australian Flora.' In the first part of this great work
he admits the truth of the descent and modification of spe-
cieSy and supports this doctrine by many •original observa-
tions.
The first edition of this work was published on November
34th, 1859, and the second edition on January Tth, i860.
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INTRODUCTION
When on board H.M.S. 'Beagle/ as naturalist, I was much struck
with certain facts in the distribution of the organic beings in-
habiting South America, and in the geological relations of the
present to the past inhabitants of that continent These facts, as
will be seen in the latter chapters of this volume, seemed to throw
some light on the origin of species— that mystery of mysteries, as
it has been called by one of our greatest philosophers. On my
return home, it occurred to me, in 1837, that something might
perhaps be made out on this question by patiently accumulating
and reflecting on all sorts of facts which could possibly have any
bearing on it. After five years' work I allowed myself to specu-
late on the subject, and drew up some short notes; these I
enlarged in 1844 into a sketch of the conclusions, which then
seemed to me probable; from that period to the present day I
have steadily pursued the same object I hope that I may be
excused for entering on these personal details, as I give them to
show that I have not been hasty in coming to a decision.
My work is now (1859) nearly finished; but as it will take me
many more years to complete it, and as my health is far from
strong, I have been urged to publish this Abstract. I have more
especially been induced to do this, as Mr. Wallace, who is now
studying the natural history of the Malay archipelago, has arrived
at almost exactly the same general conclusions that I have on the
origin of species. In 1858 he sent me a memoir on this subject,
with a request that I would forward it to Sir Charles Lyell, who
sent it to the Linnean Society, and it is published in the third,
volume of the Journal of that Society. Sir C. Lyell and Dr.
Hooker, who both knew of my work — the latter having read my
sketch of 1844:— 4ionoured me by thinking it advisable to publish,
with Mr. Wallace's excellent memoir, some brief extracts from
my manuscripts.
This Abstract, which I now publish, must necessarily be im-
perfect I cannot here give references and authorities for my
several statements ; and I must trust to the reader reposing some
confidence in my accuracy. No doubt errors will have crept in,
tfaoogh I hope I have always been cautious in trusting to good
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22 INTRODUCTION
authorities alone. I can here give only the general conclusions at
which I have arrived, with a few facts in illustration, but which,
I hope, in most cases will suffice. No one can feel more sensible
than I do of the necessity of hereafter publishing in detail all the
facts, with references, on which my conclusions have been
grounded; and I hope in a future work to do this. For I am
well aware that scarcely a single point is discussed in this volume
on which &cts cannot be adduced, often apparently leading to
conclusions directly opposite to those at which I have arrived.
A fair result can be obtained only by fully stating and balancing
the facts and arguments on both sides of each question; and this
is here impossible.
I much regret that want of space prevents my having the satis-
faction of acknowledging the generous assistance which I have
received from very many naturalists, some of them personally
unknown to me. I cannot, however, let this opportunity pass
without expressing my deep obligations to Dr. Hooker, who, for
the last fifteen years, has aided me in every possible way by his
large stores of knowledge and his excellent judgment.
In considering the Origin of Species, it is quite conceivable that
a naturalist, reflecting on the mutual affinities of organic beings,
on their embryological relations, their geographical distribution,
geological succession, and other such facts, might come to the con-
clusion that species have not been independently created, but had
descended, like varieties, from other species. Nevertheless, such
a conclusion, even if well founded, would be unsatisfactory, until
it could be shown how the innumerable species inhabiting this
world have been modified, so as to acquire that perfection of
structure and coadaptation which justly excites our admiration.
% Naturalists continually refer to external conditions, such as
climate, food, etc., as the only possible cause of variation. In one
limited sense, as we shall hereafter see, this may be true; but
it is preposterous to attribute to mere external conditions, the
structure, for instance, of the woodpecker, with its feet, tail, beak,
and tongue, so admirably adapted to catch insects under the bark
of trees. In the case of the mistletoe, which draws its nourish-
ment from certain trees, which has seeds that must be trans-
ported by certain birds, and which has flowers with separate
sexes absolutely requiring the agency of certain insects to bring
pollen from one flower to the other, it is equally preposterous to
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INTRODUCTION 23
account for the structure of this parasite, with its relations to
several distinct organic beings, by the effects of external condi-
tions, or of habit, or of the volition of the plant itself.
It is, therefore, of the highest importance to gain a clear in-
sight into the means of modification and coadaptation. At the
commencement of my observations it seemed to me probable that
a careful study of domesticated animals and of cultivated plants
would offer the best chance of making out this obscure probleoL
Nor have I been disappointed ; in this and in all other perplexing
cases I have invariably found that our knowledge, imperfect
though it be, of variation under domestication, afforded the best
and safest due. I may venture to express my conviction of the
high value of such studies, although they have been very com-
monly neglected by naturalists.
From these considerations, I shall devote the first chapter of
this Abstract to Variation under Domestication. We shall thus
see that a large amount of hereditary modification is at least pos-
sible; and, what is equally or more important, we shall see how
great is the power of man in accumulating by his Selection suc-
cessive slight variations. I will then pass on the variability of
^ecies in a state of nature; but I shall, unfortunately, be
compelled to treat this subject far too briefly, as it can be treated
properly only by giving long catalogues of facts. We shall, how-
ever, be enabled to discuss what circumstances are most favour-
able to variation. In the next chapter the Struggle for Existence I
amongst all organic beings throughout the world, which inevitably *
follows from the high geometrical ratio of their increase, will be
considered. This is the doctrine of Malthus, applied to the whole
animal and vegetable kingdoms. As many more individuals of
each species are bom than can possibly survive; and as, conse-
quently, there is a frequently recurrent struggle for existence, it
follows that any being, if it vary however slightly in any manner
profitable to itself, under the complex and sometimes varying con-
iditions of life, will have a better chance of surviving, and thus be
naturally selected. From the strong principle of inheritance, any
selected variety will tend to propagate its new and modified form.
This fundamental subject of Natural Selection will be treated
at some length in the fourth chapter; and we shall then see how
Natural Selection almost inevitably causes much Extinction of the
less improved forms of life, and leads to what I have called Diver-
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U INTRODUCTION
gence of Character. In the next chapter I shall discuss the com-
plex and little known laws of variation. In the five succeeding
chapters, the most apparent and gravest difficulties in accepting
the theory will be given: namely, first, the difficulties of transit
tions, or how a simple being or a simple organ can be changed
and perfected into a highly developed being or into an elaborately
constructed organ; secondly, the subject of Instinct, or the mental
powers of animals ; thirdly, Hybridism, or the infertility of species
and the fertility of varieties when intercrossed; and fourthly, the
imperfection of the Geological Record. In the next chapter I
shall consider the geological succession of organic beings through-
out time; in the twelfth and thirteenth, their geographical distri-
bution throughout space ; in the fourteenth, their classification or
mutual affinities, both when mature and in an embryonic condi-
tion. In the last chapter I shall give a brief recapitulation of the
whole work, and a few concluding remarics.
No one ought to feel surprise at much remaining as yet unex-
plained in regard to the origin of species and varieties, if he make
due allowance for our profound ignorance in regard to the mutual
relations of the many beings which live around us. Who can
explain why one species ranges widely and is very numerous, and
why another allied species has a narrow range and is rare? Yet
these relations are of the highest importance, for they determine
the present welfare, and, as I believe, the future success and
modification of every inhabitant of this world. Still less do we
know of the mutual relations of the innumerable inhabitants of
the world during the many past geological epochs in its history.
Although much remains obscure, and will long remain obscure, I
can entertain no doubt, after the most deliberate study and dis-
passionate judgment of which I am capable, that the view which
most naturalists until recently entertained, and which I formerly
entertained — ^namely, that each species has been independently
created — ^is erroneous. I am fully convinced that species are not
immutable ; but that those belonging to what are called the same
genera are lineal descendants of some other and generally extinct
species, in the same manner as the acknowledged varieties of any
one species are the descendants of that species. Furthermore, I
am convinced that Natural Selection has been the most important,
but not the exclusive, means of modification.
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ORIGIN OF SPECIES
CHAPTER I
Variation under Domestication
Causes of variability—Effects of habit and the use or disttse of parts-
Correlated variation— Inheritance— Character of domestic varie-
ties—Difficulty of distinguishing between varieties and species-
Origin of domestic varieties from one or more species— Domestic
pigeons, their differences and origin — ^Principles of selection, an-
ciently followed, their effects— Methodical and uncoD scions
selection — ^Unknown origin of our domestic productions — Circum-
stances favourable to man's power of selection
CAUSES OF variability
4 m THEN we compare the individuals of the same
Vrm/ variety or sub-variety of our older cultivated plants
V T and animals, one of the first points which strikes
us is, that they generally differ more from each other than
do the individuals of any one species or variety in a state of
nature. And if we reflect on the vast diversity of the plants
and animals which have been cultivated, and which have
varied during all ages under the most different climates and
treatment, we are driven to conclude that this great varia-
bility is due to our domestic productions having been raised
under conditions of life not so uniform as, and somewhat
different from, those to which the parent species had been
exposed under nature. There is, also, some probability in
the view propounded by Andrew Knight, that this variability
may be partly connected with excess of food. It seems clear
that organic beings must be exposed during several genera-
tions to new conditions to cause any great amount of varia-
tion; and that, when the organisation has once begun to
vary, it generally continues varying for many generations.
No case is on record of a variable organism ceasing to vary
under cultivation. Our oldest cultivated plants, such as
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26 ORIGIN OF SPECIES
wheats still yield new varieties : our oldest domesticated ani-
mals are still capable of rapid improvement or modification.
As far as I am able to judge, after long attending to the
subject, the conditions of life appear to act in two ways, —
directly on the whole organisation or on certain parts alone,
and indirectly by affecting the reproductive system. With re*
spect to the direct action, we must bear in mind that in every
case, as Professor Weismann has lately insisted, and as I have
incidentally shown in my work on 'Variation under Domesti-
cation,' there are two factors: namely, the nature of the
organism, and the nature of the conditions. The former
seems to be much the more important; for nearly similar
variations sometimes arise under, as far as we can judge,
dissimilar conditions; and, on the other hand, dissimilar
variations arise imder conditions which appear to be nearly
uniform. The effects on the offspring are either definite or
indefinite. They may be considered as definite when all or
nearly all the offspring of individuals exposed to certain
conditions during several generations are modified in the
same manner. It is extremely difficult to come to any con-
clusion in regard to the extent of the changes which have
been thus definitely induced. There can, however, be little
doubt about many slight changes, — such as size from the
amount of food, colour from the nature of the food, thick-
ness of the skin and hair from climate, etc. Each of the
endless variations which we see in the plumage of our fowls
must have had some efficient cause; and if the same cause
were to act uniformly during a long series of generations on
many individuals, ail probably would be modified in the
same manner. Such facts as the complex and extraordinary
out-growths which variably follow from the insertion of a
minute drop of poison by a gall-producing insect, show us
what singular modifications might result in the case of plants
from a chemical change in the nature of the sap.
Indefinite variability is a much more common result of
changed conditions than definite variability, and has prob-
ably played a more important part in the formation of our
domestic races. We see indefinite variability in the endless
slight peculiarities which distinguish the individuals of the
same species, and which cannot be accounted for by inher-
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VARIATION UNDER DOMESTICATION 27
iiance from either parent or from some more remote ances-
tor. Even strongly-marked differences occasionally appear
in the young of the same litter» and in seedlings from the
same seed capsule. At long intervals of time, out of millions
of individuals reared in the same country and fed on nearly
the same food, deviations of structure so strongly pro-
nounced as to deserve to be called monstrosities arise; but
monstrosities cannot be separated by any distinct line from
slighter variations. All such changes of structure, whether
extremely slight or strongly marked, which appear amongst
many individuals living together, may be considered as the
indefinite effects of the conditions of life on each individual
organism, in nearly the same manner as the chill affects dif-
ferent men in an indefinite manner, according to their state
of body or constitution, causing coughs or colds, rheumatism,
or inflammation of various organs.
With respect to what I have called the indirect action of
changed conditions, namely, through the reproductive sys-
tem of being affected, we may infer that variability is thus
induced, partly from the fact of this system being •extremely
sensitive to any change in the conditions, and partly
from the similarity, as Kolreuter and others have re-
marked, between the variability which follows from the
crossing of distinct species, and that which may be ob-
served with plants and animals when reared under new
or unnatural conditions. Many facts clearly show how
eminently susceptible the reproductive system is to very
slight changes in the surrounding conditions. Nothing is
more easy than to tame an animal, and few things more diffi-
cult than to get it to breed freely under confinement, even
when the male and female unite. How many animals there
are which will not breed, though kept in an almost free state
in their native country ! This is generally, but erroneously,
attributed to vitiated instincts. Many cultivated plants dis-
play the utmost vigour, and yet rarely or never seed! In
some few cases it has been discovered that a very trifling
change, such as a little more or less water at some particular
period of growth, will determine whether or not a plant will
produce seeds. I cannot here give the details which I have
collected and elsewhere published on this curious subject;
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28 ORIGIN OF SPEaBS
but to show how singular the laws are which determine the
reproduction of animals under confinement, I may mention
that carnivorous animals, even from the tropics, breed in
this country pretty freely under confinement, with the excep-
tion of the plantigrades or bear family, which seldom pro-
duce young; whereas carnivorous birds, with the rarest ex-
ceptions, hardly ever lay fertile eggs. Many exotic plants
have pollen utterly worthless, in the same condition as in the
most sterile hybrids. When, on the one hand, we see domes-
ticated animals and plants, though often weak and sickly,
breeding freely under confinement; and when, on the other
hand, we see individuals, though taken young from a state of
nature perfectly tamed, long-lived and healthy (of which I
could give numerous instances), yet, having their repro-
ductive system so seriously affected by unperceived causes as
to fail to act, we need not be surprised at this system, when
it does act under confinement, acting irregularly, and pro-
ducing offspring somewhat unlike their parents. I may add,
that as some organisms breed freely under the most unnat-
ural conditions (for instance, rabbits and ferrets kept in
hutches), showing that their reproductive organs are not
easily affected; so will some animals and plants withstand
domestication or cultivation, and vary very slightly — ^per-
haps hardly more than in a state of nature.
Some naturalists have maintained that all variations are
connected with the act of sexual reproduction; but. this is
certainly an error; for I have given in another work a long
list of "sporting plants," as they are called by gardeners; —
that is, of plants which have suddenly produced a single bud
with a new and sometimes widely different character from
that of the other buds on the same plant These bud-varia-
tions, as they may be named, can be propagated by grafts,
offsets, etc., and sometimes by seed. They occur rarely
under nature, but are far from rare under culture. As a
single bud out of the many thousands, produced year after
year on the same tree under uniform conditions, has been
known suddenly to assume a new character ; and as buds on
distinct trees, growing under different conditions, have some-
times yielded nearly the same variety — for instance, buds on
peach-trees producing nectarines, and buds on common roses
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VARIATION UNDER DOMESTICATION S9
producing moss-roses — ^we clearly see that the nature of the
condition is of subordinate importance in comparison with
the nature of the organism in determining each particular
form of variation — ^perhaps of not more importance than the
nature of the spark, by which a mass of combustible matter
is ignited, has in determining the nature of the flames.
EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS;
CORRELATED VARIATION ; INHERITANCE
Changed habits produce an inherited effect, as in the pe-
riod of the flowering of plants when transported from one
climate to another. With animals the increased use or dis-
use of parts has had a more marked influence; thus I find in
the domestic duck that the bones of the wing weigh less and
the bones of the leg more, in proportion to the whole skele-
ton, than do the same bones in the wild duck; and this
change may be safely attributed to the domestic duck flying
much less, and walking more, than its wild parents. The
great and inherited development of the udders in cows and
goats in countries where they are habitually milked, in com-
parison with these organs in other countries, is probably
another instance of the effects of use. Not one of our do-
mestic animals can be named which has not in some country
drooping ears; and the view which has been suggested that
the drooping is due to disuse of the muscles of the ear, from
the animals being seldom much alarmed, seems probable.
Many laws regulate variation, some few of which can be
dimly seen, and will hereafter be briefly discussed. I will
here only allude to what may be called correlated variation.
Important changes in the embryo or larva will probably en-
tail changes in the mature animal. In monstrosities, the
correlations between quite distinct parts are very curious;
and many instances are given in Isidore Geoffroy St.
Hilaire's great work on this subject. Breeders believe that
long limbs are almost always accompanied by an elongated
head. Some instances of correlation are quite whimsical:
thus cats which are entirely white and have blue eyes are
generally deaf ; but it has been lately stated by Mr. Tait that
tills is confined to the males. Colour and constitutional pecu-
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30 ORIGIN OF SPECIES
liarities go together, of which many remarkable cases could
be given amongst animals and plants. From facts collected
by Heusinger, it appears that white sheep and pigs are in-
jured by certain plants, whilst dark-coloured individuals es-
cape: Professor Wyman has recently communicated to me
a good illustration of this fact; on asking some farmers in
Virginia how it was that all their pigs were black, they in-
formed him that the pigs ate the paint-root (Lachnanthes),
which colored their bones pink, and which caused the hoofs
of all but the black varieties to drop off; and one of the
"crackers" (i,e, Virginia squatters) added, "we select the
black members of a litter for raising, as they alone have a
good chance of living." Hairless dogs have imperfect teeth ;
long-haired and coarse-haired, animals are apt to have, as is
asserted, long or many horns; pigeons with feathered feet
have skin between their outer toes ; pigeons with short beaks
have small feet, and those with long beaks large feet. Hence
if man goes on selecting, and thus augmenting, any pecu-
liarity, he will almost certainly modify unintentionally other
parts of the structure, owing to the mysterious laws of cor-
relation.
The results of the various, unknown, or but dimly under-
stood laws of variation arc infinitely complex and diversified.
It is well worth while carefully to study the several treatises
on some of our old cultivated plants, as on the hyacinth,
potato, even the dahlia, etc; and it is really surprising to
note the endless points of structure and constitution in which
the varieties and sub-varieties differ slightly from each
other. The whole organisation seems to have become
plastic, and departs in a slight degree from that of the
parental type.
Any variation which is not inherited is unimportant for
us. But the number and diversity of inheritable deviations
of structure, both those of slight and those of considerable
physiological importance, are endless. Dr. Prosper Lucas's
treatise, in two large volumes, is the fullest and the best on
this subject No breeder doubts how strong is the tendency
to inheritance; that like produces like is his fundamental be-
lief : doubts have been thrown on this principle only by theo-
retical writers. When any deviation of structure often
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VARIATION UNDER DOMESTICATION 31
appears, and we see it in the father and child, we cannot tell
whether it may not be due to the same cause having acted on
both; but when amongst individuals, apparently exposed to
the same conditions, any very rare deviation, due to some
extraordinary combination of circumstances, appears in the
parent — ^say, once amongst several million individuals — and
it reappears in the child, the mere doctrine of chances almost
compels us to attribute its reappearance to inheritance.
Every one must have heard of cases of albinism, prickly
skin, hairy bodies, etc, appearing in several members of the
same family. If strange and rare deviations of structure are
really inherited, less strange and commoner deviations may
be freely admitted to be inheritable. Perhaps the correct
way of viewing the whole subject would be, to look at the
inheritance of every character whatever as the rule, and
non-inheritance as the anomaly.
The laws governing inheritance are for the most part
unknown. No one can say why the same peculiarity in dif-
ferent individuals of the same species, or in different species,
is sometimes inherited and sometimes not so; why the child
often reverts in certain characters to its grandfather or
grandmother or more remote ancestor; why a peculiarity is
often transmitted from one sex to both sexes, or to one sex
alone, more commonly but not exclusively to the like sex.
It is a' fact of some importance to us, that peculiarities ap-
pearing in the males of our domestic breeds are often trans-
mitted, either exclusively or in a much greater degree, to
the males alone. A much more important rule, which I
think may be trusted, is that, at whatever period of life a
peculiarity first appears, it tends to reappear in the offspring
at a corresponding age, though sometimes earlier. In many
cases this could not be otherwise; thus the inherited pecu-
liarities in the horns of cattle could appear only in the off-
spring when nearly mature; peculiarities in the silkworm
are known to appear at the corresponding caterpillar or
cocoon stage. But hereditary diseases and some other facts
make me believe that the rule has a wider extension, and
that, when there is no apparent reason why a peculiarity
should appear at any particular age, yet that it does tend to
appear in the offspring at the same period at which it first
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32 ORIGIN OF SPEaBS
appeared in the parent I believe this rule to be of the
highest importance in explaining the laws of embryology.
These remarks are of coarse confined to the first appearance
of the peculiarity, and not to the primary cause which may
have acted on the ovules or on the male element; in nearly
the same manner as the increased length of the horns in
the offspring from a short-horned cow by a long-homed
bull, though appearing late in life, is clearly due to the male
element.
Having alluded to the subject of aversion, I may here
refer to a statement often made by naturalists — namely,
that our domestic varieties, when run wild, gradually but
invariably revert in character to their aboriginal stocks.
Hence it has been argued that no deductions can be drawn
from domestic races to species in a state of nature. I have
in vain endeavoured to discover on what decisive facts the
above statement has so often and so boldly been made.
There would be great difficulty in proving its truth: we may
safely conclude that very many of the most strongly marked
domestic varieties could not possibly live in a wild state.
In many cases we do not know what the aboriginal stock
was, and so could not tell whether or not nearly perfect re-
version had ensued. It would be necessary, in order to pre-
vent the effects of intercrossing, that only a single variety
should have been turned loose in its new home. Nei^erthe-
less, as our varieties certainly do occasionally revert in some
of their characters to ancestral forms, it seems to me not
improbable that if we could succeed in naturalising, or were
to cultivate, during many generations, the several races, for
instance, of the cabbage, in very poor soil (in which case,
however, some effect would have to be attributed to the
definite action of the poor soil), that they would, to a large
extent, or even wholly, revert to the wild aboriginal stock.
Whether or not the experiment would succeed, is not of
great importance for our line of argument; for by the ex-
periment itself the conditions of life are changed. If it
could be shown that our domestic varieties manifested a
strong tendency to reversion, — ^that is, to lose their acquired
characters, whilst kept under the same conditions, and whilst
kept in a considerable body, so that free intercrossing might
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CHARACTER OF DOMBSnC VARIETIES SS
check, by blending together, any slight deviations in their
structure, in such case, I grant that we could deduce nothing
from domestic varieties in regard to species. But there is
not a shadow of evidence in favour of this view: to assert
that we could not breed our cart- and race-horses, long- and
short-homed cattle, and poultry of various breeds, and escu-
lent vegetables, for an unlimited number of generations,
would be opposed to all experience.
CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF
DISTINGUISHING BETWEEN VARIETIES AND
species; ORIGIN OP DOMESTIC
VARIETIES FROM ONE OR
MORE SPECIES
When we look to the hereditary varieties or races of our
domestic animals and plants, and compare them with closely
allied species, we generally perceive in each domestic race,
as already remarked, less uniformity of character than in
true species. Domestic races often have a somewhat mon-
strous character; by which I mean, that, although differing
from each other, and from other species of the same genus,
in several trifling respects, they often differ in an extreme
degree in some one part, both when compared one with an-
other, and more especially when compared with the species
under nature to which they are nearest allied. With these
exceptions (and with that of the perfect fertility of varieties
when crossed, — ^a subject hereafter to be discussed), domes-
tic races of the same species differ from each other in the
same manner as do the closely allied species of the same
genus in a state of nature, but the differences in most cases
are less in degree. This must be admitted as true, for the
domestic races of many animals and plants have been ranked
by some competent judges as the descendants of aboriginally
distinct species, and by other competent judges as mere
varieties. If any well-marked distinction existed between a
domestic race and a species, this source of doubt would not
so perpetually recur. It has often been stated that domestic
races do not differ from' each other in characters of generic
vahie. It can be shown that this statement is not correct;
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34 ORIGIN OF SPEaES
but naturalists differ much in determining what characters
are of generic value; all such valuations being at present
empirical. When it is explained how genera originate under
nature, it will be seen that we have no right to expect often
to find a generic amount of difference in our domesticated
races.
In attempting to estimate the amount of structural differ-
ence between allied domestic races, we are soon involved
in doubt, from not knowing whether they are descended from
one or several parent species. This point, if it could be
cleared up, would be interesting; if, for instance, it could be
shown that the greyhound, bloodhound, terrier, spaniel, and
bulldog, which we all know propagate their kind truly, were
the offspring of any single species, then such facts would
have great weight in making us doubt about the immuta-
bility of the many closely allied natural species — for in-
stance, of the many foxes — ^inhabiting different quarters of
the world. I do not believe, as we shall presently see, that
the whole amount of difference between the several breeds
of the dog has been produced under domestication ; I believe
that a small part of the difference is due to their being
descended from distinct species. In the case of strongly
marked races of some other domesticated species, there
is presumptive or even strong evidence, that all are descended
from a single wild stock.
It has often been assumed that man has chosen for domes-
tication animals and plants having an extraordinary inherent
tendency to vary, and likewise to withstand diverse climates.
I do not dispute that these capacities have added largely to
the value of most of our domesticated productions; but how
could a savage possibly know, when he first tamed an ani-
mal, whether it would vary in succeeding generations, and
whether it would endure other climates? Has the little
variability of the ass and goose, or the small power of en-
durance of warmth by the reindeer, or of cold by the com-
mon camel, prevented their domestication? I cannot doubt
that if other animals and plants, equal in number to our
domesticated productions, and belonging to equally diverse
classes and countries, were taken from a state of nature,
and could be made to breed for an equal number of genera-
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CHARACTER OP DOMESTIC VARIETIES 35
tions under domestication, they would on an average vary as
largely as the parent species of our existing domesticated
productions have varied.
In the case of most of our anciently domesticated animals
and plants, it is not possible to come to any definite con-
clusion, whether they are descended from one or several
wild species. The argument mainly relied on by those who
believe in the multiple origin of our domestic animals is,
that we find in the most ancient times, on the monuments
of Egypt, and in the lake-habitations of Switzerland, much
diversi^ in the breeds; and that some of these ancient breeds
closely resemble, or are even identical with, those still ex-
isting. But this only throws far backwards the history of
civilisation, and shows that animals were domesticated at a
much earlier period than has hitherto been supposed. The
lake-inhabitants of Switzerland cultivated several kinds of
wheat and barley, the pea, the poppy for oil, and flax; and
they possessed several domesticated animals. They also
carried on commerce with other nations. All this clearly
shows, as Heer has remarked, that they had at this early
age progressed considerably in civilisation; and this again
implies a long continued previous period of less advanced
civilisation, durmg which the domesticated animals, kept
by different tribes in different districts, might have varied
and given rise to distinct races. Since the discovery of
flint tools in the superficial formations of many parts of
the world, all geologists believe that barbarian man existed
at an enormously remote period and we know that at the
present day there is hardly a tribe so barbarous, as not to
have domesticated at least the dog.
The origin of most of our domestic animals will prob-
ably for ever remain vague. But I may here state, that,
looking to the domestic dogs of the whole world, I have,
after a laborious collection of all known facts, come to the
conclusion that several wild species of Canidae have been
tamed, and that their blood, in some cases mingled together,
flows in the veins of our domestic breeds. In regard to
sheep and goats I can form no decided opinion. From facts
communicated to me by Mr. Blyth, on the habits, voice, con-
stitution, and structure of the humped Indian cattle, it is
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36 ORIGIN OF SPECIES
almost certain that they are descended from a different abo-
riginal stock from our European cattle and some competent
judges believe that these latter have had two or three wild
progenitors, — ^whether or not these deserve to be called
species. This conclusion, as well as that of the specific dis-
tinction between the humped and common cattle, may, in-
deed, be looked upon as established by the admirable re-
searches of Professor Rutimeyer. With respect to horses,
from reasons which I cannot here give, I am doubtfully
inclined to believe, in opposition to several authors, that all
the races belong to the same species. Having kept nearly
all the English breeds of the fowl alive, having bred and
crossed them, and examined their skeletons, it appears to
me almost certain that all are the descendants of the wild
Indian fowl, Gallus bankiva; and this is the conclusion of
Mr. Blyth, and of others who have studied this bird in
India. In regard to ducks and rabbits, some breeds of which
differ much from each other, the evidence is clear that they
are all descended from the common wild duck and rabbit
The doctrine of the origin of our several domestic races
from several aboriginal stocks, has been carried to an absurd
extreme by some authors. They believe that every race
which breeds true, let the distinctive characters be ever so
slight, has had its wild prototype. At this rate there must
have existed at least a score of species of wild cattle, as
many sheep, and several goats, in Europe alone, and several
even within Great Britain. One author believes that there
formerly existed eleven wild species of sheep peculiar to
Great Britain ! When we bear in mind that Britain has now
not one peculiar mammal, and France but few distinct from
those of Germany, and so with Hungary, Spain, etc., but
that each of these kingdoms possesses several peculiar breeds
of cattle, sheep, etc., we must admit that many domestic
breeds must have originated in Europe; from whence other-
wise could they have been derived? So it is in India. Even
in the case of the breeds of the domestic dog throughout tJie
world, which I admit are descended from several wild spe-
cies, it cannot be doubted that there has been an immense
amount of inherited variation; for who will believe that
animals closely resemUing the Italian gre^ound, the tdood-
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DOMESTIC PIOBONS 97
hound, the bull-dog, pug-dog, or Blenheim spaniel, etc. — so
unlike all wild Canidae — ever existed in a state of nature?
It has often been loosely said that all our races of dogs
have been produced by the crossing of a few aboriginal spe-
cies; but by crossing we can only get forms in some degree
intermediate between their parents; and if we account for
our several domestic races by this process, we must admit
the former existence of the most extreme forms, as tlie
Italian greyhound, bloodhound, bull-dog, etc., in the wild
state. Moreover, the possibility of making distinct races by
crossing has been greatly exaggerated. Many cases are on
record, showing that a race may be modified by occasional
crosses, if aided by the careful selection of the individuals
which present the desired character; but to obtain a race
intermediate between two quite distinct races, would be very
difficult. Sir J. Sebright expressly experimented with this
object and failed. The offspring from the first cross be-
tween two pure breeds is tolerably and sometimes (as I have
found with pigeons) quite uniform in character, and every-
thing seems simple enough; but when these mongrels are
crossed one with another for several generations, hardly
two of them are alike, and then the difficulty of the task
becomes manifest
BREEDS OP THE DOMESTIC PIGEON, THEIR DIfPERENCES AND
ORIGIN
Believing that it is always best to study some special
group, I have, after deliberation, taken up domestic pigeons.
I have kept every breed which I could purchase or obtain,
and have been most kindly favoured with skins from several
quarters of the world, more especially by the Hon. W. Elliot
from India, and by the Hon. C. Murray from Persia. Many
treatises in different languages have been published on pig-
eons, and some of them are very important, as being of con-
siderable antiquity. I have associated with several eminent
fanciers, and have been permitted to join two of the London
Pigeon Clubs. The diversity of the breeds is something as-
tonishing. Compare the English carrier and the short-faced
tumbler, and see the wonderful difference in their beaks»
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38 ORIGIN OF SPECIES
entailing corresponding differences in their skulls. The
carrier, more especially the male bird, is also remarkable
from the wonderful development of the carunculated skin
about the head ; and this is accompanied by greatly elongated
eyelids, very large external orifices to Uie nostrils, and a
wide gape of mouth. The short-faced tumbler has a beak
in outline almost like that of a finch; and the common
tumbler has the singular inherited habit of flying at a great
height in a compact flock, and tumbling in the air head over
heels. The runt is a bird of great size, with long massive
beak and large feet; some of the sub-breeds of runts have
very long necks, others very long wings and tails, others
singularly short tails. The barb is allied to the carrier, but,
instead of a long beak, has a very short and broad one. The
pouter has a much elongated body, wings, and legs; and
its enormously developed crop, which it glories in inflating,
may well excite astonishment and even laughter. The turbit
has a short and conical beak, with a line of reversed feathers
down the breast; and it has the habit of continually expand-
ing, slightly^, the upper part of the oesophagus. The Jacobin
has the feathers so much reversed along the back of the neck
that they form a hood; and it has, proportionally to its
size, elongated wing and tail feathers. The trumpeter and
laugher, as their names express, utter a very different coo
from the other breeds. The fantail has thirty or even forty
tail-feathers, instead of twelve or fourteen — the normal
number in idl the members of the great pigeon family : these
feathers are kept expanded, and are carried so erect, that in
good birds the head and tail touch: the oil-gland is quite
aborted. Several other less distinct breeds might be
specified.
In the skeletons of the several breeds, the development of
the bones of the face in length and breadth and curvature
differs enormously. The shape, as well as the breadth and
length of the ramus of the lower jaw, varies in a highly
remarkable manner. The caudal and sacral vertebra vary
in number; as does the number of the ribs, together with
their relative breadth and the presence of processes. The size
and shape of the apertures in the sternum are highly vari-
able; so is the degree of divergence and relative size of the
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DOMESTIC PIGEONS 90
two arms of the furcula. The proportional width of the
gape of mouth, the proportional length of the eyelids, of the
orifice of the nostrils, of the tongue (not always in strict
correlation with the length of beak), the size of the crop
and of the upper part of the oesophagus; the development
and abortion of the oil-gland; the number of the primary
wing and caudal feathers; the relative length of the wing
and tail to each other and to the body; the relative length
of the leg and foot ; the number of scutelbe on the toes, the
development of skin between the toes, are all points of struct-
ure which are variable. The period at which the perfect
plumage is acquired varies, as does the state of the down
with which the nestling birds are clothed when hatched.
The shape and size of the eggs vary. The manner of flight,
and in some breeds the voice and disposition, differs re-
markably. Lastly, in certain breeds, the males and females
have come to differ in a slight degree in each other.
Altogether at least a score of pigeons might be chosen,
which, if shown to an ornithologist, and he were told that
they were wild birds, would certainly be ranked by him
as well-defined species. Moreover, I do not believe that any
ornithologist would in this case place the English carrier,
the short-faced tumbler, the runt, the barb, pouter, and
fantail in the same genus; more especially as in each of
these breeds several truly inherited sub-breeds, or species, as
he would call them, cotdd be shown him.
Great as are the differences between the breeds of the
pigeon, I am fully convinced that the common opinion of
naturalists is correct, namely, that all are descended from
the rock-pigeon (Columba livia), including under this term
several geographical races or sub-species, which differ from
each other in the most trifling respects. As several of the
reasons which have led me to this belief are in some de-
gree applicable in other cases, I will here briefly give them.
If the several breeds are not varieties, and have not pro-
ceeded from the rock-pigeon, they must have descended from
at least seven or eight aboriginal stocks; for it is impossible
to make the present domestic breeds by the crossing of any
lesser number : how, for instance, could a pouter be produced
by crossing two breeds unless one of the parent-stocks pos-
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40 ORIGIN OF SPECIES
sessed the characteristic enormous crop ? The supposed abo-
riginal stocks must all have been rock-pigeons, that is, they
did not breed or willingly perch on trees. But besides C
livia, with its geographical sub-species, only two or three
other species of rock-pigeons are known and these have
not any of the characters of the domestic breeds. Hence
the supposed aboriginal stocks must either still exist in the
countries where they were originally domesticated, and yet
be unknown to ornithologists; and this, considering their
size, habits, and remarkable characters, seems improbable;
or they must have become extinct in the wild state. But
birds breeding on precipices, and good fliers, are unlikely
to be exterminated; and the common rock-pigeon, which has
the same habits with the domestic breeds, has not been ex-
terminated even on several of the smaller British islets, or
on the shores of the Mediterranean. Hence the supposed
extermination of so many species having similar habits with
the rock-pigeon seems a very rash assumption. Moreover,
the several above-named domesticated breeds have been
transported to all parts of the world, and, therefore, some
of them must have been carried back again into their native
country; but not one has become wild or feral, though the
dovecot-pigeon, which is the rock-pigeon in a very slightly
altered state, has become feral in several places. Again,
all recent experience shows that it is difficult to get wild ani-
mals to breed freely under domestication; yet on the hy-
pothesis of the multiple origin of our pigeons, it must be
assumed that at least seven or eight species were so thor-
oughly domesticated in ancient times by half-civilised man,
as to be quite prolific under confinement
An argument of great weight, and applicable in several
other cases, is, that the above-specified breeds, though agree-
ing generally with the wild rock-pigeon in constitution, habits,
voice, colouring, and in most parts of their structure, yet are
certainly highly abnormal in other parts ; we may look in vain
through the whole great family of Columbidae for a beak like
that of the English carrier, or that of the short-faced tum-
bler, or barb ; for reversed feathers like those of the Jacobin ;
for a crop like that of the pouter ; for tail-feathers like those
of the fantail. Hence it must be assumed not only that half-
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DOMESTIC PIGEONS 41
civilised man succeeded in thoroughly domesticating several
species, but that he intentionally or by chance picked out
extraordinarily abnormal species; and further, that these very
species have since all become extinct or unknown. So many
strange contingencies are improbable in the highest degree.
Some facts in regard to the colouring of pigeons well de-
serve consideration. The rock-pigeon is of a slaty-blue, with
white loins; but the Indian sub-species, C. intermedia of
Strickland, has this part bluish. The tail has a terminal dark
bar, with the outer feathers externally edged at the base with
white. The wings have two black bars. Some semi-domes-
tic breeds, and some truly wild breeds, have, besides the two
black bars, the wings chequered with black. These several
marks do not occur together in any other species of the whole
family. Now, in every one of llie domestic breeds, taking
thoroughly well-bred birds, all the above marks, even to the
white edging of the outer tail-feathers, sometimes concur
perfectly developed. Moreover, when birds belonging to two
or more distinct breeds are crossed, none of which are blue
or have any of the above-specified marks, the mongrel off-
spring are very apt suddenly to acquire these characters. To
give one instance out of several which I have observed: — I
crossed some white fantails, which breed very true, with some
black barbs — and it so happens that blue varieties of barbs
are so rare that I never heard of an instance in England ; and
the mongrels were black, brown, and mottled. I also crossed
a barb with a spot, which is a white bird with a red tail and
red spot on the forehead, and which notoriously breeds very
true; the mongrels were dusky and mottled. I then crossed
one of the mongrel barb-fantails with a mongrel barb-spot,
and they produced a bird of as beautiful a blue colour, with
the white loins, double black wing-bar, and barred and white-
edged tail-feathers, as any wild rock-pigeon I We can under-
stand these facts, on the well-known principle of reversion to
ancestral characters, if all the domestic breeds are descended
from the rock-pigeon. But if we deny this, we must make
one of the two following highly improbable suppositions.
Either, first, that all the several imagined aboriginal stocks
were coloured and marked like the rock-pigeon, although no
other existing species is thus coloured and marked, so that in
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42 ORIGIN OF SPECIES
each separate breed there might be a tendency to revert to
the very same colours and markings. Or, secondly, that each
breed, even the purest, has within a dozen, or at most within
a score, of generations, been crossed by the rock-pigeon; I
say within a dozen or twenty generations, for no instance is
known of crossed descendants reverting to an ancestor of
foreign blood, removed by a greater number of generations.
In a breed which has been crossed only once, the tendency to
revert to any character derived from such a cross will nat-
urally become less and less, as in each succeeding generation
there will be less of the foreign blood; but when there has
been no cross, and there is a tendency in the breed to revert
to a character which was lost during some former genera-
tion, this tendency, for all that we can see to the contrary,
may be transmitted undiminished for an indefinite number of
generations. These two distinct cases of reversion are often
confounded together by those who have written on inheri-
tance.
Lastly, the hybrids or mongrels from between all the breeds
of the pigeon are perfectly fertile, as I can state from my
own observations, purposely made, on the most distinct breeds.
Now, hardly any cases have been ascertained with certainty
of hybrids from two quite distinct species of animals being
perfectly fertile. Some authors believe that long-continued
domestication eliminates this strong tendency to sterility in
species. From the history of the dog, and of some other do-
mestic animals, this conclusion is probably quite correct, if
applied to species closely related to each other. But to ex-
tend it so far as to suppose that species, aboriginally as dis-
tinct as carriers, tumblers, pouters, and fantails now are,
should yield offspring perfectly fertile inter se, would be
rash in the extreme.
From these several reasons, namely, — the improbability of
man having formerly made seven or eight supposed species
of pigeons to breed freely under domestication; — ^these sup-
posed species being quite unknown in a wild state, and their
not having become anywhere feral ; — these species presenting
certain very abnormal characters, as compared with all other
Columbidse, though so like the rock-pigeon in most respects;
— the occasional re-appearance of the blue colour and various
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DOMESTIC PIGEONS 43
black marks in all the breeds, both when kept pure and when
crossed; — ^and lastly, the mongrel offspring being perfectly
fertile ; — from these several reasons, taken together, we may
safely conclude that all our domestic breeds are descended
from the rock-pigeon or Columba livia with its geographical
sub-species.
In favour of this view, I may add, firstly, that the wild C.
livia has been found capable, of domestication in Europe and
in India; and that it agrees in habits and in a great number
of points of structure with all the domestic breeds. Sec-
ondly, that, although an English carrier or a short-faced
tumbler differs immensely in certain characters from the
rock-pigeon, yet that, by comparing the several sub-breeds of
these two races, more especially those brought from distant
countries, we can make, between them and the rock-pigeon,
an almost perfect series; so we can in some other cases, but
not with all the breeds. Thirdly, those characters which are
mainly distinctive of each breed are in each eminently vari-
able, for instance the wattle and length of beak of the carrier,
the shortness of that of the tumbler, and the number of tail-
feathers in the fantail ; and the explanation of this fact will
be obvious when we treat of Selection. Fourthly, pigeons
have been watched and tended with the utmost care, and
loved by many people. They have been domesticated for
thousands of years in several quarters of the world ; the ear-
liest known record of pigeons is in the fifth iGgyptian dy-
nasty, about 3000 B.C., as was pointed out to me by Professor
Lepsius; but Mr. Birch informs me that pigeons are given
in a bill of fare in the previous dynasty. In the time of the
Romans, as we hear from Pliny, immense prices were given
for pigeons; "nay, they are come to this pass, that they can
reckon up their pedigree and race." Pigeons were much
valued by Akber Khan in India, about the year 1600; never
less than 20,000 pigeons were taken with the court. 'The
monarchs of Iran and Turan sent him some very rare birds ;"
and, continues the courtly historian, "His Majesty by cross-
ing the1)reeds, which method was never practised before, has
improved them astonishingly." About this same period the
Dutch were as eager about pigeons as were the old Romans.
The paramount importance of these considerations in ex-
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44 ORIGIN OF SPEQES
plaining the immense amount of variation which pigeons have
undergone, will likewise be obvious when we treat of Selec-
tion. We shall then, also, see how it is that the several
breeds so often have a somewhat monstrous character. It is
also a most favourable circumstance for the production of
distinct breeds, that male and female pigeons can be easily
mated for life; and thus different breeds can be kept together
in the same aviary.
I have discussed the probably origin of domestic pigeons at
some, yet quite insufficient, length ; because when I first kept
pigeons and watched the several kinds, well knowing how
truly they breed, I felt fully as much difficulty in believing
that since they had been domesticated they had all proceeded
from a common parent, as any naturalist could in coming to
a similar conclusion in regard to the many species of finches,
or other groups of birds, in nature. One circumstance has
struck me much ; namely, that nearly all the breeders of the
various domestic animals and the cultivators of plants, with
whom I have conversed, or whose treatises I have read, are
firmly convinced that the several breeds to which each has
attended, are descended from so many aboriginally distinct
species. Ask, as I have asked, a celebrated raiser of Here-
ford cattle, whether his cattle might not have descended from
Longhoms, or both from a common parent-stock, and he will
laugh you to scorn. I have never met a pigeon, or poultry,
or duck, or rabbit fancier, who was not fully convinced that
each main breed was descended from a distinct species. Van
Mons, in his treatise on pears and apples, shows how utterly
he disbelieves that the several sorts, for instance a Ribston-
pippin or Codlin-apple, could ever have proceeded from the
seeds of the same tree. Innumerable other examples could
be given. The explanation, I think, is simple: from long-
continued study they are strongly impressed with the differ-
ences between the several races ; and though they well know
that each race varies slightly, for they win their prizes by
selecting such slight differences, yet they ignore all general
arguments, and refuse to sum up in their minds slight differ-
ences accumulated during many successive generations. May
not those naturalists who, knowing far less of the laws of
inheritance than does the breeder, and knowing no more than
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SELECTION BY MAN 45
he does of the intermediate links in the long lines of descent,
yet admit that many of our domestic races are descended
from the same p.arents — may they not learn a lesson of cau-
tion, when they deride the idea of species in a state of nature
being lineal descendants of other species?
PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED^ AND
THEIR EFFECTS
Let US now briefly consider the steps by which domestic races
have been produced, either from one or from several allied
species. Some effect may be attributed to the direct and defi-
nite action of the external conditions of life, and some to
habit; but he would be a bold man who would account by
such agencies for the differences between a dray- and race-
horse, a greyhound and bloodhound, a carrier and tumbler
pigeon. One 'of the most remarkable features in our domes-
ticated races is that we see in them adaptation, not indeed to
the animal's or plant's own good, but to man's use or fancy.
Some variations useful to him have probably arisen sud-
denly, or by one step; many botanists, for instance, believe
that the fuller's teasel, with its hooks, which cannot be
rivalled by any mechanical contrivance, is only a variety of
the wild Dipsacus ; and this amount of change may have sud-
denly arisen in a seedling. So it has probably been with the
, turnspit dog ; and this is known to have been the case with
the ancon sheep. But when we compare the dray-horse and
race-horse, the dromedary and camel, the various breeds
of sheep fitted either for cultivated land or mountain pasture,
with the wool of one breed good for one purpose, and that
of another breed for another purpose; when we compare the
many breeds of dogs, each good for man in different ways;
when we compare the game-cock, so pertinacious in battle,
with other breeds so little quarrelsome, with "everlasting
layers" which never desire to sit, and with the bantam so
small and elegant ; when we compare the host of agricultural,
culinary, orchard, and flower-garden races of plants, most
useful to man at different seasons and for different ptuposes,
or so beautiful in his eyes, we jmxst, I think, look further
than to mere variability. We cannot suppose tha.t all the
0— BCZX
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46 ORIGIN OF SPECIES
breeds were suddenly produced as perfect and as useful as we
now see them ; indeed, in many cases, we know that this has
not been their history. The key is man's power of accumu-
lative selection : nature gives successive variations ; man adds
them up in certain directions useful to him. In this sense he
may be said to have made for himself useful breeds.
The great power of this principle of selection is not hypo-
thetical. It is certain that several of our eminent breeders
have, even within a single lifetime, modified to a large extent
their breeds of cattle and sheep. In order fully to realise
what they have done, it is almost necessary to read several
of the many treatises devoted to this subject, and to inspect
the animals. Breeders habitually speak of an animal's organi-
sation as something plastic, which they can model almost as
they please. If I had space I could quote numerous passages
to this effect from highly competent authorities. Youatt,
who was probably better acquainted with the works of agri-
culturists than almost any other individual, and who was him-
self a very good judge of animals, speaks of the principle of
selection as "that which enables the agriculturist, not only to
modify the character of his flock, but to change it altogether.
It is. the magician's wand, by means of which he may summon
into life whatever form and. mould he pleases." Lord Somer-
ville, speaking of what breeders have done for sheep, says : —
"It would seem as if they had chalked out upon a wall a form
perfect in itself, and then had given it existence." In Sax-
ony the importance of the principle of selection in regard to
merino sheep is so fully recognised, that men follow it as a
trade ; the sheep are placed on a table and are studied, like a
picture by a connoisseur ; this is done three times at intervals
of months, and the sheep are each time marked and classed,
so that the very best may ultimately be selected for breeding.
What English breeders have actually effected is proved by
the enormous prices given for animals with a good pedigree ;
and these have been exported to almost every quarter of the
world. The improvement is by no means generally due to
crossing different breeds; all the best breeders are strongly
opposed to this practice, except sometimes amongst closely
allied sub-breeds. And when a cross has been made, the
closest selection is far more indispensable even than in ordi-
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SELECTION BY MAN 47
nary cases. If selection consisted merely in separating some
very distinct variety, and breeding from it, the principle would
be so obvious as hardly to be worth notice ; but its importance
consists in the great effect produced by the accumulation in
one direction, during successive generations, of differences
absolutely inappreciable by an uneducated eye — differences
which I for one have vainly attempted to appreciate. Not
one man in a thousand has accuracy of eye and judgment
sufficient to become an eminent breeder. If gifted with these
qualities, and he studies his subject for years, and devotes his
lifetime to it with indomitable perseverance, he will succeed,
and may make great improvements ; if he wants any of these
qualities, he will assuredly fail. Few would readily believe
in the natural capacity and years of practice requisite to be-
come even a skilful pigeon-fancier.
The same principles are followed by horticulturists; but
the variations are here often more abrupt. No one supposes
that our choicest productions have been produced by a single
variation from the aboriginal stock. We have proofs that
this has not been so in several cases in which exact records
have been kept; thus, to give a very trifling instance, the
steadily increasing size of the common gooseberry may be
quoted. We see an astonishing improvement in many flor-
ists' flowers, when the flowers of the present day are com-
pared with drawings made only twenty or thirty years ago.
When a race of plants is once pretty well established, the
seed-raisers do not pick out the best plants, but merely go
over their seed-beds, and pull up the "rogues," as they call
the plants that deviate from the proper standard. With ani-
mals this kind of selection is, in fact, likewise followed; for
hardly any one is so careless as to breed from his worst
animals.
In regard to plants, there is another means of observing
the accumulated effects of selection — namely, by comparing
the diversity of flowers in the different varieties of the same
species in the flower-garden ; the diversity of leaves, pods, or
tubers, or whatever part is valued, in the kitchen-garden, in
comparison with the flowers of the same varieties; and the
diversity of fruit of the same species in the orchard, in com-
parison with the leaves and flowers of the same set of vari-
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48 ORIGIN OF SPEaES
etics. See how different the leaves of the cabbage are, and
how extremely alike the flowers; how unlike the flowers of
the heartsease are, and how alike the leaves; how much the
fruit of the different kinds of gooseberries differ in size,
colour, shape, and hairiness, and yet the flowers present very
slight differences. It is not that the varieties which differ
largely in some one point do not differ at all in other points ;
this is hardly ever, — I speak after careful observation, — per-
haps never, the case. The law of correlated variation, the im-
portance of which should never be overlooked, will ensure
some differences ; but, as a general rule, it cannot be doubted
that the continued selection of slight variations, either in the
leaves, the flowers, or the fruit, will produce races differing
from each other chiefly in these characters.
It may be objected that the principle of selection has been
reduced to methodical practice for scarcely more than three-
quarters of a century; it has certainly been more attended to
of late years, and many treatises have been published on the
subject; and the result has been, in a corresponding degree,
rapid and important But it is very far from true that the
principle is a modern discovery. I could give several refer-
ences to works of high antiquity, in which the full impor-
tance of the principle is acknowledged. In rude and bar-
barous periods of English history choice animals were often
imported, and laws were passed to prevent their exportation:
the destruction of horses under a certain size was ordered,
and this may be compared to the "roguing" of plants by nur-
serymen. The principle of selection I find distinctly given in
an ancient Chinese encyclopaedia. Explicit rules are laid
down by some of the Roman classical writers. From pas-
sages in Genesis, it is clear that the colour of domesticated
animals was at that early period attended to. Savages now
sometimes cross their dogs with wild canine animals, to im-
prove the breed, and th^ formerly did so, as is attested by
passages in Pliny. The savages in South Africa match their
draught cattle by colour, as do some of the Esquimaux their
teams of dc^s. Livingstone states that good domestic breeds
are highly valued by the negroes in the interior of Africa
who have not associated with Europeans. Some of these
facts do not show actual selection^ but they show that the
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UNCONSaOUS SELECTION 49
breeding of domestic animals was carefully attended to in
ancient times, and is now attended to by the lowest savages.
It would, indeed, have been a strange fact, had attention
not been paid to breeding, for the inheritance of good and
bad qualities is so obvious.
UNCONSCIOUS SELECTION
At the present time, eminent breeders try by methodical
selection, with a distinct object in view, to make a new strain
or sub-breed, superior to anything of the kind in the country.
But, for our purpose, a form of Selection, which may be
called Unconscious, and which results from every one trying
to possess and breed from the best individual animals, is more
important. Thus, a man who intends keeping pointers nat-
urally tries to get as good dogs as he can, and afterwards
breeds from his own best dogs, but he has no wish or expec-
tation of permanently altering the breed. Nevertheless we
may infer that this process, continued during centuries, would
improve and modify any breed, in the same way as Bakewell,
Collins, etc., by this very same process, only carried on more
methodically, did greatly modify, even during their lifetimes,
the forms and qualities of their cattle. Slow and insensible
changes of this kind can never be recognised unless actual
measurements or careful drawings of the breeds in question
have been made long ago, which may serve for comparison.
In some cases, however, unchanged, or but little changed
individuals of the same breed exist in less civilised districts,
where the breed has been less improved. There is reason to
believe that King Charles' spaniel has been unconsciously
modified to a large extent since the time of that monarch.
Some highly competent authorities are convinced that the
setter is directly derived from the spaniel, and has probably
been slowly altered from it. It is known that the English
pointer has been greatly changed within the last century, and
in this case the change has, it is believed, been chiefly effected
by crosses with the foxhound : but what concerns us is, that
the change has been effected unconsciously and gradually, and
yet so effectually, that, though the old Spanish pointer cer-
tainly came from Spain, Mr. Borrow has not seen, as I am
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50 ORIGIN OF SPEaES
informed by him, any native dog in Spain like our pointer.
By a simple process of selection, and by careful training,
English racehorses have come to surpass in fleetness and size
the parent Arabs, so that the latter, by the regulations for the
Goodwood Races, are favoured in the weights which they
carry. Lord Spencer and others have shown how the cattle
of England have increased in weight and in early maturity,
compared with the stock formerly kept in this country. By
comparing the accounts given in various old treatises of the
former and present state of carrier and tumbler pigeons in
Britain, India, and Persia, we can trace the stages through
which they have insensibly passed, and come to differ so
greatly from the rock-pigeon.
Youatt gives an excellent illustration of the effects of a
course of selection, which may be considered as unconscious,
in so far that the breeders could never have expected, or even
wished, to produce the result which ensued — namely, the pro-
duction of two distinct strains. The two flocks of Leicester
sheep kept by Mr. Buckley and Mr. Burgess, as Mr. Youatt
remarks, "have been purely bred from the original stock of
Mr. Bakewell for upwards of fifty years. There is not a sus-
picion existing in the mind of any one at all acquainted with
the subject, that the owner of either of them has deviated in
any one instance from the pure blood of Mr. Bakewell's flock,
and yet the difference between the sheep possessed by these
two gentlemen is so great that they have the appearance of
being quite different varieties."
If there exist savages so barbarous as never to think of the
inherited character of the offspring of their domestic animals,
yet any one animal particularly useful to them, for any
special purpose, would be carefully preserved during famines
and other accidents, to which savages are so liable, and such
choice animals would thus generally leave more offspring
than the inferior ones ; so that in this case there would be a
kind of unconscious selection going on. We see the value set
on animals even by the barbarians of Tierra del Fuego, by
their killing and devouring their old women, in times of
dearth, as of less value than their dogs.
In plants the same gradual process of improvement,
through the occasional preservation of the best individuals.
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UNCONSCIOUS SELECTION 51
whether or not suflSciently distinct to be ranked at their first
appearance as distinct varieties, and whether or not two or
more species or races have become blended together by cross-
ing, may plainly be recognised in the increased size and beauty
which we now see in the varieties of the heartsease, rose,
pelargonium, dahlia, and other plants, when compared with
the older varieties or with their parent-stocks. No one would
ever expect to get a first-rate heartsease or dahlia from the
seed of a wild plant. No one would expect to raise a first-
rate melting pear from the seed of the wild pear, though he
might succeed from a poor seedling growing wild, if it had
come from a garden-stock. The pear though cultivated in
classical times, appears, from Pliny's description, to have
been a fruit of very inferior quality. I have seen great sur-
prise expressed in horticultural works at the wonderful skill
of gardeners, in having produced such splendid results from
such poor materials; but the art has been simple, and, as far
as the final result is concerned, has been followed almost un-
consciously. It has consisted in always cultivating the best-
known variety, sowing its seeds, and, when a slightly better
variety chanced to appear, selecting it, and so onwards. But
the gardeners of the classical period, who cultivated the best
pears which they could procure, never thought what splendid
fruit we should eat; though we owe our excellent fruit in
some small degree to their having naturally chosen and pre-
served the best varieties they could anywhere find.
A large amount of change, thus slowly and unconsciously
accumulated, explains, as I believe, the well-known fact, that
in a number of cases we cannot recognise, and therefore do
not know, the wild parent-stocks of the plants which have
been longest cultivated in our flower and kitchen gardens.
If it has taken centuries or thousands of years to improve or
modify most of our plants up to their present standard of
usefulness to man, we can understand how it is that neither
Australia, the Cape of Good Hope, nor any other region in-
habited by quite uncivilised man, has afforded us a single plant
worth culture. It is not that these countries, so rich in
species, do not by a strange chance possess the aboriginal
stocks of any useful plants, but that the native plants have not
been improved by continued selection up to a standard of
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52 ORIGIN OF SPECIES
perfection comparable with that acquired by the plants in
countries anciently civilised.
In regard to the domestic animals kept by uncivilised man,
it should not be overlooked that they almost always have to
struggle for their own food, at least during certain seasons.
And in two countries very differently circumstanced, indi-
viduals of the same species, having slightly different consti-
tutions or structure, would often succeed better in the one
country than in the other; and thus by a process of "natural
selection," as will hereafter be more fully explained, two sub-
breeds might be formed. This, perhaps, partly explains why
the varieties kept by savages, as has been remarked by some
authors, have more of the character of true species than the
varieties kept in civilised countries.
On the view here given of the important part which selec-
tion by man has played, it becomes at once obvious, how it is
that our domestic races show adaptation in their structure or
in their habits to man's wants or fancies. We can, I think,
further understand the frequently abnormal character of our
domestic races, and likewise their differences being so great
in external characters, and relatively so slight in internal
parts or organs. Man can hardly select, or only with much
difficulty, any deviation of structure excepting such as is ex-
ternally visible ; and indeed he rarely cares for what is inter-
nal. He can never act by selection, excepting on variations
which are first given to him in some slight degree by nature.
No man would ever try to make a fantail till he saw a pigeon
with a tail developed in some slight degree in an unusual
manner, or a pouter till he saw a pigeon with a crop of some-
what unusual size; and the more abnormal or unusual any
character was when it first appeared, the more likely it would
be to catch his attention. But to use such an expression as
trying to make a fantail, is, I have no doubt, in most cases,
utterly incorrect. The man who first selected a pigeon with
a slightly larger tail, never dreamed what the descendants of
that pigeon would become through long-continued, partly
unconscious and partly methodical, selection. Perhaps the
parent-bird of all fantails had only fourteen tail-feathers
somewhat expanded, like the present Java fantail, or like in-
dividuals of other and distinct breeds, in which as many as
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UNCONSCIOUS SELECTION 53
seventeen tail-feathers have been counted. Perhaps the first
pouter-pigeon did not inflate its crop much more than the
turbit now does the upper part of its (esophagus, — a habit
which is disregarded by all fanciers, as it is not one of the
points of the breed.
Nor let it be thought that some great deviation of structure
would be necessary to catch the fancier's eye: he perceives
extremely small differences, and it is in human nature to
fancy any novelty, however slight, in one's own possession.
Nor must the value which would formerly have been set on
any slight differences in the individuals of the same species,
be judged of by the value which is now set on them, after
several breeds have fairly been established. It is known that
with pigeons many slight variations now occasionally appear,
but these are rejected as faults or deviations from the stand-
ard of perfection in each breed. The common goose has not
given rise to any marked varieties; hence the Toulouse and
the common breed, which differ only in colour, that most
fleeting of characters, have lately been exhibited as distinct
at our poultry-shows.
These views appear to explain what has sometimes been
noticed — namely, that we know hardly anything about the
origin or history of any of our domestic breeds. But, in
fact, a breed, like a dialect of a language, can hardly be said
to have a distinct origin. A man preserves and breads from
an individual with some slight deviation of structure, or takes
more care than usual in matching his best animals, and thus
improves them, and the improved animals slowly spread in the
immediate neighbourhood. But they will as yet hardly have
a distinct name, and from being only slightly valued, their
history will have been disregarded. When further improved
by the same slow and gradual process, they will spread more
widely, and will be recognised as something distinct and valu-
able, and will then probably first receive a provincial name.
In semi-civilised countries, with little free communication,
the spreading of a new sub-breed would be a slow process.
As soon as the points of value are once acknowledged, the
principle, as I have called it, of unconscious selection will
always tend, — ^perhaps more at one period than at another, as
the breed rises or falls in fashion, — ^perhaps more in one dis-
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54 ORIGIN OF SPEaSS
trict than in another, according to the state of civilisation of
the inhabitants, — slowly to add to the characteristic features
of the breed, whatever they may be. But the chance will be
infinitely small of any record having been preserved of such
slow, varying, and insensible changes.
CIRCUMSTANCES FAVOURABLE TO MAN's POWER OF SELECTION
I will now say a few words on the circumstances, favour-
able, or the reverse, to man's power of selection. A high de-
gree of variability is obviously favourable, as freely giving
the materials for selection to work on; not that mere indi-
vidual differences are not amply sufficient, with extreme care,
to allow of the accumulation of a large amount of modifica-
tion in almost any desired direction. But as variations mani-
festly useful or pleasing to man appear only occasionally, the
chance of their appearance will be much increased by a large
number of individuals being kept. Hence, nimiber is of the
highest importance for success. On this principle Marshall
formerly remarked, with respect to the sheep of parts of
Yorkshire, "as they generally belong to poor people, and are
mostly in small lots, they never can be improved." On the
other hand, nurserymen, from keeping large stocks of the
same plant, are generally far more successful than amateurs
in raising new and valuable varieties. A large number of
individuals of an animal or plant can be reared only where
the conditions for its propagation are favourable. When the
individuals are scanty, all will be allowed to breed, whatever
their quality may be, and this will effectually prevent selec-
tion. But probably the most important element is that the
animal or plant should be so highly valued by man, that the
closest attention is paid to even the slightest deviations in its
qualities or structure. Unless such attention be paid nothing
can be effected. I have seen it gravely remarked, that it was
most fortunate that the strawberry began to vary just when
gardeners began to attend to this plant. No doubt the straw-
berry had always varied since it was cultivated, but the slight
varieties had been neglected. As soon, however, as gar-
deners picked out individual plants with slightly larger, ear-
lier, or better fruit, and raised seedlings from them, and again
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CIRCUMSTANCES FAVOURABLE TO SELECTION 55
picked out the best seedlings and bred from them, then (with
some aid by crossing distinct species) those many admirable
varieties of the strawberry were raised which have appeared
during the last half-century.
With animals, facility in preventing crosses is an important
element in the formation of new races, — at least, in a country
which is already stocked with other races. In this respect
enclosure of the land plays a part. Wandering savages or
the inhabitants of open plains rarely possess more than one
breed of the same species. Pigeons can be mated for life, and
this is a great convenience to the fancier, for thus many races
may be improved and kept true, though mingled in the same
aviary ; and this circumstance must have largely favoured the
formation of new breeds. Pigeons, I may add, can be propa-
gated in great nimibers and at a very quick rate, and inferior
birds may be freely rejected, as when killed they serve for
food. On the other hand, cats, from their nocturnal rambling
habits, cannot be easily matched, and, although so much
valued by women and children, we rarely see a distinct breed
long kept up ; such breeds as we do sometimes see are almost
always imported from some other country. Although I do
not doubt that some domestic animals vary less than others,
yet the rarity or absence of distinct breeds of the cat, the
donkey, peacock, goose, &c., may be attributed in main part
to selection not having been brought into play: in cats, from
the difficulty in pairing them; in donkeys, from only a few
being kept by poor people, and little attention paid to their
breeding; for recently in certain parts of Spain and of the
United States this animal has been surprisingly modified and
improved by careful selection; in peacocks, from not being
very easily reared and a large stock not kept; in geese, from
being valuable only for two purposes, food and feathers, and
more especially from no pleasure having been felt in the dis-
play of distinct breeds ; but the goose, under the conditions to
which it is exposed when domesticated, seems to have a sin-
gularly inflexible organisation, though it has varied to a
slight extent, as I have elsewhere described.
Some authors have maintained that the amount of variation
in our domestic productions is soon reached, and can never
afterwards be exceeded. It would be somewhat rash to as-
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56 ORIGIN OF SPECIES
sert that the limit has been attained in any one case ; for al-
most all our animals and plants have been greatly improved in
many ways within a recent period ; and this implies variation.
It would be equally rash to assert that characters now in-
creased to their usual limit, could not, after remaining fixed
for many centuries, again vary imder new conditions of life.
No doubt, as Mr. Wallace has remarked with much truth, a
limit will be at last reached. For instance, there must be a
limit to the fleetness of any terrestrial animal, as this will
be determined by the friction to be overcome, the weight of
body to be carried, and the power of contraction in the mus-
cular fibres. But what concerns us is that the domestic vari-
eties of the same species differ from each other in almost
every character, which man has attended to and selected,
more than do the distinct species of the same genera. Isi-
dore Geoffroy St. Hilaire has proved this in regard to size,
and so it is with colour and probably with the length of hair.
With respect to fleetness, which depends on many bodily char-
acters, Eclipse was far fleeter, and a dray-horse is incom-
parably stronger than any two natural species belonging to
the same genus. So with plants, the seeds of the different
varieties of the bean or maize probably differ more in size,
than do the seeds of the distinct species in any one genus in
the same two families. The same remark holds good in re-
gard to the fruit of the several varieties of the plum, and still
more strongly with the melon, as well as in many other anal-
ogous cases.
To sum up on the origin of our domestic races of animals
and plants. Changed conditions of life are of the highest
importance in causing variability, both by acting directly on
the organisation, and indirectly by affecting the reproductive
system. It is not probable that variability is an inherent and
necessary contingent, under all circumstances. The greater
or less force of inheritance and reversion determine whether
variations shall endure. Variability is governed by many
unknown laws, of which correlated growth is probably the
most important. Something, but how much we do not know,
may be attributed to the definite action of the conditions of
life. Some, perhaps a great, effect may be attributed to the
increased use or disuse of parts. The final result is thus
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CIRCUMSTANCES FAVOURABLE TO SELECTION 57
rendered infinitely complex. In some cases the intercrossing
of aboriginally distinct species appears to have played an im-
portant part in the origin of our breeds. When several
breeds have once been formed in any country, their occa-
sional intercrossing, with the aid of selection, has, no doubt,
largely aided in the formation of new sub-breeds ; but the im-
portance of crossing has been much exaggerated, both in re-
gard to animals and to those plants which are propagated by
seed. With plants which are temporarily propagated by cut-
tings, buds, &c., the importance of crossing is immense; for
the cultivator may here disregard the extreme variability
both of hybrids and of mongrels, and the sterility of hybrids ;
but plants not propagated by seed are of little importance to
us, for their endurance is only temporary. Over all these
causes of Change, the accumulative action of Selection,
whether applied methodically and quickly, or unconsciously
and slowly but more efficiently, seems to have been the pre-
dominant Power.
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CHAPTER II
Variation Under Nature
Variabilit3^ — Individual differences — Doubtful species — ^Wide ranging^
much diffused, and common species, vary most — Species of the
larger genera in each country vary more frequently than the
species of the smaller genera — Many of the species of the larger
genera resemble varieties in being very closely, but unequally,
related to each other, and in having restricted ranges.
BEFORE applying the principles arrived at in the last
chapter to organic beings in a state of nature, we must
briefly discuss whether these latter are subject to any
variation. To treat this subject properly, a long catalogue of
dry facts ought to be given; but these I shall reserve for a
future work. Nor shall I here discuss the various definitions
which have been given of the term species. No one defini-
tion has satisfied all naturalists; yet every naturalist knows
vaguely what he means when he speaks of a species. Gen-
erally the term includes the unknown element of a distinct
act of creation. The term "variety" is almost equally difl&-
cult to define; but here community of descent is almost uni-
versally implied, though it can rarely be proved. We have
also what are called monstrosities; but they graduate into
varieties. By a monstrosity I presume is meant some consid-
erable deviation of structure, generally injurious, or not use-
ful to the species. Some authors use the term "variation" in
a technical sense, as implying a modification directly due to
the physical conditions of life ; and "variations" in this sense
are supposed not to be inherited; but who can say that the
dwarfed condition of shells in the brackish waters of the
Baltic, or dwarfed plants on Alpine summits, or the thicker
fur of an animal from far northwards, would not in some
cases be inherited for at least a few generations? and ifi this
case I presume that the form would be called a variety.
It may be doubted whether sudden and considerable devi-
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INDIVIDUAL DIFPBRENCES S»
attons of structure such as we occasionally see in our domes-
tic productions, more especially with plants, are ever perma-
nently propagated in a state of nature. Almost every part
of every organic being is so beautifully related to its complex
conditions of life that it seems as improbable that any part
should have been suddenly produced perfect, as that a com-
plex machine should have been invented by man in a perfect
state. Under domestication monstrosities sometimes occur
which resemble normal structures in widely different animals.
Thus pigs have occasionally been born with a sort of pro-
boscis, and if any wild species of the same genus had nat-
urally possessed a proboscis, it might have been argued that
this had appeared as a monstrosity; but I have as yet failed
to find, after diligent search, cases of monstrosities resem-
bling normal structures in nearly allied forms, and these alone
bear on the question. If monstrous forms of this kind ever
do appear in a state of nature and are capable of reproduc-
tion (which is not always the case), as they occur rarely and
singly, their preservation would depend on unusually favour-
able circumstances. They would, also, during the first and
succeeding generations cross with the ordinary form, and
thus their abnormal character would almost inevitably be lost
But I shall have to return in a future chapter to the pres-
ervation and perpetuation of single or occasicMial variations.
INDIVIDUAL DIFFERENCES
The many slight differences which appear in the offspring
from the same parents, or which it may be presumed have
thus arisen, from being observed in the individuals of the
same species inhabiting the same confined locality, may be
called individual differences. No one supposes that all the
individuals of the same species are cast in the same acttial
mould. These individual differences are of the highest im-
portance for us, for they are often inherited, as must be
familiar to every one; and they thus afford materials for
natural selection to act on and accumulate, in the same man-
ner a& man accumulates in any given direction individual dif-
ferences in his domesticated productions. These individual
differences generally affect what naturalists consider unim-
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GO ORIGIN OF SPBaES
portant parts ; but I could show by a long catalogue of facts,
that parts which must be called important, whether viewed
under a physiological or classificatory point of view, some-
times vary in the individuals of the same species. I am con-
vinced that the most experienced naturalist would be sur-
prised at the number of the cases of variability, even in im-
portant parts of stnicture, which he could collect on good
authority, as I have collected, during a course of years. It
should be remembered that systematists are far from being
pleased at finding variability in important characters, and that
there are not many men who will laboriously examine inter-
nal and important organs, and compare them in many speci-
mens of the same species. It would never have been expected
that the branching of the main nerves close to the great cen-
tral ganglion of an insect would have been variable in the
same species; it might have been* thought that changes of
this nature could have been effected only by slow degrees;
yet Sir J. Lubbock has shown a degree of variability in these
main nerves in Coccus, which may almost be compared to the
irregular branching of the stem of a tree. This philosoph-
ical naturalist, I may add, has also shown that the muscles in
the larvae of certain insects are far from uniform. Authors
sometimes argue in a circle when they state that important
organs never vary; for these same authors practically rank
those parts as important (as some few naturalists have hon-
estly confessed) which do not vary; and, under this point of
view, no instance will ever be found of an important part
varying; but under any other point of view many instances
assuredly can be given.
There is one point connected with individual differences,
which is extremely perplexing: I refer to those genera which
have been called "protean" or "poljrmorphic," in which the
species present an inordinate amount of variation. With re-
spect to many of these forms, hardly two naturalists agree
whether to rank them as species or as varieties. We may
instance Rubus, Rosa, and Hieracium amongst plants, several
genera of insects and of Brachiopod shells. In most poly-
morphic genera some of the species have fixed and definite
characters. Genera which are polymorphic in one country
seem to be, with a few exceptions, polymorphic in other coun-
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INDIVIDUAL DIFFERENCES 61
tries, and likewise, judging from Brachiopod shells, at former
periods of time. These facts are very perplexing, for they
seem to show that this kind of variability is independent of
the conditions of life. I am inclined to suspect that we see,
at least in some of these polymorphic genera, variations which
are of no service or disservice to the species, and which con-
sequently have not been seized on and rendered definite by
natural selection, as hereafter to be explained.
Individuals of the same species often present, as is known
to every one, great differences of structure, independently
of variation, as in the two sexes of various animals, in
the two or three castes of sterile female or workers amongst
insects, and in the immature and larval states of many of
the lower animals.
There are, also, cases of dimorphism and trimorphism,
both with animals and plants. Thus, Mr. Wallace, who
^has lately called attention to the subject, has shown
that the females of certain species of butterflies, in the Ma-
layan archipelago, regularly appear under two or even three
conspicuously distinct forms, not connected by intermediate
varieties. Fritz Mtiller has described analogous but more
extraordinary cases with the males of certain Brazilian
Crustaceans: thus, the male of a Tanais regularly occurs
under two distinct forms; one of these has strong and dif-
ferently shaped pincers, and the other has antennx much
more abundantly furnished with smelling-hairs. Although
in most of these cases, the two or three forms, both with
animals and plants, are not now connected by intermediate
gradations, it is probable that they were once thus connected.
Mr. Wallace, for instance, describes a certain butterfly which
presents in the same island a great range of varieties con-
nected by intermediate links, and the extreme links of the
chain closely resemble the two forms of an allied dimorphic
species inhabiting another part of the Malay archipelago.
Thus also with ants, the several worker-castes are generally
quite distinct; but in some cases, as we shall hereafter see,
the castes are connected together by finely graduated varie-
ties. So it is, as I have myself observed, with some dimor-
phic plants. It certainly at first appears a highly remarkable
fact that the same female butterfly should have the power
D— HCXI
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62 ORIGIN OF SPEOES
of producing at the same time three distinct female forms
and a male; and that an hermaphrodite plant should produce
from the same seed-capsule three distinct hermaphrodite
forms, bearing three different kinds of females and three or
even six different kinds of males. Nevertheless these cases
are only exaggerations of the common fact that the female
produces offspring of two sexes which sometimes differ from
each other in a wonderful manner.
DOUBTFUL SPECIES
The forms which possess in some considerable degree the
character of species, but which are so closely similar to other
forms, or are so closely linked to them by intermediate gra-
dations, that naturalists do not like to rank them as distinct
species, are in several respects the most important for us.
We have every reason to believe that many of these doubtfuK
and closely allied forms have permanently retained their
characters for a long time; for as long, as far as we know,
as have good and true species. Practically, when a naturalist
can unite by means of intermediate links any two forms, he
treats the one as a variety of the other; ranking the most
common, but sometimes the one first described, as the spe-
cies, and the other as the variety. But cases of great diffi-
culty, which I will not here enumerate, sometimes arise in
deciding whether or not to rank one form as a variety of
another, even when they are closely connected by interme-
diate links; nor will the commonly-assumed hybrid nature
of the intermediate forms always remove the difficulty. In
very many cases, however, one form is ranked as a variety
of another, not because the intermediate links have actually
been found, but because analogy leads the observer to sup-
pose either that they do now somewhere exist, or may for-
merly have existed; and here a wide door for the entry of
doubt and conjecture is opened.
Hence, in determining whether a form should be ranked
as a species or a variety, the opinion of naturalists having
sound judgment and wide experience seems the only guide to
follow. We must, however, in many cases, decide by a ma-
jority of naturalists, for few well-marked and well-known
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DOUBTFUL SPEaES 63
varieties can be named which have not been ranked as spe-
cies by at least some competent judges.
That varieties of this doubtful nature are far from un-
common cannot be disputed. Compare the several floras of
Great Britain, of France, or of the United States, drawn up
by different botanists, and see what a surprising number of
forms have been ranked by one botanist as good species,
and by another as mere varieties. Mr. H. C. Watson, to
whom I lie under deep obligation for assistance of all kinds,
has marked for me 182 British plants, which are generally
considered as varieties, but which have all been ranked by
botanists as species; and in making this list he has omitted
many trifling varieties, but which nevertheless have been
ranked by some botanists as species, and he has entirely
omitted several highly polymorphic genera. Under genera,
including the most polymorphic forms, Mr. Babington gives
251 species, whereas Mr. Bentham gives only 112, — b, differ-
ence of 139 doubtful forms ! Amongst animals which unite
for each birth, and which are highly locomotive, doubtful
forms, ranked by one zoologist as a species and by another
as a variety, can rarely be found within the same country,
but are common in separated areas. How many of the birds
and insects in North America and Europe, which differ very
slightly from each other, have been ranked by one eminent
naturalist as undoubted species, and by another as varieties,
or, as they are often called, geographical races 1 Mr. Wallace,
in several valuable papers on the various animals, especially
on the Lepidoptera, inhabiting the islands of the great Ma-
layan archipelago, show that they may be classed under four
heads, namely, as variable forms, as local forms, as geo-
graphical races or sub-species, and as true representative
species. The first or variable forms vary much within the
limits of the same island. The local forms are moderately
constant and distinct in each separate island; but when all
from the several islands are compared together, the differ-
ences are seen to be so slight and graduated, that it is im-
possible to define or describe them, though at the same time
the extreme forms are. sufficiently distinct. The geo-
graphical races or sub-species are local forms completely
fixed and isolated; but as they do not differ from each other
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64 ORIGIN OF SPEQES
by strongly marked and important characters, ''there is no
possible test but individual opinion to determine which of
them shall be considered as species and which as varieties."
Lastly, representative species fill the same place in the nat-
ural economy of each island as do the local forms and sub-
species; but as they are distinguished from each other by a
greater amount of difference than that between the local
forms and sub-species, they are almost universally ranked
by naturalists as true species. Nevertheless, no certain cri-
terion can possibly be given by which variable forms, local
forms, sub-species, and representative species can be
recognised.
Many years ago, when comparing, and seeing others com-
pare, the birds from the closdy neighbouring islands of the
Galapagos archipelago, one with another, and with those
from the American mainland, I was much struck how entirely
vague and arbitrary is the distinction between species and
varieties. On the islets of the little Madeira group there are
many insects which are characterised as varieties in Mr.
Wollaston's admirable work, but which would certainly be
ranked as distinct species by many entomologists. Even Ire-
land has a few animals, now generally regarded as varie-
ties, but which have been ranked as species by some zoolo-
gists. Several experienced ornithologists consider our
British red grouse as only a strongly-marked race of Nor-
wegian species, whereas the greater number rank it as an
undoubted species peculiar to Great Britain. A wide dis-
tance between the homes of two doubtful forms leads many
naturalists to rank them as distinct species; but what dis-
tance, it has been well asked, will suffice; if that between
America and Europe is ample, will that between Europe and
the Azores, or Madeira, or the Canaries, or between the sev-
eral islets of these small archipelagos, be sufficient?
Mr. B. D. Walsh, a distinguished entomologist of the
United States, has described what he calls Phytophagic vari-
eties and Phytophagic species. Most vegetable-feeding
insects live on one kind of plant or on one group of plants ;
some feed indiscriminately on many kinds, but do not in
consequence vary. In several cases, however, insects found
living on different plants, have been observed by Mr. Walsh
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DOUBTFUL SPECIES 65
to present in their larval or mature state, or in both states,
slight, though constant diflFerences in colour, size, or in the
nature of their secretions. In some instances the males
alone, in other instances both males and females, have been
observed thus to differ in a slight degree. When the differ-
ences are rather more strongly marked, and when both
sexes and all ages are affected, the forms are ranked by all
entomologists as good species. But no observer can deter-
mine for another, even if he can do so for himself, which of
these Phytophagic forms ought to be called species and
which varieties. Mr. Walsh ranks the forms which it may
be supposed would freely intercross, as varieties; and those
which appear to have lost this power, as species. As the
differences depend on the insects having long fed on distinct
plants, it cannot be expected that intermediate links connect-
ing the several forms should now be found. The naturalist
thus loses his best guide in deterhiining whether to rank
doubtful forms as varieties or species. This likewise neces-
sarily occurs with closely allied organisms, which inhabit
distinct continents or islands. When, on the other hand,
an animal or plant ranges over the same continent, or in-
habits many islands in the same archipelago, and presents
different forms in the different areas, there is always a good
chance that intermediate forms will be discovered which will
link together the extreme states ; and these are then degraded
to the rank of varieties.
Some few naturalists maintain that animals never present
varieties; but then these same naturalists rank the slightest
difference as of specific value; and when the same identical
form is met with in two distinct countries, or in two geologi-
cal formations, they believe that two distinct species are hid-
den under the same dress. The terni species thus comes to
be a mere useless abstraction, implying and assuming a sep-
arate act of creation. It is certain that many forms, consid-
ered by highly-competent judges to be varieties, resemble
species so completely in character, that they have been thus
ranked by other highly-competent judges. But to discuss
whether they ought to be called species or varieties, before
any definition of these terms has been generally accepted, is
vainly to beat the air.
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m ORIGIN OP SPECIRS
Many of the cases of strongly-marked varieties or doubtful
species well deserve consideration; for several interesting
lines of argument, from geographical distribution, analogical
variation, hybridism, &c,, have been brought to bear in the
attempt to determine their rank ; but space does not here per-
mit me to discuss them. Close investigation, in many cases,
will no doubt bring naturalists to agree how to rank doubt-
ful forms. Yet it must be confessed that it is in the best
known countries that we find the greatest number of them.
I have been struck with the fact, that if any animal or plant
in a state of nature be highly useful to man, or from any
cause closely attracts his attention, varieties of it will almost
universally be found recorded. These varieties, moreover,
will often be ranked by some authors as species. Look at the
common oak, how closely it has been studied ; yet a German
author makes more than a dozen species out of forms, which
are almost universally considered by other botanists to be
varieties; and in this country the highest botanical authori-
ties and practical men can be quoted to show that the sessile
and pedunculated oaks are either good and distinct species or
mere varieties.
I may here allude to a remaiicable memoir lately published
by A. de CandoUe, on the oaks of the whole world. No one
ever had more ample materials for the discrimination of the
species, or could have worked cm them with more zeal and
sagacity. He first gives in detail all the many points of struc-
ture which vary in the several species, and estimates numeri-
cally the relative frequency of the variations. He specifies
above a dozen characters which may be found varying even
on the same branch, sometimes according to age or develop-
ment, sometimes without any assignable reason. Such char-
acters are not of course* of specific value, but they are, as Asa
Gray has remarked in commenting on this memoir, such as
generally enter into specific definitions. De Candolle then
goes on to say that he gives the rank of species to the forms
that differ by characters never varying on the same tree, and
never found connected by intermediate states. After this
discussion, the result of so much labour, he emphatically re-
marks: "They are mistaken, who repeat that the greater
part of our species are clearly limited^ and that the doubtful
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DOUBTFUL SPSaES 9i
species are in a feeble minority. This seemed to be true, so
long as a genus was imperfectly known, and its ^ecies were
founded upon a few specimens, that is to say, were pro-
visional Just as we come to know them better, intermediate
forms flow in, and doubts as to specific limits augment/' He
also adds that it is the best known species which present the
greatest number of spontaneous varieties and sub-varieties.
The Quercus robur has twenty-eight varieties, all of which,
excepting six, are clustered round three su^-species, namely,
Q. pedunculata sessilifiora, and pubescens. The forms which
connect these three sub-species are comparatively rare; and,
as Asa Gray again remarks, if these connecting forms which
are now rare, were to become wholly extinct, the three sub-
species would hold exactly the same relation to each other, as
do the four or five provisionally admitted species which
closely surround the typical Quercus robur. Finally, De
Candolle admits that out of the 300 species, which will be
enumerated in his Prodromus as belonging to the oak family,
at least two-thirds are provisional species, that is, are not
known strictly to fulfil the definition above given of a true
species. It should be added that De Candolle no longer be-
lieves that species are immutable creations, but concludes
that the derivative theory is the most natural one, "and the
most accordant with the known facts in palaeontology, geo-
graphical botany and zoology, of anatomical structure and
classification."
When a young naturalist commences the study of a group
of organisms quite unknown to him, he is at first much per-
plexed in determining what differences to consider as specific,
and what as varietal; for he knows nothing of the amount
and kind of variation to which the group is subject ; and this
shows, at least, how very generally there is some variation.
But if he confine his attention to one class within one country,
he will soon make up his mind how to rank most of the doubt-
ful forms. His general tendency will be to make many
species, for he will become impressed, just like the pigeon or
poultry fancier before alluded to, with the amount of differ-
ence in the forms which he is continually studying; and he
has little general knowledge of analogical variation in other
groups and in other coimtries, by which to correct his first
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68 ORIGIN OP SPBaES
impressions. As he extends the range of his observations, he
will meet with more cases of difficulty ; for he will encounter
a greater number of closely-allied forms. But if his observa-
tionB be widely extended, he will in the end generally be able
to make up his own mind ; but he will succeed in this at the
expense of admitting much variation, — and the truth of this
admission will often be disputed by other naturalists. When
he comes to study allied forms brought from countries not
now continuous, in which case he cannot hope to find inter-
mediate links, he will be compelled to trust almost entirely to
analogy, and his difficulties will rise to a climax.
Certainly no dear line of demarcation has as yet been
drawn between species and sub-species — ^that is, the forms
which in the opinion of some naturalists come very near to,
but do not quite arrive at, the rank of species: or, again,
between sub-species and well-marked varieties, or between
lesser varieties and individual differences. These differences
blend into each other by an insensible series; and a series
impresses the mind with the idea of an actual passage.
Hence I look at individual differences, though of small
interest to the systematist, as of the highest importance for
us, as being the first steps towards such slight varieties as
are barely thought worth recording in works on natural his-
tory. And I look at varieties which are in any degree more
distinct and permanent, as steps towards more strongly-
marked and permanent varieties; and at the latter, as lead-
ing to sub-species, and then to species. The passage from
one stage of difference to another may, in many cases, be
the simple result of the nature of the organism and of the
different physical conditions to which it has long been ex-
posed; but with respect to the more important and adaptive
characters, the passage from one stage of difference to an-
other, may be safely attributed to the cumulative action of
natural selection, hereafter to be explained, and to the effects
of the increased use or disuse of parts. A well-marked vari-
ety may therefore be called an incipient species ; but whether
this belief is justifiable must be judged by the weight of the
various facts and considerations to be given throughout this
work.
It need not be supposed that all varieties or incipient
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DOMINANT SPECIES VARY MOST 69
species attain the rank of species. They may become extinct,
or they may endure as varieties for very long periods, as
has been shown to be the case by Mr. Wollaston with the
varieties of certain fossil land-shells in Madeira, and with
plants by Gaston de Saporta. If a variety were to flourish
so as to exceed in numbers the parent species, it would then
rank as the species, and the species as the variety; or it
might come to supplant and exterminate the parent species;
or both might co-exist, and both rank as independent species.
But we shall hereafter return to this subject.
From these remarks it will be seen that I look at the term
species as one arbitrarily given, for the sake of convenience,
to a set of individuals closely resembling each other, and
that it does not essentially differ from the term variety, which
is given to less distinct and more fluctuating forms. The
term variety, again, in comparison with mere individual dif-
ferences, is also applied arbitrarily, for convenience' sake.
WIDE-RANGING, MUCH DIFFUSED, AND COMMON SPECIES
VARY MOST
Guided by theoretical considerations, I thought that some
interesting results might be obtained in regard to the nature
and relations of the species which vary most, by tabulating
all the varieties in several well-worked floras. At first this
seemed a simple task; but Mr. H. C. Watson, to whom I am
much indebted for valuable advice and assistance on this
subject, soon convinced me that there were many difficulties,
as did subsequently Dr. Hooker, even in stronger terms. I
shall reserve for a future work the discussion of these diffi-
culties, and the tables of the proportional numbers of the
varying species. Dr. Hooker permits me to add that after
having carefully read my manuscript, and examined the
tables, he thinks that the following statements are fairly well
established. The whole subject, however, treated as it neces-
sarily here is with much brevity, is rather perplexing, and
allusions cannot be avoided to the "struggle for existence,"
"divergence of character," and other questions, hereafter to
be discussed.
Alphonse de CandoUe and others have shown that plants
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70 ORIGIN OF SPEaES
which have very wide ranges generally present varieties;
and this might have been expected, as they are exposed to
diverse physical conditions, and as they come into competi-
tion (which, as we shall hereafter see, is an equally or more
important circumstance) with different sets of organic beings.
But my tables further show that, in any limited country, the
species which are the most common, that is abound most in
individuals, and the species which are most widely diffused
within their own country (and this is a different considera-
tion from wide range, and to a certain extent from com-
monness), oftenest give rise to varieties sufficiently well-
marked to have been recorded in botanical works. Hence
it is the most flourishing, or, as they may be called, the
dominant species, — those which range widely, are the most
diffused in their own country, and are the most numerous
in individuals, — ^which oftenest produce well-marked varie-
ties, or, as I consider them, incipient species. And this, per-
haps, might have been anticipated; for, as varieties, in order
to become in any degree permanent, necessarily have to
struggle with the other inhabitants of the country, the spe-
cies which are already dominant will be the most likely to
yield offspring, which, though in some slight degree modi-
fied, still inherit those advantages that enabled their parents
to become dominant over their compatriots. In these re-
marks on predominance, it should be understood that refer-
ence is made only to the forms which come into competition
with each other, and more especially to the members of the
same genus or class having nearly similar habits of life.
With respect to the number of individuals or commonness
of species, the comparison of course relates only to the
members of the same group. One of the higher plants may
be said to be dominant if it be more numerous in individuals
and more widely diffused than the other plants of the same
country, which live under nearly the same conditions. A
plant of this kind is not the less dominant because some
conferva inhabiting the water or some parasitic fungus is
infinitely more numerous in individuals, and more widely
diffused. But if the conferva or parasitic fungus exceeds
its allies in the above respects, it will then be dominant
within its own class.
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SPECIES OF LARGER GENERA VARIABLE 71
SPECIES OF THE LARGER GENERA IN EACH COUNTRY VARY
MORS FREQUENTLY THAN THE SPECIES OF THE
SMALLER GENERA
If the plants inhabiting a country, as described in any
Flora, be divided into two equal masses, all those in the
larger genera (i.e., those including many species) being
placed on one side, and all those in the smaller genera on
the other side, the former will be found to include a some-
what larger number of the very common and much diffused
or dominant species. This might have been anticipated; for
the mere fact of many species of the same genus inhabiting
any country, shows that there is something in the organic
or inorganic conditions of that country favourable to the
genus; and, consequently, we might have expected to have
found in the larger genera, or those including many species,
a larger proportional number of dominant species. But so
many causes tend to obscure this result, that I am surprised
that my tables show even a small majority on the side of
the larger genera. I will here allude to only two causes of
obscurity. Fresh-water and salt-loving plants generally
have very wide ranges and are much diffused, but this seems
to be connected with the nature of the stations inhabited by
them, and has little or no relation to the size of the genera
to which the species belong. Again, plants low in the scale
of organisation are generally much more widely diffused
than plants higher in the scale; and here again there is no
close relation to the size of the genera. The cause of lowly-
organised plants ranging widely will be discussed in our
chapter on Geographical Distribution.
From looking at species as only strongly-marked and well-
defined varieties, I was led to anticipate that the species of
the larger genera in each country would oftener present
varieties, than the species of the smaller genera; for wher-
ever many closely related species (i.e., species of the same
genus) have been formed, many varieties or incipient spe-
cies ought, as a general rule, to be now forming. Where
many large trees grow, we expect to find saplings. Where
many species of a genus have been formed through varia-
tion, circumstances have been favourable fj>r variation; and
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72 ORIGIN OF SPECIES
hence we might expect that the circumstances would gener-
ally be still favourable to variation. On the other hand, if
we look at each species as a special act of creation, there is
no apparent reason why more varieties should occur in a
group having many species, than in one having few.
To test the truth of this anticipation I have arranged the
plants of twelve countries, and the coleopterous insects of
two districts, into two nearly equal masses, the species of
the larger genera on one side, and those of the smaller genera
on the other side, and it has invariably proved to be the case
that a larger proportion of the species on the side of the
larger genera presented varieties, than on the side of the
smaller genera. Moreover, the species of the large genera
which present any varieties, invariably present a larger
average number of varieties than do the species of the small
genera. Both these results follow when another division is
made, and when all the least genera, with from only one to
four species, are altogether excluded from the tables. These
facts are of plain signification on the view that species are
only strongly-marked and permanent varieties ; for wherever
many species of the same genus have been formed, or where,
if we may use the expression, the manufactory of species
has been active, we ought generally to find the manufactory
still in action, more especially as we have every reason to
believe the process of manufacturing new species to be a
slow one. And this certainly holds true, if varieties be
looked at as incipient species; for my tables clearly show as
a general rule that, wherever many species of a genus have
been formed, the species of that genus present a number of
varieties, that is of incipient species, beyond the average.
It is not that all large genera are now varying much, and
are thus increasing in the number of their species, or that
no small genera are now varying and increasing; for if this
had been so, it would have been fatal to my theory; inas-
much as geology plainly tells us that small genera have in
the lapse of time often increased greatly in size; and that
large genera have often come to their maxima, decline, and
disappeared. All that we want to show is, that, where many
species of a genus have been formed, on an average many
are still forming; and this certainly holds good.
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RESEMBLE VARIETIES 73
MANY OF THE SPECIES INCLUDED WITHIN THE LARGER
GENERA RESEMBLE VARIETIES IN BEING VERY CLOSELY^
BUT UNEQUALLY, RELATED TO EACH OTHER, AND
IN HAVING RESTRICTED RANGES
There are other relations between the species of large
genera and their recorded varieties which deserve notice. We
have seen that there is no infallible criterion by which to
distinguish species and well-marked varieties; and when in-
termediate links have not been found between doubtful
forms, naturalists are compelled to come to a determination
by the amount of difference between them, judging by anal-
ogy whether or not the amount suffices to raise one or both
to the rank of species. Hence the amount of difference is
one very important criterion in settling whether two forms
should be ranked as species or varieties. Now Fries has
remarked in regard to plants, and Westwood in regard to
insects, that in large genera the amount of difference be-
tween the species is often exceedingly small. I have en-
deavoured to test this numerically by averages, and, as far
as my imperfect results go, they confirm the view. I have
also consulted some sagacious and experienced observers,
and, after deliberation, they concur in this view. In this
respect, therefore, the species of the larger genera resemble
varieties, more than do the species of the smaller genera.
Or the case may be put in another way, and it may be said,
that in the larger genera, in which a number of varieties or
incipient species greater than the average are now manu-
facturing, many of the species already manufactured still to
a certain extent resemble varieties, for they differ from each
other by less than the usual amount of difference.
Moreover, the species of the larger genera are related to
each other, in the same manner as the varieties of any one
species are related to each other. No naturalist pretends
that all the species of a genus are equally distinct from each
other ; they may generally be divided into sub-genera, or sec-
tions, or lesser groups. As Fries has well remarked, little
groups of species are generally clustered like satellites
around other species. And what are varieties but groups of
forms, unequally related to each other, and clustered round
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74 ORIGIN OF SPEaBS
certain forms — ^that is, round their parent-species? Un-
doubtedly there is one most important point of difference
between varieties and species; namely, that the amount of
difference between varieties, when compared with each other
or with their parent-species, is much less than that between
the species of the same genus. But when we come to discuss
the principle, as I call it, of Divergence of Character, we
shall see how this may be explained, and how the lesser dif-
ferences between varieties tend to increase into the greater
differences between species.
There is one other point which is worth notice. Varieties
generally have much restricted ranges: this statement is in-
deed scarcely more than a truism, for, if a variety were
found to have a wider range than that of its supposed parent-
species, their denominations would be reversed. But there
is reason to believe that the species which are very closely
allied to other species, and in so far resemble varieties, often
have much restricted ranges. For instance, Mr. H. C. Wat-
son has marked for me in the well-sifted London Catalogue
of plants (4th edition) 63 plants which are therein ranked
as species, but which he considers as so closely allied to other
species as to be of doubtful value: these 63 reputed species
range on an average over 6*9 of the provinces into which
Mr. Watson has divided Great Britain. Now, in this same
Catalogue, 53 acknowledged varieties are recorded, and these
range over 7 7 provinces ; whereas, the species to which these
varieties belong range over 14*3 provinces. So that the ac-
knowledged varieties have nearly the same restricted aver-
age range, as have the closely allied forms, marked for me
by Mr. Watson as doubtful species, but which are almost*
universally ranked by British botanists as good and true
species.
SUMMARY
Finally, varieties cannot be distinguished from species, —
except, first, by the discovery of intermediate linking forms;
and, secondly, by a certain indefinite amount of difference
between them; for two forms, if differing very little, are
generally ranked as varieties, notwithstanding that they
cannot be closely connected; but the amount of difference
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SUMMARY 75
considered necessary to give to any two forms the rank of
species cannot be defined. In genera having more than the
average number of species in any country, the species of
these genera have more than the average number of varie-
ties. In large genera the species are apt to be closely, but
unequally, allied together, forming little clusters round other
species. Species very closely allied to other species appar-
ently have restricted ranges. In all these respects the spe-
cies of large genera present a strong analogy with varieties.
And we can clearly understand these analogies, if species
once existed as varieties, and thus originated; whereas, these
analogies are utterly inexplicable if species are independent
creations.
We have, also, seen that it is the most flourishing or dom-
inant species of the larger genera within each class which on
an average yield the greatest number of varieties ; and varie-
ties, as we shall hereafter see, tend to become converted into
new and distinct species. Thus the larger genera tend to
become larger; and throughout nature the forms of life
which are now dominant tend to become still more dominant
by leaving many modified and dominant descendants. But
by steps hereafter to be explained, the larger genera also
tend to break up into smaller genera. And thus, the forms
of life throughout the universe become divided into groups
subordinate to groups.
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CHAPTER III
Struggle for Existence
Its bearing on natural selection — The term used in a wide sense —
Geometrical ratio of increase — Rapid increase of naturalized
animals and plants — Nature of the checks to increase — Competi-
tion universal — Effects of climate — Protection from the number
of individuals — Complex relations of all animals and plants
throughout nature — Struggle for life most severe between indi-
viduals and varieties of the same species: often severe between
species of the same genus — ^The relation of organism to organism
the most important of all relations.
BEFORE entering on the subject of this chapter, I must
make a few preliminary remarks, to show how the
struggle for existence bears on Natural Selection. It
has been seen in the last chapter that amongst organic beings
in a state of nature there is some individual variability: in-
deed I am not aware that this has ever been disputed. It is
immaterial for us whether a multitude of doubtful forms be
called species or sub-species or varieties ; what rank, for in-
stance, the two or three hundred doubtful forms of British
plants are entitled to hold, if the existence of any well-marked
varieties be admitted But the mere existence of individual
variability and of some few well-marked varieties, though
necessary as the foundation for the work, helps us but little
in understanding how species arise in nature. How have all
those exquisite adaptations of one part of the organisation
to another part, and to the conditions of life, and of one
organic being to another being, been perfected? We see
these beautiful co-adaptations most plainly in the wood-
pecker and the mistletoe; and only a little less plainly
in the humblest parasite which clings to the hairs of a quad-
ruped or feathers of a bird: in the structure of the beetle
which dives through the water : in the plumed seed which is
wafted by the gentlest breeze; in short, we see beautiful
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OTRUGGLE FOR EXISTENCE 77
adaptations everywhere and in every part of the organic
world.
Again, it may be asked, how is it that varieties, which I
have called incipient species, become ultimately converted
into good and distinct species, which in most cases obviously
differ from each other far more than do the varieties of the
same species? How do those groups of species, which con-
stitute what are called distinct genera, and which differ
from each other more than do the species of the same genus,
arise? All these results, as we shall more fully see in the
next chapter, follow from the struggle for life. Owing to
this struggle, variations, however slight and from whatever
cause proceeding, if they be in any degree profitable to the
individuals of a species, in their infinitely complex relations
to other organic beings and to their physical conditions of
life, will tend to the preservation of such individuals, and
will generally be inherited by the offspring. The offspring,
also, will thus have a better chance of surviving, for, of the
many individuals of any species which are periodically born,
but a small number can survive. I have called this principle,
by which each slight variation, if useful, is preserved, by the
term Natural Sdection, in order to mark its relation to
man's power of selection. But the expression often used by
Mr. Herbert Spencer of the Survival of the Fittest is more
accurate, and is sometimes equally convenient We have
seen that man by selection can certainly produce great re-
sults, and can adapt organic beings to his own uses, through
the accumulation of slight but useful variations, given to
him by the hand of Nature. But Natural Selection, as we
shall hereafter see, is a power incessantly ready for action,
and is as immeasurably superior to man's feeble efforts, as
the works of Nature are to those of Art
We will now discuss in a little more detail the struggle for
existence. In my future work this subject will be treated,
as it well deserves, at greater length. The elder De Candolle
and Lydl have largely and philosophically shown that all
organic beings are exposed to severe competition. In regard
to plants, no one has treated this subject with more spirit
and ability than W. Herbert, Dean of Manchester, evidently
the result of his great horticultural knowledge. Nothing is
B— HCXI
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78 ORIGIN OF SPECIES
easier than to admit in words the truth of the universal
struggle for life, or more difficult — ^at least, I have found it
so— than constantly to bear this conclusion in mind. Yet
unless it be thoroughly engrained in the mind, the whole
economy of nature, with every fact on distribution, rarity,
abundance, extinction, and variation, will be dimly seen or
quite misunderstood. We behold the face of nature bright
with gladness, we often see superabundance of food; we do
not see, or we forget, that the birds which are idly singing
round us mostly live on insects or seeds, and are thus con-
stantly destroying life ; or we forget how largely these song-
sters, or their eggs, or their nestlings, are destroyed by birds
and beasts of prey; we do not always bear in mind, that,
though food may be now superabundant, it is not so at all
seasons of each recurring year.
THE TERM, STRUGGLE FOR EXISTENCE, USED IN
A LARGE SENSE
I should premise that I use this term in a large and meta-
phorical sense including dependence of one being on another,
and including (which is more important) not only the life
of the individual, but success in leaving progeny. Two
canine animals, in a time of dearth, may be truly said to
struggle with each other which shall get food and live. But
a plant on the edge of a desert is said to struggle for life
against the drought, though more properly it should be said
to be dependent on the moisture. A plant which annually
produces a thousand seeds, of which only one of an average
comes to maturity, may be more truly said to struggle with
the plants of the same and other kinds which already clothe
the ground. The mistletoe is dependent on the apple and a
few other trees, but can only in a far-fetched sense be said
to struggle with these trees, for, if too many of these para-
sites grow on the same tree, it languishes and dies. But
seversd seedling mistletoes, growing close together on the
same branch, may more truly be said to struggle with each
other. As the mistletoe is disseminated by birds, its exist-
ence depends on them ; and it may metaphorically be said to
struggle with other fruit-bearing plants, in tempting the
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GEOBfETRICAL RATIO OF INCREASE 79
birds to devour and thus disseminate its seeds. In these sev-
eral senses, which pass into each other, I use for conveni-
ence sake the general term of Struggle for Existence.
GEOMETRICAL RATIO OF INCREASE
A Struggle for existence inevitably follows from the high
rate at which all organic beings tend to increase. Every
being, which during its natural lifetime produces several
eggs or seeds, must suffer destruction during some period of
its life, and during some season or occasional year, other-
wise, on the principle of geometrical increase, its numbers
would quickly become so inordinately great that no country
could support the product Hence, as more individuals are
produced than can possibly survive, there must in every case
be a struggle for existence, either one individual with an-
other of the same species, or with the individuals of distinct
species, or with the physical conditions of life. It is the
doctrine of Malthus applied with manifold force to the whole
animal and vegetable kingdoms; for in this case there can
be no artificial increase of food, and no prudential restraint
from marriage. Although some species may be now increas-
ing, more or less rapidly, in numbers, all cannot do so, for
the world would not hold them.
There is no exception to the rule that every organic being
naturally increases at so high a rate, that, if not destroyed,
the earth would soon be covered by the progeny of a single
pair. Even slow-breeding man has doubled in twenty-five
years, and at this rate in less than a thousand years, there
would literally not be standing-room for his progeny. Lin-
naeus has calculated that if an annual plant produced only
two seeds — and there is no plant so unproductive as this —
and their seedlings next year produced two, and so on, then
in twenty years there would be a million plants. The ele^
phant is reckoned the slowest breeder of all known animals,
and I have taken some pains to estimate its probable mini-
mum rate of natural increase; it will be safest to assume
that it begins breeding when thirty years old, and goes on
breeding till ninety years old, bringing forth six young in
the interval, and surviving till one hundred years old; if this
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80 ORIGIN OF SPECIES
be so, after a period of from 740 to 750 years there woidd
be nearly nineteen million elephants alive, descended from
the first pair.
But we have better evidence on this subject than mere
theoretical calculations, namely, the numerous recorded cases
of the astonishingly rapid increase of various animals in a
state of nature, when circumstances have been favourable to
them during two or three following seasons. Still more
striking is the evidence from our domestic animals of many
kinds which have run wild in several parts of the world;
if the statements of the rate of increase of slow-breeding
cattle and horses in South America, and latterly in Australia,
had not been well authenticated, they wotdd have been in-
credible. So it is with plants; cases could be given of intro-
duced plants which have become common throughout whole
islands in a period of less than ten years. Several of the
plants, such as the cardoon and a tall thistle, which are
now the commonest over the wide plains of La Plata, cloth-
ing square leagues of surface almost to the exclusion of
every other plant, have been introduced from Europe; and
there are plants which now range in India, as I hear from
Dr. Falconer, from Cape Comorin to the Himalaya, which
have been imported from America since its discovery. In
such cases, and endless others could be given, no one sup-
poses, that the fertility of the animals or plants has been
suddenly and temporarily increased in any sensible degree.
The obvious explanation is that the conditions of life have
been highly favourable, and that there has constantly been
less destruction of the old and young, and that nearly all the
young have been enabled to breed. Their geometrical ratio
of increase, the result of which never fails to be surprising,
simply explains their extraordinarily rapid increase and wide
diffusion in their new homes.
In a state of nature almost every full-grown plant annually
produces seed, and amongst animals there are very few
which do not annually pair. Hence we may confidently as-
sert, that all plants and animals are tending to increase at a
geometrical ratio, — ^that all wotdd rapidly stock every station
in which they could anyhow exist, — ^and that this geomet-
rical tendency to increase must be checked by destruction at
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GEOMETRICAL RATIO OF INCREASE 81
some period of life. Our familiarity with the larger domes-
tic animals tends, I think, to mislead hs: we see no great
destruction falling on them, but we do not keep in mind that
thousands are annually slaughtered for food, and that in a
state of nature an equal number would have somehow to be
disposed of.
The only difference between organisms which annually pro-
duce eggs or seeds by the thousand, and those which produce
extremely few, is, that the slow-breeders would require a
few more years to people, under favourable conditions, a
whole district, let it be ever so large. The condor lays a
couple of eggs and the ostrich a score, and yet in the same
country the condor may be the more numerous of the two;
the Fulmar petrel lays but one egg, yet it is believed to be
the most numerous bird in the world. One fly deposits hun-
dreds of eggs, and another, like the hippobosca, a single
one; but this difference does not determine how many indi-
viduals of the two species can be supported in a district
A large number of eggs is of some importance to those spe-
cies which depend on a fluctuating amount of food, for it
allows them rapidly to increase in number. But the real im-
portance of a large number of eggs or seeds is to make up
for much destruction at some period of life; and this period
in the great majority of cases is an early one. If an animal
can in any way protect its own eggs or young, a small num-
ber may be produced, and yet the average stock be fully kept
up; but if many eggs or young are destroyed, many must be
produced, or the species will become extinct It would suf-
fice to keep up the full number of a tree, which lived on an
average for a thousand years, if a single seed were produced
once in a thousand years, supposing that this seed were never
destroyed, and could be ensured to germinate in a fitting
place. So that, in all cases, the average number of any ani-
mal or plant depends only indirectly on the number of its
eggs or seeds.
In looking at Nature, it is most necessary to keep the fore-
going considerations always in mind — ^never to forget that
every single organic being may be said to be striving to the
utmost to increase in numbers; that each lives by a struggle
at some period of its life; that heavy destruction inevitably
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82 ORIGIN OF SPBaSS
falls either on the young or old, during each generation or
at recurrent intervals. Lighten any check, mitigate the de-
struction ever so little, and the number of the species will
almost instantaneously increase to any amount
NATURE OF THE CHECKS TO INCREASE
The causes which check the natural tendency of each spe-
cies to increase are most obscure. Look at the most vig-
orous species; by as much as it swarms in numbers, by so
much will it tend to increase still further. We know not
exactly what the checks are even in a single instance. Nor
will this surprise any one who reflects how ignorant we are
on this head, even in regard to mankind, although so incom-
parably better known than any other animal. This subject
of the checks to increase has been ably treated by several
authors, and I hope in a future work to discuss it at con-
siderable length, more especially in regard to the feral ani-
mals of South America. Here I will make only a few re-
marks, just to recall to the reader's mind some of the chief
I>oints. Eggs or very young animals seem generally to suffer
most, but this is not invariably the case. With plants there
is a vast destruction of seeds, but, from some observations
which I have made, it appears that the seedings suffer most
from germinating in ground already thickly stocked with
other plants. Seedlings, also, are destroyed in vast numbers
by various enemies; for instance, on a piece of ground three
feet long and two wide, dug and cleared, and where there
could be uo choking from other plants, I marked all the
seedlings of our native weeds as they came up, and out of
357 no less than 295 were destroyed, chiefly by slugs and in-
sects. If turf which has long been mown, and the case would
be the same with turf closely browsed by quadrupeds, be let
to grow, the more vigorous plants gradually kill the less
vigorous, though fully grown plants ; thus out of twenty spe-
cies growing on a little plot of mown turf (three feet by
four) nine species perished, from the other species being al-
lowed to grow up freely.
The amount of food for each species of course gives the
extreme limit to which each can increase; but very fre-
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NATURE OF THE CHECKS TO INCREASE 83
quentiy it is not the obtaining food, but the serving as prey
to other animals, which determines the average numbers of
a species. Thus, there seems to be little doubt that the stock
of partridges, grouse and hares on any large estate depends
chiefly on the destruction of vermin. If not one head of
game were shot during the next twenty years in England,
and, at the same time, if no vermin were destroyed, there
would, in all probability, be less game than at present, al-
though hundreds of thousands of game animals are now
annually shot. On the other hand, in some cases, as with
the elephant, none are destroyed by beasts of prey; for even
the tiger in India most rarely dares to attack a young ele-
phant protected by its dam.
Gimate plays an important part in determining the aver-
age numbers of a species, and periodical seasons of extreme
cold or drought seem to be the most effective of all checks.
I estimated (chiefly from the greatly reduced numbers of
nests in the spring) that the winter of 1854-5 destroyed four-
fifths of the birds in my own grounds ; and this is a tremen-
dous destruction, when we remember that ten per cent, is
an extraordinarily severe mortality from epidemics with
man. The action of climate seems at first sight to be quite
independent of the struggle for existence; but in so far as
climate chiefly acts in reducing food, it brings on the most
severe struggle between the individuals, whether of the same
or of distinct species, which subsist on the same kind of
food. Even when climate, for instance extreme cold, acts
directly, it will be the least vigorous individuals, or those
which have got least food through the advancing winter,
which will suffer most. When we travel from south to
north, or from a damp region to a dry, we invariably see
some species gradually getting rarer and rarer, and finally
disappearing; and the change of climate being conspicuous,
we are tempted to attribute the whole effect to its direct
action. But this is a false view ; we forget that each species,
even where it most abounds, is constantly suffering enormous
destruction at some period of its life, from enemies or from
competitors for the same place and food; and if these ene-
mies or competitors be in the least degree favoured by any
slight change of climate, they will increase in numbers; and
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84 ORIGIN OF SPEaES
as each area is already fully stocked with inhabitants, the
other species must decrease. When we travel southward
and see a species decreasing in numbers, we may feel sure
that the cause lies quite as much in other species being fa-
voured, as in this one being hurt. So it is when we travel
northward, but in a somewhat lesser degree, for the number
of species of all kinds, and therefore of competitors, de-
creases northwards; hence in going northwards, or in as-
cending a mountain, we far oftener meet with stunted forms,
due to the directly injurious action of climate, than we do in
proceeding southwards or in descending a mountain. When
we reach the Arctic regions, or snow-capped summits, or
absolute deserts, the struggle for life is almost exclusively
with the elements.
That climate acts in main part indirectly by favouring
other species, we clearly see in the prodigious number of
plants which in our gardens can perfectly well endure our
climate, but which never became naturalised, for they can-
not compete with our native plants nor resist destruction
by our native animals.
When a species, owing to highly favoured circumstances,
increases inordinately in numbers in a small tract, epidemics
— at least, this seems generally to occur with our game ani-
mals— often ensue; and here we have a limiting check inde-
pendent of the struggle for life. But even some of these
so-called epidemics appear to be due to parasitic worms,
which have from some cause, possibly in part through fa-
cility of diffusion amongst the crowded animals, been dis-
proportionally favoured : and here comes in a sort of struggle
between the parasite and its prey.
On the other hand, in many cases, a large stock of indi-
viduals of the same species, relatively to the numbers of its
enemies, is absolutely necessary for its preservation. Thus
we can easily raise plenty of com and rape-seed, &c., in our
fields, because the seeds are in great excess, compared with
the number of birds which feed on them ; nor can the birds,
though having a superabundance of food at this one sea-
son, increase in number proportionally to the supply of
seed, as their numbers are checked during winter; but any
one who has tried, knows how troublesome it is to get seed
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OTRUGGLE FOR EXISTENCE 8S
from a few wheat or other such plants in a garden : I have
in this case lost every single seed. This view of the neces-
sity of a large stock of the same species for its preservation^
explains, I believe, some singular facts in nature such as that
of very rare plants being sometimes extremely abundant, in
the few spots where they do exist; and that of some social
plants being social, that is abounding in individuals, even on
the extreme verge of their range. For in such cases, we
may believe, that a plant could exist only where the condi-
tions of its life were so favourable that many cotdd exist
together, and thus save the species from utter destruction.
I should add that the good effects of intercrossing, and the
ill effects of close interbreeding, no doubt come into play
in many of these cases; but I will not here enlarge on this
subject.
COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS
TO EACH OTHER IN THE STRUGGLE
FOR EXISTENCE
Many cases are on record showing how complex and un-
expected are the checks and relations between organic
beings, which have to struggle together in the same coun-
try. I will give only a single instance, which, though a
simple one, interested me. In Staffordshire, on the estate
of a relation, where I had ample means of investigation,
there was a large and extremely barren heath, which had
never been touched by the hand of man; but several acres
of exactly the same nature had been enclosed twenty-five
years previously and planted with Scotch fir. The change
in the native vegetation of the planted part of the heath
was most remarkable, more than is generally seen in pass-
ing from one quite different soil to another: not only the
proportional numbers of the heath-plants were wholly
changed, but twelve species of plants (not counting grasses
and carices) flourished in the plantations, which could not
be found on the heath. The effect on the insects must have
been still greater, for six insectivorous birds were very com«»
mon in the plantations, which were not to be seen on the
heath; and the heath was frequented by two or three dis-
tinct insectivorous birds. Here we see how potent has been
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86 ORIGIN OF SPECIES
the effect of the introduction of a single tree, nothing what-
ever else having been done, with the exception of the land
having been enclosed, so that cattle could not enter.
But how important an element enclosure is, I plainly saw
near Famham, in Surrey. Here there are extensive heaths,
with a few dumps of old Scotch firs on the distant hill-
tops: within the last ten years large spaces have been en-
dosed, and self-sown firs are now springing up in multitudes,
so close together that all cannot live. When I ascertained
that these young trees had not been sown or planted, I was
so much surprised at their numbers that I went to several
points of view, whence I could examine htmdreds of acres
of the unendosed heath, and literally I could not see a
single Scotch fir, except the old planted dumps. But on
looking closely between the stems of the heath, I found a
multitude of seedlings and little trees which had been per-
petually browsed down by the cattle. In one square yard,
at a point some hundred yards distant from one of the old
dumps, I counted thirty-two little trees; and one of them,
with twenty-six rings of growth, had, during many years,
tried to raise its head above the stems of the heath, and
had failed. No wonder that, as soon as the land was en-
dosed, it became thickly clothed with vigorously growing
young firs. Yet the heath was so extremely barren and so
extensive that no one would ever have imagined that cattle
would have so dosely and effectually searched it for food.
Here we see that cattle absolutely determine the existence
of the Scotch fir; but in several parts of the world insects
determine the existence of cattle. Perhaps Paraguay offers
the most curious instance of this; for here neither cattle
nor horses nor dogs have ever run wild, though they swarm
southward and northward in a feral state; and Azara and
Rengger have shown that this is caused by the greater num-
ber in Paraguay of a certain fly, which lays its eggs in the
navds of these animals when first bom. The increase of
these flies, numerous as they are, must be habitually checked
by some means, probably by other parasitic insects. Hence,
if certain insectivorous birds were to decrease in Paraguay,
the parasitic insects wotdd probably increase; and this
would lessen the number of the navd-f requenting . flies —
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STRUGGLE FOR EXISTBNCB 87
then cattle and horses would become feral, and this would
certainly greatly alter (as indeed I have observed in parts
of South America) the vegetation : this again would largdy
affect the insects; and this, as we have just seen in Stafford-
shire, the insectivorous birds, and so onwards in ever-in-
creasing circles of complexity. Not that under nature the
relations will ever be as simple as this. Battle within battle
must be continually recurring with varying success ; and yet
in the long-run the forces are so nicely balanced, that the
face of nature remains for long periods of time uniform,
though assuredly the merest trifle would give the victory to
one organic being over another. Nevertheless, so profound
is our ignorance, and so high our presumption, that we
marvel when we hear of the extinction of an organic being;
and as we do not see the cause, we invoke cataclysms to
desolate the world, or invent laws on the duration of the
forms of life!
I am tempted to give one more instance showing how plants
and animals, remote in the scale of nature, are bound together
by a web of complex relations. I shall hereafter have occasion
to show that the exotic Lobelia ftdgens is never visited in
my garden by insects, and consequently, from its peculiar
structure, never sets a seed. Nearly all our orchidaceous
plants absolutely require the visits of insects to remove their
pollen-masses and thus to fertilise them. I find from experi-
ments that humble-bees are almost indispensable to the fer-
tilisation of the heartsease (Viola tricolor), for other bees
do not visit this flower. I have also found that the visits of
bees are necessary for the fertilisation of some kinds of
clover; for instance, 20 heads of Dutch clover (Tri folium
repens) yielded 2,290 seeds, but 20 other heads protected
from bees produced not one. Again, 100 heads of red
clover (T. pratense) produced 2,700 seeds, but the same
number of protected heads produced not a single seed.
Humble-bees alone visit red clover, as other bees cannot
reach the nectar. It has been suggested that moths may
fertilise the clovers; but I doubt whether they could do so
in the case of the red clover, from their weight not being
sufficient to depress the wing petals. Hence we may infer
as highly probable that, if the whole genus of humble-bees
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88 ORIGIN OF SPECIES
became extinct or very rare in England, the heartsease and
red clover would become very rare, or wholly disappear.
The number of humble-bees in any district depends in a
great measure upon the number of field-mice, which destroy
their combs and nests; and Col. Newman, who has long
attended to the habits of humble-bees, believes that "more
than two-thirds of them are thus destroyed all over Eng-
land." Now the number of mice is largely dependent, as
every one knows, on the number of cats; and Col. Newman
says, "Near villages and small towns I have found the nests
of humble-bees more numerous than elsewhere, which I
attribute to the number of cats that destroy the mice."
Hence it is quite credible that the presence of a feline ani-
mal in large numbers in a district might determine, through
the intervention first of mice and then of bees, the fre-
quency of certain flowers in that district!
In the case of every species, many different checks, acting
at different periods of life, and during different seasons or
years, probably come into play ; some one check or some few
being generally the most potent; but all will concur in deter-
mining the average number or even the existence of the
species. In some cases it can be shown that widely-different
checks act on the same species in different districts. When
we look at the plants and bushes clothing an entangled bank,
we are tempted to attribute their proportional numbers and
kinds to what we call chance. But how false a view is this !
Every one has heard that when an American forest is cut
down, a very different vegetation springs up ; but it has been
observed that ancient Indian ruins in the Southern United
States, which must formerly have been cleared of trees,
now display the same beautiful diversity and proportion of
kinds as in the surrounding virgin forest. What a struggle
must have gone on during long centuries between the sev-
eral kinds of trees, each annually scattering its seeds by the
thousand; what war between insect and insect — ^between
insects, snails, and other animals with birds and beasts of
prey — ^all striving to increase, all feeding on each other, or
on the trees, their seeds and seedlings, or on the other plants
which first clothed the ground and thus checked the growth
of the trees 1 Throw up a handful of feathers, and all fall
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STRUGGLE FOR EXISTENCE 89
to the ground according to definite laws; but how simple is
the problem where each shall fall compared to that of the
action and reaction of the innumerable plants and animals
which have determined, in the course of centuries, the pro-
portional numbers and kinds of trees now growing on the
old Indian ruins!
The dependency of one organic being on another, as of a
parasite on its prey, lies generally between beings remote
in the scale of nature. This is likewise sometimes the case
with those which may be strictly said to struggle with each
other for existence, as in the case of locusts and grass-
feeding quadrupeds. But the struggle will almost invariably
be most severe between the individuals of the same species,
for they frequent the same districts, require the same food,
and are exposed to the same dangers. In the case of varie-
ties of the same species, the struggle will generally be almost
equally severe, and we sometimes see the contest soon de-
cided: for instance, if several varieties of wheat be sown
together, and the mixed seed be resown, some of the varie-
ties which best suit the soil or climate, or are naturally the
most fertile, will beat the others and so yield more seed,
and will consequently in a few years supplant the other
varieties. To keep up a mixed stock of even such extremely
close varieties as the variously-coloured sweet peas, they
must be each year harvested separately, and the seed then
mixed in due proportion, otherwise the weaker kinds will
steadily decrease in number and disappear. So again with
the varieties of sheep; it has been asserted that certain
mountain-varieties will starve out other mountain-varieties,
so that they cannot be kept together. The same result has
followed from keeping together different varieties of the
medicinal leech. It may even be doubted whether the varie-
ties of any of our domestic plants or animals have so ex-
actly the same strength, habits, and constitution, that the
original proportions of a mixed stock (crossing being pre-
vented) could be kept up for half-a-dozen generations, if
they were allowed to struggle together, in the same manner
as beings in a state of nature, and if the seed or young were
not annually preserved in due proportion.
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90 ORIGIN OF SPECIES
STRUGGLE FOE LIFE MOST SEVERE BETWEEN INDIVIDUALS
AND VARIETIES OF THE SAME SPECIES
As the species of the same genus usually have, though by
no means invariably, much similarity in habits and consti-
tution, and always in structure, the struggle will generally
be more severe between them, if they come into competition
with each other, than between the species of distinct genera.
We see this in the recent extension over parts of the United
States of one species of swallow having caused the decrease
of another species. The recent increase of the missel-thrush
in parts of Scotland has caused the decrease of the song-
thrush. How frequently we hear of one species of rat taking
the place of another species under the most different cli-
mates! In Russia the small Asiatic cockroach has every-
where driven before it its great congener. In Australia
the imported hive-bee is rapidly exterminating the small,
stingless native bee. One species of charlock has been
known to supplant another species; and so in other cases.
We can dimly see why the competition should be most severe
between allied forms, which fill nearly the same place in the
economy of nature; but probably in no one case cotdd we
precisely say why one species has been victorious over
another in the great battle of life. *
A corollary of the highest importance may be deduced
from the foregoing remarks, namely, that the structure of
every organic being is related, in the mose essential yet often
hidden manner, to that of all the other organic beings, with
which it comes into competition for food or residence, or
from which it has to escape, or on. which it preys. This is
obvious in the structure of the teeth and talons of the tiger;
and in that of the legs and claws of the parasite which clings
to the hair on the tiger's body. But in the beautifully plumed
seed of the dandelion, and in the flattened and fringed legs
of the water-beetle, the relation seems at first confined to
the elements of air and water. Yet the advantage of plumed
seeds no doubt stands in the closest relation to the land being
already thickly clothed with other plants; so that the seeds
may be widely distributed and fall on unoccupied ground.
In the water-beetle, the structure of its legs, so well adapted
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STRUGGLE FOR EXISTENCE 91
for diving, allows it to compete with other aquatic insects,
to hunt for its own prey, and to escape serving as prey to
other animals.
The store of nutriment laid up within the seeds of many
plants seems at first sight to have no sort of relation to
other plants. But from the strong growth of young plants
produced from such seeds, as peas and beans, when sown in
the midst of long grass, it may be suspected that the chief
use of the nutriment in the seed is to favour the growth of
the seedlings, whilst struggling with other plants growing
all arotmd.
Look at a plant in the midst of its range, why does it not
double or quadruple its numbers? We know that it can per-
fectly well withstand a little more heat or cold, dampness or
dr3mess, for elsewhere it ranges into slightly hotter or colder,
damper or drier districts. In this case we can clearly see
that if we wish in imagination to give the plant the power of
increasing in number, we should have to give it some ad-
vantage over its competitors, or over the animals which prey
on it On the confines of its geographical range, a change
of constitution with respect to climate would clearly be an
advantage to our plant; but we have reason to believe that
only a few plants or animals range so far, that they are de-
stroyed exclusively by the rigour of the climate. Not until
we reach the extreme confines of life, in the Arctic regions
or on the borders of an utter desert, will competition cease.
The land may be extremely cold or dry, yet there will be
competition between some few species, or between the indi-
viduals of the same species, for the warmest or dampest
spots.
Hence we can see that when a plant or animal is placed
in a new cotmtry amongst new competitors, the conditions
of its life will generally be changed in an essential manner,
although the climate may be exactly the same as in its
former home. If its average numbers are to increase in its
new home, we should have to modify it in a different way to
what we should have had to do in its native country ; for we
should have to give it some advantage over a different set
of competitors or enemies.
It is good thus to try in imagination to give to any one
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92 ORIGIN OF SPECIES
species an advantage over another. Probably in no single
instance should we know what to do. This ought to con-
vince us of our ignorance on the mutual relations of all
organic beings; a conviction as necessary, as it is difficult
to acquire. All that we can do, is to keep steadily in mind
that each organic being is striving to increase in a geomet-
rical ratio ; that each at some period of its life, during some
season of the year, during each generation or at intervals,
has to struggle for life and to suffer great destruction.
When we reflect on this struggle, we may console ourselves
with the full belief, that the war of nature is not inces-
sant, that no fear is felt, that death is generally prompt,
and that the vigorous, the healthy, and the happy survive
and multiply.
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CHAPTER IV
Natural Selection ; or the Survival of the Fittest
Natural Selection — its power compared with man's selection — ^its
power on characters of trifling importance — its power at all ages
and on both sexes — Sexual selection — On the generality of inter-
crosses between individuals of the same species — Circumstances
favourable and unfavourable to the results of Natural Selection,
namely, intercrossing, isolation, number of individuals — Slow
action — Extinction caused by Natural Selection — Divergence of
Character, related to the diversity of inhabiUnts of any small
area, and to naturalisation — ^Action of Natural Selection, through
divergence of Character and Extinction, on the descendants from
a common parent — Explains the grouping of all organic beings —
Advance in organisation — Low forms preserved — Convergence of
Character — Indefinite multiplication of species — Summary.
HOW will the struggle for existence, briefly discussed
in the last chapter, act in regard, to variation? Can
the principle of selection, which we have seen is so
potent in the hands of man, apply under nature? I think
we shall see that it can act most efliciently. Let the endless
number of slight variations and individual differences occur-
ring in our domestic productions, and, in a lesser degree, in
those under nature, be borne in mind ; as well as the strength
of the hereditary tendency. Under domestication, it may be
truly said that the whole organisation becomes in some degree
plastic. But the variability, which we almost universally
meet with in our domestic productions, is not directly pro-
duced, as Hooker and Asa Gray have well remarked, by man ;
he can neither originate varieties, nor prevent their occur-
rence ; he can only preserve and accumulate such as do occur.
Unintentionally he exposes organic beings to new and chang-
ing conditions of life, and variability ensues; but similar
changes of conditions might and do occur under nature. Let
it also be borne in mind how infinitely complex and close-
fitting are the mutual relations of all organic beings to each
other and to their physical conditions of life; and conse-
93
P— HCXl
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94 ORIGIN OF SPECIES
quently what infinitely varied diversities of structure might
be of use to each being under changing conditions of life.
Can it, then, be thought improbable, seeing that variations
useful to man have undoubtedly occurred, that other vari-
ations useful in some way to each being in the great and com*
plex battle of life, should occur in the course of many suc-
cessive generations? If such do occur, can we doubt (re-
membering that many more individuals are born than can
possibly survive) that individuals having any advantage,
however slight, over others, would have the best chance of
surviviiig and of procreating their kind? On the other hand,
we may feel sure that any variation in the least degree injuri-
ous would be rigidly destroyed. This preservation of favour-
able individual differences and variations, and the destruction
of those which are injurious, I have called Natural Selection,
or the Survival of the Fittest. Variations neither useful nor
injurious would not be affected by natural selection, and
would be left either a fluctuating element, as perhaps we see
in certain polymorphic species, or would ultimately becofne
fixed, owing to the nature of the organism and the nature of
the conditions.
Several writers have misapprehended or objected to the
term Natural Selection. Some have even imagined that nat-
ural selection induces variability, whereas it implies only the
preservation of such variations as arise and are beneficial to
the being under its conditions of life. No one objects to
agriculturists speaking of the potent effects of man's selec-
tion; and in this case the individual differences given by
nature, which man for some object selects, must of necessity
first occur. Others have objected that the term selection im-
plies conscious choice in the animals which become modified;
and it has even been urged that, as plants have no vc^ition,
natural selection is not applicable to them! In the literal
sense of the word, no doubt, natural selection is a false term ;
but who ever objected to chemists speaking of the elective
affinities of the various elements? — ^and yet an add cannot
strictly be said to elect the base with which it in preference
combines. It has been said that I speak of natural selection
as an active power or Deity; but who objects to an author
speaking of the attraction of gravity as ruling the movements
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NATURAL SELECnON 85
of the planets? Every one knows what is meant and is im-
plied by such metaphorical expressions; and they are almost
necessary for brevity. So again it is difficult to avoid per-
sonifying the word Nature; but I mean by Nature, only the
^ggregBtt action and product of many natural laws, and by
laws the sequence of events as ascertained by us. With a
little familiarity such superficial objections will be forgotten.
We shall best understand the probable course of natural
selection by taking the case of a country undergoing some
slight physical change, for instance, of climate. The propor-
tional numbers of its inhabitants will almost immediately un-
dergo a change, and some species will probably become ex-
tinct We may conclude, from what we have seen of the in-
timate and complex manner in which the inhabitants of each
country are bound together, that any change in the numerical
proportions of the inhabitants, independently of the change
of climate itself, would seriously affect the others. If the
country were open on its borders, new forms would certainly
immigrate, and this would likewise seriously disturb the rela-
tions of some of the former inhabitants. Let it be remem-
bered how powerful the influence of a single introduced tree
or mammal has been shown to be. But in the case of an
island, or of a country partly surrounded by barriers, into
which new and better adapted forms could not freely enter,
we should then have places in the economy of nature which
would assuredly be better filled up, if some of the original
inhabitants were in some manner modified; for, had the area
been open to immigration, these same places would have been
seized on by intruders. In such cases, slight modifications,
which in any way favoured the individuals of any species,
by better adapting them to their altered conditions, would
tend to be preserved; and natural selection would have free
scope for the work of improvement.
We have good reason to believe, as shown in the first chap-
ter, that changes in the conditions of life give a tendency to
increased variability; and in the foregoing cases the con-
ditions have changed, and this would manifestly be favour-
able to natural selection, by affording a better chance of the
occurrence of profitable variations. Unless such occur, nat-
ural selection can do nothing. Under the term of "vari-
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96 ORIGIN OF SPECIES
ations," it must never be forgotten that mere individual dif-
ferences are included. As man can produce a great result
with his domestic animals and plants by adding up in any
given direction individual differences, so could natural selec-
tion, but far more easily from having incomparably longer
time for action. Nor do I believe that any great physical
change, as of climate, or any unusual degree of isolation to
check immigration, is necessary in order that new and un-
occupied places should be left, for natural selection to fill up
by improving some of the varying inhabitants. For as all
the inhabitants of each country are struggling together with
nicely balanced forces, extremely slight modifications in the
structure or habits of one species would often give it an ad-
vantage over others; and still further modifications of the
same kind would often still further increase the advantage,
as long as the species continued under the same conditions
of life and profited by similar means of subsistence and de-.
fence. No country can be named in which all the native in-
habitants are now so perfectly adapted to each other and to
the physical conditions under which they live, that none of
them could be still better adapted or improved; for in all
countries, the natives have been so far conquered by natural-
ised productions, that they have allowed some foreigners to
' take firm possession of the land. And as foreigners have
thus in every country beaten some of the natives, we may
safely conclude that the natives might have been modified
with advantage, so as to have better resisted the intruders.
As man can produce, and certainly has produced, a great
result by his methodical and unconscious means of selection,
what may not natural selection effect? Man can act only on
external and visible characters: Nature, if I may be allowed
to personify the natural preservation or survival of the fit-
test, cares nothing for appearances, except in so far as they
are useful to any being. She can act on every internal organ,
on every shade of constitutional difference, on the whole
machinery of life. Man selects only for his own good : Na-
ture only for that of the being which she tends. Every
selected character is fully exercised by her, as is implied 1^
the fact of their selection. Man keeps the natives of many
climates in the same country; he seldom exercises each se-
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NATURAL SELECnON 07
lected character in some peculiar and fitting manner ; he feeds
a long and a short beaked pigeon on the same food ; he does
not exercise a long-backed or long-legged quadruped in any
peculiar manner; he exposes sheep with long and short wool
to the same climate. He does not allow the most vigorous
males to struggle for the females. He does not rigidly de-
stroy all inferior animals, but protects during each varying
season, as far as lies in his power, all his productions. He
often begins his selection by some half-mouBtrous form; or
at least by some modification prominent enough to catch the
eye or to be plainly useful to hfm. Under nature, the slight-
est differences of structure or constitution may well turn the
nicely-balanced scale in the struggle for life, and so be pre-
served. How fleeting are the wishes and efforts of man!
how short his time ! and consequently how poor will be his
results, compared with those accumulated by Nature during
whole geological periods? Can we wonder, then, that Na-
ture's productions should be far "truer" in character than
man's productions; that they should be infinitely better
adapted to the most complex conditions of life, and should
plainly bear the stamp of far higher workmanship?
It may metaphorically be said that natural selection is daily
and hourly scrutinising, throughout the world, the slightest
variations; rejecting those that are bad, preserving and add-
ing up all that are good; silently and insensibly working,
whenever and wherever opportunity oifers, at the improve-
ment of each organic being in relation to its organic and in-
organic conditions of life. We see nothing of these slow
changes in progress, until the hand of time has marked the
lapse of ages, and Ihen so imperfect is our view into long-
past geological ages, that we see only that the forms of life
are now different from what they formerly were.
In order that any great amount of modification should be
effected in a species, a variety when once formed must again,
perhaps after a long interval of time, vary or present indi-
vidual differences of the same favourable nature as before;
and these must be again preserved, and so onwards step by
step. Seeing that individual differences of the same kind
perpetually recur, this can hardly be considered as an unwar-
rantable assumption. But whether it is true, we can judge
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08 ORIGIN OF SPECIES
only by seeing how far the hypothesis accords with and ex-
plains the general phenomena of nature. On the other hand,
the ordinary belief that the amount of possible variation is
a strictly limited quantity is likewise a simple assumption.
Although natural selection can act only through and for
the good of each being, yet characters and structures, which
we are apt to consider as of very trifling importance, may
thus be acted on. When we see leaf-eating insects green,
and bark-feeders mottled-grey; the alpine ptarmigan white in
winter, the red-grouse the colour of heather, we must believe
that these tints are of service to these birds and insects in
preserving them from danger. Grouse, if not destroyed at
some period of their lives, would increase in countless num-
bers; they are known to suffer largely from birds of prey;
and hawks are guided by eyesight to their prey — so much so,
that on parts of the Continent persons are warned not to keep
white pigeons, as being the most liable to destruction. Hence
natural selection might be effective in giving the proper
colour to each kind of grouse, and in keeping that colour,
when once acquired, true and constant. Nor ought we to
think that the occasional destruction of an animal of any par-
ticular colour would produce little effect: we should remem-
ber how essential it is in a flock of white sheep to destroy a
lamb with the faintest trace of black. We have seen how
the colour of the hogs, which feed on the "paint-root" in
Virginia, determines whether they shall live or die. In
plants, the down on the fruit and file colour of the flesh are
considered by botanists as characters of the most trifling im-
portance: yet we hear from an excellent horticulturist. Down-
ing, that in the United States smooth-skinned fruits suffer
far more from a beetle, a Curculio, than those with down;
that purple plums suffer far more from a certain disease than
yellow plums, whereas another disease attacks yellow-fleshed
peaches far more than those with other coloured flesh. If,
with all the aids of art, these slight differences make a great
difference in cultivating the several varieties, assuredly, in a
state of nature, where the trees would have to struggle with
other trees and with a host of enemies, such differences would
effectually settle which variety, whether a smooth or downy,
a yellow or purple fleshed fruit, should succeed.
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NATURAL SELECTION 99
In looking at many small points of difference between
species, which, as far as our ignorance permits us to judge,
seem quite unimportant, we must not forget that climate,
food, &c., have no doubt produced some direct effect. It is
also necessary to bear in mind that, owing to the law of cor-
relation, when (me part varies, and the variations are accu-
mulated through natural selection, other modifications, often
of the most unexpected nature, will ensue.
As we see that those variations which, under domestica-
tion, appear at any particular period of life, tend to reappear
in the offspring at the same period; — for instance, in the
shape, size, and flavour of the seeds of the many varieties of
our culinary and agricultural plants; in the caterpillar and
cocoon stages of the varieties of the silkworm ; in the eggs o£
poultry, and in the colour of the down of their chickens ; in
the horns of our sheep and cattle when nearly adult ; — ^so in
a state of nature natural selection will be enabled to act on
and modify organic beings at any age, by the accumulation of
variations profitable at that age, and by their inheritance at
a corresponding age. If it profit a plant to have its seeds
more and more widely disseminated by the wind, I can see no
greater difficulty in this being effected through natural selec-
tion, than in the cotton-planter increasing and improving by
selection the down in the pods on his cotton-trees. Natural
selection may modify and adapt the larva of an insect to a
score of contingencies, wholly different from those which con-
cern the mature insect; and these modifications may effect,
through correlation, the structure of the adult. So, con-
versely, modifications in the adult may affect the structure
of the larva ; but in all cases natural selection will ensure that
they shall not be injurious : for if they were so, the species
would become extinct
Natural selection will modify the structure of the young in
relation to the parent, and of the parent in relation to the
young. In social animals it will adapt the structure of each
individual for the benefit of the whole community; if the
community profits by the selected change. What natural
selection cannot do, is to modify the structure of one species,
without giving it any advantage, for the good of another
species ; and though statements to this effect may be found in
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100 ORIGIN OF SPECIES
works of natural history, I cannot find one case which will
bear investigation. A structure used only once in an ani>
mal's life, if of high importance to it, might be modified to
any extent by natural selection; for instance, the great jaws
possessed by certain insects, used exclusively for opening the
cocoon— or the hard tip to the beak of unhatched birds, used
for breaking the egg. It has been asserted, that of the best
short-beaked tumbler-pigeons a greater number perish in the
egg than are able to get out of it ; so that fanciers assist in
the act of hatching. Now if nature had to make the beak of
a full-grown pigeon very short for the bird's own advantage,
the process of modification would be very slow, and there
would be simultaneously the most rigorous selection of all the
young birds within the egg, which had the most powerful and
hardest beaks, for all with weak beaks would inevitably per-
ish ; or, more delicate and more easily broken shells might be
selected, the thickness of the shell being known to vary like
every other structure.
It may be well here to remark that with all beings there
must be much fortuitous destruction, which can have little or
no influence on the course of natural selection. For instance
a vast number of eggs or seeds are annually devoured, and
these could be modified through natural selection only if they
varied in some manner which protected them from their ene-
mies. Yet many of these eggs or seeds would perhaps, if not
destroyed, have yielded individuals better adapted to their
conditions of life than any of those which happened to sur-
vive. So again a vast number of mature animals and plants,
whether or not they be the best adapted to their conditions,
must be annually destroyed by accidental causes, which would
not be in the least degree mitigated by certain changes of
structure or constitution which would in other ways be bene-
ficial to the species. But let the destruction of the adults be
ever so heavy, if the number which can exist in any district
be not wholly kept down by such causes, — or again let the
destruction of eggs or seeds be so great that only a hundredth
or a thousandth part are developed, — ^yet of those which do
survive, the best adapted individuals, supposing that there is
any variability in a favourable direction, will tend to propa-
gate their kind in larger numbers than the less wdl adapted.
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SBXUAL SELBCnON 101
If the numbers be wholly kept down by the causes just indi-
cated, as will often have been the case, natural selection will
be powerless in certain beneficial directions; but this is no
valid objection to its efficiency at other times and in other
ways ; for we are far from having any reason to suppose that
many species ever undergo modification and improvement at
the same time in the same area.
SEXUAL SELECTION.
Inasmuch as peculiarities often appear under domestica-
tion in one sex and become hereditarily attached to that sex,
so no doubt it will be under nature. Thus it is rendered pos-
sible for the two sexes to be modified through natural selec-
tion in relation to different habits of life, as is sometimes the
case ; or for one sex to be modified in relation to the other
sex, as commonly occurs. This leads me to say a few words
on what I have called Sexual Selection. This form of selec-
tion depends, not on a struggle for existence in relation to
other organic beings or to external conditions, but on a
struggle between the individuals of one sex, generally the
males, for the possession of the other sex. The result is not
death to the unsuccessful competitor, but few or no offspring.
Sexual selection is, therefore, less rigorous than*natural se-
lection. Generally, the most vigorous males, those which are
best fitted for their places in nature, will leave most progeny.
But in many cases, victory depends not so much on general
vigour, as on having special weapons, confined to the male
sex. A hornless stag or spurless cock would have a poor
chance of leaving numerous offspring. Sexual selection, by
always allowing the victor to breed, might surely give in-
domitable courage, length to the spur, and strength to the
wing to strike in the spurred leg, in nearly the same manner
as does the brutal cockfighter by the careful selection of his
best cocks. How low in the scale of nature the law of battle
descends, I know not ; male alligators have been described as
fighting, bellowing, and whirling round, like Indians in a
war-dance, for the possession of the females; male salmons
have been observed fighting all day long; male stag-beetles
sometimes bear wounds from the huge mandibles of other
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102 ORIGIN OF SPECIES
males ; the males of certain hymenopterous insects have been
frequently seen by that inimitable observer M. Fabre, fighting
for a particular female who sits by, an apparently uncon-
cerned beholder of the struggle, and then retires with the
conqueror. The war is, perhaps, severest between the males
of polygamous animals, and these seem oftenest provide4
with special weapons. The males of carnivorous animals
are already well armed ; though to them and to others, special
means of defence may be given through means of sexual
selection, as the mane of the lion, and the hooked jaw to the
male salmon ; for the shield may be as important for victory,
as the sword or spear.
Amongst birds, the contest is often of a more peaceful
character. All those who have attended to the subject, be-
lieve that there is the severest rivalry betwen the males of
many species to attract, by singing, the females. The rock-
thrush of Guiana, birds of paradise, and some others, congre-
gate; and successive males display with the most elaborate
care, and show off in the best manner, their gorgeous plu-
mage; they likewise perform strange antics before the fe-
males, which, standing by as spectators, at last choose the most
attractive partner. Those who have closely attended to birds
in confinement well know that they often take individual
preferences and dislikes; thus Sir R. Heron has described
how a pied peacock was eminently attractive to all his hen
birds. I cannot here enter on the necessary details; but if
man can in a short time give beauty and an elegant carriage
to his bantams, according to his standard of beauty, I can see
no good reason to doubt that female birds, by selecting, dur-
ing thousands of generations, the most melodious or beautiful
males, according to their standard of beauty, might produce a
marked effect Some well-known laws, with respect to the
plumage of male and female birds, in comparison with the
plumage of the young, can partly be explained through the
action of sexual selection on variations occurring at different
ages, and transmitted to the males alone or to both se^es at
corresponding ages; but I have not space here to enter on
this subject.
Thus it is, as I believe, that when the males and females of
any animal have the same general habits of life, but differ in
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ACTION OF NATURAL SELECTION 103
structure, colour, or ornament, such differences have been
mainly caused by sexual selection : that is, by individual males
having had, in successive generations, some slight advantage
over other males, in their weapons, means of defence, or
charms, which they have transmitted to their male offspring
alone. Yet, I would not wish to attribute all sexual differ-
ences to this agency: for we see in our domestic animals
peculiarities arising and becoming attached to the male sex,
which apparently have not been augmented through selection
by man. The tuft of hair on the breast of the wild turkey-
cock cannot be of any use, and it is doubtful whether it can
be ornamental in the eyes of the female bird; — ^indeed, had
the tuft appeared under domestication, it would have been
called a monstrosity.
ILLUSTRATIONS OF THE ACTION OP NATURAL SELECTION^ OR
THE SURVIVAL OP THE FITTEST.
In order to make it clear how, as I believe, natural selec-
tion acts, I must beg permission to give one or two imaginary
illustrations. Let us take the case of a wolf, which preys on
various animals, securing some by craft, some by strength,
and some by fleetness; and let us suppose that the fleetest
prey, a deer for instance, had from any change in the country
increased in numbers, or that other prey had decreased in
numbers, during that season of the year when the wolf was
hardest pressed for food. Under such circumstances the
swiftest and slimmest wolves would have the best chance of
surviving and so be preserved or selected, — ^provided always
that they retained strength to master their prey at this or
some other period of the year, when they were compelled to
prey on other animals. I can see no more reason to doubt
that this would be the result, than that man should be able to
improve the fleetness of his greyhounds by careful and
methodical selection, or by that kind of unconscious selection
which follows from each man trying to keep the best dogs
without any thought of modifying the breed. I may add,
that, according to Mr. Pierce, there are two varieties of the
wolf inhabiting the Catskill Mountains, in the United States,
one with a light greyhound-like form, which pursues deer.
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104 ORIGIN OF SPECIES
and the other more bulky, with shorter legs, which more fre-
quently attacks the shepherd's flocks.
It should he observed that, in the above illustration, I speak
of the slimmest individual wolves, and not of any single
strongly-marked variation having been preserved. In former
editions of this work I sometimes spoke as if this latter alter-
native had frequently occurred. I saw the great importance
of individual differences, and this led me fully to discuss the
results of unconscious selection by man, which depends on
the preservation of all the more or less valuable individuals,
and on the destruction of the worst. I saw, also, that the
preservation in a state of nature of any occasional deviation
of structure, such as a monstrosity, would be a rare event;
and that, if at first preserved, it would generally be lost by
subsequent intercrossing with ordinary individuals. Never-
theless, until reading an able Und valuable article in the
'North British Review' (1867), I did not appreciate how
rarely single variations, whether slight or strongly-marked,
could be perpetuated. The author takes the case of a pair
of animals, producing during their lifetime two hundred off-
springs of which, from various causes of destruction, only two
on an average survive to pro-create their kind. This is
rather an extreme estimate for most of the higher animals,
but by no means so for many of the lower organisms. He
then shows that if a single individual were bom, which varied
in some manner, giving it twice as good a chance of life as
that of the other individuals, yet the chances would be
strongly against its survival. Supposing it to survive and to
breed, and that half its young inherited the favourable vari-
ation; .still, as the Reviewer goes on to show, the young would
have only a slightly better chance of surviving and breeding;
and this chance would go on decreasing in the succeeding
generations. The justice of these remarks cannot, I think,
be disputed. If, for instance, a bird of some kind could pro-
cure its food more easily by having its beak curved, and if
one were bom with its beak strongly curved, and which con-
sequently flourished, nevertheless there would be a very poor
chance of this one individual perpetuating its kind to the ex-
clusion of the common form ; but there can hardly be a doubt,
judging by what we see taking place under domestication.
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ACTION OF NATURAL SELECTION 105
that this result would follow from the preservation during
many generations of a large number of individuals with more
or less strongly curved beaks, and from the destruction of a
still larger number with the straightest beaks.
It should not, however, be overlooked that certain rather
strongly marked variations, which no one would rank as mere
individual differences, frequently recur owing to a similar
organisation being similarly acted on — of which fact numer-
ous instances could be given with our domestic productions.
In such cases, if the varying individual did not actually trans-
mit to its offspring its newly-acquired character, it would un-
doubtedly transmit to them, as long as the existing conditions
remained the same, a still stronger tendency to vary in the
same manner. There can also be little doubt that the ten-
dency to vary in the same manner has often been so strong
that all the individuals of the same species have been simi-
larly modified without the aid of any form of selection. Or
only a third, fifth, or tenth part of the individuals may have
been thus affected, of which fact several instances could be
given. Thus Graba estimates that about one-fifth of the
guillemots in the Faroe Islands consist of a variety so well
marked, that it was formerly ranked as a distinct species
under the name of Uria lacrymans. In cases of this kind, if
the variation were of a beneficial nature, the original form
would soon be supplanted by the modified form, through the
survival of the fittest.
To the effects of intercrossing in eliminating variations of all
kinds, I shall have to recur; but it may be here remarked that
most animals and plants keep to their proper homes, and do
not needlessly wander about ; we see this even with migratory
birds, which almost always return to the same spot. Conse-
quently each newly-formed variety would generally be at
first local, as seems to be the common rule with varieties in a
state of nature; so that similarly modified individuals would
soon exist in a small body together, and would often breed
together. If the new variety were successful in its battle for
life, it would slowly spread from a central district, competing
with and conquering the unchanged individuals on the mar*
gins of an ever-increasing circle.
It may be worth while to give another and more complex
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106 ORIGIN OF SPECIES
illustration of the action of natural selection. Certain plants
excrete sweet juice, apparently for the sake of eliminating
something injurious from the sap: this is effected, for in-
stance, by glands at the base of the stipules in some Legu-
minosae, and at the backs of the leaves of the common laurel
This juice, though small in quantity, is greedily sought by
insects; but their visits do not in any way benefit the plant
Now, let us suppose that the juice or nectar was excreted
from the inside of the flowers of a certain number of plants
of any species. Insects in seeking the nectar would get
dusted with pollen, and would often transport it from one
flower to another. The flowers of two distinct individuals
of the same species would thus get crossed; and the act of
crossing, as can be fully proved, gives rise to vigorous seed-
lings, which consequently would have the best chance of flour-
ishing and surviving. The plants which produced flowers
with the largest glands or nectaries, excreting much nectar,
would oftenest be visited by insects, and would oftenest be
crossed; and so in the long-run would gain the upper hand
and form a local variety. The flowers, also, which had their
stamens and pistils placed, in relation to the size and habits
of the particular insect which visited them, so as to favour
in any degree the transportal of the pollen, would likewise
be favoured. We might have taken the case of insects visit-
ing flowers for the sake of collecting pollen instead of nectar ;
and as pollen is formed for the sole purpose of fertilisation,
its destruction appears to be a simple loss to the plant ; yet if
a little pollen were carried, at first occasionally and then
habitually, by the pollen-devouring insects from flower to
flower, and a cross thus eflFected, although nine-tenths of the
pollen were destroyed, it might still be a great gain to the
plant to be thus robbed; and the individuals which produced
more and more pollen, and had larger anthers, would be
selected.
When our plant, by the above process long continued, had
been rendered highly attractive to insects, they would, unin-
tentionally on their part, regularly carry pollen from flower
to flower; and that they do this effectually, I could easily
show by many striking facts. I will give only one, as like-
wise illustrating one step in the separation of the sexes of
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ACTION OF NATURAL SELECTION 107
plants. Some holly-trees bear only male flowers, which have
four stamens producing a rather small quantity of pollen, and
a rudimentary pistil; other holly-trees bear only female
flowers; these have a full-sized pistil, and four stamens with
shrivelled anthers, in which not a grain of pollen can be de-
tected. Having found a female tree exactly sixty yards from
a male tree, I put the stigmas of twenty flowers, taken from
different branches, under the microscope, and on all, without
exception, there were a few pollen-grains, and on some a
profusion. As the wind had set for several days from the
female to the male tree, the pollen could not thus have been
carried. The weather had been cold and boisterous, and
therefore not favourable to bees, nevertheless every female
flower which I examined had been effectually fertilised by the
bees, which had flown from tree to tree in search of nectar.
But to return to our imaginary case : as soon as the plant had
been rendered so highly attractive to insects that pollen was
regularly carried from flower to flower, another process
might commence. No naturalist doubts the advantage of
what has been called the ''physiological division of labour;"
hence we may believe that it would be advantageous to a
plant to produce stamens alone in one flower or on one whole
plant, and pistils alone in another flower or on another plant.
In plants under culture and placed under new conditions of
life, sometimes the male organs and sometimes the female
organs become more or less impotent ; now if we suppose this
to occur in ever so slight a degree under nature, then, as
pollen is already carried regularly from flower to flower, and
as a more complete separation of the sexes of our plant would
be advantageous on the principle of the division of labour,
individuals with this tendency more and more increased, would
be continually favoured or selected, until at last a complete
separation of the sexes might be effected. It would take up
too much spate to show the various steps, through dimorph-
ism and other means, by which the separation of the sexes in
plants of various kinds is apparently now in progress; but I
may add that some of the species of holly in North America,
are, according to Asa Gray, in an exactly intermediate con-
dition, or, as he expresses it, are more or less dioeciously
polygamous.
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106 ORIGIN OF SPECIES
Let us now turn to the nectar-feeding insects; we may
suppose the plant, of which we have been slowly increasing
the nectar by continued selection, to be a common plant ; and
that certain insects depended in main part on its nectar for
food. I could give many facts showing how anxious bees are
to save time: for instance, their habit of cutting holes and
sucking the nectar at the bases of certain flowers, which with
a very little more trouble, they can enter by the mouth.
Bearing such facts in mind, it may be believed that under cer-
tain circumstances individual differences in the curvature or
length of the proboscis, &c., too slight to be appreciated by
us, might profit a bee or other insect, so that certain indi-
-viduals would be able to obtain their food more quickly than
others; and thus the communities to which they belonged
would flourish and throw off many swarms inheriting the
same peculiarities. The tubes of the corolla of the common
red and incarnate clovers (Tri folium pratense and incar-
natum) do not on a hasty glance appear to differ in length;
yet the hive-bee can easily suck the nectar out of the incar-
nate clover, but not out of the common red clover, which is
visited by humble-bees alone ; so that whole fields of the red
clover offer in vain an abundant supply of precious nectar to
the hive-bee. That this nectar is much liked by the hive-bee is
certain; for I have repeatedly seen, but only in the autumn,
many hive-bees sucking the flowers through holes bitten in
the base of the tube by humble-bees. The difference in the
length of the corolla in the two kinds of clover, which deter-
mines the visits of the hive-bee, must be very trifling; for I
have been assured that when red clover has been mown, the
flowers of the second crop are somewhat smaller, and that
these are visited by many hive-bees. I do not know whether
this statement is accurate; nor whether another published
statement can be trusted, namely, that the Ligurian bee, which
is generally considered a mere variety of the common hive-
bee, and which freely crosses with it, is able to reach and suck
the nectar of the red clover. Thus, in a country where this kind
of clover abounded, it might be a great advantage to the
hive-bee to have a slightly longer or differently constructed
proboscis. On the other hand, as the fertility of this clover
absolutely depends on bees visiting the flowers, if humble-
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ON THE INTERCROSSING OF INDIVIDUALS 100
bees were to become rare in any country, it might be a great
advantage to the plant to have a shorter or more deeply di-
vided corolla, so that the hive-bees should be enabled to suck
its flowers. Thus I can understand how a flower and a bee
might slowly become, either simultaneously or one after the
other, modified and adapted to each other in the most perfect
manner, by the continued preservation of all the individuals
which presented slight deviations of structure mutually fa-
vourable to each other.
I am well aware that this doctrine of natural selection,
exemplified in the above imaginary instances, is open to the
same objections which were first urged against Sir Charles
Lyell's noble views on "the modern changes of the earth, as
illustrative of geology ;" but we now seldom hear the agencies
which we see still at work, spoken of as trifling or insi^ifi-
cant, when used in explaining the excavation of the deepest
valleys or the formation of long lines of inland cliffs. Nat-
ural selection acts only by the preservation and accumulation
of small inherited modifications, each profitable to the pre-
served being; and as modern geology has almost banished
such views as the excavation of a great valley by a single
diluvial wave, so will natural selection banish the belief of
the continued creation of new organic beings, or of any great
and sudden modification in their structure.
ON THE INTERCROSSING OF INDIVIDUALS
I must here introduce a short digression. In the case of
animals and plants with separated sexes, it is of course obvi-
ous that two individuals must always (with the exception of
the curious and not well understood cases of parthenogene-
sis) unite for each birth; but in the case of hermaphrodites
this is far from obvious. Nevertheless there is reason to be-
lieve that with all hermaphrodites two individuals, either
occasionally or habitually, concur for the reproduction of
their kind. This view was long ago doubtfully suggested by
Sprengel, Knight and Kolreuter. We shall presently see its
importance; but I must here treat the subject with extreme
brevity, though I have the materials prepared for an ample
discussion. All vertebrate animals, all insects, and some
G — ^HCXI
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110 ORIGIN OF SPEaES
other large groups of animals, pair for each birth. Modern
research has much diminished the number of supposed her-
maphrodites, and of real hermaphrodites a large number
pair; that is, two individuals regularly unite for reproduc-
tion, which is all that concerns us. But still there are many
hermaphrodite animals which certainly do not habitually pair,
and a vast majority of plants are hermaphrodites. What
reason, it may be asked, is there for supposing in these cases
that two individuals ever concur in reproduction? As it is
impossible here to enter on details, I must trust to some gen-
eral considerations alone.
In the first place, I have collected so large a bodyof facts,
and made so many experiments, showing, in accordance with
the almost universal belief of breeders, that with animals and
plants a cross between different varieties, or between indi-
viduals of the same variety but of another strain, gives vigour
and fertility to the offspring; and on the other hand, that
close interbreeding diminishes vigour and fertility ; that these
facts alone incline me to believe that it is a general law of
nature that no organic being fertilises itself for a perpetuity
of generations; but that a cross with another individual is
occasionally — ^perhaps at long intervals of time — indispen-
sable.
On the belief that this is a law of nature, we can, I think,
understand several large classes of facts, such as the follow-
ing, which on any other view are inexplicable. Every
hybridizer knows how unfavourable exposure to wet is to
the fertilisation of a flower, yet what a multitude of flowers
have their anthers and stigmas fully exposed to the weather 1
If an occasional cross be indispensable, notwithstanding that
the plant's own anthers and pistil stand so near each other
as almost to insure self-fertilisation, the fullest freedom for
the entrance of pollen from another individual will explain
the above state of exposure of the organs. Many flowers, on
the other hand, have their organs of fructification closely en-
closed, as in the great papilionaceous or pea- family ; but these
almost invariably present beautiful and curious adaptations
in relation to the visits of insects. So necessary are the visits
of bees to many papilionaceous flowers, that their fertility is
greatly diminished if these visits be prevented. Now, it is
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ON THE INTERCROSSING OP INDIVIDUALS 111
scarcely possible for insects to fly from flower to flower, and
not to carry pollen from one to the other, to the g^eat good
of the plant. Insects act like a camel-hair pencil, and it is
suflicient, to ensure fertilisation, just to touch with the same
brush the anthers of one flower and then the stigma of an-
other ; but it must not be supposed that bees would thus pro-
duce a multitude of hybrids between distinct species ; for if a
plant's own pollen and that from another species are placed
on the same stigma, the former is so prepotent that it in-
variably and completely destroys, as has been shown by Gart-
ner, the influence of the foreign pollen.
When the stamens of a flower suddenly spring towards the
pistil, or slowly move one after the other towards it, the con-
trivance seems adapted solely to ensure self-fertilisation ; and
no doubt it is useful for this end : but the agency of insects is
often required to cause the stamens to spring forward, as
Kolreuter has shown to be the case with the barberry ; and in
this very genus, which seems to have a special contrivance
for self-fertilisation, it is well known that, if closely-allied
forms or varieties are planted near each other, it is hardly
possible to raise pure seedlings, so largely do they naturally
cross. In numerous other cases, far from self-fertilisation
being favoured, there are special contrivances which effec-
tually prevent the stigma receiving pollen from its own
flower, as I could show from the works of Sprengel and
others, as well as from my own observations: for instance,
in Lobelia fulgens, there is a really beautiful and elaborate
contrivance by which all the infinitely numerous pollen-
granules are swept out of the conjoined anthers of each
flower, before the stigma of that individual flower is ready to
receive them; and as this flower is never visited, at least in
my garden, by insects, it never sets a seed, though by placing
pollen from one flower on the stigma of another, I raise
plenty of seedlings. Another species of Lobelia, which is
visited by bees, seeds freely in my garden. In very many
other cases, though there is no special mechanical contrivance
to prevent the stigma receiving pollen from the same flower,
yet, as Sprengel, and more recently Hildebrand, and others,
have shown, and as I can confirm, either the anthers burst be-
fore the stigma is ready for fertilisation, or the stigma is
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U2 ORIGIN OF SPECIES
ready before the pollen of that flower is ready, so that these
so-named dichogamous plants have in fact separated sexes,
and must habitually be crossed. So it is with the reciprocally
dimorphic and trimorphic plants previously alluded to. How
strange are these facts I How strange liiat the pollen and
stigmatic suriEace of the same flower, though placed so close
together, as if for the very purpose of self-fertilisation,
should be in so many cases mutually useless to each other?
How simply are these facts explained on the view of an oc-
casional cross with a distinct individual being advantageous
or indispensable I
If several varieties of the cabbage, radish, onion, and of
some other plants, be allowed to seed near each other, a large
majority of the seedlings thus raised turn out, as I have
found, mongrels : for instance, I raised 233 seedling cabbages
from some plants of different varieties growing near each
other, and of these only 78 were true to their kind, and some
even of these were not perfectly true. Yet the pistil of each
cabbage-flower is surrounded not only by its own six stamens
but by those of the many other flowers on the same plant;
and the pollen of each flower readily gets on its own stigma
without insect agency; for I have found that plants carefully
protected from insects produce the full number of pods.
How, then, comes it that such a vast number of the seedlings
are mongrelized? It must arise from the pollen of a dis-
tinct variety having a prepotent effect over the flower's own
pollen ; and that this is part of the general law of good being
derived from the intercrossing of distinct individuals of the
same species. When distinct species are crossed the case is «
reversed, for a plant's own pollen is almost always prepotent
over foreign pollen; but to this subject we shall return in a
future chapter.
In the case of a large tree covered with innumerable
flowers, it may be objected that pollen could seldom be carried
from tree to tree, and at most only from flower to flower on
the same tree; and flowers on the same tree can be consid-
ered as distinct individuals only in a limited sense. I believe
this objection to be valid, but that nature has largely pro-
vided against it by giving to trees a strong tendency to bear
flowers with separated sexes. When the sexes are separated.
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ON THB INTERCROSSING OF INDIVIDUALS 113
although the male and female flowers may be produced on the
same tree, pollen must be regularly carried from flower to
flower ; and this will give a better chance of pollen being oc-
casionally carried from tree to tree. That trees belonging to
all Orders have their sexes more often separated than other
plants, I find to be the case in this country; and at my re-
quest Dr. Hooker tabulated the trees of New Zealand, and
Dr. Asa Gray those of the United States, and the result was
as I anticipated. On the other hand, Dr. Hooker informs me
that the rule does not hold good in Australia: but if most of
the Australian trees are dichogamous, the same result would
follow as if they bore flowers with separated sexes. I have
made these few remarks on trees simply to call attention to
the subject
Turning for a brief space to animals: various terrestrial
species are hermaphrodites, such as the land-moUusca and
earth-worms; but these all pair. As yet I have not found a
single terrestrial animal which can fertilise itself. This re-
markable fact, which offers so strong a contrast with terres-
trial plants, is intelligible on the view of an occasional cross
being indispensable; for owing to the nature of the fertilis-
ing element there are no means, analogous to the action of
insects and of the wind with plants, by which an occasional
cross could be effected with terrestrial animals without the
concurrence of two individuals. Of aquatic animals, there
are many self-fertilising hermaphrodites; but here the cur-
rents of water offer an obvious means for an occasional cross.
As in the case of flowers, I have as yet failed, after consulta-
tion with one of the highest authorities, namely, Professor
Huxley, to discover a single hermaphrodite animal with the
organs of reproduction so perfectly enclosed that access from
without, and the occasional influence of a distinct individual,
can be shown to be physically impossible. Cirripedes long
appeared to me to present, under this point of view, a case
of great difficulty; but I have been enabled, by a fortunate
chance, to prove that two individuals, though both are self-
fertilising hermaphrodites, do sometimes cross.
It must have struck most naturalists as a strange anomaly
that, both with animals and plants, some species of the same
family and even of the same genus, though agreeing closely
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114 ORIGIN OF SPECIES
with each other in their whole organisation, are hermaphro-
dites, and some unisexual. But if, in fact, all hermaphro-
dites do occasionally intercross, the difference between them
and unisexual species is, as far as function is concerned, very
small.
From these several considerations and from the many
special facts which I have collected, but which I am unable
here to give, it appears that with animals and plants an oc-
casional intercross between distinct individuals is a very gen-
eral, if not universal, law of nature.
CIRCUMSTANCES FAVOURABLE FOR THE PRODUCTION OF NEW
FORMS THROUGH NATURAL SELECTION.
This is an extremely intricate subject. A great amount of
variability, under which term individual differences are al-
ways included, will evidently be favourable. A large num-
ber of individuals, by giving a better chance within any given
period for the appearance of profitable variations, will com-
pensate for a lesser amount of variability in each individual,
and is, I believe, a highly important element of success.
Though Nature grants long periods of time for the work of
natural selection, she does not grant an indefinite period ; for
as all organic beings are striving to seize on each place in
the economy of nature, if any one species does not become
modified and improved in a corresponding degree with its
competitors, it will be exterminated. Unless favourable vari-
ations be inherited by some at least of the offspring, nothing
can be effected by natural selection. The tendency to rever-
sion may often check or prevent the work; but as this ten-
dency has not prevented man from forming by selection nu-
merous domestic races, why should it prevail against natucal
selection ?
In the case of methodical selection, a breeder selects for
some definite object, and if the individuals be allowed freely
to intercross, his work will completely fail. But when many
men, without intending to alter the breed, have a nearly com-
mon standard of perfection, and all try to procure and breed
from the best animals, improvement surely but slowly follows
from this unconscious process of selection, notwithstanding
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PRODUCnON OP NEW PORMS 115
that there is no separation' of selected individuals. Thus it
will be under nature; for within a confined area, with some
place in the natural pdUty not perfectly occupied, all the in-
dividuals varying in the right direction, though in different
degrees, will tend to be preserved. But if the area be large,
its several districts will almost certainly present different con-
ditions of life ; and then, if the same species undergoes modi-
fication in different districts, the newly-formed varieties will
intercross on the confines of each. But we shall see in the
sixth chapter that intermediate varieties, inhabiting inter-
mediate districts, will in the long run generally be supplanted
by one of the adjoining varieties. Intercrossing will chiefly
affect those animals which unite for each birth and wander
much, and which do not breed at a very quick rate. Hence
with animals of this nature, for instance, birds, varieties will
generally be confined to separated countries; and this I find
to be the case. With hermaphrodite organisms which cross
only occasionally, and likewise with animals which unite for
each birth, b«t which wander little and can increase at a
rapid rate, a new and improved variety might be quickly
formed on any one spot, and might there maintain itself in a
body and afterwards spread, so that the individuals of the
new variety would chiefly cross together. On this principle,
nurserymen always prefer saving seed from a large body of
plants, as the chance of intercrossing is thus lessened.
Even with animals which unite for each birth, and which
do not propagate rapidly, we must not assume that free in-
tercrossing would always eliminate the effects of natural
selection; for I can bring forward a considerable body of
facts showing that within the same area, two varieties of the
same animal may long remain distinct, from haunting differ-
ent stations, from breeding at slightly different seasons, or
from the individuals of each variety preferring to pair to-
gether.
Intercrossing plays a very important part in nature by
keeping the individuals of the same species, or of the same
variety, true and uniform in character. It will obviously
thus act far more efiiciently with those animals which unite
for each birth ; but, as already stated, we have reason to be-
lieve that occasional intercrosses take place with all animals
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116 ORIGIN OF SPEOES
and plants. Even if these take place only at long intervals
of time, the young thus produced will gain so much in vigour
and fertility over the offspring from long-continued self-fer-
tilisation, that they will have a better chance of surviving
and propagating their kind; and thus in the long run the in-
fluence of crosses, even at rare intervals, will be great With
respect to organic beings extremely low in the scale, which
do not propagate sexually, nor conjugate, and which cannot
possibly intercross, uniformity of character can be retained
by them under the same conditions of life, only through the
principle of inheritance, and through natural selection which
will destroy any individuals departing from the proper type.
If the conditions of life change and the form undergoes modi-
fication, uniformity of character can be given to the modified
offspring, solely by natural selection preserving similar fa-
vourable variations.
Isolation, also, is an important element in the modification
of species through natural selection. In a confined or iso-
lated area, if not very large, the organic and inorganic con-
ditions of life will generally be almost uniform; so that nat-
ural selection will tend to modify all the varying individuals
of the same species in the same manner. Intercrossing with
the inhabitants of the surrounding districts will, also, be thus
prevented. Moritz Wagner has lately published an interest-
ing essay on this subject, and has shown that the service
rendered by isolation in preventing crosses between newly-
formed varieties is probably greater even than I supposed.
But from reasons already assigned I can by no means agree
with this naturalist, that migration and isolation are neces-
sary elements for the formation of new species. The im-
portance of isolation is likewise great in preventing, after
any physical change in the conditions such as of climate ele-
vation of the land, &c., the immigration of better adapted or-
ganisms ; and thus new places in the natural economy of the
district will be left open to be filled up by the modification of
the old inhabitants. Lastly, isolation will give time for a
new variety to be improved at a slow rate; and this may
sometimes be of much importance. If, however, an isolated
area be very small, either from being surrounded by barriers,
or from having very peculiar physical conditions, the total
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PRODUCmON OP NEW PORMS 117
number of the inhabitants will be small ; and this will retard
the production of new species through natural selection, by
decreasing the chances of favourable variations arising.
The mere lapse of time by itself does nothing, either for
or against natural selection. I state this because it has been
erroneously asserted that the element of time has been as-
sumed by me to play an all-important part in modifying
species, as if all the forms of life were necessarily undergo-
ing change through some innate law. Lapse of time is only
so far important, and its importance in this respect is great,
that it gives a better chance of beneficial variations arising
and of their being selected, accumulated, and fixed. It like-
wise tends to increase the direct action of the physical
conditions of life, in relation to the constituticMi of each
organism.
If we turn to nature to test the truth of these remarks, and
lode at any small isolated area, such as an oceanic island, al-
though the number of species inhabiting it is small, as we
shall see in our chapter on Geographical Distribution; yet
of these species a very large proportion are endemic, — ^that
is, have been produced there and nowhere else in the world.
Hence an oceanic island at first sight seems to have been
highly favourable for the production of new species. But
we may thus deceive ourselves, for to ascertain whether a
small isolated area, or a large open area like a continent, has
been most favourable for the production of new organic
forms, we ought to make the comparison within equal times;
and this we are incapable of doing.
Although isolation is of great importance in the production
of new species, on the whole I am inclined to believe that
largeness of area is still more important, especially for the
production of species which shall prove capable of enduring
for a long period, and of spreading widely. Throughout a
great and open area, not only will there be a better chance of
favourable variations^ arising from the large number of indi-
viduals of the same species there supported, but the conditions
of life are much more complex from the large number of al-
ready existing species; and if some of these many species
become modified and improved, others will have to be im-
proved in a corresponding degree, or they will be extermi-
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118 ORIGIN OP SPEaES
nated. Each new form, also, as soon as it has been much
improved, will be able to spread over the open and continu-
ous area, and will thus come into competition with many
other forms. Moreover, great areas, though now continuous,
will often, owing to former oscillations of level, have existed
in a broken condition; so that the good effects of isolation
will generally, to a certain extent, have concurred. Finally,
I conclude that, although small isolated areas have been in
some respects highly favourable for the production of new
species, yet that the course of modification will generally have
been more rapid on large areas ; and what is more important,
that the new forms produced on large areas, which already
have been victorious over many competitors, will be those
that will spread most widely, and will give rise to the great-
est number of new varieties and species. They will thus
play a more important part in the changing history of the
organic world.
In accordance with this view, we can, perhaps, understand
some facts which will be again alluded to in our chapter on
Geographical Distribution; for instance, the fact of the pro-
ductions of the smaller continent of Australia now yielding
before those of the larger Europseo- Asiatic area. Thus, also,
it is that continental productions have everywhere become so
largely naturalised on islands. On a small island, the race
for life will have been less severe, and there will have been
less modification and less extermination. Hence, we can
understand how it is that the flora of Madeira, according to
Oswald Heer, resembles to si certain extent the extinct ter-
tiary flora of Europe. All fresh-water basins, taken together,
make a small area compared with that of the sea or of the
land. Consequently, the competition between fresh- water
productions will have been less severe than elsewhere; new
forms will have been then more slowly produced, and old
forms more slowly exterminated. And it is in fresh-water
basins that we find seven genera of Ganoid fishes, remnants
of a once preponderant order: and in fresh water we find
some of the most anomalous forms now known in the world
as the Ornithorhynchus and Lepidosiren, which, like fossils,
connect to a certain extent orders at present widely sundered
in the natural scale. These anomalous forms may be called
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PRODUCTION OF NEW FORMS 119
living fossils; they have endured to the present day, from
having inhabited a confined area, and from having been ex-
posed to less varied, and therefore less severe, competition.
To sum up, as far as the extreme intricacy of the subject
permits, the circumstances favourable and unfavourable for
the production of new species through natural selection. I
conclude that for terrestrial productions a large continental
area, which has undergone many oscillations of level, will
have been the most favourable for the production of many
new forms of life, fitted to endure for a long time and to
spread widely. Whilst the area existed as a continent, the in-
habitants will have been numerous in individuals and kinds,
and will have been subjected to severe competition. When
converted by subsidence into large separate islands, there
will still have existed many individuals of the same species
on each island ; intercrossing on the confines of the range of
each new species will have been checked; after physical
changes of any kind, immigration will have been prevented,
so that new places in the polity of each island will have had
to be filled up by the modification of the old inhabitants ; and
time will have been allowed for the varieties in each to be-
come well modified and perfected. When, by renewed eleva-
tion, the islands were reconverted into a continental area,
there will again have been very severe competition : the most
favoured or improved varieties will have been enabled to
spread: there will have been much extinction of the less im-
proved forms, and the relative proportional numbers of the
various inhabitants of the reunited continent will again have
been changed ; and again there will have been a fair field for
natural selection to improve still further the inhabitants, and
thus to produce new species.
That natural selection generally acts with extreme slow-
ness I fully admit. It can act only when there are places in
the natural polity of a district which can be better occupied
by the modification of some of its existing inhabitants. The
occurrence of such places will often depend on physical
changes, which generally take place very slowly, and on the
immigration of better adapted forms being prevented. As
some few of the old inhabitants become modified, the mutual
relations of others will often be disturbed; and this will
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120 ORIGIN OF SPECIES
create new places, ready to be filled up by better adapted
forms ; but all this will take place very slowly. Although all
the individuals of the same species differ in some slight de-
gree from each other, it would often be long before differ-
ences of the right nature in various parts of the organisation
might occur. The result would often be greatly retarded by
free intercrossing. Many will exclaim that these several
causes are amply sufficient to neutralise the power of nat-
ural selection. I do not believe so. But I do believe that
natural selection will generally act very slowly, only at long
intervals of time, and only on a few of the inhabitants of the
same region. I further believe that these slow, intermittent
results accord well with what geology tells us of the rate and
manner at which the inhabitants of the world have changed.
Slow though the process of selection may be, if feeble man
can do much by artificial selection, I can see no limit to the
amount of change, to the beauty and complexity of the co-
adaptations between all organic beings, one with another
and with their physical conditions of life, which may have
been affected in the long course of time through nature's
power of selection, that is by the survival of the fittest.
EXTINCTION CAUSED BY NATURAL SELECTION
This subject will be more fully discussed in our chapter on
Geology; but it must here be alluded to from being inti-
mately connected with natural selection. Natural selection
acts solely through the preservation of variations in some
way advantageous, which consequently endure. Owing to
the high geometrical rate of increase of all organic beings,
each area is already fully stocked with inhabitants; and it
follows from this, that as the favoured forms increase in
number, so, generally, will the less favoured decrease and
become rare. Rarity, as geology tells us, is the precursor to
extinction. We can see that any form which is represented
by few individuals will run a good chance of utter extinc-
tion, during great fluctuations in the nature of the seasons,
or from a temporary increase in the number of its enemies.
But we may go further than this ; for, as new forms are pro-
duced, unless we admit that specific forms can go on indefi-
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EXTINCTION CAUSED BY NATURAL SELECTION 121
nitely increasing in number, many old forms must become ex-
tinct. That the number of specific forms has not indefinitely
increased, geology plainly tells us; and we shall presently at-
tempt to show why it is that the number of species through-
out the world has not become immeasurably great.
We have seen that the species which are most numerous
in individuals have the best chance of producing favourable
variations within any given period. We have evidence of
this, in the facts stated in the second chapter, showing that
it is the common and diffused or dominant species which
offer the greatest number of recorded varieties. Hence, rare
species will be less quickly modified or improved within any
given period ; they will consequently be beaten in the race for
life by the modified and improved descendants of the com-
moner specie3.
From these several considerations I think it inevitably fol-
lows, that as new species in the course of time are formed
through natural selection, others will become rarer and rarer,
and finally extinct The forms which stand in closest com-
petition with those tmdergoing modification and improve*
ment, will naturally suffer most. And we have seen in the
chapter on the Struggle for Existence that it is the most
closely-allied forms, — ^varieties of the same species, and
species of the same genus or of related genera, — ^which, from
having nearly the same structure, constitution, and habits,
generally come into the severest competition with each
other; consequently, each new variety or species, during the
progress of its formation, will generally press hardest on its
nearest kindred, and tend to exterminate them. We see the
same process of extermination amongst our domesticated pro-
ductions, through the selection of improved forms by man.
Many curious instances could be given showing how quickly
new breeds of cattle, sheep, and other animals, and varieties
of flowers, take the place of older and inferior kinds. In
Yorkshire, it is historically known that the ancient black
cattle were displaced by the long-horns, and that these "were
swept away by the short-horns" (I quote the words of an
agricultural writer) "as if by some murderous pestilence."
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122 ORIGIN OF SPECIES
DIVERGENCE OF CHARACTER
The principle, which I have designated by this term, is of
high importance, and explains, as I believe, several impor-
tant facts. In the first place, varieties, even strongly-maiiced
ones, though having somewhat of the character of species —
as is shown by the hopeless doubts in many cases how to
rank them — ^yet certainly differ far less from each other than
do good and distinct species. Nevertheless, according to my
view, varieties are species in the process of formation, or are,
as I have called them, incipient species. How, then, does
the lesser difference between varieties become augmented into
the greater difference between species? That this does habit-
ually happen, we must infer from most of the innumerable
species throughout nature presenting well-marked differ-
ences; whereas varieties, the supposed prototypes and par-
ents of future well-marked species, present slight and ill-de-
fined differences. Mere chance, as we may call it, might
cause one variety to differ in some character from its parents,
and the offspring of this variety again to differ from its
parent in the very same character and in a greater degree;
but this alone would never account for so habitual and large
a degree of difference as that between the species of the same
genus.
As has always been my practice, I have sought light on this
head from our domestic productions. We shall here find
something analogous. It will be admitted that the production
of races so different as short-horn and Hereford cattle, race
and cart horses, the several breeds of pigeons, ftc, could
never have been effected by the mere chance accumulation of
similar variations during many successive generations. In
practice, a fancier is, for instance, struck by a pigeon having
a slightly shorter beak ; another fancier is struck by a pigeon
having a rather longer beak; and on the acknowledged
principle that ''fanciers do not and will not admire a me-
dium standard, but like extremes," they both go on (as
has actually occurred with the sub-bre«is of the tumbler-
pigeon) choosing and breeding from birds with longer and
longer beaks, or with shorter and shorter beaks. Again, we
may suppose that at an early period of history, the men of
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DIVBBOBNCE OF CHARACTER 123
one nation or district required swifter horses, whilst those of
another required stronger and bulkier horses. The early dif-
ferences would be very slight ; but, in the course of time, from
the continued selection of swifter horses in the one case, and
of stronger ones in the other, the differences would become
greater, and would be noted as forming two sub-breeds. Ul-
timately, after the lapse of centuries, these sub-breeds would
become converted into two well-established and distinct
breeds. As the differences became greater, the inferior ani-
mals with intermediate characters, being neither very swift
nor very strong, would not have been used for breeding, and
will thus have tended to disappear. Here, then, we see in
man's productions the action of what may be called the prin-
ciple of divergence, causing differences, at first barely appre-
ciable, steadily to increase, and the breeds to diverge in
character, both from each other and from their common
parent.
But how, it may be asked, can any analogous principle
apply in nature? I believe it can and does apply most effi-
ciently (though it was a long time before I saw how), from
the simple circumstance that the more diversified the de-
scendants from any one species become in structure, consti-
tution, and habits, by so much will they be better enabled to
seize on many and widely diversified places in the polity of
nature, and so be enabled to increase in numbers.
We can clearly discern this in the case of animals with
simple habits. Take the case of a carnivorous quadruped,
of which the number that can be supported in any country has
long ago arrived at its full average. If its natural power of
increase be allowed to act, it can succeed in increasing (the
country not undergoing any change in conditions) only by
its varying descendants seizing on places at present occupied
by other animals; some of them, for instance, being enabled
to feed on new kinds of prey, either dead or alive; some
inhabiting new stations, climbing trees, frequenting water,
and some perhaps becoming less carnivorous. The more
diversified in habits and structure the descendants of our
carnivorous animals become, the more places they will be
enabled to occupy. What applies to one animal will apply
throughout all time to all animals — ^that is, if they vary — ^for
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124 ORIGIN OF SPECIES
otherwise natural selection can effect nothing. So it will be
with plants. It has been experimentally proved, that if a
plot of .ground be sown with one species of grass, and a similar
plot be sown with several distinct genera of grasses, a greater
number of plants and a greater weight of dry herbage can
be raised in the latter than in the former case. The same
has been found to hold good when one variety and several
mixed varieties of wheat have been sown on equal spaces of
ground. Hence, if any one species of grass were to go on
varying, and the varieties were continually selected which
differed from each other in the same manner, though in a
very slight degree, as do the distinct species and genera of
grasses, a greater number of individual plants of this species,
including its modified descendants, would succeed in living
on the same piece of ground. And we know that each
species and each variety of grass is annually sowing almost
countless seeds ; and is thus striving, as it may be said, to the
utmost to increase in number. Consequently, in the course of
many thousand generations, the most distinct varieties of
any one species of grass would have the best chance of suc-
ceeding and of increasing in numbers, and thus of supplanting
the less distinct varieties; and varieties, when rendered very
distinct from each other, take the rank of species.
The truth of the principle that the greatest amount of life
can be supported by great diversification of structure, is seen
under many natural circumstances. In an extremely small
area, especially if freely open to immigration, and where the
contest between individual and individual must be very se-
vere, we always find g^eat diversity in its inhabitants. For
instance, I found that a piece of turf, three feet by four
in size, which had been exposed for many years to exactly
the same conditions, supported twenty species of plants, and
these belonged to eighteen genera and to eight orders, which
shows how much these plants differed from each other. So
it is with the plants and insects on small and uniform islets:
also in small ponds of fresh water. Farmers find that they
can raise most food by a rotation of plants belonging to the
most different orders; nature follows what may be called a
simultaneous rotation. Most of the animals and plants which
live close round aqy small piece of ground, could live on it
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DIVERGENCE OF CHARACTER 125
(supposing its nature not to be in any way peculiar), and
may be said to be striving to the utmost to live there ; but, it
is seen, that where they come into the closest competition, the
advantages of diversification of structure, with the accom-
panying differences of habit and constitution, determine that
the inhabitants, which thus jostle each other most closely,
shall, as a general rule, belong to what we call different
genera and orders.
The same principle is seen in the naturalisation of plants
through man's agency in foreign lands. It might have been
expected that the plants which would succeed in becoming
naturalised in any land would generally have been closely
allied to the indigenes ; for these are commonly looked at as
specially created and adapted for their own country. It
might also, perhaps, have been expected that naturalised
plants would have belonged to a few groups more especially
adapted to certain stations in their new homes. But the
case is very different; and Alph. de CandoUe has well re-
marked, in his great and admirable work, that floras gain by
naturalisation, proportionally with the number of the native
genera and species, far more in new genera than in new
species. To give a single instance: in the last edition of
Dr. Asa Gray's 'Manual of the Flora of the Northern United
States,' 260 naturalised plants are enumerated, and these be-
long to 162 genera. We thus see that these naturalised plants
are of a highly diversified nature. They differ, moreover, to
a large extent, from the indigenes, for out of the 162 natural-
ised genera, no less than 100 genera are not there indigenous,
and thus a large proportional addition is made to the genera
now living in the United States.
By considering the nature of the plants or animals which
have in any country struggled successfully with the indigenes,
and have there become naturalised, we may gain some crude
idea in what manner some of the natives would have to be
modified, in order to gain an advantage over their com-
patriots; and we may at least infer that diversification of
structure, amounting to new generic differences, would be
profitable to them.
The advantage of diversification of structure in the in-
habitants of the same region is, in fact, the same as that of
H— HCZI
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126 ORIGIN OF SPECIES
the physiological division of labor in the organs of the same
individual body — a subject so well elucidated by Milne Ed-
wards. No physiologist doubts that a stomach adapted to
digest vegetable matter alone, or flesh alone, draws most
nutriment from these substances. So in the general economy
of any land, the more widely and perfectly the animals and
plants are diversified for different habits of life, so will a
greater number of individuals be capable of there supporting
themselves. A set of animals, with their organisation but
little diversified, could hardly compete with a set more per-
fectly diversified in structure. It may be doubted, for in-
stance, whether the Australian marsupials, which are divided
into groups differing but little from each other, and feebly
representing, as Mr. Waterhouse and others have remarked,
our carnivorous, ruminant, and rodent mammals, could suc-
cessfully compete with these well-developed orders. In the
Australian mammals, we see the process of diversification
in an early and incomplete stage of development.
THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION
THROUGH DIVERGENCE OF CHARACTER AND EXTINC-
TION, ON THE DESCENDANTS OF A COMMON
ANCESTOR
After the foregoing discussion, which has been much com-
pressed, we may assume that the modified descendants of any
one species will succeed so much the better as they become
more diversified in structure, and are thus enabled to en-
croach on places occupied by other beings. Now let us see
how this principle of benefit being derived from divergence
of character, combined with the principles of natural selec-
tion and of extinction, tends to act.
The accompanying diagram will aid us in understanding
this rather perplexing subject. Let A to L represent the
species of a genus large in its own country; these species are
supposed to resemble each other in unequal degrees, as is
so generally the case in nature, and as is represented in the
diagram by the letters standing at unequal distances. I have
said a large genus, because as we saw in the second chapter,
on an average more species vary in large genera than in
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EFFECTS OF NATURAL SELECTION 127
small genera; and the varying species of the large genera
present a greater number of varieties. We have, also, seen
that the species, which are the commonest and the most
widely diffused, vary more than do the rare and restricted
species. Let (A) be a common, widely-diffused, and varying
species, belonging to a genus large in its own country. The
branching and diverging dotted lines of unequal lengths pro-
ceeding from (A), may represent its varying offspring. The
variations are supposed to be extremely slight, but of the
most diversified nature; they are not supposed all to appear
simultaneously, but often after long intervals of time; nor
are they all supposed to endure for equal periods. Only those
variations which are in some way profitable will be preserved
or naturally selected. And here the importance of the prin-
ciple of benefit derived from divergence of character comes
in; for this will generally lead to the most different or di-
vergent variations (represented by the outer dotted lines)
being preserved and accumulated by natural selection. When
a dotted line reaches one of the horizontal lines, and is there
marked by a small numbered letter, a sufficient amount of
variation is supposed to have been accumulated to form it
*into a fairly well-marked variety, such as would be thought
worthy of record in a systematic work.
The intervals between the horizontal lines in the diagram,
may represent each a thousand or more generations. After a
thousand generations, species (A) is supposed to have pro-
duced two fairly well-marked varieties, namely a* and i»\
These two varieties will generally still be exposed to the
same conditions which made their parents variable, and the
tendency to variability is in itself hereditary; consequently
they will likewise tend to vary, and commonly in nearly the
same manner as did their parents. Moreover, these two
varieties, being only slightly modified forms, will tend to
inherit those advantages which made their parent (A) more
numerous than most of the other inhabitants of the same
country; they will also partake of those more general advan-
tages which made the genus to which the parent-species
belonged, a large genus in its own country. And all
these circumstances are favorable to the producfion of new
varieties.
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128 ORIGIN OF SPECIES
If, then, these two varieties be variable, the most divergent
of their variations will generally be preserved during the
next thousand generations. And after this interval, variety
a* is supposed in the diagram to have produced variety a*,
which will, owing to the principle of divergence, differ more
from (A) than did variety ct. Variety trf is supposed to
have produced two varieties, namely «* and ^, differing from
each other, and more considerably from their common parent
(A). We may continue the process by similar steps for any
length of time; some of the varieties, after each thousand
generations, producing only a single variety, but in a more
and more modified condition, some producing two or three
varieties, and some failing to produce any. Thus the varie-
ties or modified descendants of the common parent (A), will
generally go on increasing in number and diverging in char-
acter. In the diagram the process is represented up to the
ten-thousandth generation, and under a condensed and sim-
plified form up to the fourteen-thousandth generation.
But I must here remark that I do not suppose that the
process ever goes on so regularly as is represented in the
diagram, though in itself made somewhat irregular, nor that
it goes on continuously; it is far more probable that each
form remains for long periods unaltered, and then again
undergoes modification. Nor do J suppose that the most di-
vergent varieties are invariably preserved; a medium form
may often long endure, and may or may not produce more
than one modified descendant; for natural selection will al-
ways act according to the nature of the places which are
either unoccupied or not perfectly occupied by other beings;
and this will depend on infinitely complex relations. But as
a general rule, the more diversified in structure the descend-
ants (rom any one species can be rendered, the more places
they will be enabled to seize on, and the more their modified
progeny will increase. In our diagram the line of succession
is broken at regular intervals by small numbered letters mark-
ing the successive forms which have become sufficiently dis^
tinct to be recorded as varieties. But these breaks are
imaginary, and might have been inserted anywhere, after
intervals long enough to allow the accumulation of a con-
siderable amount of divergent variation.
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EFFECTS OF NATURAL SELECTION 129
As all the modified descendants from a common and widely-
diffused species, belonging to a large genus, will tend tp par-
take of the same advantages which made their parent success-
ful in life, they will generally go on multipl3ring in number as
well as diverging in character ; this is represented in the dia-
gram by the several divergent branches proceeding from (A).
The modified offspring from the later and more highly im-
proved branches in the lines of descent, will, it is probable,
often take the place of, and so destroy^ the earlier and less im-
proved branches : this is represented in the diagram by some
of the lower branches not reaching to the upper horizontal
lines. In some cases no doubt the process of modification
will be confined to a single line of descent, and the number
of modified descendants wilt not be increased; although the
amount of divergent modification may have been augmented.
This case would be represented in the diagram, if all the
lines proceeding from (A) were removed, excepting that
from d to a". In the same way the English race-horse and
English pointer have apparently both gone on slowly diverg-
ing in character from their original stocks, without either
having given off any fresh branches or races.
After ten thousand generations, species (A) is supposed
to have produced three forms, rf*, f^ and w**, which, from
having diverged in character during the successive genera-
tions, will have come to differ largely, but perhaps unequally,
from each other and from their common parent. If we sup-
pose the amount of change between each horizontal line in
our diagram to be excessively small, these three forms may
still be only well-marked varieties; but we have only to
suppose the steps in the process of modification to be more
numerous or greater in amount, to convert these three forms
into doHbtful or at least into well-defined species. Thus the
diagram illustrates the steps by which the small differences
distinguishing varieties are increased into the larger differ-
ences distinguishing species. By continuing the same process
for a greater number of generations (as shown in the dia-
gram in a condensed and simplified manner), we get eight
species, marked by the letters between d^ and w", all de-
scended from (A). Thus, as I believe, species are multiplied
and genera are formed.
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ISO ORIGIN OF SPBaBS
In a large genus it is probable that more than one species
would vary. In the diagram I have assumed that a second
species (I) has produced, by analc^us steps, after ten thou-
sand generations, either two well-marked varieties («/' and
sf^) or two species, according to the amount of change sup-
posed to be represented between the horizontal lines. After
fourteen thousand generations, six new species, marked by
the letters ti^ to j?^, are supposed to have been produced. In
any genus, the species which are already very different in
character from each other, will generally tend to produce the
greatest number of modified descendants; for these will have
the best chance of seizing on new and widely different places
in the poHty of nature : hence in the diagram I have chosen
the extreme species (A), and the nearly extreme species (I),
as those which have largely varied, and have given rise to
new varieties and species. The other nine species (marked
by capital letters) of our original genus, may for long but
unequal periods continue to transmit unaltered descendants;
and this is shown in the diagram by the dotted lines unequally
prolonged upwards.
But during the process of modification, represented in the
diagram, another of our principles, namely that of extinction,
will have played an important part. As in each fully stocked
country natural selection necessarily acts by the selected
form having some advantage in the struggle for life over
other forms, there will be a constant tendency in the im-
proved descendants of any one species to supplant and ex-
terminate in each stage of descent their predecessors and
their original progenitor. For it should be remembered that
the competition will generally be most severe between those
forms which are most nearly related to each other in habits,
constitution, and structure. Hence all the intermediate forms
between the earlier and later states, that is between the less
and more improved states of the same species, as well as
the original parent-species itself, will generally tend to become
extinct So it probably will be with many whole collateral
lines of descent which will be conquered by later and
improved lines. If, however, the modified offspring of a
species get into some distinct country, or become quickly
adapted to some quite new station, in which offspring and
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EFFECTS OF NATURAL SELECTION 131
progenitor do not come into competition, both may continue
to exist.
If, then, our diagram be assumed to represent a consider-
able amount of modification, species (A) and ail the earlier
varieties will have become extinct, being replaced by eight
new species (a'* to f»") ; and species (I) will be replaced by
six (»" to «**) new species.
But we may go further than this. The original species
of our genus were supposed to resemble each other in unequal
degrees, as is so generally the case in nature; species (A)
being more nearly related to B, C, and D, than to the other
species; and species (I) more to G, H, K, L, than to the
others. These two species (A) and (I) were also.supposed
to be very coounon and widely diffused species, so that they
must originally have had some adv^tage over most of the
other species of the genus. Their modified descendants,
fourteen in number at the fourteen-thousandth generation,
will probably have inherited some of the same advantages:
they have also been modified and improved in a diversified
manner at each stage of descent, so as to have become adapted
to many related places in the natural economy of their
country. It seems, therefore, extremely probable that they
will have taken the places of, and thus exterminated, not only
their parents (A) and (I), but likewise some of the original
species which were most nearly related to their parents.
Hence very few of the original species will have transmitted
offspring to the fourteen-thousandth generation. We may
suppose that only one, (F), of the two species (E and F)
which were least closely related to the other nine original
species, has transmitted descendants to this late stage of
descent.
The new species in our diagram descended from the original
eleven species, will now be fifteen in number. Owing to the
divergent tendency of natural selection, the extreme amount
of difference in character between species a" and /* will be
much greater than that between the most distinct of the
original eleven species. The new species, moreover, will be
allied to each other in a widely different manner. Of the
eight descendants from (A) the three marked a**, ^*, p**,
will be nearly related from having recently branched off
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1^2 ORIGIN OP SPEaES
from rf*; 5", and /**, from having diverged at an earlier
period from a*, will be in some degree distinct from the three
first-named species; and lastly, a", t" and w" will be nearly
related one to the other, but, from having diverged at the first
commencement of the process of modification, will be widely
diflPerent from the other five species, and may constitute a
sub-genus or a distinct genus.
The six descendants from (I) will form two sub-genera or
genera. But as the original species (I) differed largely from
(A), standing nearly at the extreme end of the original
genus, the six descendants from (I) will, owing to inherit-
ance alone, differ considerably from the eight descendants
from (A) ; the two groups, moreover, are supposed to have
gone on diverging in different directions. The intermediate
species, also (and thi^ is a very important consideration),
which connected the original species (A) and (I), have all
become, excepting (F), extinct, and have left no descend-
ants. Hence the six new species descended from (I), and
the eight descendants from (A), will have to be ranked as
very distinct genera, or even as distinct sub-families.
Thus it is, as I believe, that two or more genera are pro-
duced by descent with modification, from two or more species
of the same genus. And the two or more parent-species are
supposed to be descended from some one species of an earlier
genus. In our diagram, this is indicated by the broken lines,
beneath the capital letters, converging in sub-branches down-
wards towards a single point ; this point represents a species,
the supposed progenitor of our several stb-genera and
genera.
It is worth while to reflect for a moment on the character
of the new species f**, which is supposed not to have diverged
much in character, but to have retained the form of (F),
either unaltered or altered only in a slight degree. In this
case, its afiinities to the other fourteen new species will be of
a curious and circuitous nature. Being descended from a
form which stood between the parent-species (A) and (I),
now supposed to be extinct and unknown, it will be in some
degree intermediate in character between the two groups
descended from these two species. But as these two groups
have gone on diverging in character from the type of their
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EFFECTS OF NATURAL SELECTION 133
parents, the new species (f^*) will not be directly interme-
diate between them, but rather between types of the two
groups; and every naturalist will be able to call such cases
before his mind.
In the diagram, each horizontal line has hitherto been sup-
posed to represent a thousand generations, but each may rep-
resent a million or more generations ; it may also represent a
section of the successive strata of the earth's crust including
extinct remains. We shall, when we come to our chapter on
Geology, have to refer again to this subject, and I think we
shall then see that the diagram throws light on the affinities
of extinct beings, which, though generally belonging to the
same orders, families, or genera, with those now living, yet
are often, in some degree, interme(|iate in character between
existing groups ; and we can understand this fact, for the ex-
tinct species lived at various remote epochs when the
branching lines of descent had diverged less.
I see no reason to limit the process of modification, as now
explained, to the formation of genera alone. If, in the dia-
gram, we suppose the amount of change represented by each
successive group of diverging dotted lines to be great, the
forms marked fl" to ^", those marked 6" and f*, and those
marked o" to m", will form three very distinct genera. We
shall also have two very distinct genera descended from (I),
differing widely from the descendants of (A). Those two
groups of genera will thus form two distinct families, or
orders, according to the amount of divergent modification
supposed to be represented in the diagram. And the two new
families, or orders, are descended from two species of the
original genus, and these are supposed to be descended from
some still more ancient and unknown form.
We have seen that in each country it is the species belong-
ing to the larger genera which oftenest present varieties or
incipient species. This, indeed, might have been expected;
for, as natural selection acts through one form having some
advantage over other forms in the struggle for existence, it
will chiefly act on those which already have some advantage ;
and the largeness of any group shows that its species have
inherited from a common ancestor some advantage in com-
mon. Hence, the struggle for the production of new and
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134 ORIGIN OF SPEaBS
modified descendants will mainly lie between the larger
groups which are all trying to increase in number. One
large group will slowly conquer another large group, reduce
Its numbers, and thus lessen its chance of further variation
and improvement Within the same large group, the later
and more highly perfected sub*groups, from branching out
and seizing on many new places in the polity of Nature, will
constantly tend to supplant and destroy the earlier and less
improved sub-groups. Small and broken groups and sub-
groups will, finally disappear. Looking to the future, we can
predict that the groups of organic beings which are now
large and triumphant, and which are least broken up, that
is, which have as yet suffered least extinction, will, for a long
period, continue to increase. But which groups will ulti-
mately prevail, no man can predict; for we know that many
groups, formerly most extensively developed, have now be-
come extinct. Looking still more remotely to the future, we
may predict that, owing to the continued and steady increase
of the larger groups, a multitude of smaller groups will
become utterly extinct, and leave no modified descendants;
and consequently that, of the species living at any one period,
extremely few will transmit descendants to a remote futurity.
I shall have to return to this subject in the chapter on Classi-
fication, but I may add that as, according to this view, ex-
tremely few of the more ancient species have transmitted
descendants to the present day, and, as all the descendants
of the same species form a class, we can understand how it
is that there exist so few classes in each main division of
the animal and vegetable kingdoms. Although few of the
most ancient species have left modified descendants, yet, at
remote geological periods, the earth may have been almost
as well peopled with species of many genera, families, orders,
and classes, as at the present time.
ON THE DEGREE TO WHICH ORGANIZATION TENDS TO ADVANCE
Natural Selection acts exclusively by the preservation and
accumulation of variations, which are beneficial under the
organic and inorganic conditions to which each creature is
exposed at all periods of life. The ultimate result is that each
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EFFECTS OF NATURAL SELECTION 135
creature tends to become more and more improved in relation
to its conditions. This improvement inevitably leads to the
gradual advancement of the organisation of the greater num-
ber of living beings throughout the world. But here we enter
on a very intricate subject, for naturalists have not defined
to each other's satisfaction what is meant by an advance in
organization. Amongst the vertebrata the degree of intellect
and an approach in structure to man clearly come into play.
It might be thought that the amount of change which the
various parts and organs pass through in their development
from the embryo to maturity would suffice as a standard of
comparison; but there are cases, as with certain parasitic
crustaceans, in which several parts of the structure become
less perfect, so that the mature animal cannot be called higher
than its larva. Von Baer's standard seems the most widely
applicable and the best, namely, the amount of differentiation
of the parts of the same organic being, in the adult state as
I should be inclined to add, and their specialisation for dif-
ferent functions; or, as Milne Edwards would express it,
the completeness of the division of physiological labour. But
we shall see how obscure this subject is if we look, for in-
stance, to fishes, amongst which some naturalists rank those
as highest which, like the sharks, approach nearest to amphi-
bians; whilst other naturalists range the common bony or
teleostean fishes as the highest, inasmuch as they are most
strictly fish-like, and differ most from the other vertebrate
classes. We see still more plainly the obscurity of the
subject by turning to plants, amongst which the standard of
intellect is of course quite excluded ; and here some botanists
rank those plants as highest which have every organ, as
sepals, petals, stamens, and pistils, fully developed in each
flower; whereas other botanists, probably with more truth,
look at the plants which have their several organs much
modified and reduced in number as the highest
If we take as the standard of high organisation, the amount
of differentiation and specialisation of the several organs in
each being when adult (and this will include the advance-
ment of the brain for intellectual purposes), natural selec-
tion clearly leads towards this standard : for all physiologists
admit that the specialisation of organs, inasmudi as in this
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136 ORIGIN OF SPECIES
state they perform their functions better, is an advantage to
each being ; and hence the accumulation of variations tending
towards specialisation is within the scope of natural selection.
On the other hand, we can see, bearing in mind that all or-
ganic beings are striving to increase at a high ratio and to
seize on every unoccupied or less well occupied place in the
economy of nature, that it is quite possible for natural selec-
tion gradually to fit a being to a situation in which several
organs would be superfluous or useless: in such cases there
would be retrogression in the scale of organisation. Whether
organisation on the whole has actually advanced from the
remotest geological periods to the present day will be more
conveniently discussed in our chapter on Geological Succes-
sion.
But it may be objected that if all organic beings thus tend
to rise in the scale, how is it that throughout the world a
multitude of the lowest forms still exist; and how is it that
in each great class some forms are far more highly developed
than others ? Why have not the more highly developed forms
everywhere supplanted and exterminated the lower? La-
marck, who believed in an innate and inevitable tendency
towards perfection in all organic beings, seems to have felt
this difficulty so strongly, that he was led to suppose that new
and simple forms are continually being produced by spon-
taneous generation. Science has not as yet proved the truth
of this belief, whatever the future may reveal. On our
theory the continued existence of lowly organisms offers no
difficulty ; for natural selection, or the survival of the fittest,
does not necessarily include progressive development — it
only takes advantage of such variations as arise and are
beneficial to each creature under its complex relations of life.
And it may be asked what advantage, as far as we can see,
would it be to an infusorian animalcule — ^to an intestinal
worm— or even to an earth-worm, to be highly organised.
If it were no advantage, these forms would be left, by natural
selection, unimproved or but little improved, and might re-
main for indefinite ages in their present lowly condition.
And geology tells us that some of the lowest forms, as the
infusoria and rhizopods, have remained for an enormous
period in nearly their present state. But to suppose that most
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EFFECTS OF NATURAL SELECTION 137
of the many now existing low forms have not in the least
advanced since the first dawn of life would be extremely
rash; for every naturalist who has dissected some of the be-
ings now ranked as very low in the scale, must have been
struck with their really wondrous and beautiful organisation.
Nearly the same remarks are applicable if we look to the
different grades of organisation within the same great group;
for instance, in the vertebrata, to the co-existence of mam-
mals and fish — amongst mammalia, to the co-existence of man
and the ornithorhynchus — ^amongst fishes, to the co-existence
of the shark and the lancelet (Amphioxus), which latter fish
in the extreme simplicity of its structure approaches the in-
vertebrate classes. But mammals and fish hardly come into
competition with each other; the advancement of the whole
class of mammals, or of certain members in this class, to the
highest grade would not lead to their taking the place of
fishes. Physiologists believe that the brain must be bathed
by warm blood to be highly active, and this requires aerial
respiration; so that warm-blooded mammals when inhabiting
the water lie under a disadvantage in having to come con-
tinually to the surface to breathe. With fishes, members
of the shark family would not tend to supplant the lancelet;
for the lancelet, as I hear from Fritz MuUer, has as sole com-
panion and competitor on the barren sandy shore of South
Brazil, an anomalous annelid. The three lowest orders of
mammals, namely, marsupials, edentata, and rodents, co-exist
in South America in the same region with numerous monkeys,
and probably interfere little with each other. Although or-
ganisation, on the whole, may have advanced and be still
advancing throughout the world, yet the scale will always
present many degrees of perfection; for the high advance-
ment of certain whole classes, or of certain members of each
class, does not at all necessarily lead to the extinction of
those groups with which they do not enter into close competi-
tion. In some cases, as we shall hereafter see, lowly or-
ganised forms appear to have been preserved to the present
day, from inhabiting confined or peculiar stations, where
they have been subjected to less severe competition, and
where their scanty numbers have retarded the chance of fav-
orable variations arising.
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138 ORIGIN OF SPECIES
Finally, I believe that many lowly organised forms now
exist throughout the worlds from various causes. In some
cases variations or individual differences of a favorable na-
ture may never have arisen for natural selection to act on and
accumulate. In no case, probably, has time sufficed for the
utmost possible amount of development. In some few cases
there has been what we must call retrogression of organisa-
tion. But the main cause lies in the fact that under very
simple conditions of life a high organisation would be of no
service, — ^possibly would be of actual disservice, as being of
a more delicate nature, and more liable to be put out of order
and injured.
Looking to the first dawn of life, when all organic beings,
as we may believe, presented the simplest structure, how, it
has been asked, could the first steps in the advancement or
differentiation of parts have arisen? Mr. Herbert Spencer
would probably answer that, as soon as simple unicellular
organism came by growth or division to be compounded of
several cells, or became attached to any supporting surface,
his law "that homologous units of any order became differ-
entiated in proportion as their relations to incident forces
became different" would come into action. But as we have
no facts to guide us, speculation on the subject is almost use-
less. It is, however, an error to suppose that there would
be no struggle for existence, and, consequently, no natural
selection, until many forms had been produced: variations
in a single species inhabiting an isolated station might be
beneficial, and thus the whole mass of individuals might be
modified, or two distinct forms might arise. But, as I re-
marked towards the close of the Introduction, no one ought
to feel surprise at much remaining as yet unexplained on
the origin of species, if we make due allowance for our pro-
found ignorance on the mutual relations of the inhabitants
of the world at the present time, and still more so during
past ages.
CONVERGENCE OF CHARACTER
Mr. H. C. Watson thinks that I have overrated the im-
portance of divergence of character (in which, however, he
apparently believes), and that convergence, as it may be
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CONVERGENCE OP CHARACTER 139
called, has likewise played a part If two species, belonging
to two distinct though allied genera, had both produced a
large number of new and divergent forms, it is conceivable
that these might approach each other so closely that they
would have all to be classed under the same genus; and thus
the descendants of two distinct genera would converge into
one. But it would in most cases be extremely rash to at*
tribute to convergence a close and general similarity of struc-
ture in the modified descendants of widely distinct forms.
The shape of a crystal is determined solely by the molecular
forces, and it is not surprising that dissimilar substances
should sometimes assume the same form; but with organic
beings we should bear in mind that the form of each depends
on an infinitude of complex relations, namely on the varia-
tions which have arisen, these being due to causes far too
intricate to be followed out,— on the nature of the variations
which have been preserved or selected, and this depends on
the surrounding physical conditions, and in a still higher
degree on the surrounding organisms with which each being
has come into competition, — and lastly, on inheritance (in it-
self a fluctuating element) from innumerable progenitors,
all of which have had their forms determined through equally
complex relations. It i& incredible that the descendants of
two organisms, which had originally differed in a marked
manner, should ever afterwards converge so closely as to lead
to a near approach to identity throughout their whole organ-
isation. If tills had occurred, we should meet with the same
form, independently of genetic connection, recurring in
widely separated geological formations; and the balance of
evidence is opposed to any such an admission.
Mr. Watson has also objected that the continued action
of natural selection, together with divergence of character,
would tend to make an indefinite number of specific forms.
As far as mere inorganic conditions are concerned, it seems
probable that a sufficient number of species would soon
become adapted to all considerable diversities of heat,
moisture, &c. ; but I fully admit that the mutual relations of
organic beings are more important; and as the number of
species in any country goes on increasing, the organic con-
ditions of life must become more and more complex. Conse-
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140 ORIGIN OF SPECIES
quently there seems at first sight no limit to the amount of
profitable diversification of structure, and therefore no limit
to the number of species which might be produced. We do
not know that even the most prolific area is fully stocked
with specific forms: at the Cape of Good Hope and in Aus-
tralia, which support such an astonishing number of species,
many European plants have become naturalised. But geology
shows us, that from an early part of the tertiary period the
number of species of shells, and that from the middle part of
this same period the number of mammals, has not greatly or
at all increased. What then checks an indefinite increase
in the number of species? The amount of life (I do not mean
the number of specific forms) supported on an area must
have a limit, depending so largely as it does on physical con-
ditions; therefore, if an area be inhabited by very many spe-
cies, each or nearly each species will be represented by few
individuals; and such species will be liable to extermination
from accidental fluctuations in the nature of the seasons
or in the number of their enemies. The process of exter-
mination in such cases would be rapid, whereas the production
of new species must always be slow. Imagine the extreme
case of as many species as individuals in England, and the
first severe winter or very dry summer would exterminate
thousands on thousands of species. Rare species, and each
species will become rare if the number of species in any
country becomes indefinitely increased, will, on the principle
often explained, present within a given period few favorable
variations; consequently, the process of giving birth to new
specific forms would thus be retarded. When any species be-
comes very rare, close interbreeding will help to exterminate
it ; authors have thought that this comes into play in account-
ing for the deterioration of the Aurochs in Lithuania, of Red
Deer in Scotland, and of Bears in Norway, &c. Lastly, and
this I am inclined to think is the most important element, a
dominant species, which has already beaten many competitors
in its own home, will tend to spread and supplant many others.
Alph, de Candolle has shown that those species which spread
widely, tend generally to spread very widely; consequently,
they will tend to supplant and exterminate several species
in several areas, and thus check the inordinate increase of
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SUMMARY OP CHAPTEB 141
specific forms throughout the world. Dr. Hooker has re-
cently shown that in the S.E. comer of Australia, where,
apparently, there are many invaders from different quarters
of the globe, the endemic Australian species have been
greatly reduced in number. How much weight to attribute
to these several considerations I will not pretend to say; but
conjointly they must limit in each country the tendency to
an indefinite augmentation of specific forms.
SUMMARY OF CHAPTER
If under changing conditions of life organic beings present
individual differences in almost every part of their structure,
and this cannot be disputed; if there be, owing to their
geometrical rate of increase, a severe struggle for life at
some age, season, or year, and this certainly cannot be dis-
puted; then, considering the infinite complexity of the rela-
tions of all organic beings to each other and to their condi-
tions of life, causing an infinite diversity in structure, consti-
tution, and habits, to be advantageous to them, it would be a
most extraordinary fact if no variaticxxs had ever occurred
useful to each being's own welfare, in the same manner as so
many variations have occurred useful to man. But if varia-
tions useful to any organic being ever do occur, assuredly
individuals thus characterised will have the best chance of
being preserved in the struggle for life ; and from the strong
principle of inheritance, these will tend to produce ofiFspring
similarly characterised. This principle of preservation, or the
survival of the fittest, I have called Natural Selection. It
leads to the improvement of each creature in relation to its
organic and inorganic conditions of life; and consequently,
in most cases, to what must be regarded as an advance in
organism. Nevertheless, low and simple forms will long
endure if well fitted for their simple conditions of life.
Natural selection, on the principle of qualities being in-
herited at corresponding ages, can modify the egg, seed, or
young, as easily as the adult. Amongst many animals, sexual
selection will have given its aid to ordinary selection, by
assuring to the most vigorous and best adapted males the
greatest number of offspring. Sexual selection will also give
X— HCZI
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142 ORIGIN OF SPBaSS
characters useful to the males alone, in their struggles or
rivalry with other males; and these characters will be trans-
mitted to one sex or to both sexes, according to the form of
inheritance which prevails.
Whether natural selection has really thus acted in adapting
the various forms of life to their several conditions and sta-
tions, must be judged by the general tenor and balance of
evidence given in the following chapters. But we have al-
ready seen how it entails extinction; and how largely ex-
tinction has acted in the world's history, geology plainly
declares. Natural selection, also, leads to divergence of
character; for the more organic beings diverge in structure,
habits, and constitution, by so much the more can a large
number be supported on the area,— of which we see proof by
looking to the inhabitants of any small spot, and to the pro-
ductions naturalised in foreign lands. Therefore, during the
modification of the descendants of any one species, and dur-
ing the incessant struggle of all species to increase in num-
bers, the more diversified the descendants become, the better
will be their chance of success in the battle for life. Thus
the small differences distinguishing varieties of the same spe-
cies, steadily tend to increase, till they equal the greater dif-
ferences between species of the same genus, or even of
distinct genera.
We have seen that it is the common, the widely-diffused
and widely-ranging species, belonging to the larger genera
within each dass, which vary most; and these tend to trans-
mit to their modified offspring that superiority which now
makes them dominant in their own countries. Natural selec-
tion, as has just been remarked, leads to divergence of
character and to much extinction of the less improved and
intermediate forms of life. On these principles, the nature
of the affinities, and the generally well-defined distinctions
between the innumerable organic beings in each dass
throughout the world, may be explained. It is a truly won-
derful fact — ^the wonder of which we are apt to overlook
from familiarity — that all animals and all plants through-
out all time and space should be related to each other in
groups, subordinate to groups, in the manner which we
everjTwhere behold— namdy, varieties of the same spedes
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SUMMARY OF CHAPTER 143
most dosely related, species of the same genus less closely
and unequally related, forming sections and sub-genera, spe-
cies of distinct genera much less closely related, and genera
related in different degrees, forming sub-families, families,
orders, sub-classes and classes. The several subordinate
groups in any class cannot be ranked in a single file, but
seem clustered round points, and these round other points,
and so on in almost endless cycles. If species had been in-
dependently created, no explanation would have been pos-
sible of this kind of classification ; but it is explained through
inheritance and the complex action of natural selection, en-
tailing extinction and divergence of character, as we have
seen illustrated in the diagram.
The affinities of all the beings of the same class have some-
times been represented by a great tree. I believe this simile
largely speaks the truth. The green and budding twigs may
represent existing species ; and those produced during former
years may represent the long succession of extinct species.
At each period of growth all the growing twigs have tried
to branch out on all sides, and to overtop and kill the sur-
rounding twigs and branches, in the same manner as species
and groups of species have at all times overmastered other
species in the great battle for life. The limbs divided into
great branches, and these into lesser and lesser branches,
were themselves once, when the tree was young, budding
twigs ; and this connection of the former and present buds by
ramifying branches may well represent the classification of
all extinct and living species in groups subordinate to groups.
Of the many twigs which flourished when the tree was a
mere bush, only two or three, now grown into great branches,
yet survive and bear the other branches; so with the species
which lived during long-past geological periods, very few
have left living and modified descendants. From the first
growth of the tree, many a limb and branch has decayed and
dropped off; and these fallen branches of various sizes may
represent those whole orders, families, and genera which have
now no living representatives, and which are known to us
only in a fossil state. As we here and there see a thin strag-
gling branch springing from a fork low down in a tree, and
which by some chance has been favoured and is still alive on
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144 ORIGIN OF SPECIES
its summit, so we occasionally see an animal like the Ornitho-
rhynchus or Lepidosiren, which in some small degree con-
nects by its affinities two large branches of life, and which
has apparently been saved from fatal competition by having
inhabited a protected station. As buds give rise by growth
to fresh buds, and these, if vigorous, branch out and overtop
on all sides many a feebler branch, so by generation I believe
it has been with the great Tree of Life, which fills with
its dead and broken branches the crust of the earth, and
covers the surface with its ever-branching and beautiful
ramifications.
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CHAPTER V
Laws of Variatioit
EflFects of changed conditioiia— Use and disuse, combined with natural
selection; organs of flight and of vision — Acclimatisation — Cor-
related rariation — Compensation and economy of growth — ^False
correlations— Multiple, rudimentary, and lowly organised struc-
tures variable — Parts developed in an unusual manner are highly
variable ; specific characters more variable than generic : second-
ary sexual characters variable — Species of the same genus vary
in an analogous manner — ^Reversions to long-lost characters
Summary.
I HAVE hitherto sometimes spoken as if the variations —
so common and multiform with organic beings imder
domestication, and in a lesser degree with those under
nature — ^were due to chance. This, of course, is a wholly
incorrect expression, but it serves to acknowledge plainly
our ignorance of the cause of each particular variation.
Some authors believe it to be as much the function of the
reproductive system to produce individual differences, or
slight deviations of structure, as to make the child like its
parents. But the fact of variations and monstrosities oc-
curring much more frequently under domestication than
under nature, and the greater variability of species having
wide ranges than of those with restricted ranges, lead to the
conclusion that variability is generally related to the condi-
tions of life to which each species has been exposed during
several successive generations. In the first chapter I at-
tempted to show that changed conditions act in two ways,
directly on the whole organisation or on certain parts alone,
and indirectly through the reproductive system. In all cases
there are two factors, the nature of the organism, which is
much the most important of the two, and the nature of the
conditions. The direct action of changed conditions leads
to definite or indefinite results. In the latter case the organi-
145
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146 ORIGIN OF SPEaES
sation seems to become plastic, and we have much flactu-
ating variability. In the former case the nature of the
organism is such that it yields readily, when subjected to
certain conditions, and all, or nearly all the individuals be-
come modified in the same way.
It is very difficult to decide how far changed conditions,
such as of climate, food, &c., have acted in a definite man-
ner. There is reason to believe that in the course of time
the effects have been greater than can be proved by clear
evidence. But we may safely conclude that the innumer-
able complex co-adaptations of structure, which we see
throughout nature between various organic beings, cannot
be attributed simply to such action. In the following cases
the conditions seem to have produced some slight definite
effect: £. Forbes asserts that shells at their southern limit,
and when living in shallow water, are more brightly col-
oured than those of the same species from further north or
from a greater depth; but this certainly does not always
hold good. Mr. Gould believes that birds of the same species
are more brightly coloured under a clear atmosphere, than
when living near the coast or on islands; and WoUaston
is convinced that residence near the sea affects the colours
of insects. Moquin-Tandon gives a list of plants which,
when growing near the sea-shore, have their leaves in
some degree fleshy, though not elsewhere fleshy. These
slightly varying organisms are interesting in as far as they
present characters analogous to those possessed by the spe-
cies which are confined to similar conditions.
When a variation is of the slightest use to any being, we
cannot tell how much to attribute to the accumulative action
of natural selection, and how much to the definite action of
the conditions of life. Thus, it is well known to furriers
that animals of the same species have thicker and better
fur the further north they live; but who can tell how much
of this difference may be due to the warmest-clad individu-
als having been favoured and preserved during many genera-
tions, and how much to the action of the severe climate?
for it would appear that climate has some direct action on
the hair of our domestic quadrupeds.
Instances could be given of similar varieties being pro-
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EFFECTS OF USB AND DISUSE 147
duced from the same species under external conditions of
life as different as can well be conceived; and, on the other
hand, of dissimilar varieties being produced under appar-
ently the same external conditions. Again, innumerable in-
stances are known to every naturalist, of species keeping
true, or not varying at all, although living under the most
opposite climates. Such considerations as these incline. me
to lay less weight on the direct action of the surrounding
conditions, than on a tendency to vary, due to causes of
which we are quite ignorant
In some sense the conditions of life may be said, not only
to cause variability, either directly or indirectly, but like-
wise to include natural selection, for the conditions deter-
mine whether this or that variety shall survive. But when
man is the selecting agent, we clearly see that the two ele-
ments of change are distinct; variability is in some manner
excited, but it is the will of man which accumulates the va-
riations in certain directions; and it is this latter agency
which answers to the survival of the fittest under nature.
aFFKCl'S OF THE INCREASED USB AND DISUSE OF PARTS,
AS CONTROLLED BY NATURAL SELECTION
From the facts alluded to in the first chapter, I think there
can be no doubt that use in our domestic animals has
strengthened and enlarged certain parts, and disuse dimin-
ished them; and that such modifications are inherited.
Under free nature, we have no standard of comparison, by
which to judge of the effects of long-continued use or dis-
use, for we know not the parent-forms; but many animals
possess structures which can be best explained by the effects
of disuse. As Professor Owen has remarked, there is no
greater anomaly in nature than a bird that cannot fly; yet
there are several in this state. The logger-headed duck
of South America can only flap along the surface of the
water, and has its wings in nearly the same condition as the
domestic Aylesbury-duck : it is a remarkable fact that the
young birds, according to Mr. Cunningham, can fly, while
the adults have lost this power. As the larger ground-
feeding birds seldom take flight except to escape danger.
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148 ORIGIN OF SPEaES
it is probable that the nearly wingless condition of several
birds, now inhabiting or which lately inhabited several
oceanic islands, tenanted by no beasts of prey, has been
caused by disuse. The ostrich indeed inhabits continents,
and is exposed to danger from which it cannot escape by
flight, but it can defend itself by kicking its enemies, as
efficiently as many quadrupeds. We may believe that the
progenitor of the ostrich genus had habits like those of
the bustard, and that, as the size and weight of its body
were increased during successive generations, its legs were
used more, and its wings less, until they became incapable
of flight
Kirby has remarked (and I have observed the same fact)
that the anterior tarsi, or feet, of many male dung-feeding
beetles are often broken off; he examined seventeen speci-
mens in his own collection, and not one had even a relic left.
In the Onites apelles the tarsi are so habitually lost, that
the insect has been described as not having them. In some
other genera they are present, but in a rudimentary condi-
tion. In the Ateuchtts or sacred beetle of the Egyptians,
they are totally deficient. The evidence that accidental mu-
tilations can be inherited is at present not decisive; but the
remarkable cases observed by Brown-Sequard in guinea-
pigs, of the inherited effects of operations, should make us
cautious in denying this tendency. Hence it will perhaps
be safest to look at the entire absence of the anterior tarsi
in Ateuchus, and their rudimentary condition in some other
genera, not as cases of inherited mutilations, but as due to
the effects of long-continued disuse; for as many dung-
feeding beetles are generally found with their tarsi lost,
this must happen early in life; therefore the tarsi cannot
be of much importance or be much used by these insects.
In some cases we might easily put down to disuse modifi-
cations of structure which are wholly, or mainly, due to
natural selection. Mr. Wollaston has discovered the remark-
able fact that 200 beetles, out of the 550 species (but more
are now known) inhabiting Madeira, are so far deficient
in wings that they cannot fly; and that, of the twenty-nine
endemic genera, no less than twenty-three have all their spe-
cies in this condition! Several facts, — ^namelv, that beetles
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EFFECTS OF USE AND DISUSE 148
in many parts of the world are frequently blown to sea and
perish; that the beetles in Madeira, as observed by Mr. Wol-
lastcm, lie much concealed, until the wand lulls and the sun
shines; that the proportion of wingless beetles is larger on
the exposed Desertas than in Madeira itself; and especially
the extraordinary fact, so strongly insisted on by Mr. Wol-
laston, that certain large groups of beetles, elsewhere ex-
cessively numerous, which absolutely require the use of their
wings, are here almost entirely absent ;— these several oon-
siderations make me believe that the wingless condition of
so many Madeira beetles is mainly due to the action of
natural selection, combined probably with disuse. For dur-
ing many successive generations each individual beetle which
flew least, either from its wings having been ever so little
less perfectly developed or from indolent habit, will have had
the best chance of surviving from not being blown out to
sea; and, on the other hand, those beetles which most readily
^took to flight would oftenest have been blown to sea, and
thus destroyed
The insects in Madeira which are not ground-feeders, and
which, as certain flower-feeding coleoptera and lepidoptera,
must habitually use their wings to gain their subsistence,
have, as Mr. Wollaston suspects, their wings not at all re-
duced, but even enlarged. This is quite compatible with
the action of natural selection. For when a new insect first
arrived on the island, the tendency of natural selection to
enlarge or to reduce the wings, would depend on whether a
greater number of individuals were saved by successfully
battling with the winds, or by giving up the attempt and
rarely or never flying. As with mariners ship-wrecked near
a coast, it would have been better for the good swimmers if
they had been able to swim still further, whereas it would
have been better for the bad swimmers if they had not been
able to swim at all and had stuck to the wreck.
The eyes of moles and of some burrowing rodents are
rudimentary in size, and in some cases are quite covered by
skin and fur. This state of the eyes is probably due to
gradual reduction from disuse, but aided perhaps by natural
selection. In South America, a burrowing rodent, the tuco-
tuco, or Ctenomys, is even more subterranean in its habits
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150 ORIGIN OF SPECIES
than the mole; and I was assured by a Spaniard, who had
often caught them, that they were frequently blind. One
which I kept alive was certainly in this condition, the cause,
as appeared on dissection, having been inflammation of the
nictitating membrane. As frequent inflammations c 1 the eyes
must be injurious to any animal, and as eyes are certainly
not necessary to animals having subterranean habits, a re-
duction in their size, with the adhesion of the eyelids and
growth of fur over them, might in such case be an advan-
tage; and if so, natural selection would aid the effects of
disuse.
It is well known that several animals, belonging to the
most different classes, which inhabit the caves of Carniola
and of Kentucky, are blind. In some of the crabs the foot-
stalk for the eye remains, though the eye is gone; — ^the
stand for the telescope is there, though the telescope with
its glasses has been lost. As it is difiicult to imagine that
eyes, though useless, could be in any way injurious to ani-
mals living in darkness, their loss may be attributed to dis-
use. In one of the blind animals, namely, the cave-rat
(Neotoma), two of which were captured by Professor Silli-
man at above half a mile distance from the mouth of the
cave, and therefore not in the profoundest depths, the eyes
were lustrous and of large size; and these animals, as I am
informed by Professor Silliman, after having been exposed
for about a month to a graduated light, acquired a dim per-
ception of objects.
It is difficult to imagine conditions of life more similar
than deep limestone caverns under a nearly similar climate;
so that, in accordance with the old view of the blind ani-
mals having been separately created for the American and
European caverns, very close similarity in their organisation
and affinities might have been expected. This is certainly
not the case if we look at the two whole faunas; and with
respect to the insects alone, Schiodte has remarked, "We are
accordingly prevented from considering the entire phenome-
non in any other light than something purely local, and the
similarity which is exhibited in a few forms between the
Mammoth cave (in Kentucky) and the caves in Carniola,
otherwise than as a very plain expression of that analogy
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EFFECTS OF USE AND DISUSE 151
which subsists generally between the fauna of Europe and
of North America." On my view we must suppose that
American animals, having in most cases ordinary powers of
vision, slowly migrated by successive generations from the
outer world into the deeper and deeper recesses of the Ken-
tucky caves, as did European animals into the caves of
Europe. We have some evidence of this gradation of habit;
for, as Schiodte remarks, "We accordingly look upon the
subterranean faunas as small ramifications which have pene-
trated into the earth from the geographically limited faunas
of the adjacent tracts, and which, as they extended them-
selves into darkness, have been accommodated to surround-
ing circumstances. Animals not far remote from ordinary
forms, prepare the transition from light to darkness. Next
follow those that are constructed for twilight; and, last of
all, those destined for total darkness, and whose formation is
quite peculiar." These remarks of Schiodte's, it should be
understood, apply not to the same, but to distinct species.
By the time that an animal had reached, after numberless
generations, the deepest recesses, disuse will on this view
have more or less perfectly obliterated its eyes, and natural
selection will often have effected other changes, such as an
increase in the length of the antennae or palpi, as a compen-
sation for blindness. Notwithstanding such modifications,
we might expect still to see in the cave-animals of America,
affinities to the other inhabitants of that continent, and in
those of Europe to the inhabitants of the European conti-
nent And this is the case with some of the American cave-
animals, as I hear from Professor Dana; and some of the
European cave-insects are very closely allied to those of the
surrounding country. It would be difficult to give any ra-
tional explanation of the affinities of the blind cave-animals
to the other inhabitants of the two continents on the ordi-
nary view of their independent creation. That several of
the inhabitants of the caves of the Old and New Worlds
should be closely related, we might expect from the well-
known relationship of most of their other productions. As
a blind species of Bathyscia is found in abundance on shady
rocks far from caves, the loss, of vision in the cave-species
of this one genus has probably had no relation to its dark
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152 ORIGIN OF SPEQES
habitadon; for it is natural that an insect already dqirived
of vision should readily become adapted to dark cayems.
Another blind genus (Anophthalmus) offers this remark-
able peculiarity, that the species, as Mr. Murray observes,
have not as yet been found anywhere except in caves, yet
those which inhabit.the several caves of Europe and America
are distinct; but it is possible that the progenitors of these
several species, whilst they were furnished with eyes, may
formerly have ranged over both continents, and then have
become extinct, excepting in their present seduded abodes.
Far from feeling surprise that some of the cave-animals
should be very anomalous, as Agassiz has remarked in re«
gard to the blind fish, the Amblyopsis, and as is the case
with the blind Proteus with reference to the reptiles of
Europe, I am only surprised that more wrecks of ancient
life have not been preserved, owing to the less severe com-
petition to which the scanty inhabitants of these dark abodes
will have been exposed.
ACCLIMATISATION
Habit is hereditary with plants, as in the period of flower-
ing, in the time of sleep, in the amount of rain requisite for
seeds to germinate, &c., and this leads me to say a few
words on acclimatisation. As it is extremely common for
distinct species belonging to the same genus to inhabit hot
and cold countries, if it be true that all the species of the
same genus are descended from a single parent-form, accli-
matisation must be readily effected during a long course of
descent. It is notorious that each species is adapted to the
climate of its own home: species from an arctic or even from
a temperate region cannot endure a tropical climate, or con-
versely. So again, many sucailent plants cannot endure a
damp climate. But the degree of adaptation of species to
the climates under which they live is often overrated. We
may infer this from our frequent inability to predict whether
or not an imported plant will endure our climate, and from
the number of plants and animals brought from different
countries which are here perfectly healthy. We have rea-
son to believe that species in a state of nature are closely
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AOCUlfATlSATION 153
limited in their ranges by the competition of other organic
beings quite as much as, or more than, by adaptation to par-
ticular climates. But whether or not this adaptation is in
most cases very dose, we have evidence with some few
plants, of their becoming, to a certain extent, naturally
habituated to different temperatures; that is, they become
acclimatised: thus the pines and rhododendrons, raised from
seed collected by Dr. Hooker from the same species grow-
ing at different heights on the Himalaya, were found to pos-
sess in this country different constitutional powers of re-
sisting cold. Mr. lliwaites informs me that he has observed
similar facts in Ceylon; analogous observations have been
made by Mr. H. C. Watson on European species of plants
brought from the Azores to England; and I could give other
cases. In regard to animals, several authentic instances
could be adduced of species having largely extended, within
historical times, their range from warmer to cooler lati-
tudes, and conversely; but we do not positively know that
these animals were strictly adapted to their native climate,
though in all ordinary cases we assume such to be the case ;
nor do we know that they have subsequently become specially
acclimatised to their new homes, so as to be better fitted for
them than they were at first
As we may infer that our domestic animals were originally
chosen by uncivilised man because they were useful and be-
cause they bred readily under confinement, and not because
they were subsequently found capable of far-extended trans-
portation, the common and extraordinary capacity in our
domestic animals of not only withstanding the most different
climates, but of being perfectly fertile (a far severer test)
under them, may be used as an argument that a large pro-
portion of other animals now in a state of nature could
easily be brought to bear widely different climates. We
must not, however, push the foregoing argument too far,
on account of the probable origin of some of our domestic
animals from several wild stocks; the blood, for instance,
of a tropical and arctic wolf may perhaps be mingled in our
domestic breeds. The rat and mouse cannot be considered as
domestic animals, but they have been transported by man to
many parts of the worlds and now have a far wider range
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154 ORIGIN OF SPECIES
than any other rodent; for they live under the cold dimate
of Faroe in the north and of the Falklands in the south,
and on many an island in the torrid zones. Hence adap-
tation to any special climate may be looked at as a quality
readily grafted on an innate wide flexibility of constitution,
common to most animals. On this view, the capacity of
enduring the most different climates by man himself and
by his domestic animals, and the fact of the extinct elephant
and rhinoceros having formerly endured a glacial climate,
whereas the living species are now all tropical or sub-tropical
in their habits, ought not to be looked at as anomalies, but
as examples of a very common flexibility of constitution,
brought, under peculiar circumstances, into action.
How mtich of the acclimatisation of species to any pecu-
liar dimate is due to mere habit, and how much to the
natural selection of varieties having different innate consti-
tutions, and how much to both means combined, is an ob-
scure question. That habit or custom has some influence, I
must believe, both from analogy and from the incessant ad-
vice given in agricultural works, even in the ancient Ency-
dopaedias of China, to be very cautious in transporting ani-
mals from one district to another. And as it is not likdy
that man should have succeeded in sdecting so many breeds
and sub-breeds with constitutions specially fitted for their
own districts, the result must, I think, be due to habit. On
the other hand, natural selection would inevitably tend to
preserve those individuals which were born with consti-
tutions best adapted to any country which they inhabited.
In treatises on many kinds of cultivated plants, certain
varieties are said to withstand certain dimates better than
others; this is strikingly shown in works on fruit-trees pub-
lished in the United States, in which certain varieties are
habitually recommended for the northern and others for the
southern States ; and as most of these varieties are of recent
origin, they cannot owe their constitutional differences to
habit. The case of the Jerusalem artichoke, which is never
propagated in England by seed, and of which consequently
new varieties have not been produced, has even been ad-
vanced, as proving that acclimatisation cannot be effected,
for it is now as tender as ever it was 1 The case, also, of the-
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CORRELATED VARIATION 155
kidney-bean has been often cited for a similar purpose, and
with much greater weight; but until someone will sow, dur-
ing a score of generations, his kidney-beans so early that a
very large proportion are destroyed by frost, and then collect
seed from the few survivors, with care to prevent accidental
crosses, and then again get seed from these seedlings, with
the same precautions, the experiment cannot be said to have
been tried. Nor let it be supposed that differences in the con-
stitution of seedling kidney-beans never appear, for an ac-
count has been published how much more hardy some seed-
lings are than others; and of this fact I have myself ob-
served striking instances.
On the whole, we may conclude that habit, or use and
disuse, have, in some cases, played a considerable part in the
modification of the constitution and structure; but that the
effects have often been largely combined with, and some-
times overmastered by, the natural selection of innate
variations.
CORRELATED VARIATION
I mean by this expression that the whole organisation is
80 tied together during its growth and development, that
when slight variations in any one part occur, and are accu-
mulated through natural selection, other parts become modi-
fied This is a very important subject, most imperfectly
understood, and no doubt wholly different classes of facts
may be here easily confounded together. We shall presently
see that simple inheritance often gives the false appearance
of correlation. One of the most obvious real cases is, that
variations of structure arising in the young or larvae nat-
urally tend to affect the structure of the mature animaL
The several parts of the body which are homologous, and
which, at an early embryonic period, are identical in struc-
ture, and which are necessarily exposed to similar condi-
tions, seem eminently liable to vary in a like manner : we see
this in the right and left sides of the body varying in the
same manner; in the front and hind legs, and even in the
jaws and limbs, varying together, for the lower jaw is be-
lieved by some anatomists to be homologous with the limbs.
These tendencies^ I do not doubt, may be mastered more or
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156 ORIGIN OP SPECIBS
less completely by natural selection; thus a family of stags
once existed with an antler only on one side; and if this
had been of any great use to the breed, it might probably
have been rendered permanent by selection.
Homologous parts, as has been remarked by some authors,
tend to cohere; this is often seen in monstrous plants: and
nothing is more common than the union of homologous
parts in normal structures, as in the union of the petals into
a tube. Hard parts seem to affect the form of adjoining
soft parts; it is believed by some authors that with birds
the diversity in the shape of the pelvis causes the remark-
able diversity in the shape of their kidneys. Others believe
that the shape of the pelvis in the human mother influences
by pressure the shape of the head of the child. In snakes,
according to Schlegel, the form of the body and the manner
of swallowing determine the position and form of several
of the most important viscera.
The nature of the bond is frequently quite obscure. M.
Is. Geoffroy St. Hilaire has forcibly remarked, that certain
malconformations frequently, and that others rarely, co-
exist, without our being able td assign any reason. What
can be more singular than the relation in cats between com-
plete whiteness and blue eyes with deafness, or between the
tortoise-shell colour and the female sex; or in pigeons be-
tween their feathered feet and skin betwixt the outer toes,
or between the presence of more or less down on the young
pigeon when, first hatched, with the future colour of its
plumage; or, again, the relation between the hair and teeth
in the naked Turkish dog, though here no doubt homology
comes into play? With respect to this latter case of corre-
lation, I think it can hardly be accidental, that the two orders
of mammals which are most abnormal in their dermal cov-
erings, viz., Cetacea (whales) and Edentata (armadilloes,
scaly ant-eaters, &c.), are likewise on the whole the most
abnormal in their teeth ; but there are so many exceptions to
this rule, as Mr. Mivart has remarked, that it has little
value.
I know of no case better adapted to show the importance
of the laws of correlation and variation, independently of
utility and therefore of natural selection, than that of the
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CORRELATED VARIATION 157
difference between the outer and inner flowers in some Com-
positous and Umbelliferous plants. Every one is familiar
with the difference between the ray and central florets of,
for instance, the daisy, and this difference is often accom-
panied with the partial or complete abortion of the repro-
ductive organs. But in some of these plants, the seeds also
differ in shape and sculpture. These differences have some-
times been attributed to the pressure of the involucra on
the florets, or to their mutual pressure, and the shape of the
seeds in the ray-florets of some Composite countenances this
idea; but with the Umbelli ferae, it is by no means, as Dr.
Hooker informs me, the species with the densest heads which
most frequently differ in their inner and outer flowers. It
might have been thought that the development of the ray-
petals by drawing nourishment from the reproductive
organs causes their abortion; but this can hardly be the sole
cause, for in some Compositae the seeds of the outer and
inner florets differ, without any difference in the corolla.
Possibly these several differences may be connected with
the different flow of nutriment towards the central and
external flowers: we know, at least, that with irregular
flowers, those nearest to the axis are most subject to peloria,
that is to become abnormally symmetrical. I may add, as
an instance of this fact, and as a striking case of correla-
tion, that in many pelargoniums, the two upper petals in the
central flower of the truss often lose their patches of darker
colour; and when this occurs, the adherent nectary is quite
aborted; the central flower thus becoming peloric or regular.
When the colour is absent from only one of the two upper
petals, the nectary is not quite aborted but is much shortened.
With respect to the development of the corolla, Sprengel's
Idea that the ray-florets serve to attract insects, whose
agency is highly advantageous or necessary for the fertili-
sation of these plants, is highly probable; and if so, natural
selection may have come into play. But with respect to the
seeds, it seems impossible that their differences in shape,
which are not always correlated with any difference in the
corolla, can be in any way beneficial : yet in the Umbelliferae
these differences are of such apparent importance— the seeds
being sometimes orthospermous in the exterior flowers and
J — HCXI
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158 ORIGIN OF SPECIES
coelospermous in the central flowers, — that the elder De
Candolle founded his main divisions in the order on such
characters. Hence modifications of structure, viewed by
systematists as of high value, may be wholly due to the laws
of variation and correlation, without being, as far as we
can judge, of the slightest service to the species.
We may often falsely attribute to correlated variation
structures which are common to whole groups of species,
and which in truth are simply due to inheritance; for an
ancient progenitor may have acquired through natural selec-
tion some one modification in structure, and, after thousands
of generations, some other and independent modification;
and these two modifications, having been transmitted to a
whole group of descendants with diverse habits, would nat-
urally be thought to be in some necessary manner correlated.
Some other correlations are apparently due to the manner
in which natural selection can alone act For instance, Alph.
de Candolle has remarked that winged seeds are never found
in fruits which do not open; I should explain this rule by
the impossibility of seeds gradually becoming winged through
natural selection, unless the capsules were open for in this
case alone could the seeds, which were a little better adapted
to be wafted by the wind, gain an advantage over others
less well fitted for wide dispersal.
COMPENSATION AND ECONOMY OF GROWTH
The elder Geoffroy and Goethe propounded, at about the
same time, their law of compensation or balancement of
growth; or, as Goethe expressed it, "in order to spend on
one side, nature is forced to economise on the other side."
I think this holds true to a certain extent with our domestic
productions: if nourishment flows to one part or organ in
excess, it rarely flows, at least in excess, to another part;
thus it is difficult to get a cow to give much milk and to fat-
ten readily. The same varieties of the cabbage do not yield
abundant and nutritious foliage and a copious supply of oil-
bearing seeds. When the seeds in our fruits become atro-
phied, the fruit itself gains largely in size and quality. In
our poultry, a large tuft of feathers on the head is gener-
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COBIPENSATION AND ECONOMY OF GROWTH 159
ally accompanied by a diminished comb and a large beard
by diminished wattles. With species in a state of nature it
can hardly be maintained that the law is of universal appli-
cation; but many good observers, more especially botanists,
believe in its truth. I will not, however, here give any in-
stances, for I see hardly any way of distinguishing between
the effects, on the one hand, of a part being largely devel-
oped through natural selection and another and adjoining
part being reduced by this same process or by disuse, and,
on the other hand, the actual withdrawal of nutriment from
one part owing to the excess of growth in another and ad-
joining part.
I suspect, also, that some of the cases of compensation
which have been advanced, and likewise some other facts,
may be merged under a more general principle, namely, that
natural selection is continually trying to economise every
part of the organisation. If under changed conditions of
life a structure, before useful, becomes less useful, its dim-
inution will be favoured, for it will profit the individual not
to have its nutriment wasted in building up an useless struc-
ture. I can thus only imderstand a fact with which I was
much struck when examining cirripedes, and of which many
analogous instances could be given: namely, that when a
cirripede is parasitic within another cirripede and is thus
protected, it loses more or less completely its own shell or
carapace. This is the case with the male Ibla, and in a truly
extraordinary manner with the Proteolepas: for the cara-
pace in all other cirripedes consists of the three highly im-
portant anterior segments of the head enormously developed,
and furnished with great nerves and muscles; but in the
parasitic and protected Proteolepas, the whole anterior part
of the head is reduced to the merest rudiment attached to
the bases of the prehensile antennse. Now the saving of a
large and complex structure, when rendered superfluous,
would be a decided advantage to each successive individual
of the species; for in the struggle for life to which every
animal is exposed, each would have a better chance of sup-
porting itself, by less nutriment being wasted.
Thus, as I believe, natural selection will tend in the long
run to reduce any part of the organisation, as soon as it be-
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160 ORIGIN OF SPEaES
comes, through changed habits, superfluous, without by any
means causing some other part to be largely developed in a
corresponding degree. And, conversely, that natural selec-
tion may perfectly well succeed in largely developing an
organ without requiring as a necessary compensation the
reduction of some adjoining part
MULTIPLE, RUDIMENTARY, AND LOWLY ORGANISED STRUC-
TURES ARE VARIABLE
It seems to be a rule, as remarked by Is. Geoffroy St.
Hilaire, both with varieties and species, that when any part
or organ is repeated many times in the same individual (as
the vertebrae in snakes, and the stamens in polyandrous flow-
ers) the number is variable; whereas the same part or organ,
when it occurs in lesser numbers, is constant The same
author as well as some botanists have further remarked that
multiple parts are extremely liable to vary in structure. As
"vegetative repetition," to use Prof. Owen's expression, is a
sign of low organisation, the foregoing statements accord
with the common opinion of naturalists, that beings which
stand low in the scale of nature are more variable than those
which are higher. I presume that lowness here means that
the several parts of the organisation have been but little
specialised for particular functions; and as long as the same
part has to perform diversified work, we can perhaps see
why it should remain variable, that is, why natural selection
should not have preserved or rejected each little deviation
of form so carefully as when the part has to serve for some
one special purpose. In the same way that a knife which
has to cut all sorts of things may be of almost any shape;
whilst a tool for some particular purpose must be of some
particular shape. Natural selection, it should never be for-
gotten, can act solely through and for the advantage of each
being.
Rudimentary parts, as it is generally admitted, are apt to be
highly variable. We shall have to recur to this subject; and
I will here only add that their variability seems to result from
their uselessness, and consequently from natural selection
having had no power to check deviations in their structure.
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STRUCTURES VARIABLE 161
A PABT DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY
DEGREE OR MANNER, IN COMPARISON WITH THE
SAME PART IN ALLIED SPECIES, TENDS TO
BE HIGHLY VARIABLE
Several years ago I was much struck by a remark, to the
above effect, made by Mr. Waterhouse. Professor Owen,
also, seems to have come to a nearly similar conclusion. It
is hopeless to attempt to convince any one of the truth of
the above proposition without giving the long array of facts
which I have collected, and which cannot possibly be here
introduced. I can only state my conviction that it is a rule
of high generality. I am aware of several causes of error,
but I hope that I have made due allowance for them.
It should be understood that the rule by no means applies to
any part, however unusually developed, unless it be unusu-
ally developed in one species or in a few species in compari-
son with the same part in many closely allied species. Thus,
the wing of a bat is a most abnormal structure in the class
of mammals, but the rule would not apply here, because the
whole group of bats possesses wings; it would apply only if
some one species had wings developed in a remarkable man-
ner in comparison with the other species of the same genus.
The rule applies very strongly in the case of secondary sex-
ual characters, when displayed in any unusual manner. The
term, secondary sexual characters, used by Hunter, relates
to characters which are attached to one sex, but are not
directly connected with the act of reproduction. The rule
applies to males and females ; but more rarely to the females,
as they seldom offer remarkable secondary sexual charac-
ters. The rule being so plainly applicable in the case of sec-
ondary sexual characters, may be due to the great variability
of these characters, whether or not displayed in any unusual
manner — of which fact I think there can be little doubt. But
that our rule is not confined to secondary sexual characters
is clearly shown in the case of hermaphrodite cirripedes; I
particularly attended to Mr. Waterhouse's remark, whilst
investigating this Order, and I am fully convinced that the
rule almost always holds good. I shall, in a future work,
give a list of all the more remarkable cases; I will here give
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162 ORIGIN OF SPEaES
only one, as it illustrates the rule in its largest application.
The opercular valves of sessile cirripedes (rock barnacles)
are, in every sense of the word, very important structures,
and they differ extremely little even in distinct genera; but
in the several species of one genus, Pyrgoma, these valves
present a marvellous amount of diversification; the homolo^
gous valves in the different species being sometimes wholly
unlike in shape; and the amount of variation in the indn
viduals of the same species is so great, that it is no exag«>
geration to state that the varieties of the same species differ
more from each other in the characters derived from these
important organs, than do the species belonging to other
distinct genera.
As with birds the individuals of the same species, inhabit-
ing the same country, vary extremely little, I have particu-
larly attended to them; and the rule certainly seems to hold
good in this class. I cannot make out that it applies to plants,
and this would have seriously shaken my belief in its truth,
had not the great variability in plants made it particularly
difficult to compare their relative degrees of variability.
When we see any part or organ developed in a remarkable
degree or manner in a species, the fair presumption is that
it is of high importance to that species: nevertheless it is in
this case eminently liable to variation. Why should this be
so? On the view that each species has been independently
created, with all its parts as we now see them, I can see no
explanation. But on the view that groups of species are de-
scended from some other species, and have been modified
through natural selection, I think we can obtain some light.
First let me make some preliminary remarks. If, in our
domestic animals, any part or the whole animal be neglected,
and no selection be applied, that part (for instance, the comb
in the Dorking fowl) or the whole breed will cease to have
a uniform character : and the breed may be said to be degen-
erating. In rudimentary organs, and in those which have
been but little specialised for any particular purpose, and
perhaps in polymorphic groups, we see a nearly parallel case ;
for in such cases natural selection either has not or cannot
have come into full play, and thus the organisation is left in
a fluctuating condition. But what here more particularly
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STRUCTURES VARIABLE 163
concerns us is, that those points in our domestic animals,
which at the present time are undergoing rapid change by
continued selection, are also eminently liable to variation.
Look at the individuals of the same breed of the pigeon, and
see what a prodigious amount of difference there is in the
beaks of tumblers, in the beaks and wattle of carriers, in the
carriage and tail of fantails, &c., these being the points now
mainly attended to by English fanciers. Even in the same
sub-breed, as in that of the short-faced tumbler, it is notori-
ously difficult to breed nearly perfect birds, many departing
widely from the standard. There may truly be said to be a
constant struggle going on between, on the one hand, the
tendency to reversion to a less perfect state, as well as an
innate tendency to new variations, and, on the other hand,
the power of steady selection to keep the breed true. In the
long run selection gains the day, and we do not expect to
fail so completely as to breed a bird as coarse as a common
tumbler pigeon from a good short- faced strain. But as long as
selection is rapidly going on, much variability in the parts
undergoing modification may always be expected.
Now let us turn to nature. When a part has been devel-
oped in an extraordinary manner in any one species, com-
pared with the other species of the same genus, we may con-
clude that this part has undergone an extraordinary amount
of modification since the period when the several species
branched off from the common progenitor of the genus. This
period will seldom be remote in any extreme degree, as species
rarely endure for more than one geological period. An extra-
ordinary* amount of modification implies an unusually large
and long-continued amount of variability, which has con-
tinually been accumulated by natural selection for the benefit
of the species. But as the variability of the extraordinarily
developed part or organ has been so great and long-continued
within a period not excessively remote, we might, as a gen-
eral rule, still expect to find more variability in such parts
than in other parts of the organisation which have remained
for a much longer period nearly constant. And this, I am
convinced, is the case. That the struggle between natural
selection on the one hand, and the tendency to reversion and
variability on the other hand, will in the course of time
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164 ORIGIN OF SPECIES
cease; and that the most abnormally developed organs may
be made constant, I see no reason to doubt Hence, when
an organ, however abnormal it may be, has been transmitted
in approximately the same condition to many modified de-
scendants, as in the case of the wing of the bat, it must have
existed, according to our theory, for an immense period in
nearly th^ same state; and thus it has come not to be more
variable than any other structure. It is only in those cases
in which the modification has been comparatively recent and
extraordinarily great that we ought to find the generative
variabiUty, as it may be called, still present in a high degree.
For in this case the variability will seldom as yet have been
fixed by the continued selection of the individuals varying
in the required manner and degree, and by the continued
rejection of those tending to revert to a former and less*
modified condition.
€
SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC
CHARACTERS
The principle discussed under the last heading may be
applied to our present subject It is notorious that specific
characters are more variable than generic. To explain by a
simple example what is meant: if in a large genus of plants
some species had blue flowers and some had red, the colour
would be only a specific character, and no one would be sur-
prised at one of the blue species varying into red, or con-
versely; but if all the species had blue flowers, the colour
would become a generic character, and its variation would
be a more unusual circumstance. I have chosen this exam-
ple because the explanation which most naturalists would
advance is not here applicable, namely, that specific charac-
ters are more variable than generic, because they are taken
from parts of less physiological importance than those com-
monly used for classing genera. I believe this explanation
is partly, yet only indirectly, true; I shall, however, have to
return to this point in the chapter on Gassification. It would
be almost superfluous to adduce evidence in support of the
statement, that ordinary specific characters are more variable
than generic; but with respect to important characters, I
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SPECIFIC CHARACTERS HIGHLY VARIABLE 16S
have repeatedly noticed in works on natural history, that
when an author remarks with surprise that some important
organ or part, which is generally very constant throughout
a large group of species, dijfers considerably in closely
allied species, it is often variable in the individuals of the
same species. And this fact shows that a character, which
is generally of generic value, when it sinks in value and
becomes only of specific value, often becomes variable,
though its physiological importance may remain the same.
Something of the same kind applies to monstrosities: at
least Is. Geoffroy St. Hilaire apparently entertains no doubt,
that the more an organ normally differs in the different spe-
cies of the same group, the more subject it is to anomalies
in the individuals.
On the ordinary view of each species having been inde-
pendently created, why should that part of the structure,
which differs from the same part in other independently
created species of the same genus, be more variable than
those parts which are closely alike in the several species?
I do not see that any explanation can be given. But on the
view that species are only strongly marked and fixed varie-
ties, we might expect often to find them still continuing to
vary in those parts of their structure which have varied
within a moderately recent period, and which have thus
come to differ. Or to state the case in another manner: —
the points in which all the species of a genus resemble each
other, and in which they differ from allied genera, are called
generic characters; and these characters may be attributed
to inheritance from a common progenitor, for it can rarely
have happened that natural selection will have modified sev-
eral distinct species, fitted to more or less widely different
habits, in exactly the same manner: and as these so-called
generic characters have been inherited from before the
period when the several species first branched off from their
common progenitor, and subsequently have not varied or
come to differ in any degree, or only in a slight degree, it is
not probable that they should vary at the present day. On
the other hand, the points in which species differ from other
species of the same genus are called specific characters; and
as these specific characters have varied and come to differ
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166 ORIGIN OF SPEQES
since the period when the species branched off from a com-
mon progenitor, it is probable that they should still often be
in some degree variable, — ^at least more variable than those
parts of the organisation which have for a very long period
remained constant.
Secondary Sexual Characters Variable. — ^I think it will be
admitted by naturalists, without my entering on details, that
secondary sexual characters are highly variable. It will also
be admitted that species of the same group differ from each
other more widely in their secondary sexual characters, than
in other parts of their organisation: compare, for instance,
the amount of difference between the males of gallinaceous
birds, in which secondary sexual characters are strongly dis-
played, with the amount of difference between the females.
The cause of the original variability of these characters is
not manifest; but we can see why they should not have been
rendered as constant and uniform as others, for they are
accumulated by sexual selection, which is less rigid in its ac-
tion than ordinary selection, as it does not entail death, but
only gives fewer offspring to the less favoured males. What-
ever the cause may be of the variability of secondary sexual
characters, as they are highly variable, sexual selection will
have had a wide scope for action, and may thus have suc-
ceeded in giving to the species of the same group a greater
amount of difference in these than in other respects.
It is a remarkable fact, that the secondary differences be-
tween the two sexes of the same species are generally dis-
played in the very same parts of the organisation in which
the species of the same genus' differ from each other. Of
this fact I will give in illustration the two first instances
which happen to stand on my list; and as the differences in
these cases are of a very unusual nature, the relation can
hardly be accidental. The same number of joints in the tarsi
is a character common to very large groups of beetles, but
in the Engidae, as Westwood has remarked, the number varies
greatly ; and the number likewise differs in the two sexes of
the same species. Again in the fossorial hjrmenoptera, the
neuration of the wings is a character of the highest impor-
tance, because common to large groups ; but in certain genera
the neuration differs in the different species, and likewise in
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SPECIFIC CHARACTERS HIGHLY VARIABLE 167
the two sexes of the same species. Sir J. Lubbock has re-
cently remarked, that several minute crustaceans offer ex-
cellent illustrations of this law. 'In Pontella, for instance,
the sexual characters are afforded mainly by the anterior
antennae and by the fifth pair of legs: the specific differences
also are principally given by these organs." This relation
has a clear meaning on my view: I look at all the species
of the same genus as having as certainly descended from
a common progenitor, as have the two sexes of any one spe-
cies. Consequently, whatever part of the structure of the
common progenitor, or of its early descendants, became vari-
ble, variations of this part would, it is highly probable, be
taken advantage of by natural and sexual selection, in order
to fit the several species to their several places in the econ-
omy of nature, and likewise to fit the two sexes of the same
species to each other, or to fit the males to struggle with
other males for the possession of the females.
Finally, then, I conclude that the greater variability of
specific characters, or those which distinguish species from
species, than of generic characters, or those which are pos-
sessed by all the species; — ^that the frequent extreme varia-
bility of any part which is developed in a species in an extra-
ordinary manner in comparison with the same part in its
congeners; and the slight degree of variability in a part,
however extraordinarily it may be developed, if it be com-
mon to a whole group of species; — ^that the great variability
of secondary sexual characters, and their great difference in
closely allied species; — ^that secondary sexual and ordinary
specific differences are generally displayed in the same parts
of the organisation, — ^are all principles closely connected to-
gether. All being mainly due to the species of the same
group being the descendants of a common progenitor, from
whom they have inherited much in common, — ^to parts which
have recently and largely varied being more likely still to go
on varying than parts which have long been inherited and
have not varied — ^to natural selection having more or less
completely, according to the lapse of time, overmastered the
tendency to reversion and to further variability, — ^to sexual
selection being less rigid than ordinary selection, — and to
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168 ORIGIN OF SPECIES
variations in the same parts having been accumulated by
natural and sexual selection, and having been thus adapted
for secondary sexual, and for ordinary purposes.
Distinct Species present analogous Variations, so that a
Variety of one Species often assumes a Character proper to
an allied Species, or reverts to some of the Characters of an
early Progenitor, — ^These propositions will be most readily
understood by looking to our domestic races. The most dis-
tinct breeds of the pigeon, in countries widely apart, present
sub-varieties with reversed feathers on the head, and with
feathers on the feet, — characters not possessed by the abo-
riginal rock-pigeon; these then are analogous variations in
two or more distinct races. The frequent presence of four-
teen or even sixteen tail-feathers in the pouter may be con-
sidered as a variation representing the normal structure of
another race, the fantail. I presume that no one will doubt
that all such analogous variations are due to the several
races of the pigeon having inherited from a common parent
the same constitution and tendency to variation, when acted
on by similar unknown influences. In the vegetable king-
dom we have a case of analogous variation, in the enlarged
stems, or as commonly called roots, of the Swedish turnip
and Ruta baga, plants which several botanists rank as varie-
ties produced by cultivation from a common parent: if this
be not so, the case will then be one of analogous variation
in two so-called distinct species ; and to these a third may be
added, namely, the common turnip. According to the ordi-
nary view of each species having been independently created,
we should have to attribute this similarity in the enlarged
stems of these three plants, not to the vera causa of com-
munity of descent, and a consequent tendency to vary in a
like manner, but to three separated yet closely related acts
of creation. Many similar cases of analogous variation have
been observed by Naudin in the great gourd-family, and by
various authors in our cereals. Similar cases occurring with
insects under natural conditions have lately been discussed
with much ability by Mr. Walsh, who has grouped them
under his law of Equable Variability.
With pigeons, however, we have another case, namely,
the occasional appearance in all the breeds, of slaty-blue
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SPEaFIC CHARACTERS HIGHLY VARIABLE 169
birds with two black bars on the wings, white loins, a bar
'at the end of the tail, with the outer feathers externally
edged near their basis with white. As all these marks are
characteristic of the parent rock-pigeon, I presume that no
one will doubt that this is a case of reversion, and not of a
new yet analogous variation, appearing in the several breeds.
We may, I think, confidently come to this conclusion, be-
cause, as we have seen, these coloured marks are eminently
liable to appear in the crossed offspring of two distinct and
differently coloured breeds ; and in this case there is nothing
in the external conditions of life to cause the reappearance
of the slaty-blue, with the several marks, beyond the influ-
ence of the mere act of crossing on the laws of inheritance.
No doubt it is a very surprising fact that characters should
reappear after having been lost for many, probably for hun-
dreds of generations. But when a breed has been crossed
only once by some ofher breed, the offspring occasionally
show for many generations a tendency to revert in character
to the foreign breed — some say, for a dozen or even a score
of generations. After twelve generations, the proportion of
blood, to use a common expression, from one ancestor, is
only I in 2048; and yet, as we see, it is generally believed
that a tendency to reversion is retained by this remnant of
foreign blood. In a breed which has not been crossed but
in which both parents have lost some character which their
progenitor possessed, the tendency, whether strong or weak,
to reproduce the lost character might, as was formerly re-
marked, for all that we can see to the contrary, be trans-
mitted for almost any number of generations. When a
character which has been lost in a breed, reappears after a
great number of generations, the most probable hypothesis
is, not that one individual suddenly takes after an ancestor
removed by some hundred generations, but that in each suc-
cessive generation the character in question has been ly:ng
latent, and at last, under unknown favourable conditions, is
developed. With the barb-pigeon, for instance, which very
rarely produces a blue bird, it is probable that there is a
latent tendency in each generation to produce blue plumage.
The abstract improbability of such a tendency being trans-
mitted through a vast number of generations, is not greater
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170 ORIGIN OF SPEQES
than that of 'quite useless or rudimentary organs being simi-
larly transmitted. A mere tendency to produce a rudiment
is indeed sometimes thus inherited.
As all the species of the same genus are supposed to be
descended from a common progenitor, it might be expected
that they would occasionally vary in an analogous manner;
so that the varieties of two or more species would resemble
each other, or that a variety of one species would resemble
in certain characters another and distinct species, — ^this 6ther
species being, according to our view, only a well-marked and
permanent variety. But characters exclusively due to analo-
gous variation would probably be of an unimportant nature,
for the preservation of all functionally important characters
will have been determined through naturd selection, in ac-
cordance with the different habits of the species. It might
further be expected that the species of the same genus would
occasionally exhibit reversions to long lost characters. As,
however, we do not know the common ancestor of any
natural group, we cannot distinguish between revisionary
and analogous characters. If, for instance, we did not know
that the parent rock-pigeon was not feather-footed or turn-
crowned, we could not have told, whether such characters in
our domestic breeds were reversions or only analogous varia-
tions ; but we might have inferred that the blue colour was a
case of reversion from the number of the markings, which
are correlated with this tint, and which would not probably
have all appeared together from simple variation. More
especially we might have inferred this, from the blue colour
and the several marks so often appearing when differently
coloured breeds are crossed. Hence, although under nature it
must generally be left doubtful, what cases are reversions to
formerly existing characters, and what are new but analo-
gous variations, yet we ought, on our theory, sometimes to
find the varying offspring of a species assuming characters
which are already present in other members of the same
group. And this undoubtedly is the case.
The difficulty in distinguishing variable species is largely
due to the varieties mocking, as it were, other species of the
same genus. A considerable catalogue, also, could be given
of forms intermediate between two other forms, which them-
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SPBaFIC CHARACTERS HIGHLY VARIABLE 171
selves can only doubtfully be ranked as species; and this
shows, unless all these closely allied forms be considered as
independently created species, that they have in varying as-
sumed some of the characters of the others. But the best
evidence of analogous variations is afforded by parts or
organs which are generally constant in character, but which
occasionally vary so as to resemble, in some degree, the
same part or organ in all species. I have collected a long
list of such cases; but here, as before, I lie under the great
disadvantage of not being able to give them. I can only re-
peat that such cases certainly occur, and seem to me very re-
markable.
I will, however, give one curious and complex case, not
indeed as affecting any important character, but from occur-
ring in several species of the same genus, partly under
domestication and partly under nature. It is a case almost
certainly of reversion. The ass sometimes has very distinct
transverse bars on its legs, like those on the legs of the
zebra : it has been asserted that these are plainest in the foal,
and, from inquiries which I have made, I believe this to be
true. The stripe on the shoulder is sometimes double, and is
very variable in length and outline. A white ass, but not an
albino, has been described without either spinal or shoulder
stripe : and these stripes are sometimes very obscure, or actu-
ally quite lost, in dark-coloured asses. The koulan of Pallas
is said to have been seen with a double shoulder-stripe. Mr.
BIyth has seen a specimen of the hemionus with a distinct
shoulder-stripe, though it properly has none ; and I have been
informed by Colonel Poole that the foals of this species are
generally striped on the legs, and faintly on the shoulder.
The quagga, though so plainly barred like a zebra over the
body, is without bars on the legs; but Dr. Gray has figured
one specimen with very distinct zebra-like bars on the hocks.
With respect to the horse, I have collected cases in Eng-
land of the spinal stripe in horses of the most distinct breeds,
and of all colours: transverse bars on the legs are not rare
in duns, mouse-duns, and in one instance in a chestnut; a
faint shoulder-stripe may sometimes be seen in duns, and I
have seen a trace in a bay horse. My son made a careful
examination and sketch for me of a dun Belgian cart-horse
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172 ORIGIN OP SPECIES
with a double stripe on each shoulder and with leg-stripes;
I have myself seen a dun Devonshire pony, and a small dim
Welsh pony has been carefully described to me, both with
three parallel stripes on each shoulder.
In the north-west part of India the Kattywar breed of
horses is so generally striped, that, as I hear from Colonel
Poole, who examined this breed for the Indian Government,
a horse without stripes is not considered as purely-bred.
The spine is always striped; the legs are generally barred;
and the shoulder-stripe, which is sometimes double and some-
times treble, is common ; the side of the face, moreover, is
sometimes striped. The stripes are often plainest in the foal ;
and sometimes quite disappear in old horses. Colonel Poole
has seen both gray and bay Kattywar horses striped when
first foaled. I have also reason to suspect, from information
given me by Mr. W. W. Edwards, that with the English
race-horse the spinal stripe is much commoner in the foal
than in the full-grown animal. I have myself recently bred
a foal from a bay mare (offspring of a Turkoman horse and
a Flemish mare) by a bay English race-horse; this foal when
a week old was marked on its hinder quarters and on its
forehead with numerous, very narrow, dark, zebra-like bars,
and its legs were feebly striped: all the stripes soon disap-
peared completely. Without here entering on further details,
I may state that I have collected cases of leg and shoulder
stripes in horses of very different breeds in various countries
from Britain to Eastern China; and from Norway in the
north to the Malay Archipelago in the south. In all parts of
the world these stripes occur far oftenest in duns and mouse-
duns; by the term dun a large range of colour is included,
from one between brown and black to a dose approach to
cream-colour.
I am aware that Colonel Hamilton Smith, who has written
on this subject, believes that the several breeds of the horse
are descended from several aboriginal species — one of which,
the dun, was striped; and that the above-described appear-
ances are all due to ancient crosses with the dun stock. But
this view may be safely rejected; for it is highly improbable
that the heavy Belgian cart-horse, Welsh ponies, Norwegian
cobs, the lanky Kattywar race, &c., inhabiting the most dis-
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SPECIFIC CHARACTERS fflGHLY VARIABLE ]73
tant parts of the world, should all have been crossed with
one supposed aboriginal stock.
Now let us turn to the effects of crossing the several spe^
cies of the horse-genus. RoUin asserts, that the common
mule from the ass and horse is particularly apt to have bars
on its legs; according to Mr. Gosse, in certain parts of the
United States about nine out of ten mules have striped legs.
I once saw a mule with its legs so much striped that any one
might have thought that it was a hybrid-zebra; and Mr.
W. C. Martin, in his excellent treatise on the horse, has
given a. figure of a similar mule. In four coloured drawings,
which I have seen, of hybrids between the ass and zebra, the
legs were much more plainly barred than the rest of the
body ; and in one of them there was a double shoulder-stripe.
In Lord Morton's famous hybrid, from a chestnut mare and
male quagga, the hybrid, and even the pure offspring subse^
quently produced from the same mare by a black Arabian
sire, were much more plainly barred across the legs than is
even the pure quagga. Las^y, and this is another most re-
markable case, a hybrid has been figured by Dr. Gray (and
he informs me that he knows of a second case) from the ass
and the hemionus; and this hybrid, though .the ass only occa-
sionally has stripes on his legs and the hemionus has none
and has not even a shoulder-stripe, nevertheless had all four
legs barred, and had three short shoulder-stripes, like those
on the dun Devonshire and Welsh ponies, and even had some
zebra-like stripes on the sides of its face. With respect to
this last fact, I was so convinced that not even a stripe of
colour appears from what is commonly called chance, that I
was led solely from the occurrence of the face-stripes on
this hybrid from the ass and hemionus to ask Colonel Poole
whether such face-stripes ever occurred in the eminently
striped Kattywar breed of horses, and was, as we have seen,
answered in the affirmative.
What now are we to say to these several facts? We see
several distinct species of the horse-genus becoming, by
simple variation, striped on the legs like a zebra, or striped
on the shoulders like an ass. In the horse we see this ten-
dency strong whenever a dun tint appears — sl tint which ap-
proaches to that of the general colouring of the other species
K — ^HC XI
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174 ORIGIN OF SPECIES
of the genus. The appearance of the stripes is not accom-
panied by any change of form or by any other new character.
We see this tendency to become striped most strongly dis-
played in hybrids from between several of the most distinct
species. Now observe the case of the several breeds of
pigeons: they are descended from a pigeon (including two or
three sub-species or geographical races) of a bluish colour,
with certain bars and other marks; and when any breed
assumes by simple variation a bluish tint, these bars and
other marks invariably reappear; but without any other
change of form or character. When the oldest and truest
breeds of various colours are crossed, we see a strong ten-
dency for the blue tint and bars and marks to reappear in
the mongrels. I have stated that the most probable hypothe-
sis to account for the reappearance of very ancient charac-
ters, is — ^that there is a tendency in the young of each suc-
cessive generation to produce the long-lost character, and
that this tendency, from unknown causes, sometimes prevails.
And we have just seen that in several species of the horse-
genus the stripes are either plainer or appear more com-
monly in the young than in the old. Call the breeds of
pigeons, some of which have bred true for centuries, species;
and how exactly parallel is the case with that of the species
of the horse-genus! For myself, I venture confidently to
look back thousands on thousands of generations, and I see
an animal striped like a zebra, but perhaps otherwise very
differently constructed, the common parents of our domestic
horse (whether or not it be descended from one or more
wild stocks), of the ass, the hemionus, quagga, and zebra.
He who believes that each equine species was indepen-
dently created, will, I presume, assert that each species has
been created with a tendency to vary, both under nature and
under domestication, in this particular manner, so as often
to become striped like the other species of the genus; and
that each has been created with a strong tendency, when
crossed with species inhabiting distant quarters of the world,
to produce hybrids resembling in their stripes, not their own
parents, but other species of the genus. To admit this view
is, as it seems to me, to reject a real for an unreal, or at
least for an unknown, cause. It makes the works of God a
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SPECIFIC CHARACTERS HIGHLY VARIABLE 175
mere mockery and deception ; I would almost as soon believe
with the old and ignorant cosmogonists, that fossil shells had
never lived, but had been created in stone so as to mock the
shells living on the sea-shore.
Summary, — Our ignorance of the laws of variation is pro-
found. Not in one case out of a hundred can we pretend to
assign any reason why this or that part has varied. But
whenever we have the means of instituting a comparison, the
same laws appear to have acted in producing the lesser differ-
ences between varieties of the same species, and the greater
differences between species of the same genus. Changed
conditions generally induce mere fluctuating variability, but
sometimes they cause direct and definite effects; and these
may become strongly marked in the course of time, though
we have not sufficient evidence on this head. Habit in pro-
ducing constitutional peculiarities and use in strengthening
and disuse in weakening and diminishing organs, appear in
many cases to have been potent in their effects. Homologous
parts tend to vary in the same manner, and homologous parts
tend to cohere. Modifications in hard parts and in external
parts sometimes affect softer and internal parts. When one
part is largely developed, perhaps it tends to draw nourish-
ment from the adjoining parts; and every part of the struc-
ture which can be saved without detriment will be saved.
Changes of structure at an early age may affect parts subse-
quently developed; and many cases of correlated variation,
the nature of which we are unable to understand, undoubt-
edly occur. Multiple parts are variable in number and in
structure, perhaps arising from such parts not having been
closely specialised for any particular function, so that their
modifications have not been closely checked by natural selec-
tion. It follows probably from this same cause, that organic
beings low in the scale are more variable than those stand-
ing higher in the scale, and which have their whole organi-
sation more specialised. Rudimentary organs, from being
useless, are not regulated by natural selection, and hence are
variable. Specific characters — ^that is, the characters which
have come to differ since the several species of the same
genus branched off from a conmion parent — are more vari-
able than generic characters, or those which have long been
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176 ORIGIN OF SPEQES
inherited, and have not differed within this same period. In
these remarks we have referred to special parts or organs
being still variable, because they have recently varied and
thus come to differ; but we have also seen in the second
chapter that the same principle applies to the whole indi-
vidual; for in a district where many species of a genus are
foundr— that is, where there has been much former variation
and differentiation, or where the manufactory of new specific
forms has been actively at work — ^in that district and amongst
these species, we now find, on an average, most varieties.
SeccMidary sexual characters are highly variable, and such
characters differ much in the species of the same group.
Variability in the same parts of the organisation has gener-
ally been taken advantage of in giving secondary sexual
differences to the two sexes of the same species, and specific
differences to the several species of the same genus. Any
part or organ developed to an extraordinary size or in an
extraordinary manner, in comparison with the same part or
organ in the allied species, must have gone through an
extraordinary amount of modification since the genus arose;
and thus we can understand why it should often still be vari-
able in a much higher degree than other parts; for variation
is a long-continued and slow process, and natural selection
will in such cases not as yet have had time to overcome the
tendency to further variability and to reversion to a less
modified state. But when a species with any extraordinarily-
developed organ has become the parent of many modified
descendants — ^which on our view must be a very slow process,
requiring a long lapse of time — in this case, natural selection
has succeeded in giving a fixed character to the organ, in
however extraordinary a manner it may have been developed.
Species inheriting nearly the same constitution from a com-
mon parent, and exposed to similar influences, naturally tend
to present analogous variations, or these same species may
occasionally revert to some of the characters of their ancient
progenitors. Although new and important modifications may
not arise from reversion and analogous variation, such modi-
fications will add to the beautiful and harmonious diversity
of nature.
Whatever the cause may be of each slight difference be-
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SPECIFIC CHARACTERS HIGHLY VARIABLE 177
tween the offspring and their parents — ^and a cause for each
must exist — ^we have reason to believe that it is the steady
accumulation of beneficial differences which has given rise
to all the more important modifications of structure in rela-
tion to the habits of each species.
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CHAPTER VI
Difficulties of the Theory
Difficolties of the theory of descent with modification — ^Absence or
rarity of transitional varieties — ^Transitions in habits of life —
Diversified habits in the same species — Species with habits widely
different from those of their allies — Organs of extreme perfec-
tion— Modes of transition — Cases of difficulty — Natura non facit
saltum — Organs of small importance — Organs not in all cases
absolutely perfect — The law of Unity of Type and of the Con-
ditions of Existence embraced by the theory of Natural
Selection.
LONG before the reader, has arrived at this part of my
work, a crowd of diflSculties will have occurred to him.
Some of them are so serious that to this day I can
hardly reflect on them without being in some degree stag-
gered; but, to the best of my judgment, the greater number
are only apparent, and those that are real are not, I think,
fatal to theory.
These difficulties and objections may be classed tmder the
following heads : — First, why, if species have descended from
other species by fine gradations, do we not everywhere see
innumerable transitional forms? Why is not all nature in
confusion, instead of the species being, as we see them, well
defined ?
Secondly, is it possible that an animal having, for instance,
the structure and habits of a bat, could have been formed by
the modification of some other animal with widely different
habits and structure ? Can we believe that natural selection
could produce, on the one hand, an organ of trifling impor-
tance, such as the tail of a giraffe, which serves as a fly-
flapper, and, on the other hand, an organ so wonderful as the
eye?
Thirdly, can instincts be acquired and modified through
natural selection? What shall we say to the instinct which
178
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TRANSITIONAL VARIETIES 179
leads the bee to make cells, and which has practically antici-
pated the discoveries of profound mathematicians?
Fourthly, how can we account for species, when crossed,
being sterile and producing sterile offspring, whereas, when
varieties are crossed, their fertility is unimpaired ?
The two first heads will here be discussed; some miscel-
laneous objections in the following chapter; Instinct and
Hybridism in the two succeeding chapters.
On the Absence or Rarity of Transitional Varieties. — As
natural selection acts solely by the preservation of profitable
modifications, each new form will tend in a fully-stocked
country to take the place of, and finally to exterminate, its
own less improved parent-form and other less-favoured forms
with which it comes into competition. Thus extinction and
natural selection go hand in hand. Hence, if we look at
each species as descended from some unknown form, both
the parent and all the transitional varieties will generally
have been exterminated by the very process of the formation
and perfection of the new form.
But, as by this theory innumerable transitional forms must
have existed, why do we not find them embedded in countless
numbers in the crust of the earth? It will be more con-
venient to discuss this question in the chapter on the Imper-
fection of the Geological Record; and I will here only state
that I believe the answer mainly lies in the record being in-
parably less perfect than is generally supposed. The crust
of the earth is a vast museum; but the natural collections
have been imperfectly made, and only at long intervals of
time.
But it may be urged that when several closely-allied
species inhabit the same territory, we surely ought to find at
the present time many transitional forms. Let us take a
simple case: in travelling from north to south over a conti-
nent, we generally meet at successive intervals with closely
allied or representative species, evidently filling nearly the
same place in the natural economy of the land. These represen-
tative species often meet and interlock; and as the one be-
comes rarer and rarer, the other becomes more and more
frequent, till the one replaces the other. But if we compare
these species where they intermingle, they are generally as ab-
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180 ORIGIN OF SPECIES
solutely distinct from each other in every detail of structure
as are specimens taken from the metropolis inhabited by each.
By my theory these allied species are descended from a com-
mon parent; and during the process of modification, each has
become adapted to the conditions of life of its own region,
and has supplanted and exterminated its original parent*
form and all the transitional varieties between its past and
present states. Hence we ought not to expect at the present
time to meet with numerous transitional varieties in each re-
gion, though they must have existed there, and may be em-
bedded there in a fossil condition. But in the intermediate
region, having intermediate conditions of life, why do we not
now find closely-linking intermediate varieties? This diffi-
culty for a long time quite confounded me. But I think it
can be in large part explained.
In the first place we should be extremely cautious in in-
ferring, because an area is now continuous, that it has been
continuous during a long period. Geology would lead us to
believe that most continents have been broken up into islands
even during the later tertiary periods; and in such islands
distinct species might have been separately formed without
the possibility of intermediate varieties existing in the inter-
mediate zones. By changes in the form of the land and of
climate, marine areas now continuous must often have ex-
isted within recent times in a far less continuous and uniform
condition than at present. But I will pass over this way of
escaping from the difficulty; for I believe that many per-
fectly defined species have been formed on strictly continu-
ous areas; though I do not doubt that the formerly broken
condition of areas now continuous, has played an important
part in the formation of new species, more especially with
freely-crossing and wandering animals.
In looking at species as they are now distributed over a
wide area, we generally find them tolerably numerous over a
large territory, then becoming somewhat abruptly rarer and
rarer on the confines, and finally disappearing. Hence the
neutral territory between two representative species is gen-
erally narrow in comparison with the territory proper to each.
We see the same fact in ascending mountains, and sometimes
it is quite remarkable how abruptly, as Alph. de Candolle has
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TRANSITIONAL VARIETIES 181
observed, a common alpine species disappears. The same
fact has been noticed by £. Forbes in sounding the depths of
the sea with the dredge. To those who look at climate and
the physical conditions of life as the all-important elements
of distribution, these facts ought to cause surprise, as cli-
mate and height or depth graduate away insensibly. But
when we bear in mind that almost every species, even in its
metropolis, would increase immensely in numbers, were it not
for other competing species ; that nearly all either prey on or
serve as prey for others ; in short, that each organic being is
either directly or indirectly related in the most important
manner to other organic beings, — ^we see that the range of the
inhabitants of any country by no means exclusively depends
on insensibly changing physical conditions, but in a large
part on the presence of other species, on which it lives, or by
which it is destroyed, or with which it comes into competi-
tion; and as these species are already defined objects, not
blending one into another by insensible gradations, the range
of any one species, depending as it does on the range of
others, will tend to be sharply defined. Moreover, each
species on the confines of its range, where it exists in less-
ened numbers, will, during fluctuations in the number of its
enemies or of its prey, or in the nature of the seasons, be ex-
tremely liable to utter extermination ; and thus its geographi-
cal range will come to be still more sharply defined.
As allied or representative species, when inhabiting a con-
tinuous area, are generally distributed in such a manner that
each has a wide range, with a comparatively narrow neutral
territory between them, in which they become rather suddenly
rarer and rarer; then, as varieties do not essentially differ
from species, the same rule will probably apply to both ; and
if we take a varying species inhabiting a very large area, we
shall have to adapt two varieties to two large areas, and a
third variety to a narrow intermediate zone. The intermedi-
ate variety, consequently, will exist in lesser numbers from
inhabiting a narrow and lesser area ; and practically, as far as
I can make out, this rule holds good with varieties in a state
of nature. I have met with striking instances of the rule in
the case of varieties intermediate between well-marked vari-
eties in the genus Balanus. And it would appear from infor-
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182 ORIGIN OF SPEaSS
mation given me by Mr. Watson, Dr. Asa Gray, and Mr.
Wollaston, that generally, when varieties intermediate be-
tween two other forms occur, they are much rarer numeri-
cally than the forms which they connect. Now, if we may
trust these facts and inferences, and conclude that varieties
linking two other varieties together generally have existed
in lesser numbers than the forms which they connect, then
we can understand why intermediate varieties should not en-
dure for very long periods: — ^why, as a general rule, they
should be exterminated and disappear, sooner than the forms
which they originally linked together.
For any form existing in lesser numbers would, as already
remarked, run a greater chance of being exterminated than
one existing in large numbers ; and in this particular case the
intermediate form would be eminently liable to the inroads of
closely-allied forms existing on both sides of it. But it is a
far more important consideration, that .during the process of
further modification, by which two varieties are supposed to
be converted and perfected into two distinct species, the two
which exist in larger numbers, from inhabiting larger areas,
will have a great advantage over the intermediate variety,
which exists in smaller numbers in a narrow and intermedi-
ate zone. For forms existing in larger numbers will have a
better chance, within any given period, of presenting further
favourable variations for natural selection to seize on, than
will the rarer forms which exist in lesser numbers. Hence,
the more common forms, in the race for life, will tend to beat
and supplant the less common forms, for these will be more
slowly modified and improved. It is the same principle
which, as I believe, accounts for the common species in each
country, as shown in the second chapter, presenting on an
average a greater number of well-marked varieties than do
the rarer species. I may illustrate what I mean by supposing
three varieties of sheep to be kept, one adapted to an exten-
sive mountainous region; a second to a comparatively narrow,
hilly tract; and a third to the wide plains at the base; and
that the inhabitants are all trying with equal steadiness and
skill to improve their stocks by selection; the chances in this
case will be strongly in favour of the great holders on the
mountains or on the plains, improving their breeds more
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TRANSITIONAL VARIETIES 183
quickly than the small holders on the intermediate narrow,
hilly tract ; and consequently the improved mountain or plain
breed will soon take the place of the less improved hill breed ; •
and thus the two breeds, which originally existed in greater
numbers, will come into close contact with each other, with-
out the interposition of the supplanted, intermediate hill
variety.
To sum up, I believe that species come to be tolerably well-
defined objects, and do not at any one period present an inex-
tricable chaos of varying and intermediate links: first, be-
cause new varieties are very slowly formed, for variation is
a slow process, and natural selection can do nothing until
favourable individual differences or variations occur, and un-
til a place in the natural polity of the country can be better ,
filled by some modification of some one or more of its inhabit-
ants. Aaid such new places will depend on slow changes of
climate, or on the occasional immigration of new inhabitants,
and, probably, in a still more important degree, on some of
the old inhabitants becoming slowly modified, with the new
forms thus produced and the old ones acting and reacting on
each other. So that, in any one region and at any one time,
we ought to see only a few species presenting slight modifi-
cations of structure in some degree permanent; and this as-
suredly we do see.
Secondly, areas now continuous must often have existed
within the recent period as isolated portions, in which many
forms, more especially amongst the classes which unite for
each birth and wander much, may have separately been ren-
dered sufficiently distinct to rank as representative species.
In this case, intermediate varieties between the several repre-
sentative species and their common parent, must formerly
have existed within each isolated portion of the land, but
these links during the process of natural selection will have
been supplanted and exterminated, so that they will no longer
be found in a living state.
Thirdly, when two or more varieties have been formed in
different portions of a strictly continuous area, intermediate
varieties will, it is probable, at first have been formed in the
intermediate zones, but they will generally have had a short
duration. For these intermediate varieties will, from reasons
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184 ORIGIN OF SPECIES
already assigned (namely from what we know of the actual
distribution of closely allied or representative species, and
likewise of acknowledged varieties), exist in the intermediate
zones in lesser numbers than the varieties which they tend to
connect. From this cause alone the intermediate varieties
. will be liable to accidental extermination; and during the
process of further modification through natural selection,
they will almost certainly be beaten and supplanted by the
forms which they connect ; for these from existing in greater
numbers will, in the aggregate, present more varieties, and
thus be further improved through natural selection and gain
further advantages.
Lastly, looking not to any one time, but to all time, if my
theory be true, numberless intermediate varieties, linking
closely together all the species of the same group, must as-
suredly have existed; but the very process of natural selec-
tion constantly tends, as has been so often remarked, to ex-
terminate the parent-forms and the intermediate links. Con-
sequently evidence of their former existence could be found
only amongst fossil remains, which are preserved, as we shall
attempt to show in a future chapter, in an extremely imper-
fect and intermittent record.
On the Origin and Transitions of Organic Beings with
peculiar Habits and Structure. — ^It has been asked by the
opponents of such views as I hold, how, for instance, could
a land carnivorous animal have been converted into one with
aquatic habits; for how could the animal in its transitional
state have subsisted? It would be easy to show that there
now exist carnivorous animals presenting close intermediate
grades from strictly terrestrial to aquatic habits ; and as each
exists by a struggle for life, it is clear that each must be well
adapted to its place in nature. Look at the Mustela vison
of North America, which has webbed feet, and which re-
sembles an otter in its fur, short legs, and form of tail. Dur-
ing the summer this animal dives for and preys on fish, but
during the long winter it leaves the frozen waters, and preys,
like other pole-cats, on mice and land animals. If a different
case had been taken« and it had been asked how an insectiv-
orous quadruped could possibly have been converted into
a flying bat, the question would have been far more
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TRANSITIONS OF ORGANIC BEINGS 185
difficult to answer. Yet I think such difficulties have little
weight
Here, as on other occasions, I lie under a heavy disadvan-
tage, for, out of the many striking cases wjrich I have col-
lected, I can give only one or two instances of transitional
habits and structures in allied species; and of diversified
habits, either constant or occasional, in the same species.
And it seems to me that nothing less than a long list of such
cases is sufficient to lessen the difficulty in any particular
case like that of the bat.
Look at the family of squirrels; here we have the finest
gradation from animals with their tails only slightly flat*
tened, and from others, as Sir J. Richardson has remarked,
with the posterior part of their bodies rather wide and with
the skin on their flanks rather full, to the so-called flying
squirrels; and flying squirrels have their limbs and even the
base of the tail united by a broad expanse of skin, which
serves as a parachute and allows them to glide through the
air to an astonishing distance from tree to tree. We cannot
doubt that each structure is of use to each kind of squirrel in
its own country, by enabling it to escape birds or beasts of
prey, to collect food more quickly, or, as there is reason to
believe, to lessen the danger from occasional falls. But it
does not follow from this fact that the structure of each
squirrel is the best that it is possible to conceive under all
possible conditions. Let the climate and vegetation change,
let other competing rodents or new beasts of prey immigrate,
or old ones become modified, and all analogy would lead us to
believe that some at least of the squirrels would decrease in
numbers or become exterminated, unless they also became
modified and improved in structure in a corresponding man-
ner. Therefore, I can see no difficulty, more especially under
changing conditions of life, in the continued preservation of
individuals with fuller and fuller flank-membranes, each modi-
fication being useful, each being propagated, until, by the ac-
cumulated effects of this process of natural selection, a per-
fect so-called flying squirrel was produced.
Now look at the Galeopithecus or so-called flying lemur,
which formerly was ranked amongst bats, but is now believed
to belong to the Insectivora. As extremely wide flank-mem-
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1»6 ORIGIN OF SPEaSS
brane stretches from the comers of the jaw to the tail, and
includes the limbs with the elongated fingers. This flank-
membrane is furnished vrith an extensor muscle. Although
no graduated lioks of structure, fitted for gliding through the
air, now connect the Galeopithecus with the other Insec-
tivora, yet there is no difficulty to supposing that such links
formerly existed, and that each was developed in the same
manner as with the less perfectly gliding squirrels; each
grade of structure having been useful to its possessor. Nor
can I see any insuperable difficulty in further believing that
the membrane connected fingers and fore-arm of the Galeopi-
thecus might have been greatly lengthened by natural selec-
tion; and this, as far as the organs of flight are concerned,
would have converted the animal into a bat In certain bats
in which the wing-membrane extends from the top of the
shoulder to the tail and includes the hind-legs, we perhaps
see traces of an apparatus originally fitted for gliding through
the air rather than for flight.
If about a dozen genera of birds were to become extinct,
who would have ventured to surmise that birds might have
existed which used their wings solely as flappers, like the
logger-headed duck (Micropterus of Eyton) ; as fins in the
water and as front-legs on the land, like the penguin; as
sails, like the ostrich; and functionally for no purpose, like
Apteryx? Yet the structure of each of these birds is
good for it, under the conditions of life to which it is exposed,
for each has to live by a struggle; but it is not necessarily
the best possible under all possible conditions. It must not
be inferred from these remarks that any of the grades of
wing-structure here alluded to, which perhaps may all be the
result of disuse, indicate the steps by which birds actually
acquired their perfect power of flight ; but they serve to show
what diversified means of transition are at least possible.
Seeing that a few members of such water-breathing classes
as the Crustacea and Mollusca are adapted to live on the
land ; and seeing that we have flying birds and mammals, fly-
ing insects of the most diversified types, and formerly had
flying reptiles, it is conceivable that flying-fish, which now
glide far through the air, slightly rising and turning by the
aid of their fluttering fins, might have been modified into per-
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TRANSITIONS OF ORGANIC BEINGS 187
fecdy winged animals. If this had been effected, who would
have ever imagined that in an early transitional state they
had been the inhabitants of the open ocean, and had used
their incipient organs of flight exclusively, as far as we know,
to escape being devoured by other fish?
When we see any structure highly perfected for any par-
ticular habit, as the wings of a bird for flight, we should bear
in mind that animals displaying early transitional grades of
the structure will seldom have survived to the present day,
for they will have been supplanted by their successors, which
were gradually rendered more perfect through natural selec-
tion. Furthermore, we may conclude that transitional states
between structures fitted for very different habits of life will
rarely have been developed at an early period in great num-
bers and under many subordinate forms. Thus, to return to our
imaginary illustration of the flying-fish, it does not seem
probable that fishes capable of true flight would have been
developed under many subordinate forms, for taking prey of
many kinds in many ways, on the land and in the water, until
their organs of flight had come to a high state of perfection,
so as to have given them a decided advantage over other ani-
mals in the battle for life. Hence the chance of discovering
species with transitional grades of structure in a fossil con-
dition will always be less, from their having existed in lesser
numbers, than in the case of species with fully developed
structures.
I will now give two or three instances both of diversified
and of changed habits in the individuals of the same species.
In either case it would be easy for natural selection to adapt
the structure of the animal to its changed habits, or exclu-
sively to one of its several habits. It is, however, difficult
to decide, and immaterial for us, whether habits generally
change first and structure afterwards; or whether slight
modifications of structure lead to changed habits; both prob-
ably often occurring almost simultaneously. Of cases of
changed habits it will suffice merely to allude to that of the
many British insects which now feed on exotic plants, or ex-
clusively on artificial substances. Of diversified habits innu-
merable instances could be given: I have often watched a
tyrant flycatcher (Saurophagus sulphuratus) in South Amer-
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188 ORIGIN OF SPECIES
ica, hovering over one spot and then proceeding to another,
like a kestrel, and at other times standing stationary on the
margin of water, and then dashing into it like a kingfisher
at a fish. In our own country the larger titmouse (Parus
major) may be seen climbing branches, almost like a creeper ;
it sometimes, like a shrike, kills small birds by blows on the
head; and I have many times seen and heard it hammering
the seeds of the yew on a branch, and thus breaking them
like a nuthatch. In North America the black bear was seen
by Hearne swimming for hours with widely open mouth, thus
catching, almost like a whale, insects in the water.
As we sometimes see individuals following habits different
from those proper to their species and to the other species of
the same genus, we might expect that such individuals would
occasionally give rise to new species, having anomalous
habits, and with their structure either slightly or considerably
modified from that of their type. And such instances occur
in nature. Can a more striking instance of adaptation be
given than that of a woodpecker for climbing trees and seiz-
ing insects in the chinks of the bark? Yetnn North America
there are woodpeckers which feed largely on fruit, and others
with elongated wings which chase insects on the wing. On
the plains of La Plata, where hardly a tree grows, there is a
woodpecker (Colaptes campestris) which has two toes before
and two behind, a long pointed tongue, pointed tail-feathers,
sufficiently stiff to support the bird in a vertical position on
a post, but not so stiff as in the typical woodpeckers, and a
straight strong beak. The beak, however, is not so straight
or so strong as in the typical woodpeckers, but it is strong
enough to bore into wood. Hence this Colaptes in all the
essential parts of its structure is a woodpecker. Even in
such trifling characters as the colouring, the harsh tone of
the voice, and undulatory flight, its close blood-relationship
to our common woodpecker is plainly declared; yet, as I can
assert, not only from my own observations, but from those
of the accurate Azara, in certain large districts it does not
climb trees, and it makes its nest in holes in banks ! In cer-
tain other districts, however, this same woodpecker, as Mr.
Hudson states, frequents trees, and bores holes in the trunk
for its nest I may mention as another illustration of the
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TRANSITIONS OF ORGANIC BEINGS 189
varied habits of this genus, that a Mexican Colaptes has been
described by De Saussure as boring holes into hard wood in
order to lay up a store of acorns.
Petrels are the most aerial and oceanic of birds, but in the
quiet sounds of Tierra del Fuego, the Puffinuria berardi, in
its general habits, in its astonishing power of diving, in its
manner of swimming and of flying when made to take flight,
would be mistaken by any one for an auk or a grebe; never-
theless it is essentially a petrel, but with many parts of its
organisation profoundly modified in relation to its new habits
of life; whereas the woodpecker of La Plata has had its
structure only slightly modified. In the case of the water-
ouzel, the acutest observer by examining its dead body would
never have suspected its sub-aquatic habits; yet this bird,
which is allied to the thrush family, subsists by diving— using
its wings under water, and grasping stones with its feet. All
the members of the great order of Hymenopterous insects
are terrestrial, excepting the genus Proctotrupes, which Sir
John Lubbock has discovered to be aquatic in its habits; it
often enters the water and dives about by the use not of its
legs but of its wings, and remains as long as four hours be-
neath the surface ; yet it exhibits no modification in structure
in accordance with its abnormal habits.
He who believes that each being has been created as we
now see it, must occasionally have felt surprise when he has
met with an animal having habits and structure not in agree-
ment. What can be plainer than that the webbed feet of
ducks and geese are formed for swimming? Yet there are up-
land geese with webbed feet which rarely go near the water ;
and no one except Audubon has seen the frigate-bird, which
has all its four toes webbed, alight on the surface of the
ocean. On the other hand, grebes and coots are eminently
aquatic, although their toes are only bordered by membrane.
What seems plainer than that the long toes, not furnished
with membrane of the Grallatores are formed for walking
over swamps and floating plants ? — ^the water-hen and land-
rail are members of .this order, yet the first is nearly as
aquatic as the coot, and the second nearly as terrestrial as
the quail or partridge. In such cases, and many others could
be given, habits have changed without a corresponding change
L— HC XI
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190 ORIGIN OF SPECIES
of structure. The webbed feet of the upland goose may be
said to have become almost rudimentary in function, though
not in structure. In the frigate-bird, the deeply scooped
membrane between the toes shows that structure has begun
to change.
He who believes in separate and innumerable acts of cre-
ation may say, that in these cases it has pleased the Creator
to cause a being of one type to take the place of one belonging
to another type ; but this seems to me only re-Stating the fact
in dignified language. He who believes in the struggle for
existence and in the principle of natural selection, will ac-
knowledge that every organic being is constantly endeavour-
ing to increase in numbers ; and that if any one being varies
ever so little, either in habits or structure, and thus gains an
advantage over some other inhabitant of the same country, it
will seize on the place of that inhabitant, however different
that may be from its own place. Hence it will cause him no
surprise that there should be geese and frigate-birds with
webbed feet, living on the dry land and rarely alighting on
the water, that there should be long-toed corncrakes, living in
meadows instead of in swamps; that there should be wood-
peckers where hardly a tree grows ; that there should be div-
ing thrushes and diving Hymenoptera, and petrels with the
habits of auks.
ORGANS OP EXTREME PERFECTION AND COMPLICATION.
To suppose that the eye with all its inimitable contrivances
for adjusting the focus to different distances, for admitting
different amounts of light, and for the correction of spherical
and chromatic aberration, could have been formed by natural
selection, seems, I freely confess, absurd in the highest de-
gree. When it was first said that the sun stood still and the
world turned round, the common sense of mankind declared
the doctrine false ; but the old saying of Vox populi, vox Dei,
as every philosopher knows, cannot be trusted in science.
Reason tells me, that if numerous gradations from a sin\ple
and imperfect eye to one complex and perfect can be shown
to exist, each grade being useful to its possessor, as is cer-
tainly the case; if further, the eye ever varies and the vari-
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ORGANS OF EXTREME PERFECTION 191
ations be inherited, as is likewise certainly the case; and if
such variations should be useful to any animal under chang-
ing conditions of life, then the difficulty of believing that a
perfect and complex eye could be formed by natural selection,
though insuperable by our imagination, should not be consid-
ered as subversive of the theory. How a nerve comes to be
sensitive to light, hardly concerns us more than how life it-
self originated ; but I may remark that, as some of the lowest
organisms, in which nerves cannot be detected, are capable of
perceiving light, it does not seem impossible that certain sen-
sitive elements in their sarcode should become aggregated
and developed into nerves, endowed with this special sensi-
bility.
In searching for the gradations through which an organ in
any species has been perfected, we ought to lode exclusively
to its lineal progenitors; but this is scarcely ever possible,
and we are forced to look to other species and genera of the
same group, that is to the collateral descendants from the
same parent-form, in order to see what gradations are pos-
sible, and for the chance of some gradations having been
transmitted in an unaltered or little altered condition. But
the state of the same organ in distinct classes may incident-
ally throw, light on the steps by which it has been perfected.
The simplest organ which can be called an eye consists of
an optic nerve, surrounded by pigment-cells and covered by
translucent skin, but without any lens or other refractive
body. We may, however, according to M. Jourdain, descend
even a step lower and find aggregates of pigment-cells, appar-
ently serving as organs of vision, without any nerves, and
resting merely on sarcodic tissue. Eyes of the above simple
nature are not capable of distinct vision, and serve only to
(tistinguish light from darkness. In certain star-fishes, small
depressions in the layer of pigment which surrounds the
nerve are filled, as described by the author just quoted, with
transparent gelatinous matter, projecting with a convex sur-
face, like the cornea in the higher animals. He suggests that
this serves not to form an image, but only to concentrate the
luminous rays and render their perception more easy. In
this concentration of the rays we gain the first and by far the
most important step towards the formation of a true, picture-
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192 ORIGIN OF SPECIES
forming eye ; for we have only to place the naked extremity
of the optic nerve, which in some of the lower animals lies
deeply buried in the body, and in some near the surface, at
the right distance from the concentrating apparatus, and an
image will be formed on it
In the great class of the Articulata, we may start from an
optic nerve simply coated with pigment, the latter sometimes
forming a sort of pupil, but destitute of a lens or other opti-
cal contrivance. With insects it is now known that the nu-
merous facets on the cornea of their great compound eyes
form true lenses, and that the cones include curiously modi-
fied nervous filaments. But these organs in the Articulata
are so much diversified that Miiller formerly made three main
classes with seven subdivisions, besides a fourth main class
of aggregated simple eyes.
When we reflect on these facts, here given much too briefly,
with respect to the wide, diversified, and graduated range of
structure in the eyes of the lower animals ; and when we bear
in mind how small the number of all living forms must be in
comparison with those which have become extinct, the diffi-
culty ceases to be very great in believing that natural selec-
tion may have converted the simple apparatus of an optic
nerve, coated with pigment and invested by transparent mem-
brane, into an optical instrument as perfect as is possessed
by any member of the Articulate Class.
He who will go thus far, ought not to hesitate to go one
step further, if he finds on finishing this volume that large
bodies of facts, otherwise inexplicable, can be explained by
the theory of modification through natural selection ; he ought
to admit that a structure even as perfect as an eagle's eye
might thus be formed, although in this case he does not know
the transitional states. It has been objected that in order to
modify the eye and still preserve it as a perfect instrument,
many changes would have to be effected simultaneously,
which, it is assumed, could not be done through natural
selection ; but as I have attempted to show in my work on the
variation of domestic animals, it is not necessary to suppose
that the modifications were all simultaneous, if they were ex-
tremely slight and gradual. Different kinds of modification
would, also, serve for the same general purpose : as Mr. Wal-
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ORGANS OF EXTREME PERFECTION 183
lace has remarked, "if a lens has too short or too long a
focus, it may be amended either by an alteration of curvature,
or an alteration of density; if the curvature be irregular, and
the rays do not converge to a point, then any increased regu-
larity of curvature will be an improvement. So the contrac-
tion of the iris and the muscular movements of the eye are
neither of them essential to vision, but only improvements
which might have been added and perfected at any stage of
the construction of the instrument." Within the highest di-
vision of the animal kingdom, namely, the Vertebrata, we can
start from an eye so simple, that it consists, as in the lance-
let, of a little sack of transparent skin, furnished with a
nerve and lined with pigment, but destitute of any other ap-
paratus. In fishes and reptiles, as Owen has remarked, "the
range of gradations of dioptric structures is very great/' It
is a significant fact that even in man, according to the high
authority of Virchow, the beautiful crystalline lens is formed
in the embryo by an accumulation of epidermic cells, lying in
a sack-like fold of the skin ; and the vitreous body is formed
from embryonic sub-cutaneous tissue. To arrive, however,
at a just conclusion regarding the formation of the eye, with
all its marvellous yet not absolutely perfect characters, it is
indispensable that the reason should conquer the imagination ;
but I have felt the difiiculty far too keenly to be surprised at
others hesitating to extend the principle of natural selection
to so startling a length.
It is scarcely possible to avoid comparing the eye with a
telescope. We know that this instrument has been perfected
by the long-continued efforts of the highest human intellects ;
and we naturally infer that the eye has been formed by a
somewhat anal(^us process. But may not this inference be
presumptuous? Have we any right to assume that the Cre-
ator works by intellectual powers like those of man? If we
must compare the eye to an optical instrument, we ought in
imagination to take a thick layer of transparent tissue, with
spaces filled with fluid, and with a nerve sensitive to light be-
neath, and then suppose every part of this layer to be con-
tinually changing slowly in density, so as to separate into
layers of different densities and thidcnesses, placed at differ-
ent distances from each other, and with the surfaces of each
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194 ORIGIN OF SPECIES
layer slowly changing in form. Further we must suppose
that there is a power, represented by natural selection or the
survival of the fittest, always intently watching each slight
alteration in the transparent layers; and carefully preserving
each which, under varied circumstances, in any way or in any
degree, tends to produce a distincter image. We must sup-
pose each new state of the instrument to be multiplied by the
million; each to be preserved until a better one is produced,
and then the old ones to be all destroyed. In living bodies,
variation will cause the slight alterations, generation will mul-
tiply them almost infinitely, and natural selection will pick
out with unerring skill each improvement. Let this process
go on for millions of years ; and during each year on millions
of individuals of many kinds ; and may we not believe that a
living optical instrument might thus be formed as superior
to one of glass, as the works of the Creator are to those of
man?
MODEiS OF TRANSITION.
If it could be demonstrated that any complex organ ex-
isted, which could not possibly have been formed by numer-
ous, successive, slight modifications, my theory would abso-
lutely break down. But I can find out no such case. No
doubt many organs exist of which we do not know the tran-
sitional grades, more especially if we look to much-isolated
species, round which, according to the theory, there has been
much extinction. Or again, if we take an organ common to
all the members of a class, for in this latter case the organ
must have been originally formed at a remote period, since
which all the many member3 of the class have been developed ;
and in order to discover the early transitional .^ades through
which the organ has passed, we should have t6 look to very
ancient ancestral forms, long since become" ^ctinct
We should be extremely cautious in concluding that an
organ could not have been formed by transitional gradations
of some kind. Numerous cases could be given amongst the
lower animals of the same organ performing at the same time
wholly distinct functions ; thus in the larva of the dragon-fiy
and in the fish Cobites the alimentary canal respires, digests,
and excretes. In the Hydra, the animal may be turned in-
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MODES OF TRANSITION IdS
side out, and the exterior surface will then digest and the
stomach respire. In such cases natural selection might spe-
cialise, if any advantage were thus gained, the whole or part
of an organ, which had previously performed two functions,
for one function alone, and thus by insensible steps greatly
change its nature. Many plants are known which regularly
produce at the same time differently constructed flowers ; and
if such plants were to produce one kind alone, a great change
would be effected with 'comparative suddenness in the char-
acter pf the species. It is, however, probable that the two
sorts of flowers borne by the same plant were originally dif-
ferentiated by finely graduated steps, which may still be
followed in some few cases.
Again, two distinct organs, or the same organ under two
very different forms, may simultaneously perform in the same
individual the same function, and this is an extremely im-
portant means of transition: to give one instance, — ^there are
fish with gills or branchiae that breathe the air dissolved in
the water, at the same time that they breathe free air in their
swimbladders, this latter organ being divided by highly vas-
cular partitions and having a ductus pneumaticus for the
supply of air. To give another instance from the vegetable
kingdom; plants climb by three distinct means, by spirally
twining, by clasping a support with their sensitive tendrils,
and by the emission of aerial rootlets; these three means are
usually found in distinct groups, but some few species exhibit
two of the means, or even all three, combined in the same in-
dividual. In all such cases one of the two organs might
readily be modified and perfected so as to perform all the
work, being aided during the progress of modification by the
other organ ;^nd then this other organ might be modified
for some oAier and quite distinct purpose, or be wholly
obliterated. a »
The illustration of the swimbladder in fishes is a good one,
because it shews us clearly the highly important fact that an
organ originally constructed for one purpose, namely, flota-
tion, may be converted into one for a widely different pur-
pose, namely, respiration. The swimbladder has, also, been
worked in as an accessory to the auditory organs of certain
fishes. All physiologists admit that the swimbladder is homol-
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196 ORiem OF SPECIES
ogous, or "ideally similar'' in position and structure with the
lungs of the higher vertebrate animals: hence there is no
reason to doubt that the swimbladder has actually been con-
verted into lungs, or an organ used exclusively for respi-
ration.
According to this view it may be inferred that all verte-
brate animals with true lungs are descended by ordinary gen-
eration from an ancient and unknown prototype, which was
furnished with a floating apparatus or swimbladder. We can
thus, as I infer from Owen's interesting description of these
parts, understand the strange fact that every particle of food
and drink which we swallow has to pass over the orifice of
the trachea, with some risk of falling into the lungs, notwith-
standing the beautiful contrivance by which the glottis is
closed. In the higher Vertebrata the branchiae have wholly
disappeared — ^but in the embryo the slits on the sides of the
neck and the loop-like course of the arteries still mark their
former position. But it is conceivable that the now utterly
lost branchiae might have been gradually worked in by nat-
ural selection for some distinct purpose: for instance, Lan-
dois has shown that the wings of insects are developed from
the tracheae ; it is therefore highly probable that in this great
class organs which once served for respiration have been
actually converted into organs for flight.
In considering transitions of organs, it is so important to
bear in mind the probability of conversion from one function
to another, that I will give another instance. Pedunculated
cirripedes have two minute folds of skin, called by me the
ovigerous frena, which serve, through the means of a sticky
secretion, to retain the eggs until they are hatched within the
sack. These cirripedes have no branchiae, the whole surface
of the body and of the sack, together with the small frena,
serving for respiration. The Balanidae or sessile cirripedes,
on the other hand, have no ovigerous frena, the eggs lying
loose at the bottom of the sack, within the well-enclosed shell ;
but they have, in the same relative position with the frena,
large, much-folded membranes, which ' freely communicate
with the circulatory lacunae of the sack and body, and which
have been considered by all naturalists to act as branchiae.
Now I think no one will dispute that the ovigerous frena in
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MODES OF TRANSITION 107
the one family are strictly homologous with the branchiae of
the other family; indeed, they graduate intQ each other.
Therefore it need not be doubted that the two little folds of
skin, which originally served as ovigerous frena, but which,
likewise, very slightly aided in the act of respiration, have
been gradually converted by natural selection into branchiae,
simply through an increase in their size and the obliteration
of their adhesive glands. If all pedunculated cirripedes had
become extinct, and they have suffered far more extinction
than have sessile cirripedes, who would ever have imagined
that the branchiae in this latter family had originally existed
as organs for preventing the ova from being washed out of
the sack?
There is another possible mode of transition, namely,
through the acceleration or retardation of the period of re-
producticHi. This has lately been insisted on by Prof. Cope
and others in the United States. It is now known that some
animals are capable of reproduction at a very early age, be-
fore they have acquired their perfect characters; and if this
power became thoroughly well developed in a species, it seems
probable that the adult stage of development would sooner or
later be lost; and in this case, especially if the larva differed
much from the mature form, the character of the species
would be greatly changed and degraded. Again, not a few
animals, after arriving at maturity, go on changing in char-
acter during nearly their whole lives. With mammals, for
instance, the form of the skull is often much altered with age,
of which Dr. Murie has given some striking instances with
seals; every one knows how the horns of stags become more
and more branched, and the plumes of some birds become
more finely developed, as they grow older. Prof. Cope states
that the teeth of certain lizards change much in shape with
advancing years ; with crustaceans not only many trivial, but
some important parts assume a new character, as recorded
by Fritz Mtiller, after maturity. In all such cases, — ^and
many could be given, — ^if the age ior reproduction were re-
tarded, the character of the species, at least in its adult state,
would be modified ; nor is it improbable that the previous and
earlier stages of development would in some cases be hurried
through and finally lost. Whether species have often or ever
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196 ORIGIN OF SPECIES
been modified through this comparatively sudden mode of
transition, I can form no opinion ; but if this has occurred, it
is probable that the differences between the young and the
mature, and between ttie mature and the old, were primor-
dially acquired by graduated steps.
SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION
Although we must be extremely cautious in concluding that
any organ could not have been produced by successive, small
transitional gradations, yet undoubtedly serious cases of dif-
ficulty occur.
One of the most serious is that of neuter insects, which are
often differently constructed from either the males or fertile
females ; but this case will be treated of in the next chapter.
The electric organs of fishes offer another case of special
difficulty; for it is impossible to conceive by what steps these
wondrous organs have been produced. But this is not sur-
prising, for we do not even know of what use they are. In
the Gymnotus and Torpedo they no doubt serve as powerful
means of defence, and perhaps for securing prey ; yet in the
Ray, as observed by Matteucci, an analogous organ in the
tail manifests but little electricity, even when the animal is
greatly irritated; so little, that it can hardly be of any use
for the above purposes. Moreover, in the Ray, besides the
organ just referred to, there is, as Dr. R. M'Donnell has
shown, another organ near the head, not known to be elec-
trical, but which appears to be the real homologue of the
electric battery in the Torpedo. It is generally admitted that
there exists between these organs and ordinary muscle a close
analogy, in intimate structure, in the distribution of the
nerves, and in the manner in which they are acted on by
various reagents. It should, also, be especially observed that
muscular contraction is accompanied by an electrical dis-
charge; and, as Dr. Radcliffe insists, "in the electrical ap-
paratus of the torpedo during rest, there would seem to be a
charge in every respect like that which is met with in muscle
and nerve during rest, and the discharge of the torpedo, in-
stead of being peculiar, may be only another form of the dis-
charge which attends upon the action of muscle and
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DIFFICULTIES OF THB THEORY 199
motor nerve." Beyond this we cannot at present go in the
way of explanation ; but as we know so little about the uses
of these organs, and as we know nothing about the habits
and structure of the progenitors of the existing electric fishes,
it would be extremely bold to maintain that no serviceable
transitions are possible by which these organs might have
been gradually developed.
These organs appear at first to offer another and far more
serious difiiculty; for they occur in about a dozen kinds of
fish, of which several are widely remote in their afiinities.
When the same organ is found in several members of the
same class, especially if in members having very different
habits of life, we may generally attribute its presence to in-
heritance from a common ancestor; and in its absence in
some of the members to loss through disuse or natural selec-
tion. So that, if the electric organs had been inherited from
some one ancient progenitor, we might have expected that
all electric fishes would have been specially related to each
other; but this is far from the case. Nor does geology at all
lead to the belief that most fishes formerly possessed electric
organs, which their modified descendants have now lost. But
when we look at the subject more closely, we find in the sev-
eral fishes provided with electric organs, that those are situ-
ated in different parts of the body, — that they differ in con-
struction, as in the arrangement of the plates, and, according
to Pacini, in the process or means by which the electricity is
excited — and lastly, in being supplied with nerves proceeding
from different sources, and this is perhaps the most important
of all the differences. Hence in the several fishes furnished
with electric organs, these cannot be considered as homol-
ogous, but only as analogous in function. Consequently there
is -no reason to suppose that they have been inherited from a
common progenitor; for had this been the case they would
have closely resembled each other in all respects. Thus the
difficulty of an organ, apparently the same, arising in several
remotely allied species, disappears, leaving only the lesser yet
still great difiiculty; namely, by what graduated steps these
organs have been developed in each separate group of fishes.
The luminous organs which occur in a few insects, belong-
ing to widely different families, and which are situated in
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200 ORIGIN OF SPECIES
different parts of the body, offer, under our present state of
ignorance, a difficulty almost exactly parallel with that of the
electric organs. Other similar cases could be given; for in-
stance in plants, the very curious contrivance of a mass of
pollen-grains, borne on a foot-stalk with an adhesive gland,
is apparently the same in Orchis and Asclepias, — genera al-
most as remote as is possible amongst flowering plants; but
here again the parts are not homologous. In all cases of be-
ings, far removed from each other in the scale of organisa*
tion, which are furnished with similar and peculiar organs,
it will be found that although the general appearance and
function of the organs may be the same, yet fundamental dif-
ferences between them can always be detected. For instance,
the eyes of cephalopods or cuttle-fish and of vertebrate ani-
mals appear wonderfully alike; and in such widely sundered
groups no part of this resemblance can be due to inheritance
from a common progenitor. Mr. Mivart has advanced this
case as one of special difficulty, but I am unable to see the
force of his argument. An organ for vision must be formed
of transparent tissue, and must include some sort of lens for
throwing an image at the back of a darkened chamber. Be-
yond this superficial resemblance, there is hardly any real
similarity between the eyes of cuttle-fish and vertebrates, as
may be seen by consulting Hensen's admirable memoir on
these organs in the Cephalopoda. It is impossible for me
here to enter on details, but I may specify a few of the points
of difference. The crystalline lens in the higher cuttle-fish
consists of two parts, placed one behind the other like two
lenses, both having a very different structure and disposition
to what occurs in the vertebrata. The retina is wholly dif-
ferent, with an actual inversion of the elemental parts, and
with a large nervous ganglion included within the mem-
branes of the eye. The relations of the muscles are as dif-
ferent as it is possible to conceive, and so in other points.
Hence it is not a little difficult to decide how far even the
same terms ought to be employed in describing the eyes of
the Cephalopoda and Vertebrata. It is, of course, open to
any one to deny that the eye in either case could have been
developed through the natural selection of successive slight
variations ; but if this be admitted in the one case, it is clearly
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DIFFICULTIES OF THE THEORY * 201
possible in the other; and fundamental differences of struc-
ture in the visual organs of two groups might have been an-
ticipated, in accordance with this vieW of their manner of
formation. As two men have sometimes independently hit
on the same invention, so in the several foregoing cases it
appears that natural selection, working for the good of each
being, and taking advantage of all favourable variations, has
produced similar organs, as far as function is concerned, in
distinct organic beings, which owe none of their structure in
common to inheritance from a common progenitor.
Fritz Miiller, in order to test the conclusions arrived at in
this volume, has followed out with much care a nearly similar
line of argument Several families of crustaceans include a
few species, possessing an air-breathing apparatus and fitted
to live out of the water. In two of these families, which were
more especially examined by Miiller, and which are nearly
related to each other, the species agree most closely in all
important characters; namely in their sense organs, circulat-
ing system, in the position of the tufts of hair within their
complex stomachs, and lastly in the whole structure of the
water-breathing branchiae, even to the microscopical hooks by
which they are cleansed. Hence it might have been expected
that in the few species belonging to both families which live
on the land, the equally-important air-breathing apparatus
would have been the same ; for why should this one apparatus,
given for the same purpose, have been made to differ, whilst
all the other important organs were closely similar or rather
identical.
Fritz Miiller argues that this close similarity in so many
points of structure must, in accordance with the views ad-
vanced by me, be accotmted for by inheritance from a com-
mon progenitor. But as that vast majority of the species in
the above two families, as well as most other crustaceans,
are aquatic in their habits, it is improbable in the highest
degree, that their common progenitor should have been
adapted for breathing air. Miiller was thus led carefully^ to
examine the apparatus in the air-breathing species; and he
found it to differ in each in several important points, as in
the position of the orifices, in the manner in which they are
opened and closed, and in some accessory details. Now such
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ORIGIN OF SPECIES
di£Ferences are intelligible, and might even have been ex-
pected, on the supposition that species belonging to distinct
families had slowly become adapted to live more and more
out of water, and to breathe the air. For these species, from
belonging to distinct families, would have differed to a cer-
tain extent, and in accordance with the principle that the
nature of each variation depends on two factors, viz., the
nature of the organism and that of the surrounding condi-
tions, their variability assuredly would not have been exactly
the same. Consequently natural selection would have had
differenf materials or variations to work on, in order to ar-
rive at the same functional result; and the structures thus
acquired would almost necessarily have differed. On the
hypothesis of separate acts of creation the whole case re*
mains imintelligible. This line of argument seems to have
had great weight in leading Fritz Miiller to accept the views
maintained by me in this volume.
Another distinguished zoologist, the late Professor Clapa-
rede, has argued in the same manner, and has arrived at
the same result. He shows that there are parasitic mites
(Acaridae), belonging to distinct sub- families and families,
which are furnished with hair-claspers. These organs must
have been independently developed, as they could not have
been inherited from a common progenitor ; and in the several
groups they are formed by the modification of the fore-legs,
—of the hind-legs, — of the maxillae or lips, — ^and of append-
ages on the under side of the hind part of the body.
In the foregoing cases, we see the same end gained and the
same function performed, in beings not at all or only re-
motely allied, by organs in appearance, though not in de-
velopment, closely similar. On the oth^er hand, it is a com-
mon rule throughout nature that the same end should be
gained, even sometimes in the case of closely-related beings,
by the most diversified means. How differently constructed
is -the feathered wing of a bird and the membrane-covered
wing of a bat ; and still more so the four wings of a butter-
fly, the two wings of a fly, and the two wings with the elytra
of a beetle. Bivalve shells are made to open and shut, but
on what a number of patterns is the hinge constructed,^
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DIFFICULTIES OF THE THEORY -203
from the long row of neatly interlocking teeth in a Nucula
to the simple ligament of a Mussel ! Seeds are disseminated
by their minuteness, — ^by their capsule being converted into a
light balloon-like envelope, — ^by being embedded in pulp or
flesh, formed of the most diverse parts, and rendered nutri-
tious, as well as conspicuously coloured, so as to attract and
be devoured by birds, — ^by having hooks and grapnels of
many kinds and serrated awns, so as to adhere to the fur of
quadrupeds, — ^and by being furnished with wings and plumes,
as different in shape as they are elegant in structure, so as to
be wafted by every breeze. I will give one other instance;
for this subject of the same end being gained by the most
diversified means well deserves attention. Some authors
maintain that organic beings have been formed in many ways
for the sake of mere variety, almost like toys in a shop, but
such a view of nature is incredible. With plants having
separated sexes, and with those in which, though hermaphro-
dites, the pollen does not spontaneously fall on the stigma,
some aid is necessary for their fertilisation. With several
kinds this is effected by the pollen-grains, which are light
and incoherent, being blown by the wind through mere chance
on to the stigma; and this is the simplest plan which can
well be conceived. An almost equally simple, though very
different, plan occurs in many plants in which a symmetrical
flower secretes a few drops of nectar, and is consequently
visited by insects; and these carry the pollen from the anthers
to the stigma.
From this simple stage we may pass through an inex-
haustible number of contrivances, all for the same purpose
and effected in essentially the same manner, but entailing
changes in every part of the flower. The nectar may be
stored in variously shaped receptacles, with the stamens and
pistils modified in many ways, sometimes forming trap-like
contrivances, and sometimes capable of neatly adapted move-
ments through irritability or elasticity. From such structures
we may advance till we come to such a case of extraordinary
adaptions as that lately described by Dr. Criiger in the
Coryanthes. This orchid has part of its labellum or lower
lip hollowed out into a great bucket, into which drops of
almost pure water continually fall from two secreting horna
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204 ORIGIN OF SPECIES
which stand above it; and when the bucket is half full, the
water overflows by a spout on one side. The basal part of
the labellum stands over the bucket, and is itself hollowed
out into a sort of chamber with two lateral entrances ; with-
in this chamber there are curious fleshy ridges. The most
ingenious man, if he had not witnessed what takes place,
could never have imagined what purpose all these parts serve.
But Dr. Crtiger saw crowds of large humble-bees visiting the
gigantic flowers of this orchid, not in order to suck nectar,
but to gnaw off the ridges within the chamber above the
bucket; in doing this they frequently pushed each other into
the bucket, and their wings being thus wetted they could not
fly away, but were compdled to crawl out through the pas-
sage formed by the spout or overflow. Dr. Criiger saw a
"continual procession" of bees thus crawling out of their
involuntary bath. The passage is narrow, and is roofed over
by the column, so that a bee, in forcing its way out, first rubs
its back against the viscid stigma and then against the viscid
glands of the pollen-masses. The pollen-masses are thus
glued to the back of the bee which first happens to crawl out
through the passage of a lately expanded flower, and are
thus carried away. Dr. Cruger sent me a flower in spirits of
wine, with a bee which he had killed before it had quite
crawled out with a pollen-mass still fastened to its back.
When the bee, thus provided, flies to another flower, or to
the same flower a second time, and is pushed by its comrades
into the bucket and then crawls out by the passage, the
pollen-mass necessarily comes first into contact with the
viscid stigma, and adheres to it, and the flower is fertilised.
Now at last we see the full use of every part of the flower,
of the water-secreting horns, of the bucket half full of water,
which prevents the bees from flying away, and forces them
to crawl out through the spout, and rub against the properly
placed viscid pollen-masses and the viscid stigma.
The construction of the flower in another closely allied
orchid, namely the Catasetum, is widely different, though
serving the same end; and is equally curious. Bees visit
these flowers, like those of the Coryanthes, in order to gnaw
the labellum; in doing this they inevitably touch a long,
tapering, sensitive projection, or, as I have called it, the
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DIFFICULTIES OF THE THEORY 205
antenna. This antenna, when touched, transmits a sensation
or vibration to a certain membrane which is instantly rup-
tured; this sets free a spring by which the pollen-mass is shot
forth, like an arrow, in the right direction, and adheres by
its viscid extremity to the back of the bee. The pollen-mass
of the male plant (for the sexes are separate in this orchid)
is thus carried to the flower of the female plant, where it is
brought into contact with the stigma, which is viscid enough
to break certain elastic threads, and retaining the pollen,
fertilisation is effected.
How, it may be asked, in the foregoing and in innumer-
able other instances, can we understand the graduated scale of
complexity and the multifarious means for gaining the same
end. The answer no doubt is, as already remarked, that when
two forms vary, which already differ from each other in some
slight degree, the variability will not be of the same exact
nature, and consequently the results obtained through natural
selection for the same general purpose will not be the same.
We should also bear in mind that every highly developed
organism has passed through many changes; and that each
modified structure tends to be inherited, so that each modifi-
cation will not readily be quite lost, but may be again and
again further altered. Hence the structure of each part of
each species, for whatever purpose it may serve, is the sum
of many inherited changes, through which the species has
passed during its successive adaptations to changed habits
and conditions of life.
Finally then, although in many cases it is most difiicult
even to conjecture by what transitions organs have arrived
at their present state ; yet, considering how small the propor-
tion of living and known forms is to the extinct and un-
known, I have been astonished how rarely an organ can be
named, towards which no transitional grade is known to lead.
It certainly is true, that new organs appearing as if created
for some special purpose, rarely or never appear in any
being; — as indeed is shown by that old, but somewhat exag-
gerated, canon in natural history of "Natura non facit sal-
tum." We meet with this admission in the writings of almost
every experienced naturalist; or as Milne Edwards has well
expressed it, Nature is prodigal in variety, but niggard in
M— HCXI
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206 ORIGIN OF SPECIES
innovation. Why, on the theory of Creation, should there
be so much variety and so little real novelty? Why should
all the parts and organs of many independent beings, each
supposed to have been separately created for its proper place
in nature, be so commonly linked together by graduated
steps? Why should not Nature take a sudden leap from
structure to structure? On the theory of natural sdection,
we can clearly understand why she should not; for natural
selection acts only by taking advantage of slight successive
variations; she can never take a great and sudden leap, but
must advance by short and sure, though slow steps.
ORGANS OF LITTLE APPARENT IMPORTANCE, AS AFFECTED
BY NATURAL SELECTION
As natural selection acts by life and death, — ^by the sur-
vival of the fittest, and by the destruction of the less well-
fitted individuals, — I have sometimes felt great difficulty in
understanding the origin or formation of parts of little im-
portance; almost as great, though of a very different kind,
as in the case of the most perfect and complex organs.
In the first place, we are much too ignorant in regard to
the whole economy of any one organic being, to say what
slight modifications would be of importance or not. In a
former chapter I have given instances of very trifling char-
acters, such as the down on fruit and the colour of its flesh,
the colour of the skin and hair of quadrupeds, which, from
being correlated with constitutional differences or from de-
termining the attacks of insects, might assuredly be acted on
by natural selection. The tail of the giraffe looks like an
artificially constructed fly-fiapper; and it seems at first in-
credible that this could have been adapted for its present
purpose by successive slight modifications, each better and
better fitted, for so trifling an object as to drive away flies;
yet we should pause before being too positive even in this
case, for we know that the distribution and existence of
cattle and other animals in South America absolutely depend
on their power of resisting the attacks of insects: so that
individuals which could by any means defend themselves
from these small enemies, would be able to range into new
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ORGANS AFPBCTED 207
pastures and thus gain a great advantage. It is not that the
larger quadrupeds are actually destroyed (except in some
rare cases) by flies, but they are incessantly harassed and
their strength reduced, so that they are more subject to
disease, or not so well enabled in a coming dearth to search
for food, or to escape from beasts of prey.
Organs now of trifling importance have probably in some
cases been of high importance to an early progenitor, and,
after having been slowly perfected at a former period, have
been transmitted to existing species in nearly the same date,
although now of very slight use; but any actually injurious
deviations in their structure would of course have been
checked by natural selection. Seeing how important an
organ of locomotion the tail is in most aquatic animals, its
general presence and use for many purposes in so many land
animals, which in their lungs or modified swimbladders be-
tray their aquatic origin, may perhaps be thus accounted
for. A well-developed tail having been formed in an aquatic
animal, it might subsequently come to be worked in for all
sorts of purposes, — ^as a fly-flapper, an organ of prehension,
or as an aid in turning, as in the case of the dog, though the
aid in this latter respect must be slight, for the hare, with
hardly any tail, can double still more quickly.
In the second place, we may easily err in attributing im-
portance to characters, and in believing that they have been
developed through natural selection. We must by no means
overlook the effects of the definite action of changed condi-
tions of life, — of so-called spontaneous variations, which
seem to depend in a quite subordinate degree on the nature
of the conditions,— of the tendency to reversion to long-lost
characters,— of the complex laws of growth, such as of cor-
relation, compensation, of the pressure of one part on an-
other, etc., — ^and finally of sexual selection, by which charac-
ters of use to one sex are often gained and then transmitted
more or less perfectly to the other sex, though of no use
to this sex. But structures thus indirectly gained, although
at first of no advantage to a species, may subsequently have
been taken advantage of by its modified descendants, under
new conditions of life and newly acquired habits.
If green woodpeckers alone had existed, and we did not
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206 ORIGIN OP SPEaES
know that there were many black and pied kinds, I dare say
that we should have thought that the green colour was a
beautiful adaptation to conceal this tree-frequenting bird
from its enemies; and consequently that it was a character
of importance, and had been acquired through natural selec-
tion; as it is, the colour is probably in chief part due to
sexual selection. A trailing palm in the Malay Archipelago
climbs the loftiest trees by the aid of exquisitely constructed
hooks clustered around the ends of the branches, and this
contrivance, no doubt, is of the highest service to the plant;
* but as we see nearly similar hooks on many trees which are
not climbers, and which, as there is reason to believe from
the distribution of the thorn-bearing species in Africa and
South America, serve as a defence against browsing quadru-
peds, so the spikes on the palm may at first have been de-
veloped for this object, and subsequently have been improved
and taken advantage of by the plant, as it underwent further
modification and became a climber. The naked skin on the
head of a vulture is generally considered as a direct adapta-
tion for wallowing in putridity; and so it may be, or it may
possibly be due to the direct action of putrid matter; but we
should be very cautious in drawing any such inference, when
we see that the skin on the head of the dean-feeding male
Turkey is likewise naked. The sutures in the skulls of young
mammals have been advanced as a beautiful adaptation for
aiding parturition, and no doubt they facilitate, or may be
indispensable for this act; but as sutures occur in the skulls
of young birds and reptiles, which have only to escape from
a broken egg, we may infer that this structure has arisen
from the laws of growth, and has been taken advantage of in
the parturition of the higher animals.
We are profoundly ignorant of the cause of each slight
variation or individual difference; and we are immediately
made conscious of this by reflecting on the differences be-
tween the breeds of our domesticated animals in different
countries, — ^more especially in the less civilised countries
where there has been but little methodical selection. Animals
kept by savages in different countries often have to struggle
for their own subsistence, and are exposed to a certain extent
to natural selection, and individuals with slightly different
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UnLTTARIAN DOCTRINB «»
constitiitions would succeed best under different climates.
With cattle susceptibility to the attacks of flies is correlated
with colour, as is the liability to be poisoned by certain
plants; so that even colour would be thus subjected to the
action of natural selection. Some observers are convinced
that a damp climate affects the growth of the hair, and that
with the hair the horns are correlated Mountain breeds al-
ways differ from lowland breeds ; and a mountainous country
would probably affect the hind limbs from exercising them
more, and possibly even the form of the pelvis; and then
by the law of homologous variation, the front limbs and th^
head would probably be affected. The shape, also, of the
pelvis might affect by pressure the shape of certain parts of
the young in the womb. The laborious breathing necessary
in high regions tends, as we have good reason to believe,
to increase the size of the chest; and again correlation
would come into play. The effects of lessened exercise to-
gether with abundant food on the whole organisation is
probably still more important ; and this, as H. von Nathusius
has lately shown in his excellent Treatise, is apparently one
chief cause of the g^eat modification which the breed of
swine have undergone. But we are far too ignorant to specu-
late on the relative importance of the several known and un-
known causes of variation; and I have made these remarks
only to show that, if we are unable to account for the char-
acteristic differences of our several domestic breeds, which
nevertheless are generally admitted to have arisen through
ordinary generation from one or a few parent-stocks, we
ought not to lay too much stress on our ignorance of the pre-
cise cause of the slight analogous differences between true
species.
UTILITAEIAN DOCTRINE, HOW PAR TRUE: BEAUTY, HOW
ACQUIRED
The foregoing remarks lead me to say a few words on the
protest lately made by some naturalists, against the utilitarian
doctrine that every detail of structure has been produced for
the good of its possessor. They believe that many structures
have been created for the sake of beauty, to delight man or
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210 ORIGIN OF fiPBClES
the Creator (but this latter point is beyond the scope of
scientific discussion), or for the sake of mere variety, a view
already discussed. Such doctrines, if true, would be abso-
lutely fatal to my theory. I fully admit that many structures
are now of no direct use to their possessors, and may never
have been of any use to their progenitors; but this does not
prove that they were formed solely for beauty or variety.
No doubt the definite action of changed conditions, and the
various causes of modifications, lately specified, have all
produced an effect, probably a g^eat effect, independently of
^ny advantage thus gained. But a still more important con-
sideration is that the chief part of the organisation of every
living creature is due to inheritance; and consequently,
though each being assuredly is well fitted for its place in
nature, many structures have now no very close and direct
relation to present habits of life. Thus, we can hardly be-
lieve that the webbed feet of the upland goose or of the
frigate-bird are of special use to these birds; we cannot be-
lieve that the similar bones in the arm of the monkey, in the
fore-leg of the horse, in the wing of the bat, and in the
flipper of the seal, are of special use to these animals. We
may safely attribute these structures to inheritance. But
webbed feet no doubt were as useful to the progenitor of
the upland goose and of the frigate-bird, as they now are to
the most aquatic of living birds. So we may believe that the
progenitor of the seal did not possess a flipper, but a foot
with five toes fitted for walking or grasping; and we may
further venture to believe that the several bones in the limbs
of the monkey, horse, and bat, were originally developed,
on the principle of utility, probably through the reduction, of
more numerous bones in the fin of some ancient fish-like
progenitor of the whole class. It is scarcely possible to de*
cide how much allowance ought to be made for such causes
of change, as the definite action of external conditions, so-
called spontaneous variations, and the complex laws of
growth; but with these important exceptions, we may con-
clude that the structure of every living creature either now
is, or was formerly, of some direct or indirect use to its
possessor.
With respect to the belief that organic beings have been
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imUTARIAN DOCTRINE 211
created beautiful for the delight of man, — ^a belief which it
has been pronounced is subversive of my whole theory, — I
may first remark that the sense of beauty obviously depends
on the nature of the mind, irrespective of any real quality
in the admired object; and that the idea of what is beautiful,
is not innate or unalterable. We see this, for instance, in
the men of different races admiring an entirely different
standard of beauty in their women. If beautiful objects had
been created solely for man's gratification, it ought to be
shown that before man appeared, there was less beauty on
the face of the earth than since he came on the stage. Wer^
the beautiful volute and cone shells of the Eocene epoch, and
the gracefully sculptured ammonites of the Secondary period,
created that man might ages afterwards admire them in his
cabinet? Few objects are more beautiful than the minute
siliceous cases of the diatomaceae: were these created that
they might be examined and admired tmder the higher
powers of the microscope? The beauty in this latter case,
and in many others, is apparently wholly due to symmetry of
growth. Flowers rank amongst the most beautiful produc-
tions of nature; but they have been rendered conspfcuous in
contact with the green leaves, and in consequence at the
same time beautiful, so that they may be easily observed by
insects. I have come to this conclusion from finding it an
invariable rule that when a flower is fertilised by the wind
it never has a gaily-coloured corolla. Several plants habitu-
ally produce two kinds of flowers; one kind open and col-
oured so as to attract insects; the other closed, not coloured,
destitute of nectar, and never visited by insects. Hence we
may conclude that, if insects had not been developed on the
face of the earth, our plants would not have been decked with
beautiful flowers, but would have produced only such poor
flowers as we see on our fir, oak, nut and ash trees, on
grasses, spinach, docks, and nettles, which are all fertilised
through the agency of the wind. A similar line of argument
holds good with fruits; that a ripe strawberry or cherry
is as pleasing to the eye as to the palate — ^that the gaily-
coloured fruit of the spindle-wood tree and the scarlet ber-
ries of the holly are beautiful objects, — ^will be admitted by
every one. But this beauty serves merely as a guide to birds
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212 ORIGIN OF SPECIES
and beasts, in order that the fruit may be devoured and the
manured seeds disseminated: I infer that this is the case
from having as yet found no exception to the rule that seeds
are always thus disseminated when embedded within a fruit
of any kind (that is within a fleshy or pulpy envelope), if it
be coloured of any brilliant tint, or rendered conspicuous by
being white or black.
On the other hand, I willingly admit that a great number
of male animals, as all our most gorgeous birds, some fishes,
reptiles, and mammals, and a host of magnificently coloured
butterflies, have been rendered beautiful for beauty's sake;
but this has been effected through sexual selection, that is, by
the more beautiful males having been continually preferred
by the females, and not for the delight of man. So it is with
the music of birds. We may infer from all this that a nearly
similar taste for beautiful colours and for musical sounds
runs through a large part of the animal kingdom. When
the female is as beautifully coloured as the male, which is
not rarely the case with birds and butterflies, the cause ap-
parently lies in the colours acquired through sexual selection
having been transmitted to both sexes, instead of to the
males alone. How the sense of beauty in its simplest form —
that is, the reception of a peculiar kind of pleasure from
certain colours, forms, and sounds — ^was first developed in
the mind of man and of the lower animals, is a very obscure
subject. The same sort of difficulty is presented, if we en-
quire how it is that certain flavours and odours give pleasure,
and others displeasure. Habit in all these cases appears to
have come to a certain extent into play; but there must be
some fundamental cause in the constitution of the nervous
system in each species.
Natural selection cannot possibly produce any modifica-
tion in a species exclusively for the good of another species ;
though throughout nature one species incessantly takes ad-
vantage of, and profits by, the structures of others. But
natural selection can and does often produce structures for
the direct injury of other animals, as we see in the fang of
the adder, and in the ovipositor of the ichneumon, by which
its eggs are deposited in the living bodies of other insects.
If it could be proved that any part of the structure of any
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uhlttarian doctrine 213
one species had been formed for the exclusive good of an-
other species, it would annihilate my theory, for such could
not have been produced through natural selection. Although
many statements may be fotmd in works on natural history
to this effect, I cannot find even one which seems to me of
any weight. It is admitted that the rattlesnake has a poison-
fang for its own defence, and for the destruction of its prey;
but some authors suppose that at the same time it is furnished
with a rattle for its own injury, namely, to warn its prey.
I would almost as soon believe that the cat curls the end
of its tail when preparing to spring, in order to warn the
doomed mouse. It is a much more probable view that the
rattlesnake uses its rattle, the cobra expands its frill, and
the puflf-adder swells whilst hissing so loudly and harshly,
in order to alarm the many birds and beasts which are known
to attack even the most venomous species. Snakes act on the
same principle which makes the hen ruffle her feathers and
expand her wings when a dog approaches her chickens; but
I have not space here to enlarge on the many ways by which
animals endeavour to frighten away their enemies.
Natural selection will never produce in a being any struc-
ture more injurious than beneficial to that being, for natural
selection acts solely by and for the good of each. No organ
will be formed, as Paley has remarked, for the purpose of
causing pain or for doing an injury to its possessor. If a fair
balance be struck between the good and evil caused by each
part, each will be found on the whole advantageous. After
the lapse of time, under changing conditions of life, if any
part comes to be injurious, it will be modified ; or if it be not
so, the being will become extinct as myriads have become
extinct.
Natural selection tends only to make each organic being
as perfect as, or slightly more perfect than, the other inhabi-
tants of the same country with which it comes into competi-
tion. And we see that this is the standard of perfection
attained under nature. The endemic productions of New Zea-
land, for instance, are perfect one compared with another;
but they are now rapidly yielding before the advancing le-
gions of plants and animals introduced from Europe. Natural
selection will not produce absolute perfection, nor do we
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214 ORIGIN OF SPEaES
always meet, as far as we can judge, with this high standard
tinder nature. The correction for the aberration of light
is said by Mtiller not to be perfect even in that most perfect
organ, the human eye. Helmholtz, whose judgment no one
will dispute, after describing in the strongest terms the won-
derful power of the human eye, adds these remarkable
words: "That which we have discovered in the way of in-
exactness and imperfection in the optical machine and in
the image on the retina, is as nothing in comparison with
the incongruities which we have just come across in the
domain of the sensations. One might say that nature has
taken delight in accumulating contradictions in order to re-
move all foundations from the theory of a pre-existing har-
mony between the external and internal worlds." If our
reason leads us to admire with enthusiasm a multitude of
inimitable contrivances in nature,- this same reason tells us,
though we may easily err on both sides, that some other con-
trivances are less perfect. Can we consider the sting of the
bee as perfect, which, when used against many kinds of
enemies, cannot be withdrawn, owing to the backward serra-
tures, and thus inevitably causes the death of the insect by
tearing out its viscera?
If we look at the sting of the bee, as having existed in a
remote progenitor, as a boring and serrated instrument, like
that in so many members of the same great order, and that
it has since been modified, but not perfected for its present
purpose, with the poison originally adapted for some other
object, such as to produce galls, since intensified, we can per-
haps understand how it is that the use of the sting should so
often cause the insect's own death: for if on the whole the
power of stinging be useful to the social community, it will
fulfil all the requirements of natural selection, though it
may cause the death of some few members. If we admire
the truly wonderful power of scent by which the males of
many insects find their females, can we admire the produc-
tion for this single purpose of thousands of drones, which
are utterly useless to the community for any other purpose,
and which are ultimately slaughtered by their industrious and
sterile sisters? It may be difficult, but we ought to admire
the savage instinctive hatred of the queen-bee, which urges
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SUMMARY tli
her to destroy the yoting queens, her daughters, as soon as
they are bom, or to perish herself in the combat: for un-
doubtedly this is for the good of the community ; and mater-
nal love or maternal hatred, though the latter fortunately is
most rare, is all the same to the inexorable principle of
natural selection. If we admire the several ingenious contri-
vances, by which orchids and many other plants are fertilised
through insect agency, can we consider as equally perfect
the elaboration of dense clouds of pollen by our fir-trees, so
that a few granules may be wafted by chance on to the ovules ?
summary: the law op unity of type and of the
conditions of existence embraced by the
theory of natural selection
We have in this chapter discussed some of the difficulties
and objections which may be urged against the theory.
Many of them are serious; but I think that in the discussion
light has been thrown on several facts, which on the belief
of independent acts of creation are utterly obscure. We have
seen that species at any one period are not indefinitely vari-
able, and are not linked together by a multitude of interme-
diate gradations, partly because the process of natural selec-
tion is always very slow, and at any one time acts only on a
few forms; and partly because the very process of natural
selection implies the continual supplanting and extinction
of preceding and intermediate gradations. Qosely allied
species, now living on a continuous area, must often have
been formed when the area was not continuous, and when the
conditions of life did not insensibly graduate away from one
part to another. When two varieties are formed in two dis-
tricts of a continuous area, an intermediate variety will often
be formed, fitted for an intermediate zone; but from
reasons assigned, the intermediate variety will usually exist
in lesser numbers than the two forms which it connects ; con-
sequently the two latter, during the course of further modi-
fication, from existing in greater numbers, will have a great
advantage over the less numerous intermediate variety, and
will thus generally succeed in supplanting and extermi-
nating it
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ae ORIGIN OF SPECIES
We have seen in this chapter how cautious we should be
in concluding that the most different habits of life could not
graduate into each other; that a bat, for instance, could not
have been formed by natural selection from an animal which
at first only glided through the air.
We have seen that a species under new conditions of life
may change its habits; or it may have diversified habits, with
some very unlike those of its nearest congeners. Hence we
can understand, bearing in mind that each orgastic being is
trying to live wherever it can live, how it has arisen that
there are upland geese with webbed feet, ground woodpeck-
ers, diving thrushes, and petrels with the habits of auks.
Although the belief that an organ so perfect as the eye
could have been formed by natural selection, is enough to
stagger any one ; yet in the case of any organ, if we know of
a long series of gradations in complexity, each good for its
possessor, then, under changing conditions of life, there is
no logical impossibility in the acquirement of any conceivable
degree of perfection through natural selection. In the cases
in which we know of no intermediate or transitional states,
we should be extremely cautious in concluding that none can
have existed, for the metamorphoses of many organs show
what wonderful changes in function are at least possible.
For instance, a swimbladder has apparently been converted
into an air-breathing lung. The same organ having per-
formed simultaneously very different functions, and then
having been in part or in whole specialised for one function ;
and two distinct organs having performed at the same time
the same function, the one having been perfected whilst aided
by the other, must often have largely facilitated transitions.
We have seen that in two beings widely remote from each
other in the natural scale, organs serving for the same pur-
pose and in external appearance closely similar may have
been separately and independently formed; but when such
organs are closely examined, essential differences in their
structure can almost always be detected; and this naturally
follows from the principle of natural selection. On the
other hand, the common rule throughout nature is infinite
diversity of structure for gaining the same end; and this
again naturally follows from the same great principle.
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SUMMARY 217
In many cases we are far too ignorant to be enabled to
assert that a part or organ is so unimportant for the welfare
of a species, that modifications in its structure could not
have been slowly accumulated by means of natural selection.
In many other cases, modifications are probably the direct
result of the laws of variation or of growth, independently
of any good having been thus gained. But even such struc-
tures have often, as we may feel assured, been subsequently
taken advantage of, and still further modified, for the good
of species under new conditions of life. We may, also, be-
lieve that a part formerly of high importance has frequently
been retained (as the tail of an aquatic animal by its terres-
trial descendants), though it has become of such small im-
portance that it could not, in its present state, have been
acquired by means of natural selection.
Natural selection can produce nothing in one species for
the exclusive good or injury of another ; though it may well
produce parts, organs, and excretions highly useful or even
indispensable, or again highly injurious to another species,
but in all cases at the same time useful to the possessor. In
each well-stocked country natural selection acts through the
competition of the inhabitants, and consequently leads to suc-
cess in the battle for life, only in accordance with the
standard of that particular country. Hence the inhabitants
of one country, generally the smaller one, often yield to the
inhabitants of another and generally the larger country.
For in the larger country there will have existed more indi-
viduals and more diversified forms, and the competition will
have been severer, and thus the standard of perfection will
have been rendered higher. Natural selection will not neces-
sarily lead to absolute perfection ; nor, as far as we can judge
by our limited faculties, can absolute perfection be every-
where predicated.
On the theory of natural selection we can clearly under-
stand the full meaning of that old canon in natural history,
"Natura non facit saltum." This canon, if we look to the
present inhabitants alone of the world, is not strictly cor-
rect ; but if we include all those of past times, whether known
or unknown, it must on this theory be strictly true.
It is generally acknowledged that all organic beings have
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218 ORIGIN OF SPEaBS
been formed on two great lawd — ^Unity of Type, and the
Conditions of Existence. By unity of type is meant that
fmidamental agreement in stntcttire which we see in organic
beings of the same class, and which is quite independent of
their habits of life. On my theory, unity of type is explained
by unity of descent. The expression of conditions of exist-
ence, so often insisted on by the illustrious Cuvier, is fully
embraced by the principle of natural selection. For natural
selection acts by either now adapting the varying parts of
each being to its organic and inorganic conditions of life;
or by having adapted them during past periods of time: the
adaptations being aided in many cases by the increased use
or disuse of parts, being affected by the direct action of the
external conditions of life, and subjected in all cases to the
several laws of growth and variation. Hence, in fact, the
law of the Conditions of Existence is the higher law; as it
includes, through the inheritance of former variations and
adaptations, that of Unity of Type.
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CHAPTER VII
Miscellaneous Objections to* the Theory op. Natural
Selection
Longevity — Modifications not necessarily simultaneous — ^Modifications
apparently of no direct service — Progressive development —
Characters of small functional importance, the most constant —
Supposed incompetence of natural selection to account for the
incipient stages of useful structures — Causes which interfere with
the acquisition through natural selection of useful structures —
Gradations of structure with changed ftmctions — Widely different
organs in members of the same class, developed from one and
the same source — Reasons for disbelieving in great and abrupt
modifications.
I WILL devote this chapter to the consideration of various
miscellaneous objections which have been advanced
against my views, as some of the previous discus-
sions may thus be made clearer; but it would be useless
to discuss all of them, as many have been made by writers
who have not taken the trouble to understand the subject
.Thus a distinguished German naturalist has asserted that
the weakest part of my theory is, that I consider all organic
beings as imperfect: what I have really said is, that all are
not as perfect as they might have been in relation to their
conditions; and this is shown to be the case by so many
native forms in many quarters of the world having yielded
their places to intruding foreigners. Nor can organic beings,
even if they were at any one time perfectly adapted to their
conditions of life, have remained so, when their conditions
changed, unless they themselves likewise changed*^ and no
one will dispute that the physical conditions of each country,
as well as the numbers and kinds of its inhabitants, have
undergone many mutations.
A critic has lately insisted, with some parade of mathe-
matical accuracy, that longevity is a great advantage to all
species, so that he who believes in natural selection ^'must
219
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220 ORIGIN OF SPECIES
arrange his genealogical tree'' in such a manner that all the
descendants have longer lives than their progenitors! Can-
^not our critic conceive that a biennial plant or one of the
lower animals might range into a cold climate and perish
there every winter; and yet, owing to advantages gained
through natural selection, survive from year to year, by
means of its seeds or oval^ Mr. £. Ray Lankester has re-
cently discussed this subject, and he concludes, as far as its
extreme complexity allows him to form a judgment, that
longevity is generally related to the standard of each species
in the scale of organisation, as well as to the amount of ex-
penditure in reproduction and in general activity. And these
conditions have, it is probable, been largely determined
through natural selection.
It has been argued that, as none of the animals and plants
of Egypt, of which we know anything, have changed during
the last three or four thousand years, so probably have none
in any part of the world. But, as Mr. G. H. Lewes has re-
marked, this line of argument proves too much, for the
ancient domestic races figured on the Egyptian monuments,
or embalmed, are closely similar or even identical with those
now living; yet all naturalists admit that such races have
been produced through the modification of their original
types. The many animals which have remained unchanged
since the commencement of the glacial period, would have
been an incomparably stronger case, for these have been
exposed to great changes of climate and have migrated over
great distances; whereas, in Egypt, during the last several
thousand years, the conditions of life, as far as we know, have
remained absolutely uniform. The fact of little or no modifi-
cation having been effected since the glacial period would have
been of some avail against those who believe in an innate and
necessary law of development, but is powerless against the
doctrine of natural selection or the survival of the fittest,
which implies that when variations or individual differences
of a beneficial nature happen to arise, these will be preserved;
but this will be effected only under certain favourable cir-
cumstances.
The celebrated palaeontologist, Bronn, at the close of his
German translation of this work, asks, how, on the principle
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THEORY OP NATURAL SELECTION 221
of natural selection, can a variety live side by side with the
parent species? If both have become fitted for slightly dif-
ferent habits of life or conditions, they might live together;
and if we lay on one side polymorphic species, in which thft
variability seems to be of a peculiar nature, and all mere
temporary variations, such as size, albinism, &c., the more
permanent varieties are generally found, as far as I can
discover, inhabiting distinct stations, — such as high land or
low land, dry or moist districts. Moreover, in the case of
animals which wander much about and cross freely, their
varieties seem to be generally confined to distinct regions.
Bronn also insists that distinct species never differ from
each other in single characters, but in many parts; and he
asks, how it always comes that many parts of the organisa-
tion should have been modified at the same time through
variation and natural selection? But there is no necessity
for supposing that all the parts of any being have been
simultaneously modified. The most striking modifications,
excellently adapted for some purpose, might, as was formerly
remarked, be acquired by successive variations, if slight,
first in one part and then in another; and as they would be
transmitted all together, they would appear to us as if they
had been simultaneously develc^ed. The best answer, how-
ever, to the above objection is afforded by those domestic
races which have been modified, chiefly through man's power
of selection, for some special purpose. Look at the race
and dray horse, or at the grey-hound and mastiff. Their
whole frames and even their mental characteristics have been
modified; but if we could trace each step in the history of
their transformation, — and the latter steps can be traced, —
we should not see great and simultaneous changes, but first
one part and then another slightly modified and improved.
Even when selection has been applied by man to some one
character alone, — of which our cultivated plants offer the
best instances, — it will invariably be found that although
this one part, whether it be the flower, fruit, or leaves, has
been greatly changed, almost all the other parts have been
slightly modified. This may be attributed partly to the prin-
ciple of correlated growth, and partly to so-called spon-
taneous variation.
N— HCXI
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222 ORIGIN OF SPECIES
A much more serious objection has been urged by Bronn,
and recently by Broca, namely, that many characters appear
to be of no service whatever to their possessors, and therefore
cannot have been influenced through natural selection.
Bronn adduces the length of the ears and tails in the dif-
ferent species of hares and mice, — the complex folds of
enamel in the teeth of many animals, and a multitude of
analogous cases. With respect to plants, this subject has
been discussed by Nageli in an admirable essay. He admits
that natural selection has effected much, but he insists that
the families of plants differ chiefly from each other in mor-
phological characters, which appear to be quite unimportant
for the welfare of the species. He consequently believes in
an innate tendency towards progressive and more perfect
development. He specifies the arrangement of the cells in
the tissues, and of the leaves on the axis, as cases in which
natural selection could not have acted. To these may be
added the numerical divisions in the parts of the flower, the
position of the ovules, the shape of the seed, when not of any
use for dissemination, &c.
There is much force in the above objection. Nevertheless,
we ought, in the first place, to be extremely cautious in
pretending to decide what structures now are, or have for-
merly been, of use to each species. In the second place, it
should always be borne in mind that when one part is modi-
fied, so will be other parts, through certain dimly seen causes,
such as an increased or diminished flow of nutriment to a
part, mutual pressure, an early developed part affecting one
subsequently developed, and so forth, — as well as through
other causes which lead to the many mysterious cases of
correlation, which we do not in the least understand. These
agencies may be all grouped together, for the sake of brevity,
under the expression of the laws of growth. In the third
place, we have to allow for the direct and definite action of
changed conditions of life, and for so-called spontaneous
variations, in which the nature of the conditions apparently
plays a quite subordinate part. Bud-variations, such as the
appearance of a moss-rose on a common rose, or of a nec-
tarine on a peach-tree, offer good instances of spontaneous
variations; but even in these cases, if we bear in mind the
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THEORY OF NATURAL SELECTION 223
power of a minute drop of poison in producing complex galls,
we ought not to feel too sure that the above variations are
not the effect of some local change in the nature of the sap,
due to some change in the conditions. There must be some
efficient cause for each slight individual difference, as well
as for more strongly marked variations which occasionally
arise; and if the unknown cause were to act persistently, it
is almost certain that all the individuals of the species would
be similarly modified.
In the earlier editions of this work I under-rated, as it now
seems probable, the frequency and importance of modifica-
tions due to spontaneous variability. But it is impossible to
attribute to this cause the innumerable structures which are
so well adapted to the habits of life of each species. I can
no more believe in this, than that the well-adapted form of a
race-horse or greyhound, which before the principle of selec-
tion by man was well understood, excited so much surprise in
the minds of the older naturalists, can thus be explained.
It may be worth while to illustrate some of the foregoing
remarks. With respect to the assumed inutility of various
parts and organs, it is hardly necessary to observe that even
in the higher and best-known animals many structures exist,
which are so highly developed that no one doubts that they
are of importance, yet their use has not been, or has only
recently been, ascertained. As Bronn gives the length of
the ears and tail in the several species of mice as instances,
though trifling ones, of differences in structure which can
be of no special use, I may mention that, according to Dr.
Schobl, the external ears of the common mouse are supplied
in an extraordinary manner with nerves, so that they no
doubt serve as tactile organs; hence the length of the ears
can hardly be quite unimportant We shall, also, presently
see that the tail is a highly useful prehensile organ to some
of the species ; and its use would be much influenced by its
length.
With respect to plants, to which on account of Nageli's
essay I shall confine myself in the following remarks, it will
be admitted that the flowers of orchids present a multitude of
curious structures, which a few years ago would have been
considered as mere morphological differences without any
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224 0BI6IN OP SFECTBS
special function ; but they are now known to be of the highest
importance for the fertilisation of the species through the
aid of insects, and have probably been gained through natural
selection. No one until lately would have imagined that in
dimorphic and trimorphic plants the different lengths of the
stamens and pistils, and their arrangement, could have been
of any service, but now we know this to be the case.
In certain whole groups of plants the ovules stand erect,
and in others they are suspended; and within the same
ovarium of some few plants, cme ovule holds the former and
a second ovule the latter position. These positions seem at
first purely morphological, or of no physiological significa-
tion; but Dr. Hooker informs me that within the same
ovarium, the upper ovules alone in some cases, and in other
cases the lower ones alone are fertilised ; and he suggests that
this probably depends on the direction in which the pollen-
tubes enter the ovarium. If so, the position of the ovules,
even when one is erect and the other suspended within the
same ovarium, would follow from the selection of any slight
deviations in position which favoured their fertilisation, and
the production of seed.
Several plants belonging to distinct orders habitually pro-
duce flowers of two kinds, — ^the one open of the ordinary
structure, the other closed and imperfect. These two kinds
of flowers sometimes differ wonderfully in structure, yet may
be seen to graduate into each other on the same plant The
ordinary and open flowers can be intercrossed ; and the bene-
fits which certainly are derived from this process are thus
secured. The closed and imperfect flowers are, however,
manifestly of high importance, as they yield with the utmost
safety a large stock of seed, with the expenditure of won-
derfully little pollen. The two kinds of flowers often differ
much, as just stated, in structure. The petals in the imperfect
flowers almost always consist of mere rudiments, and the
pollen-grains are reduced in diameter. In Ononis columns
five of the alternate stamens are rudimentary; and in some
species of Viola three stamens are in this state, two retaining
their proper function, but being of very small size. In six
out of thirty of the closed flowers in an Indian violet (name
unknown, for the plants have never produced with me per-
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THEORY OF NATURAL SELECTION 225
feet flowers), the sepals are reduced from the normal num-
ber of five to three. In one section of the Malpighiacese the
closed flowers, according to A. de Jussieu, are still further
modified, for the five stamens which stand opposite to the
sepals are all aborted, a sixth stamen standing opposite to
a petal being alone developed; and this stamen is not present
in the ordinary flowers of these species ; the style is aborted ;
and the ovaria are reduced from three to two. Now although
natural selection may well have had the power to prevent
some of the flowers from expanding, and to reduce the amount
of pollen, when rendered by the closure of the flowers super-
fluous, yet hardly any of the above special modifications can
have been thus determined, but must have followed from
the laws of growth, including the functional inactivity of
parts, during the progress of the reduction of the pollen and
the closure of the flowers.
It is so necessary to appreciate the important effects of
the laws of growth, that I will give some additional cases of
another kind, namely of differences in the same part or organ,
due to differences in relative position on the same plant.
In the Spanish chestnut, and in certain fir-trees, the angles of
divergence of the leaves differ, according to Schacht, in
the nearly horizontal and in the upright branches. In the
common rue and some other plants, one flower, usually the
central or terminal one, opens first, and has five sepals and
petals, and five divisions to the ovarium ; whilst all the other
flowers on the plant are tetramerous. In the British Adoxa
the uppermost flower generally has two calyx-lobes with the
other organs tetramerous, whilst the surrounding flowers
generally have three calyx-lobes with the other organs pen-
tamerous. In many Compositse and Umbelliferse (and in
some other plants) the circumferential flowers have their
corollas much more developed than those of the centre;
and this seems often connected with the abortion of the re-
productive organs. It is a more curious fact, previously
referred to, that the achenes or seeds of the circumference
and centre sometimes differ greatly in form, colour, and
other characters. In Carthamus and some other Compositae
the central achenes alone are furnished with a pappus; and
in Hyoseris the same head yields achenes of three different
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226 ORIGIN OP SPECIBS
forms. In certain Umbelli ferae the exterior seeds, according
to Tausch, are orthospermous, and the central one coelosper-
mous, and this is a character which was considered by De
Candolle to be in other species of the highest systematic im-
portance. Prof. Braun mentions a Fumariaceous genus in
which the flowers in the lower part of the spike bear oval,
ribbed, one-seeded nutlets ; and in the upper part of the spike,
lanceolate, two-valved, and two-seeded siliques. In these
several cases, with the exception of that of the well developed
ray-florets, which are of service in making the flowers con-
spicuous to insects, natural selection cannot, as far as we can
judge, have come into play, or only in a quite subordinate
manner. All these modifications follow from the relative
position and inter-action of the parts; and it can hardly be
doubted that if all the flowers and leaves on the same plant
had been subjected to the same external and internal con-
dition, as are the flowers and leaves in certain positions, all
would have been modified in the same manner.
In numerous other cases we find modifications of structure,
which are considered by botanists to be generally of a highly
important nature, affecting only some of the flowers on the
same plant, or occurring on distinct plants, which grow close
together under the same conditions. As these variations
seem of no special use to the plants, they cannot have been
influenced by natural selection. Of their cause we are quite
ignorant; we cannot even attribute them, as in the last class
of cases, to any proximate agency, such as relative position.
I will give only a few instances. It is so common to observe
on the same plant, flowers indifferently tetramerous, pentam-
erous, &c., that I need not give examples ; but as numerical
variations are comparatively rare when the parts are few, I
may mention that, according to De QandoUe, the flowers of
Papaver bracteatum offer either two sepals with four petals
(which is the common type with poppies), or three sepals
with six petals. The manner in which the petals are folded
in the bud is in most groups a very constant morphological
character; but Professor Asa Gray states that with some
species of Mimulus, the aestivation is almost as frequently
that of the Rhinanthideae as of the Antirrhinideae, to which
latter tribe the genus belongs. Aug. St. Hilaire gives the
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THEORY OP NATURAL SELECTION 227
following cases : the genus Zanthoxylon belongs to a division
of the Rutaceae with a single ovary, but in some species
flowers may be found on the same plant, and even in the
same panicle, with either one or two ovaries. In Helian-
themum the capsule has been described as unilocular or
3-locular; and in H. mutabile, "Une lame, plus ou moins
large, s'etend cntre le pericarpe et le placenta." In the
flowers of Saponaria officinalis. Dr. Masters has observed
instances of both marginal and free central placentation.
Lastly, St Hilaire found towards the southern extreme of
the range of Gomphia oleseformis two forms which he did^
not at first doubt were distinct species, but he subsequently
saw them growing on the same bush; and he then adds,
"Voili done dans un meme individu des loges et nn style qui
se rattachent tantot k un axe verticale et tantot i un
gynobase."
We thus see that with plants many morphological changes
may be attributed to the laws of growth and the inter-actlon
of parts, independently of natural selection. But with re-
spect to Nageli's doctrine of an innate tendency towards
perfection or progressive development, can it be said in the
case of these strongly pronounced variations, that the plants
have been caught in the act of progressing towards a higher
state of development? On the contrary, I should infer from
the mere fact of the parts in question differing or varying
greatly on the same plant, that such modifications were of
extremely small importance to the plants themselves, of
whatever importance they may generally be to us for our clas-
sifications. The acquisition of a useless part can hardly be said
to raise an organism in the natural scale ; and in the case of the
imperfect, closed flowers above described, if any new principle
has to be invoked, it must be one of retrogression rather than
of progression; and so it must be with many parasitic and
degraded animals. We are ignorant of the exciting cause of
the above specified modifications; but if the unknown cause
were to act almost uniformly for a length of time, we may
infer that the result would be almost uniform; and in this
case all the individuals of the species would be modified in
the same manner.
From the fact of the above characters being unimportant
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228 ORIGIN OF SPECIBS
for the welfare of the species, any slight rariations which oc-
curred in them would not have been accumulated and aug-
mented through natural selection. A structure which has been
developed through long-continued selection, when it ceases to
be of service to a species, generally becomes variable, as we
see with rudimentary organs; for it will no longer be regu-
lated by this same power of selection. But when, from the
nature of the organism and of the conditions, modifications
have been induced which are unimportant for the welfare of
the species, they may be, and apparently often have been,
transmitted in nearly the same state to numerous, otherwise
modified, descendants. It cannot have been of much impor-
tance to the greater number of mammals, birds, or reptiles,
whether they were clothed with hair, feathers, or scales ; yet
hair has been transmitted to almost all mammals, feathers
to all birds, and scales to all true reptiles. A structure, what-
ever it may be, which is common to many allied forms, is
ranked by us as of high systematic importance, and conse-
quently is often assumed to be of high vital importance to the
species. Thus, as I am inclined to believe, morphological
differences, which we consider as important — such as the ar-
rangement of the leaves, the divisions of the flower or of the
ovarium, the position of the ovules, &c. — ^first appeared in
many cases as fluctuating variations, which sooner or later
became constant through the nature of the organism and of
the surrounding conditions, as well as through the inter-
crossing of distinct individuals, but not through natural selec-
tion; for as these morphological characters do not affect the
welfare of the species, any slight deviations in them could
not have been governed or accumulated through this latter
agency. It is a strange result which we thus arrive at,
namely that characters of slight vital importance to the spe-
cies, are the most important to the systematist; but, as we
shall hereafter see when we treat of the genetic principle of
classification, this is by no means so paradoxical as it may
at first appear.
Although we have no good evidence of the existence in
organic beings of an innate tendency towards progressive
development, yet this necessarily follows, as I have attempted
to show in the fourth chapter, through the continued action
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THEORY OP NATURAL SELECTION 229
of natural selection. For the best definition which has ever
been given of a high standard of organisation is the degree
to which the parts have been specialised or differentiated;
and natural selection tends towards this end, inasmuch as
the parts are thus enabled to perform their functions more
efficiently.
A distinguished zoologist, Mr. St. George Mivart, has
recently collected all the objections which have ever been
advanced by myself and others against the theory of natural
selection, as propounded by Mr. Wallace and myself, and has
illustrated them with admirable art and force. When thus
marshalled, they make a formidable array; and as it forms
no part of Mr. Mivart's plan to give the various facts and
considerations opposed to his conclusions, no slight effort
of reason and memory is left to the reader, who may wish
to weigh the evidence on both sides. When discussing special
cases, Mr. Mivart passes over the effects of the increased
use and disuse of parts, which I have always maintained to
be highly important, and have treated in my 'Variation under
Domestication' at greater length than, as I believe, any other
writer. He likewise often assumes that I attribute nothing
to variation, independently of natural selection, whereas in
the work just referred to I have collected a greater number of
well-established cases than can be found in any other work
known to me. My judgment may not be trustworthy, but
after reading with care Mr. Mivart's book, and comparing
each section with what I have said on the same head, I never
before felt so strongly convinced of the general truth of the
conclusions here arrived at, subject, of course, in so intricate
a subject, to much partial error.
All Mr. Mivart's objections will be, or have been, con-
sidered in the present volume. The one new point which
appears to have struck many readers is, **that natural selec-
tion is incompetent to account for the incipient stages of
useful structures." This subject is intimately connected with
that oi the gradation of characters, often accompanied by
a change of function, — for instance, the conversion of a
swim-bladder into lungs, — points which were discussed in the
last chapter under two headings. Nevertheless, I will here
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290 ORIGIN OF SPEaSS
consider in some detail several of the cases advanced by Mr.
Mivart, selecting those which are the most illustrative, as
want of space prevents me from considering all.
The giraffe, by its lofty stature, much elongated neck,
fore legs, head and tongue, has its whole frame beautifully
adapted for browsing on the higher branches of trees. It can
thus obtain food beyond the reach of the other Ungulata or
hoofed animals inhabiting the same country; and this must
be a great advantage to it during dearths. The Niata cattle
in S. America show us how small a difference in structure
may make, during such periods, a great difference in preserv-
ing an animal's life. These cattle can brovrse as well as
others on grass, but from the projection of the lower jaw
they cannot, during the often recurrent droughts, browse on
the twigs of trees, reeds, &c., to which food the common
cattle and horses are then driven ; so that at these times the
Niatas perish, if not fed by their owners. Before coming
to Mr. Mivart's objections, it may be well to explain once
again how natural selection will act in all ordinary cases.
Man has modified some of his animals, without necessarily
having attended to special points of structure, by simply pre-
serving and breeding from the fleetest individuals, as with
the race-horse and greyhound^ or as with the game-cock, by
breeding from the victorious birds. So under nature with
the nascent giraffe, the individuals which were the highest
browsers and were able during dearths to reach even an inch
or two above the others, will often have been preserved;
for they will have roamed over the whole country in search
of food. That the individuals of the same species often
differ slightly in the relative lengths of all their parts may
be seen in many works of natural history, in which careful
measurements are given. These slight proportional differ-
ences, due to the laws of growth and variation, are not of the
slightest use or importance to most species. But it will have
been otherwise with the nascent giraffe, considering its prob-
able habits of life ; for those individuals which had some one
part or several parts of their bodies rather more elongated
than usual, would generally have survived. These will have
intercrossed and left offspring, either inheriting the same
bodily peculiarities, or with a tendency to vary again in the
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THEORY OF NATURAL SBLECTION 2S1
same manner; whilst the individuals, less favoured in the
same respects, will have been the most liable to perish.
We here see that there is no need to separate single pairs,
as man does, when he methodically improves a breed ; natural
selection will preserve and thus separate all the superior
individuals, allowing them freely to intercross, and will de-
stroy all the inferior individuals. By this process long-
continued, which exactly corresponds with what I have called
unconscious selection by man, combined no doubt in a most
important manner with the inherited effects of the increased
use of parts, it seems to me almost certain that an ordinary
hoofed quadruped might be converted into a giraffe.
To this conclusion Mr. Mivart brings forward two objec-
tions. One is that the increased size of the body would
obviously require an increased supply of food, and he con-
siders it as "very problematical whether the disadvantages
thence arising would not, in times of scarcity, more than
counterbalance the advantages." But as the giraffe does
actually exist in large numbers in S. Africa, and as some of
the largest antelopes in the world, taller than an ox, abound
there, why should we doubt that, as far as size is concerned,
intermediate gradations could formerly have existed there,
subjected as now to severe dearths? Assuredly the being
able to reach, at each stage of increased size, to a supply of
food, left untouched by the other hoofed quadrupeds of the
country, would have been of some advantage to the nascent
giraffe. Nor must we overlook the fact, that increased bulk
would act as a protection against almost all beasts of prey
excepting the lion; and against this animal, its tall neck, —
and the taller the better, — ^would, as Mr. Chauncey Wright
has remarked, serve as a watch-tower. It is from this cause,
as Sir S. Baker remarks, that no animal is more difficult to
stalk than the giraffe. This animal also uses its long neck
as a means of offence or defence, by violently swinging its
head armed with stump-like horns. The preservation of
each species can rarely be determined by any one advantage
but by the union of all, great and small.
Mr. Mivart then asks (and this is his second objection),
if natural selection be so potent, and if high browsing be so
great an advantage, why has not any other hoofed quadruped
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2d2 ORIGIN OF SPECIES
acquired a long neck and lofty stature, besides the giraffe,
and, in lesser degree, the camel, guanaco, and macrauchenia?
Or, again, why has not any member of the group acquired a
long proboscis? With respect to S. Africa, which was for-
merly inhabited by numerous herds of the giraffe, the answer
is not difficult, and can best be given by an illustration. In
every meadow in England in which trees grow, we see the
lower branches trimmed or planed to an exact level by the
browsing of the horses or cattle ; and what advantage would
it be, for instance, to sheep, if kept there, to acquire slightly
longer necks? In every district some one kind of animal
will almost certainly be able to browse higher than the
others; and it is almost equally certain that this one kind
alone could have its neck elongated for this purpose, through
natural selection and the effects of increased use. In S.
Africa the competition for browsing on the higher branches
of the acacias and other trees must be between giraffe and
giraffe, and not with the other utigulate animals.
Why, in other quarters of the world, various animals be-
longing to this same order have not acquired either an
elongated neck or a proboscis, cannot be distinctly answered;
but it is as unreasonable to expect a distinct answer to such
a question, as why some event in the history of mankind did
not occur in one country, whilst it did in another. We are
ignorant with respect to the conditions which determine the
numbers and range of each species ; and we cannot even con-
jecture what changes of structure would be favourable to
its increase in some new country. We can, however, see in a
general manner that various causes might have interfered
with the development of a long neck or proboscis. To reach
the foliage of a considerable height (without climbing, for
which hoofed animals are singularly ill-constructed) implies
greatly increased bulk of body ; and we know that some areas
support singularly few large quadrupeds, for instance S.
America, though it is so luxuriant ; whilst S. Africa abounds
with them to an uilparalleled degree. Why this should be
so, we do not know ; nor why the later tertiary periods should
have been much more favourable for their existence than the
present time. Whatever the causes may have been, we can
see that certain districts and times would have been much
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THEORY OF NATURAL SELECTION 253
more favourable than others for the development of so large
a quadruped as the giraffe.
In order that an animal should acquire some structure
specially and largely developed, it is almost indispensable
that several other parts should be modified and co-adapted.
Although every part of the body varies slightly, it does not
follow that the necessary parts should always vary in the
right direction and to the right degree. With the different
species of our domesticated animals we know that the parts
vary in a different manner and degree ; and that some species
are much more variable than others. Even if the fitting vari-
ations did arise, it does not follow that natural selection
would be able to act on them, and produce a structure which
apparently would be beneficial to the species. For instance,
if the number of individuals existing in a country is deter-
mined chiefly through destruction by beasts of prey, — ^by ex-
ternal or internal parasites, etc., — ^as seems often to be the
case, then natural selection will be able to do little, or will be
greatly retarded, in modifying any particular structure for ob-
taining food. Lastly, natural selection is a slow process, and
the same favourable conditions must long endure in order
that any marked effect should thus be produced. Except by
assigning such general and vague reasons, we cannot explain
why, in many quarters of the world, hoofed quadrupeds have
not acquired much elongated necks or other means for brows-
ing on the higher branches of trees.
Objections of the same nature as the foregoing have been
advanced by many writers. In each case various causes, be-
sides the general ones just indicated, have probably inter-
fered with the acquisition through natural selection of struc-
tures, which it is thought would be beneficial to certain
species. One writer asks, why has not the ostrich acquired
the power of flight? But a moment's reflection will show
what an enormous supply of food would be necessary to give
to this bird of the desert force to move its huge body through
the air. Oceanic islands are inhabited by bats and seals, but
by no terrestrial mammals; yet as some of these bats are
peculiar species, they must have long inhabited their present
homes. Therefore Sir C. Lyell asks, and assigns certain rea-
sons in answer, why have not seals and bats given birth on
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234 ORIGIN OP SPEaSS
such islands to forms fitted to live on the land? But seals
would necessarily be first converted into terrestrial carnivor-
ous animals of considerable size, and bats into terrestrial
insectivorous animals; for the former there would be no
prey; for the bats ground-insects would serve as food, but
these would already be largely preyed on by the reptiles or
birds, which first colonise and abound on most oceanic islands.
Gradations of structure, with each stage beneficial to a chang-
ing species, will be favoured only under certain peculiar con-
ditions. A strictly terrestrial animal, by occasionally hunting
for food in shallow water, then in streams or lakes, might at
last be converted into an animal so thoroughly aquatic as to
brave the open ocean. But seals would not find on oceanic
islands the conditions favourable to their gradual reconver-
sion into a terrestrial form. Bats, as formerly shown, prot>-
ably acquired their wings by at first gliding through the air
from tree to tree, like the so-called flying squirrels, for the
sake of escaping from their enemies, or for avoiding falls;
but when the power of true flight had once been acquired, it
would never be reconverted back, at least for the above pur-
poses, into the less eflicient power of gliding throu^ the air.
Bats might, indeed, like many birds, have had their wings
greatly reduced in size, or completely lost, through disuse;
but in this case it would be necessary that they should first
have acquired the power of running quickly on the ground,
by the aid of their hind legs alone, so as to compete with
birds or other ground animals ; and for such a change a bat
seems singularly ill-fitted. These conjectural remarks have
been made merely to show that a transition of structure, with
each step beneficial, is a highly complex affair ; and that there
is nothing strange in a transition not having occurred in any
particular case.
Lastly, more than one writer has asked, why have some
animals had their mental powers more highly developed than
others, as such development would be advantageous to all?
Why have not apes acquired the intellectual powers of man ?
Various causes could be assigned; but as lliey are conjec-
tural, and their relative probability cannot be weighed, it
would be useless to give them. A definite answer to the lat-
ter question ought not to be expected, seeing that no one can
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THEORY OF NATURAL SELECTION 235
solve the simpler problem why, of two races of savages, one
has risen higher in the scale of civilisation than the other;
and this apparently implies increased brain-power.
We will return to Mr. Mivart's other objections. Insects
often resemble for the sake of protection various objects, such
as green or decayed leaves, dead twigs, bits of lichen, flowers,
spines, excrement of birds, and living insects ; but to this lat-
ter point I shall hereafter recur. The resemblance is often
wonderfully close, and is not confined to colour, but extends
to form, and even to the manner in which the insects hold
themselves. The caterpillars which project motionless like
dead twigs from the bushes on which they feed, offer an ex-
cellent instance of a resemblance of this kind. The cases of
the imitation of such objects as the excrement of birds, are
rare and exceptional. On this head, Mr. Mivart remarks,
"As, according to Mr. Darwin's theory, there is a constant
tendency to indefinite variation, and as the minute incipient
variations will be in all directions, they must tend to neutral-
ise each other, and at first to form such unstable modifications
that it is difficult, if not impossible, to see how such indefinite
oscillations of infinitesimal beginnings can ever build up a
sufficiently appreciable resemblance to a leaf, bamboo, or other
object, for Natural Selection to seize upon and perpetuate."
But in all the foregoing cases the insects in their original
state no doubt presented some rude and accidental resem-
blance to an object commonly found in the stations frequented
by them. Nor is this at all improbable, considering the al-
most infinite number of surrounding objects and the diver-
sity in form and colour of the hosts of insects which exist
As some rude resemblance is necessary for the first start, we
can understand how it is that the larger and higher animals
do not (with the exception, as far as I know, of one fish")
resemble for the sake of protection special objects, but only
the surface which commonly surrounds them, and this chiefly
in colour. Assuming that an insect originally happened to
resemble in some degree a dead twig or a decayed leaf, and
that it varied slightly in many ways, then all die variations
which rendered the insect at all more like any such object,
and thus favoured its escape, would be preserved, whilst other
variations would be neglected and ultimately lost; or, if they
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236 ORIGIN OP SPECIES
rendered the insect at all less like the imitated object, they
would be eliminated. There would indeed be force in Mr.
Mivart's objection, if we were to attempt to account for the
above resemblances, independently of natural selection,
through mere fluctuating variability; but as the case stands
there is none.
Nor can I see any force in Mr. Mivarfs difficulty with re-
spect to "the last touches of perfection in the mimicry;" as
in the case given by Mr. Wallace, of a walking-stick insect
(Ceroxylus laceratus), which resembles "a stick grown over
by a creeping moss or jungermannia." So close was this
resepiblance, that a native Dyak maintained that the foli-
aceous excrescences were really moss. Insects are preyed on
by birds and other enemies, whose sight is probably sharper
than ours, and every grade in resemblance which aided an
insect to escape notice or detection, would tend towards its
preservation; and the more perfect the resemblance so much
the better for the insect Considering the nature of the dif-
ferences between the species in the group which includes the
above Ceroxylus, there is nothing improbable in this insect
having varied in the irregularities on its surface, and in these
having become more or less green-coloured; for in every
group the characters which differ in the several species are
tht most apt to vary, whilst the generic characters, or those
common to all the species, are the most constant.
The Greenland whale is one of the most wonderful animals
in the world, and the baleen, or whale-bone, one of its great-
est peculiarities. The baleen consists of a row, on* each side,
of the upper jaw, of about 300 plates or laminae, which stand
close together transversely to the longer axis of the mouth.
Within the main row there are some subsidiary rows. The
extremities and inner margins of all the plates are frayed
into stiff bristles, which clothe the whole gigantic palate, and
serve to strain or sift the water, and thus to secure the
minute prey on which these great animals subsist. The
middle and longest lamina in the Greenland whale is ten,
twelve, or even fifteen feet in length; but in the different
species of Cetaceans there are gradations in length; the
middle lamina being in one species, according to Scoresby,
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THEORY OF NATURAL SELECTION 237
four feet, in another three, in another eighteen inches, and in
the Balaenoptera rostrata only about nine inches in length.
The quality of the whale-bone also differs in the different
species.
With respect to the baleen, Mn Mivart remarks that if it
''had once attained such a size and development as to be at
all useful, then its preservation and augmentation within
serviceable limits would be promoted by natural selection
alone. But how to obtain the beginning of such useful de-
velopment?" In answer, it may be asked, why should not
the early progenitors of the whales with baleen have pos-
sessed a mouth constructed something like the lamellated
beak of a duck? Ducks, like whales, subsist by sifting the
mud and water; and the family has sometimes been called
Criblatores, or sifters. I hope that I may not be miscon-
strued into saying that the progenitors of whales did actually
possess mouths lamellated like the beak of a duck. I wish
only to show that this is not incredible, and that the immense
plates of baleen in the Greenland whale might have been
developed from such lamellae by finely graduated steps, each
of service to its possessor.
The beak of a shoveller-duck (Spatula clypeata) is a more
beautiful and complex structure than the mouth of a whale.
The upper mandible is furnished on each side (in the speci-
men examined by me) with a row or comb formed of i88
thin, elastic lamellae, obliquely bevelled so as to be pointed,
and placed transversely to the longer axis of the mouth.
They arise from the palate, and are attached by flexible mem-
brane to the sides of the mandible. Those standing towards
the middle are the longest, being about one-third of an inch
in length, and they project '14 of an inch beneath the edge.
At their bases there is a short subsidiary row of obliquely
transverse lamellae. In these several respects they resemble
the plates of baleen in the mouth of a whale. But towards
the extremity of the beak they differ much, as they pro-
ject inwards, instead of straight downwards. The entire
head of the shoveller, though incomparably less bulky, is
about one-eighteenth of the length of the head of a mod-
erately large Balaenoptera rostrata, in which species the
baleen is only nine inches long; so that if we were to make
O— HC XI
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238 ORIGIN OF SPECIES
the bead of the shoveller as long as that of the Balaenoptera,
the lamellae would be six inches in length, — ^that is, two-thirds
of the length of the baleen in this species of whale. The
lower mandible of the shoveller^luck is furnished with
lamellae of equal length with those above, but finer; and in
being thus furnished it differs conspicuously from the lower
jaw of a whale, which is destitute of baleen. On the other
hand, the extremities of these lower lamellae are frayed into
fine bristly points, so that they thus curiously resemble the
plates of baleen. In the genus Prion, a member of the dis-
tinct family of the Petrels, the upper mandible alone is fur-
nished witli lamellae, which are well developed and project
beneath the margin; so that the beak of this bird resembles
in this respect the mouth of a whale.
From the highly developed structure of the shoveller's
beak we may proceed (as I have learnt from information and
specimens sent to me by Mr. Salvin), without any great
break, as far as fitness for sifting is concerned, through the
beak of the Merganetta armata, and in some respects through
that of the Aix sponsa, to the beak of the common duck.
In this latter species, the lamellae are much coarser than
in the shoveller, and are firmly attached to the sides of the
mandible ; they are only about 50 in number on each side, and
do not project at all beneath the margin. They are square-
topped, and are edged with translucent hardish tissue, as if
for crushing food. The edges of the lower mandible are
crossed by numerous fine ridges, which project very little.
Although the beak is thus very inferior as a sifter to that
of the shoveller, yet this bird, as every one knows, ccMistantly
uses it for this purpose. There are other species, as I hear
from Mr. Salvin, in which the lamellae are considerably less
developed than in the common duck; but I do not know
whether they use their beaks for sifting the water.
Turning to another group of the same family. In the
Egyptian goose (Chenalopex) the beak closely resembles that
of the common duck; but the lamellae are not so numerous,
nor so distinct from each other, nor do they project so much
inwards; yet this goose, as I am informed by Mr. E. Bartlett,
"uses its bill like a duck by throwing the waters out at the
comers." Its chief food, however, is grass, which it crops
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THEORY OF NATURAL SELECTION 239
like the common goose. In this latter bird, the lamellae of the
upper mandible are much coarser than in the common duck,
almost confluent, about 27 in number on each side, and ter-
minating upwards in teeth-like knobs. The palate is also
covered with hard rounded knobs. The edges of the lower
mandible are serrated with teeth much more prominent,
coarser, and sharper than in the duck. The common goose
does not sift the water, but uses its beak exclusively for tear-
ing or cutting herbage, for which purpose it is so well fitted,
that it can crop grass closer than almost any other animal.
There are other species of geese, as I hear from Mr. Bartlett,
in which the lamellae are less developed than in the common
goose.
We thus see that a member of the duck family, with a beak
constructed like that of the common goose and adapted solely
for grazing, or even a member with a beak having less well-
developed lamellae, might be converted by small changes into
a species like the Egyptian goose, — ^this into one like the com-
mon duck, — ^and, lastly, into one like the shoveller, provided
with a beak almost exdusively adapted for sifting the water;
for this bird could hardly use any part of its beak, except
the hooked tip, for seizing or tearing solid food. The beak
of a goose, as I may add, might also be converted by small
changes into one provided with prominent, recurved teeth,
like those of the Merganser (a member of the same family),
serving for the widely different purpose of securing live fish.
Returning to the whales. The Hyperoodon bidens is desti-
tute of true teeth in an efficient condition, but its palate is
roughened, according to Lacepede, with small, unequal, hard
points of hprn. There is, therefore, nothing improbable in
supposing that some early Cetacean form was provided with
similar points of horn on the palate, but rather more regu-
larly placed, and which, like the knobs on the beak of the
goose, aided it in seizing or tearing its food. If so, it will
hardly be denied that the points might have been converted
through variation and natural selection into lamellae as well-
developed as those of the Egyptian goose, in which case they
would have been used both for seizing objects and for sift-
ing the water; then into lamellae like those of the domestic
duck; and so onwards, until they became as well constructed
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240 ORIGIN OF SPEaES
as those of the shoveller, in which case they would have
served exclusively as a sifting apparatus. From this stage,
in which the lamellae would be two-thirds of the length of
the plates of baleen in the Balaenoptera rostrata, gradations,
which may be observed in still-existing Cetaceans, lead us
onwards to the enormous plates of baleen in the Greenland
whale. Nor is there the least reason to doubt that each step
in this scale might have been as serviceable to certain an-
cient Cetaceans, with the functions of the parts slowly chang-
ing during the progress of development, as are the grada-
tions in the beaks of the different existing members of the
duck family. We should bear in mind that each species of
duck is subjected to a severe struggle for existence, and that
the structure of every part of its frame must be weU adapted
to its conditions of life.
The Pleuronectidae, or Flat-fish, are remarkable for their
asymmetrical bodies. They rest on one side, — ^in the greater
number of species on the left, but in some on the right side;
and occasionally reversed adult specimens occur. The lower,
or resting-surface, resembles at first sight the ventral sur-
face of an ordinary fish : it is of a white color, less developed
in many ways than the upper side, with the lateral fins often
of smaller size. But the eyes offer the most remarkable pecu-
liarity; for they are both placed on the upper side of the
head. During early youth, however, they stand opposite to
each other, and the whole body is then symmetrical, with
both sides equally coloured. Soon the eye proper to the
lower side begins to glide slowly round the head to the upper
side; but does not pass right through the skull, as was for-
merly thought to be the case. It is obvious that unless the
lower eye did thus travel round, it could not be used by the
fish whilst lying in its habitual position on one side. The
lower eye would, also, have been liable to be abraded by the
sandy bottom. That the Pleuronectidae are admirably adapted
by their flattened and as3rmmetrical structure for their habits
of life, is manifest from several species, such as soles, floun-
ders, &c, being extremely common. The chief advantaged
thus gained seem to be protection from their enemies, and
facility for feeding on the ground. The different members,
however, of the family present, as Schiodte remarks, "a long
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THEORY OF NATURAL SELECTION M
series of forms exhibiting a gradtial transition from Hippo*
glossus pinguis, which does not in any considerable degree
alter the shape in which it leaves the ovum, to the soles,
which are entirely thrown to one side."
Mr. Mivart has taken up this case, and remarks that a
sudden spontaneous transformation in the position of the
eyes is hardly conceivable, in which I quite agree with him.
He then adds: "if the transit was gradual, then how such
transit of one eye a minute fraction of the journey towards
the other side of the head could benefit the individual is, in-
deed, far from clear. It seems, even, that such an incipient
transformation must rather have been injurious." But he
might have found an answer to this objection in the excel-
lent observations published in 1867 by Malm. The Pleuro-
nectidae, whilst very young and still symmetrical, with their
eyes standing on opposite sides of the head, cannot long re-
tain a vertical position, owing to the excessive depth of their
bodies, the small size of their lateral fins, and to their being
destitute of a swimbladder. Hence soon growing tired, they
fall to the bottom on one side. Whilst thus at rest they often
twist, as Malm observed, the lower eye upwards, to see above
them; and they do this so vigorously that the eye is pressed
hard against the upper part of the orbit. The forehead be-
tween the eyes consequently becomes, as could be plainly
seen, temporarily contracted in breadth. On one occasion
Malm saw a young fish raise and depress the lower eye
through an angular distance of about seventy degrees.
We should remember that the skull at this early age is car-
tilaginous and flexible, so that it readily yields to muscular
action. It is also known with the higher animals, even after
early youth, that the skull yields and is altered in shape, if
the skin or muscles be permanently contracted through dis-
ease or some accident. With long-eared rabbits, if one ear
lops forwards and downwards, its weight drags forward all
the bones of the skull on the same side, of which I have given
a figure. Malm states that the newly hatched young of
perches, salmon, and several other symmetrical fishes, have
the habit of occasionally resting on one side at the bottom;
and he has observed that they often then strain their lower
eyes so as to look upwards; and their skulls are thus ren-
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242 ORIGIN OF SPECIES
dered rather crooked. These fishes, however, are soon able
to hold themselves in a vertical position, and no permanent
effect is thus produced. With the Pleuronectidae, on the
other handy the older they grow the more habitually they
rest on one side, owing to the increasing flatness of their
bodies, and a permanent effect is thus produced on the form
of the head, and on the position of the eyes. Judging from
analogy, the tendency to distortion would no doubt be in-
creased through the principle of inheritance. Schiodte be*
lieves, in opposition to some other naturalists, that the Pleu-
ronectidae are not quite symmetrical even in the embryo ; and
if this be so, we could understand how it is that certain spe«
cies, whilst young, habitually fall over and rest on the left
side, and other species on the right side. Malm adds, in con-
firmation of the above view, that the adult Trachypterus arc-
ticus, which is not a member of the Pleuronectidse, rests on
its left side at the bottom, and swims diagonally through the
water; and in this fish, the two sides of the head are said to
be somewhat dissimilar. Our great authority on Fishes, Dr.
Giinther, concludes his abstract of Malm's paper, by remark-
ing that "the author gives a very simple explanation of the
abnormal condition of the Pleuronectoids."
We thus see that the first stages of the transit of the eye
from one side of the head to the other, which Mr. Mivart
considers would be injurious, may be attributed to the habit,
no doubt beneficial to thie individual and to the species, of
endeavouring to look upwards with both eyes, whilst resting
on one side at the bottom. We may also attribute to the in-
herited effects of use the fact of the mouth in several kinds
of flat-fish being bent towards the lower surface, with the
jaw bones stronger and more effective on this, the eyeless
sicje of the head, than on the other, for the sake, as Dr. Tra-
quair supposes, of feeding with ease on the ground. Disuse,
on the other hand, will account for the less developed con-
dition of the whole inferior half of the body, including the
lateral fins; though Yarrell thinks that the reduced size of
these fins is advantageous to the fish, as "there is so much
less room for their action, than with the larger fins above."
Perhaps the lesser ntunber of teeth in the proportion of four
to seven in the upper halves of the two jaws of the plaice, to
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THEORY OF NATURAL SELECnON 243
twenty-five to thirty in the lower halves, may likewise be
accounted for by disuse. From the colourless state of the
ventral surface of most fishes and of many other animals, we
may reasonably suppose that the absence of colour in flat*
fish on the side, whether it be the right or left, which is
undermost, is due to the exclusion of light. But it cannot
be supposed that the peculiar speckled appearance of the
upper side of the sole, so like the sandy bed of the sea, or
the power in some species, as recently shown by Pouchet, of
changing their colour in accordance with the surrounding
surface, or the presence of bony tubercles on the upper side
of the turbot, are due to the action of the light. Here natural
selection has probably come into play, as well as in adapting
the general shape of the body of these fishes, and many other
peculiarities, to their habits of life. We should keep in mind,
as I have before insisted, that the inherited effects of the
increased use of parts, and perhaps of their disuse, will be
strengthened by natural selection. For all spontaneous varia-
tions in the right direction will thus be preserved; as will
those individuals which inherit in the highest degree the
effects of the increased and beneficial use of any part. How
much to attribute in each particular case to the effects of use,
and how much to natural selection, it seems impossible to
decide.
I may give another instance of a structure which appar-
ently owes its origin exclusively to use or habit. The ex-
tremity of the tail in some American monkeys has been con-
verted into a wonderfully perfect prehensile organ, and
serves as a fifth hand. A reviewer who agrees with Mr.
Mivart in every detail, remarks on this structure: "It is im-
possible to believe that in any number of ages the first slight
incipient tendency to grasp could preserve the lives of the
individuals possessing it, or favour their chance of having
and of rearing offspring." But there is no necessity for any
such belief. Habit, and this almost implies that some benefit
great or small is thus derived, would in all jprobability suffice
for the work. Brehm saw the young of an African monkey
(Cercopithecus) clinging to the under surface of their mother
by their hands, and at the same time they hooked their little
tails round that of their mother. Professor Henslow kept in
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944 ORIGIN OF SPECIES
confinement some harvest mice (Mus messorias) which do
not possess a structurally prehensile tail; but he frequently
observed that they curled their tails round the branches of a
bush placed in the cage, and thus aided themselves in climb-
ing. I have received an analogous account from Dn Gtin*
ther, who has seen a mouse thus suspend itself. If the har-
vest mouse had been more strictly arboreal, it would perhaps
have had its tail rendered structurally prehensile, as is the
case with some members of the same order. Why Cercopi-
thecus, considering its habits whilst young, has not become
thus provided, it would be difficult to say. It is, however,
possible that the long tail of this monkey may be of more
service to it as a balancing organ in making its prodigious
leaps, than as a prehensile organ.
The mammary glands are common to the whole class of
mammals, and are indispensable for their existence; they
must, therefore, have been developed at an extremely remote
period, and we can know nothing positively about their man-
ner of development. Mr. Mivart asks: "Is it conceivable
that the young of any animal was ever saved from destruction
by accidentally sucking a drop of scarcely nutritious fluid
from an accidentally hypertrophied cutaneous gland of its
mother? And even if one was so, what chance was there of
the perpetuation of such a variation?" But the case is not
here put fairly. It is admitted by most evolutionists that
maomnals are descended from a marsupial form; and if so,
the mammary glands will have been at first developed within
the marsupial sack. In the case of the fish (Hippicampus)
the eggs are hatched, and the young are reared for a time,
within a sack of this nature; and an American naturalist,
Mr. Lockwood, believes from what he has seen of the devel-
opment of the young, that they are nourished by a secretion
from the cutaneous glands of the sack. Now with the early
progenitors of mammals, almost before they deserved to be
thus designated, is it not at least possible that the young
might have been similarly nourished? And in this case, the
individuals which secreted a fluid, in some degree or manner
the most nutritious, so as to partake of the nature of milk,
would in the long run have reared a larger number of well-
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THEORY OF NATURAL SELECTION 245
nourished offspring, than would the individuals which se-
creted a poorer fluid ; and thus the cutaneous glands, which
are tiie homologues of the mammary glands, would have been
improved or rendered more effective. It accords with the
widely extended principle of specialisation, that the glands
over a certain space of the sack should have become more
highly developed than the remainder; and they would then
have formed a breast, but at first without a nipple, as we see
in the Ornithorhyncus, at the base of the mammalian series.
Through what agency the glands over a certain space be-
came more highly specialised than the others, I will not pre-
tend to decide, whether in part through compensation of
growth, the effects of use, or of natural selection.
The development of the mammary glands would have been
of no service, and could not have been effected through nat-
ural selection, unless the young at the same time were able
to partake of the secretion. There is no greater difficulty in
understanding how young mammals have instinctively learnt
to suck the breast, than in understanding how unhatched
chickens have learnt to break the egg-shell by tapping against
it with their specially adapted beaks; or how a few hours
after leaving the shell they have learnt to pick up grains of
food. In 6uch cases the most probable solution seems to be,
that the habit was at first acquired by practice at a more ad-
vanced age, and afterwards transmitted to the offspring at an
earlier age. But the young kangaroo is said not to suck,
only to cling to the nipple of its mother, who has the power
of injecting milk into the mouth of her helpless, half-formed
offspring. On this head Mr. Mivart remarks: "Did no spe-
cial provision exist, the young one must infallibly be choked
by the intrusion of the milk into the windpipe. But there is
a special provision. The larynx is so elcmgated that it rises
up into the posterior end of the nasal passage, and is thus
enabled to give free entrance to the air for the lungs, while
the milk passes harmlessly on each side of this elongated
larynx, and so safely attains the gullet behind it." Mr. Mi-
vart then asks how did natural selection remove in the adult
kangaroo (and in most other mammals, on the assumption
that they are descended from a marsupial form), "this at
least perfectly innocent and harmless structure?" It may
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246 ORIGIN OF SPEaES
be suggested in answer that the voice, which is certainly of
high importance to many animals, could hardly have been
used with full force as long as the larynx entered the nasal
passage; and Professor Flower has suggested to me that this
structure would have g^reatly interfered with an animal swal-
lowing solid food.
We will now turn for a short space to the lower divisions
of the animal kingdom. The Echinodermata (star-fishes,
sea-urchins, &c.) are furnished with remarkable organs,
called pedicellariae, which consist, when well developed, of a
tridactyle forceps — ^that is, of one formed of three serrated
arms, neatly fitting together and placed on the summit of a
flexible stem, moved by muscles. These forceps can seize
firmly hold of any object; and Alexander Agassiz has seen
an Echinus or sea-urchin rapidly passing particles of excre-
ment from forceps to forceps down certain lines of its body,
in order that its -shell should not be fouled But there is no
doubt that besides removing dirt of all kinds, they subserve
other functions; and one of these apparently is defence.
With respect to these organs, Mr. Mivart, as on so many
previous occasions, asks : "What would be the utility of the
first rudimentary beginnings of such structures, and how
could such incipient buddings have ever preserved the life of
a single Echinus?" He adds, "not even the sudden develop-
ment of the snapping action could have been beneficial with-
out the freely moveable stalk, nor could the latter have been
efficient without the snapping jaws, yet no minute merely in-
definite variations could simultaneously evolve these complex
co-ordinations of structure ; to deny this seems to do no less
than to affirm a startling paradox." Paradoxical as this may
appear to Mr. Mivart, tridactyle forcepses, immovably fixed
at the base, but capable of a snapping action, certainly exist
on some star-fishes; and this is intelligible if they serve, at
least in part, as a means of defence. Mr. Agassiz, to whose
great kindness I am indebted for much information on the
subject, informs me that there are other star-fishes, in which
one of the three arms of the forceps is reduced to a support
for the other two ; and again, other genera in which the third
arm is completely lost. In Echinoneus, the shell is described
by M. Perrier as bearing two kinds oi pedicellariae, one re-
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THEORY OF NATURAL SELECTION 247
sembling those of Echinus, and the other those of Spatan-
gus; and such cases are always interesting as affording the
means of apparently sudden transitions, through the abortion
of one of die two states of an organ.
With respect to the steps by which these curious organs
have been evolved, Mr. Agassiz infers from his own re-
searches and those of Mtiller, that both in star-fishes and sea-
urchins the pedicellariae must undoubtedly be looked at as
modified spines. This may be inferred from their manner of
development in the individual, as well as from a long and
perfect series of gradations in different species and genera,
from simple granules to ordinary spines, to perfect tridactyle
pedicellariae. The gradation extends even to the manner in
which ordinary spines and the pedicellariae with their sup-
porting calcareous rods are articulated to the shell. In cer-
tain genera of star-fishes, "the very combinations needed to
show that the pedicellariae are only modified branching spines"
may be found. Thus we have fixed spines, with three equi-
distant, serrated, moveable branches, articulated to near their
bases; and higher up, on the same spine, three other move-
able branches. Now when the latter arise from the summit
of a spine they form in fact a rude tridactyle pedicellaria,
and such may be seen on the same spine together with the
three lower branches. In this case the identity in nature be-
tween the arms of the pedicellariae and the moveable branches
of a spine, is unmistakable. It is generally admitted that the or-
dinary spines serve as a protection; and if so, there can be
no reason to doubt that those furnished with serrated and
moveable branches likewise serve for the same purpose; and
they would thus serve still more effectively as soon as by
meeting together they acted as a prehensile or snapping ap-
paratus. Thus every gradation, from an ordinary fixed spine
to a fixed pedicellaria, would be of service.
In certain genera of star-fishes these organs, instead of
being fixed or borne on an immovable support, are placed on
the summit of a flexible and muscular, though short, stem;
and in this case they probably subserve some additional func-
tion besides defence. In the sea-urchins the steps can be fol-
lowed by which a fixed spine becomes articulated to the shell,
and is* thus rendered moveable. I wish I had space here to
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248 ORIGIN OF SPECIES
give a fuller abstract of Mr. Agassiz's interesting observa-
tions on the development of the pedicellariae. All possible
gradations, as he adds, may likewise be found between the
pedicellariae of the star-fishes and the hooks of the Ophiuri-
ans, another group of the Echinodermata; and again between
the pedicellariae of sea-urchins and the anchors of the Holo-
thuriae, also belonging to the same great class.
Certain compound animals, or zoophytes as they have been
termed, namely the Polyzoa, are provided with curious or-
gans called avicularia. These differ much in structure in the
different species. In their most perfect condition, they curi-
ously resemble the head and beak of a vulture in miniature,
seated on a neck and capable of movement, as is likewise the
lower jaw or mandible. In one species observed by me all the
avicularia on the same branch often moved simultaneously
backwards and forwards, with the lower jaw widely open,
through an angle of about 90*, in the course of five seconds;
and their movement caused the whole polyzoary to tremble.
When the jaws are touched with a needle they seize it so
firmly that the branch can thus be shaken.
Mr. Mivart adduces this case, chiefly on account of the
supposed difficulty of organs, namely the avicularia of the
Polyzoa and the pedicellariae of the Echinodermata, which
he considers as ''essentially similar," having been developed
through natural selection in widely distinct divisions of the
animal kingdom. But, as far as structure is concerned, I can
see no similarity between tridactyle pedicellariae and avicu-
laria. The latter resemble somewhat more closely the chelae
or pincers of Crustaceans; and Mr. Mivart might have ad-
duced with equal appropriateness this resemblance as a special
difficulty; or even their resemblance to the head and beak of
a bird. The avicularia are believed by Mr. Busk, Dr. Smitt,
and Dr. Nitsche — ^naturalists who have carefully studied this
group — ^to be homologous with the zooids and their cells
which compose the zoophyte; the moveable lip or lid of the
cell corresponding with the lower and moveable mandible of
the avicularium. Mr. Busk, however, does not know of any
gradations now existing between a zooid and an avicularium.
It is therefore impossible to conjecture by what serviceable
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THEORY OF NATURAL SELECTION 249
gradations the one could have been converted into the other:
but it by no means folloMrs from this that such gradations
have not existed.
As the chelse of Crustaceans resemble in some degree the
avicularia of Polyzoa, both serving as pincers, It may be
worth while to show that with the former a long series of
serviceable gradations still exists. In the first and simplest
stage, the terminal segment of a limb shut down either on
the square summit of the broad penultimate segment or
against one whole side; and is thus enabled to catch hold of
an object ; but the limb still serves as an organ of locomotion.
We next find one comer of the broad penultimate segment
slightly prominent, sometimes furnished with irregular teeth;
and against these the terminal segment shuts down. By an
increase in the size of this projection, with its shape, as well
as that of the terminal segment, slightly modified and im-
proved, the pincers are rendered more and more^ perfect un-
til we have at last an instrument as efficient as the chelx of
a lobster; and all these gradations can be actually traced.
Besides the avicularia, the Polyzoa possess curious organs
called vibracula. These generally consist of long bristles,
capable of movement and easily excited. In one species ex-
amined by me the vibracula were slightly curved and ser-
rated along the outer margin; and all of them on the same
polyzoary often moved simultaneously; so that, acting like
long oars, they swept a branch rapidly across the object-
glass of my microscope. When a branch was placed on its
face, the vibracula became entangled, and they made violent
efforts to free themselves. They are supposed to serve as a
defence, and may be seen, as Mr. Busk remaiks, "to sweep
slowly and carefully over the surface of the polyzoary, re-
moving what might be noxious to the delicate inhabitants of
the cells when their tentacula are protruded." The avicu-
laria, like the vibracula, probably serve for defence, but they
also catch and kill small living animals, which it is believed
are afterwards swept by the currents within reach of the
tentacula of the zooids. Some species are provided with
avicularia and vibracula; some with avicularia alone, and a
few with vibracula alone.
It is not easy to imagine two objects more widely different
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250 ORIGIN OF SPECIES
in appearance than a bristle or vibraculum, and an avicu-
larium like the head of a bird; yet they are almost certainly
homologous and have been developed from the same common
source, namely a zooid with its cell. Hence we can under-
stand how it is that these organs graduate in some cases, as
I am informed by Mr. Busk, into each other. Thus with the
avicularia of several species of Lep;ralia, the moveable
mandible is so much produced and is so like a bristle,
that the presence of the upper or fixed beak alone serves
to determine its avicularian nature. The vibracula may
have been directly developed from the lips of the cells,
without having passed through the avicularian stage; but
it seems more probable that they have passed through this
stage, as during the early stages of the transformation, the
other parts of the cell with the included zooid could hardly
have disappeared at once. In many cases the vibracula have
a grooved support at the base, which seems to represent the
fixed beak; diough this support in some species is quite ab-
sent. This view of the development of the vibracula, if trust-
worthy, is interesting; for supposing that all the species pro-
vided with avicularia had become extinct, no one with the
most vivid imagination would ever have thought that the
vibracula had originally existed as part of an organ, resem-
bling a bird's head or an irregular box or hood. It is inter-
esting to see two such widely different organs developed from
a conunon origin; and as the moveable lip of the cell serves
as a protection to the zooid, there is no difficulty in believing
that all the gradations, by which the lip became converted
first into the lower mandible of an avicularium and then into
an elongated bristle, likewise served as a protection in differ-
ent ways and under different circumstances.
In the vegetable kingdom Mr. Mivart only alludes to two
cases, namely the structure of the flowers of orchids, and the
movements of climbing plants. With respect to the former,
he says, "the explanation of their origin is deemed thoroughly
unsatisfactory — ^utterly insufficient to explain the incipient,
infinitesimal beginnings of structures which are of utility
only when they are considerably developed." As I have
fully treated this subject in another work, I will here give
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THEORY OF NATURAL SELECTION 251
only a few details on one alone of the most striking pecu-
liarities of the flowers of orchids, namely their pollinia. A
pollinimn when highly developed consists of a mass of pollen-
grains, affixed to an elastic foot-stalk or caudicle, and this
to a little mass of extremely viscid matter. The pollinia are
by this means transported by insects from one flower to the
stigma of another. In some orchids there is no caudicle to
the pollen-masses, and the grains are merely tied together by
fine threads; but as these are not confined to orchids, they
need not here be considered; yet I may mention that at the
base of the orchidaceous series, in Cypripedium, we can see
how the threads were probably first developed. In other
orchids the threads cohere at one end of the pollen-masses ;
and this forms the first or nascent trace of a caudicle. That
this is the origin of the caudicle, even when of considerable
length and highly developed, we have good evidence in the
aborted pollen-grains which can sometimes be detected
embedded within the central and solid parts.
With respect to the second chief peculiarity, namely the
little mass of viscid matter attached to the end of the caudicle,
a long series of gradations can be specified, each of plain
service to the plant In most flowers belonging to other
orders the stigma secretes a little viscid matter. Now in cer-
tain orchids similar viscid matter is secreted, but in much
larger quantities by one alone of the three stigmas ; and this
stigma, perhaps in consequence of the copious secretion, i»
rendered sterile. When an insect visits a flower of this kind,
it rubs off some of the viscid matter and thus at the same
time drags away some of the pollen-grains. From this
simple condition, which differs but little from that of a mul-
titude of common flowers, there are endless gradations, — to
species in which the pollen-mass terminates in a very short,
free caudicle, — ^to others in which the caudicle becomes firmly
attached to the viscid matter, with the sterile stigma itself
much modified. In this latter case we have a pollinium in its
most highly developed and perfect condition. He who will
carefully examine the flowers of orchids for himself will not
deny the existence of the above series of gradations — from a
mass of pollen-grains merely tied together by threads, with
the stigma differing but little from that of an ordinary flower.
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252 ORIGIN OF SPEQES
to a highly complex poUinium, admirably adapted for trans-
portal by insects ; nor will he deny that all the gradations in
the several species are admirably adapted in relation to the
general structure of each flower for its fertilisation by differ-
ent insects. In this, and in almost every other case, the en-
quiry may be pushed further backwards; and it may be asked
how did the stigma of an ordinary flower become viscid, but
as we do not know the full history of any one group of be-
ings, it is as useless to ask, as it is hopeless to attempt
answering, such questions.
We will now turn to climbing plants. These can be ar-
ranged in a long series, from those which simply twine round
a support, to those which I have called leaf-climbers, and to
those provided with tendrils. In these two latter classes the
stems have generally, but not always, lost the power of twin-
ing, though they retain the power of revolving, which the
tendrils likewise possess. The gradations from leaf-dimbers
to tendril-bearers are wonderfully close, and certain plants
may be indifferently placed in either class. But in ascending
the series from simple twiners to leaf-climbers, an important
quality is added, namely sensitiveness to a touch, by which
means the foot-stalks of the leaves or flowers, or these modi-
fied and converted into tendrib, are excited to bend round
and clasp the touching object He who will read my memoir
on these plants will, I think, admit that all the many grada-
itions in function and structure between simple twiners and
tendril-bearers are in each case beneficial in a high degree to
the species. For instance, it is clearly a great advantage to
a twining plant to become a leaf-climber; and it is probable
that every twiner which possessed leaves with long foot-
stalks would have been developed into a leaf-climber, if the
foot-stalks had possessed in any slight degree the requisite
sensitiveness to a touch.
As twining is the simplest means of ascending a supp(^t,
and forms the basis of our series, it may naturally be asked
how did plants acquire this power in an incipient degree,
afterwards to be improved and increased through natural se-
lection. The power of twining depends, firstly, on the stems
whilst young being extremely flexible (but this is a character
common to many plants which are not climbers) ; and, sec-
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THBORY OF NATURAL SELECnON 253
ondly, on their continually bending to all points of the com-
pass, one after the other in succession, in the same order. By
this movement the stems are inclined to all sides, and are
made to move round and round. As soon as the lower part
of a stem strikes against any object and is stopped, the upper
part still goes on bending and revolving, and thus necessarily
twines round and up the support The revolving movement
ceases after the early growth of each shoot. As in many
widely separated families of plants, single species and single
genera possess the power of revolving, and have thus become
twiners, they must have independently acquired it, and cannojt
have inherited it from a common progenitor. Hence I was
led to predict that some slight tendency to a movement of this
kind would be found to be far from uncommon with plants
which did not climb ; and that this had afforded the basis for
natural selection to work on and improve. When I made
this prediction, I knew of only one imperfect case, namely of
the young flower-peduncles of a Maurandia which revolved
slightly and irregularly, like the stems of twining plants, but
without making any use of this habit. Soon afterwards
Fritz Mtiller discovered that the young stems of an Alisma
and of a Linum, — ^plants which do not climb and are widely
separated in the natural system, — ^revolved plainly, though
irregularly ; and he states that he has reason to suspect that
this occurs with some other plants. These slight movements
appear to be of no service to the plants in question; anyhow,
they are not of the least use in the way of climbing, which
is the point that concerns us. Nevertheless we can see that
if the stems of these plants had been flexible, and if under the
conditions to which liiey are exposed it had profited them to
ascend to a height, then the habit of slightly and irregularly
revolving might have been increased and utilised through
natural selection, until they had become converted into well-
developed twining species.
With respect to the sensitiveness of the foot-stalks of the
leaves and flowers, and of tendrils, nearly the same remarks
are applicable as in the case of the revolving movements of
twining plants. As a vast number of species, belonging to
widely distinct groups, are endowed with this kind of sensi-
tiveness, it ought to be found in a nascent condition in many
P— HCXI
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254 ORIGIN OF SPECIES
plants which have not become climbers. This is the case: I
observed that the young flower-peduncles of the above Mau-
randia curved themselves a little towards the side which was
touched. Morren found in several species of Oxalis that the
leaves and their foot-stalks moved, especially after exposure
to a hot sun, when they were gently and repeatedly touched,
or when the plant was shaken. I repeated these observations
on some other species of Oxalis with the same result; in
some of them the movement was distinct, but was best seen
in the young leaves ; in others it was extremely slight. It is
a more important fact that according to the high authority
of Hofmeister, the young shoots and leaves of all plants move
after being shaken; and with climbing plants it is, as we
know, only during the early stages of growth that the foot-
stalks and tendrils are sensitive.
It is scarcely possible that the above slight movements, due
to a touch or shake, in the young and growing organs of
plants, can be of any functional importance to them. But
plants possess, in obedience to various stimuli, powers of
movement, which are of manifest importance to them; for
instance, towards and more rarely from the light, — ^in oppo-
sition to, and more rarely in the direction of, the attraction
of gravity. When the nerves and muscles of an animal are
excited by galvanism or by the absorption of strychnine, the
consequent movements may be called an incidental result, for
the nerves and muscles have not been rendered specially sen-
sitive to these stimtdi. So with plants it appears that, from
having the power of movement in obedience to certain stim-
uli, they are excited in an incidental manner by a touch, or
by being shaken. Hence there is no great difficulty in ad-
mitting that in the case of leaf-climbers and tendril-bearers,
it is this tendency which has been taken advantage of and in-
creased through natural selection. It is, however, probable,
from reasons which I have assigned in my memoir, that this
will have occurred only with plants which had already ac-
quired the power of revolving, and had thus become twiners.
I have already endeavoured to explain how plants became
twiners, namely, by the increase of a tendency to slight and
irregular revolving movements, which were at first of no use
to them; this movement, as well as that due to a touch or
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THEORY OF NATURAL SELECTION 255
shake, being the incidental result of the power of moving,
gained for other and beneficial purposes. Whether, during
the gradual development of climbing plants, natural selection
has been aided by the inherited effects of use, I will not pre-
tend to decide; but we know that certain periodical move-
ments, for instance the so-called sleep of plants, are governed
by habit
I have now considered enough^ perhaps more than enough,
of the cases, selected with care by a skilful naturalist, to
prove that natural selection is incompetent to account for the
incipient stages of useful structures; and I have shown, as I
hope, that there is no great difficulty on this head. A good
opportunity has thus been afforded for enlarging a little on
gradations of structure, often associated with changed func-
tions,— an important subject, which was not treated at suf-
ficient length in the former editions of this work. I will now
briefly recapitulate the foregoing cases.
With the giraffe, the continued preservation of the indi-
viduals of some extinct high-reaching ruminant, which had
the longest necks, legs, &c., and could browse a little above
the average height, and the continued destruction of those
which could not browse so high, would have sufficed for the
production of this remarkable quadruped; but the prolonged
use of all the parts together with inheritance will have aided
in an important manner in their co-ordination. With the
many insects which imitate various objects, there is no im-
probability in the 'belief that an accidental resemblance to
some common object was in each case the foundation for the
work of natural selection, since perfected through the occa-
sional preservation of slight variations which made the re-
semblance at all closer; and this will have been carried on
as long as the insect continued to vary, and as long as a more
and more perfect resemblance led to its escape from sharp-
sighted enemies. In certain species of whales there is a ten-
dency to the formation of irregular little points of horn on
the palate; and it seems to be quite within the scope of nat-
ural selection to preserve all favourable variations, until the
points were converted first into lamellated knobs or teeth,
like those on the beak of a goose,— then into short lamellse,
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256 ORIGIN OF SPEaSS
like those of the domestic ducks — ^and then into lamellae, as
perfect as those of the shoveller-duck, — and finally into the
gigantic plates of baleen, as in the mouth of the Greenland
whale. In the family of the ducks, the lamellae are first used
as teeth, then partly as teeth and partly as a sifting ap-
paratus, and at last almost exclusively for this latter purpose.
With such structures as the above lamellae of horn or whale-
bone, habit or use can have done little or nothing, as far as
we can judge, towards their development. On the other
hand, the transportal of the lower eye of a flat-fish to the
upper side of the head, and the formation of a prehensile tail,
may be attributed almost wholly to continued use, together
wi^ inheritance. With respect to the mammae of the higher
animals, the most probable conjecture is that primordially
the cutaneous glands over the whole surface of a marsupial
sack secreted a nutritious fluid; and that these glands were
improved in function through natural selection^ and concen-
trated into a confined area, in which case they would have
formed a mamma. There is no more difficulty in under-
standing how the branched spines of some ancient Echino-
derm, which served as a defence, became developed through
natural selection into tridactyle pedicellariae, than in under-
standing the development of the pincers of crustaceans,
through slight, serviceable modifications in the ultimate and
penultimate segments of a limb, which was at first used solely
for locomotion. In the avicularia and vibracula of the
Polyzoa we have organs widely different in appearance de-
veloped from the same source; and with* the virbracula we
can understand how the successive gradations might have
been of service. With the pollinia of orchids, the threads
which originally served to tie together the pollen-grains, can
be traced cohering into caudicles ; and the steps can likewise
be followed by which viscid matter, such as that secreted by
the stigmas of ordinary flowers, and still subserving nearly
but not quite the same purpose, became attached to the free
ends of the caudicles; — ^all these gradations being of mani-
fest benefit to the plants in question. With respect to climb-
ing plants, I need not repeat what has been so lately said.
It has often been asked, if natural selection be so potent,
why has not this or that structure been gained by certain
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THEORY OF NATURAL SELECTION 257
species, to which it would apparently have been advantage-
ous? But it is unreasonable to expect a precise answer to
such questions, considering our ignorance of the past history
of each species, and of the conditions which at the present
day determine its numbers and range. In most cases only
general reasons, but in some few ca^es special reasons, can
be assigned. Thus to adapt a species to new habits of life,
many co-ordinated modifications are almost indispensable,
and it may often have happened that the requisite parts did
not vary in the right manner or to the right degree. Many
species must have been prevented from increasing in numbers
through destructive agencies, which stood in no relation to
certain structures, which we imagine would have been gained
through natural selection from appearing to us advantageous
to the species. In this case, as the struggle for life did not
depend on such structures, they could not have been acquired
through natural selection. In many cases complex and long-
enduring conditions, often of a peculiar nature, are necessary
for the development of a structure; and the requisite con-
ditions may seldom have concurred. The belief that any
given structure, which we think, often erroneously, would
have been beneficial to a species, would have been gained
under all circumstances through natural selection, is opposed
to what we can understand of its manner of action. Mr.
Mivart does not deny that natural selection has effected
something; but he considers it as ''demonstrably insufficient"
to account for the phenomena which I explain by its agency.
His chief arguments have now been considered, and the
others will hereafter be considered They seem to me to par-
take little of the character of demonstration, and to have
little weight in comparison with those in favour of the power
of natural selection, aided by the other agencies often speci-
fied. I am bound to add, that some of the facts and argu-
ments here used by me, have been advanced for the same
purpose in an able article lately published in the 'Medico-
Qiirurgical Review.'
At the present day almost all naturalists admit evolution
under some form. Mr. Mivart believes that species change
through "an internal force or tendency," about which it is
not pretended that anything is known. That species have a
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258 ORIGIN OF SPEaES
capacity for change will be admitted by all evolutionists; but
there is no need, as it seems to me, to invoke any internal
force beyond the tendency to ordinary variability, which
through the aid of selection by man has given rise to many
well-adapted domestic races, and which through the aid of
natural selection would equally well give rise by graduated
steps to natural races or species. The final result will gen-
erally have been, as already explained, an advance, but in
some few cases a retrogression, in organisation.
Mr. Mivart is further inclined to believe, and some nat*
uralists agree with him, that new species manifest themselves
"with suddenness and by modifications appearing at once."
For instance, he supposes that the differences between the
extinct three-toed Hipparion and the horse arose suddenly.
He thinks it difficult to believe that the wing of a bird "was
developed in any other way than by a comparatively sudden
modification of a marked and important kind;" and appa-
rently he would extend the same view to the wings of bats
and pterodactyles. This conclusion, which implies great
breaks or discontinuity in the series, appears to me improb-
able in the highest degree.
Every one who believes in slow and gradual evolution, will
of course admit that specific changes may have been as abrupt
and as great as any single variation which we meet with
under nature, or even under domestication. But as species
are more variable when domesticated or cultivated than under
their natural conditions, it is not probable that such
great and abrupt variations have often occurred under
nature, as are known occasionally to arise under domestica-
tion. Of these latter variations several may be attributed to
reversion; and the characters which thus reappear were, it
is probable, in many cases at first gained in a gradual man-
ner. A still greater number must be called monstrosities,
such as six-fingered men, porcupine men, Ancon sheep, Niata
cattle, &c. ; and as they are widely different in character from
natural species, they throw very little light on our subject.
Excluding such cases of abrupt variations, the few which re-
main would at best constitute, if found in a state of nature,
doubtful species, closely related to their parental types.
My reasons for doubting whether natural species have
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THEOBY OF NATURAL SELECTION 259
changed as abruptly as have occasionally domestic races, and
for entirely disbelieving that they have changed in the won-
derful manner indicated by Mr. Mivart, are as fdlows. Ac-
cording to our experience, abrupt and strongly marked vari-
Jtions occur in our domesticated productions, singly and at
kther long intervals of time. If such occurred under na-
ture, they would be liable, as formerly explained, to be lost
by accidental causes of destruction and by subsequent inter-
crossing; and so it is known to be under domestication, un-
less abrupt variations of this kind are specially preserved and
separated by the care of man. Hence in order that a new
species should suddenly appear in the manner supposed by
Mr. Mivart, it is almost necessary to believe, in opposition to
all analogy, that several wonderfully changed individuals
appeared simultaneously within the same district This dif-
ficulty, as in the case of unconscious selection by man, is
avoided on the theory of gradual evolution, through the pres-
ervation of a large number of individuals, which varied more
or less in any favourable direction, and of the destruction of
a large number which varied in an opposite manner.
That many species have been evolved in an extremely
gradual manner, there can hardly be a doubt. The species
and even the genera of many large natural families are so
closely allied together, that it is difficult to distinguish not a
few of them. On every continent in proceeding from north
to south, from lowland to upland, &c., we meet with a host
of .closely related or representative species; as we likewise
do on certain distinct continents, which we have reason to
believe were formerly connected. But in making these and
the following remarks, I am compelled to allude to subjects
hereafter to be discussed. Look at the many outlying islands
round a continent, and see how many of their inhabitants can
be raised only to the rank of doubtful species. So it is if we
look to past times, and compare the species which have just
passed away with those still living within the same areas ; or
if we compare the fossil species embedded in the sub-stages
of the same geological formation. It is indeed manifest that
multitudes of species are related in the closest manner to
other species that still exist, or have lately existed ; and it will
hardly be maintained that such species have been developed
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260 ORIGIN OF SPECIES
in an abrupt or sudden manner. Nor should it be forgotten,
when we look to the special parts of allied species, instead of
to distinct species, that numerous and wonderfully fine grada-
tions can be traced, connecting together widely . different
structures.
Many large groups of facts are intelligible only on the
principle that species have been evolved by very small steps.
For instance, the fact that the species included in the larger
genera are more closely related to each other, and present a
greater number of varieties than do the species in the smaller
genera. The former are also grouped in little clusters, like
varieties round species ; and they present other analogies with
varieties, as was shown in our second chapter. On this same
principle we can tmderstand how it is that specific characters
are more variable than generic characters; and how the parts
which are developed in an extraordinary degree or manner
are more variable than other parts of the same species.
Many analogous facts, all pointing in the same direction,
could be added
Although very many species have almost certainly been
produced by steps not greater than those separating fine vari-
eties; yet it may be maintained that some have been devel-
oped in a different and abrupt manner. Such an admission,
"however, ought not to be made without strong evidence being
assigned. The vague and in some respects false analogies,
as they have been shown to be by Mr. Chauncey Wright,
which have been advanced in favour of this view, such as the
sudden crystallisation of inorganic substances, or the falling
of a facetted spheroid from one facet' to another, hardly de-
serve consideration. One class of facts, however, namely, the
sudden appearance of new and distinct forms of life in our geo-
logical formations supports at first sight the belief in abrupt
development. But the value of this evidence depends entirely
on the perfection of the geological record, in relation to
periods remote in the history of the world. If the record is
as fragmentary as many geologists strenuously assert, there
is nothing strange in new forms appearing as if suddenly
developed.
Unless we admit transformations as prodigious as those
advocated by Mr. Mivart, such as the sudden development of
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THEORY OF NATURAL SELECTION 261
the wings of birds or bats, or the sudden conversion of a
Hipparion into a horse, hardly any light is thrown by the be-
lief in abrupt modifications on the deficiency of connecting
links in our geological formations. But against the belief in
such abrupt changes, embryology enters a strong protest. It
is notorious that the wings of birds and bats, and the legs of
horses or other quadrupeds, are undistinguishable at an early
embryonic period, and that they become differentiated by in-
sensibly fine steps. Embryological resemblances of all kinds
can be accounted for, as we shall hereafter see, by the pro-
genitors of our existing species having varied after early
youth, and having transmitted their newly acquired char-
acters to their offspring, at a corresponding age. The em-
bryo is thus left almost unaffected, and serves as a record of
the past condition of the species. Hence it is that existing
species during the early stages of their development so often
resemble ancient and extinct forms belonging to the same
class. On this view of the meaning of embryological resem-
blances, and indeed on any view, it is incredible that an ani-
mal should have undergone such momentous and abrupt trans-
formations, as those above indicated ; and yet should not bear
even a trace in its embryonic condition of any sudden modi-
fication; every detail in its structure being developed by in-
sensibly fine steps.
He who believes that some ancient form was transformed
suddenly through an internal force or tendency into, for in-
stance, one furnished with wings, will be almost compelled
to assume, in opposition to all analogy, that many individuals
varied simultaneously. It cannot be denied that such abrupt
and great changes of structure are widely different from
those which most species apparently have undergone. He
will further be compelled to believe that many structures
beautifully adapted to all the other parts of the same creature
and to the surrounding conditions, have been suddenly pro-
duced; and of such complex and wonderful co-adaptations,
he will not be able to assign a shadow of an explanation.
He will be forced to admit that these great and sudden trans-
formations have left no trace of their action on the embryo.
To admit all this is, as it seems to me, to enter into the
realms of miracle, and to leave those of Science.
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CHAPTER VIII
Instinct
Instincts comparable with habits, but different in their origin — ^In-
stincts graduated — Aphides and ants — Instincts variable — Do-
mestic instincts, their origin — Natural instincts of the cuckoo,
molothrus, ostrich, and parasitic bees— Slave-making ants — ^Hive-
bee, its cell-making instinct — Changes of instinct and structure
not necessarily simultaneous — Difficulties of the theory of the
Natural Selection of instincts — ^Neuter or sterile insects-
Summary.
MANY instincts are so wonderful that their develop*
ment will probably appear to the reader a difficulty
sufficient to overthrow my whole theory. I may
here premise, that I have nothing to do with the origin of
the mental powers, any more than I have with that of life
itself. Vjft are concerned only with the diversities of instinct
and of the other mental faculties in animals of the same class.
I will not attempt any definition of instinct. It would be
easy to show that several distinct mental actions are com-
monly embraced by this term; but every one understands
what is meant, when it is said that instinct impels the cuckoo
to migrate and to lay her eggs in other birds' nests. An ac-
tion, which we ourselves require experience to enable us to
perform, when performed by an animal, more especially by a
very young one, without experience, and when performed by
many individuals in the same way, without their knowing
for what purpose it is performed, is usually said to be in-
stinctive. But I could show that none of these characters
are universal. A little dose of judgment or reason, as Pierre
Huber expresses it, often comes into play, even with animals
low in the scale of nature.
Frederick Cuvier and several of the older metaphysicians
have compared instinct with habit This comparison gives,
I think, an accurate notion of the frame of mind under
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INSTINCT 263
which an instinctive action is performed, but not necessarily
of its origin. How unconsciously many habitual actions are
performed, indeed not rarely in direct opposition to our con-
scious will I yet they may be modified by the will or reason.
Habits easily become associated with other habits, with cer-
tain periods of time, and states of the body. When once
acquired, they often remain constant throughout life. Sev-
eral other points of resemblance between instincts and habits
could be pointed out. As in repeating a well-known song, so
in instincts, one action follows another by a sort of rhythm;
if a person be interrupted in a song, or in repeating anything
by rote, he is generally forced to go back to recover the
habitual train of thought: so P. Huber found it was with a
caterpillar, which makes a very complicated hammock; for if
he took a caterpillar which had completed its hammock up to,
say, the sixth stage of construction, and put it into a ham-
mock completed up only to the third stage, the caterpillar
simply re-performed the fourth, fifth, and sixth stages of
construction. If, however, a caterpillar were taken out of a
hammock made up, for instance, to the third stage, and were
put into one finished up to the sixth stage, so that much of
its work was already done for it, far from deriving any bene-
fit from this, it was much embarrassed, and in order to com-
plete its hammock, seemed forced to start from the third
stage, where it had left off, and thus tried to complete the
already finished work.
If we suppose any habitual action to become inherited— and
it can be shown that this does sometimes happen — then the
resemblance between what originally was a habit and an in-
stinct becomes so close as not to be distinguished. If Mozart,
instead of playing the pianoforte at three years old with won-
derfully little practice, had played a tune with no practice at
all, he might truly be said to have done so instinctively. But
it would be a serious error to suppose that the greater num-
ber of instincts have been acquired by habit in one genera-
tion, and then transmitted by inheritance to succeeding gen-
erations. It can be clearly shown that the most wonderful
instincts with which we are acquainted, namely, those of the
hive-bee and of many ants, could not possibly have been ac-
quired by habit.
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264 ORIGIN OF SPEQES
It will be universally admitted that instincts are as im-
portant as corporeal structures for the welfare of each spe-
cies, under its present conditions of life. Under changed con-
ditions of life, it is at least possible that slight modifications
of instinct might be profitable to a species; and if it can be
shown that instincts do vary ever so little, then I can see no
difficulty in natural selection preserving and continually accu-
mulating variations of instinct to any extent that was profit-
able. It is thus, as I believe, that all the most complex and
wonderful instincts have originated. As modifications of
corporeal structure arise from, and are increased by, use or
habit, and are diminished or lost by disuse, so I do not doubt
it has been with instincts. But I believe that the effects of
habit are in many cases of subordinate importance to the
effects of the natural selection of what may be called spon-
taneous variations of instincts; — ^that is of variations pro-
duced by the same unknown causes which produce slight
deviations of bodily structure.
No complex instinct can possibly be produced through
natural selection, except by the slow and gradual accumula-
tion of numerous slight, yet profitable, variations. Hence, as
in the cases of corporeal structures, we ought to find in
nature, not the actusd transitional gradations by which each
complex instinct has been acquired — for these could be found
only in the lineal ancestors of each species — ^but we ought to
find in the collateral lines of descent some evidence of such
gradations ; or we. ought at least be able to show that grada-
tions of some kind are possible ; and this we certainly can do.
I have been surprised to find, making allowance for the in-
stincts of animaJs having been but little observed except in
Europe and North America, and for no instinct being known
amongst extinct species, how very generally gradations, lead-
ing to the most complex instincts, can be discovered. Changes
of instinct may sometimes be facilitated by the same species
having different instincts at different periods of life, or at
different seasons of the year, or when placed under different
circumstances, &c. ; in which case either the one or the other
instinct might be preserved by natural selection. And such
instances of diversity of instinct in the same species can be
shown to occur in nature.
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INSTINCT 265
Again, as in the case of corporeal structure, and conform-
ably to my theory, the instinct of each species is good for
itself, but has never, as far as we can judge, been produced
for the exclusive good of others. One of the strongest in-
stances of an animal apparently performing an action for the
sole good of another, with which I am acquainted, is that of
aphides voluntarily yielding, as was first observed by Huber,
their sweet excretion to ants : that they do so voluntarily, the
following facts show. I removed all the ants from a group
of about a dozen aphides on a dock-plant, and prevented their
attendance during several hours. After this interval, I felt
sure that the aphides would want to excrete. I watched them
for some time through a lens, but not one excreted; I then
tickled and stroked them with a hair in the same manner, as
well as I could, as the ants do with their antennae ; but not one
excreted. Afterwards I allowed an ant to visit them, and it
immediately seemed, by its eager way of running about, to be
well aware what a rich flock it had discovered ; it then began
to play with its antennae on the abdomen first of one aphis and
then of another; and each, as soon as it felt the antennae,
immediately lifted up its abdomen and excreted a limpid drop
of sweet juice, which was eagerly devoured by the ant. Even
the quite young aphides behaved in this manner, showing that
the action was instinctive, and not the result of experience.
It is certain, from the observations of Huber, that the aphides
show no dislike to the ants : if the latter be not present they
are at last compelled to eject their excretioy. But as the ex-
cretion is extremely viscid, it is no doubt a convenience to
the aphides to have it removed; therefore probably they do
not excrete solely for the good of the ants. Although there
is no evidence that any animal performs an action for the
exclusive good of another species, yet each tries to take ad-
vantage of the instincts of others, as each takes advantage
of the weaker bodily structure of other species. So again
certain instincts cannot be considered as absolutely perfect;
but as details on this and other such points are not indis-
pensable, they may be here passed over.
As some degree of variation in instincts under a state of
nature, and the inheritance of such variations, are indis-
pensaUe for the action of natural selection, as many instances
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266 ORIGIN OF SPEaES
as possible ought to be given ; but want of space prevents me.
I can only assert that instincts certainly do vary — for in-
stance, the migratory instinct, both in extent and direction,
and in its total loss. So it is with the nests of birds, which
vary partly in dependence on the situations chosen, and on
the nature and temperature of the country inhabited, but
often from causes wholly unknown to us : Audubon has given
several remarkable cases of differences in the nests of the
same species in the northern and southern United States.
Why, it has been asked, if instinct be variable, has it not
granted to the bee "the ability to use some other material
when wax was deficient"? But what other natural material
could bees use? They will work, as I have seen, With wax
hardened with vermilion or softened with lard. Andrew
Knight observed that his bees, instead of laboriously collect-
ing ^ propolis, used a cement of wax and turpentine, with
which he had covered decorticated trees. It has lately been
shown that bees, instead of searching for pollen, will gladly
use a very different substance, namely oatmeal. Fear of any
particular enemy is certainly an instinctive quality, as may
be seen in nestling birds, though it is strengthened by experi-
ence, and by the sight of fear of the same enemy in other
animals. The fear of man is slowly acquired, as I have else-
where shown, by the various animals which inhabit desert
islands; and we see an instance of this even in England, in
the greater wildness of all our large birds in comparison with
our small birds ; for the large birds have been most persecuted
by man. We may* safely attribute the greater wildness of our
large birds to this cause ; for in uninhabited islands large birds
are not more fearful than small ; and the magpie, so wary in
England, is tame in Norway, as is the hooded crow in Egypt.
That the mental qualities of animals of the same kind, born
in a state of nature, vary much, could be shown by many
facts. Several cases could also be adduced of occasional and
strange habits in wild animals, which, if advantageous to the
species, might have given rise, through natural selection, to
new instincts. But I am well aware that these general state-
ments, without the facts in detail, will produce but a feeble
effect on the reader's mind. I can only repeat my assurance,
that I do not speak without good evidence.
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CHANGES OF HABIT OR INSTINCT 267
INHBKITED CHANGES OF HABIT OR INSTINCT IN
DOMESTICATED ANIMALS
The possibility, or even probability, of inherited variations
of instinct in a state of nature will be strengthened by briefly
considering a few cases under domestication. We shall thas
be enabled to see the part which habit and the selection of so-
called spontaneous variations have played in modifying the
mental qualities of our domestic animals. It is notorious
how much domestic animals vary in their mental qualities.
With cats, for instance, one naturally takes to catching rats,
and another mice, ^nd these tendencies are known to be in-
herited. One cat, according to Mr. St. John, always brought
home game-birds, another hares or rabbits, and another
hunted on marshy ground and almost nightly caught wood-
cocks or snipes. A number of curious and authentic instances
could be given of various shades of disposition and of taste,
and likewise of the oddest tricks, associated with certain
frames of mind or periods of time, being inherited. But let
us look to the familiar case of the breeds of the dogs : it can-
not be doubted that young pointers (I have myself seen a
striking instance) will sometimes point and even back other
dogs the very first time that they are taken out; retrieving
is certainly in some degree inherited by retrievers ; and a ten-
dency to run round, instead of at, a flock of sheep, by shep-
herd dogs. I cannot see that these actions, performed vrithout
experience by the young, and in nearly the same manner by
each individual, performed with eager delight by each breed,
and without the end being known — for the young pointer can
no more know that he points to aid his master, than the white
butterfly knows why she lays her eggs on the leaf of the cab-
bage— I cannot see that these actions differ essentially from
true instincts. If we were to behold one kind of wolf, when
young and without any training, as soon ^s it scented its prey,
stand motionless like a statue, and then slowly crawf forward
with a peculiar gait ; and another kind of wolf rushing round,
instead of at, a herd of deer, and driving them to a distant
point, we should assuredly call these actions instinctive.
Domestic iilstincts, as they may be called, are certainly far
less fixed than natural instincts ; but they have been acted on
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268 ORIGIN OF SPBaBS
by far less rigorous selection, and have been transmitted for
an incomparably shorter period, under less fixed conditions
of life.
How strongly these domestic instincts, habits, and disposi-
tions are inherited, and how curiously they become mingled,
is well shown when different breeds of dogs are crossed.
Thus it is known that a cross with a bull-dog has affected for
many generations the courage and obstinacy of greyhounds;
and a cross with a greyhound has given to a whole family of
shepherd-dogs a tendency to hunt hares. These domestic in-
stincts, when thus tested by crossing, resemble natural in-
stincts, which in a like manner become curiously blended
together, and for a long period exhibit traces of the instincts
of either parent : for example, Le Roy describes a dog, whose
great-grandfather was a wolf, and this dog showed a trace
of its wild parentage only in one way, by not coming in a
straight line to his master, when called.
Domestic instincts are sometimes spoken of as actions which
have become inherited solely from long-continued and com-
pulsory habit; but this is not true. No one would ever have
thought of teaching, or probably could have taught, the
tumbler-pigeon to tumble, — ^an action which, as I have wit-
nessed, is performed by young birds, that have never seen a
pigeon tumble. We may believe that some one pigeon showed
a slight tendency to this strange habit, and that the long-
continued selection of the best individuals in successive gen-
erations made tumblers what they now are; and near Glasgow
there are house-tumblers, as I hear from Mr. Brent, which
cannot fly eighteen inches high without going head over
heels. It may be doubted whether any one would have
thought of training a dog to point, had not some one dog
naturally shown a tendency in this line; and this is known
occasionally to happen, as I once saw, in a pure terrier: the
act of pointing is probably, as many have thought, only the
exaggerated pause of an animal preparing to spring on its
prey. When the first tendency to point was once displayed,
methodical selection and the inherited effects of compulsory
training in each successive generation would soon complete
the work; and unconscious selection is still in progress, as
each man tries to procure, without intending to improve the
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CHANGES OF HABIT OR INSTINCT 2G9
breed, dogs which stand and hunt best. On the other hand,
habit alone in some cases has sufficed; hardly any animal is
more difficult to tame than the young of tiie wild rabbit;
scarcely any animal is tamer than the young of the tame rab-
bit; but I can hardly suppose that domestic rabbits have often
been selected for tameness alone ; so that we must attribute at
least the greater part of the inherited change from extreme
wildness to extreme tameness, to habit and long-continued
close confinement
Natural instincts are lost under domestication: a remark-
able instance of this is seen in those breeds of fowls which
very rarely or never become "broody," that is, never wish to
sit on their eggs. Familiarity alone prevents our seeing how
largely and how permanently the minds of our domestic ani-
mals have been modified. It is scarcely possible to doubt that
the love of man has become instinctive in the dog. All wolves,
foxes, jackals, and species of the cat genus, when kept tame,
are most eager to attack poultry, sheep, and pigs; and this
tendency has been found incurable in dogs which have been
brought home as puppies from countries such as Tierra del
Fuego and Australia, where the savages do not keep these
domestic animals. How rarely, on the other hand, do our
civilised dogs, even when quite young, require to be taught
not to attack poultry, sheep, and pigs ! No doubt they occa-
sionally do make an attack, and are then beaten; and if not
cured, they are destroyed; so that habit and some degree of
selection have probably concurred in civilising by inheritance
our dogs. On the other hand, young chickens have lost,
wholly by habit, that fear of the dog and cat which no doubt
was originally instinctive in them; for I am informed by
Captain Hutton that the young chickens of the parent-stock,
the Gallus bankiva, when reared in India under a hen, are af
first excessively wild. So it is with young pheasants reared
in England under a hen. It is not that chickens have lost all
fear, but fear only of dogs and cats, for if the hen gives the
danger-chuckle, they will run (more especially young tur-
keys) from under her, and conceal themselves In the sur-
rounding grass or thickets ; and this is evidently done for the
instinctive purpose of allowing, as we see in wild ground-
birds, their mother to fly away. But this instinct retained by
Q — HC XI f
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270 ORIGIN OF SPECIES
our chickens has become useless under domestication, for the
mother-hen has almost lost by disuse the power of flight.
Hence, we may conclude, that under domestication instincts
have been acquired, and natural instincts have been lost,
partly by habit, and partly by man selecting and accumulating,
during successive generations, peculiar mental habits and ac-
tions, which at first appeared from what we must in our
ignorance call an accident. In some cases compulsory habit
alone has sufficed to produce inherited mental changes; in
other cases, compulsory habit has done nothing, and all has
been the result of selection, pursued both mediodically and
unconsciously: but in most cases habit and selection have
probably concurred.
SPECIAL INSTINCTS
We shall, perhaps, best understand how instincts in a state
of nature have become modified by selection, by considering
a few cases. I will select only three, — ^namely, the instinct
which leads the cuckoo to lay her eggs in other birds' nests;
the slave-making instinct of certain ants ; and the cell-making
power of the hive-bee. These two latter instincts have gener-
ally and justly been ranked by naturalists as the most won-
derful of all known instincts.
Instincts of the Cuckoo. — ^It is supposed by some naturalists
that the more immediate cause of the instinct of the cuckoo
is, that she lays her eggs, not daily, but at intervals of two
or three days; so that, if she were to make her own nest and
sit on her own eggs, those first laid would have to be left for
some time unincubated, or there would be eggs and young
birds of different ages in the same nest If this were the
case, the process of laying and hatching might be inconveni-
ently long, more especially as she migrates at a very early
period ; and the first hatched young would probably have to
be fed by the male alone. But the American cuckoo is in this
predicament; for she makes her own nest, and has eggs and
young successively hatched, all at the same time. It has been
both asserted and denied that the American cuckoo occasion-
ally lays her eggs in other birds' nests ; but I have lately heard
from Dr. Merrell, of Iowa, that he once found in Illinois a
j^otmg cuckoo together with a young jay in the nest of a Blue
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INSTINCTS OF THE CUCKOO 271
jay (Garrulus cristatus) ; and as both were nearly full feath-
ered, there could be no mistake in their identification. I could
also give several instances of various birds which have been
known occasionally to lay their eggs in other birds' nests.
Now let us suppose that the ancient progenitor of our Euro-
pean cuckoo had the habits of the American cuckoo, and that
she occasionally laid an egg in another bird's nest If the
old bird profited by this occasional habit through being enabled
to migrate earlier or through any other cause; or if the young
were made more vigorous by advantage being taken of the
mistaken instinct of another species than when reared by their
own mother, encumbered as she could hardly fail to be by
having eggs and young of different ages at the same time;
then the old birds or the fostered young would gain an ad-
vantage. And analogy would lead us to believe, that the
young thus reared would be apt to follow by inheritance the
occasional and aberrant habit of their mother, and in their
turn would be apt to lay their eggs in other birds' nests, and
thus be more successful in rearing their young. By a con-
tinued process of this nature, I believe that the strange in-
stinct of our cuckoo has been generated. It has, also, re-
cently been ascertained on sufficient evidence, by Adolf
Miiller, that the cuckoo occasionally lays her eggs on the bare
ground, sits on them, and feeds her young. This rare event is
probably a case of reversion to the long-lost, aboriginal in-
stinct of nidification.
It has been objected that I have not noticed other related
instincts and adaptations of structure in the cuckoo, which
are spoken of as necessarily co-ordinated. But in all cases,
speculation on an instinct known to us only in a single species,
is useless, for we have hitherto had no facts to guide us.
Until recently the instincts of the European and of the non-
parasitic American cuckoo alone were known; now, owing to
Mr. Ramsay's observations, we have learnt something about
three Australian species, which lay their eggs in other birds'
nests. The chief points to be referred to are three: first, that
the common cuckoo, with rare exceptions, lays only one egg
in a nest, so that the large and voracious young bird receives
ample food. Secondly, that the eggs are remarkably small,
not exceeding those of the skylark,— a bird about one-fourth
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272 ORIGIN OF SPECIES
as large as the cuckoo. That the small size of the tgg is a
real case of adaptation we may infer from the fact of
the non-parasitic American cuckoo laying full-sized eggs.
Thirdly, that the young cuckoo, soon after birth, has the in-
stinct, the strength, and a properly shaped back for ejecting
its foster-brothers, which then perish from cold and hunger.
This has been boldly called a beneficial arrangement, in order
that the young cuckoo may get sufficient food, and that its
foster-brothers may perish before they had acquired much
feeling !
Turning now to the Australian species; though these birds
generally lay only one tgg in a nest, it is not rare to find two
and even three eggs in the same nest In the Bronze cuckoo
the eggs vary greatly in size, from eight to ten lines in length.
Now if it had been of an advantage to this species to have
laid eggs even smaller than those now laid, so as to have de«
ceived certain foster-parents, or, as is more probable, to have
been hatched within a shorter period (for it is asserted that
there is a relation between the size of eggs and the period of
their incubation), then there is no difficulty in believing that
a race or species might have been formed which would have
laid smaller and smaller eggs; for these would have been
more safely hatched and reared. Mr. Ramsay remarks that
two of the Australian cuckoos, when they lay their eggs in
an open nest, manifest a decided preference for nests con-
taining eggs similar in colour to their own. The European
species apparently manifests some tendency towards a similar
instinct, but not rarely departs from it, as is shown by her
laying her dull and pale-coloured eggs in the nest of the
Hedge-warbler with bright greenish-blue eggs. Had our
cuckoo invariably displayed the above instinct, it would as-
suredly have been added to those which it is assumed mu^t
all have been acquired together. The eggs of the Australiaii
Bronze cuckoo vary, according to Mr. Ramsay, to an ex->
traordinary degree in colour; so that in this respect, as well
as in size, natural selection might have secured and fixed any
advantageous variation.
In the case of the European cuckoo, the offspring, of the
foster-parents are commonly ejected from the nest within
three days after the cuckoo is hatched; and as the latter at
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INSTINCTS OF THE MOLOTHRUS 273
this age is in a most helpless condition, Mr. Gould was for-
merly inclined to believe that the act of ejection was per-
formed by the foster-parents themselves. But he has now re-
ceived a trustworthy account of a young cuckoo which was
actually seen, whilst still blind and not able even to hold up
its own head, in the act of ejecting its foster-brothers. One
of these was replaced in the nest by the observer, and was
again thrown out. With respect to the means by which this
strange and odious instinct was acquired, if it were of great
importance for the young cuckoo, as is probably the case, to
receive as much food as possible soon after birth, I can see
no special difficulty in its having gradually acquired, during
successive generations, the blind desire, the strength, and
structure necessary for the work of ejection; for those young
cuckoos which had such habits and structure best developed
wotdd be the most securely reared. The first step towards
the acquisition of the proper instinct might have been mere
unintentional restlessness on the part of the young bird, when
somewhat advanced in age and strength; the habit having
been afterwards improved, and transmitted to an earlier age.
I can see no more difficulty in this, than in the unhatched
young of other birds acquiring the instinct to break through
their own shells ; — or than in young snakes acquiring in their
upper jaws, as Owen has remarked, a transitory sharp tooth
for cutting through the tough egg-shell. For if each part is
liable to individual variations at all ages, and the variations
tend to be inherited at a corresponding or earlier age, — ^propo-
sitions which cannot be disputed, — ^then the instincts and
structure of the young could be slowly modified as surely as
those of the adult ; and both cases must stand or fall together
with the whole theory of natural selection.
Some species of Molothrus, a widely distinct genus of
American birds, allied to our starlings, have parasitic habits
like those of the cuckoo ; and the species present an interest-
ing gradation in the perfection of their instincts. The sexes
of Molothrus badius are stated by an excellent observer, Mr.
Hudson, sometimes tb live promiscuously together in flocks,
and sometimes to pair. They either build a nest of their own,
or seize on one belonging to some other bird, occasionally
throwing out the nestlings of the stranger. They either lay
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274 ORIGIN OF SPEaBS
their eggs in the nest thus appropriated, or oddly enough build
one for themselves on the top of it They usually sit on their
own eggs and rear their own young; but Mr. Hudson says it
is probable that they are occasionally parasitic, for he has
seen the young of this species following old birds of a distinct
kind and clamouring to be fed by them. The parasitic habits
of another species of Molothrus, the M. bonariensis, are much
more highly developed than those of the last, but are still far
from perfect This bird, as far as it is known, invariably
lays its eggs in the nests of strangers; but it is remarkable
that several together sometimes commence to build an irregu-
lar untidy nest of their own, placed in singularly ill-adapted
situations, as on the leaves of a large thistle. They never,
however, as far as Mr. Hudson has ascertained, complete a
nest for themselves. They often lay so many eggs — from
fifteen to twenty — in the same foster-nest, that few or none
can possibly be hatched. They have, moreover, the extraordi-
nary habit of pecking holes in the eggs, whether of their own
species or of their foster-parents, which they find in the ap-
propriated nests. They drop also many eggs on the bare
ground, which are thus wasted. A third species, the M. pecoris
of North America, has acquired instincts as perfect as those
of the cuckoo, for it never lays more than one tgg in a foster-
nest, so that the young bird is securely reared. Mr. Hudson is
a strong disbeliever in evolution, but he appears to have been
so much struck by the imperfect instincts of the Molothrus
bonariensis that he quotes my words, and asks, "Must we con-
sider these habit6, not as especially endowed or created in-
stincts, but as small consequences of one general law, namely,
transition?"
Various birds, as has already been remarked, occasionally
lay their eggs in the nests of other birds. This habit is not
very uncommon with the Gallinacese, and throws some light
on the singular instinct of the ostrich. In this family several
hen-birds unite and lay first a few eggs in one nest and then
in another; and these are hatched by the males. This instinct
may probably be accounted for by the fact of the hens laying
a large number of eggs, but, as with the cuckoo, at intervals
of two or three days. The instinct, however, of the American
ostrichy as in the case of the Molothrus bonariensis, has not
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SLAVE-MAKING INSTINCT 275
as yet been perfected ; for a surprising number of eggs lie
strewed over the plains, so that in one day's hunting I picked
up no less than twenty lost and wasted eggs.
Many bees are parasitic, and regularly lay their eggs in the
nests of other kinds of bees. This case is more remarkable
than that of the cuckoo; for these bees have not only had
their instincts but their structure modified in accordance with
their parasitic habits; for they do not possess the pollen-
collecting apparatus which would have been indispensable if
they had stored up food for their own young. Some species
of Sphegidae (wasp-like insects) are likewise parasitic; and
M. Fabre has lately shown good reason for believing that,
although the Tachytes nigra generally makes its own burrow
and stores it with paralysed prey for its own larvae, yet that,
when this insect finds a burrow already made and stored by
another sphex, it takes advantage of the prize, and becomes
for the occasion parasitic. In this case, as with that of the
Molothrus or cuckoo, I can see no difficulty in natural selec-
tion making an occasional habit permanent, if of advantage
to the species, and if the insect whose nest and stored food
are feloniously appropriated, be not thus exterminated.
Slave-making instinct. — ^This remarkable instinct was first
discovered in the Formica (Polyerges) rufescens by Pierre
Huber, a better observer even than his celebrated father. This
ant is absolutely dependent on its slaves; without their aid,
the species would certainly become extinct in a single year.
The males and fertile females do no work of any kind, and
the workers or sterile females, though most energetic and
courageous in capturing slaves, do no other work. They are
incapable of making their own nests, or of feeding their own
larvae. When the old nest is found inconvenient, and they
have to migrate, it is the slaves which determine the migra-
tion, and actually carry their masters in their jaws. So
utterly helpless are the masters, that when Huber shut up
thirty of them without a slave, but with plenty of the food
which they like best, and with their own larvae and pupae to
stimulate them to work, they did nothing; they could not
even feed themselves, and many perished of hunger. Huber
then introduced a single slave (F. fusca), and she instantly
set to work, fed and saved the survivors; made some cells
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276 ORIGIN OF SPEaES
and tended the larvae, and put all to rights. What can be
more extraordinary than these well-ascertained facts? If
we had not known of any other slave-making ant, it would
have been hopeless to speculate how so wonderful an instinct
could have been perfected.
Another species, Formica sanguinea, was likewise first dis-
covered by P. Huber to be a slave-making ant. This species
is found in the southern parts of England, and its habits
have been attended to by Mr. F. Smith, of the British Mu-
seum, to whom I am much indebted for information on this
and other subjects. Although fully trusting to the statements
of Huber and Mr. Smith, I tried to approach the subject in a
sceptical frame of mind, as any one may well be excused for
doubting the existence of so extraordinary an instinct as
that of making slaves. Hence, I will give the observations
which I made in some little detail. I opened fourteen nests
of F. sanguinea, and found a few slaves in all. Males and
fertile females of the slave species (F. fusca) are found
only in their own proper communities, and have never been
observed in the nests of F. sanguinea. The slaves are black
and not above half the size of their red masters, so that the
contrast in their appearance is great. When the nest is
slightly disturbed, the slaves occasionally come out, and like
their masters are much agitated and defend the nest: when
the nest is much disturbed, and the larvae and pupae are ex-
posed, the slaves work energetically together with their mas-
ters in carrying them away to a place of safety. Hence, it
is clear, that the slaves feel quite at home. During the
months of June and July, on three successive years, I watched
for many hours several nests in Surrey and Sussex, and
never saw a slave either leave or enter a nest. As, during
these months, the slaves are very few in number, I thought
that they might behave differently when more numerous ; but
Mr. Smith informs me that he has watched the nests at
various hours during May, June, and August, both in Surrey
and Hampshire, and has never seen the slaves, though pres-
ent in large nmnbers in August, either leave or enter the
nest. Hence he considers them as strictly household slaves.
The masters, on the other hand, may be constantly seen
bringing in materials for the nest, and food of all kinds.
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SLAVB-MAKINO INSTINCT 277
During the year i860, however, in the month of July, I came
across a community with an unusually large stock of slaves,
and I observed a few slaves mingled with their masters
leaving the nest, and marching along the same road to a tall
Scotch-fir tree, twenty-five yards distant, which they ascended
together, probably in search of aphides or cocci. According
to Ruber, who had ample opportunities for observation, the
slaves in Switzerland habitually work with their masteis in
making the nest, and they alone open and close the doors in
the morning and evening; and, as Ruber expressly states,
their principal office is to search for aphides. This* differ-
ence in the usual habits of the masters and slaves in the two
countries, probably depends merely on the slaves being cap-
tured in greater numbers in Switzerland than in England.
One day I fortunately witnessed a migration of F. san-
guinea from one nest to another, and it was a most interest-
ing spectacle to behold the masters carefully carrying their
slaves in their jaws instead of being carried by them, as in
the case of F. rufescens. Another day my attention was
struck by about a score of the slave-makers haunting the
same spot, and evidently not in search of food; they ap-
proached and were vigorously repulsed by an independent
community of the slave-species (F. fusca) ; sometimes as
many as three of these ants clinging to the legs of the slave-
making F. sanguinea. The latter ruthlessly killed their small
opponents, and carried their dead bodies as food to their
nest, twenty-nine yards distant; but they were prevented
from getting any pupae to rear as slaves. I then dug up a
small parcel of the pupae of F. fusca from another nest, and
put them down on a bare spot near the place of combat ;
they were eagerly seized and carried off by the tyrants, who
perhaps fancied that, after all, they had been victorious in
their late combat.
At the same time I laid on the same place a small parcel
of the pupae of another species, F. flava, with a few of these
little yellow ants still clinging to the fragments of their
nest This species is sometimes, though rarely, made into
slaves, as has been described by Mr. Smith. Although so
small a species, it is very courageous, and I have seen it
ferociously attack other ants. In one instance I found to my
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278 ORIGIN OF SPECIES
surprise an independent community of F. flava under a stone
beneath a nest of the slave-making F. sanguinea; and when
I had accidentally disturbed both nests, the little ants at-
^ tacked their big neighbours with surprising courage. Now
I was curious to ascertain whether F. sanguinea could dis-
tinguish the pupae of F. fusca, which they habitually make
into, slaves, from those of the little and furious F. flava,
which they rarely capture, and it was evident that they did
at once distinguish them ; for we have seen that they eagerly
and instantly seized the pupae of F. fusca, whereas Uiey were
much terrified when they came across the pupae, or even the
earth from the nest, of F. flava, and quickly ran away; but
in about a quarter of an hour, shortly after all the little yel-
low ants had crawled away, they took heart and carried off
the pupae.
One evening I visited another community of F. sanguinea,
and found a number of these ants returning home and enter-
ing their nests, carrying the dead bodies of F. fusca (show-
ing that it was not a migration) and numerous pupae. I
traced a long file of ants burthened with booty, for about
forty yards back, to a very thick clump of heath, whence I
saw the last individual of F. sanguinea emerge, carrying a
pupa; but I was not able to find the desolated nest in the
thick heath. The nest, however, must have been close at
hand, for two or three individuals of F. fusca were rushing
about in the greatest agitation, and one was perched motion-
less with its own pupa in its mouth on the top of a spray
of heath, an image of despair over its ravaged home.
Such are the facts, though they did not need confirmation
by me, in regard to the wonderful instinct of making slaves.
Let it be observed what a contrast the instinctive habits of
F. sanguinea present with those of the continental F. rufes-
cens. The latter does not build its own nest, does not deter-
mine its own migrations, does not collect food for itself or
its young, and cannot even feed itself: it is absolutely depen-
dent on its numerous slaves. Formica sanguinea, on the
other hand, possesses much fewer slaves, and in the early
part of the summer extremely few: the masters determine
when and where a new nest shall be formed, and when they
migrate, the masters carry the slaves. Both in Switzerland
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CBLL-MAKING INSTINCT 279
'and England the slaves seem to have the exclusive care of
the larvas, and the masters alone go on slave-making expe*
ditions. In Switzerland the slaves and masters work to-
gether, making and bringing materials for the nest; both,
but chiefly the slaves, tend, and milk, as it may be called,
their aphides; and thus both collect food for the community.
In England the masters alone usually leave the nest to col-
lect building materials and food for themselves, their slaves
and larvae. So that the masters in this country receive much
less service from their slaves than they do in Switzerland.
By what steps the instinct of F. sanguinea originated I
will not pretend to conjecture. But as ants which are not
slave-makers will, as I have seen, carry off the pups of
other species, if scattered near their nests, it is possible that
such pupae originally stored as food might become developed;
and the foreign ants thus unintentionally reared would then
follow their proper instincts, and do what work they could.
If their presence proved useful to the species which had
seized them — if it were more advantageous to this species
to capture workers than to procreate them — the habit of col-
lecting pupae, originally for food, might by natural selection
be strengthened and rendered permanent for the very dif-
ferent purpose of raising slaves. When the instinct was
once acqiiired, if carried out to a much less extent even
than in our British F. sanguinea, which, as we have seen, is
less aided by its slaves than the same species in Switzerland,
natural selection might increase and modify the instinct —
always supposing each modification to be of use to the spe-
cies— ^until an ant was formed as abjectly dependent on its
slaves as is the Formica rufescens.
Cell-making instinct of the Hive-Bee. — ^I will not here
enter on minute details on this subject, but will merely give
an outline of the conclusions at which I have arrived. He
must be a dull man who can examine the exquisite structure
of a comb, so beautifully adapted to its end, without enthusi-
astic admiration. We hear from mathematicians that bees
have practically solved a recondite problem, and have made
their cells of the proper shape to hold the greatest possible
amount of honey, with the least possible consumption of
precious wax in their construction. It has been remarked
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280 ORIGIN OF SPECIES
that a skilful workman with fitting tools and measures, ^
would find it very difficult to make cells of wax of the true
form, though this is effected by a crowd of bees working
in a dark hive. Granting whatever instincts you please, it
seems at first quite inconceivable how they can make all
the necessary angles and planes, or even perceive when they
are correctly made. But the difficulty is not nearly so great
as it at first appears: all this beautiful work can be shown,
I think, to follow from a few simple instincts.
I was led to investigate this subject by Mr. Waterhouse,
who has shown that the form of the cell stands in close
relation to the presence of adjoining cells; and the follow-
ing view may, perhaps, be considered only as a modification
of his theory. Let us look to the great principle of grada-
tion, and see whether [Nature does not reveal to us her
method of work. At one end of a short series we have
humble-bees, which use their old cocoons to hold honey,
sometimes adding to them short tubes of wax, and likewise
making separate and very irregular rounded cells of wax.
At the other end of the series we have the cells of the hive-
bee, placed in a double layer: each cell, as is well known,
is an hexagonal prism, with the basal edges of its six sides
bevelled so as to join an inverted pyramid, of three rhombs.
These rhombs have certain angles, and the three which form
the pyramidal base of a single cell on one side of the comb
enter into the composition of the bases of three adjoining
cells on the opposite side. In the series between the extreme
perfection of the cells of the hive-bee and the simplicity of
those of the humble-bee we have the cells of the Mexican
Melipona domestica, carefully described and figured by Pierre
Huber. The Melipona itself is intermediate in structure be-
tween the hive and humble-bee, but more nearly related to
the latter; it forms a nearly regular waxen comb of cylin-
drical cells, in which the young are hatched, and, in addi-
tion, some large cells of wax for holding honey. These
latter cells are nearly spherical and of nearly equal sizes, and
are aggregated into an irregular mass. But the important
point to notice is, that these cells are always made at that
degree of nearness to each other that they would have inter-
sected or broken into each other if the spheres had been
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CEZ.L-1IAKINO INSTINCT 281
completed; but this is never permitted, the bees building per-
fectly flat walls of wax between the spheres which thus
tend to intersect. Hence, each cell consists of an outer
spherical portion, and of two, three, or more flat surfaces,
according as the cell adjoins two, three, or more other cells.
When one cell rests on three other cells, which, from the
spheres being nearly of the same size, is very frequently
and necessarily the case, the three flat surfaces are united
into a pyramid; and this pyramid, as Huber has remarked,
is manifestly a gross imitation of the three-sided pyramidal
base of the cell of the hive-bee. As in the cells of the hive-
bee, so here, the three plane surfaces in any one cell neces-
sarily enter into the construction of three adjoining cells.
It is obvious that the Melipona saves wax, and what is more
important, labour, by this manner of building; for the flat
walls between the adjoining cells are not double, but are
of the same thickness as the outer spherical portions, and
yet each flat portion forms a part of two cells.
Reflecting on this case, it occurred to me that if the Meli-
pona had made its spheres at some given distance from each
other, and had made them of equal sizes and had arranged
them symmetrically in a double layer, the resulting structure
would have been as perfect as the comb of the hive-bee. Ac-
cordingly I wrote to Professor Miller of Cambridge, and
this geometer has kindly read over the following statement,
drawn up from his information, and tells me that it is
strictly correct: —
If a number of equal spheres be described with their
centres placed in two parallel layers ; with the centre of each
sphere at the distance of radius X V^» ^^ radius X ^ '41421
(or at some lesser distance), from the centres of the six
surrounding spheres in the same layer; and at the same dis-
tance from the centres of the adjoining spheres in the other
and parallel layer; then, if planes of intersection between
the several spheres in both layers be formed, there will re-
sult a double layer of hexagonal prisms united together by
pyramidal bases formed of three rhombs; and the rhombs
and the sides of the hexagonal prisms will have every angle
identically the same with the best measurements which have
been made of the cells of the hive-bee. But I hear from
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282 ORIGIN OF SPECIBS
Prof. Wyman, who has made numerous careful measure-
ments, that the accuracy of the workmanship of the bee has
been greatly exaggerated; so much so, that ¥diatever the
typical form of the cell may be, it is rarely, if ever, realised.
Hence we may safely conclude that, if we could slightly
modify the instincts already possessed by the Melipona, and
in themselves not very wonderful, this bee would make a
structure as wonderfully perfect as that of the hive-bee. We
must suppose the Melipona to have the power of forming
her cells truly spherical, and of equal sizes; and this would
not be very surprising, seeing that she already does so to a
certain extent, and seeing what perfectly cylindrical bur-
rows many insects make in wood, apparency by turning
round on a fixed point. We must suppose the Melipona to
arrange her cells in level layers, as she already does her
cylindrical cells; and we must further suppose, and this is
the greatest difficulty, that she can somehow judge accu-
rately at what distance to stand from her fellow-labourers
when several are making their spheres; but she is already
so far enabled to judge of distance, that she always describes
her spheres so as to intersect to a certain extent; and then
she unites the points of intersection by perfectly flat sur-
faces. By such modifications of instincts which in them-
selves are not very wonderful — ^hardly more wonderful than
those which guide a bird to make its nest, — ^I believe that
the hive-bee has, acquired, through natural selection, her
inimitable architectural powers.
But this theory can be tested by experiment Following
the example of Mr. Tegetmeier, I separated two combs,
and put between them a long, thick, rectangular strip of
wax: the bees instantly began to excavate minute circular
pits in it; and as they deepened these little pits, they made
them wider and wider until they were converted into shal-
low basins, appearing to the eye perfectly true or parts of
a sphere, and of about the diameter of a cell. It was most
interesting to observe that, wherever several bees had be-
gun to excavate these basins near together, they had begun
their work at such a distance from each other, that by the
time the basins had acquired the above-stated width (». e,
about the width of an ordinary cell), and were in depth
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CELL-MAKING INSTINCT 283
about one-sixth of the diameter of the sphere of which they
formed a part, the rims of the basins intersected or broke
into each other. As soon as this occurred, the bees ceased to
excavate, and began to build up flat walls of wax on the
lines of intersection between the basins, so that each hex-
agonal prism was built upon the scalloped edge of a smooth
basin, instead of on the straight edges of a three-sided pyra-
mid as in the case of ordinary cells.
I then put into the hive, instead of a thick, rectangular
piece of wax, a thin and narrow, knife-edged ridge, coloured
with vermilion. The bees instantly began on both sides to
excavate little basins near to each other, in the same way as
before; but the ridge of wax was so thin, that the bottoms
of the basins, if they had been excavated to the same depth
as in the former experiment, would have broken into each
other from the opposite sides. The bees, however, did not
suffer this to happen, and they stopped their excavations In
due time ; so that the basins, as soon as they had been a little
deepened, came to have flat bases; and these flat bases,
formed by thin little plates of the vermilion wax left un-
gnawed, were situated, as far as the eye could judge, exactly
along the planes of imaginary intersection between the
basins on the opposite sides of the ridge of wax. In some
parts, only small portions, in other parts, large portions of a
rhombic plate were thus left between the opposed basins,
but the work, from the unnatural state of things, had not
been neatly performed. The bees must have worked at very
nearly the same rate in circularly gnawing away and deep-
ening the basins on both sides of the ridge of vermilion wax,
in order to have thus succeeded in leaving flat plates between
the basins, by stopping work at the planes of intersection.
Considering how flexible thin wax is, I do not see that
there is any difiBculty in the bees, whilst at work on the two
sides of a strip of wax, perceiving when they have gnawed
the wax away to the proper thinness, and then stopping their
work. In ordinary combs it has appeared to me that the
bees do not always succeed in working at exactly the same
rate from the opposite sides; for I have noticed half-com-
pleted rhombs at the base of a just commenced cell, which
were slightly concave on one side, where I suppose that the
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284 ORIGIN OF SPEQES
bees had excavated too quickly, and convex on the opposed
side where the bees had worked less qtuckly. In one well
marked instance, I put the comb back into the hive, and
allowed the bees to go on working for a short time, and
again examined the cell, and I fomid that the rhombic plate
had been completed, and had become perfectly Hat: it was
absolutely impossible, from the extreme thinness of the little
plate, that they could have effected this by gnawing away
the convex side; and I suspect that the bees in such cases
stand on opposite sides and push and bend the ductile and
warm wax (which as I have tried is easily done) into its
proper intermediate plane, and thus flatten it
From the experiment of the ridge of vermilion wax we
can see that, if the bees were to build for themselves a thin
wall of wax, they could make their cells of the proper shape,
by standing at the proper distance from each other, by exca-
vating at the same rate, and by endeavouring to make equal
spherical hollows, but never allowing the spheres to break
into each other. Now bees, as may be clearly seen by exam-
ining the edge of a growing comb, do make a rough, circum-
ferential wall or rim all round the comb ; and they gnaw this
away from the opposite sides, always working circularly as
they deepen each cell. They do not make the whole three-
sided pyramidal base of any one cell at the same time, but
only that one rhombic plate which stands on the extreme
growing margin, or the two plates, as the case may be ; and
they never complete the upper edges of the rhombic plates,
until the hexagonal walls are commenced. Some of these
statements differ from those made by the justly celebrated
elder Huber, but I am convinced of their accuracy; and if
I had space, I could show that they are conformable with
my theory.
Ruber's statement, that the very first cell is excavated out
of a little parallel-sided wall of wax, is not, as far as I have
seen, strictly correct ; the first commencement having always
been a little hood of wax; but I will not here enter on de-
tails. We see how important a part excavation plays in the
construction of the cdls; but it would be a great error to
suppose that the bees cannot build up a rough wall of wax in
the proper position — ^that is, along the plane of intersection
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CELL-MAKING INSTINCT 285
between two adjoining spheres. I have several specimens
showing clearly that they can do this. Even in the rude
circumferential rim or wall of wax round a growing comb,
flexures may sometimes be observed, corresponding in posi-
tion to the planes of the rhombic basal plates of future cells.
But the rough wall of wax has in every case to be finished
off, by being largely gnawed away on both sides. The
manner in wliJch the bees build is curious; they always make
the first rough wall from ten to twenty times thicker than
the excessively thin finished wall of the cell, which will
ultimately be left. We shall understand how they work, by
supposing masons first to pile up a broad ridge of cement,
and then to begin cutting it away equally on both sides near
the ground, till a smooth, very thin wall is left in the middle;
the masons always piling up the cut-away cement, and
adding fresh cement on the summit of the ridge. We shall
thus have a thin wall steadily growing upward but always
crowned by a gigantic coping. From all the cells, both those
just commenced and those completed, being thus crowned by
a strong coping of wax, the bees can duster and crawl over
the comb without injuring the delicate hexagonal walls.
These walls, as Professor Miller has kindly ascertained for
me, vary greatly in thickness; being, on an average of
twelve measurements made near the border of the comb,
y^ of an inch in thickness; whereas the basal rhomboidal
plates are thicker, nearly in the proportion of three to two,
having a mean thickness, from twenty-one measurements,
of y^ of an inch. By the above singular manner of build-
ing, strength is continually given to the comb, with the ut-
most ultimate economy of wax.
It seems at first to add to the difficulty of understanding
how the cells are made, that a multitude of bees all work
together; one bee after working a short time at one cell
going to another, so that, as Huber has stated, a score of in-
dividuals work even at the commencement of the first cell.
I was able practically to show this fact, by covering the
edges of the hexagonal walls of a single cell, or the extreme
margin of the circumferential rim of a growing comb, with
an extremely thin layer of melted vermilion wax; and I in-
variably found that the colour was most delicately diffused
R— BCZI
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286 ORIGIN OF SPEaHS
by the bees — as delicately as a painter could have done it
with his brush — by atoms of the coloured wax having been
taken from the spot on which it had been placed, and worked
into the growing edges of the cells all round The work
of construction seems to be a sort of balance struck between
many bees, all instinctively standing at the same relative
distance from each other, all trying to sweep equal spheres,
and then building up, or leaving ungnawed, the planes of
intersection between these spheres. It was really curious to
note in cases of difficulty, as when two pieces of comb met
at an angle, how often the bees would pull down and rebuild
in different ways the same cell, sometimes recurring to a
shape which they had at first rejected.
When bees have a place on which they can stand in their
proper positions for working, — for instance, on a slip of
wood, placed directly under the middle of a comb growing
downwards, so that the comb has to be built over one face
of the slip— in this case the bees can lay the foundations
of one waill of a new hexagon, in its strictly proper place,
projecting beyond the other completed cells. It suffices that
the bees should be enabled to stand at their proper relative
distances from each other and from the walls of the last
completed cells, and then, by striking imaginary spheres,
they can build up a wall intermediate between two adjoin-
ing spheres; but, as far as I have seen, they never gnaw
away and finish off the angles of a cell till a large part both
of that cell and of the adjoining cells has been built. This
capacity in bees of laying down under certain circumstances
a rough wall in its proper place between two just-commenced
cells, is important, as it bears on a fact, which seems at
first subversive of the foregoing theory; namely, that the
cells on the extreme margin of wasp-combs are sometimes
strictly hexagonal; but I have not space here to enter on
this subject. Nor does there seem to me any great difficulty
in a single insect (as in the case of a queen-wasp) making
hexagonal cells, if she were to work alternately on the in-
side and outside of two or three cells commenced at the
same time, always standing at the proper relative distance
from the parts of the cells just begun, sweeping spheres or
cylinders, and building up intermediate planes.
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CELL-fifAKING INSTINCT 287
As natural selection acts only by the accumtilation of
slight modifications of structure or instinct, each profitable
to the individual under its conditions of life, it may reason-
ably be asked, how a long and graduated succession of modi-
fied architectural instincts, all tending towards the present
perfect plan of construction, could have profited the progeni-
tors of the hive-bee? I think the answer is not difficult:
cells constructed like those of the bee or the wasp gain in
strength, and save much in labour and space, and in the ma-
terials of which they are constructed. With respect to the
formation of wax, it is known that bees are often hard
pressed to get sufficient nectar, and I am informed by Mr.
Tegetmeier that it has been experimentally proved that from
twdve to fifteen pounds of dry sugar are consumed by a
hive of bees for die secretion of a pound of wax; so that
a prodigious quantity of fluid nectar must be collected and
consumed by the bees in a hive for the secretion of the wax
necessary fcM* the construction of their combs. Moreover,
many bees have to remain idle for many days during the
process of secretion. A large store of honey is indispensable
to support a large stock of bees during the winter; and the
security of the hive is known mainly to depend on a large
number of bees being supported. Hence the saving of wax
by largely saving honey and the time consumed in collect-
ing the honey must be an important element of success to
any family of bees. Of course the success of the species
may be dependent on the number of its enemies, or parasites,
or on quite distinct causes, and so be altogether independent
of the quantity of honey which the bees can collect But
let us suppose that this latter circumstance determined, as
it probably often has determined, whether a bee allied to
our humble-bees could exist in large numbers in any coun-
try; and let us further suppose Uiat the community lived
through the winter, and consequently required a store of
honey: there can in this case be no doubt that it would be
an advantage to our imaginary humble-bee, if a slight modi-
fication in her instincts led her to make her waxen cells
near together, so as to intersect a little; for a wall in com-
mon even to two adjoining cells would save some little labour
and wax. Hence it wovdd continually be more and more
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288 ORIGIN OF SPECIES
advantageous to our humble-bees, if they were to make their
cells more and more regular, nearer together, and aggre-
gated into a mass, like the cells of the Melipona; for in this
case a large part of the bounding surface of each cell would
serve to bound the adjdining cells, and much labour and wax
would be saved Again, from the same cause, it would be
advantageous to the Melipona, if she were to make her cells
closer together, and more regular in every way than at pres-
ent; for then, as we have seen, the spherical surfaces would
wholly disappear and be replaced by plane surfaces; and
the Melipona would make a comb as perfect as that of the
hive-bee. Beyond this stage of perfection in architecture,
natural selection could not lead; for the comb of the hive-
bee, as far as we can see, is absolutely perfect in economis-
ing labour and wax.
Thus, as I believe, the most wonderful of all known in-
stincts, that of the hive-bee, can be explained by natural
selection having taken advantage of numerous, successive,
slight modifications of simpler instincts; natural selection
having, by slow degrees, more and more perfectly led the
bees to sweep equal spheres at a given distance from each
other in a double layer, and to build up and excavate the wax
along the planes of intersection ; the bees, of course, no more
knowing that they swept their spheres at one particular dis-
tance from each other, than they know what are the several
angles of the hexagonal prisms and of the basal rhombic
plates ; the motive power of the process of natural selection
having been the construction of cells of due strength and of
the proper size and shape for the larvse, this being effected
with the greatest possible economy of labour and wax; that
individual swarm which thus made the best cells with least
labour, and least waste of honey in the secretion of wax,
having succeeded best, and having transmitted their newly
acquired economical instincts to new swarms, which in their
turn will have had the best chance of succeeding in the
struggle for existence.
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OBJECTIONS TO THB THEORY 288
OBJECTIONS TO THE THEORY OF NATURAL SELECTION AS APPLIED
TO INSTINCTS I NEUTER AND STERILE INSECTS
It has been objected to the foregoing view of the origin of
instincts that "the variations of structure and of instinct must
have been simultaneous and accurately adjusted to each other
as a modification in the one without an immediate correspond-
ing change in the other would have been fatal." The force
of this objection rests entirely on the assumption that the
changes in the instincts and structure are abrupt To take
as an illustration the case of the larger titmouse (Parus
major) alluded to in a previous chapter; this bird often holds
the seeds of the yew between its feet on a branch, and ham-
mers with its beak till it gets at the kernel. Now what spe-
cial difficulty would there be in natural selection preserving
all the slight individual variations in the shape of the beak,
which were better and better adapted to break open the seeds,
until a beak was formed, as well constructed for this purpose
as that of the nuthatch, at the same time that habit, or com-
pulsion, or spontaneous variations of taste, led the bird to
become more and more of a seed-eater ? In this case the beak
is supposed to be slowly modified by natural selection, subse-
quently to, but in accordance with, slowly changing habits
or taste; but let the feet of the titmouse vary and grow larger
from correlation with the beak, or from any other unknown
cause, and it is not improbable that such larger feet would
lead the bird to climb more and more until it acquired the
remarkable climbing instinct and power of the nuthatch. In
this case a gradual change of structure is supposed to lead to
changed instinctive habits. To take one more case: few
instincts are more remarkable than that which leads the swift
of the Eastern Islands to make its nest wholly of inspissated
saliva. Some birds build their nests of mud, believed to be
moistened with saliva; and one of the swifts of North
America makes its nest (as I have seen) of sticks aggluti-
nated with saliva, and even with flakes of this substance. Is
it then very improbable that the natural selection of individual
swifts, which secreted more and more saliva, should at last
produce a species with instincts leading it to neglect other
materials, and to make its nest exclusively of inspissated
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290 ORIGIN OP SPECIES
saliva ? And so in other cases. It must, however, be admitted
that in many instances we cannot conjecture whether it was
instinct or structure which first varied.
No doubt many instincts of very difficult explanation could
be opposed to the theory of natural selection — cases, in which
we cannot see how an instinct could have originated; cases,
in which no intermediate gradations are known to exist;
cases of instincts of such trifling importance, that they could
hardly have been acted on by natural selection; cases of in-
stincts almost identically the same in animals so remote in
the scale of nature, that we cannot account for their simi-
larity by inheritance from a common progenitor, and conse-
quently must believe that they were independently acquired
through natural selection. I will not here enter on these
several cases, but will confine myself to one special difficulty,
which at first appeared to me insuperable, and actually fatal
to the whole theory. I allude to the neuters or sterile females
in insect-communities; for these neuters often differ widely
in instinct and in structure from both the males and fertile
females, and yet, from being sterile, they cannot propagate
their kind.
The subject well deserves to be discussed at great length,
but I will here take only a single case, that of working or
sterile ants. How the workers have been rendered sterile
is a difficulty; but not much greater than that of any other
striking modification of structure; for it can be shown that
some insects and other articulate animals in a state of nature
occasionally become sterile; and if such insects had been
social, and it had been profitable to the community that a
number should have been annually bom capable of work, but
incapable of procreation, I can see no especial difficulty in
this having been effected through natural selection. But I
must pass over this preliminary difficulty. The great difficulty
lies in the working ants differing widely from both the males
and the fertile females in structure, as in the shape of the
thorax^ and in being destitute of wings and sometimes of
eyes, and in instinct. As far as instinct alone is concerned,
the wonderful difference in this respect between the workers
and the perfect females, would have been better exemplified
by the hive-bee. If a working ant or other neuter insect had
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OBJECTIONS TO THE THEORY 291
been an ordinary animal, I should have unhesitatingly as-
sumed that all its characters had been slowly acquired through
natural selection; namely, by individuals having been bom
with slight profitable modifications, which were inherited by
the offspring; and that these again varie4 and again were
selected, and so onwards. But with the working ant we have
an insect differing greatly from its parents, yet absolutely
sterile, so that it could never have transmitted successively
acquired modifications of structure or instinct to its progeny.
It may well be askeld how is it possible to reconcile this case
with the theory of natural selection?
First, let it be remembered that we have innumerable in-
stances, both in our domestic productions and in those in a
state of nature, of all sorts of differences of inherited struc-
ture which are correlated with certain ages, and with either
sex. We have differences correlated not only with one sex,
but with that short period when the reproductive system is
active, as in the nuptial plumage of many birds, and in the
hooked jaws of the male salmon. We have even slight dif-
ferences in the horns of different breeds of cattle in relation
to an artificially imperfect state of the male sex; for oxen
of certain breeds have longer horns than the oxen of other
breeds, relatively to the length of the horns in both the bulls
and cows of these same breeds. Hence I can see no great
difficulty in any character becoming correlated with the sterile
condition of certain members of insect-communities : the dif-
ficulty lies in understanding how such correlated modifications
of structure could have been slowly accumulated by natural
selection.
This difficulty, though appearing insuperable, is lessened,
or, as I believe, disappears, when it is remembered that selec-
tion may be applied to the family, as well as to the individual,
and may thus gain the desired end. Breeders of cattle wish
the flesh and fat to be well marbled together: an animal thus
characterised has been slaughtered, but the breeder has gone
with confidence to the same stock and has succeeded. Such
faith may be placed in the power of selection, that a breed
of cattle, always yielding oxen with extraordinarily long
horns, could, it is probable, be formed by carefully watching
which individual bulls and cows, when matched, produce oxen
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29t ORIGIN OP SPECIES
with the longest horns; and yet no one ox would ever have
propagated its kind. Here is a better and real illustration:
according to M. Verlot, some varieties of the double annual
Stock from having been long and carefully selected to the
right degree, always produce a large proportion of seedlings
bearing double and quite sterile flowers; but they likewise
yield some single and fertile plants. These latter, by which
alone the variety can be propagated, may be compared with
the fertile male and female ants, and the double sterile plants
with the neuters of the same community.^ As with the varie-
ties of the stock, so with social insects, selection has been
applied to the family, and not to the individual, for the sake
of gaining a serviceable end. Hence we may conclude that
slight modifications of structure or of instinct, correlated
with the sterile condition of certain members of the com-
munity, have proved advantageous: consequently the fertile
males and females have flourished, and transmitted to their
fertile offspring a tendency to produce sterile members with
the same modifications. This process must have been re-
peated many times, until that prodigious amount of difference
between the fertile and sterile females of the same species
has been produced, which we see in many social insects.
But we have not as yet touched on the acme of the difii-
culty; namely, the fact that the neuters of several ants differ,
not only from the fertile females and males, but from each
other, sometimes to an almost incredible degree, and are thus
divided into two or even three castes. The castes, moreover,
do not commonly graduate into each other, but are perfectly
well defined ; being as distinct from each other as are any two
species of the same genus, or rather as any two genera of the
'same family. Thus in Eciton, there are working and soldier
neuters, with jaws and instincts extraordinarily different: in
Cryptocerus, the workers of one caste alone carry a wonder-
ful sort of shield on their heads, the use of which is quite
unknovm: in the Mexican Myrmecocystus, the workers of
one caste never leave the nest; they are fed by the workers
of another caste, and they have an enormously developed ab-
domen which secretes a sort of honey, supplying the place of
that excreted by the aphides, or the domestic cattle as they
may be called, which our European ants guard and imprison.
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OBJECTIONS TO THE THEORY 293
It will indeed be thought that I have an overweening con-
fidence in the principle of natural selection, when I do not
admit that such wonderful and well-established facts at once
annihilate the theory. In the simpler case of neuter insects
all of one caste, which, as I believe, have been rendered dif-
ferent from the fertile males and females through natural
selection, we may conclude from the analogy of ordinary
variations, that the successive, slight, profitable modifications
did not first arise in all the neuters in the same nest, but in
some few alone ; and that by the survival of the communities
with females which produced most neuters having the ad-
vantageous modification, all the neuters ultimately came to be
thus characterized. According to this view we ought occa-
sionally to find in the same nest neuter insects, presenting
gradations of structure ; and this we do find, even not rarely
considering how few neuter insects out of Europe have been
carefully examined. Mr. F. Smith has shown that the neuters
of several British ants differ surprisingly from each other in
size and sometimes in colour; and that the extreme forms can
be linked together by individuals taken out of the same nest :
I have myself compared perfect gradations of this kind. It
sometimes happens that the larger or the smaller sized
workers are the most numerous ; or that both large and small
are numerous, whilst those of an intermediate size are scanty
in numbers. Formica flava has larger and smaller workers,
with some i ew of intermediate size ; and, in this species, as
Mr. F. Smith has observed, the larger workers have simple
eyes (ocelli), which though small can be plainly distinguished,
whereas the smaller workers have their ocelli rudimentary.
Having carefully dissected several specimens of these
workers, I can afiirm that the eyes are far more rudi-
mentary in the smaller workers than can be accounted
for merely by their proportionally lesser size; and I fully
believe, though I dare not assert so positively, that the workers
of intermediate size have their ocelli in an exactly inter-
mediate condition. So that here we have two bodies of sterile
workers in the same nest, differing not only in size, but in
their organs of vision, yet connected by some few members
in an intermediate condition. I may digress by adding, that
if the smaller workers had been the most useful to the com-
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294 ORIGIN OF SPECIES
munity, and those males and females had been continually
selected, which produced more and more of the smaller
workers, until all the workers were in this condition; we
should then have had a species of ant with neuters in nearly
the same condition as those of Myrmica. For the workers of
Myrmica have not even rudiments of ocelli, though the male
and female ants of this genus have well-devel(^d ocelli.
I may give one other case: so confidently did I expect
occasionally to find gradations of important structures be-
tween the different castes of neuters in the same species, that
I ^adly availed myself of Mr. F. Smith's offer of numerous
specimens from the same nest of the driver ant (Anomma)
of West Africa. The reader will perhaps best appreciate the
amount of difference in these workers, by my giving not the
actual measurements, but a strictly accurate illustration: the
difference was the same as if we were to see a set of work-
men building a house, of whom many were five feet four
inches high, and many sixteen feet high; but we must in
addition suppose that the larger workmen had heads four
instead of three times as big as those of the smaller men,
and jaws nearly five times as big. The jaws, moreover, of
the working ants of the several sizes differed wonderfully in
shape, and in the form and number of the teeth. But the
important fact for us is, that, though the workers can be
grouped into castes of different sizes, yet they graduate in-
sensibly into each other, as does the widely-different struc-
ture of their jaws. I speak confidently on this latter point,
as Sir J. Lubbock made drawings for me, with the camera
lucida, of the jaws which I dissected from the workers of
the several sizes. Mr. Bates, in his interesting '^Naturalist on
the Amazons,' has described analogous cases.
With these facts before me, I believe that natural selec-
tion, by acting on the fertile ants or parents, could form a
species which should regularly produce neuters, all of large
size with one form of jaw, or all of small size with widely
different jaws; or lastly, and this is the greatest difficulty,
one set of workers of one size and structure, and simultane-
ously another set of workers of a different size and struc-
ture;— z graduated series having first been formed, as in the
case of the driver ant, and then the extreme forms having
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OBJECTIONS TO THB THEORY 205
been produced in greater and greater numbers, througb the
survival of the parents which generated them, until none
with an intermediate structure were produced.
An analogous explanation has been given by Mr. Wallace,
of the equally complex case, of certain Malayan Butterflies
regularly appearing under two or even three distinct female
forms; and by Fritz Mtiller, of certain Brazilian crustaceans
likewise appearing under two widely distinct male forms.
But this subject need not here be discussed
I have now explained how, as I believe, the wonderful fact
of two distinctly defined castes of sterile workers existing in
the same nest, both widely different from each other and from
their parents, has originated. We can see how useful their
production may have been to a social community of ants, on
the same principle that the division of labour is useful to
civilised man. Ants, however, work by inherited instincts
and by inherited organs or tools, whilst man works by
acquired knowledge and manufactured instruments. But I
must confess, that, with all my faith in natural selection, I
should never have anticipated that this principle could
have been efficient in so high a degree, had not the case of
these neuter insects led me to this conclusion. I have, there-
fore, discussed this case, at some little but wholly insufficient
length, in order to show the power of natural selection, and
likewise because this is by far the most serious special dif-
ficulty which my theory has encountered. The case, also, is
very interesting, as it proves that with animals, as with
plants, any amount of modification may be effected by the
accumulation of numerous, slight, spontaneous variaticMis,
which are in any way profitable, without exercise or habit
having been brought into play. For peculiar habits confined
to the workers or sterile females, however long they might
be followed, could not possibly affect the males and fertile
females, which alone leave descendants. I am surprised that
no one has hitherto advanced this demonstrative case of
neuter insects, against the well-known doctrine of inherited
habit, as advanced by Lamarck.
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296 ORIGIN OF SPEOES
SUMMARY
I have endeavored in this chapter briefly to show that the
mental qualities of our domestic animals vary, and that the
variations are inherited. Still more briefly I have attempted
to show that instincts vary slightly in a state of nature. No
one will dispute that instincts are of the highest importance
to each animal. Therefore there is no real difficulty, under
changing conditions of life, in natural selection accumulating
to any extent slight modifications of instinct which are in
any way useful. In many cases habit or use and disuse have
probably come into play. I do not pretend that the facts
given in this chapter strengthen in any great degree my
theory; but none of the cases of difficulty, to the best of my
judgment, annihilate it On the other hand, the fact that
instincts are not always absolutely perfect and are liable t^
mistakes: — ^that no instinct can be shown to have been pro-
duced for the good of other animals, though animals take
advantage of the instincts of others; — ^that the canon in
natural history, of "Natura non facit saltum," is applicable
to instincts as well as to corporeal structure, and is plainly
explicable on the foregoing views, but is otherwise inexplic-
able,— ^all tend to corroborate the theory of natural selection.
This theory is also strengthened by some few other facts in
regard to instincts ; as by that common case of closely allied,
but distinct, species, when inhabiting distant parts of the
world and living under considerably different conditions of
life, yet often retaining nearly the same instincts. For in-
stance, we can understand, on the principle of inheritance,
how it is that the thrush of tropical South America lines its
nest with mud, in the same peculiar manner as does our
British thrush; how it is that the Hombills of Africa and
India have the same extraordinary instinct of plastering up
and imprisoning the females in a hole in a tree, with only a
small hole left in the plaster through which the males feed
them and their young when hatched ; how it is that the male
wrens (Troglodytes) of North America build "cock-nests,"
to roost in, like the males of our Kitty-wrens, — a habit wholly
unlike that of any other known bird. Finally, it may not be
a logical deduction, but to my imagination it is far more satis-
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SUMMARY 297
factory to look at such instincts as the young cuckoo ejecting
its foster-brothers, — ants making slaves, — ^the larvae of ichneu-
monidae feeding within the live bodies of caterpillars, — ^not
as specially endowed or created instincts, but as small conse-
quences of one general law leading to the advancement of all
organic beings, — ^namely, multiply, vary, let the strongest live
and the weakest die.
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CHAPTER IX
Hybridism
Distinctioii between the sterility of first crosses and of hybrids —
Sterility various in degree, not universal, affected by dose inter-
breeding, removed by domestication — ^Laws governing the ster-
ility of hybrids — Sterility not a special endowment, but incidental
on other differences, not accumulated by natural selection —
Causes of the sterility of first crosses and of hybrids — Parallel-
ism between the effects of changed conditions of life and of
crossing — Dimorphism and Trimorphism — Fertility of varieties
when crossed, and of their mongrel offspring not universal —
Hybrids and mongrels compared independently of their fertility
—-Summary*
THE view commonly entertained by naturalists is that
species, when intercrossed, have been specially en-
dowed with sterility, in order to prevent their con-
fusion. This view certainly seems at first highly probable,
for species living together could hardly have been kept dis-
tinct had they been capable of freely crossing. The subject
is in many ways important for us, more especially as the
sterility of species when first crossed, and that of their hybrid
offspring, cannot have been acquired, as I shall show, by the
preservation of successive profitable degrees of sterility. It
is an incidental result of differences in the reproductive sys-
tems of the parent-species.
In treating this subject, two classes of facts, to a large
extent fundamentally different, have generally been con-
founded; namely, the sterility of species when first crossed,
and the sterility of the hybrids produced from them.
Pure species have of course their organs of reproduction
in a perfect condition, yet when intercrossed they produce
either few or no offspring. Hybrids, on the other hand, have
their reproductive organs functionally impotent, as may be
clearly seen in the state of the male element in both plants
and animals; though the formative organs themselves are
296
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DBGRBBS OF STBRIUTY 289
perfect in structure, s^ far as the microscope reveals. In the
first case the two sexual elements which go to form the
embryo are perfect; in the second case they are either not at
all developed, or are imperfectly developed. This distinction
is important, when the cause of the sterility, which is common
to the two cases, has to be considered. The distinction prob-
ably has been slurred over, owing to the sterility in both cases
being looked on as a special endowment, beyond the province
of our reasoning powers.
The fertility of varieties, that is of the forms known or
believed to be descended from common parents, when crossed,
and likewise the fertility of their mongrel offspring, is, with
reference to my theory, of equal importance with the sterility
of species ; for it seems to make a broad and clear distinction
between varieties and species.
Degrees of Sterility. — First, for the sterility of species
when crossed and of Uieir hybrid offspring. It is impossible
to study the several memoirs and works of those two con-
scientious and admirable observers, Kolreuter and Gartner,
who almost devoted their lives to this subject, without being
deeply impressed with the high generality of some degree of
sterility. Kolreuter makes the rule universal; but £en h»
cuts the knot, for in ten cases in which he found two forms,
considered by most authors as distinct species, quite fertile
together, he unhesitatingly ranks them as varieties. Gartner,
also, maJces the rule equally universal; and he disputes the
entire fertility of Kolreuter's ten cases. But in these and in
many other cases, Gartner is obliged carefully to count the
seeds, in order to show that there is any degree of sterility. He
always compares the maximum number of seeds produced by
two species when first crossed, and the maximum produced
by their hybrid offspring, with the average number produced
by their pure parent-species in a state of nature. But causes
of serious error here intervene: a plant, to be hybridised,
must be castrated, and, what is often more important, must
be secluded in order to prevent pollen being brought to it
by insects from other plants. Nearly all the plants experi-
mented on by Gartner were potted, and were kept in a
chamber in his house. That Uiese processes are often in-
jurious to the fertility of a plant cannot be doubted; for
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300 ORIGIN OF SPECIES
Gartner gives in his table about a score of cases of plants
which he castrated, and artificially fertilised with their own
pollen, and (excluding all cases such as the Leguminosae, in
which there is an acknowledged difficulty in the manipula-
tion) half of these twenty plants had their fertility in some
degree impaired. Moreover, as Gartner repeatedly crossed
some forms, such as the common red and blue pimpernels
(Anagallis arvensis and coeulea), which the best botanists
rank as varieties, and found them absolutely sterile, we may
doubt whether many species are really so sterile, when inter-
crossed, as he believed.
It is certain, on the one hand, that the sterility of various
species when crossed is so different in degree and graduates
away so insensibly, and, on the other hand, that the fertility
of pure species is so easily affected by various circumstances,
that for all practical purposes it is most difficult to say where
perfect fertility ends and sterility begins. I think no better
evidence of this can be required than that the two most ex-
perienced observers who have ever lived, namely Kolreuter
and Gartner, arrived at diametrically opposite conclusions in
regard to some of the very same forms. It is also most in-
* structive to compare — ^but I have not space here to enter into
details — ^the evidence advanced by our best botanists on the
question whether certain doubtful forms should be ranked as
species or varieties, with the evidence from fertility adduced
by different hybridisers, or by the same observer from ex-
periments made during different years. It can thus be shown
that neither sterility nor fertility affords any certain distinc-
tion between species and varieties. The evidence from this
source graduates away, and is doubtful in the same degree as
is the evidence derived from other constitutional and struc-
tural differences.
In regard to the sterility of hybrids in successive genera-
tions ; though Gartner was enabled to rear some hybrids, care-
fully guarding them from a cross with either pure parent, for
six or seven, and in one case for ten generations, yet he
asserts positively that their fertility never increases, but gen-
erally decreases greatly and suddenly. With respect to this
decrease, it may first be noticed that when any deviation in
structure or constitution is common to both parents, this is
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DEGREES OF STERIUTT 901
often transmitted In an augmented degree to the offspring;
and both sexual elements in hybrid plants are already affected
in some degree. But I believe that their fertility has been
diminished in nearly all these cases by an independent cause,
namely, by too close interbreeding. I have made so many
experiments and collected so many facts, showing on the one
hand that an occasional cross with a distinct individual or
variety increases the vigour and fertility of the offspring, and
on the other hand that very close interbreeding lessens their
vigour and fertility, that I cannot doubt the correctness of
this conclusion. Hybrids are seldom raised by experimental-
ists in great numbers; and as the parent-species, or other
allied hybrids, generally grow in the same garden, the visits
of insects must be carefully prevented during the flowering
season ; hence hybrids, if left to themselves, will generally be
fertilised during each generation by pollen from the same
flower; and this would probably be injurious to their fertility,
already lessened by their hybrid origin. I am strengthened
in this conviction by a remarkable statement repeatedly made
by Gartner, namely, that if even the less fertile hybrids be
artificially fertilised with hybrid pollen of the same kind, their
fertility, nothwithstanding the frequent ill effects from manip-'
ulation, sometimes decidedly increases, and goes on increas-
ing. Now, in the process of artificial fertilisation, pollen Is
as often taken by chance (as I know from my own experi-
ence) from the anthers of another flower, as from the anthers
of the flower itself which is to be fertilised; so that a cross
between two flowers, though probably often on the same
plant, would be thus effected. Moreover, whenever compli-
cated experiments are in progress, so careful an observer as
Gartner would have castrated his hybrids, and this would
have ensured in each generation a cross with pollen from
a distinct flower, either from the same plant or from another
plant of the same hybrid nature. And thus, the strange fact
of an increase of fertility in the successive generations of
artificially fertilised hybrids, in contrast with those spon-
taneously self-fertilised, may, as I believe, be accounted for
by too close interbreeding having been avoided.
Now let us turn to the results arrived at by a third most
experienced hybridiser, namely, the Hon. and Rev. W. Her-
B — HC XI
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302 ORIGIN OF SPEaSS
bert. He is as emphatic in his conclusion that some hybrids
are perfectly fertile — ^as fertile as the pure parent-st^eiies —
as are Kolreuter and Gartner that some degree of sterility
between distinct species is a universal law of nature. He
experimented on some of the very same species as did
Gartner. The difference in their results may, I think, be in
part accounted for by Herbert's great horticultural skill, and
by his having hot-houses at his command. Of his many im-
portant statements I will here give only a single one as an
example, nfimely, that "every ovule in a pod of Crinum
capense fertilised by C. revolutum produced a plant, which
I never saw to occur in a case of its natural fecundation."
So that here we have perfect or even more than com-
monly perfect fertility, in a first cross between t^o distinct
species.
This case of the Crinum leads me to refer to a singfular
fact, namely, that individual plants of certain species of
Lobelia, Verbascum and Passiflora, can easily be fertilised by
pollen from a distinct species, but not by pollen from the
same plant, though this pollen can be proved to be perfectly
sound by fertilising other plants or species. In the genus
Hippeastrum, in Corydalis as shown by Professor Hilde-
brand, in various orchids as shown by Mr. Scott and Fritz
Muller, all the individuals are in this peculiar condition. So
that with some species, certain abnormal individuals, and in
other species all the individuals, can actually be hybridised
much more readily than they can be fertilised by pollen from
the same individual plant ! To give one instance, a bulb of
Hippeastrum aulicum produced four flowers ; three were fer-
tilised by Herbert with their own pollen, and the fourth was
subsequently fertilised by the pollen of a compound hybrid
descended from three distinct species: the result was that
"the ovaries of the three first flowers soon ceased to grow,
and after a few days perished entirely, whereas the pod im-
pregnated by the pollen of the hybrid made vigorous growth
and rapid progress to maturity, and bore good seed, which
vegetated freely." Mr. Herbert tried similar experiments
during many years, and always with the same result. These
cases serve to show on what slight and mysterious causes the
lesser or greater fertility of a species sometimes depends.
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DEGREES OF STEBILITY 303
The practical experiments of horticulturists, though not
made with scientific precision, deserve some notice. It is
notorious in how complicated a manner the species of Pelar-
gonium, Fuchsia, Calceolaria, Petunia, Rhododendron, &c.,
have been crossed, yet many of these hybrids seed freely.
For instance, Herbert asserts that a hybrid from Calceolaria
integrifolia and plantaginea, species most widely dissimilar
in general habit, ''reproduces itself as perfectly as if it had
been a natural species from the mountains of Chili." I have
taken some pains to ascertain the degree of fertility of some
of the complex crosses of Rhododendrons, and I am assured
that many of them are perfectly fertile. Mr. C. Noble, for
instance, informs me that he raises stocks for grafting from
a hybrid between Rhod. ponticum and catawbiense, and that
this hybrid "seeds as freely as it is possible to imagine." Had
hybrids, when fairly treated, always gone on decreasing in
fertility in each successive generation, as Gartner believed
to be the case, the fact would have been notorious to nursery-
men. Horticulturists raise large beds of the same hybrid, and
such alone are fairly treated, for by insect-agency the several
individuals are allowed to cross freely with eadi other, and
the injurious influence of close interbreeding is thus pre-
vented. Any one may readily convince himself of the efiici-
ency of insect-agency by examining the flowers of the more
sterile kinds of hybrid Rhododendrons, which produce no
pollen, for he will find on their stigmas plenty of pollen
brought from other flowers.
In regard to animals, much fewer experiments have been
carefully tried than with plants. If our systematic arrange-
ments can be trusted, that is, if the genera of animals are as
distinct from each other as are the genera of plants, then
we may infer that animals more widely distinct in the scale
of nature can be crossed more easily than in the case of
plants; but the hybrids themselves are, I think, more sterile.
It should, however, be borne in mind that, owing to few
animals breeding freely under confinement, few experiments
have been fairly tried : for instance, the canary-bird has been
crossed with nine distinct species of finches, but, as not one
of these breeds freely in confinement, we have no right to
expect that the first crosses between them and the canary.
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304 ORIGIN OF SPECIES
or that their hybrids, should be perfectly fertile. Again, with
respect to the fertility in successive generations of the more
fertile hybrid animals, I hardly know of an instance in which
two families of the same hybrid have been raised at the same
time from different parents, so as to avoid the ill effects of
close interbreeding. On the contrary, brothers and sisters
have usually been crossed in each successive generation, in
opposition to the constantly repeated admonition of every
breeder. And in this case, it is not at all surprising that the
inherent sterility in the hybrids should have gone on in-
creasing.
Although I know of hardly any thoroughly well-authen-
ticated cases of perfectly fertile hybrid animals, I have reason
to believe that the hybrids from Cervulus vaginalis and Ree-
vesii, and from Phasianus colchicus with P. torquatus, are
perfectly fertile. M. Quatrefages states that the hybrids from
two moths (Bombyx cynthia and arrindia) were proved in
Paris to be fertile inter se for eight generations. It has lately
been asserted that two such distinct species as the hare and
rabbit, when they can be got to breed together, produce off-
spring, which are highly fertile when crossed with one of
the parent-species. The hybrids from the common and Chi-
nese geese (A. cygnoides), species which are so different that
they are generally ranked in distinct genera, have often bred
in this country with either pure parent, and in one single in-
stance they have bred inter se. This was effected by Mr.
Eyton, who raised two hybrids from the same parents, but
from different hatches; and from these two birds he raised
no less than eight hybrids (grandchildren of the pure gees«)
from one nest. In India, however, these cross-bred geese
must be far more fertile ; for I am assured by two eminently
capable judges, namely Mr. Blyth and Capt. Hutton, that
whole flocks of these crossed geese are kept in various parts
of the country; and as they are kept for profit, where neither
pure parent-species exists, they must certainly be highly or
perfectly fertile.
With our domesticated animals, the various races when
crossed together are quite fertile ; yet in many cases they are
descended from two or more wild species. From this fact we
must conclude either that the aboriginal parent-species at
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LAWS GOVERNING THE STERILITY 305
first produced perfectly fertile hybrids, or that the hybrids
subsequently reared under domestication became quite fertile.
This latter alternative, which was first propounded by Pallas,
seems by far the most probable, and can, indeed, hardly be
doubted. It is, for instance, almost certain that our dogs are
descended from several wild stocks; yet, with perhaps the
exception of certain indigenous domestic dogs of South
America, all are quite fertile together; but analogy makes
me greatly doubt, whether the several aboriginal species would
at first have freely bred together and have produced quite
fertile hybrids. So again I have lately acquired decisive evi-
dence that the crossed offspring from the Indian humped and
common cattle are inter se perfectly fertile; and from the
observations by Riitimeyer on their important osteological
differences, as well as from those by Mr. Blyth on their dif-
ferences in habits, voice, constitution, &c., these two forms
must be regarded as good and distinct species. The same re-
marks may be extended to the two chief races of the pig.
We niust, therefore, either give up the belief of the universal
sterility of species when crossed; or we must look at this
sterility in animals, not as an indelible characteristic, but as
one capable of being removed by domestication.
Finally, considering all the ascertained facts on the inter-
crossing of plants and animals, it may be concluded that some
degree of sterility, both in first crosses and in hybrids, is an
extremely general result ; but that it cannot, under our present
state of knowledge, be considered as absolutely universal.
LAWS GOVBRNING THE STBRILITY OF FIRST CROSSES AND OF
HYBRIDS.
We will now consider a little more in detail the laws gov-
erning the sterility of first crosses and of hybrids. Our chief
object will be to see whether or not these laws indicate that
species have been specially endowed with this quality, in order
to prevent their crossing and blending together in utter con-
fusion. The following conclusions are drawn up chiefly from
Gartner's admirable work on the hybridisation of plants. I
have taken much pains to ascertain how far they apply to
animals, and, considering how scanty our knowledge is in re-
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306 ORIGIN OF SPECIBS
gard to hybrid animals, I have been surprised to find how
generally the same rules apply to both kingdoms.
It has been already remarked, that the degree of fertility,
both of first crosses and of hybrids, graduates from zero to
perfect fertility. It is surprising in how many curious ways
this gradation can be shown; but only the bsirest outline of
the facts can here be given. When pollen from a plant of
one family is placed on the stigma of a plant of a distinct
family, it exerts no more influence than so much inorganic
dust. From this absolute zero of fertility, the pollen of dif-
ferent species applied to the stigma of some one species of
the same genus, yields a perfect gradation in the number of
seeds produced, up to nearly complete or even quite complete
fertility; and, as we have seen, in certain abnormal cases,
even to an excess of fertility, beyond that which the plant's
own pollen produces. So in hybrids themselves, there are
some which never have produced, and probably never would
produce, even with the pollen of the pure parents, a single
fertile seed: but in some of these cases a first trace of fer-
tility may be detected, by the pollen of one of the pure parent-
species causing the flower of the hybrid to wither earlier
than it otherwise would have done; and the early withering
of the flower is well known to be a sign of incipient fertilisa-
tion. From this extreme degree of sterility we have self-
fertilised hybrids producing a greater and greater number of
seeds up to perfect fertility.
The hybrids raised from two species which are very diffi-
cult to cross, and which rarely produce any offspring, are
generally very sterile; but the parallelism between the diffi-
culty of making a first cross, and the sterility of the hybrids
thus produced — two classes of facts which are generally con-
founded together — is by no means strict. There are many
cases, in which two pure species, as in the genus Verbascum,
can be united with unusual facility, and produce numerous
hybrid-offspring, yet these hybrids are remarkably sterile.
On the other hand, there are species which can be crossed
very rarely, or with extreme difficulty, but the hybrids, when
at last produced, are very fertile. Even within the limits of
the same genus, for instance in Dianthus, these two opposite
cases occur.
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LAWS GOVERNING THE STERILITY 307
The fertility, both of first crosses and of hybrids, is more
easily affected by unfavorable conditions, than is that of
pure species. But the fertility of first crosses is likewise in-
nately variable ; for it is not adways the same in degree when
the same two species are crossed under the same circum-
stances; it depends in part upon the constitution of the in-
dividuals which happen to have been chosen for the experi-
ment. So it is with hybrids, for their degree of fertility is
often found to differ greatly in tha several individuals raised
from seed out of the same capsule and exposed to the same
conditions.
By the term systematic affinity is meant, the general re-
semblance between species in* structure and constitution. Now
the fertility of first crosses, and of the hybrids produced from
them, is largely governed by their systematic affinity. This
is clearly shown by hybrids never having been raised between
species ranked by systematists in distinct families; and on
the other hand, by very closely allied species generally uniting
with facility. But the correspondence between systematic
affinity and the facility of crossing is by no means strict. A
multitude of cases could be given of very closely allied species
which will not unite, or only with extreme difficulty; and on
the other hand of very distinct species which unite with the
utmost facility. In the same family there may be a genus,
as Dianthus, in which very many species can most readily be
crossed ; and another genus, as Silene, in which the most per-
severing efforts have failed to produce between extremely
close species a single hybrid. Even within the limits of the
same genus, we meet with this same difference ; for instance,
the many species of Nicotiana have been more largely crossed
than the species of almost any other genus; but Gartner
found that N. acuminata, which is not a particularly distinct
species, obstinately failed to fertilise, or to be fertilised by no
less than eight other species of Nicotiana. Many analogous
facts could be given.
No one has been able to point out what kind or what
amount of difference, in any recognisable character, is suf-
ficient to prevent two species crossing. It can be shown that
plants most widely different in habit and general appearance,
and having strongly marked differences in every part of the
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306 ORIGIN OF SPECDES
flower, even in the pollen, in the fruit, and in the cotyledons,
can be crossed Annual and perennial plants, dedduoms and
evergreen trees, plants inhabiting different stations and fitted
for extremely different climates, can often be crossed with
ease.
By a reciprocal cross between two species, I mean the case,
for instance, of a female-ass being first crossed by a stallion,
and then a mare by a male-ass; these two species may then
be said to have been reciprocally crossed. There is often the
widest possible difference in the facility of making reciprocal
crosses. Such cases are highly important, for they prove
that the capacity in any two species to cross is often com-
pletely independent of their systematic affinity, that is of any
difference in their structure or constitution, excepting in
their reproductive systems. The diversity of the result in
reciprocal crosses between the same two species was long
ago observed by Kolreuter. To give an instance: Mirabilis
jalapa can easily be fertilised by the pollen of M. longiilora,
and the hybrids thus produced are sufficiently fertile; but
Kolreuter tried more than two huntlred times, during eight
following years, to fertilise reciprocally M. longiflora with
the pollen of M. jalapa, and utterly failed. Several other
equally striking cases could be given. Thuret has observed
the same fact with certain sea-weeds or Fuci. Gartner,
moreover, found that this difference of facility in making
reciprocal crosses is extremely common in a lesser degree.
He has observed it even between closely related forms (as
Matthiola annua and glabra) which many botanists rank only
as varieties. It is also a remarkable fact, that hybrids raised
from reciprocal crosses, though of course compounded of the
very same two species, the one species having first been used
as the father and then as the mother, though they rarely
differ in external characters, yet generally differ in fertility
in a small, and occasionally in a high degree.
Several other singular rules could be given from Gartner:
for instance, some species have a remarkable power of cross-
ing with other species ; other species of the same genus have
a remarkable power of impressing their likeness on their
hybrid offspring; but these two powers do not at all neces-
sarily go together. There are certain hybrids which, instead
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LAWS GOVERNING THB STERILITY 309
of having, as is usual, an intermediate character between their
two parents, always closely resemble one of them ; and such
hybrids, though externally so like one of their pure parent-
species, are with rare exceptions extremely sterile. So again
amongst hybrids which are usually intermediate in' structure
between their parents, exceptional and abnormal individuals
sometimes are born, which closely resemble one of their pure
parents ; and these hybrids are almost always utterly sterile,
even when the other hybrids raised from seed from the same
capsule have a considerable degree of fertility. These facts
show how completely the fertility of a hybrid may be inde-
pendent of its external resemblance to either pure parent
Considering the several rules now given, which govern the
fertility of first crosses and of hybrids, we see that when
forms, which must be considered as good and distinct species,
are united, their fertility graduates from zero to perfect fer-
tility, or even to fertility under certain conditions in excess;
that their fertility, besides being eminently susceptible to
favourable and unfavourable conditions, is innately variable;
that it is by no means always the same in degree in the first
cross and in the hybrids produced from this cross; that the
fertility of hybrids is not related to the degree in which they
resemble in external appearance either parent; and lastly,
that the facility of making a first cross between any two
species is not always governed by their systematic affinity or
degree of resemblance to each other. This latter statement
is clearly proved by the difference in the result of reciprocal
crosses between the same two species, for, according as the
one species or the other is used as the father or the mother,
there is generally some difference, and occasionally the widest
possible difference, in the facility of effecting an union. The
hybrids, moreover, produced from reciprocal crosses often
differ in fertility.
Now do these complex and singular rules indicate that
species have been endowed with sterility simply to prevent
their becoming confounded in nature? I think not. For
why should the sterility be so extremely different in degree,
when various species are crossed, all of which we must sup-
pose it would be equally important to keep from blending to-
gether ? Why should the degree of sterility be innately vari-
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310 ORIGIN OF SPEaSS
able in the individuals of the same species? Why should
some species cross with facility, and yet produce very sterile
hybrids; and other species cross with extreme difficulty, and
yet produce fairly fertile hybrids? Why should there often
be so great a difference in the result of a reciprocal cross
between the same two species? Why, it may even be asked,
has the production of hybrids been permitted? To grant to
species tiie special power of producing hybrids, and then to
stop their further propagation by different degrees of sterility,
not strictly related to the facility of the first union between
their parents, seems a strange arrangement
The foregoing rules and facts, on the other hand, appear to
me clearly to indicate that the sterility both of first crosses
and of hybrids is simply incidental or dependent on unknown
differences in their reproductive systems; the differences be-
ing of so peculiar and limited a nature, that, in reciprocal
crosses between the same two species, the male sexual ele-
ment of the one will often freely act on the female sexual
element of the other, but not in a reversed direction. It will
be advisable to explain a little more fully by an example what
I mean by sterility being incidental on other differences, and
not a specially endowed quality. As the capacity of one
plant to be grafted or budded on another is unimportant for
their welfare in a state of nature, I presume that no one will
suppose that this capacity is a specially endowed quality, but
will admit that it is incidental on differences in the laws of
growth of the two plants. We can sometimes see the reason
why one tree will not take on another, from differences in
their rate of growth, in the hardness of their wood, in the
period of the How or nature of their sap, &c. ; but in a multi-
tude of cases we can assign no reason whatever. Great di-
versity in the size of two plants, one being woody and the other
herbaceous, one being evergreen and the other decidu-
ous, an adaptation to widely different climates, do not
always prevent the two grafting together. As in hybridisa-
tion, so with grafting, the capacity is limited by systematic
affinity, for no one has been able to graft together trees be-
longing to quite distinct families; and, on the other hand,
closely allied species, and varieties of the same species, can
usually, but aot invariably, be grafted with ease. But this
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LAWS GOVERNING THE STERILITY 311
capacity, as in hybridisation, is by no means absolutely gov-
erned by systematic affinity. Although many distinct genera
within the same family have been grafted together, in other
cases species of the same genus will not take on each other.
The pear can be grafted far more readily on the quince,
which is ranked as a distinct genus, than on the apple, which
is a member of the same genus. Even different varieties of
the pear take with different degrees of facility on the quince ;
so do different varieties of the apricot and peach on certain
varieties of the plum.
As Gartner found that there was sometimes an innate dif-
ference in different individuals of the same two species in
crossing; so Sageret believes this to be the case with different
individuals of the same two species in being grafted together.
As in reciprocal crosses, the facility of effecting an union is
often very far from equal, so it sometimes is in grafting ; the
common gooseberry, for instance, cannot be grafted on the
currant, whereas the currant will take, though with difficulty,
on the gooseberry.
We have seen that the sterility of hybrids, which have
their reproductive organs in an imperfect condition, is a dif-
ferent case from the difficulty of uniting two pure species,
which have their reproductive organs perfect; yet these two
distinct classes of cases run to a large extent parallel. Some-
thing analogous occurs in grafting; for Thouin found that
three species of Robinia, which seeded freely on their own
roots, and which could be grafted with no great difficulty on
a fourth species, when thus grafted were rendered barren.
On the other hand, certain species of Sorbus, when grafted
on other species yielded twice as much fruit as when on their
own roots. We are reminded by this latter fact of the extra-
ordinary cases of Hippeastrum, Passiflora, &c., which seed
much more freely when fertilised with the pollen of a dis-
tinct species, than when fertilised with pollen from the same
plant
We thus see, that, although there is a clear and great dif-
ference between the mere adhesion of grafted stocks, and the
union of the male and female elements in the act of repro-
duction, yet that there is a rude degree of parallelism in the
results of grafting and of crossing distinct species. And as
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312 ORIGIN OP SPEaBS
we must look at the curious and complex laws govemix^ the '
facility with which trees can be grafted on each other as in-
cidental on unknown differences in their vegetative systems,
so I believe that the still more complex laws governing the
facility of first crosses are incidental on unknown differences
in their reproductive systems. These differences in both
cases, follow to a certain extent, as might have been expected,
systematic affinity, by which term every kind of resemblance
and dissimilarity between organic beings is attempted to be
expressed. The facts by no means seem to indicate that the
greater or lesser difficulty of either grafting or crossing vari-
ous species has been a special endowment; although in the
case of crossing, the difficulty is as important for the endur-
ance and stability of specific forms, as in the case of graft-
ing it is unimportant for their welfare.
ORIGIN AND CAUSES OF THE STERILITY OP FIRST CROSSES
AND OF HYBRIDS
At one time it appeared to me probable, as it has to others,
that the sterility of first crosses and of hybrids might have
been slowly acquired through the natural selection of slightly
lessened degrees of fertHity, which, like any other variation,
spontaneously appeared in certain individuals of one variety
when crossed with those of another variety. For it would
clearly be advantageous to two varieties or incipient species,
if they could be kept from blending, on the same principle
that, when man is selecting at the same time two varieties,
it is necessary that he should keep them separate. In the
first place, it may be remarked that species inhabiting dis-
tinct regions are often sterile when crossed; now it could
clearly have been of no advantage to such separated species
to have been rendered mutually sterile, and consequently this
could not have been effected through natural selection; but
it may perhaps be argued, that, if a species was rendered
sterile with some one compatriot, sterility with other species
would follow as a necessary contingency. In the second
place, it is almost as much opposed to the theory of natural
selection as to that of special creation, that in reciprocal
crosses the male element of one form should have been ren-
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CAUSES OF THE STEBIUTY 313
dered utterly impotent on a second form, whilst at the same
time the male element of this second form is enabled freely
to fertilise the first form ; for this peculiar state of the repro-
ductive system could hardly have been advantageous to either
species.
In considering the probability of natural selection having
come into action, in rendering species mutually sterile, the
greatest difficulty will be found to lie in the existence of many
graduated steps from slightly lessened fertility to absolute
sterility. It may be admitted that it would profit an incipient
species, if it were rendered in some slight degree sterile when
crossed with its parent form or with some other variety; for
thus fewer bastardised and deteriorated offspring would be
produced to commingle their blood with the new species in
process of formation. But he who will take the trouble to
reflect on the steps by which this first degree of sterility
could be increased through natural selection to that high de-
gree which is common with so many species, and which is
universal with species which have been differentiated to a
generic or family rank, will find the subject extraordinarily
complex. After mature reflection it seems to me that this
could not have been effected through natural selection. Take
the case of any two species which, when crossed, produced
few and sterile offspring; now, what is there which could
favour the survival of those individuals which happened to
be endowed in a slightly higher degree with mutual infer-
tility, and which thus approached by one small step towards
absolute sterility ? Yet an advance of this kind, if the theory
of natural selection be brought to bear, must have incessantly
occurred with many species, for a multitude are mutually
quite barren. With sterile neuter insects we have reason to
believe that modifications in their structure and fertility
have been slowly acctnnulated by natural selection, from an
advantage having been thus indirectly given to the com-
munity to which they belonged over other communities of the
same species; but an individual animal not belonging to a
social community, if rendered slightly sterile when crossed
with some other variety, would not thus itself gain any ad-
vantage or indirectly give any advantage to the other individ-
uals of the same variety, thus leading to their preservation.
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314 ORIGIN OP SPECIES
But it wotdd be superfluous to discuss this question in de-
tail; for with plants we have conclusive evidence that the
sterility of crossed species must be due to some principle,
quite independent of natural selection. Both Gartner and
Kolreuter have proved that in genera including numerous
species, a series can be formed from species which when
crossed yield fewer and fewer seeds, to species which never
produce a single seed, but yet are affected by the pollen of
certain other species, for the germen swells. It is here mani-
festly impossible to select the more sterile individuals, which
have already ceased to yield seeds ; so that this acme of ster-
ility, when the germen alone is affected, cannot have been
gained through selection; and from the laws governing the
various grades of sterility being so uniform throughout the
animal and vegetable kingdoms, we may infer that the cause,
whatever it may be, is the same or nearly the same in all
cases.
We will now look a little closer at the probable nature of
the differences between species which induce sterility in first
crosses and in hybrids. In the case of first crosses, the
greater or less difficulty in effecting an union and in obtain-
ing offspring apparently depends on several distinct causes.
There must sometimes be a physical impossibility in the male
element reaching the ovule, as would be the case with a plant
having a pistil too long for the pollen-tubes to reach the
ovarium. It has also been observed that when the pollen of
one species is placed on the stigma of a distantly allied spe-
cies, though the pollen-tubes protrude, they do not penetrate
the stigmatic surface. Again, the male element may reach the
female element but be incapable of causing an embryo to be
developed, as seems to have been the case with some of Thu-
ret's experiments on Fuci. No explanation can be given of
these facts, any more than why certain trees cannot be grafted
on others. Lastly an embryo may be developed, and then perish
at an early period. This latter alternative has not been suf-
ficiently attended to; but I believe, from observations com-
municated to me by Mr. Hewitt, who has had great experi-
ence in hybridising pheasants and fowls, that the early death
of the embryo is a very frequent cause of sterility in first
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CAUSES OP THE STERILITY 315
crosses. Mr. Salter has recently given the results of an ex-
amination of about 500 eggs produced from various crosses
between three species of Gallus and their hybrids; the ma-
jority of these eggs had been fertilised; and in the majority
of the fertilised eggs, the embryos had either been partially
developed and had then perished, or had become nearly ma-
ture, but the young chickens had been unable to break through
the shells. Of the chickens which were bom, more than four-
fifths died within the first few days, or at latest weeks, "with-
out any obvious cause, apparently from mere inability to
live;" so that from the 500 eggs only twelve chickens were
reared. With plants, hybridised embryos probably often
perish in a like manner; at least it is known that hybrids
raised from very distinct species are sometimes weak and
dwarfed, and perish at an early age; of which fact Max
Wichura has recently given some striking cases with hybrid
willows. It may be here worth noticing that in some cases of
parthenogenesis, the embryos within the eggs of silk moths
which had not been fertilised, pass through their early stages
of development and then perish like the embryos produced by
a cross between distinct species. Until becoming acquainted
with these facts, I was unwilling to believe in the frequent
early death of hybrid embryos ; for hybrids, when once bom,
are generally healthy and long-lived, as we see in the case
of the common mule. Hybrids, however, are differently cir-
cumstanced before and after birth; when bom and living in
a country where their two parents live, they are generally
placed under suitable conditions of life. But a hybrid par-
takes of only half of the nature and constitution of its
mother; it may therefore before birth, as long as it is nour-
ished within its mother's womb, or within the egg or seed
produced by the mother, be exposed to conditions in some de-
gree unsuitable, and consequendy be liable to perish at an early
period; more especially as all very young beings are eminently
sensitive to injurious or unnatural conditions of life. But af-
ter all, the cause more probably lies in some imperfection
in the original act of impregnation, causing the embryo to be
imperfectly developed, rather than in the conditions to which
it is subsequently exposed.
In regard to the sterility of hybrids, in which the sexual
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316 ORIGIN OP SPECIES
elements are imperfectly developed, the case is somewhat dif-
ferent. I have more than once alluded to a large body of
facts showing that, when animals and plants are removed
from their natural conditions, they are extremely liable to
have their reproductive systems seriously affected. This, in
fact, is the great bar to the domestication of animals. Be-
tween the sterility thus superinduced and that of hybrids,
there are many points of similarity. In both cases the steril-
ity is independent of general health, and is often accompanied
by excess of size or great luxuriance. In both cases the
sterility occurs in various degrees ; in both, the male element
is the most liable to be affected; but sometimes the female
more than the male. In both, the tendency goes to a certain
extent with systematic affinity, for whole groups of animals
and plants are rendered impotent by the same unnatural con-
ditions; and whole groups of species tend to produce sterile
hybrids. On the other hand, one species in a group will some-
times resist great changes of conditions with unimpaired
fertility ; and certain species in a group will produce unusually
fertile hybrids. No one can tell, till he tries, whether any
particular animal will breed under confinement, or any exotic
plant seed freely under culture; nor can he tell till he tries,
whether any two species of a genus will produce more or
less sterile hybrids. Lastly, when organic beings are placed
during several generations under conditions not natural to
them, they are extremely liable to vary, which seems to be
partly due to their reproductive systems having been specially
affected, though in a lesser degree than when sterility ensues.
So it is with hybrids, for their offspring in successive genera-
tions are eminently liable to vary, as every experimentalist
has observed.
Thus we see that when organic beings are placed under new
and unnatural conditions, and when hybrids are produced
by the unnatural crossing of two species, the reproductive
system, independently of the general state of health, is af-
fected in a very similar manner. In the one case, the condi-
tions of life have been disturbed, though often in so slight
a degree as to be inappreciable by us; in the other case, or
that of hybrids, the external conditions have remained the
same, but the organisation has been disturbed by two dis-
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CAUSES OF THE STERILITY 317
tinct structures and constitutions, including of course the
reproductive systems, having been blended into one. For
it is scarcely possible that two organisations should be
compounded into one, without some disturbance occur-
ring in the development, or periodical action, or mutual
relations of the different parts and organs one to another or
to the conditions of life. When hybrids are able to breed
inter se, they transmit to their offspring from generation to
generation the same compounded organisation, and hence we
need not be surprised that their sterility, though in some
degree variable, does not diminish ; it is even apt to increase,
this being generally the result, as before explained, of too
close interbreeding. The above view of the sterility of hy-
brids being caused by two constitutions being compounded
into one has been strongly maintained by Max Wichura.
It must, however, be owned that we cannot understand, on
the above or any other view, several facts with respect to the
sterility of hybrids ; for instance, the unequal fertility of hy-
brids produced from reciprocal crosses ; or the increased ster-
ility in those hybrids which occasionally and exceptionally
resemble closely either pure parent. Nor do I pretend that
the foregoing remarks go to the root of the matter; no ex-
planation is offered why an organism, when placed under nat-
il^al conditions, is rendered sterile. All that I have attempted
to show is, that in two cases, in some respects allied, sterility
is the common result, — in the one case from the conditions
of life having been disturbed, in the other case from the
organisation having been disturbed by two organisations
being compounded into one.
A similar parallelism holds good with an allied yet very dif-
ferent class of facts. It is an old and almost universal be-
lief founded on a considerable body of evidence, which I have
elsewhere given, that slight changes in the conditions of life
are beneficial to all living things. We see this acted on by
farmers and gardeners in their frequent exchanges of seed,
tubers, &c., from one soil or climate to another, and back
again. During the convalescence of animals, great benefit
is derived from almost any change in their habits of life.
Again, both with plants and animals, there is the clearest
evidence that a cross between individuals of the same spe-
T— HC XI
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318 ORIGIN OF SPECIES
cies, which differ to a certain extent, gives vigour and fer-
tility to the offspring; and that close interbreeding continued
during several generations between the nearest relations, if
these be kept under the same conditions of life, almost always
leads to decreased size, weaknessi or sterility.
Hence it seems that, on the one hand, slight changes in the
conditions of life benefit all organic beings, and on the other
hand, that slight crosses, that is crosses between the males
and females of the same species, which have been subjected
to slightly different conditions, or which have slightly varied,
give vigour and fertility to the offspring. But, as we have
seen, organic beings long habituated to certain uniform condi-
tions under a state of nature, when subjected, as under con-
finement, to a considerable change in their conditions, very
frequently arc rendered more or less sterile; and we know
that a cross between two forms, that have become widely or
specifically different, produce hybrids which are almost al-
ways in some degree sterile. I am fully persuaded that this
double, parallelism is by no means an accident or an illusion.
He who is able to explain why the elephant and a multitude
of other animals are incapable of breeding when kept under
only partial confinement in their native country, will be
able to explain the primary cause of hybrids being so gener-
ally sterile. He will at the same time be able to expla^j^
how it is that the races of some of our domesticated animals,
which have often been subjected to new and not uniform con-
ditions, are quite fertile together, although they are descended
from distinct species, which would probably have been sterile
if aboriginally crossed. The above two parallel series of
facts seem to be connected together by some common but
unknown bond, which is essentially related to the principle of
life; this principle, according to Mr. Herbert Spencer, being
that life depends on, or consists in, the incessant action and
reaction of various forces, which, as throughout nature, are
always tending towards an equilibrium; and when this ten-
dency IS slightly disturbed by any change, the vital forces
gain in power.
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DIMORPHISM AND TRIMORPHISM 319
KECIPROCAL DIMORPHISM AND TRIMORPHISM
This subject may be here briefly discussed, and will be
found to throw some light on hybridism. Several plants be-
longing to distinct orders present two forms, which exist
in about equal numbers and which differ in no respect ex-
cept in their reproductive organs; one form having a long
pistil with short stamens, the other a short pistil with long
stamens; the two having differently sized pollen-grains.
With trimorphic plants there are three forms likewise differ-
ing in the lengths of their pistils and stamens, in the size
and colour of ^e pollen-grains, and in some other respects;
and as in each of the three forms there are two sets of sta-
mens, the three forms possess altogether six sets of stamens
and three kinds of pistils. These organs are so proportioned
in length to each other, that half the stamens in two of the
forms stand on a level with the stigma of the third form.
Now I have shown, and the result has been confirmed by
other observers, that, in order to obtain full fertility with
these plants, it is necessary that the stigma of the one form
should be fertilised by pollen taken from the stamens of cor-
responding height in another form. So that with dimorphic
species two unions, which may be called legitimate, are
fdlly fertile; and two, which may be called illegitimate,
are more or less infertile. With trimorphic species six
unions arc legitimate, or fully fertile, — and twelve are ille-
gitimate, or more or less infertile.
The infertility which may be observed in various dimorphic
and trimorphic plants, when they are illegitimately fertilised,
that is by pollen taken from stamens not corresponding in
height with the pistil, differs much in degree, up to absolute
and utter sterility; just in the same manner as occurs in
crossing distinct species. As the degree of sterility in the
latter case depends in an eminent degree on the conditions
of life being more or less favourable, so I have found it
with illegitimate unions. It is well known that if pollen of a
distinct species be placed on the stigma of a flower, and its
own pollen be afterwards, even after a considerable interval
of time, placed on the same stigma, its action is so strongly
prepotent that it generally annihilates the effect of the foreign
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320 ORIGIN OF SPECIES
pollen; so it is with the pollen of the several forms of the
same species, for legitimate pollen is strongly prepotent over
illegitimate pollen, when both are placed on the same stigma.
I ascertained this by fertilising several flowers, first ille-
gitimately, and twenty-four hours afterwards legitimately,
with pollen taken from a peculiarly coloured variety, and
all the seedlings were similarly coloured; this shows that
the legitimate pollen, though applied twenty-four hours sub-
sequently, had wholly destroyed or prevented the action of
the previously applied illegitimate pollen. Again, as in
making reciprocal crosses between the same two species,
there is occasionally a great difference in the result, so the
same thing occurs with trimorphic plants; for instance, the
mid-styled form of Lythrum salicaria was illegitimately fer-
tilised with the greatest ease by pollen from the longer sta-
mens of the short-styled form, and yielded many seeds; but
the latter form did not yield a single seed when fertilised by
the longer stamens of the mid-styled form.
In all these respects, and in others which might be added,
the forms of the same undoubted species when illegitimately
united behave in exactly the same manner as do two distinct
species when crossed. This led me carefully to observe
during four years many seedlings, raised from several illegiti-
mate unions. The chief result is that these illegitimate plants,
as they may be called, are not fully fertile. It is possible to
raise from dimorphic species, both long-styled and short-
styled illegitimate plants, and from trimorphic plants all three
illegitimate forms. These can then be properly united in a
legitimate manner. When this is done, there is no apparent
reason why they should not yield as many seeds as did their
parents when legitimately fertilised. But such is not the
case. They are all infertile, in various degrees; some being
so utterly and incurably sterile that they did not yield dur-
ing four seasons a single seed or even seed-capsule. The
sterility of these illegitimate plants, when united with each
other in a legitimate manner, may be strictly compared with
that of hybrids when crossed inter se. If, on the other hand,
a hybrid is crossed with either pure parent-species, the steril-
ity is usually much lessened ; and so it is when an illegitimate
plant is fertilised by a legitimate plant In the same man-
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DIMORPHISM AND TRIMORPHISM 321
ner as the sterility of hybrids does not always run parallel
with the difficulty of making the first cross between the two
parent-species, so the sterility of certain illegitimate plants
was unusually great, whilst the sterility of the union from
which they were derived was by no means great. With hy-
brids raised from the same seed-capsule the degree of ster-
ility is innately variable, so it is in a marked manner with
illegitimate plants. lastly, many hybrids are profuse and
persistent fiowerers, whilst other and more sterile hybrids
produce few flowers, and are weak, miserable dwarfs;
exactly similar cases occur with the illegitimate offspring of
various dimorphic and trimorphic plants.
Altogether there is the closest identity in character and
behaviour between illegitimate plants and hybrids. It is
hardly an exaggeration to maintain that illegitimate plants are
hybrids, produced within the limits of the same species by
the improper union of certain forms, whilst ordinary hybrids
are produced from an improper union between so-called dis-
tinct species. We hav6 also already seen that there is the
closest similarity in all respects between first illegitimate
unions and first crosses between distinct species. This will
perhaps be made more fully apparent by an illustration; we
may suppose that a botanist found two well-marked varieties
(and such occur) of the long-styled form of the trimorphic
Lythrum salicaria, and that he determined to try by cross-
ing whether they were specifically distinct. He would find
that they yielded only about one-fifth of the proper number of
seed, and that they behaved in all the other above specified
respects as if they had been two distinct species. But to make
the case sure, he would raise plants from his supposed hy-
bridized seed, and he would find that the seedlings were mis-
erably dwarfed and utterly sterile, and that they behaved in
all other respects like ordinary hybrids. He might then main-
tain that he had actually proved, in accordance with the
common view, that his two varieties were as good and as
distinct species as any in the world; but he would be com-
pletely mistaken.
The facts now given on dimorphic and trimorphic plants
are important, because they show us, first, that the physio-
logical test of lessened fertility, both in first crosses and in
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322 ORIGIN OP SPECIES
hybrids, is no safe criterion of specific distinction; secondly,
because we may conclude that there is some unknown bond
which connects the infertility of illegitimate unions with
that of their illegitimate offspring, and we are led to extend
the same view to first crosses and hybrids; thirdly, because
we find, and this seems to me of especial importance, that
two or three forms of the same species may exist and may
differ in no respect whatever, either in structure or in con-
stitution, relatively to external conditions, and yet be sterile
when united in certain ways. For we must remember that
it is the union of the sexual elements of individuals of the
same form, for instance, of two long-styled forms, which
results in sterility; whilst it is the union of the sexual
elements proper to two distinct forms which is fertile. Hence
the case appears at first sight exactly the reverse of what
occurs, in the ordinary unions of the individuals of the same
species and with crosses between distinct species. It is,
however, doubtful whether this is really so; but I will not
enlarge on this obscure subject.
We may, however, infer as probable from the consideration
of dimorphic and trimorphic plants^ that the sterility of dis-
tinct species when crossed and of their hybrid progeny, de-
pends exclusively on the nature of their sexual elements, and
not on any difference in their structure or general constitur
tion. We are also led to this same conclusion by considering
reciprocal crosses, in which the male of one species cannot
be united, or can be united with great difficulty, with the
female of a second species, whilst the converse cross can be
effected with perfect facility. That excellent observer, Gart-
ner, likewise concluded that species when crossed are sterile
owing to differences confined to their reproductive systems.
FERTILITY OF VARIETIES WHEN CROSSED, AND OF THEIR
MONGREL OFFSPRING, NOT UNIVERSAL
It may be urged, as an overwhelming argument, that there
must be some essential distinction between species and vari-
eties, inasmuch as the latter, however much they may differ
from each other in external appearance, cross with perfect
facility, and yield perfectly fertile offspring. With some
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FERTILITY OP VARIETIES 323
exceptions, presently to be given, I fully admit that this is
the rule. But the subject is surrounded by difficulties, for,
looking to varieties produced under nature, if two forms
hitherto reputed to be varieties be found in any degree sterile
together, they are at once ranked by most naturalists as
species. For instance, the blue and red pimpernel, which
are considered by most botanists as varieties, are said by
Gartner to be quite sterile when crossed, and he conse-
quently ranks them as undoubted species. If we thus argue
in a circle, the fertility of all varieties produced under
nature will assuredly have to be granted.
If we turn to varieties, produced, or supposed to have been
produced, under domestication, we are still involved in some
doubt. For when it is stated, for instance, that certain South
American indigenous domestic dogs do not readily unite with
European dogs, the explanation which will occur to every
one, and probably the true one, is that they are descended
from aboriginally distinct species. Nevertheless the perfect
fertility of so many domestic races, differing widely from
each other in appearance, for instance those of the pigeon,
or of the cabbage, is a remarkable fact ; more especially when
we reflect how many species there are, which, though re-
sembling each other most closely, are utterly sterile when
intercrossed. Several considerations, however, render the
fertility of domestic varieties less remarkable. In the first
place, it may be observed that the amount of external differ-
ence between two species is no sure guide to their degree of
mutual sterility, so that similar differences in the case of
varieties would be no sure guide. It is certain that with
species the cause lies exclusively in differences in their sex-
ual constitution. Now the varying conditions to which do-
mesticated animals and cultivated plants have been subjected,
have had so little tendency towards modifying the repro-
ductive system in a manner leading to mutual sterility, that
we have good grounds for admitting the directly opposite
doctrine of Pallas, namely, that such conditions generally
eliminate this tendency ; so that the domesticated descendants
of species, which in their natural state probably would have
been in some degree sterile when crossed, become perfectly
fertile together. With plants, so far is cultivation from giving
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324 ORIGIN OF SPECIBS
a tendency towards sterility between distinct species, that in
several well-authenticated cases already alluded to, certain
plants have been affected in an opposite manner, for they have
become self -impotent whilst still retaining the capacity of
fertilising, and being fertilised by, other species. If the
Pallasian doctrine of the elimination of sterility through
long-continued domestication be admitted, and it can hardly
be rejected, it becomes in the highest degree improbable that
similar conditions, long-continued should likewise induce this
tendency; though in certain cases, with species having a
peculiar constitution, sterility might occasionally be thus
caused. Thus, as I believe, we can understand why with
domesticated animals varieties have not been produced which
are mutually sterile; and why with plants only a few such
cases, immediately to be given,, have been observed.
The real difficulty in our present subject is not, as it ap-
pears to me, why domestic varieties have not become mutually
infertile when crossed, but why this has so generally occurred
with natural varieties, as soon as they have been permanently
modified in a sufficient degree to take rank as species. We
are far from precisely knowing the cause; nor is this sur-
prising, seeing how profoundly ignorant we are in regard
to the normal and abnormal action of the reproductive sys-
tem. But we can see that species, owing to their struggle
for existence with numerous competitors, will have been
exposed during long periods of time to more uniform condi-
tions, than have domestic varieties; and this may well make
a wide difference in the result For we know how com-
monly wild animals and plants, when taken from their natural
conditions and subjected to captivity, are rendered sterile;
and the reproductive functions of organic beings which have
always lived under natural conditions would probably in like
manner be eminently sensitive to the influence of an un-
natural cross. Domesticated productions, on the other hand,
which, as shown by the mere fact of their domestication, were
not originally highly sensitive to changes in their conditions
of life, and which can now generally resist with undiminished
fertility repeated changes of conditions, might be expected
to produce varieties, which would be little liable to have
their reproductive powers injuriously affected by the act
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FERTILITY OF VARIETIES S25
of crossing with other varieties which had originated in a
like manner.
I have as yet spoken as if the varieties of the same species
were invariably fertile when intercrossed But it is im-
possible to resist the evidence of the existence of a certain
amount of sterility in the few following cases, which I will
briefly abstract. The evidence is at least as good as that
from which we believe in the sterility of a multitude of spe-
cies. The evidence is, also, derived from hostile witnesses,
who in all other cases consider fertility and sterility as safe
criterions of specific distinction. Gartner kept during sev-
eral years a dwarf kind of maize with yellow seeds, and a
tall variety with red seeds growing near each other in his
garden; and although these plants have separated sexes, they
never naturally crossed. He then fertilised thirteen flowers
of the one kind with pollen of the other; but only a single
head produced any seed, and this one head produced only
five grains. Manipulation in this case could not have been
injurious, as the plants have separated sexes. No one, I
believe, has suspected that these varieties of maize are dis-
tinct species; and it is important to notice that the hybrid
plants thus raised were themselves perfectly fertile; so that
even Gartner did not venture to consider the two varieties
as specifically different.
Girou de Buzareingues crossed three varieties of gourd,
which like the maize has separated sexes, and he asserts
that their mutual fertilisation is by so much the less easy as
their differences are greater. How far these experiments
may be trusted, I know not; but the forms experimented
on are ranked by Sageret, who mainly founds his classifica-
tion by the test of infertility, as varieties, and Naudin has
come to the same conclusion.
The following case is far more remarkable, and seems
at first incredible ; but it is the result of an astonishing num-
ber of experiments made during many years on nine species
of Verbascum, by so good an observer and so hostile a wit-
ness as Gartner : namely that the yellow and white varieties
when crossed produce less seed than the similarly coloured
varieties of the same species. Moreover, he asserts that
when yellow and white varieties of one species are crossed
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326 ORIGIN OF SPBaBS
with yellow and white varieties of a distinct species, more
seed is produced by the crosses between the similarly coloured
flowers, than between those which are differently coloured.
Mr. Scott also has experimented on the species and varieties
of Verbascum; and although unable to confirm Gartner's
results on the crossing of the distinct species, he finds that
the dissimilarly coloured varieties of the same species yield
fewer seeds, in the proportion of 86 to lOO, than the similarly
coloured varieties. Yet these varieties differ in no respect
except in the colour of their flowers; and one variety can
sometimes be raised from the seed of another.
Kolreuter, whose accuracy has been confirmed by every
subsequent observer, has proved the remarkable fact, that
one particular variety of the common tobacco was more
fertile than the other varieties, when crossed with a widely
distinct species. He experimented on five forms which are
c(Mnmonly reputed to be varieties, and which he tested by
the severest trial, namely, by reciprocal crosses, and he found
their mongrel offspring perfectly fertile. But one of these
five varieties, when used either as the father or mother, and
crossed with the Nicotiana glutinosa, always yielded hybrids
not so sterile as those which were produced from the four
other varieties when crossed with N. glutinosa. Hence the
reproductive system of this one variety must have been
in some manner and in some degree modified.
From these facts it can no longer be maintained that var-
ieties when crossed are invariably quite fertile. From the
great difficulty of ascertaining the infertility of varieties in
a state of nature, for a supposed variety, if proved to be in-
fertile in any degree, would almost universally be ranked as
a species; — from man attending only to external characters
in his domestic varieties, and from such varieties not hav-
ing been exposed for very long periods to uniform conditions
of life; — from these several considerations we may conclude
that fertility does not constitute a fundamental distinction
between varieties and species when crossed. The general
sterility of crossed species may safely be looked at, not as a
special acquirement or endowment, but as incidental on
changes of an unknown nature in their sexual elements.
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HYBRIDS AND MONGRELS COMPARED 327
HYBRIDS AND MONGRELS COMPARED, INDEPENDENTLY OF
THEIR FERTILITY
Independently of the question of fertility, the offspring
of species and of varieties when crossed may be compared
in several other respects. Gartner, whose strong wish it was
to draw a distinct line between species and varieties, could
find very few, and, as it seems to me, quite unimportant dif-
ferences between the so-called hybrid offspring of species,
and the so-called mongrel offspring of varieties. And, on the
other hand, they agree most closely in many important re-
spects.
I shall here discuss this subject with extreme brevity. The
most important distinction is, that in the first generation
mongrels are more variable than hybrids ; but Gartner admits
that hybrids from species which have long been cultivated are
often variable in the first generation ; and I have myself seen
striking instances of this fact. Gartner further admits that
hybrids between very closely allied species are more variable
than those from very distinct species; and this shows that
the difference in the degree of variability graduates away.
When mongrels and the more fertile hybrids are propagated
for several generations, an extreme amount of variability in
the offspring in both cases is notorious; but some few in-
stances of both hybrids and mongrels long retaining a uniform
character could be given. The variability, however, in the
successive generations of mongrels is, perhaps, greater than
in hybrids.
This greater variability in mongrels than in hybrids does
not seem at all surprising. For the parents of mongrels
are varieties, and mostly domestic varieties (very few ex-
periments having been tried on natural varieties,) and this
implies that there has been recent variability, which would
often continue and would augment that arising from the act
of crossing. The slight variability of hybrids in the first
generation, in contrast with that in the succeeding genera-
tions, is a curious fact and deserves attention. For it bears
on the view which I have taken of one of the causes of
ordinary variability; namely, that the reproductive system
from being eminently sensitive to changed conditions of life,
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328 ORIGIN OF SPEOBS
fails under these circumstances to perform its proper func-
tion of producing offspring closely similar in all respects
to the parent-form. Now hybrids in the first generation are
descended from specie^ (excluding those long-cultivated)
which have not had their reproductive systems in any way
affected, and they are not variable; but hybrids themselves
have their reproductive systems seriously affected, and their
descendants are highly variable.
But to return to our comparison of mongrels and hybrids:
Gartner states that mongrels are more liable than hybrids
to revert to either parent-form; but this, if it be true, is cer-
tainly only a difference in degree. Moreover, Gartner ex-
pressly states that hybrids from long cultivated plants are
more subject to reversion than hybrids from species in their
natural state; and this probably explains the singular differ-
ence in the results arrived at by different observers: thus
Max Wichura doubts whether hybrids ever revert to their
parent-forms, and he experimented on uncultivated species
of willows; whilst Naudin, on the other hand, insists in the
strongest terms on the almost universal tendency to reversion
in hybrids, and he experimented chiefly on cultivated plants.
Gartner further states that when any two species, although
most closely allied to each other, are crossed with a third
species, the hybrids are widely different from each other;
whereas if two very distinct varieties of one species are
crossed with another species, the hybrids do not differ much.
But this conclusion, as far as I can make out, is founded
on a single experiment; and seems directly opposed to the
results of several experiments made by Kolreuter.
Such alone are the unimportant differences which Gartner
is able to point out between hybrid and mongrel plants. On
the other hand, the degrees and kinds of resemblance in
mongrels and in hybrids to their respective parents, more
especially in hybrids produced from nearly related species,
follow according to Gartner the same laws. When two
species are crossed, one has sometimes a prepotent power
of impressing its likeness on the hybrid. So I believe it to
be with varieties of plants ; and with animals one variety cer-
tainly often has this prepotent power over another variety.
Hybrid plants produced from a reciprocal cross, generally
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HYBRIDS AND MONGRELS COMPARED 329
resemble each other closely ; and so it is with mongrel plants
from a reciprocal cross. Both hybrids and mongrels can be
reduced to cither pure parent- form, by repeated crosses in
successive generations with either parent.
These several remarks are apparently applicable to ani-
mals; but the subject is here much complicated, partly owing
to the existence of secondary sexual characters; but more
especially owing to prepotency in transmitting likeness run-
ning more strongly in one sex than in the other, both when
one species is crossed with another, and when one variety is
crossed with another variety. For instance, I think those
authors are right who maintain that the ass has a prepo-
tent power over the horse, so that both the mule and the
,hinny resemble more closely the ass than the horse;
but that the prepotency runs more strongly in the male
than in the female ass, so that the mule, which is the
offspring of the male ass and mare, is more like an ass,
than is the hinny, which is the offspring of the female
ass and stallion.
Much stress has been laid by some authors on the sup-
posed fact, that it is only with mongrels that the offspring
are not intermediate in character, but closely resemble one
of their parents; but this does sometimes occur with hy-
brids, yet I grant much less frequently than with mongrels.
Looking to the cases which I have collected of cross-bred
animals closely resembling one parent, the resemblances
seem chiefly confined to characters almost monstrous in their
nature, and which have suddenly appeared — such as albinism,
melanism, deficiency of tail or horns, or additional fingers
and toes; and do not relate to characters which have been
slowly acquired through selection. A tendency to sudden
reversions to the perfect character of either parent would,
also, be much more likely to occur with mongrels, which are
descended from varieties often suddenly produced and semi-
monstrous in character, than with hybrids, which are de-
scended from species slowly and naturally produced. On the
whole, I entirely agree with Dr. Prosper Lucas, who, after
arranging an enormous body of facts with respect to animals,
comes to the conclusion that the laws of resemblance of the
child to its parents are the same, whether the two parents
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330 ORIGIN OF SPECIES
differ little or much from each other, namely, in the union
of individuals of the same variety, or of different varieties,
or of distinct species.
Independently of the question of fertility and sterility, in
all other respects there seems to he a general and close simi-
larity in the offspring of crossed species, and of crossed vari-
eties. If we look at species as having heen specially created,
and at varieties as having heen produced by secondary laws,
this similarity would be an astonishing fact. But it har-
monises perfectly with the view that there is no essential
distinction between species and varieties.
SUMMARY OF CHAPTER.
First crosses between forms, sufficiently distinct to be
ranked as species, and their hybrids, are very generally,
but not universally, sterile. The sterility is of all degrees,
and is often so slight that the most careful experimentalists
have arrived at diametrically opposite conclusions in ranking
forms by this test. The sterility is innately variable in indi-
viduals of the same species, aod is eminently susceptible to
the action of favourable and unfavourable conditions. The
degree of sterility does not strictly follow systematic affinity,
but is governed by several curious and complex laws. It is
generally different, and sometimes widely different in
reciprocal crosses between the same two species. It is not
always equal in degree in a first cross and in the hybrids
produced from this cross.
In the same manner as in grafting trees, the capacity in
one species or variety to take on another, is incidental on
differences, generally of an unknown nature, in their vege-
tative systems, so in crossing, the greater or less facility of
one species to unite with another is incidental on unknown
differences in their reproductive systems. There is no more
reason to think that species have been specially endowed
with various degrees of sterility to prevent their crossing
and blending in nature, than to think that trees have been
specially endowed with various and somewhat analogous
degrees of difficulty in being grafted together in order to pre-
vent their inarching in our forests.
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SUBIMARY 391
The sterility of first crosses and of their hybrid progeny
has not been acquired through natural selection. In the
case of first crosses it seems to depend on several circum-
stances; in some instances in chief part on the early death
of the embryo. In the case of hybrids, it apparently depends
on their whole organisation having been disturbed by being
compounded from two distinct forms; the sterility being
closely allied to that which so frequently affects pure species,
when exposed to new and unnatural conditions of life. He
who will explain these latter cases will be able to explain
the sterility of hybrids. This view is strongly supported by
a parallelism of another kind: namely, tha^ firstly, slight
changes in the conditions of life add to the vigour and fertil-
ity of all organic beings ; and secondly, that the crossing of
forms, which have been exposed to slightly different condi-
tions of life or which have varied, favours the size, vigour,
and fertility of their offspring. The facts g^ven on the
sterility of the illegitimate unions of dimorphic and trimor-
phic plants and of their illegitimate progeny, perhaps ren-
der it probable that some unknown bond in all cases connects
the degree of fertility of first unions with that of their
offspring. The consideration of these facts on dimorphism,
as well as of the results of reciprocal crosses, clearly leads
to the conclusion that the primary cause of the sterility
of crossed species is confined to differences in their sexual
elements. But why, in the case of distinct species, the sexual
elements should so generally have become more or less modi-
fied, leading to their mutual infertility, we do not know;
but it seems to stand in some close relation to species hav-
ing been exposed for long periods of time to nearly uniform
conditions of life.
It is not surprising that the difficulty in crossing any two
species, and the sterility of their hybrid offspring, should
in most cases correspond, even if due to distinct causes: for
both depend on the amount of difference between the species
which are crossed. Nor is it surprising that the facility of
effecting a first cross, and the fertility of the hybrids thus
produced, and the capacity of being grafted together — ^though
this latter capacity evidently depends on widely different cir-
cumstances— should all run, to a certain extent, parallel with
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332 ORIGIN OF SPEQES
the systematic affinity of the forms subjected to experimient;
for systematic affinity includes resemblances of all kinds.
First crosses between forms known to be varieties, or suffi-
ciently alike to be considered as varieties, and their mon-
grel offspring, are very generally, but not, as is so often
stated, invariably fertile. Nor is this almost universal and
perfect fertility surprising, when it is remembered how
liable we are to argue in a circle with respect to varieties
in a state of nature ; and when we remember that the greater
number of varieties have been produced under domestication
by the selection of mere external differences, and that they
have not been long exposed to uniform conditions of life. It
should also be especially kept in mind, that long-continued
domestication tends to eliminate sterility, and is therefore
little likely to induce this same quality. Independently of the
question of fertility, in all other respects there is the closest
general resemblance between hybrids and mongrels, — ^in their
variability, in their power of absorbing each other by re-
peated crosses, and in their inheritance of characters from
both parent-forms. Finally, then, although we are as ig-
norant of the precise cause of the sterility of first crosses
and of hybrids as we are why animals and plants removed
from their natural conditions become sterile, yet the facts
given in this chapter do not seem to me opposed to the belief
that species aboriginally existed as varieties.
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CHAPTER X
On ths Imperfection of the Geological Record
On the absence of intermediate varieties at the present day — On the
nature of extinct intermediate varieties; on their number — On
the lapse of time, as inferred from the rate of denudation and
of deposition — On the lapse of time as estimated by years —
On the poorness of our palsontological collections-^n the in-
termittence of geological formations — On the denudation of
granitic areas — On the absence of intermediate varieties in any
one formation — On the sudden appearance of groups of species
— On their sudden appearance in the lowest known fossiliferous
strata — ^Antiquity of the habitable earth.
IN the sixth chapter I entnnerated the chief objections
which might be justly urged against the views main-
tained in this volume. Most of them have now been dis-
cussed. One, namely the distinctness of specific forms, and
their not being blended together by innumerable transitional
links, is a very obvious difficulty. I assigned reasons why
such links do not commonly occur at the present day under
the circumstances apparently most favourable for their pres-
ence, namely on an extensive and continuous area with grad-
uated physical conditions. I endeavoured to show, that the
life of each species depends in a more important manner on
the presence of other already defined organic forms, than on
climate, and, therefore, that the really governing conditions
of life do not graduate away quite insensibly like heat or
moisture. I endeavoured, also, to show that intermediate va-
rieties, from existing in lesser numbers than the forms which
they connect, will generally be beaten out and exterminated
during the course of further modification and improvement
The main cause, however, of innumerable intermediate links
not now occurring. ever)rwhere throughout nature, depends on
the very process of natural selection, through which new va-
rieties continually take the places of and supplant their
parent-forms. But jiist in proportion as this process of ez-
333
U— HCZI
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334 ORIGIN OF SPEQES
termination has acted on an enormous scale, so must the
number of intermediate varieties, which have formerly ex-
isted, be truly enormous. Why then is not every geological
formation and every stratum full of such intermediate links ?
Geology assuredly does not reveal any such finely-graduated
organic chain; and this, perhaps, is the most obvious and
serious objection which can be urged against the theory. The
explanation lies, as I believe, in the extreme imperfection of
the geological record.
In the first place, it should always be borne in mind what
sort of intermediate forms must, on the theory, have formerly
existed. I have found it difficult, when looking at any two
species, to avoid picturing to myself forms directly intermedi-
ate between them. But this is a wholly false view ; we should
always look for forms intermediate between each species and
a common but unknown progenitor; and the progenitor will
generally have differed in some respects from all its modified
descendants. To give a simple illustration: the fantail and
pouter pigeons are both descended from the rock-pigeon; if
we possessed all the intermediate varieties which have ever
existed, we should have an extremely close series between
both and the rock-pigeon; but we should have no varieties
directly intermediate between the fantail and pouter; none,
for instance, combining a tail somewhat expanded with a crop
somewhat enlarged, the characteristic features of these two
breeds. These two breeds, moreover, have become so much
modified, that, if we had no historical or indirect evidence
regarding their origin, it would not have been possible to
have determined, from a mere comparison of their structure
with that of the rock-pigeon, C. livia, whether they had de-
scended from this species or from some other allied form,
such as C. oenas.
So, with natural species, if we look to forms very distinct,
for instance to the horse and tapir, we have no reason to
suppose that links directly intermediate between them ever
existed, but between each and an unknown common parent.
The common parent will have had in its whole organisation
much general resemblance to the tapir and to the horse; but
in some points of structure may have differed considerably
from both, even perhaps more than they differ from each
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THB LAI^B OF TIME 335
other. Hence, in all such cases, we should be unable to rec-
ognise the parent-form of any two or more species, even if
we closely compared the structure of the parent with that of
its modified descendants, unless at the same time we had a
nearly perfect chain of the intermediate links.
It is just possible by the theory, that one of two living
forms might have descended from the other; for instance, a
horse from a tapir ; and in this case direct intermediate links
will have existed between them. But such a case would im-
ply that one form had remained for a very long period unal-
tered, whilst its descendants had undergone a vast amount
of change ; and the principle of competition between organism
and organism, between child and parent, will render this a
very rare event ; for in all cases the new and improved forms
of life tend to supplant the old and unimproved forms.
By the theory of natural selection all living species have
been connected with the parent-species of each genus, by dif-
ferences not greater than we see between the natural and
domestic varieties of the same species at the present day ; and
these parent-species, now generally extinct, have in their
turn been similarly connected with more ancient forms; and
so on backwards, always converging to the common ancestor
of each great class. So that the number of intermediate and
transitional links, between all living and extinct species, must
have been inconceivably great. But assuredly, if this theory
be true, such have lived upon the earth.
ON THE LAPSE OF TIME^ AS INFERRED FROM THE RATE OF
DEPOSITION AND EXTENT OF DENUDATION
Independently of our not finding fossil remains of such in-
finitely numerous connecting links, it may be objected that
time cannot have sufficed for so great an amount of organic
change, all changes having been effected slowly. It is hardly
possible for me to recall to the reader who is not a practical
geologist, the facts leading the mind feebly to comprehend the
lapse of time. He who can read Sir Charles Lyell's grand
work on the Principles of Geology, which the future historian
will recognise as having produced a revolution in natural
science, and yet does not admit how vast have been the past
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336 ORIGIN OF SPEaES
periods of time, may at once close this volume. Not that it
suffices to study the Principles of Geology, or to read special
treatises by different observers on separate formations, and
to mark how each author attempts to give an inadequate idea
of the duration of each formation, or even of each stratum.
We can best gain some idea of past time by knowing the
agencies at work, and learning how deeply the surface of the
land has been denuded, and how much sediment has been de-
posited. As Lyell has well remarked, the extent and thick-
ness of our sedimentary formations are the result and the
measure of the denudation which the earth's crust has else-
where undergone. Therefore a man should examine for
himself the great piles of superimposed strata, and watch the
rivulets bringing down mud^.and the waves wearing away the
sea-cliffs, in order to comprehend something about the dura-
tion of past time, the monuments of which we see all
around us.
It is good to wander along the coast, when formed of mod-
erately hard rocks, and mark the process of degradation. The
tides in most cases reach the cliffs only for a short time twice
a day, and the waves eat into them only when they are
charged with sand or pebbles ; for there is good evidence that
pure water effects nothing in wearing away rock. At last
the base of the cliff is undermined, huge fragments fall down,
and these, remaining fixed, have to be worn away atom by
atom, until after being reduced in size they can be rolled
about by the waves, and then they are more quickly ground
into pebbles, sand, or mud. But how often do we see along
the bases of retreating cliffs rounded boulders, all thickly
clothed by marine productions, showing how little they are
abraded and how seldom they are rolled about! Moreover,
if we follow for a few miles any line of rocky cliff, which is
undergoing degradation, we find that it is only here and there,
along a short length or round a promontory, that the cliffs
are at the present time suffering. The appearance of the sur-
face and the vegetation show that elsewhere years have
elapsed since the waters washed their base.
We have, however, recently learnt from the observations
of Ramsay, in the van of many excellent observers — of Jukes,
Geikie, Croll, and others, that subaerial degradation is a
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THE LAPSE OF TIME 337
much more important agency than coast-action, or the power
of the waves. The whole surface of the land is exposed to
the chemical action of the air and of the rain-water with its
dissolved carbonic acid, and in colder countries to frost; the
disintegrated matter is carried down even gentle slopes dur-
ing heavy rain, and to a greater extent than might be sup-
posed, especially in arid districts, by the wind; it is then
transported by the streams and rivers, which when rapid
deepen their channels, and triturate the fragments. On a
rainy day, even in a gently undulating country, we see the
effects of subaerial degradation in the muddy rills which flow
down every slope. Messrs. Ramsay and Whitaker have
shown, and the observation is a most striking one, that the
great lines of escarpment in the Wealden district and those
ranging across England, which formerly were looked at as
ancient sea-coasts, cannot have been thus formed, for each
line is composed of one and the same formation, whilst our
sea-cliffs are everywhere formed by the intersection of vari-
ous formations. This being the case, we are compelled to
admit that the escarpments owe their origin in chief part to
the rocks of which they are composed having resisted subae-
rial denudation better than the surrounding surface ; this sur-
face consequently has been gradually lowered, with the lines
of harder rock left projecting. NoUiing impresses the mind
with the vast duration of time, according to our ideas of time,
more forcibly than the conviction thus gained that subaerial
agencies which apparently have so little power, and which
seem to work so slowly, have produced great results.
When thus impressed with the slow rate at which the. land
is worn away through subaerial and littoral action, it is good,
in order to appreciate the past duration of time, to consider
on the one hand, the masses of rock which have been re-
moved over many extensive areas, and on the other hand the
thickness of our sedimentary formations. I remember hav-
ing been much struck when viewing volcanic islands, which
have been worn by the waves and pared all round into per-
pendicular cliffs of one or two thousand feet in height; for
the gentle slope of the lava-streams, due to their formerly
liquid state, showed at a glance how far the hard, rocky beds
had once extended into the open ocean. The same story is
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338 ORIGIN OF SPEaES
told still more plainly by faults, — ^those great cracks along
which the strata have been upheaved on one side, or thrown
down on the other, to the height or depth of thousands of
feet; for since the crust cracked, and it makes no great dif-
ference whether the upheaval was sudden, or, as most geolo-
gists now believe, was slow and effected by many starts, the
surface of the land has been so completely planed down that
no trace of these vast dislocations is externally visible. The
Craven fault, for instance, extends for upwards of 30 miles,
and along this line the vertical displacement of the strata
varies from 600 to 3000 feet. Professor Ramsay has pub-
lished an account of a downthrow in Anglesea of 2300 feet;
and he informs me that he fully believes that there is one in
Merionethshire of 12,000 feet; yet in these cases there is
nothing on the surface of the land to show such prodigious
movements; the pile of rocks on either side of the crack
having been smoothly swept away.
On the other hand, in all parts of the world the piles of
sedimentary strata are of wonderful thickness. In the Cor-
dillera I estimated one mass of conglomerate at ten thou-
sand feet; and although conglomerates have probably been
accumulated at a quicker rate than finer sediments, yet from
being formed of worn and rounded pebbles, each of which
bears the stamp of time, they are good to show how slowly
the mass must have been heaped together. Professor Ramsay
has given me the maximum thickness, from actual measure-
ment in most cases, of the successive formations in different
parts of Great Britain; and this is the result: —
Feet
Palsosoic strata (not including Igneons beds) 57»i54
Secondary strata ^3i^90
Tertlaty strata 8,240
—making altogether 72,584 feet; that is, very nearly thirteen
and three-quarters British miles. Some of the formations,
which are represented in England by thin beds, are thousands
of feet in thickness on the Continent. Moreover, between
each successive formation, we have, in the opinion of most
geologists, blank periods of enormous length. So that the
lofty pile of sedimentary rocks in Britain gives but an inade-
quate idea of the time which has elapsed during their accu-
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THB LAPSE OP TIIIB S99
mulation. The consideration of these various facts impresses
the mind almost in the same manner as does the vain en-
deavour to grapple with the idea of eternity.
Nevertheless this impression is- partly false. Mr. Croll, in
an interesting paper, remarks that we do not err "in forming
too great a conception of the length of geological periods/'
but in estimating them by years. When geologists look at
large and complicated phenomena, and then at the figures rep-
resenting several million years, the two produce a totally
different effect on the mind, and the figures are at once pro-
nounced too small. In regard to subaerial denudation, Mr.
Croll shows, by calculating the known amount of sediment
annually brought down by certain rivers, relatively to their
areas of drainage, that looo feet of solid rock, as it became
gradually disintegrated, would thus be removed from the
mean level of the whole area in the course of six million
years.
This seems an astonishing result, and some considera-
tions lead to the suspicion that it may be too large, but even
if halved or quartered it is still very surprising. Few of us,
however, know what a million really means : Mr. Croll gives
the following illustration: take a narrow strip of paper, 83
feet 4 inches in length, and stretch it along the wall of a large
hall; then mark off at one end the tenth of an inch. This
tenth of an inch will represent one hundred years, and the
entire strip a million years. But let it be borne in mind, in
relation to the subject of this work, what a hundred years
implies, represented as it is by a measure utterly insignificant
in a hall of the above dimensions. Several eminent breeders,
during a single lifetime, have so largely modified some of the
higher animals, which propagate their kind much more slowly
than most of the lower animals, that they have formed what
well deserves to be called a new sub-breed. Few men have
attended with due care to any one strain for more than half
a century, so that a hundred years represents the work of two
breeders in succession. It is not to be supposed that species
in a state of nature 'ever change so quickly as domestic ani-
mals under the guidance of methodical selection. The com-
parison would be in every way fairer with the effects which
follow from unconscious selection, that is the preservation of
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M) 0EI6IN OP SPBaBS
the most useful or beautiful animals, with no intention of
modifying the breed; but by this process of unconscious
selection, various breeds have been sensibly changed in the
course of two or three centuries.
Species, however, probably change muoh more slowly, and
within the same country only a few change at the same time.
This slowness follows from all the inhabitants of the same
country being already so well adapted to each other, that new
places in the polity of nature do not occur until after long
intervals, due to the occurrence of physical changes of some
kind, or through the immigration of new forms. Moreover
variations or individual differences of the right nature, by
which some of the inhabitants might be better fitted to their
new places under the altered circumstances, would not always
occur at once. Unfortunately we have no means of deter-
mining, according to the standard of years, how long a
period it takes to modify a species ; but to the subject of time
we must return.
ON THE POORNESS OP PAUBONTOLOGICAL COLLECTIONS
Now let us turn to our richest geological museums, and
what a paltry display we behold! That our collections are
imperfect is admitted by every one. The remark of that ad-
mirable palaeontologist, Edward Forbes, should never be for-
gotten, namely, that very many fossil species are known and
named from single and often broken specimens, or from a
few specimens collected on some one spot Only a small por-
tion of the surface of the earth has been geologically ex-
plored, and no part with sufficient care, as the important
discoveries made every year in Europe prove. No organism
wholly soft can be preserved. Shells and bones decay and
disappear when left on the bottom of the sea, where secUment
is not accumulating. We probably take a quite erroneous
view, when we assume that sediment is being deposited over
nearly the whole bed of the sea, at a rate sufficiently quick
to embed and preserve fossil remains. Throughout an enor-
mously large proportion of the ocean, the bright blue tint of
the water bespeaks its purity. The many cases on record of
a formation conformably covered, after an immense interval
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PALJBOMTOLOGICAL COLLECnONS 341
of time, by another and later formation, without the under-
lying bed having suffered in the interval any wear and tear,
seem explicable only on the view of the bottom of the sea not
rarely lying for ages in an unaltered condition. The remains
which do become embedded, if in sand or gravel, will, when
the beds are upraised, generally be dissolv^ by the percola-
tion of rain-water charged with carbonic acid. Some of the
many kinds of animals which live on the beach between high
and low water mark seem to be rarely preserved. For in-
stance, the several species of the Chthamalinae (a sub-family
of sessile cirripedes) coat the rocks all over the world in
infinite numbers ; they are all strictly littoral, with the excep-
tion of a single Mediterranean species, which inhabits deep
water, and this has been found fossil in Sicily, whereas not
one other species has hitherto been found in any tertiary
formation; yet it is known that the genus Chthamalus ex-
isted during the Chalk period. Lastly, many great deposits
requiring a vast length of time for their accumulation, are
entirely destitute of organic remains, without our being able
to assign any reason: one of the most striking instances is
that of the Flysch formation, which consists of shale and
sandstone, several thousand, occasionally even six thousand
feet in thickness, and extending for at least 300 miles from
Vienna to Switzerland; and although this great mass has
been most carefully searched, no fossils, except a few vege-
table remains, have been found.
With respect to the terrestrial productions which lived
during the Secondary and Palaeozoic periods, it is superfluous
to state that our evidence is fragmentary in an extreme de-
gree. For instance, until recently not a land-shell was known
belonging to either of these vast periods, with the exception
of one species discovered by Sir C. Lyell and Dr. Dawson in
the carboniferous strata of North America; but now land-
shells have been found in the lias. In regard to mammifer-
ous remains, a glance at the historical table published in
Lyell's Manual will bring home the truth, how accidental and
rare is their preservation, far better than pages of detail.
Nor is their rarity surprising, when we remember how large
a proportion of the bones of tertiary mammals have been
discovered either in caves or in lacustrine deposits; and that
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342 ORIGIN OF SPECIES
not a cave or true lacustrine bed is known belonging to the
age of our secondary or palaeozoic formations.
But the imperfection in the geological record largely re-
sults from another and more important cause than any of the
foregoing; namely, from the several formations being sep-
arated from each other by wide intervals of time. This doc-
trine has been emphatically admitted by many geologists and
palaeontologists, who, like £. Forbes, entirely disbelieve in
the change of species. When we see the formations tabulated
in written works, or when we follow them in nature, it is
difficult to avoid believing that they are closely consecutive.
But we know, for instance, from Sir R. Murchison's great
work on Russia, what wide gaps there are in that country
between the superimposed formations; so it is in North
America, and in many other parts of the world. The most
skilful geologist, if his attention had been confined exclusively
to these large territories, would never have suspected that,
during the periods which were blank and barren in his own
country, great piles of sediment, charged with new and pe-
culiar forms of life, had elsewhere been accumulated. And
if, in each separate territory, hardly any idea can be formed
of the length of time which has elapsed between the consecu-
tive formations, we may infer that this could nowhere be
ascertained. The frequent and great changes in the mineral-
ogical composition of consecutive formations, generally im-
plying great changes in the geography of the surrounding
lands, whence the sediment was derived, accord with the
belief of vast intervals of time having elapsed between each
formation.
We can, I think, see why the geological formations of each
region are almost invariably intermittent; that is, have not
followed each other in close sequence. Scarcely any fact
struck me more when examining many hundred miles of the
South American coasts, which have been upraised several
hundred feet within the recent period, than the absence of
any recent deposits sufficiently extensive to last for even a
short geological period. Along the whole west coast, which
is inhabited by a peculiar marine fauna, tertiary beds are so
poorly developed, that no record of several successive and
peculiar marine faunas will probably be preserved to a distant
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PAL^ONTOLOGICAL COLLECTIONS 343
age. A little reflection will explain why, along the rising
coast of the western side of South America, no extensive
formations with recent or tertiary remains can an3rwhere be
found, though the supply of sediment must for ages have
been great, from the enormous degradation of the coast-rocks
and from muddy streams entering the sea. The explanation,
no doubt, is, that the littoral and sub-littoral deposits are
continually worn away, as soon as they are brought up by
the slow and gradual rising of the land within the grinding
action of the coast-waves.
We may, I think, conclude that sediment must be accumu-
lated in extremely thick, solid, or extensive masses, in order
to withstand the incessant action of the waves, when first
upraised and during successive oscillations of level, as well as
the subsequent subaerial degradation. Such thick and ex-
tensive accumulations of sediment may be formed in two
ways; either in profound depths of the sea, in which case
the bottom will not be inhabited by so many and such varied
forms of life, as the more shallow seas; and the mass when
upraised will give an imperfect record of the organisms
which existed in the neighbourhood during the period of its
accumulation. Or, sediment may be deposited to any thick-
ness and extent over a shallow bottom, if it continue slowly
to subside. In this latter case, as long as the rate of subsi-
dence and the supply of sediment nearly balance each other,
the sea will remain shallow and favourable for many and
varied forms, and thus a rich fossiliferous formation, thick
enough, when upraised, to resist a large amount of denuda-
tion, may be formed.
I am convinced that nearly all our ancient formations,
which are throughout the greater part of their thickness rich
in fossils, have thus been formed during subsidence. Since
publishing my views on this subject in 1845, I have watched
the progress of Geology, and have been surprised to note how
author after author, in treating of this or that great forma-
tion, has come to the conclusion that it was accumulated
during subsidence. I may add, that the only ancient tertiary
formation on the west coast of South America, which has
been bulky enough to resist such degradation as it has as yet
suffered, but which will hardly last to a distant geological
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344 OEIGIN OF 9PECIES
age, was deposited during a downward oscillation of level,
and thus gained considerable thickness.
All geological facts tell us plainly that each area has under-
gone numerous slow oscillations of level, and apparently these
oscillations have affected wide spaces. Consequently, forma-
tions rich in fossils and sufficiently thick and extensive to
resist subsequent degradation, will have been formed over
wide spaces during periods of subsidence, but only where the
supply of sediment was sufficient to keep the sea shallow and
to embed and preserve the remains before they had time to
decay. On the other hand, as long as the bed of the sea
remains stationary, thick deposits cannot have been accumu-
lated in the shallow parts, which are the most favourable to
life. Still less can this have happened during the alternate
periods of elevation; or, to speak more accurately, the beds
which were then accumulated will generally have been de-
stroyed by being upraised and brought within the limits of
the coast-action.
These remarks apply chiefly to littoral and sub-littoral de-
posits. In the case of an extensive and shallow sea, such as
that within a large part of the Malay Archipelago, where the
depth varies from 30 or 40 to 60 fathoms, a widely extended
formation might be formed during a period of elevation, and
yet not suffer excessively from denudation during its slow
upheaval; but the thickness of the formation could not be
great, for owing to the elevatory movement it would be less
than the depth in which it was formed ; nor would the deposit
be much consolidated, nor be capped by overlying formations,
so that it would run a good chance of being worn away by
atmospheric degradation and by the action of the sea during
subsequent oscillations of level. It has, however, been sug-
gested by Mr. Hopkins, that if one part of the area, after
rising and before being denuded, subsided, the deposit formed
during the rising movement, though not thick, might after-
wards become protected by fresh accumulations, and thus be
preserved for a long period.
Mr. Hopkins also expresses his belief that sedimentary beds
of considerable horizontal extent have rarely been completely
destroyed. But all geologists, excepting the few who believe
that our present metamorphic schists and plutonic rocks once
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4pALJB0NT0L0GICAL COLLECTIONS 345
formed the primordial nucleus of the globe, will admit that
these latter rocks have been stript of their covering to an
enormous extent. For it is scarcely possible that such rocks
could have been solidified and crystallized whilst uncovered;
but if the metamorphic action occurred at profound depths of
the ocean, the former protecting mantle of rock may not have
been very thick. Admitting then that gneiss, mica-schist,
granite, diorite, &c., were once necessarily covered up, how
can we account for the naked and extensive areas of such
rocks in many parts of the world, except on the belief that
they have subsequently been completely denuded of all over-
lying strata? That such extensive areas do exist cannot be
doubted; the granitic region of Parime is described by Hum-
boldt as being at least nineteen times as large as Switzerland.
South of the Amazon, Boue colours an area composed of
rocks of this nature as equal to that of Spain, France, Italy,
part of Germany, and the British Islands, all conjoined. This
region has not been carefully explored, but from the concur-
rent testimony of travellers, the granitic area is very large;
thus. Von Eschwege gives a detailed section of these rocks,
stretching from Rio de Janeiro for 260 geographical miles
inland in a straight line; and I travelled for 150 miles in
another direction, and saw nothing but granitic rocks. Nu-
merous specimens, collected along the whole coast from near
Rio Janeiro to the mouth of the Plata, a distance of iioo geo-
graphical miles, were examined by n«e, and they all belonged
to this class. Inland, along the whole northern bank of the
Plata I saw, besides modem tertiary beds, only one small
patch of slightly metamorphosed rock, which alone could
have formed a part of the original capping of the granitic
series. Turning to a well-known region, namely, to the
United States and Canada, as shown, in Professor H. D.
Rogers's beautiful map, I have estimated the areas by cutting
out and weighing the paper, and I find that the metamorphic
(excluding "the semi-metamorphic") and granitic rocks ex-
ceed, in the proportion of 19 to 12-5, the whole of the newer
Palaeozoic formations. In many regions the metamorphic and
granitic rocks would be found much more widely extended
than they appear to be, if all the sedimentary beds were re-
moved which rest tmconformably on them, and which could
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346 OBI6IN OF SPEOES
not have formed part of the origiiial mantle under which they
were crystallized. Hence it is probable that in some parts
of the world whole formations have been completely de-
nuded, with not a wreck left behind.
One remark is here worth a passing notice. During periods
of elevation the area of the land and of the adjoining shoal
parts of the sea will be increased, and new stations will often
be formed: — all circumstances favourable, as previously ex-
plained, for the formation of new varieties and species; but
during such periods there will generally be a blank in the
geological record. On the other hand, during subsidence, the
inhabited area and number of inhabitants will decrease (ex-
cepting on the shores of a continent when first broken up into
an archipelago), and consequently during subsidence, though
there will be much extinction, few new varieties or species
will be formed; and it is during these very periods of subsi-
dence, that the deposits which are richest in fossils have been
accumulated.
ON THE ABSENCE OP NUMEROUS INTERMEDIATE VARIETIES
IN ANY SINGLE FORMATION
From these several considerations, it cannot be doubted
that the geological record, viewed as a whole, is extremely
imperfect; but if we confine our attention to any one forma-
tion, it becomes much m#re difficult to understand why we do
not therein find closely graduated varieties between the allied
species which lived at its commencement and at its close.
Several cases are on record of the same species presenting
varieties in the upper and lower parts of the same formation ;
thus, Trautschold gives a number of instances with Ammo-
nites; and Hilgendorf has described a most curious case of
ten graduated forms of Planorbis multiformis in the succes-
sive beds of a fresh-water formation in Switzerland. Although
each formation has indisputably required a vast number of
years for its deposition, several reasons can be given why
each should not commonly include a graduated series of links
between the species which lived at its commenceraent and
close; but I cannot assign due proportional weight to the
following considerations.
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ABSENCE OF INTBRBfEDIATB VARIETIES 347
Although each formation may mark a very long lapse of
years, each probably is short compared with the period requi-
site to change one species into another. I am aware that two
palaeontologists, whose opinions are worthy of much defer-
ence, namely Bronn and Woodward, have concluded that the
average duration of each formation is twice or thrice as long
as the average duration of specific forms. But insuperable
difficulties, as it seems to me, prevent us from coming to any
just conclusion on this hdad. When we sec a species first
appearing in the middle of any formation, it would be rash
in the extreme to infer that it had not elsewhere previously
existed. So again when we find a species disappearing before
the last layers have beep deposited) it would be equally rash
to suppose that it then became extinct. We forget how small
the area of Europe is compared with the rest of the world;
nor have the several stages of the same formation throughout
Europe been correlated with perfect accuracy.
We may safely infer that with marine animals of all kinds
there has been a large amount of migration due to climatal
and other changes; and when we see a species first appearing
in any formation, the probability is that it only then first im-
migrated into that area. It is well known, for instance, that
several species appear somewhat earlier in the palaeozoic beds
of North America than in those of Europe; time having ap-
parently been required for their migration from the American
to the European seas. In examining the latest deposits in
various quarters of the world, it has everywhere been noted,
that some few still existing species are common in the de>
posit, but have become extinct in the immediately surround-
ing sea; or, conversely, that some are now abundant in the
neighbouring sea, but are rare or absent in this particular
deposit. It is an excellent lesson to reflect on the ascer-
tained amount of migration of the inhabitants of Europe dur-
ing the glacial epoch, which forms only a part of one whole
geological period; and likewise to reflect on the changes of
level, on the extreme change of climate, and on the great
lapse of time, all included within this same glacial period.
Yet it may be doubted whether, in any quarter of the world,
sedimentary deposits, including fossil remains, have gone on
accumulating within the same area during the whole of this
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348 ORIGIN OF SPEaSS
period. It is not, for instance, probable that sediment was
deposited during the whole of the glacial period near the
mouth of the Mississippi, within that limit of depth at which
marine animals can best flourish: for we know that great
geographical changes occurred in other parts of America dur-
ing this space of time. When such beds as were deposited in
shallow water near the mouth of the Mississippi during some
part of the glacial period shall have been upraised, organic
remains will probably first appear and disappear at different
levels, owing to the migrations of species and to geographical
changes. And in the distant future, a geologist, examining
those beds, would be tempted to conclude that the average
duration of life of the embedded fossils had been less than
that of the glacial period, instead of having been really far
greater, that is, extending from before the glacial epoch to
the present day.
In order to get a perfect gradation between two forms in
the upper and lower parts of the same formation, the deposit
must have gone on continuously accumulating during a long
period, sufficient for the slow process of modification; hence
the deposit must be a very- thick one ; and the species under-
going change must have lived in the same district throughout
the whole time. But we have seen that a thick formation,
fossiliferous throughout its entire thickness, can accumulate
only during a period of subsidence ; and to keep the depth ap-
proximately the same, which is necessary that the same
marine species may live on the same space, the supply of
sediment must nearly counterbalance the amount of subsi-
dence. But this same movement of subsidence will tend to
submerge the area whence the sediment is derived, and thus
diminish the supply, whilst the downward movement con-
tinues. In fact, this nearly exact balancing between the
supply of sediment and the amount of subsidence is probably
a rare contingency; for it has been observed by more than
one palaeontologist, that very thick deposits are usually
barren of organic remains, except near their upper or lower
limits.
It would seem that each separate formation, like the whole
pile of formations in any country, has generally been inter-
mittent in its accumulation. When we see, as is so often the
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ABSENCE OF INTERMEDIATE VARIETIES 340
case, a formation composed of beds of widely different min-
eralogical composition, we may reasonably suspect that the
process of deposition has been more or less interrupted. Nor
will the closest inspection of a formation give us any idea of
the length of time which its deposition may have consumed.
Many instances could be given of beds only a few feet
in thickness, representing formations, which are elsewhere
thousands of feet in thickness, and which must have required
an enormous period for their accumulation; yet no one igno-
rant of this fact would have even suspected the vast lapse of
time represented by the thinner formation. Many cases could
be given of the lower beds of a formation having been up-
raised, denuded, submerged, and then re-covered by the upper
beds of the same formation, — facts, showing what wide, yet
easily overlooked, intervals have occurred in its accumula-
tion. In other cases we have the plainest evidence in great
fossilised trees, still standing upright as they grew, of many
long intervals of time and changes of level during the process
of deposition, which would not have been suspected, had not
the trees been preserved: thus Sir C. Lyell and Dr. Dawson
found carboniferous beds 1400 feet tnick in Nova Scotia, with
ancient root-bearing strata, one above the other at no less
than sixty-eight different levels. Hence, when the same
species occurs at the bottom, middle, and top of a formation,
the probability is that it has not lived on the same spot during
the whole period of deposition, but has disappeared and reap-
peared, perhaps many times, during the same geological
period. Consequently if it were to undergo a considerable
amount of modification during the deposition of any one geo-
logical formation, a section would not include all the fine
intermediate gradations which must on our theory have ex-
isted, but abrupt, though perhaps slight, changes of form.
It is all-important to remember that naturalists have no
golden rule by which to distinguish species and varieties;
they grant some little variability to each species, but when
they meet with a somewhat greater amount of difference be-
tween any two forms, they rank both as species, unless they
are enabled to connect them together by the closest inter-
mediate gradations ; and this, from the reasons just assigned,
we can seldom hope to effect in any one geological section.
V^HCXI •
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350 ORIGIN OF SPECIES
Supposing B and C to be two species, and a third, A, to be
found in an older and underlying bed ; even if A were strictly
intermediate between B and C, it would simply be ranked as a
third and distinct species, unless at the same time it could be
closely connected by intermediate varieties with either one or
both forms. Nor should it be forgotten, as before explained,
that A might be the actual progenitor of B and C, and yet
would not necessarily be strictly intermediate between them
in all respects. So that we might obtain the parent-species
and its several modified descendants from the lower and
upper beds of the sanie formation, and unless we obtained
numerous transitional gradations, we should not recognise
their blood-relationship, and should consequently rank them
as distinct species.
It is notorious on what excessively slight differences many
palaeontologists have founded their species; and they do this
the more readily if the specimens come from different sub-
stages of the same formation. Some experienced concholo-
gists are now sinking many of the very fine species of
D'Orbigny and others in|p the rank of varieties ; and on this
view we do find the kind of evidence of change which on the
theory we ought to find. Look again at the later tertiary de-
posits, which include many shells believed by the majority of
naturalists to be identical with existing species ; but some ex-
cellent naturalists, as Agassiz and Pictet, maintain that all
these tertiary species are specifically distinct, though the dis-
tinction is admitted to be very slight ; so that here, unless we
believe that these eminent naturalists have been misled by
their imaginations, and that these late tertiary species really
present no difference whatever from their living representa-
tives, or unless we admit, in opposition to the judgment of
most naturalists, that these tertiary species are all truly dis-
tinct from the recent, we have evidence of the frequent oc-
currence of slight modifications of the kind required. If we
lock to rather wider intervals of time, namely, to distinct but
consecutive stages of the same great formation, we find that
the embedded fossils, though universally ranked as specific-
ally different, yet are far more closely related to each other
than are the species found in more widely separated forma-
tions; so that here again we have undoubted evidence of
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ABSENCE OF INTERMEDIATE VARIETIES 351
change in the direction required by the theory; but to this
latter subject I shall return in the following chapter.
With animals and plants that propagate rapidly and do not
wander much, there is reason to suspect, as we have formerly
seen, that their varieties are generally at first local ; and that
such local varieties do not spread widely and supplant
their parent-forms until they have been modified and per-
fected in some considerable degree. According to this view,
the chance of discovering in a formation in any one country
all the early stages of transition between any two forms, is
small, for the successive changes are supposed to have been
local or confined to some one spot. Most marine animals
have a wide range; and we have seen that with plants it is
those which have the widest range, that oftenest present va-
rieties; so that, with shells and other maripe animals, it is
probable that those which had the widest range, far exceed-
ing the limits of the known geological formations in Europe,
have oftenest given rise, first to local varieties and ultimately
to new species; and this again would greatly lessen the
chance of our being able to trace the stages of transition in
any one geological formation.
It is a more important consideration, leading to the same
result, as lately insisted on by Dr. Falconer, namely, that the
period during which each species underwent modification,
though long as measured by years, was probably short in
comparison with that during which it remained without un-
dergoing any change.
It should not be forgotten, that at the present day, with
perfect specimens for examination, two forms can seldom be
connected by intermediate varieties, and thus proved to be
the same species, until many specimens are collected from
' many places ; and with fossil species this can rarely be donie.
We shall, perhaps, best perceive the improbability of our
being enabled to connect species by numerous, fine, inter-
mediate, fossil links, by asking ourselves whether, for in-
stance, geologists at some future period will be able to prove
that our different breeds of cattle, sheep, horses, and dogs are
descended from a single stock or from several aboriginal
stocks; or, again, whether certain sea-shells inhabiting the
shores of North America, which are ranked by some con-
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352 ORIGIN OF' SPECIES
chologists as distinct species from their European representa-
tives, and by other conchologists as only varieties, are really
varieties, or are, as it is called, specifically distinct This
could be effected by the future geologist only by his discov-
ering in a fossil state numerous intermediate gradations; and
such success is improbable in the highest degree.
It has been asserted over and over again, by writers who
believe in the immutability of species, that geology yields
no linking forms. This assertion, as we shall see in the next
chapter, is certainly erroneous. As Sir J. Lubbock has re-
marked, "Every species is a link between other allied forms."
If we take a genus having a score of species, recent and ex-
tinct, and destroy four-fifths of them, no one doubts that the
remainder will stand much more distinct from each other.
If the extreme forms in the genus happen to have been thus
destroyed, the genus itself will stand more distinct from
other allied genera. What geological research has not re-
vealed, is the former existence of infinitely numerous grada-
tions, as fine as existing varieties, connecting together nearly
all existing and extinct species. But this ought not to be ex-
pected; yet this has been repeatedly advanced as a most
serious objection against my views.
It may be worth while to sum up the foregoing remarks on
the causes of the imperfection of the geological record under
an imaginary illustration. The Malay Archipelago is about
the size of Europe from the North Cape to the Mediter-
ranean, and from Britain to Russia; and therefore equals all
the geological formations which have been examined with any
accuracy, excepting those of the United States of America.
I fully agree with Mr. Godwin-Austen, that the present con-
dition of the Malay Archipelago, with its numerous large
islands separated by wide and shallow seas, probably repre-
sents the former state of Europe, whilst most of our forma-
tions were accumulating. The Malay Archipelago is one of
the richest regions in organic beings; yet if all the species
were to be collected which have ever lived there, how im-
perfectly would they represent the natural history of the
world !
But we have every reason to believe that the terrestrial
productions of the archipelago would be preserved in an ex-
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ABSENCE OF INTERMEDIATE VARIETIES 353
trcmely imperfect manner in the formations which we sup-
pose to be there accumulating. Not many of the strictly
littoral animals, or of those which lived on naked submarine
rocks, would be embedded; and those embedded in gravel or
sand would not endure to a distant epoch. Wherever sedi-
ment did not accumulate on the bed of the sea, or where it
did not accumulate at a sufficient rate to protect organic
bodies from decay, no remains could be preserved.
Formations rich in fossils of many kinds, and of thickness
sufficient to last to an age as distant in futurity as the sec-
ondary formations lie in the past, would generally be formed
in the archipelago only during periods of subsidence. These
periods of subsidence would be separated from each other
by immense intervals of time, during which the area would
be either stationary or rising; whilst rising, the fossiliferous
formations on the steeper shores would be destroyed, almost
as soon as accumulated, by the incessant coast-action, as we
now see on the shores of South America. Even throughout
the extensive and shallow seas -within the archipelago, sedi-
mentary beds could hardly be accumulated of great thickness
during the periods of elevation, or become capped and pro-
tected by subsequent deposits, so as to have a good chance of
enduring to a very distant future. During the periods
of subsidence, there would probably be much extinction
of life ; during the periods of elevation, there would be much
variation, but the geological record would then be less
perfect.
It may be doubted whether the duration of any one great
period of subsidence over the whole or part of the archipel-
ago, together with a contemporaneous accumulation of sedi-
ment, would exceed the average duration of the same specific
forms ; and these contingencies are indispensable for the pres-
ervation of all the transitional gradations between any two or
more species. If such gradations were not all fully pre-
served, transitional varieties would merely appear as so many
new, though closely allied species. It is also probable that
each great period of subsidence would be interrupted by os-
cillations of level, and that slight climatal changes would
intervene during such lengthy periods; and in these cases the
inhabitants of the archipelago would migrate, and no closely
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354 ORIGIN OF SPEaES
consecutive record of their modifications could be preserved
in any one formation.
Very many of the marine inhabitants of the archipelago
now range thousands of miles beyond its confines; and anal-
ogy plainly leads to the belief that it would be chiefly these
far-ranging species, though only some of them, which would
oftenest produce new varieties; and the varieties would at
first be local or confined to one place, but if possessed of any
decided advantage, or when further modified and improved,
they would slowly spread and supplant their parent-forms.
When such varieties returned to their ancient homes, as they
would differ from their former state in a nearly uniform,
though perhaps extremely slight degree, and as they would
be found embedded in slightly different sub-stages of the
same formation, they would, according to the principles fol-
lowed by many palaeontologists, be ranked as new and distinct
species.
If then there be some degree of truth in these remarks, we
have no right to expect to find, in our geological formations,
an infinite number of those fine transitional forms which, on
our theory, have connected all the past and present species
of the same group into one long and branching chain of life.
We ought only to look for a few links, and such assuredly
we do find — some more distantly, some more closely, related
to each other; and these links, let them be ever so close, if
found in different stages of the same formation, would, by
many palaeontologists, be ranked as distinct species. But I
do not pretend that I should ever have suspected how poor
was the record in the best preserved geological sections, had
not the absence of innumerable transitional links between the
species which lived at the commencement and close of each
formation, pressed so hardly on my theory.
ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF
ALLIED SPECIES
The abrupt manner in which whole groups of species sud-
denly appear in certain formations, has been urged by several
palaeontologists — for instance, by Agassiz, Pictet, and Sedg-
wick—as a fatal objection to the belief in the transmutation
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APPEARANCE OF WHOLE GROUPS SS5
of species. If numerous species, belonging to the same gen-
era or families, have really started into life at once, the fact
would be fatal to the theory of evolution through natural
selection. For the development by this means of a group of
forms, all of which are descended from some one progenitor,
must have been an extremely slow process; and the progeni-
tors must have lived long before their modified descendants.
But we continually overrate the perfection of the geological
record, and falsely infer, because certain genera or families
have not been found beneath a certain stage, that they did
not exist before that stage. In all cases positive pakeonto-
logical evidence may be implicitly trusted; negative evidence
is worthless, as experience has so often shown. We contin-
ually forget how large the world is, compared with the area
over which our geological formations have been carefully ex-
amined ; we forget that groups of species may elsewhere have
long existed, and have slowly multiplied, before they invaded
the ancient archipelagoes of Europe and the United States.
We do not make due allowance for the intervals of time
which have elapsed between our consecutive formations, —
longer perhaps in many cases than the time required for the
accumulation of each formation. These intervals will have
given time for the multiplication of species from some one
parent- form: and in the succeeding formation, such groups
or species will appear as if suddenly created.
I may here recall a remark formerly made, namely, that it
might require a long succession of ages to adapt an organism
to some new and peculiar line of life, for instance, to fly
through the air ; and consequently that the transitional forms
would often long remain confined to some one region; but
that, when this adaptation had once been effected, and a few
species had thus acquired a great advantage over other or-
ganisms, a comparatively short time would be necessary to
produce many divergent forms, which would spread rapidly
and widely, throughout the world. Professor Pictet, in his
excellent Review of this work, in commenting on early
transitional forms, and taking birds as an illustration, cannot
see how the successive modifications of the anterior limbs of
a supposed prototype could possibly have been of any advan-
tage. But look at the penguins of the Southern Ocean ; have
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356 OBIGW OP SPECIES
not these birds their front limbs in this precise intermediate
state of "neither true arms nor true wings" ? Yet these birds
hold their place victoriously in the battle for life; for they
exist in infinite numbers and of many kinds. I do not sup-
pose that we here see the real transitional grades through
which the wings of birds have passed; but what special diffi-
culty is there in believing that it might profit the modified
descendants of the penguin; first to become enabled to flap
along the surface of the sea like the logger-headed duck, and
ultimately to rise from its surface and glide through the air?
I will now give a few examples to illustrate the foregoing
remarks, and to show how liable we are to error in supposing
that whole groups of species have suddenly been produced.
Even in so short an interval as that between the first and
second editions of Pictet's great work on Palaeontol(^;yy pub-
lished in 1844-46 and 1853-57, the conclusions on the first ap-
pearance and disappearance of several groups of animals
have been considerably modified; and a third edition would
require still further changes. I may recall the well-known
fact that in geological treatises, published not many years
ago, mammals were always spoken of as having sd>ruptly
come in at the commencement of the tertiary series. And
now one of the richest known accumulations of fossil mam-
mals belongs to the middle of the secondary series; and true
mammals have been discovered in the new red sandstone at
nearly the commencement of this great series. Cuvier used
to urge that no monkey occurred in any tertiary stratum ; but
now extinct species have been discovered in India, South
America, and in Europe, as far back as the miocene stage.
Had it not been for the rare accident of the preservation of
footsteps in the new red sandstone of the United States, who
would have ventured to suppose that no less than at least
thirty different bird-like animals, some of gigantic size, existed
during that period? Not a fragment of bone has been dis-*
covered in these beds. Not long ago, palaeontologists main-
tained that the whole class of birds came suddenly into ex-
istence during the eocene period; but now we know, on the
authority of Professor Owen, that a bird certainly lived dur-
ing the deposition of the upper greensand ; and still more re-
cently, that strange bird, the Archeopteryx, with a long
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APPEARANCB OP WHOLE GROUPS 9S7
lizard-like tail, bearing a pair of feathers on each joint, and
with its wings furnished with two free claws, has been dis-
covered in the oolitic slates of Solenhofen. Hardly any recent
discovery shows more forcibly than this, how little we as yet
know of the former inhabitants of the world.
I may give another instance, which, from having passed
under my own eyes, has much struck me. In a memoir on
Fossil Sessile Cirripedes, I stated that, from the large number
of existing and extinct tertiary species ; from the extraordi-
nary abundance of the individuals of many species all over
the world, from the Arctic regions to the equator, inhabiting
various zones of depths from the upper tidal limits to 50
fathoms; from the perfect manner in which specimens are
preserved in the oldest tertiary beds; from the ease with
which even a fragment of a valve can be recognized; from
all these circumstances, I inferred that, had sessile cirripedes
existed during the secondary periods, they would certainly
have been preserved and discovered; and as not one species
had then been discovered in beds of this age, I concluded that
this great group had been suddenly developed at the com-
mencement of the tertiary series. This was a sore trouble
to me, adding as I then thought one more instance of the
abrupt appearance of a great group of species. But my work
had hardly been published, when a skilful palaeontologist, M.
Bosquet, sent me a drawing of a perfect specimen of an un-
mistakeable sessile cirripede, which he had himself extracted
from the chalk of Belgium. And, as if to make the case as
striking as possible, this cirripede was a Chthamalus, a very
common, large, and ubiquitous genus, of which not one
species has as yet been found even in any tertiary stratum.
Still more recently, a Pyrgoma, a member of a distinct sub-
family of sessile cirripedes, has been discovered by Mr.
Woodward m the upper chalk; so that we now have abundant
evidence of the existence of this group of animals during the
secondary period.
The case most frequently insisted on by palaeontologists of
the apparently sudden appearance of a whole group of species,
is that of the teleostean fishes, low down, according to Agas-
siz, in the Chalk period. This group includes the large ma-
jority of existing species. But certain Jurassic and Triassic
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858 ORIGIN OF SPECIES
forms are now commonly admitted to be teleostean ; and even
some palaeozoic forms have thus been classed by one high
authority. If the teleosteans had really appeared suddenly in
the northern hemisphere at the commencement of the chalk
formation, the fact would have been highly remarkable; but
it would not have formed an insuperable difficulty, unless it
could likewise have been shown that at the same period the
species were suddenly and simultaneously developed in other
quarters of the world. It is almost superfluous to remark
that hardly any fossil-fish are known from south of the
equator ; and by running through Pictet's Palaeontology it will
be seen that very few species are known from several forma-
tions in Europe. Some few families of fish now have a con-
fined range; the teleostean fishes might formerly have had a
similarly confined range, and after having been largely de-
veloped in some one sea, have spread widely. Nor have we
any right to suppose that the seas of the world have always
been so freely open from south to north as they are at pres-
ent. Even at this day, if the Malay Archipelago were con-
verted into land, the tropical parts of the Indian Ocean would
form a large and perfectly enclosed basin, in which any great
group of marine animals might be multiplied; and here they
would remain confined, until some of the species became
adapted to a cooler climate, and were enabled to double the
Southern capes of Africa or Australia, and thus reach other
and distant seas.
From these considerations, from our ignorance of the geol-
ogy of other countries beyond the confines of Europe and the
United States, and from the revolution in our palaeontological
knowledge effected by the discoveries of the last dozen years,
it seems to me to be about as rash to dogmatize on the suc-
cession of organic forms throughout the world, as it would
be for a naturalist to land for five minutes on a barren point
in Australia, and then to discuss the number and range of its
productions.
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SUDDEN APPEARANCE OF GROUPS 359
ON THE SUDDEN APPEARANCE OP GROUPS OF ALLIED SPECIES
IN THE LOWEST KNOWN FOSSILIFEROUS STRATA
There is another and allied difficulty, which is much more
serious. I allude to the manner in which species belonging
to several of the main divisions of the animal kingdom sud-
denly appear in the lowest known fossiliferous rocks. Most
of the arguments which have convinced me that all the ex-
isting species of the same group are descended from a single
progenitor, apply with equal force to the earliest known
species. For instance, it cannot be doubted that all the
Cambrian and Silurian trilobites are descended from some
one crustacean, which must have lived long before the Cam-
brian age, and which probably differed greatly from any
known animal. Some of the most ancient animals, as the
Nautilus, Lingula, &c., do not differ much from living species ;
and it cannot on our theory be supposed, that these old spe-
cies were the progenitors of all the species belonging to the
same groups which have subsequently appeared, for they arc
not in any degree intermediate in character.
Consequently, if the theory be true, it is indisputable that
before the lowest Cambrian stratum was deposited long peri-
ods elapsed, as long as, or probably far longer than, the whole
interval from the Cambrian age to the present day; and that
during these vast periods the world swarmed with living
creatures. Here we encounter a formidable objection; for it
seems doubtful whether the earth, in a fit state for the habi-
tation of living creatures, has lasted long enough. Sir W.
Thompson concludes that the consolidation of the crust can
hardly have occurred less than 20 or more than 400 million
years ago, but probably not less than 98 or more than 200
million years. These very wide limits show how doubtful
the data are; and other elements may have hereafter to be
introduced into the problem. Mr. Croll estimates that about
60 million years have elapsed since the Cambrian period, but
this, judging from the small amount of organic change since
the commencement of the Glacial epoch, appears a very short
time for the many and great mutations of life, which have
certainly occurred since the Cambrian formation; and the
previous 140 million years can hardly be considered as suffi-
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960 ORIGIN OF SPECIES
cient for the development of the varied forms of life which
already existed during the Cambrian period. It is, however,
probable, as Sir William Thompson insists, that the world at
a very early period was subjected to more rapid and violent
changes in its physical conditions than those now occurring;
and such changes would have tended to induce changes at a
corresponding rate in the organisms which then existed.
To the question why we do not find rich fossiliferous de-
posits belonging to these assumed earliest periods prior to the
Cambrian system, I can give no satisfactory answer. Sev-
eral eminent geologists, with Sir R. Murchison at their head,
were until recently convinced that we beheld in the organic
remains of the lowest Silurian stratum the first dawn of life.
Other highly competent judges, as Lyell and E. Forbes, have
disputed this conclusion. We should not forget that only a
small portion of the world is known with accuracy. Not very
long ago M. Barrande added another and lower stage,
abounding with new and peculiar species, beneath the then
known Silurian system; and now, still lower down in the
Lower Cambrian formation, Mr. Hicks has found in South
Wales beds rich in trilobites, and containing various molluscs
and annelids. The presence of phosphatic nodules and bitu-
minous matter, even in some of the lowest azoic rocks, prob-
ably indicates life at these periods; and the existence of the
Eozoon in the Laurentian formation of Canada is generally
admitted. There are three great series of strata beneath the
Silurian system in Canada, in the lowest of which the Eozoon
is found. Sir W. Logan states that their "united thickness
"may possibly far surpass that of all the succeeding rocks,
"from the base of the palseozoic series to the present time. We
"are thus carried back to a period so remote that the appear-
"ance of the so-called Primordial fauna (of Barrande) may
"by some be considered as a comparatively modem event"
The Eozoon belongs to the most lowly organised of all
classes of animals, but is highly organised for its class; it
existed in countless numbers, and, as Dr. Dawson has re-
marked, certainly preyed on other minute organic beings,
which must have lived in great numbers. Thus the words,
which I wrote in 1859, about the existence of living beings
long before the Cambrian period, and which are almost the
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SUDDEN APFBARANGB OF GROUPS 361
same with those since used by Sir W. Logan, have proved
true. Nevertheless, the difficulty of assigning any good
reason for the absence of vast piles of strata rich in fossils
beneath the Cambrian system is very great It does not seem
probable that the most ancient beds have been quite worn
away by denudation, or that their fossils have been wholly
obliterated by metamorphic action, for if this had been the
case we should have found only small remnants of the forma-
tions next succeeding them in age, and these would always
have existed in a partially metamorphosed condition. But
the descriptions which we possess of the Silurian deposits
over immense territories in Russia and in North America, do
not support the view, that the older a formation is, the more
invariably it has suffered extreme denudation and meta-
morphism.
The case at present must remain inexplicable; and may
be truly urged as a valid argument against the views here
entertained. To show that it may hereafter receive some
explanation, I will give the following hypothesis. From the
nature of the organic remains which do not appear to have
inhabited profoimd depths, in the several formations of
Europe and of the United States; and from the amount of
sediment, miles in thickness, of which the formations are
composed, we may infer that from first to last large islands
or tracts of land, whence the sediment was derived, occurred
in the neighbourhood of the now existing continents of
Europe and North America. The same view has since been
maintained by Agassiz and others. But we do not know
what was the state of things in the intervals between the
several successive formations; whether Europe and the
United States during these intervals existed as dry land, or
as a submarine surface near land, on which sediment was
not deposited, or as the bed on an open and unfathomable sea.
Looking to the existing oceans, which are thrice as exten-
sive as the land, we see them studded with many islands;
but hardly one truly oceanic island (with the exception of
New Zealand, if this can be called a truly oceanic island) is
as yet known to afford even a remnant of any palaeozoic and
secondary formation. Hence we may perhaps infer that
during the palaeozoic and secondary periods, neither' conti-
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362 ORIGIN OF SPECIES
nents nor continental islands existed where our oceans now
extend ; for had they existed, palaeozoic and secondary forma-
tions would in all probability have been accumulated from
sediment derived from their wear and tear ; and these would
have been at least partially upheaved by the oscillations of
level, which must have intervened during these enormously
long periods. If then we may infer anything from these
facts, we may infer that, where our oceans now extend,
oceans have extended from the remotest period of which we
have any record; and on the other hand, that where conti-
nents now exist, large tracts of land have existed, subjected
no doubt to great oscillations of level, since the Cambrian
period. The colored map appended to my volume on Coral
Reefs, led me to conclude that the great oceans are still
mainly areas of subsidence, the great archipelagoes still areas
of oscillations of level, and the continents areas of elevation.
But we have no reason to assume that things have thus
remained from the beginning of the world. Our continents
seem to have been formed by a preponderance, during many
oscillations of level, of the force of elevation; but may not
the areas of preponderant movement have changed in the
lapse of ages? At a period long antecedent to the Cambrian
epoch, continents may have existed where oceans are now
spread out; and clear and open oceans may have existed
where our continents now stand. Nor should we be justified
in assuming that if, for instance, the bed of the Pacific Ocean
were now converted into a continent we should there find
sedimentary formations in a recognisable condition older
than the Cambrian strata, supposing such to have been for-
merly deposited; for it might well happen that strata which
had subsided some miles nearer to the centre of the earth,
and which had been pressed on by an enormous weight of
super-incumbent water, might have undergone far more
metamorphic action than strata which have always remained
nearer to the surface. The immense areas in some parts of the
world, for instance in South America, of naked metamorphic
rocks, which must have been heated under great pressure,
have always seemed to me to require some special explana-
tion ; and we may perhaps believe that we see in these large
areas,' the many formations long anterior to the Cambrian
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SUDDEN APPEARANCE OF GROUPS 363
epoch in a completely metamorphosed and denuded con-
dition.
The several difficulties here discussed, namely — ^that,
though we find in our geological formations many links be«
tween the species which now exist and which formerly
existed, we do not find infinitely numerous fine transitional
forms closely joining them all together; — ^the sudden man-
ner in which several groups of species first appear in our
European formations; — ^the almost entire absence, as at
present known, of formations rich in fossils beneath the
Cambrian strata, — are all undoubtedly of the most serious
nature. We see this in the fact that the most eminent
palaeontologists, namely, Cuvier, Agassiz, Barrande, Pictet,
Falconer, E. Forbes, &c., and all our greatest geologists, as
Lyell, Murchison, Sedgwick, &c, have unanimously, often
vehemently, maintained the immutability of species. But
Sir Charles Lyell now gives the support of his high author-
ity to the other side ; and most geologists and palaeontologists
are much shaken in their former belief. Those who believe
that the geological record is in any degree perfect, will un-
doubtedly at once reject the theory. For my part, follow-
ing out Lyeirs metaphor, I look at the geological record
as a history of the world imperfectly kept, and written in
a changing dialect; of this history we possess the last vol-
ume alone, relating only to two or three countries. Of this
volume, only here and there a short chapter has been pre-
served; and of each page, only here and there a few lines.
Each word of the slowly-changing language, more or less
diflferent in the successive chapters, may represent the forms
of life, which are entombed in our consecutive formations,
and which falsely appear to have been abruptly introduced.
On this view, the difficulties above discussed are greatly
diminished, or even disappear.
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CHAPTER XI
On the Geological Succession of Organic Beings
On the slow and successive appearance of new species — ^On their
different rates of change — Species once lost do not reappear —
Groups of species follow the same general rules in their appear-
ance and disappearance ad do single species— On extinction —
On simultaneous changes in the forms of life throughout the
world — On the affinities of extinct species to each other and to
living species — On the state of development of ancient forms —
On the succession of the same tsrpes within the same areas —
Summary of preceding and present chapter.
1ET US now see whether the several facts and laws relat-
. ing to the geological succession of organic beings
■ accord best with the common view of the immutability
of species, or with that of their slow and gradual modifica-
tion, through variation and natural selection.
New species have appeared very slowly, one after another,
both on the land and in the waters. Lyell has shown that
it is hardly possible to resist the evidence on this head in the
case of the several tertiary stages; and every year tends
to fill up the blanks between the stages, and to make the pro-
portion between the lost and existing forms more gradual.
In some of the most recent beds, though undoubtedly of high
antiquity if measured by years, only one or two species are
extinct, and only one or two are new, having appeared there
for the first time, either locally, or, as far as we know, on
the face of the earth. The secondary formations are more
broken; but, as Bronn has remarked, neither the appear-
ance nor disappearance of the many species embedded in
each formation has been simultaneous.
Species belonging to different genera and classes have not
changed at the same rate, or in the same degree. In the
older tertiary beds a few living shells may still be found in
the midst of a multitude of extinct forms. Falconer has
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GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 365
given a striking instance of a similar fact, for an existing
crocodile is associated with many lost mammals and reptiles
in the sub-Himalayan deposits. The Silurian Lingula differs
but little from the living species of this genus ; whereas most
of the other Silurian Molluscs and all the Crustaceans have
changed greatly. The productions of the land seem to have
changed at a quicker rate than those of the sea, of which
a striking instance has been observed in Switzerland. There
is some reason to believe that organisms high in the scale,
change more quickly than those that are low: though there
are exceptions to this rule. The amount of organic change,
as Pictet has remarked, is not the same in each successive
so-called formation. Yet if we compare any but the most
closely related formations, all the species will be found to
have undergone some change. When a species has once dis-
appeared from the face of the earth, we have no reason to
believe that the same identical form ever reappears. The
strongest apparent exception to this latter rule is that of
the so-called "colonies" of M. Barrande, which intrude for a
period in the midst of an older formation, and then allow
the pre-existing fauna to reappear; but Lyell's explanation,
namely, that it is a case of temporary migration from a
distinct geographical province, seems satisfactory.
These several facts accord well with our theory, which
includes no fixed law of development, causing all the in-
habitants of an area to change abruptly, or simultaneously,
or to an equal degree. The process of modification must be
slow, and will generally affect only a few species at the
same time ; for the variability of each species is independent
of that of all others. Whether such variations or individual
differences as may arise will be accumulated through natural
selection in a greater or less degree, thus causing a greater
or less amount of permanent modification, will depend on
many complex contingencies — on the variations being of a
beneficial nature, on the freedom of intercrossing, on the
slowly changing physical conditions of the country, on the
immigration of new colonists, and on the nature of the other
inhabitants with which the varying species come into com-
petition. Hence it is by no means surprising that one species
should retain the same identical form much longer than
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366 ORIGIN OF SPEaSS
others; or, if changing, should change in a less degree. We
find similar relations between the existing inhabitants of dis-
tinct countries ; for instance, the land-shells and coleopterous
insects of Madeira have come to differ considerably from
their nearest allies on the continent of Europe, whereas the
marine shells and birds have remained unaltered. We can
perhaps understand the apparently quicker rate of change in
terrestrial and in more highly organised productions com-
pared with marine and lower productions, by the more com-
plex relations of the higher beings to their organic and in-
organic conditions of life, as explained in a former chapter.
When many of the inhabitants of any area have become
modified and improved, we can understand, on the principle
of competition, and from the all-important relations of or-
ganism to organism in the struggle for life, that any form
which did not become in some degree modified and improved,
would be liable to extermination. Hence we see why all
the species in the same region do at last, if we look to long
enough intervals of time, become modified, for otherwise
they would become extinct.
In members of the same class the average amount of
change during long and equal periods of time, may, perhaps,
be nearly the same; but as the accumulation of enduring
formation, rich in fossils, depends on great masses of sedi-
ment being deposited on subsiding areas, our formations have
been almost necessarily accumulated at wide and irregularly
intermittent intervals of time; consequently the amount of
organic change exhibited by the fossils embedded in consecu-
tive formations is not equal. Each formation, on this view,
does not mark a new and complete act of creation, but only
an occasional scene, taken almost at hazard in an ever
slowly changing drama.
We can clearly understand why a species when once lost
should never reappear, even if the very same conditions of
life, organic and inorganic, should recur. For though the
offspring of one species might be adapted (and no doubt
this has occurred in innumerable instances) to fill the i^ace
of another species in the economy of nature, and thus sup-
plant it; yet the two forms — ^the old and the new — ^would
not be identically the same ; for both would almost certainly.
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GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 367
inherit different characters from their distinct progenitors;
and organisms already differing wotdd vary in a different
manner. For instance, it is possible, if all our fantail
pigeons were destroyed, that fanciers might make a new
breed hardly distinguishable from the present breed; but
if the parent rock-pigeon were likewise destroyed, and under
nature we have every reason to believe that parent-forms
are generally supplanted and exterminated by their improved
offspring, it is incredible that a fantail, identical with the
existing breed, could be raised from any other species of
pigeon, or even from any other well-established race of the
domestic pigeon, for the successive variations would almost
certainly be in some degree different, and the newly-formed
variety would probably inherit from its progenitor some char-
acteristic differences.
Groups of species, that is, genera and families, follow the
same general rules in their appearance and disappearance as
do single species, changing more or less quickly, and in a
greater or lesser degree. A group, when it has once dis-
appeared, never reappears ; that is, its existence, as long as it
lasts, is continuous. I am aware that there are some ap-
parent exceptions to this rule, but the exceptions are surpris-
ingly few, so few that E. Forbes, Pictet, and Woodward
(though all strongly opposed to such views as I maintain)
admit its truth ; and the rule strictly accords with the theory.
For all the species of the same group, however long it may
have lasted, are the modified descendants one from the other,
and all from a common progenitor. In the genus Lingula,
for instance, the species which have successively appeared at all
ages must have been connected by an -unbroken series of gen-
erations, from the lowest Silurian stratum to the present day.
We have seen in the last chapter that whole groups of
species sometimes falsely appear to have been abruptly devel-
oped; and I have attempted to give an explanation of this
fact, which if true would be fatal to my views. But such
cases are certainly exceptional; the general rule being a
gradual increase in number, until the group reaches its maxi-
mum, and then, sooner or later, a gradual decrease. If the
number of the species included within a genus, or the number
of the genera within a family, be represented by a vertical
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368 ORIGIN OF SPEaES
line of varying thickness, ascending through the successive
geological formations, in which the species are found, the
line will sometimes falsely appear to begin at its lower end,
not in a sharp point, but abruptly ; it then gradually thickens
upwards, often keeping of equal thickness for a space, and
ultimately thins out in the upper beds, marking the decrease
and final extinction of the species. This gradual increase in
number of the species of a group is strictly conformaUe
with the theory, for the species of the same genus,
and the genera of the same family, can increase only slowly
and progressively; the process of modification and the pro-
duction of a number of allied forms necessarily being a slow
and gradual process,-— one species first giving rise to two
or three varieties, these being slowly converted into species,
which in their turn produce by equally slow steps other
varieties and species, and so on, like the branching of a great
tree from a single stem, till the group becomes large.
ON EXTINCTION
We have as yet only spoken incidentally of the disappear-
ance of species and of groups of species. On the theory of
natural selection, the extinction of dd forms and the pro-
duction of new and improved forms are intimately con-
nected together. The old notion of all the inhabitants of the
earth having been swept away by catastrophes at successive
periods is very generally given up, even by those geologists,
as Elie de Beaumont, Murchison, Barrande, &c., whose gen-
eral views would naturally lead them to this conclusion.
On the contrary, we have every reason to believe, from the
study of the tertiary formations, that species and groups of
species gradually disappear, one after another, first from one
spot, then from another, and finally from the world. In
some few cases, however, as by the breaking of an isthmus
and the consequent irruption of a multitude of new inhabi-
tants into an adjoining sea, or by the final subsidence of an
island, the process of extinction may have been rapid. Both
single species and whole groups of species last for very un-
equal periods; some groups, as we have seen, have endured
from the earliest known dawn of life to the present day;
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EXTINCTION 309
some have disappeared before the close of the palaeozoic
period. No fixed law seems to determine the length of time
during which any single species or any single genus en-
dures. There is reason to believe that the extinction of a
whole group of species is generally a slower process than
their production: if their appearance and disappearance be
represented, as before, by a vertical line of varying thickness
the line is found to taper more gradually at its upper end,
which marks the progress of extermination, than at its
lower end, which marks the first appearance and the early
increase in number of the species. In some cases, however,
the extermination of whole groups, as of ammonites, towards
the close of the secondary period, has been wonderfully
sudden.
The extinction of species has been involved in the most
gratuitous mystery. Some authors have even supposed that,
as the individual has a definite length of life, so have species
a definite duration. No one can have marvelled more than I
have done at the extinction of species. When I found in La
Plata the tooth of a horse embedded with the remains of
Mastodon, Megatherium, Toxodon, and other extinct mon-
sters, which all co-existed with still living shells at a very
late geological period, I was filled with astonishment; for,
seeing that the horse, since its introduction by the Span-
iards into South America, has run wild over the whole coun-
try and has increased in numbers at an unparalleled rate, I
asked myself what could so recently have exterminated the
former horse under conditions of life apparently so favour-
able. But my astonishment was groundless. Professor
Owen soon perceived that the tooth, though so like that of
the existing horse, belonged to an extinct species. Had this
horse been still living, but in some degree rare, no naturalist
would have felt the least surprise at its rarity; for rarity
is the attribute of a vast number of species of all classes, in
all countries. If we ask ourselves why this or that species
is rare, we answer that something is unfavourable in its
conditions of life ; but what that something is we can hardly
ever tell. On the supposition of the fossil horse still existing
as a rare species, we might have felt certain, from the
analogy of all other mammals, even of the slow-breeding
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S70 ORIGIN OP SPBCIBS
elephant, and from the history of the naturalisation of
the domestic horse in South America, that under more
favourable conditions it would in a very few years have
stocked the whole continent. But we could not have told
what the unfavourable conditions were which checked its in-
crease, whether some one or several contingencies, and at
what period of the horse's life, and in what degree they
severally acted. If the conditions had gone on, however
slowly, becoming less and less favouraUe, we assuredly
should not have perceived the fact, yet the fossil horse would
certainly have become rarer and rarer, and finally extinct;
— ^its place being seized on by some more successful com-
petitor.
It is most difficult always to remember that the increase
of every creature is constantly being checked by unperceived
hostile agencies; and that these same unperceived agencies
are amply sufficient to cause rarity, and finally extinction.
So little is this subject understood, that I have heard sur-
prise repeatedly expressed at such great monsters as the
Mastodon and the more ancient Dinosaurians having be-
come extinct; as if mere bodily strength gave victory in the
battle of life. Mere size, on the contrary, would in some
cases determine, as has been remarked by Owen, quicker
extermination from the greater amount of requisite food.
Before man inhabited India or Africa, some cause must
have checked the continued increase of the existing ele-
phant A highly capable judge. Dr. Falconer, believes that
it is chiefly insects which, from incessantly harassing and
weakening the elephant in India, check its increase; and
this was Bruce's conclusion with respect to the African ele-
phant in Abyssinia. It is certain that insects and blood-
sucking bats determine the existence of the larger natural-
ized quadrupeds in several parts of S. America.
We see in many cases in the more recent tertiary forma-
tions, that rarity precedes extinction ; and we know that this
has been the progress of events with those animals which
have been exterminated, either locally or wholly, through
man's agency. I may repeat what I puUished in 1845,
namely, that to admit that species generally become rare
before they become extinct— to feel no surprise at the rarity
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EXTINCTION 371
of a species, and yet to marvel greatly when the species
ceases to exist, is much the same as to admit that sickness
in the individual is the forerunner of death — ^to feel no sur-
prise at sickness, but, when the sick man dies, to wonder and
to suspect that he died by some deed of violence.
The theory of natural selection is grounded on the belief
that each new variety and ultimately each new species, is
produced and maintained by having some advantage over
those with which it comes into competition; and the conse-
quent extinction of the less favoured forms almost inevitably
follows. It is the same with our domestic productions; when
a new and slightly improved variety has been raised, it at
first supplants the less improved varieties in the same neigh-
bourhood; when much improved it is transported far and
near, like our short-horn cattle, and takes the place of other
breeds in other countries. Thus the appearance of new
forms and the disappearance of old forms, both those natu-
rally and those artificially produced, are bound together. In
flourishing groups, the number of new specific forms which
have been produced within a given time has at some periods
probably been greater than the number of the old specific
forms which have been exterminated; but we know that spe-
cies have not gone on indefinitely increasing, at least during
the later geological epochs, so that, looking to later times,
we may believe that the production of new forms has caused
the extinction of about die same number of old forms.
The competition will generally be most severe, as formerly
explained and illustrated by examples, between the forms
which are most like each other in all respects. Hence the
improved and modified descendants of a species will gener-
ally cause the extermination of the parent species; and if
many new forms have been developed from any one species,
the nearest allies of that species, i.e., the species of the same
genus, will be the most liable to extermination. Thus, as I
believe, a number of new species descended from one species,
that is a new genus, comes to supplant an old genus, belong-
ing to the same family. But it must often have happened
that a new species belonging to some one group has seized
on the place occupied by a species belonging to a distinct
group, and thus have caused its extermination. If many
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372 ORIGIN OF SPECIES
allied forms be developed from the successful intnider, many
will have to yield their places; and it will generally be the
allied forms, which will suffer from some inherited inferior-
ity in common. But whether it be species belonging to the
same or to a distinct class, which have yielded their places
to other modified and improved species, a few of the sufferers
may often be preserved for a long time, from being fitted to
some peculiar line of life, or from inhabiting some distant
and isolated station, where they will have escaped severe
competition. For instance, some species of Trigonia, a great
genus of shells in the secondary formations, survive in the
Australian seas; and a few members of the great and almost
extinct group of Ganoid fishes still inhabit our fresh waters.
Therefore the utter extinction of a group is generally, as
we have seen, a slower process than its production.
With respect to the apparently sudden extermination of
whole families or orders, as of Trilobites at the close of the
palaeozoic period and of Ammonites at the close of the sec-
ondary period, we must remember what has been already
said on the probable wide intervals of time between our con-
secutive formations; and in these intervals there may have
been much slow extermination. Moreover, when, by sud-
den immigration or by unusually rapid development, many
species of a new group have taken possession of an area,
many of the older species will have been exterminated in a
correspondingly rapid manner; and the forms which thus
yield their places will commonly be allied, for they will par-
take of the same inferiority in common.
Thus, as it seems to me, tiie manner in which single species
and whole groups of species become extinct accord well with
the theory of natural selection. We need not marvel at ex-
tinction ; if we must marvel, let it be at our own presumptipn
in imagining for a moment that we understand the many
complex contingencies on which the existence of each spe-
cies depends. If we forget for an instant that each species
tends to increase inordinately, and that some check is aiways
in action, yet seldom perceived by us, the whole economy of
nature will be utterly obscured. Whenever we can precisely
say why this species is more abundant in individuals than
that; why this species and not another can be naturalised in
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FORMS OF UFB CHANGING 373
a given country; then, and not until then, we may justly feel
surprise why we cannot account for the extinction of any
particular species or group of species.
ON THE FORMS OF LIFE CHANGING ALMOST SIMULTANE-
OUSLY THROUGHOXnr THE WORLD
Scarcely any palaeontological discovery is more striking
than the fact that the forms of life change almost simulta-
neously throughout the world. Thus our European Chalk
formation can be recognised in many distinct regions, under
the most different climates, where not a fragment of the
mineral chalk itself can be found; namely in North America,
in equatorial South America, in Tierra del Fuego, at the
Cape of Good Hope, and in the peninsula of India. For at
these distant points, the organic remains in certain beds pre-
sent an unmistakeable resemblance to those of the Chalk. It
is not that the same species are met with; for in some cases
not one species is identically the same, but they belong to the
same families, genera, and sections of genera, and sometimes
are similarly characterised in such trifling points as mere
superficial sculpture. Moreover, other forms, which are not
found in the Chalk of Europe, but which occur in the forma-
tions either above or below, occur in the same order at these
distant points of the world. In the several successive palaeo-
zoic formations of Russia, Western Europe, and North
America, a similar parallelism in the forms of life has been
observed by several authors; so it is, according to Lyell, with
the European and North American tertiary deposits. Even
if the few fossil species which are common to the Old and
New Worlds were kept wholly out of view, the general par-
allelism in the successive forms of life, in the palaeozoic and
tertiary stages, would still be manifest, and the several for-
mations could be easily correlated.
These observations, however, relate to the marine inhabi-
tants of the world: we have not sufficient data to judge
whether the productions of the land and of fi;esh water at
distant points change in the same parallel manner. We may
doubt whether they have thus changed: if the Megatherium,
Mylodon, Macrauchenia, and Toxodon had been brought to
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374 ORIGIN OF SPECIBS
Europe from La Plata, without any information in regBid
to their geological position, no one would have suspected
that they had co-existed with sea-shells all still living; but
as these anomalous monsters co-existed with the Mastodon
and Horse, it might at least have been inferred that they
had lived during one of the later tertiary stages.
When the marine forms of life are spoken of as having
changed simultaneously throughout the world, it must not be
supposed that this expression relates to the same year, or to
the same country, or even that it has a very strict geological
sense; for if all the marine animals now living in Europe,
and all those that lived in Europe during the pleistocene
period (a very remote period as measured by years, includ-
ing the whole glacial epoch) were compared with those now
existing in South America or in Australia, the most skilful
naturalist would hardly be able to say whether the present
or the pleistocene inhabitants of Europe resembled most
closely those of the southern hemisphere. So, again, several
highly competent observers maintain that the existing pro-
ductions of the United States are iftore closely related to
those which lived in Europe during certain late tertiary
stages, than to the present inhabitants of Europe ; and if this
be so, it is evident that fossiliferous beds now deposited on
the shores of I^orth America would hereafter be liable to be
classed with somewhat older European beds. Nevertheless,
looking to a remotely future epoch, there can be little doubt
that all the more modem marine formations, namely, the
upper pliocene, the pleistocene and strictly modem beds of
Europe, North and South America, and Australia, from con-
taining fossil remains in some degree allied, and from not
including those forms which are found only in the older
underlying deposits, would be correctly ranked as simulta-
neous in a geological sense.
The fact of the forms of life changing simultaneously, in
the above large sense, at distant parts of the world, has
greatly struck those admirable observers, MM. de Verneuil
and d'Archiac. After referring to the parallelism of the
palaeozoic forms of life in various parts of Europe, they add,
"If, struck by this strange sequence, we turn our attention
to North America, and there discover a series of analogous
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FORMS OF LIFE CHANGING 375
phenomena, it will appear certain that all these modifications
of species, their extinction, and the introduction of new ones,
cannot be owing to mere changes in marine currents or other
causes more or less local and temporary, but depend on gen-
eral laws which govern the whole animal kingdonL" M.
Barrande has made forcible remarks to precisely the same
effect It is, indeed, quite futile to look to changes of cur-
rents, climate, or other physical conditions, as the cause of
these great mutations in the forms of life throughout the
world, under the most different climates. We must, as Bar-
rande has remarked, look to some special law. We shall see
this more clearly when we treat of the present distribution
of organic beings, and find how slight is tiie relation between
the physical conditions of various countries and the nature
of their inhabitants.
This great fact of the parallel succession of the forms of
life throughout the world, is explicable on the theory of
natural selection. New species are formed by having some
advantage over older forms; and the forms, which are al-
ready dominant, or have some advantage over the other
forms in their own country, give birth to the greatest num-
ber of new varieties or incipient species. We have distinct
evidence on this head, in the plants which are dominant, that
is, which are commonest and most widely diffused, producing
the greatest number of new varieties. It is also natural that
the dominant, varying, and far-spreading species, which have
already invaded to a certain extent the territories of other
species, should be those which would have the best chance
of spreading stiU further, and of giving rise in new countries
to other new varieties and species. The process of diffusion
would often be very slow, depending on dimatal and geo-
graphical changes, on strange accidents, and on the gradual
acclimatisation of new species to the various climates
through which they might have to pass, but in the course
of time the dominant forms would generally succeed in
spreading and would ultimately prevail. The diffusion
would, it is probable, be slower with the terrestrial inhabi-
tants of the distinct continents than with the marine inhabi-
tants of the continuous sea. We might therefore expect to
find, as we do find, a less strict degree of parallelism in the
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376 ORIGIN OF SPEaBS
succession of the productions of the land than with those of
the sea.
Thus, as it seems to me, the parallel, and, taken in a large
sense, simultaneous, succession of the same forms of life
throughout the world, accords well with the principle of new
species having been formed by dominant species spreading
widely and varying; the new species thus produced being
themselves dominant, owing to their having had some ad-
vantage over their already dominant parents, as well as over
other species, and again spreading, varying, and producing
new forms. The old forms which are beaten and which
yield their places to the new and victorious forms, will gen-
erally be allied in groups, from inheriting some inferiority
in common; and therefore, as new and improved groups
spread throughout the world, old groups disappear from the
world; and the succession of forms everywhere tends to
correspond both in their ^rst appearance and final disappear-
ance.
There is one other remark connected with this subject
worth making. I have given my reasons for believing that
most of our great formations, rich in fossils, were deposited
during periods of subsidence; and that blank intervals of
vast duration, as far as fossils are concerned, occurred dur-
ing the periods when the bed of the sea was either stationary
or rising, and likewise when sediment was not thrown down
quickly enough to embed and preserve organic remains.
During these long and blank intervals I suppose that the in-
habitants of each region underwent a considerable amount
of modification and extinction, and that there was much
migration from other parts of the world. As we have rea-
son to believe that large areas are affected by the same move-
ment, it is probable that strictly contemporaneous formations
have often been accumulated over very wide spaces in the
same quarter of the world; but we are very far from having
any right to conclude that this has invariably been the case,
and that large areas have invariably been affected by the
same movements. When two formations have been deposited
in two regions during nearly, but not exactly, the same
period, we should find in both, from the causes explained in
the foregoing paragraphs, the same general succession in
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AFFINITIES OF EXTINCT SPEOES 377
the forms of life; but the species would not exactly corre-
spond; for there will have been a little more time in the one
region than in the other for modification^ extinction, and
immigration.
I suspect that cases of this nature occur in Europe. Mr.
Prestwich, in his admirable Memoirs on the eocene deposits
of England and France, is able to draw a close general par-
allelism between the successive stages in the two countries;
but when he compares certain stages in England with those
in France, although he finds in both a curious accordance in
the numbers of the species belonging to the same genera, yet
the species themselves differ in a manner very difficult to
account for considering the proximity of the two areas,—
unless, indeed, it be assumed that an isthmus separated two
seas inhabited by distinct, but contemporaneous, faunas.
Lyell has made similar observations on some of the later ter-
tiary formations. Barrande, also, shows that there is a strik-
ing general parallelism in the successive Silurian deposits of
Bohemia and Scandinavia; nevertheless he finds a surprising
amount of difference in the species. If the several forma-
tions in these regions have not been deposited during the
same exact periods, — a formation in one region often cor-
responding with a blank interval in the other, — ^and if in
both regions the species have gone on slowly changing dur-
ing the accumulation of the several formations and during
the long intervals of time between them ; in this case the sev-
eral formations in the two regions could be arranged in the
same order, in accordance with the general succession of the
forms of life, and the order would falsely appear to be
strictly parallel; nevertheless the species would not be all
the same in the apparendy corresponding stages in the two
regions.
ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER
AND TO LIVING FORMS
Let US now look to the mutual affinities of extinct and
living species. All fall into a few grand classes; and this
fact is at once explained on the principle of descent The
more ancient any form is, the more, as a general rule, it dif-
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378 ORIGIN OF SPEaES
fers from living forms. But, as Buckland long ago re-
marked, extinct species can all be classed either in still ex-
isting groups, or between them. That the extinct forms of
life help to fill lip the intervals between existing genera,
families, and orders, is certainly true; but as this statement
has often been ignored or even denied, it may be well to
make some remarks on this subject, and to give some in-
stances. If we confine our attention either to the living or
to the extinct species of the same class, the series is far less
perfect that if we combine both into one general system. In
the writings of Professor Owen we continually meet with
the expression of generalised forms, as applied to extinct
animals ; and in the writings of Agassiz, of prophetic or syn-
thetic types; and these terms imply that such forms are in
fact intermediate or connecting links. Another distinguished
paleontologist, M. Gaudry, has shown in the most striking
manner that many of the fossil mammals discovered by him
in Attica serve to break down the intervals between existing
genera. Cuvier ranked the Ruminants and Pachyderms, as
two of the most distinct orders of mammals: but so many
fossil links have been disentombed that Owen has had to
alter the whole classification, and has placed certain pachy-
derms in the same sub-order with ruminants ; for example, he
dissolves by gradations the apparently wide interval between
the pig and the camel. The Ungulata or hoofed quadrupeds
are now divided into the even-toed or odd-toed divisions;
but the Macrauchenia of S. America connects to a certain
extent these two grand divisions. No one will deny that
the Hipparion is intermediate between the existing horse
and certain older ungulate forms. What a wonderful con-
necting link in the chain of mammals is the Typotherium
from S. America, as the name given to it by Professor Ger-
vais expresses, and which cannot be placed in any existing
order. The Sirenia form a very distinct group of mammals,
and one of the most remarkable peculiarities in the existing
dugong and lamentin is the entire absence of hind limbs
without even a rudiment being left; but the extinct Hali-
therium had, according to Professor Flower, an ossified
thigh-bone "articulated to a well-defined acetabulum in the
pelvis," and it thus makes some approach to ordinary hoofed
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AFFINITIES OF EXTINCT SPECIES 379
quadrupeds, to which the Sirenia are in other respects allied.
I'he cetaceans or whales are widely different from all other
mammals, but the tertiary Zeuglodon and Squalodon, which
have been placed by some naturalists in an order by them-
selves, are considered by Professor Huxley to be undoubt-
edly cetaceans, "and to constitute connecting links with the
aquatic camivora."
Even the wide interval between birds and reptiles has been
shown by the naturalist just quoted to be partially bridged
over in the most unexpected manner, on the one hand, by the
ostrich and extinct Archeopteryx, and on the other hand, by
the Compsognathus, one of the Dinosaurians — ^that group
which includes the most gigantic of all terrestrial reptiles.
Turning to the Invertebrata, Barrande asserts, a higher au-
thority could not be named, that he is every day taught that,
although palsozoic animals can certainly be classed under
existing groups, yet that at this ancient period the groups
were not so distinctly separated from each other as they
now are.
Some writers have objected to any extinct species, or
group of species, being considered as intermediate between
any two living species, or groups of species. If by this term
it is meant that an extinct form is directly intermediate in
all its characters between two living forms or groups, the
objection is probably valid. But in a natural classification
many fossil species certainly stand between living species,
and some extinct genera between living genera, even be-
tween genera belonging to distinct families. The most com-
mon case, especially with respect to very distinct groups,
such as fish and reptiles, seems to be, that, supposing them
to be distinguished at the present day by a score of char-
acters, the ancient members are separated by a somewhat
lesser number of characters; so that the two groups formerly
made a somewhat nearer approach to each other than they
now do.
It is a common belief that the more ancient a form is, by
so much the more it tends to connect by some of its char-
acters groups now widely separated from each other. This
remark no. doubt must be restricted to those groups which
have undergone much change in the course of geological
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380 ORIGIN OF SPEaES
ages; and it would be difficult to prove the truth of the propo-
sition, for every now and then a living animal, as the Lepi-
dosiren, is discovered having affinities directed towards very
distinct groups. Yet if we compare the older Reptiles and
Batrachians, the older Fish, the older Cephalopods, and the
eocene Mammals, with the more recent members of the same
classes, we must admit that there is truth in the remark.
Let us see how far these several facts and inferences ac-
cord with the theory of descent with modification. As the
subject is somewhat complex, I must request the reader to
turn to the diagram in the fourth chapter. We may suppose
that the numbered letters in italics represent genera, and the
dotted lines diverging from them the species in each genus.
The diagram is much too simple, too few genera and too few
species being given, but this is unimportant for us. The
horizontal lines may represent successive geological forma-
tions, and all the forms beneath the uppermost line may be
considered as extinct The three existing genera a**, (f^, p^,
will form a small family; 5" and /** a closely allied family
or sub- family; and o" e^\ tn^, a third family. These three
families, together with the many extinct genera on the sev-
eral lines of descent diverging from the parent-form (A)
will form an order, for all will have inherited something in
common from their ancient progenitor. On the principle of
the continued tendency to divergence of character, which
was formerly illustrated by this diagram, the more recent
any form is, the more it will generally differ from its ancient
progenitor. Hence we can understand the rule that the most
ancient fossils differ most from existing forms. We must
not, however, assume that divergence of character is a neces-
sary contingency; it depends solely on the descendants from
a species being thus enabled to seize on many and different
places in the economy of nature. Therefore it is quite pos-
sible, as we have seen in the case of some Silurian forms,
that a species might go on being slightly modified in relation
to its slightly altered conditions of life, and yet retain
throughout a vast period the same general characteristics.
This is represented in the diagram by the letter f**.
All the many forms, extinct and recent, descended from
(A), make, as before remarked, one order; and this order.
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AFFINITIBS OF EXTINCT SPECIES S81
from the continued effects of extinction and divergence of
character, has become divided into several sub-families and
families, some of which are supposed to have perished at
different periods, and some to have endured to the present
day.
By looking at the diagram we can see that if many of the
extinct forms supposed to be imbedded in the successive
formations, were discovered at several points low down in
the series, the three existing families on the uppermost line
would be rendered less distinct from each other. If, for in-
stance, the genera a*, cf, d^, f, m*, w*, nf, were disinterred,
these three families would be so closely linked together that
they probably would have to be united into one great fam-
ily, in nearly the same manner as has occurred with rumi-
nants and certain pachyderms. Yet he who objected to con-
sider as intermediate the extinct genera, which thus link
together the living genera of three families, would be partly
justified, for they are intermediate, not directly, but only by
a long and circuitous course through many widely different
forms. If many extinct forms were to be discovered above
one of the horizontal lines or geological formations — for in-
stance, above No. VI. — ^but none from beneath this line, then
only two of the families (those on the left hand, cf^, &c., and
5," &c) would have to be united into one; and there would
remain two families, which would be less distinct from each
other than they were before the discovery of the fossils.
So again if the three families formed of eight genera (a^* to
n^)y on the uppermost line, be supposed to differ from each
other by half-a-dozen important characters, then the fami-
lies which existed at the period marked VI. would certainly
have differed from each other by a less number of char-
acters; for they would at this early stage of descent have
diverged in a less degree from their common progenitor.
Thus it comes that ancient and extinct genera are often in a
greater or less degree intermediate in character between
their modified descendants, or between their collateral
relations.
Under nature the process will be far more complicated
than is represented in the diagram ; for the groups will have
been more ntunerous ; they will have endured for extremely
X— HCZI
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382 ORIGIN OF SPECIES
unequal lengths of time, and will have been modified in vari-
ous degrees. As we possess only the last volume of the geo-
logical record, and that in a very broken condition, we have
no right to expect, except in rare cases, to fill up the wide
intervals in the natural system, and thus to imite distinct
families or orders. All that we have a right to expect is,
that those groups which have, within known geological peri-
ods, undergone much modification, should in the older for-
mations make some slight approach to each other; so that
the older members should differ less from each other in some
of their characters than do the existing members of the
same groups ; and this by the concurrent evidence of our best
paleontologists is frequently the case.
Thus, on the theory of descent with modification, the main
facts with respect to the mutual affinities of the extinct
forms of life to each other and to living forms, are explained
in a satisfactory manner. And they are wholly inexplicable
on any other view.
On this same theory, it is evident that the fauna during
any one great period in the earth's history will be inter-
mediate in general character between that which preceded
and that which succeeded it Thus the species which lived
at the sixth great stage of descent in the diagram are the
modified offspring of those which lived at the fifth stage,
and are the parents of those which became still more modi-
fied at the seventh stage; hence they could hardly fail to be
nearly intermediate in character between the forms of life
above and below. We must, however, allow for the entire
extinction of some preceding forms, and in any one region
for the immigration of new forms from other regions, and
for a large amount of modification during the long and blank
interval between the successive formations. Subject to these
allowances, the fauna of each geological period undoubtedly
is intermediate in character, between the preceding and suc-
ceeding faunas. I need give only one instance, namely, the
manner in which the fossils of the Devonian system, when
this system was first discovered, were at once recognised by
palaeontologists as intermediate in character between those
of the overl3ring carboniferous, and underlying Silurian sys-
tems. But each fauna is not necessarily exactly intermediate.
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AFFINITIES OF EXTINCT SPECIES 383
as unequal intervals of time have elapsed between consecu-
tive formations.
It is no real objection to the truth of the statement that
the fauna of each period as a whole is nearly intermediate
in character between the preceding and succeeding faunas,
that certain genera offer exceptions to the rule. For in-
stance, the species of mastodons and elephants, when ar-
ranged by Dr. Falconer in two series, — ^in the first place
according to their mutual affinities, and in the second place
according to their periods of existence,— do not accord in
arrangement. The species extreme in character are not the
oldest or the most recent; nor are those which are interme-
diate in character, intermediate in age. But supposing for
an instant, in this and other such cases, that the record of
the first appearance and disappearance of the species was
complete, which is far from the case, we have no reason to
believe that forms successively produced necessarily endure
for corresponding lengths of time. A very ancient form
may occasionally have lasted much longer than a form else-
where subsequently produced, especially in the case of terres-
trial productions inhabiting separated districts. To compare
small things with great; if the principal living and extinct
races of the domestic pigeon were arranged in serial affinity,
this arrangement would not closely accord with the order in
time of their production, and even less with the order of
their disappearance; for the parent rock-pigeon still lives;
and many varieties between the rock-pigeon and the carrier
have become extinct; and carriers which are extreme in the
important character of length of back originated earlier than
short-beaked tumblers, which are at the opposite end of the
series in this respect
Closely connected with the statement, that the organic re-
mains from an intermediate formation are in some degree
intermediate in character, is the fact, insisted on by all
palaeontologists, that fossils from two consecutive formations
are far more closely related to each other, than are the fos-
sils from two remote formations. Pictet gives as a well-
known instance, the general resemblance of the organic re-
mains from the several stages of the Chalk formation,
though the species are distinct in each stage. This fact
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384 ORIGIN OF SPECIES
alone, from its generality, seems to have shaken Professor
Pictet in his belief in the immutability of species. He who
is acquainted with the distribution of existing species over
the globe, will not attempt to account for the close resem-
blance of distinct species in closely consecutive formations,
by the physical conditions of the ancient areas having re*
mained nearly the same. Let it be remembered that the
forms of life, at least those inhabiting the sea, have changed
almost simultaneously throughout the world, and therefore
under the most different climates and conditions. Consider
the prodigious vicissitudes of climate during the pleistocene
period, which includes the whole glacial epoch, and note how
little the specific forms of the inhabitants of the sea have
been affected.
On the theory of descent, the full meaning of the fossil
remains from closely consecutive formations being closely
related, though ranked as distinct species, is obvious. As
the accumulation of each formation has often been inter-
rupted, and as long blank intervals have intervened between
successive formations, we ought not to expect to find, as I '
attempted to show in the last chapter, in any one or in any
two formations, all the intermediate varieties between the
species which appeared at the commencement and close of
these periods : but we ought to find after intervals, very long
as measured by years, but only moderately long as measured
geologically, closely allied forms, or, as they have been called
by some authors, representative species; and these assuredly
we do find. We find, in short, such evidence of the slow
and scarcely sensible mutations of specific forms, as we have
the right to ^qieot.
OK THE CTATE OF DEVELOPMENT OP ANCIENT COMPARED
WITH LIVING FORMS
We have seen in the fourth chapter that the degree of
differentiation and specialisation of the parts in organic
beings, when arrived at maturity, is the best standard, as yet
suggested, of their degree of perfection or highness. We
have also seen that, as the specialisation of parts is an ad-
vantage to each being, so natural selection will tend to Tender
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STATE OF DB¥BLOPMBNT COMPARED 38S
the organisation of- each being more specialised and perfect,
and in this sense higher; not but that it may leave many
creatures with simple and unimproved structures fitted for
simple conditions of life, and in some cases will even de-
ifrade or simplify the organisation, yet leaving such degraded
beings better fitted for their new walks of life. In another
and more general manner, new species become superior to
their predecessors; for they have to beat in the struggle for
life all the older forms, with which they come into close
competition. We may therefore conclude that if under a
nearly similar climate the eocene inhabitants of the world
could be put into competition with the existing inhabitants,
the former would be beaten and exterminated by the latter,
as would* the secondary by the eocene, and the palaeozoic by
the secondary forms. So that by this fundamental test of
victory in the battle for life, as well as by the standard of
the specialisadon of organs, modem forms ought^ on* the
theory of natural selection, to stand higher than ancient
forms. Is this the case? A large majority of palaeon-
tologists would answer in the affirmative; and it seems
that this answer must be admitted as true, though difficult
of proof.
It is no valid objection to this conclusion, that certain
Brachiopods have been but slightly modified from an ex-
tremely remote geological epoch; and that certain land and
fresh-water shells have remained nearly the same, from the
time when, as far as is known, they first appeared. It is not
an insuperable difficulty that Foraminifera have not, as in-
sisted on by Dr. Carpenter, progressed in organisation since
even the Laurentian epoch; for some organisms would have
to remain fitted for simple conditions of life, and what could
be better fitted for this^ end than these lowly organised Pro-
tozoa? Such objections as the above would be fatal to my
view, if it included advance in organisation as a necessary
contingent. They would likewise be fatal, if the above Font-
minifera, for instance, could be proved to have first come
into existence during the Laurentian epoch, or the above
Brachiopods during the Cambrian formation; for in this
case, there would not have been time sufficient for the de-
velopment of these organisms up to the standard which they
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386 ORIGIN OF SPECIES
had then reached. When advanced up to any given point,
there is no necessity, on the theory of natural selection, for
their further continued progress; though they will, during
each successive age, have to he slightly modified, so as to
hold their places in relation to slight changes in their condi-
tions. The foregoing objections hinge on the question
whether we really know how old the world is, and at what
period the various forms of life first appeared; and this may
well be disputed.
The problem whether organisation on the whole has ad-
vanced is in many ways excessively intricate. The geological
record, at all times imperfect, does not extend far enough
back, to show with unmistakeable clearness that within the
known history of the world organisation has largely ad-
vanced. Even at the present day, looking to members of the
same dass, naturalists are not unanimous which forms ought
to be ranked as highest: thus, some look at the selaceans or
sharks, from their approach in some important points of
structure to reptiles, as the highest fish; others look at the
teleosteans as the highest The ganoids stand intermediate
between the selaceans and teleosteans; the latter at the
present day are largely preponderant in number; but for-
merly selaceans and ganoids alone existed; and in this case,
according to the standard of highness chosen, so will it be
said that fishes have advanced or retrograded in organisa-
tion. To attempt to compare members of distinct types in
the scale of highness seems hopeless ; who will decide whether
a cuttle-fish be higher than a bee — ^that insect which the
great Von Baer believed to be "in fact more highly organised
than a fish, although upon another type"? In the complex
struggle for life it is quite credible that crustaceans, not very
high in their own class, might beat cephalopods, the highest
molluscs ; and such crustaceans, though not highly developed,
would stand very high in the scale of invertebrate animals, if
judged by the most decisive of all trials — ^the law of battle.
Beside these inherent difficulties in deciding which forms
are the most advanced in organisation, we ought not solely
to compare the highest members of a class at any two
periods — ^though undoubtedly this is one and perhaps the
most important element in striking a balance — ^but we ought
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STATE OF DEVELOPMENT COBfPARED 387
to compare all the members, high and low, at the two periods.
At an ancient epoch the highest and lowest moUitscoidal ani-
mals, namely, cephalopods and brachiopods, swarmed in
numbers; at the present time both groups are greatly re«
duced, whilst others, intermediate in organisation, have
largely increased; consequently some naturalists maintain
that molluscs were formerly more highly developed than at
present; but a stronger case can be made out on the oppo-
site side, by considering the vast reduction of the brachio*
pods, and the fact that our existing cephalopods, though few
in number, are more highly organised than iheir ancient rep-
resentatives. We ought also to compare the relative propor-
tional numbers at any two periods of the high and low classes
throughout the world: if, for instance, at the present day
fifty thousand kinds of vertebrate animals exist, and if we
knew that at some former period only ten thousand kinds
existed, we ought to look at this increase in number in the
highest class, which implies a great displacement of lower
forms, as a decided advance in the organisation of the world.
We thus see how hopelessly difficult it is to compare with
perfect fairness under such extremely complex relations, the
standard of organisation of the imperfectly-known faunas
of successive. periods.
We shall appreciate this difficulty more clearly, by looking
to certain existing faunas and floras. From the extraordi-
nary manner in which European productions have recently
spread over New Zealand, and have seized on places which
must have been previously occupied by the indigenes, we
must believe, that if all the animals and plants of Great
Britain were set free in New Zealand, a multitude of British
forms would in the course of time become thoroughly nat-
uralised there, and would exterminate many of the natives.
On the other hand, from the fact that hardly a single inhabi-
tant of the southern hemisphere has become wild in any part
of Europe, we may well doubt whether, if all the productions
of New Zealand were set free in Great Britain, any consid-
erable number would be enabled to seize on places now occu-
pied by our native plants and animals. Under this point of
view, the productions of Great Britain stand much higher in
the scale than those of New Zealand. Yet the most skilful
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368 ORIGIN OF SPEaSS
naturalist, from an examination of the species of the two
countries, could not have foreseen this result.
Agassiz and. several other highly competent judges insist
that ancient animals resemble to a. certain extent the em-
bryos of recent animals belonging to the same dasses; and
that the geological succession of extinct forms is nearly par-
allel with the embryological development of existing forms.
This view accords admirably well with our theory. In a
future chapter I shall attempt to show that the adtdt differs
from its embiyo, owing to variations having supervened at a
not early age, and having been inherited at a corresponding
age. This process, whilst it leaves the embryo almost unal-
tered, continually adds, in the course of successive genera-
tions, more and more difference to the adult. Thus the
embryo oomes to be left as a sort of picture, preserved by.
nature, of. the former and less modified condition of the
species. This view may be true, and yet may never be
capable of proof. Seeing, for instance, that the oldest known
mammals, reptiles, and fishes strictly belong to their proper
classes, though some of these old fonns are in a slight de-
gree less distinct from each other than are the typical mem-
bers of the same groups at the present day, it would be vain
to look for animals having the common embryological char-
acter of the Vertebrata, until beds rich in fossils are discov-
ered far beneath the lowest Cambrian strataT-*a discovery, of
which the chance is small.
ON THB SUCCESSION OP THE SAMS TYPES WITHIN. THB
SAME ABEAS, DURING THE LATER TERTIARY PERIODS
Mr. Clift many years ago showed that the fossil m^immals
from the Australian cave& were closely allied to the living
marsupials of that continent. In. South America, a similar
relationship is manifest, even to an uneducated eye, in the
gigantic pieces of armour, like those of the armadillo, found
in severalparts of La Plata; and Professor Owen has shown
in the most striking manner that, most of the fossil mammals,
buried there in such numbers, are related to South American
types. This relationship is even, more clearly seen in the
wonderful, collection of fossil hones mode by MM. Luqd and
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SUCCESSION OF SAME TYPES S8»
Clausen in the oaves of- Brazil. I was so much impressed
with these facts that I strongly insisted, in 1839 and 1845,
on this "law of the succession of types," — on "this won-
derful relationship in the same< continent between the dead
and the living." Professor Owen has subsequently extended
the same generalisation to the mammals of the Old World;
We see the same law in this author's restorations of the
extinct and gigantic birds of New Zealand. We see it also
in the birds of the caves of Braeili Mr. Woodward has
shown that the same law hold^ good with sea-shells, but,
from the wide distributioni of most molluscs, it is not well
displayed by them. Other cases could* be added; as the rela-
tion between the extinct and living land-shells of Mlaidfeira;
and between the extinct and living brackish water-shells of
the Aralo-Caspian Sea.
Now what does this remarkable law of the succession of
the same types within the same areas mean ? He would be
a bold man who, after comparing the present climate of Aus-
tralia and of' parts of South Amerita, under the same lati-
tude, would attempt to account, on die one hand through
dissimilar physical conditions, for the dissimilarity of the
inhabitants of these two continents; and; on the other hand
through similarity of conditions, for the uniformity of the
same types in each continent during the later tertiary periods.
Nor can it be pretended that it is an immutable law that
marsupials should have been chiefly or solely produced in
Australia; or that Edentata and other American types should
have been solely produced in South America. For we know
that Europe in ancient times was peopled by numerous mar-
supials; and I have shown in the publications above alluded
to, that in America the law- of distribution of terrestrial
mammals was formerly different from what it now is. North
America formerly partook strongly of the present character
of the southern half of the continent; and' the southern half
was formerly more cldsely allied, than it is at present, to the
northern half. In a similar manner we know, from Faltoncr
and Cautley's discoveries, that Northern India was formerly
more closely related in its mammals to Africa than* it is at
the present time. Analogous facts could be given in rela«-
tion to the distribution of marine animals.
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990 ORIGIN OF SPEaES
On the theory of descent with modification, the great law
of the long enduring, but not immutable, succession of the
same types within the same areas, is at once explained; for
the inhabitants of each quarter of the world will obviously
tend to leave in that quarter, during the next succeeding
period of time, closely allied though in some degree modified
descendants. If the inhabitants of one continent formerly
differed greatly from those of another continent, so will
their modified descendants still differ in nearly the same
manner and degree. But after very long intervals of time,
and after great geographical changes, permitting much inter-
migration, the feebler will yield to the more dominant forms,
and there will be nothing immutable in the distribution of
organic beings.
It may be asked in ridicule, whether I suppose that the
megatherium and other allied huge monsters, which formerly
lived in South America, have left behind them the sloth,
armadillo, and anteater, as their degenerate descendants.
This cannot for an instant be admitted. These huge animals
have become wholly extinct, and have left no progeny. But
in the caves of Brazil, there are many extinct species which
are closely allied in size and in all other characters to the
species still living in South America; and some of these
fossils may have been the actual progenitors of the living
species.
. It must not be forgotten that, on our theory, all the
species of the same genus are the descendants of some one
species; so that, if six genera, each having eight species, be
found in one geological formation, and in a succeeding
formation there be six other allied or representative genera
each with the same number of species, then we may con-
clude that generally only one species of each of the older
genera has left modified descendants, which constitute the
new genera containing the several species; the other seven
species of each old genus having died out and left no progeny.
Or, and this will be a far commoner case, two or three spe-
cies in two or three alone of the six older genera will be
the parents of the new genera : the other species and the other
old genera having become utterly extinct. In failing orders,
with the genera and species decreasing in numbers as is the
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SUMMARY 991
case with the Edentata of South America, still fewer genera
and species will leave modified blood-descendants.
SUMMARY OF THE PRECEDING AND PRESENT CHAPTERS
I have attempted to show that the geological record is ex«
tremely imperfect ; that only a small portion of the globe has
been geologically explored with care; that only certain
classes of organic beings have been largely preserved in a
fossil state; that the number both of specimens and of spe-
cies, preserved in our museums, is absolutely as nothing com-
pared with the number of generations which must have
passed away even during a single formation; that, owing to
subsidence being almost necessary for the accumulation of
deposits rich in fossil species of many kinds, and thick enough
to outlast future degradation, great intervals of time must
have elapsed between most of our successive formations;
that there has probably been more extinction during the
periods of subsidence, and more variation during the periods
of elevation, and during the latter the record will have been
least perfectly kept; that each single formation has not been
continuously deposited; that the duration of each formation
is probably short compared with the average duration of
specific forms; that migration has played an important part
in the first appearance of new forms in any one area and
formation ; that widely ranging species are those which have
varied most frequently, and have oftenest given rise to new
species; that varieties have at first been local; and lastly,
although each species must have passed through numerous
transitional stages, it is probaUe that the periods, during
which each underwent modification, though many and long
as measured by years, have been short in comparison with
the periods during which each remained in an unchanged
condition. These causes, taken conjointly, will to a large ex-
tent explain why — ^though we do find many links — we do not
find interminable varieties, connecting together all extinct
and existing forms by the finest graduated steps. It should
also be constantly borne in mind that any linking variety
between two forms, which might be found, would be ranked,
unless the whole chain could be perfectly restored, as a new
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302 ORIGIN OP SPECIES
and distinct species; for it is not pretended; that we have
any sure ciiterion by which species and varieties can be
discriminated.
He who rejects this view of the imperfection of the geo-
logical record, will rightly reject the whole theory. For he
may ask in vain where are .the numberless transitional links
which must formerly have connected the closely allied or
representative species, found in the successive stages of the
same great formation? He may disbelieve in the immense
intervals of time which must have elapsed between our conr
secutive formations; he may overlook how important a part
migration has played, when the formations of any one great
region, as those of Europe, are considered; he may urge the
apparent, but often falsely apparent, sudden coming in of
whole groups of species. He may ask where are the remains
of those infinitely numerous organisms which must have ex*
isted long before the Cambrian system was deposited? We
now know that at least one animal did then exist; but I can
answer this last question only by supposing that where our
oceans now extend they have extended for an enormous
period, and where our oscillating continents now stand they
have stood since the commencement of the Cambrian system ;
but that, long before that epoch, the world presented a widely
different aspect;, and. that the older continents, formed of
formations older than any known to us, exist now only as
remnants in a metamorphosed condition, or lie still buried
under the ocean.
Passing from these difficulties, the other great leading
facts in palaeontology agree admirably with the theory of
descent with modification through variation and natural
selection. We can thus understand how it is that new spe-
cies oome in slowly and successively; how species of. dif-
ferent classes do not necessarily change together, or at the
same rate, or in the same degree ; yet in the long run that all
undergo modification to some extent. The extinction of old
forms is the almost inevitable consequence of the production
of new forms. We can understand why, when a species has
once disappeared, it never reappears. Groups of species in-
crease in numbers slowly, and endure for unequal periods
of time ; for the process of modification is necessarily slow.
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SUMMART mS
and depends on many complex contingencies. The dominant
species belonging to large and dominant groups tend to leave
many modified descendants, which form new sub-groups and
groups. As these are formed, the species of the less vig-
orous groups, from their inferiority inherited from a com-
mon progenitor, tend to become extinct together, and to leave
no modified offspring on the face of the earth. But the utter
extinction of a whole group of species has sometimes been a
slow process, from the survival of a few descendants, lin-
gering in protected and isolated situations. When a group
has once wholly disappeared, it does not reappear; for the
link of generation has been broken.
We can understand how it is that dominant forms which
spread widely and yield the greatest number of varieties tend
to people the world with allied, but modified, descendants;
and these will generally succeed in displacing the groups
which are their inferiors in the struggle for existence.
Hence, after long intervals of time, the productions of the
world appear to have changed simultaneously.
We can understand how it is that all the forms of life,
ancient and recent, make together a few grand classes. We
can understand, from the continued tendency to divergence
of character, why the more' ancient a form is, the more it
generally differs from those now living; why ancient and
extinct forms often tend to fill up gaps between existing
forms, sometimes blending two groups, previously classed
as distinct, into one; but more commonly bringing them only
a little closer together. The more ancient a form is, the
more often it stands in some degree intermediate between
groups now distinct; for the more ancient a form is, the
more nearly it will be related to, and consequently resemble,
the common progenitor of groups, since become widely
divergent. Extinct forms are seldom directly intermediate
between existing forms; but are intermediate only by a long
and circuitous course through other extinct and different
forms. We can clearly see why the organic remains of
closely consecutive formations are closely allied; for they
are closely linked together by generation. We can clearly
see why the remains of an intermediate formation are inter-
mediate in character.
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994 ORIGIN OF SPEQES
The inhabitants of the world at each successive period in
its history have beaten their predecessors in the race for
life, and are, in so far, higher in the scale, and their struc-
ture has generally become more specialised; and this may
account for the common belief held by so many palaeontolo-
gists, that organisation on the whole has progressed. Extinct
and ancient animals resemble to a certain extent the embryos
of the more recent animals belonging to the same classes,
and this wonderful fact receives a simple explanation accord-
ing to our views. The succession of the same types of
structure within the same areas during the later geological
periods ceases to be mysterious, and is intelligible on the
principle of inheritance.
If then the geological record be as imperfect as many be-
lieve, and it may at least be asserted that the record cannot
be proved to be much more perfect, the main objections to
the theory of natural selection are greatly diminished or dis-
appear. On the other hand, all the chief laws of palaeontology
plainly proclaim, as it seems to me, that species have been
produced by ordinary generation : old forms having been sup-
planted by new and improved forms of life, the products of
Variation and the Survival of the Fittest.
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CHAPTER XII
Geographical Distribution
Present distribution cannot be accounted for by differences in physi*
cal conditions — Importance of barriers — Affinity of the produc-
tions of the same continent — Centres of creation — Means of
dispersal, by changes of climate and of the level of the land, and
by occasional means — Dispersal during the Glacial period —
Alternate Glacial periods in the North and South.
IN considering the distribution of organic beings over the
face of the globe, the first great fact which strikes us is,
that neither the similarity nor the dissimilarity of the
inhabitants of various regions can be wholly accotmted for by
climatal and other physical conditions. Of late, almost every
author who has studied the subject has come to this conclu-
sion. The case of America alone would almost suffice to
prove its truth; for if we exclude the arctic and northern
temperate parts, all authors agree that one of the most fun-
damental divisions in geographical distribution is that be-
tween the New and Old Worlds; yet if we travel over the
vast American continent, from the central parts of the
United States to its extreme southern point, we meet with
the most diversified conditions ; humid districts, arid deserts,
lofty motmtains, grassy plains, forests, marshes, lakes, and
great rivers, under almost every temperature. There is
hardly a climate or condition in the Old World which can-
not be paralleled in the New — at least as closely as the same
species generally require. No doubt small areas can be
pointed out in the Old World hotter than any in the New
World ; but these are not inhabited by a fauna different from
that of the surrounding districts ; for it is rare to find a group
of organisms confined to a small area, of which the con-
ditions are peculiar in only a slight degree. Notwithstand-
ing this general parallelism in the conditions of the Old and
New Worlds, how widely different are their living pro-
ductions I
3d5
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996 ORIGIN OF SPECIES
In the southern hemisphere, if we compare large tracts of
land in Australia, South Africa, and western South America,
between latitudes 25* and 35*, we shall find parts extremely
similar in all their conditions, yet it would not be possible to
point out three faunas and floras more utterly dissimilar.
Or, again, we may compare the productions of South Amer-
ica south of lat 35** with those north of 25**, which conse-
quently are separated by a space of ten degrees of latitude,
and are exposed to considerably different conditions ; yet they
are incomparably more closely related to each other than
they are to the productions of Australia or Africa under
nearly the -same climate. Analogous facts could be given
with respect to the inhabitants of the sea.
A second great fact which strikes us in our general review
is, that barriers of any kind, or obstacles to free migration,
are related in a close and important manner to the differ-
ences between the productions of various regions. We see
this in the great differences in nearly all the terrestrial pro-
ductions of the New and Old Worlds, excepting in the
northern parts, where the land almost joins, and where, under
a slightly different climate, there might have been free mi-
gration for the northern temperate forms, as there now is
for the strictly arctic productions. We see the same fact in
the great difference between the inhabitants of Australia,
Africa, and South America under the same latitude; for
these countries are almost as much isolated from each other
as is possible. On each continent, also, we see the same
fact ; for on the opposite sides of lofty and continuous moun-
tain-ranges, of great deserts and even of large rivers, we
find different productions; though as mountain-chains, des-
erts, &c, are not as impassable, or likely to have endure^ so
long, as the oceans separating continents, the differences are
very inferior in degree to those characteristic of distinct
continents.
Turning to the sea, we find the same law. The marine
inhabitants of the eastern and western shores of South
America are very distinct, with extremely few shells, Crus-
tacea, or echinodermata in common; but Dr. Gunther has
recently shown that about thirty per cent of the fishes are
the same on the opposite sides of the isthmus of Panama;
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GEOGRAPHICAL DISTRIBUTION 397
and this fact has led naturalists to believe that the isthmus
was formerly open. Westward of the shores of America, a
wide space of open ocean extends, with not an island as a
halting-place for emigrants; here we have a barrier of an-
other kind, and as soon as this is passed we meet in the east-
ern islands of the Pacific with another and totally distinct
fauna. So that three marine faunas range far northward
and southward in parallel lines not far from each other,
under corresponding climates ; but from being separated from
each other by impassable barriers, either of land or open sea,
they are almost wholly distinct. On the other hand, proceed-
ing still farther westward from the eastern islands of the
tropical parts of the Pacific, we encounter no impassable
barriers, and we have innumerable islands as halting-places,
or continuous coasts, until, after travelling over a hemisphere,
we come to the shores of Africa; and over this vast space
we meet with no well-defined and distinct marine faunas.
Although so few marine animals are common to the above-
named three approximate faunas of Eastern and Western
America and the eastern Pacific islands, yet many fishes
range from the Pacific into the Indian Ocean, and many
shells are common to the eastern islands of the Pacific and
the eastern shores of Africa on almost exactly opposite
meridians of longitude.
A third great fact, partly included in the foregoing state-
ment, is the affinity of the productions of the same continent
or of the same sea, though the species themselves are dis-
tinct at different points and stations. It is a law of the
widest generality, and every continent offers innumerable
instances. Nevertheless, the naturalist, in travelling, for
instance, from north to south, never 'fails to be struck by
the manner in which successive groups of beings, specifically*
distinct, though nearly related, replace each other. He hears
from closely allied, yet distinct kinds of birdsj notes nearly
similar, and sees their nests similarly constructed, but not
quite alike, with eggs coloured in nearly the same manner.
The plains near the Straits of Magellan are inhabited by
one species of Rhea (American ostrich), and northward the
plains of La Plata by another species of the same genus ; and
not by a true ostrich or emu, like those inhabiting Africa
y— Hcxi
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396 ORIGIN OP SPBaES
and Australia under the same latitude. On these same plains
of La Plata we see the agouti and bizcacha, animals having
nearly the same habits as our hares and rabbits, and belong-
ing to the same order of Rodents, but they plainly display
an American type of structure. We ascend the lofty peaks
of the Cordillera, and we find an alpine species of bizcacha;
we look to the waters, and we do not find the beaver or
musk-rat, but the coypu and capybara, rodents of the S.
American type. Innumerable other instances could be given.
If we look to the islands off the American shore, however
much they may differ in geological structure, the inhabitants
are essentially American, though they may be all peculiar
species. We may look back to past ages, as shown in the
last chapter, and we find American types then prevailing on
the American continent and in the American seas. We see
in these facts some deep organic bond, throughout space and
time, over the same areas of land and water, independently
of physical conditions. The naturalist must be dull m^x) is
not led to inquire what this bond is.
The bond is simply inheritance, that cause which alone,
as far as we positively know, produces organisms quite like
each other, or, as we see in the case of varieties, nearly
alike. The dissimilarity of the inhabitants of different re-
gions may be attributed to modification through variation
and natural selection, and probably in a subordinate degree
to the definite influence of different physical conditions. The
degrees of dissimilarity will depend on the migration of the
more dominant forms of life from one region into another
having been more or less effectually prevented, at periods
more or less remote;— on the nature and number of the for-
^mer immigrants; — and on the action of the inhabitants on
each other in leading to the preservation of different modifi-
cations ; the relation of organism to organism in the struggle
for life being, as I have already often remarked, the most
important of all relations. Thus the high importance of
barriers comes into play by checking migration ; as does time
for the slow process of modification through natural selec-
tion. Widely-ranging species, abounding in individuals,
which have already triumphed over many competitors in
their own widely-extended homes, will have the best chance
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GEOGRAPHICAL DISTRIBUTION 999
of seizing on new places, when they spread into new coun-
tries. In their new homes they will be exposed to new con-
ditions, and will frequently undergo further modification and
improvement; and thus they will become stUl further vic-
torious, and will produce groups of modified descendants.
On this principle of inheritance with modification we can
understand how it is that sections of genera, whole genera,
and even families, are confined to the same areas, as is so
commonly and notoriously the case.
There is no evidence, as was remarked in the last chapter,
of the existence of any law of necessary development. As
the variability of each species is an independent property,
and will be taken advantage of by natural selection, only so
far as it profits each individual in its complex struggle for
life, so the amount of modification in different species will
be no uniform quantity. If a number of species, after hav-
ing long competed with each other in their old home, were
to migrate in a body into a new and afterwards isolated
country, they would be little liable to modification; for
neither migration nor isolation in themselves effect anything.
These principles come into play only by bringing organisms
into new relations with each other and in a lesser degree
with the surrounding physical conditions. As we have seen
in the last chapter that some forms have retained nearly the
same character from an enormously remote geological period,
so certain species have migrated over vast spaces, and have
not become greatly or at all modified.
According to these views, it is obvious that the several
species of the same genus, though inhabiting the most dis-
tant quarters of the world, must originally have proceeded
from the same source, as they are descended from the same
progenitor. In the case of those species which have under-
gone during whole geological periods little modification,
there is not much difficulty in believing that they have mi-
grated from the same region ; for during the vast geographi-
cal and climatal changes which have supervened since ancient
times, almost any amount of migration is possible. But in
many other cases, in which we have reason to believe that
the species of a genus have been produced within compara-
tively recent times, there is great difficulty on this head. It
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400 ORIGIN OF SPEaSS
is also obvious that the individuals of the same species,
though now inhabiting distant and isolated regions, must have
proceeded from one spot, where their parents were first pro-
duced: for, as has been explained, it is incredible that indi-
viduals identically the same should have been produced from
parents specifically distinct.
Single Centres of supposed Creation. — ^We are thus
brought to the question which has been largely discussed by
naturalists, namely, whether species have been created at
one or more points of the earth's surface. Undoubtedly
there are many cases of extreme difficulty in understanding
how the same species could possibly have migrated from
some one point to the several distant and isolated points,
where now found. Nevertheless the simplicity of the view
that each species was first produced within a single region
captivates the mind. He who rejects it, rejects the vera
causa of ordinary generation with subsequent migration, and
calls in the agency of a miracle. It is universally admitted,
that in most cases the area inhabited by a species is con-
tinuous ; and that when a plant or animal inhabits two points
so distant from each other, or with an interval of such a
nature, that the space could not have been easily passed over
by migration, the fact is given as something remarkable and
exceptional. The incapacity of migrating across a wide sea
is more plear in the case of terrestrial mammals than perhaps
with any other organic beings; and, accordingly, we find no
inexplicable instances of the same mammals inhabiting dis-
tant points of the world. No geologist feels any difficulty in
Great Britain possessing the same quadrupeds with the rest
of Europe, for they were no doubt once united. But if the
same species can be produced at two separate points, why do
we not find a single mammal common to Europe and Aus-
tralia or South America? The conditions of life are nearly
the same, so that a multitude of European animals and plants
have become naturalised in America and Australia; and
some of the aboriginal plants are identically the same at
these distant points of the northern and southern hemi-
spheres. The answer, as I believe, is, that mammals have
not been able to migrate, whereas some plants, from their
varied means of dispersal, have migrated across the wide and
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CENTRES OF SUPPOSED CREATION 401
broken interspaces. The great and striking influence of bar-
riers of all kinds, is intelligible only on the view that the
great majority of species have been produced on one side,
and have not been able to migrate to the opposite side.
Some few families, many sub-families, very many genera,
and a still greater number of sections of genera, are con-
fined to a single region ; and it has been observed by several
naturalists that the most natural genera, or those genera in
which the species are most closely related to each other, are
generally confined to the same country, or if they have a
wide range that their range is continuous. What a strange
anomaly it would be, if a directly opposite rule were to pre-
vail, when we go down one step lower in the series, namely,
to the individuals of the same species, and these had not
been, at least at first, confined to some one region!
Hence it seems to me, as it has to many other naturalists,
that the view of each species having been produced in one
area alone, and having subsequently migrated from that area
as far as its powers of migration and subsistence under past
and present conditions permitted, is the most probable. Un-
doubtedly many cases occur, in which we cannot explain how
the same species could have passed from one point to the
other. But the geographical and climatal changes which
have certainly occurred within recent geological times, must
have rendered discontinuous the formerly continuous range
of many species. So that we are reduced to considei^ whether
the exceptions to continuity of range are so numerous and
' of so grave a nature, that we ought to give up the belief,
rendered probable by general considerations, that each species
has been produced within one area, and has migrated thence
as far as it could. It would be hopelessly tedious to discuss
all the exceptional cases of the same species, now living at
distant and separated points, nor do I for a moment pretend
that any explanation could be offered of many instances.
But, after some preliminary remarks, I will discuss a few of
the most striking classes of facts; namely, the existence of
the same species on the summits of distant mountain ranges,
and at distant points in the arctic and antarctic regions ; and
secondly (in the following chapter), the wide distribution of
fresh-water productions; and thirdly, the occurrence of the
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402 ORIGIN OP SPECIES
same terrestrial species on islands and on the nearest main-
land, though separated by hundreds of miles of open sea.
If the existence of the same species at distant and isolated
points of the earth's surface, can in many instances be ex-
plained on the view of each species having migrated from a
single birthplace; then, considering our ignorance with re-
spect to former climatal and geographical changes and to
the various occasional means of transport, the belief that a
single birthplace is the law, seems to me incomparably the
safest.
In discussing this subject, we shall be enabled at the same
time to consider a point equally important for us, namely,
whether the several species of a genus which must on our
theory all be descended from a common progenitor, can have
migrated, undergoing modification during their migration,
from some one area. If, when most of the species inhabiting
one region are different from those of another region, though
closely allied to them, it can be shown that migration from
the one region to the other has probably occurred at some
former period, our general view will be much strengthened;
for the explanation is obvious on the principle of descent
with modification. A volcanic island, for instance, upheaved
and formed at the distance of a few hundreds of miles from
a continent, would probably receive from it in the course of
time a few colonists, and their descendants, though modified,
would still be related by inheritance to the inhabitants of
that continent. Cases of this nature are common, and are,
as we shall hereafter see, inexplicable on the theory of inde-
pendent creation. This view of the relation of the species
of one region to those of another, does not differ much from
that advanced by Mr. Wallace, who concludes that "every
species has come into existence coincident both in space and
time with a pre-existing closely allied species." And it is
now well known that he attributes this coincidence to descent
with modification.
The question of single or multiple centres of creation dif-
fers from another though allied question, — ^namely, whether
all the individuals of the same species are descended from a
single pair, or single hermaphrodite, or whether, as some
authors suppose, from many individuals simultaneously cre-
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UEANS OF DISPEBSAL 408
ated With organic beings which never intercross, if such
exist, each species must be descended from a succession of
modified varieties, that have supplanted each other, but have
never blended vnih other individuals or varieties of the same
species; so that, at each successive stage of modification, all
the individuals of the same form will be descended from a
single parent. But in the great majority of cases, namely,
with all organisms which habitually unite for each birth, or
which occasionally intercross, the individuals of the same
species inhabiting the same area will be kept nearly uniform
t:^^ intercrossing; so that many individuals will go on simul-
taneously changing, and the whole amount of modification at
each stage will not be due to descent from a single parent.
To illustrate what I mean: our English race-horses differ
from the horses of every other breed; but they do not owe
their difference and superiority to descent from any single
pair, but to continued care in the selecting and training of
many individuals during each generation.
Before discussing the three classes of facts, which I have
selected as presenting the greatest amount of difficulty on the
theory of "single centres of creation," I must say a few
words on the means of dispersal.
MBANS OP DISPERSAL
Sir C. Lyell and other authors have ably treated this sub-
ject. I can give here only the briefest abstract of the more
important facts. Change of climate must have had a power-
ful influence on migration. A region now impassable to cer-
tain organisms from the nature of its climate, might have
been a high road for migration, when the climate was dif-
ferent. I shall, however, presently have to discuss this
branch of the subject in some detail. Changes of level in
the land must also have been highly influential: a narrow
isthmus now separates two marine faunas; submerge it, or
let it formerly have been submerged, and the two faunas
will now blend together, or may formerly have blended
Where the sea now extends, land may at a former period
have connected islands or possibly even continents together,
and thus have allowed terrestrial productions to pass from
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404 ORIGIN OP SPEaES
one to the other. No geologist disputes that great muta-.
tions of level have occurred within the period of existing
organisms. Edward Forbes insisted that all the islands in
the Atlantic must have been recently connected with Europe
or Africa, and Europe likewise with America. Other authors
have thus hypothetically bridged over every ocean, and
united almost every island with some mainland. If indeed
the arguments used by Forbes are to be trusted, it must be
admitted that scarcely a single island exists which has not
recently been united to some continent. This view cuts the
Gordian knot of the dispersal of the same species to the most
distant points, and removes many a difficulty ; but to the best
of my judgment we are not authorised in admitting such
enormous geographical changes within the period of existing
species. It seems to me that we have abundant evidence of
great oscillations in the level of the land or sea; but not of
such vast changes in the position and extension of our con-
tinents, as to have united them within the recent period to
each other and to the several intervening oceanic islands.
I freely admit the former existence of many islands, now
buried beneath the sea, which may have served as halting-
places for plants and for many animals during their migra-
tion. In the coral-producing oceans such sunken islands are
now marked by ring^ of coral or atolls standing over them.
Whenever it is fully admitted, as it will some day be, that
each species has proceeded from a single birthplace, and
when in the course of time we know something definite about
the means of distribution, we shall be enabled to speculate
with security on the former extension of the land. But I do
not believe that it will ever be proved that within the recent
period most of our continents which now stand quite sep-
arate, have been continuously, or almost continuously united
with each other, and with the many existing oceanic islands.
Several facts in distribution — ^such as the great difference in
the marine faunas on the opposite sides of almost every con-
tinent,— the close relation of the tertiary inhabitants of sev-
eral lands and even seas to their present inhabitants, — ^the
degree of affinity between the mammals inhabiting islands
with those of the nearest continent, being in part determined
(as we shall hereafter see) by the depth of the intervening
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BIEANS OF DISPERSAL 405
ocean, — ^these and other such facts are opposed to the admis-
sion of such prodigious geographical revolutions iivithin the
recent period, as are necessary on the view advanced by
Forbes and admitted by his followers. The nature and rela-
tive proportions of the inhabitants of oceanic islands are
likewise opposed to the belief of their former continuity with
continents. Nor does the almost universally volcanic com-
position of such islands favour the admission that they are
the wrecks of sunken continents; — ^if they had originally
existed as continental mountain ranges, some at least of the
islands would have been formed, like other mountain sum-
mits, of granite, metamorphic schists, old fossiliferous and
other rocks, instead of consisting of mere piles of volcanic
matter.
I must now say a few words on what are called accidental
means, but which more properly should be called occasional
means of distribution. I shall here confine myself to plants.
In botanical works, this or that plant is often stated to be ill
adapted for wide dissemination ; but the greater or less facili-
ties for transport across the sea may be said to be almost
wholly unknown. Until I tried, with Mr. Berkeley's aid, a
few experiments, it was not even known how far seeds
could resist the injurious action of sea-water. To my sur-
prise I found that out of 87 kinds, 64 germinated after an
immersion of 28 days, and a few survived an immersion o£
137 days. It deserves notice that certain orders were far
more injured than others : nine Leguminosae were tried, and,
with one exception, they resisted the salt-water badly ; seven
species of the allied orders, Hydrophyllaceae and Polemo-
niaceae, were all killed by a month's immersion. For con-
venience' sake I chiefly tried small seeds without the cap-
sule or fruit; and as all of these sank in a few days they
could not have been floated across wide spaces of the sea,
whether or not they were injured by the salt-water. After-
wards I tried some larger fruits, capsules, &c., and some of
these floated for a long time. It is well known what a dif-
ference there is in the buoyancy of green and seasoned tim-
ber; and it occurred to me that floods would often wash into
the sea dried plants or branches with seed-capsules or fruit
attached to them. Hence I was led to dry the stems and
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406 ORIGIN OF SPfiCIBS
branches of 94 plants with ripe fruit, and to place them on
sea-water. The majority sank quickly, but some which,
whilst green, floated for a very short time, when dried floated
much longer ; for instance, ripe hazel-nuts sank immediately,
but when dried they floated for 90 days, and afterwards when
planted germinated; an asparagus-plant with ripe berries
floated for 23 days, when dried it floated for 85 days, and
the seeds afterwards germinated; the ripe seeds of Helosci-
adium sank in two days, when dried they floated for above
90 days, and afterwards germinated. Altogether, out of the
94 dried plants, 18 floated for above 28 days; and some of
the 18 floated for a very much longer period So that as f4
kinds of seeds germinated after an immersion of 28 days;
and as ^ distinct species with ripe fruit (but not all the same
species as in the foregoing experiment) floated, after being
dried, for above 28 days, we may conclude, as far as anything
can be inferred from these scanty facts, that the seeds of -^
kinds of plants of any country might be floated by sea-cur-
rents during 28 days, and would retain their power of ger-
mination. In Johnston's Physical Atlas, the average rate of
the several Atlantic currents is 33 miles per diem (some cur-
rents running at the rate of 60 miles per diem) ; on this
average, the seeds of -ffy plants belonging to one country
might be floated across 924 miles of sea to another country,
and when stranded, if blown by an inland gale to a favour-
able spot, would germinate.
Subsequently to my experiments, M. Martens tried similar
ones, but in a much better manner, for he placed the seeds
in a box in the actual sea, so that they were alternately wet
and exposed to the air like really floating plants. He tried
98 seeds, mostly different from mine; but he chose many
large fruits and likewise seeds from plants which live near
the sea; and this would have favoured both the average
length of their flotation and their resistance to the injurious
action of the salt-water. On the other hand, he did not pre-
viously dry the plants or branches with the fruit; and this,
as we have seen, would have caused some of them to have
floated much longer. The result was that ^ of his seeds of
different kinds floated for 42 days, and were then capable of
germination. But I do not doubt that plants exposed to the
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MEAi^S OF DISPERSAL 407
waves would float for a less time than those protected from
violent movement as in our experiments. Therefore it would
perhaps be safer to assume that the seeds of about ^fif plants
of a flora, after having been dried, could be floated across a
space of sea 900 miles in width, and would then germinate.
The fact of the larger fruits often floating longer than the
small, is interesting; as plants with large seeds or fruit which,
as Alph. de Candolle has shown, generally have restricted
ranges, could hardly be transported by any other means.
Seeds may be occasionally transported in another manner.
Drift timber is thrown up on most islands, even on those in
the midst of the widest oceans; and the natives of the coral-
islands in the Pacific procure stones for their tools, solely
from the roots of drifted trees, these stones being a valuable
royal tax. I find that when irregularly shaped stones are
embedded in the roots of trees, small parcels of earth are fre-
quently enclosed in their interstices and behind them, — so
perfectly that not a particle could be washed away during the
longest transport: out of one small portion of earth thus
completely enclosed by the roots of an oak about 50 years
old, three dicotyledonous plants germinated; I am certain of
the accuracy of this observation. Again, I can show that
the carcases of birds, when floating on the sea, sometimes
escape being immediately devoured : and many kinds of seeds
in the crops of floating birds long retain their vitality: peas
and vetches, for instance, are killed by even a few days' im-
mersion in sea-water; but some taken out of the crop of a
pigeon, which had floated on artificial sea-water for 30 days,
to my surprise nearly all germinated.
Living birds can hardly fail to be highly effective agents
in the transportation of seeds. I could give many facts
showing how frequently birds of many kinds are blown by
gales to vast distances across the ocean. We may safely
assume that under such circumstances their rate of flight
would often be 25 miles an hour; and some authors have
given a far higher estimate. I have never seen an instance
of nutritious seeds passing through the intestines of a bird ;
but hard seeds of fruit pass uninjured through even the di-
gestive organs of a turkey. In the course of two months, I
picked up in my garden 12 kinds of seeds, out of the excre-
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406 ORIGIN OF SPEaES
ment of small birds, and these seemed perfect, and some of
them, which were tried, germinated. But the following fact
is more important: the crops of birds do not secrete gastric
juice, and do not, as I know by trial, injure in the least the
germination of seeds; now, after a bird has found and de-
voured a large supply of food, it is positively asserted that
all the grains do not pass into the gizzard for twelve or even
eighteen hours. A bird in this interval might easily be
blown to the distance of 500 miles, and hawks are known to
look out for tired birds, and the contents of their torn crops
might thus readily get scattered. Some hawks and owls
bolt their prey whole, and, after an interval of from twelve
to twenty hours, disgorge pellets, which, as I know from
experiments made in the Zoological Gardens, include seeds
capable of germination. Some seeds of the oat, wheat, mil-
let, canary, hemp, clover, and beet germinated after having
been from twelve to twenty-one hours in the stomachs of
different birds of prey; and two seeds of beet grew after hav-
ing been thus retained for two days and fourteen hours.
Fresh-water fish, I find, eat seeds of many land and water
plants; fish are frequently devoured by birds, and thus the
seeds might be transported from place to place. I forced
many kinds of seeds into the stomachs of dead fish, and then
gave their bodies to fishing-eagles, storks, and pelicans;
these birds, after an interval of many hours, either rejected
the seeds in pellets or passed them in their excrement; and
several of these seeds retained the power of germination.
Certain seeds, however, were always killed by this process.
Locusts are sometimes blown to great distances from the
land ; I myself caught one 370 miles from the coast of Africa,
and have heard of others caught at greater distances. The
Rev. R. T. Lowe informed Sir C. Lyell that in November
1844 swarms of locusts visted the island of Madeira. They
were in countless numbers, as thick as the flakes of snow in
the heaviest snowstorm, and extended upwards as far as
could be seen with a telescope. During two or three days
they slowly careered round and round in an immense ellipse,
at least five or six miles in diameter, and at night alighted
on the taller trees, which were completely coated with them.
They then disappeared over the sea, as suddenly as they had
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Darwin s Study at Down, Kent
From an etckii^ by Axel Haig
In his autobiography, Darwin writes:
''In June, 1S42, I first allowed
myself the satisfaction of
writing a very brief abstract of my
(species J theory in pencil in
35 P^gf^ * * *
''September 14. Settled at the village
of Down in Kent. I think I
was never in a more
perfectly quiet country
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MEANS OF DISPERSAL 409
appeared, and have not since visited the island. Now, in
parts of Natal it is believed by some farmers, though on in-
sufficient evidence, that injurious seeds are introduced into
their grassland in the dung left by the great flights of locusts
which often visit that country. In consequence of this be-
lief Mr. Weale sent me in a letter a small packet of the dried
pellets, out of which I extracted under the microscope several
seeds, and raised from them seven grass plants, belonging to
two species, of two genera. Hence a swarm of locusts, such
as that which visited Madeira, might readily be the means of
introducing several kinds of plants into an island lying far
from the mainland.
Although the beaks and feet of birds are generally clean,
earth sometimes adheres to them: in one case I removed
sixty-one grains, and in another case twenty-two grains of
dry argillaceous earth from the foot of a partridge, and in
the earth there was a pebble as large as the seed of a vetch.
Here is a better case : the leg of a woodcock was sent to me
by a friend, with a little cake of dry earth attached to the
shank, weighing only nine grains; and this contained a seed
of the toad-rush (Juncus bufonius) which germinated and
flowered. Mr. Swaysland, of Brighton, who during the last
forty years has paid close attention to our migratory birds,
informs me that he has often shot wagtails (Motacillae),
wheatears, and whincats (Saxicolae), on their first arrival
on our shores, before they had alighted; and he has several
times noticed little cakes of earth attached to their feet
Many facts could be given showing how generally soil is
charged with seeds. For instance, Prof. Newton sent me
the leg of a red-legged partridge (Caccabis rufa) which had
been wounded and could not fly, with a ball of hard earth
adhering to it, and weighing six and a half ounces. The
earth had been kept for three years, but when broken,
watered and placed under a bell-glass, no less than 82 plants
sprung from it : these consisted of 12 monocotyledons, includ-
ing the common oat, and at least one kind of grass, and of 70
dicotyledons, which consisted, judging from the young leaves,
of at least three distinct species. With such facts before us,
can we doubt that the many birds which are annually blown
by gales across great spaces of ocean, and which annually
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410 ORIGIN OF SPEaES
migtate — for instance, the millions of quails across the Medi-
terranean— ^must occasionally transport a few seeds embedded
in dirt adhering to their feet or beaks? But I shall have to
recur to this subject
As icebergs are known to be sometimes loaded with earth
and stones, and have even carried brushwood, bones, and the
nest of a land-bird, it can hardly be doubted that they must
occasionally, as suggested by Lyell, have transported seeds
form one part to another of the arctic and antarctic regions;
and during the Glacial period from one part of the now tem-
perate regions to another. In the Azores, from the large
number of plants common to Europe, in comparison with the
species on the other islands of the Atlantic, which stand
nearer to the mainland, and (as remarked by Mr. H. C.
Watson) from their somewhat northern character in com-
parison with the latitude, I suspected that these islands had
been partly stocked by ice-borne seeds, during the Glacial
epoch. At my request Sir C. Lyell wrote to M. Hartung
to inquire whether he had observed erratic boulders on these
islands, and he answered that he had found large fragments
of granite and other rocks, which do not occur in the archi-
pelago. Hence we may safely infer that icebergs formerly
landed their rocky burthens on the shores of these mid-ocean
islands, and it is at least possible that they may have brought
thither some few seeds of northern plants.
Considering that these several means of transport, and that
other means, which without doubt remain to be discovered,
have been in action year after year for tens of thousands of
years, it would, I think, be a marvellous fact if many plants
had not thus become widely transported. These means of
transport are sometimes called accidental, but this is not
strictly correct: the currents of the sea are not accidental,
nor is the direction of prevalent gales of wind. It should be
observed that scarcely any means of transport would carry
seeds for very great distances: for seeds do not retain their
vitality when exposed for a great length of time to the acticm
of sea-water; nor could they be long carried in the crops or
intestines of birds. These means, however, would suffice for
occasional transport across tracts of sea some hundred miles
in breadth, or from island to island, or from a continent to a
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DISPERSAL DURING GLACIAL PERIOD 411
neighbouring island, but not from one distant continent to
another. The floras of distant continents would not by such
means become mingled ; but would remain as distinct as they
now are. The currents, from their course, would never
bring seeds from North America to Britain, though they
might and do bring seeds from the West Indies to our west-
em shores, where, if not killed by their long immersion in
salt-water, they could not endure our climate. Almost every
year, one or two land-birds are blown across the whole At-
lantic Ocean, from North America to the western shores of
Ireland and England ; but seeds could be transported by these
rare wanderers only by one means, namely, by dirt adhering
to their feet or beaks, which is in itself a rare accident.
Even in this case, how small would be the chance of a seed
falling on favourable soil, and coming to maturity I But it
would be a great error to argue that because a well-stocked
island, like Great Britain, has not, as far as is known (and
it would be very difficult to prove this), received within the
last few centuries, through occasional means of transport,
immigrants from Europe or any other continent, that a
poorly-stocked island, though standing more remote from the
mainland, would not receive colonists by similar means. Out
of a hundred kinds of seeds or animals transported to an
island, even if far less well-stocked than Britain, perhaps
not more than one would be so well fitted to its new home,
as to become naturalised. But this is no valid argument
against what would be effected by occasional means of trans-
port, during the long lapse of geological time, whilst the
island was being upheaved, and before it had become fully
stocked with inhabitants. On almost bare land, with few or
no destructive insects or birds living there, nearly every seed
which chanced to arrive, if fitted for the climate, would ger-
minate and survive.
DISPERSAL DURING THE GLACIAL PERIOD
The identity of many plants and animals, on mountain-
summits, separated from each other by hundreds of miles of
lowlands, where Alpine species could not possibly exist, is
one of the most striking cases known of the same species
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412 ORIGIN OF SPECIES
living at distant points, without the apparent possibility of
their having migrated from one point to the other. It is in-
deed a remarkable fact to see so many plants of the same
species living on the snowy regions of the Alps or Pyrenees,
and in the extreme northern parts of Europe; but it is far
more remarkable, that the plants on the White Mountains,
in the United States of America, are all the same with those
of Labrador, and nearly all the same, as we hear from Asa
Gray, with those on the loftiest mountains of Europe. Even
as long ago as 1747, such facts led Gmelin to conclude that
the same species must have been independently created at
many distinct points; and we might have remained in this
same belief, had not Agassiz and others called vivid atten-
tion to the Glacial period, which, as we shall immediately
see, affords a simple explanation of these facts. We have
evidence of almost every conceivable kind, organic and in-
organic, that, within a very recent geological period, central
Europe and North America suffered under an arctic climate.
The ruins of a house burnt by fire do not tell their tale more
plainly than do the mountains of Scotland and Wales, with
their scored flanks, polished surfaces, and perched boulders,
of the icy streams with which their valleys were lately filled.
So greatly has the climate of Europe changed, that in North-
em Italy, gigantic moraines, left by old glaciers, are now
clothed by the vine and maize. Throughout a large part of
the United States, erratic boulders and scored rocks plainly
reveal a former cold period.
The former influence of the glacial climate on the distribu-
tion of the inhabitants of Europe, as explained by Edward
Forbes, is substantially as follows. But we shall follow the
changes more readily, by supposing a new glacial period
slowly to come on, and then pass away, as formerly occurred.
As the cold came on, and as each more southern zone be-
came fitted for the inhabitants of the north, these would take
the places of the former inhabitants of the temperate regions.
The latter, at the same time, would travel further and fur-
ther southward, unless they were stopped by barriers, in
which case they would perish. The mountains would become
covered with snow and ice, and their former Alpine inhabit-
ants would descend to the plains. By the time that the cold
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DISPERSAL DURING GLACIAL PERIOD 413
had reached its maximum, we should have an arctic fauna
and flora, covering the central parts of Europe, as far south
as the Alps and Pyrenees, and even stretching into Spain.
The now temperate regions of the United States would like-
wise he covered hy arctic plants and animals and these would
be nearly the same with those of Europe; for the present
circumpolar inhabitants, which we suppose to have every-
where travelled southward, are remarkably uniform round
the world.
As the warmth returned, the arctic forms would retreat
northward, closely followed up in their retreat by the produc-
tions of the more temperate regions. And as the snow
melted from the bases of the mountains, the arctic forms
would seize on the cleared and thawed ground, always as-
cending, as the warmth increased and the snow still further
disappeared, higher and higher, whilst their brethren were
pursuing their northern journey. Hence, when the warmth
had fully returned, the same species, which had lately lived
together on the European and North American lowlands,
would again be found in the arctic regions of the Old and
New Worlds, and on many isolated mountain-summits far
distant from each other.
Thus we can understand the identity of many plants at
points so immensely remote as the mountains of the United
States and those of Europe. We can thus also understand
the fact that the Alpine plants of each mountain-range are
more especially related to the arctic forms living due north
or nearly due north of them: for the first migration when
the cold came on, and the re-migration on the returning
warmth, would generally have been due south and north.
The Alpine plants, for example, of Scotland, as remarked
by Mr. H. C. Watson, and those of the Pyrenees, as re-
marked by Ramond, are more especially allied to the plants
of northern Scandinavia ; those of the United States to Lab-
rador ; those of the mountains of Siberia to the arctic regions
of that country. These views, grounded as they are on the
perfectly well-ascertained occurrence of a former Glacial
period, seem to me to explain in so satisfactory a manner
the present distribution of the Alpine and Arctic productions
of Europe and America, that when in other regions we find
Z— RCXI
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414 ORIGIN OF SPECIES
the same species on distant mountain-sununits, we may al-
most conclude, without other evidence, that a colder climate
formerly permitted their migration across the intervening
lowlands, now become too warm for their existence.
As the arctic forms moved first southward and afterwards
backwards to the north, in unison with the changing climate,
they will not have been exposed during their long migrations
to any great diversity of temperature; and as they all mi-
grated in a body together, their mutual relations will not
have been much disturbed. Hence, in accordance with the
principles inculcated in this volume, these forms will not have
been liable to much modification. But with the Alpine pro-
ductions, left isolated from the moment of the returning
warmth, first at the bases and ultimately on the summits of
the mountains, the case will have been somewhat different;
for it is not likely that all the same arctic species will have
been left on mountain-ranges far distant from each other,
and have survived there ever since ; they will also in all prob-
ability, have become mingled with ancient Alpine species,
which must have existed on the mountains before the com-
mencement of the Glacial epoch, and which during the cold-
est period will have been temporarily driven down to the
plains; they will, also, have been subsequently exposed to
somewhat different climatal influences. Their mutual rela-
tions will thus have been in some degree disturbed; conse-
quently they will have been liable to modification; and they
have been modified; for if we compare the present Alpine
plants and animals of the several great European mountain-
ranges one with another, though many of the species remain
identically the same, some exist as varieties, some as doubt-
ful forms or sub-species, and some as distinct yet closely
allied species representing each other on the several ranges.
In the foregoing illustration I have assumed that at the
commencement of our imaginary Glacial period, the arctic
productions were as uniform round the polar regions as they
are at the present day. But it is also necessary to assume
that many sub-arctic and some few temperate forms were
the same round the world, for some of the species which
now exist on the lower mountain-slopes and on the plains of
North America and Europe are the same; and it may be
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DISPERSAL DURING GLAOAL PERIOD 415
asked how I account for this degree of uniformity in the
sub-arctic and temperate forms round the world, at the com-
mencement of the real Glacial period. At the present day,
the sub-arctic and northern temperate productions of the Old
and New Worlds are separated from each other by the whole
Atlantic Ocean and by the northern part of the Pacific.
During the Glacial period, when the inhabitants of the Old
and New Worlds lived farther southwards than they do at
present, they must have been still more completely separated
from each other by wider spaces of ocean; so that it may
well be asked how the same species could then or previously
have entered the two continents. The explanation, I believe,
lies in the nature of the climate before the commencement of
the Glacial period. At this, the newer Pliocene period, the
majority of the inhabitants of the world were specifically the
same as now, and we have good reason to believe that the
climate was warmer than at the present day. Hence we
may suppose that the organisms«.which now live under lati-
tude 60°, lived during the Pliocene period farther north
under the Polar Circle, in latitude 66°-67*; and that the
present arctic productions then lived on the broken land still
nearer to the pole. Now, if we look at a terrestrial globe,
we see under the Polar Circle that there is almost continuous
land from western Europe, through Siberia, to eastern Amer-
ica. And this continuity of the circumpolar land, with the
consequent freedom under a more favourable climate for
intermigration, will account for the supposed uniformity of
the sub-arctic and temperate productions of the Old and New
Worlds, at a period anterior to the Glacial epoch.
Believing, from reasons before alluded to, that our conti-
nents have long remained in nearly the same relative posi-
tion, though subjected to great oscillations of level, I am
strongly inclined to extend the above view, and to infer that
during some still earlier and still warmer period, such as the
older Pliocene period, a large number of the same plants and
animals inhabited the almost continuous circumpolar land;
and that these plants and animals, both in the Old and New
Worlds, began slowly to migrate southwards as the climate
became less warm, long before the commencement of the
Glacial period. We now see, as I believe, their descendants.
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416 ORIGIN OF SPBaSS
mostly in a modified condidoiiy in the central parts of Europe
and the United States. On this view we can understand the
relationship with very little identity, between the productions
of North America and Europe, — a relationship which is
highly remarkable, considering the distance of the two areas,
and their separation by the whole Atlantic Ocean. We can
further understand the singular fact remarked on by several
observers that the productions of Europe and America dur-
ing the later tertiary stages were more closely related to
each other than they are at the present time; for during
these warmer periods the northern parts of the Old and New
Worlds will have been almost continuously united by land,
serving as a bridge, since rendered impassable by cold, for
the intermigration of their inhabitants.
During the slowly decreasing warmth of the Pliocene
period, as soon as the species in common, which inhabited
the New and Old Worlds, migrated south of the Polar
Circle, they will have been completely cut off from each
other. This separation, as far as the more temperate produc-
tions are concerned, must have taken place long ages ago.
As the plants and animals migrated southward, they will
have become mingled in the one great region with the native
American productions, and would have had to compete with
them; and in the other great region, with those of the Old
World. Consequently we have here everything favourable
for much modification, — for far more modification than with
the Alpine productions, left isolated, within a much more
recent pefiod, on the several mountain-ranges and on the
arctic lands of Europe and N. America. Hence it has come,
that when we compare the now living productions of the tem-
perate regions of tiie New and Old Worlds, we find very few
identical species (though Asa Gray has lately shown that
more plants are identical than was formerly supposed), but
we find in every great class many forms, which some nat-
uralists rank as geographical races, and others as distinct
species; and a host of closely allied or representative forms
which are ranked by all naturalists as specifically distinct.
As on the land, so in the waters of the sea, a slow south-
em migration of a marine fauna, which, during the Pliocene
or even a somewhat earlier period, was nearly uniform along
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ALTERNATE GLACIAL PERIODS 417
the continuous shores of the Polar Circle, will account, on
the theory of modification, for many closely allied forms now
living in marine areas completely sundered. Thus, I think,
we can understand the presence of some closely allied, still
existing and extinct tertiary forms, on the eastern and west-
ern shores of temperate North America; and the still more
striking fact of many closely allied crustaceans (as described
in Dana's admirable work), some fish and other marine ani-
mals, inhabiting the Mediterranean and the seas of Japan, —
these two areas being now completely separated by the
breadth of a whole continent and by wide spaces of ocean.
These cases of close relationship in species either now or
formerly inhabiting the seas on the eastern and western
shores of North America, the Mediterranean and Japan, and
the temperate lands of North America and Europe, are inex-
plicable on the theory of creation. We cannot maintain that
such species have been created alike, in correspondence with
the nearly similar physical conditions of the areas ; for if we
compare, for instance, certain parts of South America with
parts of South Africa or Australia, we see countries closely
similar in all their physical conditions, with their inhabitants
utterly dissimilar.
ALTERNATE GLACIAL PERIODS IN THE NORTH AND SOUTH
But we must return to our more immediate subject. I am
convinced that Forbes' view may be largely extended. In
Europe we meet with the plainest evidence of the Glacial
period, from the western shores of Britain to the Oural range,
and southward to the Pyrenees. We may infer from the
frozen mammals and nature of the mountain vegetation, that
Siberia was similarly affected. In the Lebanon, according
to Dr. Hooker, perpetual snow formerly covered the central
axis, and fed glaciers which rolled 4000 feet down the val-
leys. The same observer has recently found great moraines
at a low level on the Atlas range in N. Africa. Along the
Himalaya, at points 900 miles apart, glaciers have left the
marks of their former low descent; and in Sikkim, Dr.
Hooker saw maize growing on ancient and gigantic moraines.
Southward of the Asiatic continent, on the opposite side of
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418 ORIGIN OF SPEaES
the equator, we know, from the excellent researches of Dr.
J. Haast and Dr. Hector, that in New Zealand immense
glaciers formerly descended to a low level; and the same
plants found by Dr. Hooker on widely separated mountains
in this island tell the same story of a former cold period.
From facts communicated to me by the Rev. W. B. Clarke,
it appears also that there are traces of former glacial action
on the mountains of the south-eastern comer of Australia.
Looking to America ; in the northern half, ice-borne frag-
ments of rock have been observed on the eastern side of the
continent, as far south as lat. 36'*-37'*, and on the shores of
the Pacific, where the climate is now so different, as far
south as lat. 46"*. Erratic boulders have, also, been noticed
on the Rocky Mountains. In the Cordillera of South Amer-
ica, nearly under the equator, glaciers once extended far be-
low their present level. In Central Chile I examined a vast
mound of detritus with great boulders, crossing the Portillo
valley, which there can hardly be a doubt once formed a huge
moraine; and Mr. D. Forbes informs me that he found in
various parts of the Cordillera, from lat. 13* to 30** S., at
about the height of 12,060 feet, deeply-furrowed rocks, re-
sembling those with which he was familiar in Norway, and
likewise great masses of detritus, including grooved pebbles.
Along this whole space of the Cordillera true glaciers do not
now exist even at much more considerable heights. Farther
south on both sides of the continent, from lat. 41* to the
southernmost extremity, we have the clearest evidence of
former glacial action, in numerous immense boulders trans-
ported far from their parent source.
From these several facts, namely from the glacial action
having extended all round the northern and southern hemi-
spheres— from the period having been in a geological sense
recent in both hemispheres — from its having lasted in both
during a great length of time, as may be inferred from the
amount of work effected — and lastly from glaciers having
recently descended to a low level along the whole line of the
Cordillera, it at one time appeared to me that we could not
avoid the conclusion that the temperature of the whole world
had been simultaneously lowered during the Glacial period.
But now Mr. Croll, in a series of admirable memoirs, has
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ALTERNATE GLACXAL PERIODS 419
attempted to show that a glacial condition of climate is the
result of various physical causes, brought into operation by
an increase in the eccentricity of the earth's orbit. All these
causes tend towards the same end; but the most powerful
appears to be the indirect influence of the eccentricity of the
orbit upon oceanic currents. According to Mr. Croll, cold
periods regularly recur every ten or fifteen thousand years;
and these at long intervals are extremely severe, owing to
certain contingencies, of which the most important, as Sir C.
Lyell has shown, is the relative position of the land and
water. Mr. Croll believes that the last great Glacial period
occurred about 240,000 years ago, and endured with slight
alterations of climate for about 160,000 years. With respect
to more ancient Glacial periods, several geologists are con-
vinced from direct evidence that such occurred during the
Miocene and Eocene formations, not to mention still more
ancient formations. But the most important result for us,
arrived at by Mr. Croll, is that whenever the northern hemi-
sphere passes through a cold period the temperature
of the southern hemisphere is actually raised, with the win-
ters rendered much milder, chiefly through changes in the
direction of the ocean-currents. So conversely it will be
with the northern hemisphere, whilst the southern passes
through a Glacial period. This conclusion throws so much
light on geographical distribution that I am strongly inclined
to trust in it; but I will first give the facts, which demand
an explanation.
In South America, Dr. Hooker has shown that besides
many closely allied species, between forty and fifty of the
flowering plants of Tierra del Fuego, forming no inconsider-
able part of its scanty flora, are common to North America
and Europe, enormously remote as these areas in opposite
hemispheres are from each other. On the lofty mountains
of equatorial America a host of peculiar species belonging
to European genera occur. On the Organ mountains of
Brazil, some few temperate European, some Antarctic, and
some Andean genera were found by Gardner, which do not
exist in the low intervening hot countries. On the Silla of
Caraccas, the illustrious Humboldt long ago found species
belonging to genera characteristic of tl^ Cordillera.
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420 OtUGIN OF SPECIBS
In Africa, several forms characteristic of Europe and some
few representatives of the flora of the Cape of Good Hope
occur on the mountains of Abyssinia. At the Cape of Good
Hope a very few European species, believed not to have been
introduced by man, and on the mountains several representa-
tive European forms are found, which have not been dis-
covered in the intertropical parts of Africa. Dr. Hooker
has also lately shown that several of the plants living 6n the
upper parts of the lofty island of Fernando Po and on the
neighbouring Cameroon mountains, in the Gulf of Guinea,
are closely related to those on the mountains of Abyssinia,
and likewise to those of temperate Europe. It now also
appears, as I hear from Dr. Hooker, that some of these same
temperate plants have been discovered by the Rev. R. T.
Lowe on the mountains of the Cape Verde islands. This
extension of the same temperate forms, almost under the
equator, across the whole continent of Africa and to the
mountains of the Cape Verde archipelago, is one of the most
astonishing facts ever recorded in the distribution of plants.
On the Himalaya, and on the isolated mountain-ranges of
the peninsula of India, on the heights of Ceylon, and on the
volcanic cones of Java, many plants occur, either identically
the same or representing each other, and at the same time
representing plants of Europe, not found in the intervening
hot lowlands. A list of the genera of plants collected on
the loftier peaks of Java, raises a picture of a collection made
on a hillock in Europe ! Still more striking is the fact that
peculiar Australian forms are represented by certain plants
growing on the summits of the mountains of Borneo. Some
of these Australian forms, as I hear from Dr. Hooker, ex-
tend along the heights of the peninsula of Malacca, and are
thinly scattered on the one hand over India, and on the other
hand as far north as Japan.
On the southern mountains of Australia, Dr. F. Miiller has
discovered several European species; other species, not in-
troduced by man, occur on the lowlands; and a long list can
be given, as I am informed by Dr. Hooker, of European
genera, found in Australia, but not in the intermediate torrid
regions. In the admirable 'Introduction to the Flora of New
Zealand,' by Dr. Hooker, analogous and striking facts are
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ALTERNATE GLACIAL PERIODS 421
given in regard to the plants of that large island. Hence we
see that certain plants growing on the more lofty mountains
of the tropics in all parts of the world, and on the temperate
plains of the north and south, are either the same species or
varieties of the same species. It should, however, be ob-
served that these plants are not strictly arctic forms ; for, as
Mr. H. C. Watson has remarked, ''in receding from polar
towards equatorial latitudes, the Alpine or mountain floras
really become less and less Arctic." Besides these identical
and closely allied forms, many species inhabiting the same
widely sundered areas, belong to genera not now found in
the intermediate tropical lowlands.
These brief remarks apply to plants alone; but some few
analogous facts could be given in regard to terrestrial ani-
mals. In marine productions, similar cases likewise occur;
as an example, I may quote a statement by the highest
authority. Prof. Dana, that "it is certainly a wonderful fact
that New Zealand should have a closer resemblance in its
Crustacea to Great Britain, its antipode, than to any other
part of the world" Sir J. Richardson, also, speaks of the re-
appearance on the shores of New Zealand, Tasmania, &c., of
northern forms of fish. Dr. Hooker informs me diat
twenty-five species of Algae are common to New Zealand
and to Europe, but have not been found in the intermediate
tropical seas.
From the foregoing facts, namely, the presence of tem-
perate forms on the highlands across the whole of equatorial
Africa, and along the Peninsula of India, to Ceylon and the
Malay Archipelago, and in a less well-marked manner across
the wide expanse of tropical South America, it appears
almost certain that at some former period, no doubt during
the most severe part of a Glacial period, the lowlands of
these great continents were everywhere tenanted under the
equator by a considerable number of temperate forms. At
this period the equatorial climate at the level of the sea was
probably about the same with that now experienced at the
height of from five to six thousand feet under the same lati-
tude, or perhaps even rather cooler. During this, the coldest
period, the lowlands under the equator must have been
clothed with a mingled tropical and temperate vegetation^
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422 ORIGIN OF SPECIES
like that described by Hooker as growing luxuriantly at the
height of from four to five thousand feet on the lower slopes
of the Himalayas, but with perhaps a still greater prepon-
derance of temperate forms. So again in the mountainous
islands of Fernando Po, in the Gulf of Guinea, Mr. Mann
found temperate European forms beginning to appear at the
height of about five thousand feet. On the motmtains of
Panama, at the height of only two thousand feet, Dr. See-
mann found the vegetation like that of Mexico, "with forms
of the torrid zone harmoniously blended with those of the
temperate."
Now let us see whether Mr. Croll's conclusion that when
the northern hemisphere suffered from the extreme cold of
the great Glacial period, the southern hemisphere was actu-
ally warmer, throws any dear light on the present apparently
inexplicable distribution of various organisms in the tem-
perate parts of both hemispheres, and on the mountains of
the tropics. The Glacial period, as measured by years, must
have been very long ; and when we remember over what vast
spaces some naturalised plants and animals have spread
within a few centuries, this period will have been ample for
any amount of migration. As the cold became more and
more intense, we know that Arctic forms invaded the tem-
perate regions; and, from the facts just given, there can
hardly be a doubt that some of the more vigorous, dominant
and widest-spreading temperate forms invaded the equa-
torial lowlands. The inhabitants of these hot lowlands would
at the same time have migrated to the tropical and sub-
tropical regions of the south, for the southern hemisphere
was at this period warmer. On the decline of the Glacial
period, as both hemispheres gradually recovered their former
temperatures, the northern temperate forms living on the
lowlands under the equator, would have been driven to their
former homes or have been destroyed, being replaced by the
equatorial forms returning from the south. Some, however,
of the northern temperate forms would almost certainly have
ascended any adjoining high land, where, if sufficiently lofty,
they would have long survived like the Arctic forms on the
mountains of Europe. They might have survived, even if
the climate was not perfectly fitted for them, for the change
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ALTERNATE GLACIAL PERIODS 423
of temperature must have been very slow, and plants un-
doubtedly possess a certain capacity for acclimatisation, as
shown by their transmitting to their offspring different con-
stitutional powers of resisting heat and cold.
In the regular course of events the southern hemisphere
would in its turn be subjected to a severe Glacial period, with
the northern hemisphere rendered warmer; and then the
southern temperate forms would invade the equatorial low-
lands. The northern forms which had before been left on
the mountains would now descend and mingle with the south-
em forms. These latter, when the warmth returned, would
return to their former homes, leaving some few species on
the mountains, and carrying southward with them some of
the northern temperate forms which had descended from
their mountain fastnesses. Thus, we should have some few
species identically the same in the northern and southern
temperate zones and on the mountains of the intermediate
tropical regions. But the species left during a long time 00
these mountains, or in opposite hemispheres, would have to
compete with many new forms and would be exposed to
somewhat different physical conditions; hence they would
b^ eminently liable to modification, and would generally now
exist as varieties or as representative species ; and this is the
case. We must, also, bear in mind the occurrence in both
hemispheres of former Glacial periods; for these will ac-
count, in accordance with the same principles, for the many
quite distinct species inhabiting the same widely separated
areas, and belonging to genera not now found in the inter-
mediate torrid zones.
It is a remarkable fact strongly insisted on by Hooker in
regard to America, and by Alph. de Candolle in regard to
Australia, that many more identical or slightly modified spe-
cies have migrated from the north to the south, than in a
reversed direction. We see, however, a few southern forms
on the mountains of Borneo and Abyssinia. I suspect that
this preponderant migration from the north to the south is
due to the greater extent of land in the north, and to the
northern forms having existed in their own homes in greater
numbers, and having consequently been advanced through
natural selection and competition to a higher stage of per-
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424 ORIGIN OP SPECIES
fection, or dominating power, than the southern forms. And
thus, when the two sets became commingled in the equatorial
regions, during the alternations of the Glacial periods, the
northern forms were the more powerful and were able to
hold their places on the mountains, and afterwards to mi-
grate southward with the southern forms; but not so the
southern in regard to the northern forms. In the same
manner at the present day, we see that very many European
productions cover the ground in La Plata, New Zealand, and
to a lesser degree in Australia, and have beaten the natives ;
whereas extremely few southern forms have become natu-
ralised in any part of the northern hemisphere, though hides,
wool, and other objects likely to carry seeds have been
largdy imported into Europe during the last two or three
centuries from La Plata and during the last forty or fifty
years from Australia. The Neilgherrie mountains in India,
however, offer a partial exception; for here, as I hear from
Dr. Hooker, Australian forms are rapidly sowing themselves
and becoming naturalised. Before the last great Glacial
period, no doubt the intertropical mountains were stocked
with endemic Alpine forms; but these have almost every-
where yielded to the more dominant forms generated in the
larger areas and more efficient workshops of the north. In
many islands the native productions are nearly equalled, or
even outnumbered, by those which have become naturalised;
and this is the first stage towards their extinction. Moun-
tains are islands on the land, and their inhabitants have
yielded to those produced within the larger areas of the
north, just in the same way as the inhabitants of real islands
have everywhere yielded and are still yielding to continental
forms naturalised through man's agency.
The same principles apply to the distribution of terrestrial
animals and of marine productions, in the northern and
southern temperate zones, and on the intertropical mountains.
When, during the height of the Glacial period, the ocean-
currents were widely different to what they now are, some
of the inhabitants of the temperate seas might have reached
the equator; of these a few would perhaps at once be able to
migrate southward, by keeping to the cooler currents, whilst
others might remain and survive in the colder depths until
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ALTERNATE GLACLAL PERIODS 425
the southern hemisphere was in its turn subjected to a glacial
climate and permitted their further progress; in nearly the
same manner as, according to Forbes, isolated spaces inhab-
ited by Arctic productions exist to the t)resent day in the
deeper parts of the northern temperate seas.
I am far from supposing that all the difficulties in regard
to the distribution and affinities of the identical and allied
species, which now live so widely separated in the north and
south, and sometimes on the intermediate mountain-ranges,
are removed on the views above given. The exact lines of
migration cannot be indicated. We cannot say why certain
species and not others have migrated; why certain species
have been modified and have given rise to new forms, whilst
others have remained unaltered. We cannot hope to explain
such facts, until we can say why one species and not another
becomes naturalised by man's agency in a foreign land ; why
one species ranges twice or thrice as far, and is twice or
thrice as common, as another species within their own homes.
Various special difficulties also remain to be solved; for
instance, the occurrence, as shown by Dr. Hooker, of the
same plants at points so enormously remote as Kerguelen
Land, New Zealand, and Fuegia; but icebergs, as suggested
by Lyell, may have been concerned in their dispersal. The
existence at these and other distant points of the southern
hemisphere, of species, which, though distinct, belong to
genera exclusively confined to the south, is a more remark-
able case. Some of these species are so distinct, that we
cannot suppose that there has been time since the commence-
ment of the last Glacial period for their migration and sub-
sequent modification to the necessary degree. The facts
seem to indicate that distinct species belonging to the same
genera have migrated in radiating lines from a common
genera; and I am inclined to look in the southern, as in the
northern hemisphere, to a former and warmer period, before
the commencement of the last Glacial period, when the Ant-
arctic lands, now covered with ice, supported a highly
peculiar and isolated flora. It may be suspected that before
this flora was exterminated during the last Glacial epoch, a
few forms had been already widely dispersed to various
points of the southern hemisphere by occasional means of
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426 ORIGIN OF SPECIES
transport, and by the aid as halting-places, of now sunken
islands. Thus the southern shores of America, Australia,
and New Zealand may have become slightly tinted by the
same peculiar forms of life.
Sir C. Lyell in a striking passage has speculated, in lan-
guage almost identical with mine, on the effects of great
alterations of climate throughout the world on geographical
distribution. And we have now seen that Mr. CroU's conclu-
sion that successive Glacial periods in the one hemisphere
coincide with warmer periods in the opposite hemisphere,
together with the admission of the slow modification of spe-
cies, explains a multitude of facts in the distribution of the
same and of the allied forms of life in all parts of the globe.
The living waters have flowed during one period from the
north and during another from the south, and in both cases
have reached the equator ; but the stream of life has flowed
with greater force from the north than in the opposite direc-
tion, and has consequently more freely inundated the south.
As the tide leaves its drift in horizontal lines, rising higher
on the shores where the tide rises highest, so have the living
waters left their living drift on our mountain summits, in a
line gently rising from the Arctic lowlands to great altitude
under the equator. The various beings thus left stranded
may be compared with savage races of man, driven up and
surviving in the mountain fastnesses of almost every land,
which serves as a record, full of interest to us, of the former
inhabitants of the surrounding lowlands.
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CHAPTER XIII
Geographical Distribution — continued
Distribation of fresh-water productiona— On the inhabitants of
oceanic islands — ^Absence of Batrachians and of terrestrial Mam-
mals— On the relation of the inhabitants of islands to those of
the nearest mainland — On colonisation from the nearest source
with subsequent modification — Summary of the last and present
chapter.
• FRESH-WATER PRODUCTIONS
▲ S lakes and river-systems are separated from each
I\ other by barriers of land, it might have been thought
JL JL that fresh-water productions would not have ranged
widely within the same country, and as the sea is apparently
a still more formidable barrier, that they would never have
extended to distant countries. But the case is exactly the re-
verse. Not only have many fresh-water species, belonging
to different classes, an enormous range, but allied species
prevail in a remarkable manner throughout the world. When
first collecting in the fresh waters of Brazil, I well remember
feeling much surprise at the similarity of the fresh-water
insects, shells, &c., and at the dissimilarity of the surrotmd-
ing terrestrial beings, compared with those of Britain.
But the wide ranging power of fresh-water productions
can, I think, in most cases be explained by their having be-
come fitted, in a manner highly useful to them, for short
and frequent migrations from pond to pond, or from stream
to stream, within their own countries; and liability to wide
dispersal would follow from this capacity as an almost nieces-
sary consequence. We can here consider only a few cases;
of these, some of the most difficult to explain are presented
by fish. It was formerly believed that the same fresh-water
species never existed on two continents distant from each
other. But Dr. Gtinther has lately shown that the Galaxias
427
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428 ORIGIN OF SPEQES
attenuatus inhabits Tasmania, New Zealand, the Falkland
Islands, and the mainland of South America. This is a won-
derful case, and probably indicates dispersal from an Ant-
arctic centre during a former warm period. This case, how-
ever, is rendered in some degree less surprising by the spe-
cies of this genus having the power of crossing by some
unknown means considerable spaces of open ocean : thus
there is one species common to New Zealand and to the
Auckland Islands, though separated by a distance of about
230 miles. On the same continent fresh-water fish often
range widely, and as if capriciously; for in two adjoining
river-systems some of the species may be the same, and some
wholly different.
It is probable that they are occasionally transported by
what may be called accidental means. Thus fishes still alive
are not very rarely dropped at distant points by whirlwinds;
and it is known that the ova retain their vitality for a con-
siderable time after removal from the water. Their dispersal
may, however, be mainly attributed to changes in the level
of the land within the recent period, causing rivers to flow
into each other. Instances, also, could be given of this
having occurred during floods, without any change of level.
The wide difference of the fish on the opposite sides of most
mountain-ranges, which are continuous, and which conse-
quently must from an early period have completely prevented
the inosculation of the river-system on the two sides, leads to
the same conclusion. Some fresh- water fish belong to very
ancient forms, and in such cases there will have been ample
time for great geographical changes, and consequently time
and means for much migration. Moreover Dr. Gunther has
recently been led by several considerations to infer that with
fishes the same forms have a long endurance. Salt-water
fish can with care be slowly accustomed to live in fresh
water; and, according to Valenciennes, there is hardly a
single group of which all the members are confined to fresh
water, so that a marine species belonging to a fresh-water
group might travel far along the shores of the sea, and
could, it is probable, become adapted without much difficulty
to the fresh waters of a distant land.
Some species of fresh-water shells have very wide ranges,
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FRESH-WATER PRODUCTIONS 429
and allied species which, on our theory, are descended from
a common parent, and must have proceeded from a single
source, prevail throughout the world Their distribution at
first perplexed me much, as their ova are not likely to be
transported by birds; and the ova, as well as the adults, are
immediately killed by sea-water. I could not even under-
stand how some naturalised species have spread rapidly
throughout the same country. But two facts, which I have
observed — ^and many others no doubt will be discovered —
throw some light on this subject. When ducks suddenly
emerge from a pond covered with duck-weed, I have twice
seen these little plants adhering to their backs; and it has
happened to me, in removing a little duck-weed from one
aquarium to another, that I have unintentionally stocked the
one with fresh-water shells from the other. But another
agency is perhaps more effectual: I suspended the feet of a
duck in an aquarium, where many ova of fresh-water shells
were hatching; and I fotmd that numbers of the extremely
minute and just-hatched shells crawled on the feet, and clung
to them so firmly that when taken out of the water they
could not be jarred off, though at a somewhat more advanced
age they would voluntarily drop off. These just-hatched
molluscs, though aquatic in their nature, survived on the
duck's feet, in damp air, from twelve to twenty hours; and
in this length of time a duck or heron might fly at least six
or seven hundred miles, and if blown across the sea to an
oceanic island, or to any other distant point, would be sure
to alight on a pool or rivulet Sir Charles Lyell informs me
that a Dy tiscus has been caught with an Ancylus (a fresh-
water shell like a limpet) firmly adhering to it; and a water-
beetle of the same family, a Col)rmbetes, once flew on board
the 'Beagle,' when forty-five miles distant from the nearest
land: how much farther it might have been blown by a
favouring gale no one can tell.
With respect to plants, it has long been known what enor-
mous ranges many fresh-water, and even marsh species,
have, both over continents and to the most remote oceanic
islands. This is strikingly illustrated, according to Alph. de
Candolle, in those large groups of terrestrial plants, which
have very few aquatic members; for the latter seem immedl-
AA— HCXI
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430 ORIGIN OF SPEaSS
ately to acquire, as if in consequence, a wide range. I think
favourable means of dispersal explain this fact I have be-
fore mentioned that earth occasionally adheres in some quan-
tity to the feet and beaks of birds. Wading birds, which
frequent the muddy edges of ponds, if suddenly flushed,
wotdd be the most likely to have muddy feet. Birds of this
order wander more than those of any other; and they are
occasionally found on the most remote and barren islands
of the open ocean ; they would not be likely to alight on the
surface of the sea, so that any dirt on their feet would not be
washed off; and when gaining the land, they would be sure to
fly to their natural fresh-water haunts. I do not believe that
botanists are aware how charged the mud of ponds is with
seeds; I have tried several little experiments, but will here
give only the most striking case: I took in February three
table-spoonfuls of mud from three different points, beneath
water, on the edge of a little pond: this mud when dried
weighed only 6}i ounces; I kept it covered up in my study
for six months, pulling up and counting each plant as it
grew; the plants were of many kinds, and were altogether
537 in number; and yet the viscid mud was all contained in
a breakfast cup! Considering these facts, I think it would
be an inexplicable circumstance if water-birds did not trans-
port the seeds of fresh-water plants to unstocked ponds and
streams, situated at very distant points. The same agency
may have come into play with the ^:gs of some of the
smaller fresh-water animals.
Other and unknown agencies probably have also played a
part. I have stated that fresh-water fish eat some kinds of
seeds, though they reject many other kinds after having
swallowed them; even small fish swallow seeds of moderate
size, as of the yellow water-lily and Potamogeton. Herons
and other birds, century after century, have gone on daily
devouring fish; they then take flight and go to other waters,
or are blown across the sea; and we have seen that seeds
retain their power of germination, when rejected many hours
afterwards in pellets or in the excrement. When I saw the
great size of the seeds of that fine water-lily, the Nelumbium,
and remembered Alph. de CandoUe's remarks on the distribu-
tion of this plant, I though that the means of its dispersal
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INHABITANTS OF OCEANIC ISLANDS 431
must remain inexplicable; but Audubon states that he found
the seeds of the great southern water-lily (probably, accord-
ing to Dr. Hooker, the Nelumbium luteum) in a heron's
stomach. Now this bird must often have flown with its
stomach thus well stocked to distant ponds, and then getting
a hearty meal of fish, analogy makes me believe that it
would have rejected the seeds in a pellet in a fit state for
germination.
In considering these several means of distribution, it should
be remembered that when a pond or stream is first formed,
for instance, on a rising islet, it will be unoccupied; and a
single seed or egg will have a good chance of succeeding.
Although there will always be a struggle for life between
the inhabitants of the same pond, however few in kind, yet
as the number even in a well-stocked pond is small in com-
parison with the number of species inhabiting an equal area
of land, the competition between them will probably *be less
severe than between terrestrial species; consequently an in-
truder from the waters of a foreign country would have a
better chance of seizing on a new place, than in the case
of terrestrial colonists. We should also remember that many
fresh-water productions are low in the scale of nature, and
we have reason to believe that such beings become modified
more slowly than the high; and this will give time for the
migration of aquatic species. We should not forget the
probability of many fresh- water forms having formerly
ranged continuously over immense areas, and then having
become extinct at intermediate points. But the wide distri*
bution of fresh-water plants and of the lower animals,
whether retaining the same identical form or in some degree
modified, apparently depends in main part on the wide dis-
persal of their seeds and eggs by animals, more especially by
fresh-water birds, which have great powers of flight, and
naturally travel from one piece of water to another.
ON THE INHABITANTS OF OCEANIC ISLANDS
We now come to the last of the three classes of facts,
which I have selected as presenting the greatest amount of
difficulty with respect to distribution, on the view that not
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4» ORIGIN OF SPBCIES
only all the individuals of the same species have migrated
from some one area, but that allied species^ although now
inhabiting the most distant points, have proceeded from a
single area, — the birthplace of their early progenitors. I
have already given my reason for disbelieving in continental
extensions within the period of existing species, on so enor-
mous a scale that all the many islands of the several oceans
were thus stocked with their present terrestrial inhabitants.
This view removes many difficulties, but it does not accord
with all the facts in regard to the productions of islands. In
the following remarks I shall not confine myself to the mere
question of dispersal, but shall consider some other cases
bearing on the truth of the two theories of independent crea-
tion and of descent with modification.
The species of all kinds which inhabit oceanic islands are
few in number compared with those on equal continental
areas: Alph. de Candolle admits this for plants, and WoUas-
ton for insects. New Zealand, for instance, with its lofty
mountains and diversified stations, extending over 780 miles
of latitude, together with the outlying islands of Auckland,
Campbell and Chatham, contain altogether only 960 kinds of
flowering plants; if we compare this moderate number with
the species which swarm over equal areas in South- Western
Australia or at the Cape of Good Hope, we must admit that
some cause, independently of different physical conditions,
has given rise to so great a difference in number. Even the
uniform cotmty of Cambridge has 847 plants, and the little
island of Anglesea 764, but a few ferns and a few intro-
duced plants are included in these numbers, and the compari-
son in some other respects is not quite fair. We have
evidence that the barren island of Ascension aboriginally
possessed less than half-a-dozen flowering plants; yet many
species have now become naturalised on it, as they have in
New Zealand and on every other oceanic island which can
be named.
In St. Helena there is reason to believe that the natu-
ralised plants and animals have nearly or quite extermi-
nated many native productions. He who admits the doctrine
of the creation of each separate species, will have to admit
that a sufficient number of the best adapted plants and ani-
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INHABITANTS OF OCEANIC ISLANDS 439
mals were not created for oceanic islands ; for man has unin-
tentionally stocked them far more fully and perfectly than
did nature.
Although in oceanic islands the species are few in number,
the proportion of endemic kinds (i.e, those found nowhere
else in the world) is often extremely large. If we compare,
for instance, the number of endemic land-shells in Madeira,
or of endemic birds in the Galapagos Archipelago, with the
number found on any continent, and then compare the area
of the island with that of the continent, we shall see that this
is true. This fact might have been theoretically expected,
for, as already explained, species occasionally arriving after
long intervals of time in the new and isolated district, and
having to compete with new associates, would be eminently
liable to modification, and would often produce groups of
modified descendants. But it by no means follows that, be-
cause in an island nearly all the species of one class are
peculiar, those of another class, or of another section of the
same class, are peculiar ; and this difference seems to depend
partly on the species which are not modified having immi-
grated in a body, so that their mutual relations have not
been much disturbed; and partly on the frequent arrival of
unmodified immigrants from the mother-country, with which
the insular forms have intercrossed. It should be borne in
mind that the offspring of such crosses would certainly gain
in vigour; so that even an occasional cross would produce
more effect than might have been anticipated. I will give a
few illustrations of the foregoing remarks : in the Galapagos
Islands there are 26 land-birds; of these 21 (or perhaps 23)
are peculiar, whereas of the 11 marine birds only 2 are
peculiar; and it is obvious that marine birds could arrive at
these islands much more easily and frequently than land-
birds. Bermuda, on the other hand, which lies at about the
same distance from North America as the Galapagos Islands
do from South America, and which has a very peculiar soil,
does not possess a single endemic land-bird; and we know
from Mr. J. M. Jones' admirable account of Bermuda, that
very many North American birds occasionally or even fre-
quently visit this island. Almost every year, as I am in-
formed by Mr. E. V. Harconrt, many European and African
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434 ORIGIN OP SPBCIBS
birds are blown to Madeira; this island is inhabited by 99
kinds, of which one alone is peculiar, though very closely
related to a European form; and three or four other species
are confined to this island and to the Canaries. So that the
Islands of Bermuda and Madeira have been stocked from
the neighbouring continents with birds, which for long ages
have there struggled together, and have become mutually
co-adapted. Hence when settled in their new homes, each
kind will have been kept by the others to its proper place
and habits, and will consequently have been but little liable
to modification. Any tendency to modification vnll also have
been checked by intercrossing with the unmodified immi-
grants, often arriving from the mother-country. Madeira
again is inhabited by a wonderful number of peculiar land-
shells, whereas not one species of sea-shell is peculiar to its
shores ; now, though we do not know how sea-shells are dis-
persed, yet we can see that their eggs or larvx, perhaps at-
tached to seaweed or floating timber, or to the feet of wading-
birds, might be transported across three or four hundred
miles of open sea far more easily than land-shells. The dif-
ferent orders of insects inhabiting Madeira present nearly
parallel cases.
Oceanic islands are sometimes deficient in animals of cer-
tain whole classes, and their places are occupied by other
classes; thus in the Galapagos Islands reptiles, and in New
Zealand gigantic wingless birds, take, or recently took, the
place of mammals. Although New Zealand is here spoken
of as an oceanic island, it is in some degree doubtful whether
it should be so ranked; it is of large size, and is not sep-
arated from Australia by a profoundly deep sea; from its
geological character and the direction of its mountain-ranges,
the Rev. W. B. Clarke has lately maintained that this island,
as well as New Caledonia, should be considered as appur-
tenances of Australia. Turning to plants, Dr. Hooker has
shown that in the Galapagos Islands the proportional num-
bers of the different orders are very different from what they
are elsewhere. All such differences in number, and the ab-
sence of certain whole groups of animals and plants, are gen-
erally accounted for by supposed differences in the physical
conditions of the islands; but this explanation is not a little
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ABSENCE OF BATRACHIANS 435
doubtful. Facility of immigration seems to have been fully
as important as the nature of the conditions.
Many remarkable little facts could be given with respect
to the inhabitants of oceanic islands. For instance, in cer-
tain islands not tenanted by a single mammal, some of the
endemic plants have beautifully hooked seeds; yet few rela-
tions are more manifest than that hooks serve for the trans-
portal of seeds in the wool or fur of quadrupeds. But a
hooked seed might be carried to an island by other means;
and the plant then becoming modified would form an endemic
species, still retaining its hooks, which would form a useless
appendage like the shrivelled wings under the soldered wing-
covers of many insular beetles. Again, islands often possess
trees or bushes belonging to orders which elsewhere include
only herbaceous species; now trees, as Alph. de CandoUe
has shown, generally have, whatever the cause may be, con-
fined ranges. Hence trees would be little likely to readi dis-
tant oceanic islands ; and an herbaceous plant, which had no
chance of successfully competing with the many fully devel-
oped trees growing on a continent, might, when established
on an island, gain an advantage over other herbaceous plants
by growing taller and taller and overtopping them. In this
case, natural selection would tend to add to the stature of the
plant, to whatever order it belonged, and thus first convert
it into a bush and then into a tree.
ABSENCE OF BATRACHIANS AND TERRESTRIAL MAMMALS ON
OCEANIC ISLANDS.
With respect to the absence of whole orders of animals on
oceanic islands, Bory St. Vincent long ago remarked that
Batrachians (frogs, toads, newts) are never found on any of
the many islands with which the great oceans are studded.
I have taken pains to verify this assertion, and have found
it true, with the exception of New Zealand, New Caledonia,
the Andaman Islands, and perhaps the Salomon Islands and
the Seychelles. But I have already remarked that it is
doubtful whether New Zealand and New Caledonia ought to
be classed as oceanic islands; and this is still more doubtful
with respect to the Andaman and Salomon groups and the
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436 ORIGIN OF SPECIES
Seychelles. This general absence of frogs, toads, and newts
on so many true oceanic islands cannot be accounted for by
their physical conditions: indeed it seems that islands are
peculiarly fitted for these animals ; for frogs have been intro-
duced into Madeira, the Azores, and Mauritius, and have
multiplied so as to become a nuisance. But as these animals
and their spawn are immediately killed (with the exception,
as far as known, of one Indian species) by sea-water, there
would be great difficulty in their transportal across the sea,
and therefore we can see why they do not exist on strictly
oceanic islands. But why, on the theory of creation, they
should not have been created there, it would be very difficult
to explain.
Mammals offer another and similar case. I have carefully
searched the oldest voyages, and have not found a single
instance, free from doubt, of a terrestrial mammal (excluding
domesticated animals kept by the natives) inhabiting an island
situated above 300 miles from a continent or great continental
island ; and many islands situated at a much less distance are
equally barren. The Falkland Islands, which are inhabited
by a wolf-like fox, come nearest to an exception; but this
group cannot be considered as oceanic, as it lies on a bank
in connection with the mainland at the distance of about 280
miles; moreover, icebergs formerly brought boulders to its
western shores, and they may have formerly transported
foxes, as now frequently happens in the arctic regions. Yet
it cannot be said that small islands will not support at least
small mammals, for they occur in many parts of the world
on very small islands, when lying close to a continent; and
hardly an island can be named on which our smaller quadru-
peds have not become naturalised and greatly multiplied. It
cannot be said, on the ordinary view of creation, that there
has not been time for the creation of mammals; many vol-
canic islands are sufficiently ancient, as shown by the stu-
pendous degradation which they have suffered, and by their
tertiary strata: there has also been time for the production
of endemic species belonging to other classes; and on conti-
nents it is known that new species of mammals appear and
disappear at a quicker rate than other and lower animals.
Although terrestrial mammals do not occur on oceanic
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ABSENCB OF BATRACHIANS 4S7
islands, aerial mammals do occur on almost every island.
New Zealand possesses two bats found nowhere else in the
world: Norfolk Island, the Viti Archipelago, the Bonin
Islands, the Caroline and Marianne Archipelagoes, and Mau-
ritius, all possess their peculiar bats. Why, it may be asked,
has the supposed creative force produced bats and no other
mammals on remote islands? On niy view this question can
easily be answered ; for no terrestrial mammal can be trans-
ported across a wide space of sea, but bats can fly across.
Bats have been seen wandering by day far over the Atlantic
Ocean; and two North American species either regularly or
occasionally visit Bermuda, at the distance of 600 miles from
the mainland. I hear from Mr, Tomes, who has specially
studied this family, that many species have enormous ranges,
and are found on continents and on far distant islands.
Hence we have only to suppose that such wandering species
have been modified in their new homes in relation to their
new position, and we can understand the presence of endemic
bats on oceanic islands, with the absence of all other terres-
trial mammals.
Another interesting relation exists, namely between the
depth of the sea separating islands from each other or from
the nearest continent, and the degree of affinity of their mam-
malian inhabitants. Mr. Windsor Earl has made some strik-
ing observations on this head, since greatly extended by Mr.
Wallace's admirable researches, in regard to the great Malay
Archipelago, which is traversed near Celebes by a space of
deep ocean, and this separates two widely distinct mam-
malian faunas. On either side the islands stand on a mod-
erately shallow submarine bank, and these islands are inhab-
ited by the same or by closely allied quadrupeds. I have not
as yet had time to follow up this subject in all quarters of
the world ; but as far as I have gone, the relation holds good.
For instance, Britain is separated by a shallow channel from
Europe, and the mammals are the same on both sides ; and so
it is vith all the islands near the shores of Australia. The
West Indian Islands, on the other hand, stand on a deeply
submerged bank, nearly 1000 fathoms in depth, and here we
find American forms, but the species and even the genera are
quite distinct As the amount of modification which animals
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438 ORIGIN OP SPECIES
of all kinds undergo partly depends on the lapse of time, and
as the islands which are separated from each other or from
the mainland by shallow channels, are more likely to have
been continuously united within a recent period than the
islands separated by deeper channels, we can understand how
it is that a relation exists between the depth of the sea sep-
arating two mammalian* faunas, and the degree of their
affinity, — a relation which is quite inexplicable on the theory
of independent acts of creation.
The foregoing statements in regard to the inhabitants of
oceanic islands, — ^namely, the fewness of the species, with a
large proportion consisting of endemic forms — ^the members
of certain groups, but not those of other groups in the same
class, having been modified — the absence of certain whole
orders, as of batrachians and of terrestrial mammals, not-
withstanding the presence of aerial bats, — the singular pro-
portions of certain orders of plants, — ^herbaceous forms
having been developed into trees, &c., — seem to me to accord
better with the belief in the efficiency of occasional means of
transport, carried on during a long course of time, than with
the belief in the former connection of all oceanic islands with
the nearest continent; for on this latter view it is probable
that the various classes would have immigrated more uni-
formly, and from the species having entered in a body their
mutual relations would not have been much disturbed, and
consequently they would either have not been modified, or all
the species in a more equable manner.
I do not deny that there are many and serious difficulties
in understanding how many of the inhabitants of the more
remote islands, whether still retaining the same specific form
or subsequently modified, have reached their present homes.
But the probability of other islands having once existed as
halting-places, of which not a wreck now remains, must not
be overlooked I will specify one difficult case. Almost all
oceanic islands, even the most isolated and smallest, are in-
habited by land-shells, generally by endemic species, but
sometimes by species found elsewhere, — striking instances of
which have been given by Dr. A. A. Gould in relation to the
Pacific. Now it is notorious that land-shells are easily killed
by sea-water; their eggs, at least such as I have tried, sink in
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INHABITANTS OF ISLANDS 499
it and are killed. Yet there must be some unknown, but
occasionally efficient means for their transportal. Would the
just-hatched young sometimes adhere to the feet of birds
roosting on the ground, and thus get transported? It oc-
curred to me that land-shells, when hybernating and having a
membranous diaphragm over the mouth of the shell, might
be floated in chinks of drifted timber across moderately wide
arms of the sea. And I find that several species in this state
withstand uninjured an immersion in sea- water during seven
days: one shell, the Helix pomatia, after having been thus
treated and again hybernating was put into sea-water for
twenty days, and perfectly recovered. During this length of
time the shell might have been carried by a marine current
of average swiftness, to a distance of 660 geographical miles.
As this Helix has a thick calcareous operculum, I removed
it, and when it had formed a new membranous one, I again
immersed it for fourteen days in sea-water, and again it
recovered and crawled away. Baron Aucapitaine has since
tried similar experiments; he placed 100 land-shells, belong-
ing to ten species, in a box pierced with holes, and immersed
it for a fortnight in the sea. Out of the hundred shells,
twenty-seven recovered. The presence of an operculum
seems to have been of importance, as out of twelve specimens
of Cyclostoma elegans, which is thus furnished, eleven re-
vived. It is remarkable, seeing how well the Helix pomatia
resisted with me the salt-water, that not one of fifty-four
specimens belonging to four other species of Helix tried by
Aucapitaine, recovered. It is, however, not at all probable
that land-shells have often been thus transported; the feet
of birds offer a more probable method.
ON THE RELATIONS OF THE INHABITANTS OF ISLANDS TO
THOSE OF THE NEAREST MAINLAND
The most striking and important fact for us is the affinity
of the species which inhabit islands to those of the nearest
mainland, without being actually the same. Numerous in-
stances could be given. The Galapagos Archipelago, situ-
ated under the equator, lies at the distance of between 500
and 600 miles from the shores of South America. Here
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440 ORIGIN OP SPECIBS
almost every product of the land and of the water bears the
unmistakeable stamp of the American continent There are
twenty-six land-birds; of these, twenty-one, or perhaps
twenty-three, are ranked as distinct species, and would ccwn-
monly be assumed to have been here created: yet the dose
affinity of most of these birds to American species is mani-
fest in every character^ in their habits, gestures, and tones
of voice. So it is with the other animals, and with a large
proportion of the plants, as shown by Dr. Hooker in his
admirable Flora of this archipelago. The naturalist, looking
at the inhabitants of these volcanic islands in the Pacific,
distant several hundred miles from the continent, feds that
he is standing on American land. Why should this be so?
why should the species which are supposed to have been
created in the Galapagos Archipelago, and nowhere dse,
bear so plainly the stamp of affinity to those created in
America? There is nothing in the conditions of life, in the
geological nature of the islands, in their height or climate,
or in the proportions in which the several dasses are asso-
ciated together, which closely resembles the conditions of
the South American coast: in fact, there is a considerable
dissimilarity in all these respects. On the other hand, there
is a considerable degree of resemblance in the volcanic na-
ture of the soil, in the dimate, height and size of the islands,
between the Galapagos and Cape Verde Archipdagoes : but
what an entire and absolute difference in thdr inhabitants!
The inhabitants of the Cape Verde Islands are rdated to
those of Africa, like those of the Galapagos to America.
Facts such as these, admit of no sort of explanation on the
ordinary view of independent creation : whereas on the view
here maintained, it is obvious that the Galapagos Islands
would be likely to receive colonists from America, whether
by occasional means of transport or (though I do not believe
in this doctrine) by formerly continuous land, and the Cape
Verde Islands from Africa ; such colonists would be liable to
modification, — ^the principle of inheritance still betraying
their original birthplace.
Many analogous facts could be given: indeed it is an al-
most universal rule that the endemic productions of islands
are related to those of the nearest continent, or of the near-
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INHABITANTS OF ISLANDS 441
est large island. The exceptions are few, and most of them
can be explained. Thus although Kerguelen Land stands
nearer to Africa than to America, the plants are related, and
that very closely, as we know from Dr. Hooker's account,
to those of America: but on the view that this island has
been mainly stocked by seeds brought with earth and stones
on icebergs, drifted by the prevailing currents, this anomaly
disappears. New Zealand in its endemic planes is much
more closely related to Australia, the nearest mainland, than
to any other region: and this is what might have been ex-
pected ; but it is also plainly related to South America, which,
although the next nearest continent, is so enormously remote,
that the fact becomes an anomaly. But this difficulty par-
tially disappears on the view that New Zealand, South
America, and the other southern lands have been stocked in
part from a nearly intermediate though distant point, namely
from the antarctic islands, when they were clothed with vege-
tation, during a warmer tertiary period, before the com-
mencement of the last Glacial period. The affinity, which
though feeble, I am assured by Dr. Hooker is real, between
the flora of the south-western comer of Australia and of the
Cape of Good Hope, is a far more remarkable case : but this
affinity is confined to the plants, and will, no doubt, some day
be explained.
The same law which has determined the relationship be-
tween the inhabitants of islands and the nearest mainland, is
sometimes displayed on a small scale, but in a most interest-
ing manner, within the limits of the same archipelago. Thus
each separate island of the Galapagos Archipelago is ten-
anted, and the fact is a marvellous one, by many distinct
species ; but these species are related to each other in a very
much closer manner than to the inhabitants of the American
continent, or of any other quarter of the world. This is
what might have been expected, for islands situated so near
to each other would almost necessarily receive immigrants
from the same original source, and from each other. But
how is it that many of the immigrants have been differently
modified, though only in a small degree, in islands situated
within sight of each other, having the same geological na-
ture, the same height, climate, &c.? This long appeared to
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442 ORIGIN OP SPECIES
me a great difficulty: but it arises in chief part from the
deeply-seated error of considering the physical conditions of
a country as the most important: whereas it cannot be dis-
puted that the nature of the other species with which each
has to compete, is at least as important, and generally a far
more important element of success. Now if we look to the
species which inhabit the Galapagos Archipelago, and are
likewise found in other parts of the wwld, we find that they
differ considerably in the several islands. This difference
might indeed have been expected if the islands have been
stocked by occasional means of transport — z, seed, for in-
stance, of one plant having been brought to one island, and
that of another plant to another island, though all proceeding
from the same general source. Hence, when in former times
an immigrant first settled on one of the islands, or when it
subsequently spread from one to another, it would undoubt-
edly be exposed to different conditions in die different islands,
for it would have to compete with a different set of organ-
isms; a plant, for instance, would find the ground best fitted
for it occupied by somewhat different species in the different
islands, and would be exposed to the attacks of somewhat
different enemies. If then it varied, natural selection would
probably favour different varieties in the different islands.
Some species, however, might spread and yet retain the same
character throughout the group, just as we see some species
spreading widely throughout a continent and remaining the
same.
The really surprising fact in this case of the Galapagos
Archipelago, and in a lesser degree in some analogous cases,
is that each new species after being formed in any one island,
did not spread quickly to the other islands. But the islands,
though in sight of each other, are separated by deep arms of
the sea, in most cases wider than the British Channel, and
there is no reason to suppose that they have at any former
period been continuously united. The currents of the sea are
rapid and sweep between the islands, and gales of wind are
extraordinarily rare ; so that the islands are far more effect-
ually separated from each other than they appear on a map.
Nevertheless some of the species, both of those found in other
parts of the world and of those confined to the archipelago,
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INHABITANTS OF ISLANDS 443
are common to the several islands ; and we may inier from
their present manner of distribution, that they have spread
from one island to the others. But we often take, I think, an
erroneous view of the probability of closely-allied species in*
vading each other's territory, when put into free intercom-
munication. Undoubtedly, if one species has any advantage
over another, it will in a very brief time wholly or in part
supplant it; but if both are equally well fitted for their own
places, both will probably hold their separate places for al-
most any length of time. Being familiar with the fact that
many species, naturalised through man's agency, have
spread with astonishing rapidity over wide areas, we are apt
to infer that most species would thus spread; but we should
remember that the species which become naturalised in new
countries are not generally closely allied to the aboriginal
inhabitants, but are very distinct forms, belonging in a large
proportion of cases, as shown by Alph. de CandoUe, to dis-
tinct genera. In the Galapagos Archipelago, many even ot
the birds, though so well adapted for flying from island to
island, differ on the different islands; thus there are three
closely-allied species of mocking-thrush, each confined to its
own island. Now let us suppose 'the mocking-thrush of Chat-
ham Island to be blown to Charles Island, which has its own
mocking-thrush; why should it succeed in establishing itself
there? We may safely infer that Charles Island is well
stocked with its own species, for annually more eggs are laid
and young birds hatched, than can possibly be reared; and
we may infer that the mocking-thrush peculiar to Charles
Island is at least as well fitted for its home as is the species
peculiar to Chatham Island Sir C. Lyell and Mr. Wollaston
have communicated to me a remarkable fact bearing on this
subject; namely, that Madeira and the adjoining islet of
Porto Santo possess many distinct but representative species
of land-shells, some of which live in crevices of stone; and
although large quantities of stone are annually transported
from Porto Santo to Madeira, yet this latter island has not
become colonised by the Porto Santo species; nevertheless
both islands have been colonised by European land-shells,
which no doubt had some advantage over the indigenous spe-
cies. From these considerations I think we need not greatly
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444 ORIGIN OP SPECIES
marvel at the endemic species which inhabit the several
islands of the Galapagos Archipelago, not having all spread
from island to island. On the same continent, also, preoccu-
pation has probably played an important part in checking
the commingling of the species which inhabit different dis-
tricts with nearly the same physical conditions. Thus, the
south-east and south-west comers of Australia have nearly
the same physical conditions, and nre united by continuous
land, yet they are inhabited by a vast number of distinct
mammals, birds, and plants ; so it is, according to Mr. Bates,
with the butterflies and other animals inhabiting the great,
open, and continuous valley of the Amazons.
The same principle which governs the general character of
the inhabitants of oceanic islands, namely, the relation to the
source whence colonists could have been most easily derived,
together with their subsequent modification, is of the widest
application throughout nature. We see this on every moun-
tain-summit, in every lake and marsh. For Alpine species,
excepting in as far as the same species have become widely
spread during the Glacial epoch, are related to those of the
surrounding lowlands; thus we have in South America, Al-
pifle humming-birds, Alpine rodents, Alpine plants, &c., all
strictly belonging to American forms; and it is obvious that
a mountain, as it became slowly upheaved, would be colonised
from the surrounding lowlands. So it is with the inhabitants
of lakes and marshes, excepting in so far as great facility of
transport has allowed the same forms to prevail throughout
large portions of the world. We see this same principle in
the character of most of the blind animals inhabiting the
caves of America and of Europe. Other analogous facts
could be given. It will, I believe, be found universally true,
that wherever in two regions, let them be ever so distant,
many closely allied or representative species occur, there will
likewise be found some identical species ; and wherever many
closely-allied species occur, there will be found many forms
which some naturalists rank as distinct species, and others as
mere varieties ; these doubtful forms showing us the steps in
the progress of modification.
The relation between the power and extent of migration in
certain species, either at the present or at some former pe*
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INHABITANTS OF ISLANDS 445
riod, and the existence at remote points of the world of
closely-allied species, is shown in another and more general
way. Mr. Gould remarked to me long ago, that in those
genera of birds which range over the world, many of the
species have very wide ranges. I can hardly doubt that this
rule is generally true, though difficult of proof. Amongst
mammals, we see it strikingly displayed in Bats, and in a
lesser degree in the Felidae and Canidx. We see the same
rule in the distribution of butterflies and beetles. So it is
with most of the inhabitants of fresh water, for many of the
genera in the most distinct classes range over the world, and
many of the species have enormous ranges. It is not meant
that all, but that some of the species have very wide ranges
in the genera which range very widely. Nor is it meant that
the species in such genera have on an average a very wide
range; for this will largely depend on how far the process
of modification has gone; for instance, two varieties of the
same species inhabit America and Europe, and thus the spe-
cies has an immense range ; but, if variation were to be car-
ried a little further, the two varieties would be ranked as
distinct species, and their range would be greatly reduced.
Still less is it meant, that species which have the capacity of
crossing barriers and ranging widely, as in the case of cer-
tain powerfully-winged birds, will necessarily range widely;
for we should never forget that to range widely implies not
only the power of crossing barriers, but the more important
power of being victorious in distant lands in the struggle for
life with foreign associates. But according to the view that
all the species of a genus, though distributed to the most
remote points of the world, are descended from a single pro-
genitor, we ought to find, and I believe as a general rule we
do find, that some at least of the species range very widely.
We should bear in mind that many genera in all classes are
of ancienf origin, and the species in this case will have had
ample time for dispersal and subsequent modification. There
is also reason to believe from geological evidence that within
each great class the lower organisms change at a slower rate
than the higher; consequently they will have had a better
chance of ranging widely and of still retaining the same spe-
cific character. This fact, together with that of the seeds
BB— HC zi
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446 ORIGIN OF SPECIES
and eggs of most lowly organised forms being very minute
and better fitted for distant transportal, probably accounts for
a law which has long been observed, and which has lately
been discussed by Alph. de CandoUe in regard to plants,
namely, that the lower any group of organisms stands the
more widely it ranges.
The relations just discussed, — namely, lower organisms
ranging more widely than the higher, — ^some of the species of
widely-ranging genera themselves ranging widely,— sucli
facts, as alpine, lacustrine, and marsh productions being gen^
erally related to those which live on the surrounding low
lands and dry lands, — ^the striking relationship between the
inhabitants of islands and those of the neatest mainland —
the still closer relationship of the distinct inhabitants of the
islands in the same archipelago — ^are inexplicable on the ordi-
nary view of the independent creation of each species, but
are explicable if we admit colonisation from the nearest or
readiest source, together with the subsequent adaptation of
the colonists to their new homes.
SUMMARY OF THE LAST AND PRESENT CHAPTERS
In these chapters I have endeavoured to show, that if we
make due allowance for our ignorance of the full effects of
changes of climate and of the level of the land, which have
certainly occurred within the recent period, and of other
changes which have probably occurred, — if we remember
how ignorant we are with respect to the many curious means
of occasional transport, — if we bear in mind, and this is a
very important consideration, how often a species may have
ranged continuously over a wide area, and then have become
extinct in the intermediate tracts, — ^the difficulty is not insu-
perable in believing that all the individuals of the same
species, wherever found, are descended from conAnon par-
ents. And we are led to this conclusion, which has been ar-
rived at by many naturalists under the designation of single cen-
tres of creation, by various general considerations, more espe-
cially from the importance of barriers of all kinds, and from
the analogical distribution of sub-genera, genera, and families.
With respect to distinct species belonging to tise saoie
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SUMMARY 4A7
genus, which on our theory have spread from one parent-
source; if we make the same allowances as before for our
ignorance, and remember that some forms of life have
changed very slowly, enormous periods of time having been
thus granted for their migration, the difficulties are far from
insuperable ; though in this case, as in that of the individuals
of the same species, they are often great.
As exemplifying the effects of climatal changes on distribu-
tion, I have attempted to show how important a part the last
Glacial period has played, which affected even the equa-
torial regions, and which, during the alternations of the cold
in the north and south, allowed the productions of opposite
hemispheres to mingle, and left some of them stranded on the
mountain-summits in all parts of the world. As showing how
diversified are the means of occasional transport, I have dis-
cussed at some little length the means of dispersal of fresh-
water productions.
If the difficulties be not insuperable in admitting that in the
long course of time all the individuals of the same species,
and likewise of the several species belonging to the same
genus, have proceeded from some one source; then all the
grand leading facts of geographical distribution are explic-
able on the theory of migration, together with subsequent
modification and the multiplication of new forms. We can
thus understand the high importance of barriers, whether
of land or water, in not only separating, but in apparently
forming the several zoological and botanical provinces. We
can thus tmderstand the concentration of related species within
the same areas ; and how it is that under different latitudes,
for instance in South America^ the inhabitants of the plains
and mountains, of the forests, marshes, and deserts, are
linked together in so mysterious a manner, and are likewise
linked to the extinct beings which formerly inhabited the
same continent. Bearing in mind that the mutual relation
of organism to organism is of the highest importance, we can
see why two areas having nearly the same physical condi-
tions should often be inhabited by very different forms of
life; for according to the length of time which has elapsed
since the colonists entered one of the regions, or both; ac-
cording to the nature of the communication which allowed
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448 ORIGIN OP SPECIES
certain forms and not others to enter, either in greater or
lesser numbers; according or not, as those which entered
happened to come into more or less direct competition with
each other and with the aborigines : and according as the im-
migrants were capable of varying more or less rapidly, there
would ensue in the two or more regions, independently of
their physical conditions, infinitely diversified conditions of
life, — there would be an almost endless amount of organic
action and reaction, — ^and we should find some groups of
beings greatly, and some only slightly modified, — some de-
veloped in great force, some existing in scanty numbers —
and this we do find in the several great geographical prov-
inces of the world.
On these same principles we can understand, as I have
endeavoured to show, why oceanic islands should have few
inhabitants, but that of these, a large proportion should be
endemic or peculiar; and why, in relation to the means of
migration, one group of beings should have all its species pe-
culiar, and another group, even within the same class, should
have all its species the same with those in an adjoining
quarter of the world. We can see why whole groups of or-
ganisms, as batrachians and terrestrial mammals, should be
absent from oceanic islands, whilst the most isolated islands
should possess their own peculiar species of aerial mammals
or bats. We can see why, in islands, there should be some
relation between the presence of mammals, in a more or less
modified condition, and the depth of the sea between such
islands and the mainland. We can clearly see why all the
inhabitants of an archipelago, though specifically distinct on
the several islets, should be closely related to each other;
and should likewise be related, but less closely, to those of
the nearest continent, or other source whence immigrants
might ha^e been derived. We can see why, if there exist
very closely allied or representative species in two areas,
however distant from each other, some identical species will
almost always there be found.
As the late Edward Forbes often insisted, there is a strik-
ing parallelism in the laws of life throughout time and
space; the laws governing the succession of forms in past
times being nearly the same with those governing at the
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SUBffMART 449
present time the differences in different areas. We see this
in many facts. The endurance of each species and group of
species is continuous in time; for the apparent exceptions to
the rule are so few, that they may fairly be attributed to our
not having as yet discovered in an intermediate deposit cer-
tain forms which are absent in it, but which occur both
above and below: so in space, it certainly is the general rule
that the area inhabited by a single species, or by a group of
species, is continuous, and the exceptions, which are not rare,
may, as I have attempted to show, be accounted for by
former migrations under different circumstances, or through
occasional means of transport, or by the species having be-
come extinct in the intermediate tracts. Both in time and
space species and groups of species have their points of maxi-
mum development. Groups of species, living during the
same period of time, or living within the same area, are often
characterised by trifling features in common, as of sculpture
or colour. In looking to the long succession of past ages, as
in looking to distant provinces throughout the world, we find
that species in certain classes differ little from each other,
whilst those in another class, or only in a different section of
the same order, differ greatly from each other. In both time
and space the lowly organised members of each class gen-
erally change less than the highly organised; but there are
in both cases marked exceptions to the rule. According to
our theory, these several relations throughout time and
space are intelligible ; for whether we look to the allied forms
of life which have changed during successive ages, or to
those which have changed after having migrated into distant
quarters, in both cases they are connected by the same bond
of ordinary generation; in both cases the laws of variation
have been the same, and modifications have been accumulated
by the same means of natural selection.
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CHAPTER XIV
Mutual Affinities of Organic Beings: Morphology:
Embryology: Rudimentary Organs
aassiiication, groups mbordinate to gnyupB — ^Natural system — Rules
and difficulties in dassificatiott, explained on the theory of
descent with modification — Classification of yarieties — Descent
always used in classification — ^Analogical or adaptive characters
— Affinities, general, complex, and radiating — ^Extinction sepa-
rates and defines groups — MoapBOLOGY, between members of
the same class, between parts of tiie same individual —
Embryology, laws of, explained by variations not supervening
at an early age, and being inherited at a corresponding age-^
RuDiMENTASY ORGANS ; their origin explained — Summary.
classification
FROM the most remote period in the history of the world
organic beings have been found to resemble each other
in descending degrees, so that they can be classed in
groups under groups. This classification is not arbitrary like
the grouping of the stars in constellations. The existence of
groups would have been of simple significance, if one group
had been exclusively fitted to inhabit the land, and another
the water; one to feed on flesh, another on vegetable matter,
and so on; but the case is widely different, for it is notorious
how commonl3r members of even the same sub-group have
different habits. In the second and fourth chapters, on Vari-
ation and on Natural Selection, I have attempted to show
that within each country it is the widely ranging, the much
diffused and common, that is the dominant species, belonging
to the larger genera in each class, which vary most. The
varieties, or incipient species, thus produced, ultimately be-
come converted into new and distinct species; and these, on
the principle of inheritance, tend to produce other new and
dominant species. Consequently the groups which are now
large, and which generally include many dominant species*
450
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OASSIFICATION 451
tend to go on increasing in size. I further attempted to show
that from the varying descendants of each species trying to
occupy as many and as different places as possible in the
economy of nature, they constantly tend to diverge in char-
acter. This latter conclusion is supported by observing the
great diversity of forms which, in any small area, come into
the closest competition, and by certain facts in natural-
isation.
I attempted also to show that there is a steady tendency in
the forms which are increasing in number and diverging in
character, to supplant and exterminate the preceding, less
divergent and less improved forms. I request the reader to
turn to the diagram illustrating the action, as formerly ex-
plained, of these several principles; and he will see that the
inevitable result is, that the modified descendants proceeding
from one progenitor become broken up into groups subordi-
nate to groups. In the diagram each letter on the uppermost
line may represent a genus including several species ; and the
whole of the genera along this upper line form together one
class, for all are descended from one ancient parent, and,
consequently, have inherited something in common. But the
three genera on the left hand have, on this same principle,
much in common, and form a sub-family, distinct from that
containing the next two genera on the right hand, which
diverged from a common parent at the fifth stage of descent
These five genera have also much in common, though less
than when grouped in sub-families; and they form a family
distinct from that containing the three genera still farther to
the right hand, which diverged at an earlier period. And all
these genera, descended from (A), form an order distinct
from the genera descended from (I). So that we here have
many species descended from a single progenitor grouped
into genera; and the genera into sub-families, families, and
orders, all under one great class. The grand fact of the
natural subordination of organic beings in groins under
groups, which, from its familiarity, does not always suffi-
ciently strike us, is in my judgment thus explained. No
doubt organic beings, like all other objects, can be classed in
many ways, either artificially by single, characters, or more
naturally by a number of characters. We know, for instance.
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452 ORIGIN OF SPBCIES
that minerals and the elemental substances can be thus ar-
ranged. In this case there is of course no relation to gene-
alogical succession, and no cause can at present be assigned
for their falling into groups. But with organic beings the
case is different, and the view above given accords with their
natural arrangement in group under group; and no other
explanation has ever been attempted.
Naturalists, as we have seen, try to arrange the species,
genera, and families in each class, on what is called the
Natural System. But what is meant by this system? Some
authors look at it merely as a scheme for arranging together
those living objects which are most alike, and for separating
those which are most unlike; or as an artificial method of
enunciating, as briefly as possible, general propositions, —
that is, by one sentence to give the characters common, for
instance, to all mammals, by another those common to all
camivora, by another those common to the dog-genus, and
then, by adding a single sentence, a full description is given
of each kind of dog. The ingenuity and utility of this system
are indisputable. But many naturalists think that something
more is meant by the Natural System; they believe that it
reveals the plan of the Creator; that unless it be specified
whether order in time or space, or both, or what else is meant
by the plan of the Creator, it seems to me- that nothing is
thus added to our knowledge. Expressions such as that fa-
mous one by Linnaeus, which we often meet with in a more
or less concealed form, namely, that the characters do not
make the genus, but that the genus gives the characters, seem
to imply that some deeper bond is included in our classifica-
tions than mere resemblance. I believe that this is the case,
and that community of descent — the one known cause of close
similarity in organic beings — is the bond, which though ob-
served by various degrees of modification, is partially re-
vealed to us by our classifications.
Let us now consider the rules followed in classificationr,
and the difficulties which are encountered on the view that
classification either gives some unknown plan of creation, or
is simply a scheme for enunciating general propositions and
of placing together the forms most like each other. It might
have been thought (and was in ancient times thou^t) that
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CLASSIFICATION 453
those parts of the structure which determined the habits of
life, and the general place of each being in the economy of
nature, would be of very high importance in classification.
Nothing can be more false. No one regards the external
similarity of a mouse to a shrew, of a dugong to a whale, of
a whale to a fish, as of any importance. These resemblances,
though so intimately connected with the whole life of the
being, are ranked as merely ''adaptive or analogical charac-
ters;" but to the consideration of these resemblances we
shall recur. It may even be given as a general rule, that the
less any part of the organisation is concerned with special
habits, the more important it becomes for classification. As
an instance: Owen, in speaking of the dugong, says, "The
generative organs, being those which are most remotely re-
lated to the habits and food of an animal, I have always
regarded as affording very clear indications of its true
affinities. We are least likely in the modifications of these
organs to mistake a merely adaptive for an essential char-
acter." With plants how remarkable it is that the organs
of vegetation, on which their nutrition and life depend, are
of little signification; whereas the organs of reproduction,
with their product the seed and embryo, are of paramotmt
importance! So again in formerly discussing certain mor-
phological characters which are not functionally important,
we have seen that they are often of the highest service in
classification. This depends on their constancy throughout
many allied groups; and their constancy chiefly depends on
any slight deviations not having been preserved and accumu-
lated by natural selecticMi, which acts only on serviceable
characters.
That the mere physiological importance of an organ does
not determine its classificatory value, is almost proved by the
fact, that in allied groups, in which the same organ, as we
have every reason to suppose, has nearly the same physiolog-
ical value, its classificatory value is widely different. No
naturalist can have worked long at any group without being
struck with this fact; and it has been fully acknowledged in
the writings of almost every author. It will suffice to quote
the highest authority, Robert Brown, who, in speaking of
certain organs in the Proteaceae, says their generic impor-
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454 ORIGIN OF SPECIES
tance, "like that of all their parts, not only in this, hot, as I
apprehend, in every natural family, is very unequal, and in
some cases seems to be entirely lost." Again, in another
work he says, the genera of the Connaraceae ''differ in having
one or more ovaria, in the existence or absence of albumen,
in the imbricate or valvular aestivation. Any one of these
characters singly is frequently of more than generic impor-
tance, thou^ here even when all taken together they appear
insufficient to separate Cnestis from Connarus." To give an
example amongst insects: in one great division of the Hy-
menoptera, the antennae, as Westwood has remarked, are
most constant in structure; in another division they differ
much, and the differences are of quite subordinate value in
classification; yet no one will say that the antennae in these
two divisions of the same order are of unequal physiological
importance. Any number of instances could be given of the
varying importance for classification of the same important
organ within the same group of beings.
Again, no one will say that rudimentary or atrophied or-
gans are of high physiological or vital importance; yet, un-
doubtedly, organs in this condition are often of much value
in classification. No one will dispute that the rudimentary
teeth in the upper jaws of young ruminants, and certain
rudimentary bones of the leg, are highly serviceable in ex-
hibiting the close affinity between ruminants and pachyderms.
Robert Brown has strongly insisted on the fact that the posi-
tion of the rudimentary florets is of the highest importance
in the classification of the grasses.
Numerous instances could be given of characters derived
from parts which must be considered of very trifling physio-
logical importance, but which are universally admitted as
highly serviceable in the definition of whole groups. For in-
stance, whether or not there is an open passage from the
nostrils to the mouth, the only character, according to Owen,
which absolutely distinguishes fishes and reptiles — the inflec-
tion of the angle of the lower jaw in Marsupials — the man-
ner in which the wings of insects are folded — mere colour in
certain Algae — ^mere pubescence on parts of the flower in
grasses — ^the nature of the dermal covering, as hair or
feathers, in the Vertebrata. If the Omithorhynchus had
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CLASSIFICATION 4S5
been covered with feathers instead of hair, this external and
trifling character would have been considered by naturalists
as an important aid in determining the degree of affinity of
this strange creature to birds.
The importance, for classification, of trifling characters,
mainly depends on their being correlated with many other
characters of more or less importance. The value indeed of
an aggregate of characters is very evident in natural history.
Hence, as has often been remarked, a species may depart
from its allies in several characters, both of high physiologi-
cal importance, and of almost universal prevalence, and yet
leave us in no doubt where it should be ranked. Hence, also,
it has been found that a classification founded on any single
character, however important that may be, has always failed ;
for no part of the organisation is invariably constant The
importance of an aggregate of characters, even when none
are important, alone explains the aphorism enunciated by
Linnseus, namely, that the characters do not give the genus,
but the genus gives the characters; for this seems founded
on the appreciation of many trifling points of resemblance, too
slight to be defined. Certain plants, belonging to the Mai-
pighiaceae, bear perfect and degraded flowers; in the latter,
as A. de Jussieu has remarked, "the greater number of the
characters proper to the species, to the genus, to the family,
to the class, disappear, and thus laugh at our classification."
When Aspicarpa produced in France, during several years,
only these degraded flowers, departing so wonderfully in a
number of the most important points of structure from the
proper type of the order, yet M. Richard sagaciously saw,
as Jussieu observes, that this genus should still be retained
amongst the Malpighiaceae. This case well illustrates the
spirit of our classifications.
Practically, when naturalists are at work, they do not
trouble themselves about the physiological value of the char-
acters which they use in definii^ a group or in allocating any
particular species. If they find a character nearly uniform,
and common to a great number of forms, and not common
to others, they use it as one of high value; if common to
some lesser number, they use it as of subordinate value. This
principle has been broadly confessed by some naturalists to
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456 ORIGIN OF SPECIES
be the true one; and by none more clearly than by that ex-
cellent botanist, Aug. St. Hilaire. If several trifling char-
acters are always found in combination, though no apparent
bond of connection can be discovered between them, especial
value is set on them. As in most groups of animals, impor-
tant organs, such as those for propelling the blood, or for
aerating it, or those for propagating the race, are found
nearly uniform, they are considered as highly serviceable in
classification; but in some groups all these, the most impor-
tant vital organs, are found to offer characters of quite sub-
ordinate values. Thus, as Fritz MuUer has lately remarked,
in the same group of crustaceans, C3rpridina is furnished with
a heart, whilst in too closely alli^ genera, namely Cypris
and Cytherea, there is no such organ ; one species of Cypri-
dina has well-developed branchiae, whilst another species is
destitute of them.
We can see why characters derived from the embryo
should be of equal importance with those derived from the
adult, for a natural classification of course includes all ages.
But it is by no means obvious, on the ordinary view, why
the structure of the embryo should be more important for
this purpose than that of the adult, which alone plays its full
part in the economy of nature. Yet it has been strongly
urged by those great naturalists, Milne Edwards and Agassiz,
that embtyological characters are the most important of all;
and this doctrine has very generally been admitted as true.
Nevertheless, their importance has sometimes been exag-
gerated, owing to the adaptive characters of larvae not hav-
ing been excluded; in order to show this, Fritz Miiller
arranged by the aid of such characters alone the great class
of crustaceans, and the arrangement did not prove a natural
one. But there can be no doubt that embryonic, excluding
larval characters, are of the highest value for classification,
not only with animals but with plants. Thus the main di-
visions of flowering plants are founded on differences in the
embryo, — on the number and position of the cotyledons, and
on the mode of development of the plumule and radicle. We
shall immediately see why these characters possess so high a
value in classification, namely, from the natural system being
genealogical in its arrangement.
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CLASSIFICATION 457
Our classifications are often plainly influenced by chains
of affinities. Nothing can be easier than to define a number
of characters common to all birds ; but with crustaceans, any
such definition has hitherto been found impossible. There
are crustaceans at the opposite ends of the series, which have
hardly a character in common; yet the species at both ends,
from being plainly allied to others, and these to others,
and so onwards, can be recognised as unequivocally belonging
to this, and to no other class of the Articulata.
Geographical distribution has often been used, though
perhaps not quite logically, in classification, more especiaOy
in very large groups of closely allied forms. Temminck in-
sists on the utility or even necessity of this practice in certain
groups of birds; and it has been followed by several ento-
mologists and botanists.
Finally, with respect to the comparative value of the vari-
ous groups of species, such as orders, sub-orders, families,
sub-families, and genera, they seem to be, at least at present,
almost arbitrary. Several of the best botanists, such as Mr.
Bentham and others, have strongly insisted on their arbi-
trary value. Instances could be given amongst plants and
insects, of a group first ranked by practised naturalists
as only a genus, and then raised to the rank of a sub-family
or family; and this has been done, not because further re-
search has detected important structural differences, at
first overlooked, but because numerous allied species with
slightly different grades of difference, have been subse-
quently discovered.
All the foregoing rules and aids and difficulties in classifi-
cation may be explained, if I do not greatly deceive myself,
on the view that the Natural System is founded on descent
with modification; — ^that the characters which naturalists
consider as showing true affinity between any two or more
species, are those which have been inherited from a common
parent, all true classification being genealogical; — ^that com-
munity of descent is the hidden bond which naturalists have
been unconsciously seeking, and not some unknown plan of
creation, or the enunciation of general propositions, and the
mere putting together and separating objects more or less
alike.
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458 ORIGIN OF SPECIES
Bttt I must explain my meaning more fully. I beKeve that
the arrangement of the groups within each class, in due sub-
ordination and relation to each other, must be strictly genea-
logical in order to be natural ; but that the amount of differ-
ence in the several branches or groups, though allied in .the
same degree in blood to their common progenitor, may differ
greatly, being due to the different degrees of modification
which they have undergone; and this is expressed by the
forms being ranked under different genera, families, sections,
or orders. The reader will best understand what- is meant,
if he will take the trouble to refer to the diagram in the
fourth chapter. We will suppose the letters A to L to repre-
sent allied genera existing during the Silurian epoch, and
descended from some still earlier form. In three of these
genera (A, F, and I), a species has transmitted modified de-
scendants to the present day, represented by the fifteen
genera (a" to tf*) on the 'uppermost horizontal line. Now
all these modified descendants from a single species, are re-
lated in blood or descent in the same degree ; they may meta^
phorically be called cousins to the same millionth degree;
yet they differ widely and in different degrees from each
other. The forms descended from A, now broken up into
two or three families, constitute a distinct order from those
descended from I, also broken up into two families. Nor
can the existing species, descended from A, be ranked in the
same genus with the parent A; or those from I, with the
parent I. But the existing genus F" may be supposed to have
been but slightly modified; and it will then rank with the
parent-genus F; just as some few still living organisms be-
long to Silurian genera. So that the comparative value of
the differences between these organic beings, which are all
related to each other in the same degree in blood, has come
to be widely different. Nevertheless their genealogical
arrangement remains strictly true, not only at the present
time, but at each successive period of descent All the modi-
fied descendants from A will have inherited something in
common from their common parent, as will all the descend-
ants from I; so will it be with each subordinate branch of
descendants, at each successive stage. If, however, we sup-
pose any descendant of A, or of I, to have become so mudi
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CLASSIFICATION 450
modified as to have lost all traces of its parentage, in this
case, its place in the natural system will be lost, as seems
to have occurred with some few existing organisms. AD
the descendants of the genus F,' along its whole line of
descent, are supposed to have been but little modified, and
they form a single genus. But this genus, though much
isolated, will still occupy its proper intermediate position.
The representation of the groups, as here given in the dia-
gram on a flat surface, is much too simple. The branches
ought to have diverged in all directions. If the names of
the groups had been simply written down in a linear series
the representation would have been still less natural ; and it
is notoriously not possible to represent in a series, on a flat
surface, the affinities which we discover in nature amongst
the beings of the same group. Thus, the natural system is
genealogical in its arrangement, like a pedigree: but the
amount of modification which the different groups have
undergone has to be expressed by ranking them under differ-
ent so-called genera, sub-families, families, sections, orders,
and classes.
It may be worth while to illustrate this view of classifica-
tion, by taking the case of Fanguages. If we possessed a
perfect pedigree of mankind, a genealogical arrangement of
the races of man would afford the best classification of the
various languages now spoken throughout the world; and if
all extinct languages, and all intermediate and slowly chang-
ing dialects, were to be included, such an arrangement would
be the only possible one. Yet it might be that some ancient
languages had altered very little and had given rise to few
new languages, whilst others had altered much owing to the
spreading, isolation, and state of civilisation of the several
co-descended races, and had thus given rise to many new
dialects and languages. The various degrees of difference
between the languages of the same stock, would have to be
expressed by groups subordinate to groups; but the proper
or even the only possible arrangement would still be genea-
logical; and this would be strictly natural, as it would con-
nect together all languages, extinct and recent, by the closest
affinities, and would give the filiation and origin of each
tongue.
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460 ORIGIN OF SPECIES *
In confirmation of this view, let us glance at the classifi-
cation of varieties, which are known or believed to be
descended from a single species. These are grouped under
the species^ with the sub-varieties under the varieties; and
in some cases, as with the domestic pigeon, with several
other grades of difference. Nearly the same rules are fol-
lowed as in classifying species. Authors have insisted on
the necessity of arranging varieties on a natural instead of
an artificial system; we are cautioned, for instance, not to
class two varieties of the pine-apple together, merely because
their fruit, though the most important part, happens to be
nearly identical ; no one puts the Swedish and common turnip
together, though the esculent and thickened stems are so
similar. Whatever part is found to be most constant, is used
in classing varieties; thus the great agriculturist Marshall
says the horns are very useful for this purpose with cattle,
because they are less variable than the shape or colour of the
body, &c. ; whereas with sheep the horns are much less serv-
iceable, because less constant. In classing varieties, I
apprehend that if we had a real pedigree, a genealogical
classification would be universally preferred; and it has been
attempted in some cases. For we might feel sure, whether
there had been more or less modification, that the principle
of inheritance would keep the forms together which were
allied in the greatest number of points. In tumbler pigeons,
though some of the sub-varieties differ in the important
character of the length of the beak, yet all are kept together
from having the common habit of tumbling; but the short-
faced breed has nearly or quite lost this habit; nevertheless,
without any thought on the subject, these tumblers are kept
in the same group, because allied in blood and alike in some
other respects.
With species in a state of nature, every naturalist has in
fact brought descent into his classification; for he includes
in his lowest grade, that of species, the two sexes; and how
enormously these sometimes differ in the most important
characters, is known to every naturalist: scarcely a single
fact can be predicated in common of the adult males and
hermaphrodites of certain cirripedes, and yet no one dreams
of separating them. As soon as the three Orchidean forms»
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CLASSIFICATION 461
Monachanthus, Myanthus, and Catasetum, which had previ-
ously been ranked as three distinct genera, were known to be
sometimes produced on the same plant, they were immedi-
ately considered as varieties; and now I have been able to
show that they are the male, female, and hermaphrodite
forms of the same species. The naturalist includes as one
species the various larval stages of the same individual, how-
ever much they may differ from each other and from the
adult, as well as the so-called alternate generations of Steen-
strup, which can only in a technical sense be considered as
the same individual. He includes monsters and varieties, not
from their partial resemblance to the parent-form, but be-
cause they are descended from it.
As descent has universally been used in classing together
the individuals of the same species, though the males and
females and larvae are sometimes extremely different; and as
it has been used in classing varieties which have undergone
a certain, and sometimes a considerable amount of modifica-
tion, may not this same element of descent have been uncon-
sciously used in grouping species under genera, and genera
under higher groups, all under the so-called natural system?
I believe it has been unconsciously used; and thus only can
I understand the several rules and guides which have been
followed by our best systematists. As we have no written
pedigrees, we are forced to trace community of descent by
resemblances of any kind. Therefore we choose those char-
acters which are the least likely to have been modified, in
relation to the conditions of life to which each species has
been recently exposed. Rudimentary structures on this view
are as good as, or even sometimes better than, other parts
of the organisation. We care not how trifling a character
may be — let it be the mere inflection of the angle of the jaw,
the manner in which an insect's wing is folded, whether the
skin be covered by hair or feathers — if it prevail through-
out many and different species, especially those having very
different habits of life, it assumes high value; for we can
account for its presence in so many forms with such differ-
ent habits, only by inheritance from a common parent. We
may err in this respect in regard to single points of structure,
but when several characters, let them be ever so trifling,-
CC— HC XI
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462 ORIGIN OF SPECIES
concur throughout a large group of heings having different
habits, we may feel almost sure, oa the theory of descent,
that these characters have been inherited from a common
ancestor ; and we know that such ag^egated characters have
especial value in classification.
We can understand why a species or a group of species
may depart from its allies, in several of its most important
characteristics, and yet be safely classed with them. This
may be safely done, and is often done, as long as a sufficient
number of characters, let them be ever so unimportant, be-
trays the hidden bond of community of descent Let two
forms have not a single character in common, yet, if these
extreme forms are connected together by a chain of inter-
mediate groups, we may at once infer their conmiunity of
descent, and we put them all into the same class. As we find
organs of high physiological importance — ^those which serve
to preserve life under the most diverse conditions of exist-
ence— ^are generally the most constant, we attach especial
value to them; but if these same organs, in another group
or section of a group, are found to differ much, we at once
value them less in our classification. We shall presently see
why embryological characters are of such high classificatory
importance. Geographical distribution may sometimes be
brought usefully into play in classing large genera, because
all the species of the same genus, inhabiting any distinct and
isolated region, are in all probability descended from the
same parents.
Analogical Resemblances. — ^We can understand, on the
above views, the very important distinction between real
affinities and analogical or adaptive resemblances. Lamarck
first called attention to this subject, and he has been ably fol-
lowed by Madeay and others. The resemblance in the shape
of the body and in the fin-like anterior limbs between du-
gongs and whales, and between these two orders of mam-
mals and fishes are analogical. So is the resemblance
between a mouse and a shrew-mouse (Sorex), which belong
to different orders ; and the still closer resemblance, insisted
on by Mr. Mivart, between the mouse and a small marsupial
animal (Antechinus) of Australia. These latter resem-
blances may be accounted for, as it seems to me, by adapta-
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ANALOGICAL RESfiMBLANCBS 463
tion for similarly active movements through thickets and
herbage, together with concealment from enemies.
Amongst insects there are innumerable similar instances;
thus Linnseus, misled by external appearances, actually
classed an homopterous insect as a moth. We see something
of the same kind even with our domestic varieties, as in the
strikingly similar shape of the body in the improved breeds
of the Chinese and common pig, which are descended from
distinct species; and in the similarly thickened stems of the
common and specifically distinct Swedish turnip. The re-
semblance between the greyhound and the racehorse is hardly
more fanciful than the analogies which have been drawn by
some authors between widely different animals.
On the view of characters being of real importance for
classification, only in so far as they reveal descent, we can
clearly understand why analogical or adaptive characters,
although of the utmost importance to the welfare of the
being, are almost valueless to the systematist. For animals,
belonging to two most distinct lines of descent, may have
become adapted to similar conditions, and thus have assumed
a close external resemblance ; but such resemblances will not
reveal — ^will rather tend to conceal their blood-relationship.
We can thus also understand the apparent paradox, that the
very same characters are analogical when one group is com-
pared with another, but give true afiinities when the members
of the same group are compared together : thus, the shape of
the body and fin-like limbs are only analogical when whales
are compared with fishes, being adaptations in both classes
for swimming through the water; but between the several
members of the whale family, the shape of the body and the
fin-like limbs offer characters exhibiting true affinity; for as
these parts are so nearly similar throughout the whole fam-
ily, we cannot doubt that they have been inherited from a
common ancestor. So it is with fishes.
Ntunerous cases could be g^ven of striking resemblances
in quite distinct beings between single parts or organs, which
have been adapted for the same functions. A good instance
is afforded by the close resemblance of the jaws of the dog
and Tasmanian wolf or Thylacinus, — ^animals which are
widely sundered in the natural system. But this resemblance
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464 ORIGIN OF SPECIES
is confined to general appearance, as in the prominence of
the canines, and in the cHtting shape of the molar teeth. For
the teeth really differ much: thus the dog has on each side
of the upper jaw four pre-molars and only two molars;
whilst the Thyladnus has three pre-molars and four molars.
The molars also differ much in the two animals in relative
size and structure. The adult dentition is preceded by a
widely different milk dentition. Any one may of course deny
that the teeth in either case have been adapted for tearing
flesh, through the natural selection of successive variations;
but if this be admitted in the one case, it is unintelligible to
me that it should be denied in the other. I am glad to find
that so high an authority as Professor Flower has come to
this same conclusion.
The extraordinary cases given in a former chapter, of
widely different fishes possessing electric organs, — of widely
different insects possessing luminous organs, — ^and of orchids
and asdepiads having pollen-masses with viscid discs, come
under this same head of analogical resemblances. But these
cases are so wonderful that they were introduced as diffi-
culties or objections to our theory. In all such cases some
fundamental difference in the growth or development of the
parts, and generally in their matured structure, can be de-
tected. The end gained is the same, but the means, though
appearing superficially to be the same, are essentially differ-
ent. The principle formerly alluded to under the term of
analogical variation has probably in these cases often come
into play; that is, the members of the same class, although
only distantly allied, have inherited so much in common in
their constitution, that they are apt to vary under similar
exciting causes in a similar manner; and this would obvi-
ously aid in the acquirement through natural selection of
parts or organs, strikingly like each other, independendy of
their direct inheritance from a common progenitor.
As species belonging to distinct classes have often been
adapted by successive slight modifications to live under
nearly similar circumstances, — ^to inhabit, for instance, the
three elements of land, air, and water, — ^we can perhaps un-
derstand how it is that a numerical parallelism has sometimes
been observed between the sub-groups of distinct classes. A
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ANALOGICAL RESEMBLANCES 465
naturalist, struck with a parallelism of this nature, by arbi-
trarily raising or sinking the value of the groups in several
classes (and all our experience shows that their valuation
is as yet arbitrary), could easily extend the parallelism over
a wide range; and thus the septenary, quinary, quaternary
and ternary classifications have probably arisen.
There is another and curious class of cases in which dose
external resemblance does not depend on adaptation to sim-
ilar habits of life, but has been gained for the sake of pro-
tection. I allude to the wonderful manner in which certain
butterflies imitate, as first described by Mr. Bates, other and
quite distinct species. This excellent observer has shown
that in some districts of S. America, where, for instance, an
Ithomia abounds in gaudy swarms, another butterfly, namely,
a Leptalis, is often found mingled in the same flock; and the
latter so closely resembles the Ithomia in every shade and
stripe of colour and even in the shape of its wings, that Mr.
Bates, with his eyes sharpened by collecting during eleven
years, was, though always on his guard, continually deceived.
When the mockers and the mocked are caught and compared,
they are found to be very different in essential structure, and
to belong not only to distinct genera, but often to distinct
families. Had this mimicry occurred in only one or two in-
stances, it might have been passed over as a strange coinci-
dence. But, if we proceed from a district where one Leptalis
imitates an Ithomia, another mocking and mocked species
belonging to the same two genera, equally close in their
resemblance, may be found. Altogether no less than ten
genera are enumerated, which include species that imitate
other butterflies. The mockers and mocked always inhabit
the same region; we never find an imitator living remote
from the form which it imitates. The mockers are almost
invariably rare insects; the mocked in almost every case
abound in swarms. In the same district in which a species
of Leptalis closely imitates an Ithomia, there are sometimes
other Lepidotera mimicking the same Ithomia : so that in the
same place, species of three genera of butterflies and even a
moth are found all closely resembling a butterfly belonging
to a fourth genus. It deserves especial notice that many of
the mimicking forms of the Leptalis, as well as of the miio-
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466 ORIGIN OF SPECIBS
icked forms, can be shown by a graduated series to be merely
varieties of the same species; whilst others are undoubtedly
distinct species. But why, it may be asked, are certain forms
treated as the mimicked and others as the mimickers? Mr.
Bates satisfactorily answers this question, by showing that
the form which is imitated keeps the usual dress of the group
to which it belongs, whilst the counterfeiters have changed
their dress and do not resemble their nearest allies.
We are next led to inquire what reason can be assigned
for certain butterflies and moths so often assuming the dress
of another and quite distinct form ; why, to the perplexity of
naturalists, has nature condescended to the tricks of the
stage ? Mr. Bates has, no doubt, hit on the true explanation.
The mocked forms, which always abound in numbers, must
habitually escape destruction to a large extent, otherwise
they could not exist in such swarms; and a large amount of
evidence has now been collected, showing that they are dis-
tasteful to birds and other insect-devouring animals. The
mocking forms, on the other hand, that inhabit the same dis-
trict, are comparatively rare, and belong to rare groups;
hence they must suffer habitually from some danger, for
otherwise, from the number of eggs laid by all butterflies,
they would in three or four generations swarm over the
whole country. Now if a member of one of these perse-
cuted and rare groups were to assume a dress so like that of
a well-protected species that it continually deceived the prac-
tised eyes of an entomologist, it would often deceive preda-
ceous birds and insects, and thus often escape destruction.
Mr. Bates may almost be said to have actually witnessed the
process by which the mimickers have come so closely to re-
semble the mimicked; for he found that some of the forms
of Leptalis which mimic so many other butterflies, varied in
an extreme degree. In one district several varieties oc-
curred, and of these one alone resembled to a certain ex-
tent, the common Ithomia of the same district. In another
district there were two or three varieties, one of which was
much commoner than the others, and this closely mocked
another form of Ithomia. From facts of this nature, Mr.
Bates concludes that the Leptalis first varies; and when a
variety happens to resemble in some degree any common
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AFFINITIES CONNECTING ORGANIC BEINGS 467
butterfly inhabiting the same district, this variety, from its
resemblance to a flourishing and little-persecuted kind, has:
a better chance of escaping destruction from predaceoua
birds and insects, and is consequently oftener preserved;—
"the less perfect degrees of resemblance being generatiim
after generation eliminated, and only the others left to pro-
pagate their kind" So that we have an excellent illus-
tration of natural selection.
Messrs. Wallace and Trimen have likewise described sev^
era! equally striking cases of imitation in the Lepidoptera of
the Malay Archipelago and Africa, and with some other in-
sects. Mr. Wallace has also detected one such case with
birds, but we have none with the larger quadrupeds. The
much greater frequency of imitation with insects than with
other animals, is probably the consequence of their small
size; insects cannot defend themselves, excepting indeed the
kinds furnished with a sting, and I have never heard of an
instance of such kinds mocking other insects, though they
are mocked; insects cannot easily escape by flight from the
larger animals which prey on them; therefore, speaking
metaphorically, they are reduced, like most weak creatures,
to trickery and dissimulation.
It should be observed that the process of imitation prob-
ably never commenced between forms widely dissimilar in
colour. But starting with species already somewhat like
each other, the closest resemblance, if beneficial, could read-
ily be gained by the above means; and if the imitated form
was subsequently and gradually modified through any agency,
the imitating form would be led along the same track, and
thus be altered to almost any extent, so that it might ulti-
mately assume an appearance or colouring wholly unlike that
of the other members of the family to which it belonged.
There is, however, some difficulty on this head, for it is nec-
essary to suppose in some cases that ancient members belong-
ing to several distinct groups, before they had diverged to
their present extent, accidentally resembled a member of
another and protected group in a sufficient degree to afford
some slight protection; this having given the basis for the
subsequent acquisition of the most perfect resemblance.
On the Nature of the Affinities connecting Organic
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40B . ORIGIN OF SPEOBS
Beings, — ^As the modified descendants of dominant species,
belonging to the larger genera, tend to inherit the advan-
tages which made the groups to which they belong large and
their parents dominant, they are almost sure to spread widely,
and to seize on more and more places in the economy of na-
ture. The larger and more dominant groups within each
class thus tend to go on increasing in size; and they conse-
quently supplant many smaller and feebler groups. Thus we
can account for the fact that all organisms, recent and ex-
tinct, are included under a few great orders, and under still
fewer classes. As showing how few the higher groups are
in number, and how widely they are spread throughout the
world, the fact is striking that the discovery of Australia
has not added an insect belonging to a new class; and that
in the vegetable kingdom, as I learn from Dr. Hooker, it
has added only two or three families of small size.
In the chapter on Geological Succession I attempted to
show, on the principle of each group having generally
diverged much in character during the long-continued proc-
ess of modification, how it is that the more ancient forms of
life often present characters in some degree intermediate
between existing groups. As some few of the old and in-
termediate forms have transmitted to the present day de-
scendants but little modified, these constitute our so-called
osculant or aberrant species. The more aberrant any form
is, the greater must be the number of connecting forms which
have been exterminated and utterly lost. And we have some
evidence of aberrant groups having suffered severely from
extinction, for they are almost always represented by ex-
tremely few species; and such species as do occur are gen-
erally very distinct from each other, which again implies
extinction. The genera Omithorhynchus and Lepidosiren,
for example, would not have been less aberrant had each
been represented by a dozen species, instead of as at present
by a single one, or by two or three. We can, I think, account
for this fact only by looking at aberrant groups as forms
which have been conquered by more successful competitors,
with a few members still preserved under unusually favour-
able conditions.
Mr. Waterhouse has remarked that, when a member be*
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AFFINITIES CONNECTING ORGANIC BEINGS 469
longing to one group of animals exhibits an affinity to a
quite distinct group, this affinity in most cases Is general and
not special; thus, according to Mr. Waterhouse, of all Ro-
dents, the bizcacha is most nearly related to Marsupials ; but
in the points in which it approaches this order, its relations
are general, that is, not to any one marsupial species more
than to another. As these points of affinity are believed to
be real and not merely adaptive, they must be due in accord-
ance with our view to inheritance from a common progenitor.
Therefore we must suppose either that all Rodents, including
the bizcacha, branched off from some ancient Marsupial,
which will naturally have been more or less intermediate in
character with respect to all existing Marsupials; or that
both Rodents and Marsupials branched off from a common
progenitor, and that both groups have since undergone much
modification in divergent directions. On either view we
must suppose that the bizcacha has retained, by inheritance,
more of the characters of its ancient progenitor than have
other Rodents; and therefore it will not be specially related
to any one existing Marsupial, but indirectly to all or nearly
all Marsupials, from having partially retained the character
of their common progenitor, or of some early member of the
group. On the other hand, of all Marsupials, as Mr. Water-
house has remarked, the Phascolomys resembles most nearly,
not any one species, but the general order of Rodents. Iti
this case, however, it may be strongly suspected that the re-
semblance is only analogical, owing to the Phascolomys
having become adapted to habits like tiiose of a Rodent The
elder De Candolle has made nearly similar observations on the
general nature of the affinities of distinct families of plants.
On the principle of the multiplication and gradual diver*
gence in character of the species descended from a common
progenitor, together with their retention by inheritance of
some characters in common, we can understand the exces-
sively complex and radiating affinities by which all the mem-
bers of the same family or higher group are connected to-
gether. For the common progenitor of a whole family, now
broken up by extinction into distinct groups and sub-groups,
will have transmitted some of its characters, modified in
various ways and degrees, to all the species; and they will
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470 ORIGIN OF SPECIES
consequently be related to each other by circuitous lines of
affinity of various lengths (as may be seen in the diagram so
often referred to), mounting up through many predecessors.
As it is difficult to show the blood relationship between the
numerous kindred of any ancient and noble family even by
the aid of a genealogical tree, and almost impossible to do so
without this aid, we can understand the extraodinary diffi-
culty which naturalists have experienced in describing, with-
out the aid of a diagram, the various affinities whidi they
perceive between the many living and extinct members of
the same great natural class.
Extinction, as we have seen in the fourth chapter, has
played an important part in defining and widening the inter*
vals between the several groups in each dass. We may thus
account for the distinctness of whole classes from each other
— for instance, of birds from all other vertebrate animals-^
by the belief tiiat many ancient forms of life have been ut-
terly lost, through which the early progenitors of birds were
formerly connected with the early progenitors of the other
and at that time less differentiated vertebrate classes. There
has been much less extinction of the forms of life which once
connected fishes with batrachians. There has been still less
within some whole classes, for instance the Crustacea, for
here the most wonderfully diverse forms are still linked to-
gether by a long and only partially broken chain of affinities.
Extinction has only defined the groups: it has by no means
made them; for if every form which has ever lived on this
earth were suddenly to reappear, though it would be quite
impossible to give definitions by which each group could be
distinguished, still a natural classification, or at least a natu-
ral arrangement, would be possible. We shall see this by
turning to the diagram; the letters, A to L, may represent
eleven Silurian genera, some of which have produced large
groups of modified descendants, with every link in each
branch and sub-branch still alive; and the links not greater
than those between existing varieties. In this case it would
be quite impossible to give definitions by which the several
members of the several groups could be distinguished from
their more immediate parents and descendants. Yet the
arrangement in the diagram would still hold good and would
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AFFINITIES CONNECTING ORGANIC BEINGS 471
be natural; for, on the principle of inheritance, all the forms
descended, for instance, from A, would have something in
common. In a tree we can distinguish this or that branch,
though at the actual fork the two unite and blend together.
We could not» as I have said, define the several groups; but
we could pick out types, or forms, representing most of the
characters of each group, whether large or small, and thus
give a general idea of the value of the differences between
them. This is what we should be driven to, if we were ever
to succeed in collecting all the forms in any one class which
have lived throughout all time and space. Assuredly we shall
never succeed in making so perfect a collection : nevertheless,
in certain classes, we are tending towards this end; and
Milne Edwards has lately insisted, in an able paper, on the
high importance of looking to types, whether or not we can
separate and define the groups to which such types belong.
Finally, we have seen that natural selection, which follows
from the struggle for existence, and which almost inevitably
leads to extinction and divergence of character in the de-
scendants from any one parent-species, explains that great
and universal feature in the affinities of all organic beings,
namely, their subordination in group under group. We use
the element of descent in classing the individuals of both
sexes and of all ages under one species, although they may
have but few characters in common ; we use descent in class-
ing acknowledged varieties, however different they may be
from their parents ; and I believe that this element of descent
is the hidden bond of connexion which naturalists have
sought under the term of the Natural System. On this idea
of the natural system being, in so far as it is has been per-
fected, genealogical in its arrangement, with the grades of
difference expressed by the terms genera, families, orders,
&C., we can understand the rules which we are compelled to
follow in our classification. We can understand why we value
certain resemblances far more than others ; why we use rudi-
mentary and useless organs, or others of trifling physio-
logical importance ; why, in finding the relations between one
group and another, we summarily reject analogical or adap-
tive characters, and yet use these same characters within the
limits of the same group. We can clearly see how it is that
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472 ORIGIN OP SPECIES
all living and extinct forms can be grouped together within
a few great classes; and how the several members of each
class are connected together by the most complex and radi-
ating lines of affinities. We shall never, probably, disen-
tangle the inextricable web of the affinities between the mem-
bers of any one class ; but when we have a distinct object in
view, and do not look to some unknown plan of creation, we
may hope to make sure but slow progress.
Professor Hackd in his 'Generdle Morphologic' and in
other works, has recently brought his great knowledge and
abilities to bear on what he calls phylogeny, or the lines of
descent of all organic beings. In drawing up the several
series he trusts chiefly to embryological characters, but re-
ceives aid from homologous and rudimentary organs, as well
as from the successive periods at which the various forms of
life are believed to have first appeared in our geological for-
mations. He has thus boldly made a great beginning, and
shows us how classification will in the future be treated.
MORPHOLOGY
We have seen that the members of the same dass, inde-
pendently of their habits of life, resemble each other in the
general plan of their organisation. This resemblance is often
expressed by the term "unity of type ;" or by saying that the
several parts and organs in the different species of the dass
are homologous. The whole subject is included under the
general term of Morphology. This is one of the most inter-
esting departments of natural history, and may almost be
said to be its very soul. What can be more curious than
that the hand of a man, formed for grasping, that of a mole
for digging, the leg of the horse, the paddle of the porpoise,
and the wing of the bat, should all be constructed on the
same pattern, and should indude similar bones, in the same
relative positions? How curious it is, to give a subordinate
though striking instance, that the hind-feet of the kangaroo,
which are so well fitted for bounding over the open plains,
— ^those of the climbing, leaf-eating koala, equally well fitted
for grasping the branches of trees, — ^those of the ground-
dwelling, insect or root-eating, bandicoots, — ^and those of
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MORPHOLOGY 473
some other Australian marsupials, — should all be constructed
on the same extraordinary t3rpey namely with the bones of
the second and third digits extremely slender and enveloped
within the same skin, so that they appear like a single toe
furnished with two daws. Notwithstanding this similarity
of pattern, it is obvious that the hind feet of these severed
animals are used for as widely different purposes as it is pos-
sible to conceive. The case is rendered all the more striking
by the American opossums, which follow nearly the same
habits of life as some of their Australian relatives, having
feet constructed on the ordinary plan. Professor Flower,
from whom these statements are taken, remarks in conclu-
sion : "We may call this conformity to type, without getting
much nearer to an explanation of ^e phenomenon ;" and he
then adds, "but is it not powerfully suggestive of true rela-
tionship, of inheritance from a common ancestor?"
Geoffroy St Hilaire has strongly insisted on the high im-
portance of relative position or connexion in homologous
parts ; they may differ to almost any extent in form and size,
and yet remain connected together in the same invariable
order. We never find, for instance, the bones of the arm
and fore-arm, or of the thigh and leg, transposed. Hence
the same names can be given to the homologous bones in
widely different animals. We see the same great law in the
construction of the mouths of insects: what can be more dif-
ferent than the immensely long spiral proboscis of a sphinx-
moth, the curious folded one of a bee or bug, and the great
jaws of a beetle? — ^yet all these organs, serving for such
widely different purposes, are formed by infinitely numerous
modifications of an upper lip, mandibles, and two pairs of
maxillae. The same law governs the construction of the
mouths and limbs of crustaceans. So it is with the flowers
of plants.
Nothing can be more hopeless than to attempt to explain
this similarity of pattern in members of the same class, by
utility or by the doctrine of final causes. The hopelessness
of the attempt has been expressly admitted by Owen in his
most interesting work on the 'Nature of Limbs.' On the
ordinary view of^the independent creation of each being, we
can only say that so it is; — that it has pleased the Creator
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474 ORIGIN OF SPECIES
to construct all the animals and plants in each great dass on
a uniform plan ; but this is not a scientific explanation.
The explanation is to a large extent simple on the theory
of the selection of successive slight modifications, — each
modification being profitable in some way to the modified
form, but often affecting by correlation other parts of the
organisation. In changes of this nature, there will be little
or no tendency to alter the original pattern, or to transpose
the parts. The bones of a limb might be shortened and flat-
tened to any extent, becoming at the same time enveloped in
thick membrane, so as to serve as a fin ; or a webbed hand
might have all its bones, or certain bones, lengthened to any
extent, with the membrane connecting them increased, so as
to serve as a wing; yet all these modifications would not
tend to alter the framework of the bones or the relative con-
nexion of the parts. If we suppose that an early pr(^;enitor
— the archetype as it may be called— of all mammals, birds,
and reptiles, had its limbs constructed on the existing general
pattern, for whatever purpose they served, we can at once
perceive the plain signification of the homologous construc-
tion of the limbs throughout the dass. So with the mouths
of insects, we have only to suppose that their common pro-
genitor had an upper lip, mandibles, and two pairs of max-
illae, these parts being perhaps very simple in form ; and then
natural sdection will account for the infinite diversity in the
structure and functions of the mouths of insects. Never-
theless, it is conceivable that the general pattern of an organ
might become so much obscured as to be finally lost, by the
reduction and ultimatdy by the complete abortion of certain
parts, by the fusion of other parts, and by the doubling or
multiplication of others, — ^variations which we know to be
within the limits of possibility. In the paddles of the gigantic
extinct sea-lizards, and in the mouths of certain suctorial
crustaceans, the general pattern seems thus to have become
partially obscured.
There is another and equally curious branch of our sub-
ject; namdy, serial homologies, or the comparison of the
different parts or organs in the same individual, and not of
the same parts or organs in different members of the same
dass. Most physiologists believe that the bones of the skull
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MORPHOLOGY 475
are homologous — that is, correspond in number and in rela-
tive connexion — ^with the elemental parts of a certain number
of vertebrae. The anterior and posterior limbs in all the
higher vertebrate classes are plainly homologous. So it is
with the wonderfully complex jaws and legs of crustaceans.
It is familiar to almost every one, that in a flower the rela-
tive position of the sepals, petals, stamens, and pistils, as well
as their intimate structure, are intelligible on the view that
they consist of metamorphosed leaves, arranged in a spire.
In monstrous plants, we often get direct evidence of the pos-
sibility of one organ being transformed into another; and
we can actually see, during the early or embryonic stages of
development in flowers, as well as in crustaceans and many
other animals, that organs, which when mature become ex-
tremely different are at first exactly alike.
How inexplicable are the cases of serial homologies on the
ordinary view of creation I Why should the brain be en-
closed in a box composed of such numerous and such extra-
ordinarily shaped pieces of bone, apparently representing ver-
tebrae ? As Owen has remarked, the benefit derived from the
yielding of the separate pieces in the act of parturition by
mammals, will by no means explain the same construction in
the skulls of birds and reptiles. Why should similar bones
have been created to form the wing and the leg of a bat,
used as they are for such totally different purposes, namely
flying and walking? Why should one crustacean, which has
an extremely complex mouth formed of many parts, conse-
quently always have fewer legs; or conversely, those with
many legs have simpler mouths? Why should the sepals,
petals, stamens, and pistils, in each flower, though fitted for
such distinct purposes, be all constructed on the same
pattern?
On die theory of natural selection, we can, to a certain
extent, answer these questions. We need not here consider
how the bodies of some animals first became divided into a
series of segments, or how they became divided into right
and left sides, with corresponding organs, for such questions
are almost beyond investigation. It is, however, probable
that some serial structures are the result of cells multiply-
ing by division, entailing the multiplication of the parts
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476 ORIGIN OP SPECIES
developed from such cells. It must suffice for our purpose
to bear in mind that an indefinite repetition of the same part
or organ is the common characteristic, as Owen has re-
marked, of all low or little specialised forms; therefore the
unknown progenitor of the Vertebrata probably possessed
many vertebrs; the unknown progenitor of the Articulata,
many segments; and the unknown progenitor of flowering
plants, many leaves arranged in one or more spires. We
have also formerly seen that parts many times repeated are
eminently liable to vary, not only in number, but in form.
Consequently such parts, being already present in consider-
able numbers, and being highly variable, would naturally
afford the materials for adaptation to the most different pur-
poses; yet they would generally retain, through the force
of inheritance, plain traces of their original or fundamental
resemblance. They would retain this resemblance all the
more, as the variations, which afforded the basis for their
subsequent modification through natural selection, would tend
from the first to be similar ; the parts being at an early stage
of growth alike, and being subjected to nearly the same con-
ditions. Such parts, whether more or less modified, unless
their common origin became wholly obscure, would be se-
rially homologous.
In the great class of molluscs, though the parts In distinct
species can be shown to be homologous, only a few serial
homologies, such as the valves of Chitons, can be indicated;
that is, we are seldom enabled to say that one part is homol-
ogous with another part in the same individual. And we
can understand this fact ; for in molluscs, even in the lowest
members of the class, we do not find nearly so much indefi-
nite repetition of any one part as we find in the other great
classes of the animal and vegetable kingdoms.
But morphology is a much more complex subject th^ it at
first appears, as has lately been well shown in a remarkable
paper by Mr. E. Ray Lankester, who has drawn an important
distinction between certain classes of cases which have all
been equally ranked by naturalists as homologous. He pro-
poses to call the structures which resemble each other in
distinct animals, owing to their descent from a common pro-
genitor with subsequent modification, homogenous; and the
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MORPHOLOGY 477
resemblances which cannot thus be accounted for, he pro-
poses to call homoplastic. For instance, he believes that the
hearts of birds and mammals are as a whole homogenous, —
that is, have been derived from a common progenitor; but
that the four cavities of the heart in the two classes are
homoplastic, — that Is, have been independently developed.
Mr. Lankester also adduces the close resemblance of the
parts on the right and left sides of the body, and in the suc-
cessive segments of the same individual animal ; and here we
have parts commonly called homologous, which bear no rela-
tion to the descent of distinct species from a common pro-
genitor. Homoplastic structures are the same with those
which I have classed, though in a very imperfect manner,
as analogous modifications or resemblances. Their forma-
tion may be attributed in part to distinct organisms, or to
distinct parts of the same organism, having varied in an
analogous manner; and in part to similar modifications,
having been preserved for the same general purpose or func-
tion,—of which many instances have been given.
Naturalists frequently speak of the skull as formed of
metamorphosed vertebrae; the jaws of crabs as metamor-
phosed legs; the stamens and pistils in flowers as meta-
morphosed leaves; but it would in most cases be more
correct, as Professor Huxley has remarked, to speak of
both skull and vertebrae, jaws and legs, &c., as having been
metamorphosed, not one from the other, as they now exist,
but from some common and simpler element. Most natu-
ralists, however, use such language only in a metaphorical
sense ; they are far from meaning that during a long course
of descent, primordial organs of any kind — ^vertebrae in the
one case and legs in the other — ^have actually been converted
into skulls or jaws. Yet so strong is the appearance of this
having occurred, that naturalists can hardly avoid employing
language having this plain signification. According to the
views here maintained, such language may be used literally ;
and the wonderful fact of the jaws, for instance, of a crab
retaining numerous characters, which they probably would
have retained through inheritance, if they had really been
metamorphosed from true though extremely simple legs, is
in part explained.
DD— HCXI
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478 ORIGIN OF SPECIES
DEVELOPMENT AND EMBRYOLOGY
This is one of the most important subjects in the whole
round of natural history. The metamorphoses of insects,
with which every one is familiar, are generally effected ab-
ruptly by a few stages ; but the transformations are in reality
numerous and gradual, though concealed. A certain ephem-
erous insect (Chloeon) during its development, moults, as
shown by Sir J. Lubbock, above twenty times, and each
time undergoes a certain amount of change; and in this
case we see the act of metamorphosis performed in a pri-
mary and gradual manner. Many insects, and especially cer-
tain crustaceans, show us what wonderful changes of struc-
ture can be effected during development. Such changes,
however, reach their acme in the so-called alternate genera-
tions of some of the lower animals. It is, for instance, an
astonishing fact that a delicate branching coralline, studded
with polypi and attached to a submarine rock, should pro-
duce, first by budding and then by transverse division, a
host of huge floating jelly-fishes; and that these should pro-
duce eggs, from which are hatched swimming animalcules,
which attach themselves to rocks and become developed into
branching corallines; and so on in an endless cycle. The
belief in the essential identity of the process of alternate
generation and of ordinary metamorphosis has been greatly
strengthened by Wagner's discovery of the larva or maggot
of a fiy, namely the Cecidomyia, producing asexually other
larvae, and these others, which finally are developed into
mature males and females, propagating their kind in the
ordinary manner by eggs.
It may be lyorth notice that when Wagner's remarkable
discovery was first announced, I was asked how was it
possible to account for the larvae of this fly having acquired
the power of asexual reproduction. As long as the case
remained unique no answer could be given. But already
Grimm has shown that another fly, a Chironomus, reproduces
itself in nearly the same manner, and he believes that this
occurs frequently in the Order. It is the pupa, and not the
larva, of the Chironomus which has this power; and Grimm
further shows that this case, to a certain extent, "unites that
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DEVELOPMENT AND EMBRYOLOGY 479
of the Cecidomyia with the parthenogenesis of the Coc-
cidx;" — ^the term parthenogenesis implying that the mature
females of the Coccidae are capable of producing fertile eggs
without the concourse of the male. Certain animals belong-
ing to several classes are now known to have the power of
ordinary reproduction at an tmusually early age; and we
have only to accelerate parthenogenetic reproduction by
gradual, steps to an earlier and earlier age, — Chironomus
showing us an almost exactly intermediate stage, viz., that of
the pupa — and we can perhaps accoimt for the marvellous
case of the Cecidomyia.
It has already been stated that various parts in the same
individual which are exactly alike duriag an early embryonic
period, become widely different and serve for widely differ-
ent purposes in the adult state. So again it has been shown
that generally the embryos of the most distinct species be-
longing to the same class are closely similar, but become,
when fully developed, widely dissimilar. A better proof of
this latter fact cannot be given than the statement of Von
Baer that "the embryos of mammalia, of birds, lizards, and
"snakes, probably also of chelonia, are in their earliest states
"exceedingly like one another, both as a whole and in the
"mode of development of their parts; so much so, in fact,
"that we can often distinguish the embryos only by their
"size. In my possession are two little embryos in spirit,
"whose names I have omitted to attach, and at present I am
"quite unable to say to what class they belong. They may
"be lizards or small birds, or very young mammalia, so
"complete is the similarity in the mode of formation of the
"head and trunk in these animals. The extremities, however,
"are still absent in these embryos. But even if they had
"existed in the earliest stage of their development we should
"learn nothing, for the feet of lizards and mammals, the
"wings and feet of birds, no less than the hands and feet
"of man, all arise from the same fundamental form." The
larvae of most crustaceans, at corresponding stages of devel-
opment, closely resemble each other, however different the
adults may become; and so it is with very many other ani-
mals. A trace of the law of embryonic resemblance occa-
sionally lasts till a rather late age: thus birds of the same
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480 ORIGIN OP SPECIES
genus, and of allied genera, often resemble each other in
their immature plumage; as we see in the spotted feathers
in the young of the thrush group. In the cat tribe, most
of the species when adult are striped or spotted in lines ; and
stripes or spots can be plainly distinguished in the whdp of
the lion and the puma. We occasionally though rarely see
something of the same kind in plants; thus the first leaves
of the ulex or furze, and the first leaves of the phyllodineous
acacias, are pinnate or divided like the ordinary leaves of the
leguminosse.
The points of structure, in which the embryos of widely
different animals within the same class resemble each other,
often have no direct relation to their condition of existence.
We cannot, for instance, suppose that in the embryos of the
vertebrata the peculiar loop-like courses of the arteries near
the branchial slits are related to similar conditions, — in the
young mammal which is nourished in the womb of its mother,
in the egg of the bird which is hatched in a nest, and in the
spawn of a frog under water. We have no more reason to
believe in such a relation, than we have to believe that the
similar bones in the hand of a man, wing of a bat, and fin
of a porpoise, are related to similar conditions of life. No
one supposes that the stripes on the whelp of a lion, or the
spots on the young blackbird, are of any use to these animals.
The case, however, is different when an animal during any
part of its embryonic career is active, and has to provide for
itself. The period of activity may come on earlier or later
in life; but whenever it comes on, the adaptation of the larva
to its conditions of life is just as perfect and as beautiful as
in the adult animal. In how important a manner this has
acted, has recently been well shown by Sir J. Lubbock in his
remarks on the close similarity of the larvae of some insects
belonging to very different orders, and on the dissimilarity
of the larvae of other insects within the same order, accord-
ing to their habits of life. Owing to such adaptations, the
similarity of the larvae of allied animals is sometimes greatly
obscured ; especially when there is a division of labour during
the different stages of development, as when the same larva
has during one stage to search for food, and during another
stage has to search for a place of attachment. Cases can
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DEVELOPMENT AND EMBRYOLOGY 481
even be given of the larvse of allied species, or groups of
species, differing more from each other than do the adults.
In most cases, however, the larvs, though active, still obey,
more or less closely, the law of common embryonic reseni-
blance. Cirripedes afford a good instance of this; even the
illustrious Cuvier did not perceive that a barnacle was a
crustacean: but a glance at the larva shows this in an un-
mistakable manner. So again the two main divisions of
cirripedes, the pedunculated and sessile, though differing
widely in external appearance, have larvae in all their stages
barely distinguishable.
The embryo in the course of development generally rises
in organisation; I use this expression, though I am aware
that it is hardly possible to define clearly what is meant by
the organisation being higher or lower. But no one probably
will dispute that the butterfly is higher than the caterpillar.
In some cases, however, the mature animal must be consid-
ered as lower in the scale than the larva, as with certain
parasitic crustaceans. To refer once again to cirripedes: the
larvs in the first stage have three pairs of locomotive organs,
a simple single eye, and a probosci formed mouth, with which
they feed largely, for they increase much in size. In the
second stage, answering to the chrysalis stage of butterflies,
they have six pairs of beautifully constructed natatory legs,
a pair of magnificent compound eyes, and extremely complex
antennae; but they have a closed and imperfect mouth, and
cannot feed: their function at this stage is, to search out by
their well-developed organs of sense, and to reach by their
active powers of swinuning, a proper place on which to be-
come attached and to undergo their final metamorphosis.
When this is completed they are fixed for life: their legs are
now converted into prehensile organs; they again obtain a
well-constructed mouth ; but they have no antennae, and their
two eyes are now reconverted into a minute, single, simple
eye-spot In this last and complete state, cirripedes may be
considered as either more highly or more lowly organised
than they were in the larval condition. But in some genera
the larvae become developed into hermaphrodites having the
ordinary structure, and into what I have called complemental
males; and in the latter the development has assuredly been
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488 ORIGIN OF SPECIES
retrograde, for the male is a mere sack, which lives for a
short time and is destitute of mouth, stomach, and every
other organ of importance, excepting those for reproduction.
We are so much accustomed to see a difference in structure
between the embryo and the adult, that we are tempted to
look at this difference as in some necessary manner contin-
gent on growth. But there is no reason why, for instance,
the wing of a bat, or the fin of a porpoise, should not have
been sketched out with all their parts in proper proportion,
as soon as any part became visible. In some whole groups
of animals and in certain members of other groups this is
the case, and the embryo does not at any period differ widely
from the adult: thus Owen has remarked in regard to cuttle-
fish, 'Hhere is no metamorphosis; the cephalopodic character
is manifested long before the parts of the embryo are com-
pleted." Land-shells and fresh-water crustaceans are bom
having their proper forms, whilst the marine members of the
same two great classes pass through considerable and often
great changes during their development Spiders, again,
barely undergo any metamorphosis. The larvae of most in-
sects pass through a worm-like stage, whether they are active
and adapted to diversified habits, or are inactive from being
placed in the midst of proper nutriment or from being fed
by their parents ; but in some few cases, as in that of Aphis,
if we look to the admirable drawings of the development of
this insect, by Professor Huxley, we see hardly any trace
of the vermiform stage.
Sometimes it is only the earlier developmental stages which
fail. Thus Fritz Muller has made the remarkable discovery
that certain shrimp-like crustaceans (sdlied to Penonis) first
appear under the simple nauplius-form, and after passing
through two or more zoea-stages, and then through the
mysis-stage, finally acquire their mature structure: now in
the whole great malacostracan order, to which these crusta^
ceans belong, no other member is as yet known to be first
developed under the nauplius-form, though many appear as
zoeas; nevertheless Miiller assigns reasons for his belief,
that if there had been no suppression of development, all
these crustaceans would have appeared as nauplii.
How, then, can< we explain diese several facts in embry-
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DEVELOPMENT AND EMBAYOLOGY 48S
ology, — ^namely, the very general, though not universal, dif-
ference in structure between the embryo and the adult; —
the various parts in the same individual embryo, which ulti-
mately become very unlike and serve for diverse purposes,
being at an early period of growth alike; — ^the common, but
not invariable, resemblance between the embryos or larvae
of the most distinct species in the same class; — ^the em-
bryo often retaining whilst within the tgg or womb, struc-
tures which are of no service to it, either at that or at a
later period of life; on the other hand larvae, which have to
provide for their own wants, being perfectly adapted to the
surrotmding conditions ; — and lastly the fact of certain larvae
standing higher in the scale of organisation than the mature
animal into which they are developed? I believe that all
these facts can be explained, as follows.
It is commonly assumed, perhaps from monstrosities affect-
ing the embryo at a very early period, that slight variations
or individual differences necessarily appear at an equally
early period. We have little evidence on this head, but what
we have certainly points the other way; for it is notorious
that breeders of cattle, horses, and various fancy animals,
cannot positively tell, until some time after birth, what will
be the merits or demerits of their young animals. We see
this plainly in our own children; we cannot tdl whether a
child will be tall or short, or what its precise features will
be. The question is not, at what period of life each varia-
tion may have been caused, but at what period the effects are
displayed. The cause may have acted, and I believe often
has acted, on one or both parents before the act of genera-
tion. It deserves notice that it is of no importance to a very
young animal, as long as it remains in its mother's womb or
in the tgg, or as long as it is nourished and protected by its
parent, whether most of its characters are acquired a little
earlier or later in life. It would not signify, for instance, to
a bird which obtained its food by having a much-curved
beak whether or not whilst young it possessed a beak of this
shape, as long as it was fed by its parents.
I have stated in the first chapter, that at whatever age a
variation first appears in the parent, it tends to reappear at
a corresponding age in the offspring. Certain variations can
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484 ORIGIN OF SPECIES
only appear at corresponding ages; for instance, peculiarities
in the caterpillar, cocoon, or imago states of the silk-moth:
or, again, in the full-grown horns of cattle. But variations,
which, for all that we can see might have first appeared
either earlier or later in life, likewise tend to reappear at a
corresponding age in the offspring and parent I am far
from meaning that this is invariaUy the case, and I could
give several exceptional cases of variations (taking the word
in the largest sense) which have supervened at an earlier
age in the child than in the parent
These two principles, namely, that slight variations gen*
erally appear at a not very early period of life, and are in-
herited at a corresponding not early period, explain, as I
believe, all the above specified leading facts in embryology.
But first let us look to a few analogous cases in our domestic
varieties. Some authors who have written on Dogs, main-
tain that the greyhound and bulldog, though so different,
are really closely allied varieties, descended from the same
wild stodc ; hence I was curious to see how far their puppies
differed from each other: I was told by breeders that they
differed just as much as their parents, and this, judging by
the eye, seemed almost to be the case ; but on actually meas-
uring the old dogs and their six-days-old puppies, I found
that the puppies had not acquired nearly their full amount of
proportional difference. So, again, I was told that the foals
of cart and race-horses — ^breeds which have been almost
wholly formed by selection under domestication— differed as
much as the full-grown animals; but having had careful
measurements made of the dams and of the three-days-old
colts of race and heavy cart-horses, I find that this is by no
means the case.
As we have conclusive evidence that the breeds of the
Pigeon are descended from a single wild species, I compared
the young within twelve hours after being hatched; I care-
fully measured the proportions (but will not here give the
details) of the beak, width of mouth, length of nostril and
of eyelid, size of feet and length of leg, in the wild parent-
species, in pouters, faiitails, runts, barbs, dragons, carriers,
and tumblers. Now some of these birds, when mature, differ
in so extraordinary a manner in the length and form of beak.
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DEVELOPMENT AND EMBRYOLOGY 485
and in other characters, that they would certainly have been
ranked as distinct genera if found in a state of nature. But
when the nestling birds of these several breeds were placed
in a row, though most of them could just be distinguished,
the proportional differences in the above specified points
were incomparably less than in the full-grown birds. Some
characteristic points of difference — for instance, that of the
width of mouth — could hardly be detected in the young. But
there was one remarkable exception to this rule, for the
young of the short-faced tumbler differed from the young
of the wild rock-pigeon and of the other breeds, in almost
exactly the same proportions as in the adult state.
These facts are explained by the above two principles.
Fanciers select their dogs, horses, pigeons, &c., for breeding,
when nearly grown up : they are indifferent whether the de-
sired qualities are acquired earlier or later in life, if the
full-grown animal possesses them. And the cases just given,
more especially that of the pigeons, show that the charac-
teristic differences which have been accumulated by man's
selection, and which give value to his breeds, do not gen-
erally appear at a very early period of life, and are inherited
at a corresponding not early period. But the case of the
short-faced tumbler, which when twelve hours old possessed
its proper characters, proves that this is not the universal
rule; for here the characteristic differences must either have
appeared at an earlier period than usual, or, if not so, the
differences must have been inherited, not at a corresponding,
but at an earlier age.
Now let us apply these two principles to species in a state
of nature. Let us take a group of birds, descended from
some ancient form and modified through natural selection
for different habits. Then, from the many slight successive
variations having supervened in the several species at a not
early age, and having been inherited at a corresponding age,
the young will have been but little modified, and they will still
resemble each other much more closely than do the adults, —
just as we have seen with the breeds of the pigeon. We may
extend this view to widely distinct structures and to whole
classes. The fore-limbs, for instance, which once served
as legs to a remote progenitor, may have become, through
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486 ORIGIN OF SPECIES
a long course of modification, adapted in one descendant to
act as hands, in another as paddles, in another as wings;
but on the above two principles the fore-limbs will not have
been much modified in the embryos of these several forms;
although in each form the fore-limb will differ greatly in the
adult state. Whatever influence long-continued use or disuse
may have had in modifying the limbs or other parts of any
species, this will chiefly or solely have affected it when nearly
mature, when it was compelled to use its full powers to gain
its own living; and the effects thus produced will have been
transmitted to the offspring at a corresponding nearly mature
age. Thus the young will not be modified, or will be modi-
fied only in a slight degree, through the effects of the in-
creased use or disuse of parts.
With some animals the successive variations may have
supervened at a very early period of life, or the steps may
have been inherited at an earlier age than that at which they
first occurred. In either of these cases, the young or embryo
will closely resemble the mature parent-form, as we have
seen with the short-faced tumbler. And this is the rule of
development in certain whole groups, or in certain sub-
groups alone, as with cuttle-fish, land-shells, fresh-water
crustaceans, spiders, and some members of the great class of
insects. With respect to the final cause of the young in
such groups not passing through any metamorphosis, we
can see that this would follow from the following contin-
gencies ; namely, from the young having to provide at a very
early age for their own wants, and from their following the
same habits of life with their parents; for in this case, it
would be indispensable for their existence that they should
be modified in the same manner as their parents. Again, with
respect to the singular fact that many terrestrial and fresh-
water animals do not undergo any metamorphosis, whilst
marine members of the same groups pass through various
transformations, Fritz Muller has suggested that the process
of slowly modifying and adapting an animal to live on the
land or in fresh water, instead of in the sea, would be greatly
simplified by its not passing through any larval stage; for
it is not probable that places well adapted for both the larval
and mature stages, under such new and greatly changed
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DEVELOPMENT AND EMBRYOLOGY 487
habits of life» would commonly be found unoccupied or ill-
occupied by other organisms. In this case the gradual ac^
quirement at an earlier and earlier age of the adult structure
would be favoured by natural selection; and all traces of
former metamorphoses would finally be lost.
If, on the other hand, it profited the young of an animal
to follow habits of life slightly different from those of the
parent-form, and consequently to be constructed on a slighdy
different plan, or if it profited a larva already different from
its parent to change still further, then, on the principle of
inheritance at corresponding ages, the young or the larvae
might be rendered by natural selection more and more dif^
ferent from their parents to any conceivable extent. Differ-
ences in the larva might, also, become correlated with suc-
cessive stages of its development; so that the larva, in the
first stage, might come to differ greatly from the larva in the
second stage, as is the case with many animals. The adult
might also become fitted for sites or habits, in which organs
of locomotion or of the senses, &c., would be useless; and
in this case the metamorphosis would be retrograde.
From the remarks just made we^ can see how by changes
of structure in the young, in conformity with changed habits
of life, together with inheritance at corresponding ages,
animals might come to pass through stages of development,
perfectly distinct from the primordial condition of their
adult progenitors. Most of our best authorities are now
convinced that the various larval and pupal stages of insects
have thus been acquired through adaptation, and not through
inheritance from some ancient form. The curious case of
Sitaris — ^a beetle which passes through certain unusual stages
of development — ^will illustrate how this might occur. The
first larval form is described by M. Fabre, as an active,
minute insect, furnished with six legs, two long antennae, and
four eyes. These larvae are hatched in the nests of bees;
and when the male-bees emerge from their burrows, in the
spring, which they do before the females, the larvae spring
on them, and afterwards crawl on to the females whilst
paired with the males. As soon as the female bee deposits
her eggs on the surface of the honey stored in the cells, the
larvae of the Sitaris leap on the eggs and devour them.
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488 ORIGIN OF SPECIES
Afterwards they undergo a complete change; their eyes dis-
appear; their legs and antennae become rudimentary, and
they feed on honey ; so that they now more closely resemble
the ordinary larvae of insects; ultimately they undergo a
further transformation, and finally emerge as the perfect
beetle. Now, if an insect, undergoing transformations like
those of the Sitaris, were to become the progenitor of a
whole new dass of insects, the course of development of the
new class would be widely different from that of our exist-
ing insects; and the first larval stage certainly would not
represent the former condition of any adult and ancient
form. •
On the other hand it is highly probable that with many
animals the embryonic or larval stages show us, more or less
completely, the condition of the progenitor of the whole
group in its adult state. In the great class of the Crustacea,
forms wonderfully distinct from each other, namely, suctorial
parasites, cirripedes, entomostraca, and even the malacos-
traca, appear at first as larvae under the nauplius-f orm ; and
as these larvae live and feed in the open sea, and are not
adapted for any peculiar habits of life, and from other
reasons assigned by Fritz Miiller, it is probable that at some
very remote period an independent adult animal, resembling
the Nauplius, existed, and subsequently produced, along sev-
eral divergent lines of descent, the above-named great Crus-
tacean groups. So again it is probable, from what we know
of the embryos of mammals, birds, fishes, and reptiles, that
these animals are the modified descendants of some ancient
progenitor, which was furnished in its adult state with
branchiae, a swim-bladder, four fin-like limbs, and a long tail,
all fitted for an aquatic life.
As all the organic beings, extinct and recent, which have
ever lived, can be arranged within a few great classes; and
as all within each -class have, according to our theory, been
connected together by fine gradations, the best, and, if our
collections were nearly perfect, the only possible arrange-
ment, would be genealogical; descent being the hidden bond
of connexion which naturalists have been seeking under the
term of the Natural System. On this view we can under-
stand how it is that, in the eyes of most naturalists, the
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DEVELOPMENT AND EMBRYOLOGY 489
structure of the embryo is even more important for classi-
fication than that of the adult. In two or more groups of
animals, however much they may differ from each other in
structure and habits in their adult condition, if they pass
through closely similar embryonic stages, we may feel assured
that they all are descended from one parent-form, and are
therefore closely related. Thus, community in embryonic
structure reveals community of descent; but dissimilarity in
embryonic development does not prove discommunity of
descent, for in one of two groups the developmental stages
may have been suppressed, or may have been so greatly
modified through adaptation to new habits of life, as to be
no longer recognisable. Even in groups, in which the adults
have been modified to an extreme degree, community of
origin is often revealed by the structure of the larvae; we
have seen, for instance, that cirripedes, though externally so
like shell-fish, are at once known by their larvae to belong to
the great class of crustaceans. As the embryo often shows
us more or less plainly the structure of the less modified
and ancient progenitor of the group, we can see why ancient
and extinct forms so often resemble in their adult state the
embryos of existing species of the same dass. Agassiz be-
lieves this to be a universal law of nature ; and we may hope
hereafter to see the law proved true. It can, however, be
proved true only in those cases in which the ancient state of
the progenitor of the group has not been wholly obliterated,
either by successive variations having supervened at a very
early period of growth, or by such variations having been
inherited at an earlier age than that at which they first ap-
peared. It should also be borne in mind, that the law may
be true, but yet, owing to the geological record not extending
far enough back in time, may remain for a long period, or
for ever, incapable of demonstration. The law will not
strictly hold good in those cases in which an ancient form
became adapted in its larvae state to some special line of life,
and transmitted the same larval state to a whole group of
descendants; for such larval will not resemble any still more
ancient form in its adtdt state.
Thus, as it seems to me, the leading facts in embryology,
which are second to none in importance, are explained on
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490 ORIGIN OF SPECIES
the principle of variations in the many descendants from
some one ancient progenitor, having appeared at a not very
early period of life, and having been inherited at a cor-
responding period. Embryology rises greatly in interest,
when we look at the embryo as a picture, more or less ob-
scured, of the progenitor, either in its adult or larval state,
of all the members of the same great class.
RUDIMENTARY, ATROPHIED, AND ABORTED ORGANS
Organs or parts in this strange condition, bearing the plain
stamp of inutility, are extremely common, or even general,
throughout nature. It would be impossible to name one of
the higher animals in which some part or other is not in a
rudimentary condition. In the mammalia, for instance, the
males possess rudimentary mammae ; in snakes one lobe of the
lungs is rudimentary ; in birds the "bastard-wing" may safely
be considered as a rudimentary digit, and in some species the
whole wing is so far rudimentary that it cannot be used for
flight. What can be more curious than the presence of teeth
in foetal whales, which when grown up have not a tooth in
their heads ; or the teeth, which never cut through the gums,
in the upper jaws of unborn calves?
Rudimentary organs plainly declare their origin and mean-
ing in various ways. There are beetles belonging to closely
allied species, or even to the same identical species, which
have either full-sized and perfect wings, or mere rudiments
of membrane, which not rarely lie under wing-covers firmly
soldered together; and in these cases it is impossible to
doubt, that the rudiments represent wings. Rudimentary
organs sometimes retain their potentiality: this occasionally
occurs with the mamnue of male mammals, which have been
known to become well developed and to secrete milk. So
again in the udders in the genus Bos, there are normally four
developed and two rudimentary teats; but the latter in our
domestic cows sometimes become well developed and yield
milk. In regard to plants the petals are sometimes rudimen-
tary, and sometimes well-developed in the individuals of
the same species. In certain plants having separated sexes
Kolreuter found that by crossing a species, in which the male
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RUDIMENTARY ORGANS 491
flowers included a rudiment of a pistil, with an hermaphro-
dite species, having of course a well-developed pistil, the
rudiment in the hybrid offspring was much increased in size ;
and this clearly shows that the rudimentary and perfect
pistils are essentially alike in nature. An animal may pos-
sess various parts in a perfect state, and yet they may in one
sense be rudimentary, for they are useless: thus the tadpole
of the common Salamander or Water-newt, as Mr. G. H.
Lewes remarks, "has gills, and passes its existence in the
"water ; but the Salamandra atra, which lives high up among
"the mountains, brings forth its yotmg full-formed. This
"animal never lives in the water. Yet if we open a gravid
"female, we find tadpoles inside her with exquisitely feath-
"ered gills; and when placed in water they swim about like
"the tadpoles of the water-newt Obviously this aquatic
"organisation has no reference to the future life of the
"animal, nor has it any adaptation to its embryonic condition ;
"it has solely reference to ancestral adaptations, it repeats
"a phase in the development of its progenitors."
An organ, serving for two purposes, may become rudimen-
tary or utterly aborted for one, even the more important
purpose, and remain perfectly efficient for the other. Thus
in plants, the office of the pistil is to allow the pollen-tubes
to reach the ovules within the ovarium. The pistil consists
of a stigma supported on a style; but in some Compositse,
the male florets, which of course cannot be fecundated, have
a rudimentary pistil, for it is not crowned with a stigma ; but
the style remains well developed and is clothed in the usual
manner with hairs, which serve to brush the pollen out of
the surrounding and conjoined anthers. Again, an organ
may become rudimentary for its proper purpose, and be used
for a distinct one: in certain fishes the swim-bladder seems
to be rudimentary for its proper function of giving buoyancy,
but has become converted into a nascent breathing organ or
lung. Many similar instances could be given.
Useful organs, however little they may be developed, un-
less we have reason to suppose that they were formerly more
highly developed, ought not to be considered as rudimentary.
They may be in a nascent condition, and in progress towards
further development. Rudimentary organs, on the other hand.
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4d2 ORIGIN OF SPECIES
are either quite useless, such as teeth which never cut through
the gums, or almost useless, such as the wings of an ostrich,
which serve merely as sails. As organs in this condition
would formerly, when still less developed, have been of even
less use, than at present, they cannot formerly have been
produced through variation and natural selection, which acts
solely by the preservation of useful modifications. They
have been partially retained by the power of inheritance, and
relate to a former state of things. It is, however, often
difficult to distinguish between rudimentary and nascent
organs ; for we can judge only by analogy whether a part is
capable of further development, in which case alone it de-
serves to be called nascent. Organs in this condition will
always be somewhat rare; for beings thus provided will
commonly have been supplanted by their successors with the
same organ in a more perfect state, and consequently will
have become long ago extinct. The wing of the penguin
is of high service, acting as a fin; it may, therefore, repre-
sent the nascent state of the wing: not that I believe this to
be the case; it is more probably a reduced organ, modified
for a new function: the wing of the Apteryx, on the other
hand, is quite useless, and is truly rudimentary. Owen con-
siders the simple filamentary limbs of the Lepidosiren as the
"beginnings of organs which attain full functional develop-
ment in higher vertebrates ;" but, according to the view lately
advocated by Dr. Gunther, they are probably remnants, con-
sisting of the persistent axis of a fin, with the lateral rays or
branches aborted. The mammary glands of the Ornitho-
rhynchus may be considered, in comparison with the udders
of a cow, as in a nascent condition. The ovigerous frena of
certain cirripedes, which have ceased to give attachment to
the ova and are feebly developed, are nascent branchiae.
Rudimentary organs in the individuals of the same species
are very liable to vary in the degree of their development
and in other respects. In closely allied species, also, the
extent to which the same organ has been reduced occasionally
differs much. This latter fact is well exemplified in the
state of the wings of female moths belonging to the same
family. Rudimentary organs may be utterly aborted; and
this implies, that in certain animals or plants, parts are en-
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RUDIBfENTARY ORGANS 483
tirely absent which analogy would lead us to expect to find in
them, and which are occasionally found in monstrous indi-
viduals. Thus in most of the Scrophulariaceae the fifth
stamen is utterly .aborted ; yet we may conclude that a fifth
stamen once existed, for a rudiment of it is found in many
species of the family, and this rudiment occasionally be-
comes perfectly developed, as may sometimes be seen in the
common snap-dragon. In tracing the homologies of any
part in different members of the same class, nothing is more
common, or, in order fully to understand the relations of the
parts, more useful than the discovery of rudiments. This is
well shown in the drawings given by Owen of the leg-bones
of the horse, ox, and rhinoceros.
It is an important fact that rudimentary organs, such as
teeth in the upper jaws of whales and ruminants, can often
be detected in the embryo, but afterwards wholly disappear.
It is also, I believe, a universal rule, that a rudimentary part
is of greater size in the embryo relatively to the adjoining
parts, than in the adult; so that the organ at this early age is
less rudimentary, or even cannot be said to be in any degree
rudimentary. Hence rudimentary organs in the adult are
often said to have retained their embryonic condition.
I have now given the leading facts with respect to rudi-
mentary organs. In reflecting on them, every one must be
struck with astonishment; for the same reasoning power
which tells us that most parts and organs are exquisitely
adapted for certain purposes, tells us with equal plainness
that these rudimentary or atrophied organs are imperfect and
useless. In works on natural history, rudimentary organs
are generally said to have been created "for the sake of
symmetry," or in order "to complete the scheme of nature."
But this is not an explanation, merely a re-statement of the
fact. Nor is it consistent with itself: thus the boa-constrictor
has rudiments of hind-limbs and of a pelvis, and if it be
said that these bones have been retained "to complete the
scheme of nature," why, as Professor Weismann asks, have
they not been retained by other snakes, which do not possess
even a vestige of these same bones ? What would be thought
of an astronomer who maintained that the satellites revolve
in elliptic courses round their planets " for the sake of sym-
BB— EC XI
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494 ORIGIN OF SPECIBS
metry/' because the planets thus revolve round the sun? An
eminent physiologist accounts for the presence of rudimen-
tary organs, by supposing that they serve to excrete matter
in excess, or matter injurious to the system; but can we sup-
pose that the minute papilla, which often represents the pistil
in male flowers, and which is formed of mere cellular tissue,
can thus act? Can we suppose that rudimentary teeth, which
are subsequently absorbed, are beneficial to the rapidly grow-
ing embryonic calf by removing matter so precious as phos-
phate of lime? When a man's fingers have been amputated,
imperfect nails have been known to appear on the stumps,
and I could as soon believe that these vestiges of nails are
developed in order to excrete homy matter, as that the rudi-
mentary nails on the fin of the manatee have been developed
for this same purpose.
On the view of descent with modification, the origin of
rudimentary organs is comparatively simple; and we can
understand to a large extent the laws governing their imper-
fect development. We have plenty of cases of rudimentary
organs in our domestic productions, — as the stump of a tail
in tailless breeds, — ^the vestige of an ear in earless breeds of
sheep, — ^the reappearance of minute dangling horns in horn-
less breeds of cattle, more especially, according to Youatt, in
young animals, — and the state of the whole flower in the
cauliflower. We often see rudiments of various parts in
monsters; but I doubt whether any of these cases throw
light on the origin of rudimentary organs in a state of nature,
further than by showing that rudiments can be produced ; for
the balance of evidence clearly indicates that species under
nature do not undergo great and abrupt changes. But we
learn from the study of our domestic productions that the
disuse of parts leads to their reduced size; and that the result
is inherited
It appears probable that disuse has been the main agent in
rendering organs rudimentary. It would at first lead by slow
steps to the more and more complete reduction of a part,
until at last it became rudimentary, — as in the case of the
eyes of animals inhabiting dark caverns, and of the wings
of birds inhabiting oceanic islands, which have seldom been
forced by beasts of prey to take flight, and have ultimately
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RUDIMENTARY ORGANS 485
lost the power of flying. Again, an organ, useful under cer*
tain conditions, might become injurious under others, as with
the wings of beetles living on small and exposed islands;
and in this case natural selection will have aided in reducing
the organ, until it was rendered harn^less and rudimentary.
Any change in structure and function, which can be effected
by small stages, is within the power of natural selection; so
that an organ rendered, through changed habits of life, use-
less or injurious for one purpose, might be modified and used
for another purpose. An organ might, also, be retained for
one alone of its former functions. Organs, originally formed
by the aid of natural selection, when rendered useless may
well be variable, for their variations can no longer be checked
by natural selection. All this agrees well with what we see
under nature. Moreover, at whatever period of life either
disuse or selection reduces an organ, and this will generally
be when the being has come to maturity and has to exert
its full powers of action, the principle of inheritance at
corresponding ages will tend to reproduce the organ in its
reduced state at the same mature age, but will seldom affect
it in the embryo. Thus we can understand the greater size
of rudimentary organs in the embryo relatively to the ad-
joining parts, and their lesser relative size in the adult. If,
for instance, the digit of an adult animal was used less and
less during many generations, owing to some change of
habits, or if an organ or gland was less and less functionally
exercised, we may infer that it would become reduced in size
in the adult descendants of this animal, but would retain
nearly its original standard of development in the embryo.
There remains, however, this difficulty. After an organ has
ceased being used, and has become in consequence much re-
duced, how can it be still further reduced in size until the
merest vestige is left; and how can it be finally quite obliter-
ated? It is scarcely possible that disuse can go on producing
any further effect after the organ has once been rendered
functionless. Some additional explanation is here requisite
which I cannot give. If, for instance, it could be proved
that every part of the organisation tends to vary in a greater
degree towards diminution than towards augmentation of
size, then we should be able to understand how an organ
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496 ORIGIN OP SPECIES
which has become useless would be rendered, independently
of the effects of disuse, rudimentary and would at last be
wholly suppressed; for the variations towards diminished
size would no longer be checked by natural selection. The
principle of the economy of growth, explained in a former
chapter, by which the materials forming any part, if not
useful to the possessor, are saved as far as is possible, will
perhaps come into play in rendering a useless part rudimen-
tary. But this principle will almost necessarily be confined
to the earlier stages of the process of reduction ; for we can-
not suppose that a minute papilla, for instance, representing
in a male flower the pistil of the female flower, and formed
merely of cellular tissue, could be further reduced or ab-
sorbed for the sake of economising nutriment
Finally, as rudimentary organs, by whatever steps they
may have been degraded into their present useless condition,
are the record of a former state of things, and have been
retained solely through the power of inheritance, — we can
understand, on the genealogical view of classification, how it
is that systematists, in placing organisms in their proper
places in the natural system, have often found rudimentary
parts as useful as, or even sometimes more useful than, parts
of high physiological importance. Rudimentary organs may
be compared with the letters in a word, still retained in the
spelling, but become useless in the pronunciation, but which
serve as a clue for its derivation. On the view of descent
with modification, we may conclude that the existence of
organs in rudimentary, imperfect, and useless condition, or
quite aborted, far from presenting a strange difficulty, as
they assuredly do on the old doctrine of creation, might even
have been anticipated in accordance with the views here
explained.
SUMMARY
In this chapter I have attempted to show, that the arrange-
ment of all organic beings throughout all time in groups
under groups— that the nature of the relationships by which
all living and extinct organisms are united by complex, radi-
ating, and circuitous lines of affinities into a few grand
classes,— the rules followed and the difficulties encountered
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SUMMARY 497
by naturalists in their classifications, — ^the value set upon
characters, if constant and prevalent, whether of high or
of the most trifling importance, or, as with rudimentary
organs, of no importance, — ^the wide opposition in value be-
tween analogical or adaptive characters, and characters of
true affinity; and other such rules; — ^all naturally follow if
we admit the common parentage of allied forms, together
with their modification through variation and natural selec-
tion, with the contingencies of extinction and divergence of
character. In considering this view of classification, it
should be borne in mind that the element of descent has been
universally used in ranking together the sexes, ages, dimor-
phic forms, and acknowledged varieties of the same species,
however much they may differ from each other in structure.
If we extend the use of this element of descent, — the one
certainly known cause of similarity in organic beings, — we
shall understand what is meant by the Natural System: it is
genealogical in its attempted arrangement, with the grades
of acquired difference marked by the terms, varieties, species,
genera, families, orders, and classes.
On this same view of descent with modification, most of
the great facts in Morphology become intelligible, — ^whether
we look to the same pattern displayed by the different species
of the same class in their homologous organs, to whatever
purpose applied; or to the serial and lateral homologies in
each individual animal and plant
On the principle of successive slight variations, not neces-
sarily or generally supervening at a very early period of life,
and being inherited at a corresponding period, we can under-
stand the leading facts in Embryology; namely, the close
resemblance in the individual embryo of the parts which are
homologous, and which when matured become widely dif-
ferent in structure and function ; and the resemblance of the
homologous parts or organs in allied though distinct species,
though fitted in the adult state for habits as diiTerent as is
possible. Larvae are active embryos, which have been spe-
cially modified in a greater or less degree in relation to their
habits of life, with their modifications inherited at a corre-
sponding early age. On these same principles, — and bearing
in mind that when organs are reduced in size, either from
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488 SUMMARY
disuse or through natural selection, it will generally be at
that period of life when the being has to provide for its own
wants, and bearing in mind how strong is the force of in-
heritance— the occurrence of rudimentary organs might even
have been anticipated. The importance of embryological
characters and of rudimentary organs in classification is
intelligible, on the view that a natural arrangement must be
genealogical.
Finally, the several classes of facts which have been con-
sidered in this chapter, seem to me to proclaim so plainly,
that the innumerable species, genera and families, with which
this world is peopled, are all descended, each within its own
class or group, from common parents, and have all. been
modified in the course of descent, that I should without hesi-
tation adopt this view, even if it were unsupported by other
facts or arguments.
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CHAPTER XV
Recapitulation and Conclusion
Recapitulation of the objections to the theory of Natural Selection —
Recapitulation of the general and special circumstances in its
favour — Causes of the general belief in the immutability of
species — How far the theory of Natural Selection may be ex-
tended— Effects of its adoption on the study of Natural History
—Concluding remarks.
A S this whole volume is one long argument, it may be
/\ convenient to the reader to have the leading facts
-A m. and inferences briefly recapitulated.
That many and serious objections may be advanced against
the theory of descent with modification through variation
and natural selection, I do not deny. I have endeavoured to
give to them their full force. Nothing at first can appear
more difficult to believe than that the more complex organs
and instincts have been perfected, not by means superior to,
though analogous with, human reason, but by the accumu-
lation of innumerable slight variations, each good for the
individual possessor. Nevertheless, this difficulty, though
appearing to our imagination insuperably great, cannot be
considered real if we admit the following propositions,
namely, that all parts of the organisation and instincts offer,
at least, individual differences — ^that there is a struggle for
existence leading to the preservation of profitable deviations
of structure or instinct — ^and, lastly, that gradations in the
state of perfection of each organ may have existed, each good
of its kind. The truth of these propositions cannot, I think,
be disputed.
It is, no doubt, extremely difficult even to conjecture by
what gradations many structures have been perfected, more
especially amongst broken and failing groups of organic
beings, which have suffered much extinction; but we see so
many strange gradations in nature, that we ought to be ex-
489
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500 ORIGIN OF SPSaES
tremely cautious in saying that any organ or instinct, or any
whole structure, could not have arrived at its present state by
many graduated steps. There are, it must be admitted, cases
of special difficulty opposed to the theory of natural selec-
tion ; and one of the most curious of these is the existence in
the same commtmity of two or three defined castes of workers
or sterile female ants; but I have attempted to show how
these difficulties can be mastered.
With respect to the almost universal sterility of species
when first crossed, which forms so remarkable a contrast with
the almost universal fertility of varieties when crossed, I
must refer the reader to the recapitulation of the facts given
at the end of the ninth chapter, which seem to me conclu-
sively to show that this sterility is no more a special endow-
ment than is the incapacity of two distinct kinds of trees to
be grafted together; but that it is incidental on differences
confined to the reproductive systems of the intercrossed
species. We see the truth of this conclusion in the vast
difference in the results of crossing the same two species
reciprocally, — that is, when one species is first used as the
father and then as the mother. Analogy from the consider-
ation of dimorphic and trimorphic plants clearly leads to the
same conclusion, for when the forms are illegitimately united,
they yield few or no seed, and their offspring are more or
less sterile; and these forms belong to the same undoubted
species, and differ from each other in no respect except in
their reproductive organs and functions.
Although the fertility of varieties when intercrossed and
of their mongrel offspring has been asserted by so many
authors to be universal, this cannot be considered as quite
correct after the facts given on the high authority of Gartner
and Kolreuter. Most of the varieties which have been ex-
perimented on have been produced under domestication; and
as domestication (I do not mean mere confinement) almost
certainly tends to eliminate that sterility which, judging from
analogy, would have affected the parent-species if inter-
crossed, we ought not to expect that domestication would
likewise induce sterility in their modified descendants when
crossed. This elimination of sterility apparently fol-
lows from the same cause which allows our domestic
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RECAPITULATION AND CONCLUSION SOI
animals to breed freely under diversified circumstances; and
this again apparently follows from their having been grad-
ually accustomed to frequent changes in their conditions
of life.
A double and parallel series of facts seems to throw much
light on the sterility of species, when first crossed, and of
their hybrid offspring. On the one side, there is good reason
to believe that slight changes in the conditions of life give
vigour and fertility to all organic beings. We know also
that a cross between the distinct individuals of the same
variety, and between distinct varieties, increases the number
of their offspring, and certainly gives to them increased size
and vigour. This is chiefly owing to the forms which are
crossed having been exposed to somewhat different con-
ditions of life ; for I have ascertained by a laborious series of
experiments that if all the individuals of the same variety be
subjected during several generations to the same conditions,
the good derived from crossing is often much diminished or
wholly disappears. This is one side of the case. On the
other side, we know that species which have long been ex-
posed to nearly uniform conditions, when they are subjected
under confinement to new and greatly changed conditions,
either perish, or if they survive, are rendered sterile, though
retaining perfect health. This does not occur, or only in a
very slight degree, with our domesticated productions, which
have long been exposed to fluctuating conditions. Hence
when we find that hybrids produced by a cross between two
distinct species are few in number, owing to their perishing
soon after conception or at a very early age, or if surviving
that they are rendered more or less sterile, it seems highly
probable that this result is due to their having been in fact
subjected to a great change in their conditions of life, from
being compounded of two distinct organisations. He who
will explain in a definite manner why, for instance, an ele-
phant or a fox will not breed under confinement in its native
country, whilst the domestic pig or dog will breed freely under
the most diversified conditions, will at the same time be able
to give a definite answer to the question why two distinct
species, when crossed, as well as their hybrid offspring, are
generally rendered more or less sterile, whilst two domesti-
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502 ORIGIN OP SPECIES
cated varieties when crossed and their mongrel offspring are
perfectly fertile.
Turning to geographical distribution, the difficulties en-
countered on the theory of descent 'with modification are
serious enough. « All the individuals of the same species, and
all the species of the same genus, or even hi^er group, are
descended from common parents; and therefore, in however
distant and isolated parts of the world they may now be found,
they must in the course of successive generations have
travelled from some one point to all the others. We are
often wholly unable even to conjecture how this could have
been effected. Yet, as we have reason to believe that some
species have retained the same specific form for very long
periods of time, immensely long as measured by years, too
much stress ought not to be laid, cb the occasional wide dif-
fusion of the same species; for 'during very long periods
there will always have been a good chance for wide migra-
tion by many means. A broken or interrupted range may
often be accounted for by the extinction of the species in the
intermediate regions. It cannot be denied that we are as yet
very ignorant as to the full extent of the various dimatal
and geographical changes which have affected the earth dur-
ing modern periods ; and such changes will often have facili-
tated migration. As an example, I have attempted to show
how potent has been the influence of the Glacial period on
the distribution of the same and of allied species throughout
the world. We are as yet profoundly ignorant of the many
occasional means of transport With respect to distinct
species of the same genus inhabiting distant and isolated
regions, as the process of modification has necessarily been
slow, all the means of migration will have been possible dur-
ing a very long period ; and consequently the difficulty of the
wide diffusion of the species of the same genus is in some
degree lessened.
As according to the theory of natural selection an inter-
minable number of intermediate forms must have existed,
linking together all the species in each group by gradations
as fine as are our existing varieties, it may be asked. Why do
we not see these linking forms all around us ? Why are not all
organic beings blended together in an inextricable chaos?
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With respect to existing forms, we should remember that we
have no right to expect (excepting in rare cases) to discover
directly connecting links between them, but only between
each and some extinct and supplanted form. Even on a wide
area, which has during a long period remained continuous,
and of which the climatic and other conditions of life change
insensibly in proceeding from a district occupied by one
species into another district occupied by a closely allied
species, we have no just right to expect often to find inter-
mediate varieties in the intermediate zones. For we have
reason to believe that only a few species of a genus ever
undergo change; the other species becoming utterly extinct
and leaving no modified progeny. Of the species which do
change, only a few within the same country change at the
same time ; and all modifioations are slovfly effected. I have
also shown that the intermediate varieties which probably at
first existed in the intermediate zones, would be liable to be
supplanted by the allied forms on either hand ; for the latter,
from existing in greater numbers, would generally be modi-
fied and improved at a quicker rate than the intermediate vari-
eties, which existed in lesser numbers; so that the inter-
mediate varieties would, in the long run, be supplanted and
exterminated.
On this doctrine of the extermination of an infinitude of
connecting links, between the living and extinct inhabitants
of the world, and at each successive period between the
extinct and still older species, why is not every geological
formation charged with such links ? Why does not every col- .
lection of fossil remains afford plain evidence of the grada-
tion and mutation of the forms of life? Although geological
research has undoubtedly revealed the former existence of
many links, bringing numerous forms of life much closer to-
gether, it does not 3rield the infinitely many fine gradations
between past and present species required on the theory; and
this is the most obvioiis of the many objections which may
be urged against it Why, again, do whole jg:roups of allied
species appear, though this appearance is often false, to have
come in suddenly on the successive geological stages? Al-
though we now know that organic beings appeared on this
globe, at a period incalculably remote, long before the lowest
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504 ORIGIN OP SPECIES
bed of the Cambrian system was deposited, why do we not
find beneath this system great piles of strata stored with the
remains of the progenitors of the Cambrian fossils? For on
the theory, such strata must somewhere have been deposited
at these ancient and utterly unknown epochs of the world's
history.
I can answer these questions and objections only on the
supposition that the geological record is far more imperfect
than most geologists believe. The number of specimens in
all our museums is absolutely as nothing compared with the
countless generations Of countless species which have cer-
tainly existed. The parent-form of any two or more species
would not be in all its characters directly intermediate be- '
tween its modified offspring, any more than the rock-pigeon
is directly intermediate in crop and tail between its descend-
ants, the pouter and fantail pigeons. We should not be able
to recognise a species as the parent of another and modified
species, if we were to examine the two ever so closely, unless
we possessed most of the intermediate links; and owing to
the imperfection of the geological record, we have no just
right to expect to find so many links. If two or three, or
even more linking forms were discovered, they would simply
be ranked by many naturalists as so many new species, more
especially if found in different geological sub-stages, let their
differences be ever so slight. Numerous existing doubtful
forms could be named which are probably varieties ; but who
will pretend that in future ages so many fossil links will be
discovered, that naturalists will be able to decide whether or
not these doubtful forms ought to be called varieties? Only
a small portion of the world has been geologically explored.
Only organic beings of certain Classes can be preserved in a
fossil condition, at least in any great number. Many species
when once formed never undergo any further change but be-
come extinct without leaving modified descendants; and the
periods, during which species have undergone modification,
though long as measured by years, have probably been short
in comparison with the periods during which they retained
the same form. It is the dominant and widely ranging species
which vary most frequently and vary most, and varieties are
often at first local — ^both causes rendering the discovery of
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RECAPITULATION AND CONCLUSION 50S
intermediate links in any one formation less likely. Local
varieties will not spread into other and' distant regions until
they are considerably modified and improved ; and when they
have spread, and are discovered in a geological formation,
they appear as if suddenly created there, and will be simply
classed as new species. Most formations have been inter-
mittent in their accumulation; and their duration has prob-
ably b^en shorter than the average duration of specific forms.
Successive formations are in most cases separated from each
other by blank intervals of time of great length; for fos-
siliferous formations thick enough to resist future degrada-
tion can as a general rule be accumulated only where much
sediment is deposited on the subsiding bed of the sea. Dur-
ing the alternate periods of elevation and of stationary level
the record will generally be blank. During these latter
periods there will probably be more variability in the forms
of life ; during periods of subsidence, more extinction.
With respect to the absence of strata rich in fossils beneath
the Cambrian formation, I can recur only to the hypothesis
given in the tenth chapter; namely, that though our conti-
nents and oceans have endured for an enormous period in
nearly their present relative* positions, we have no reason to
assume that this has always been the case ; consequently for-
mations much older than any now known may lie buried be-
neath the great oceans. With respect tq^ the lapse of time
not having been sufficient sinfce our planet was consolidated
for the assumed amount of organic change, and this objection,
as urged by Sir William Thompson, is probably one of the
gravest as yet advanced, I can only say, firstly, that we do
not know at what rate species change as measured by years,
and secondly, that many philosophers are not as yet willing
to admit that we know enough of the constitution of the uni-
verse and of the interior of our globe to speculate with safety
on its past duration.
That the geological record is imperfect all will admit; but
that it is imperfect to the degree required by our theory, few
will be inclined to admit If we look to long enough intervals
of time, geology plainly declares that species have all
changed; and they have changed in the manner required by
the theory, for they have changed slowly and in a graduated
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506 ORIGIN OF SPECIES
manner. We clearly see this in the fossil remains from con-
secutive formations invariably being much more closely re-
lated to each other, than are the fossils from widely separated
formations.
Such is the sum of the several chief objections and diffi-
culties which may be justly urged against the theory; and I
have now briefly recapitulated the answers and explanations
which, as far as I can see, may be given. I have felt these
difficulties far too heavily during many years to doubt their
weight. But it deserves especial notice that the more im-
portant objections relate to questions on which we are con-
fessedly ignorant; nor do we know how ignorant we are.
We do not know all the possible transitional gradations be-
tween the simplest and the most perfect organs ; it cannot be
pretended that we know all the varied means of Distribution
during the long lapse of years, or that we know how imper-
fect is the Geological Record. Serious as these several ob-
jections are, in njy judgment they are by no means sufficient to
overthrow the theory of descent with subsequent modification.
Now let us turn to the other side of the argument Under
domestication we see much variability, caused, or at least
excited, by changed conditions of life ; but often in so obscure
a manner, that we are tempted to consider the variations as
spontaneous. Variability is governed by many complex laws,
— ^by correlated growth, compensation, the increased use and
disuse of parts, and the definite action of the surrounding
conditions. There is much difficulty in ascertaining how
largely our domestic productions have been modified; but we
may safely infer that the amount has been large, and that
modification can be inherited for long periods. As long as
the conditions of life remain the same, we have reason to
believe that a modification, which has already been inherited
for many generations, may continue to be inherited for an
almost infinite number of generations. On the other hand,
we have evidence that variability when it has once come into
play, does not cease under domestication for a very long
period ; nor do we know that it ever ceases, for new varieties
are still occasionally produced by our oldest domesticated
productions.
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RECAPITULATION AND CX)NCLUSION 507
Variability is not actually caused by man ; he only uninten>
tionally exposes organic beings to new conditions of life, and
then nature acts on the organisation and causes it to vary.
But man can and does select the variations given to him by
nature, and thus accumulates them in any desired manner.
He thus adapts animals and plants for his own benefit or
pleasure. He may do this methodically, or he may do it
unconsciously by preserving the individuals most useful or
pleasing to him without any intention of altering the breed.
It is certain that he can largely influence the character of a
breed by selecting, in each successive generation, individual
differences so slight as to be inappreciable except by an edu-
cated eye. This unconscious process of selection has been
the great agency in the formation of the most distinct and
useful domestic breeds. That many breeds produced by man
have to a large extent the character of natural species, is
shown by the inextricable doubts whether many of them are
varieties or aboriginally distinct species.
There is no reason why the principles which have acted so
efficiently under domestication should not have acted under
nature. In the survival of favoured individuals and races,
during the constantly-recurrent Struggle for Existence, we
see a powerful and ever-acting form of Selection. The
sirug^le for existence inevitably follows from the high geo-
metrical ratio of increase which is common to all organic
beings. This high rate of increase is proved by calculation, —
by the rapid increase of many animals and plants during a
succession of peculiar seasons, and when naturalised in new
countries. More individuals are bom than can possibly sur-
vive. A grain in the balance may determine which indi-
viduals shall live and which shall die, — ^which variety or
species shall increase in number, and which shall decrease,
or finally become extinct. As the individuals of the same
species come in all respects into the closest competition with
each other, the struggle will generally be most severe between
them; it will be almost equally severe between the varieties
of the same species, and next in severity between the species
of the same genus. On the other hand the struggle will often
be severe between beings remote in the scale of nature. The
slightest advantage in certain individuals, at any age or dur-
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506 ORIGIN OF SPECIES
ing any season, over those with which they come into com-
petition, or better adaptation in however slight a degree to
the surrounding physical conditions, will, in the long run,
turn the balance.
With animals having separated sexes, there will be in most
cases a struggle between the males for the possession of the
females. The most vigorous males, or those which have most
successfully struggled with their conditions of life, will gen-
erally leave most progeny. But success will often depend on
the males having special weapons, or means of defence, or
charms; and a slight advantage will lead to victory.
As geology plainly proclaims that each land has undergone
great physical changes, we might have expected to find that
organic beings have varied under nature, in the same way as
they have varied under domestication. And if there has been
any variability under nature, it would be an unaccountable
fact if natural selection had not come into play. It has often
been asserted, but the assertion is incapable of proof, that the
amount of variation under nature is a strictly limited quan-
tity. Man, though acting on external characters alone and
often capriciously, can produce within a short period a great
result by adding up mere individual differences in his domes-
tic productions; and every one admits that species present
individual differences. But, besides such differences, all nat-
uralists admit that natural varieties exist, which are consid-
ered sufficiently distinct to be worthy of record in systematic
works. No one has drawn any clear distinction between in-
dividual differences and slight varieties; or between more
plainly marked varieties and sub-species, and species. On
separate continents, and on different parts of the same con-
tinent when divided by barriers of any kind, and on outlying
islands, what a multitude of forms exist, which some experi-
enced naturalists rank as varieties, others as geographical
races or sub-species, and others as distinct, though closely
allied species 1
If then, animals and plants do vary, let it be ever so slightly
or slowly, why should not variations or individual differences,
which are in any way beneficial, be preserved and accumu-
lated through natural selection, or the survival of the fittest?
If man can by patience select variations useful to him, why,
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RECAPITULATION AND CONCLUSION 509
under changing and complex conditions of life, should not
variations useful to nature's living products often arise, and
be preserved or selected? What limit can be put to this power,
acting during long ages and rigidly scrutinising the whole
constitution, structure, and habits of each creature, — favour-
ing the good and rejecting the bad? I can see no limit to
this power, in slowly and beautifully adapting each form to
the most complex relations of life. The theory of natural
selection, even if we look no farther than this, seems to be
in the highest degree probable. I have already recapitulated,
as fairly as I could, the opposed difficulties and objections:
now let us turn to the special facts and arguments in favour
of the theory.
On the view that species are only strongly marked and
permanent varieties, and that each species first existed as a
variety, we can see why it is that no line of demarcation can
be drawn between species, commonly supposed to have been
produced by special acts of creation, and varieties which are
acknowledged to have been produced by secondary laws. On
this same view we can understand how it is that in a region
where many species of a genus have been produced, and
where they now flourish, these same species should present
many varieties; for where the manufactory of species has
been active, we might expect, as a general rule, to find it still
in action ; and this is the case if varieties be incipient species.
Moreover, the species of the larger genera, which afford the
greater number of varieties or incipient species, retain to a
certain degree the character of varieties ; for they differ from
each other by a less amount of difference than do the species
of smaller genera. The closely allied species also of the
larger genera apparently have restricted ranges, and in their
affinities they are clustered in little groups round other
species — in both respects resembling varieties. These are
strange relations on the view that each species was inde-
pendently created, but are intelligible if each existed first as
a variety.
As each species tends by its geometrical rate of reproduc-
tion to increase inordinately in number; and as the modified
descendants of each species will be enabled to increase by as
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510 ORIGIN OF SPECIES
much as they become more diversified in habits and structure,
so as to be able to seize on many and widely different places
in the economy of nature, there will be a constant tendency
in natural selection to preserve the most divergent offspring
of any one species. Hence, during a long-continued course
of modification, the slight differences characteristic of varie-
ties of the same species, tend to be augmented into the greater
differences characteristic of the species of the same genus.
New and improved varieties will inevitably supplant and ex-
terminate the older, less improved, and intermediate vari-
eties; and thus species are rendered to a large extent defined
and distinct objects. Dominant species belonging to the
larger groups within each class tend to give birth to new and
dominant forms; so that each large group tends to become
still larger, and at the same time more divergent in char-
acter. But as all groups cannot thus go on increasing in
size, for the world would not hold them, the more dominant
groups beat the less dominant. This tendency in the large
groups to go on increasing in size and diverging in character,
together with the inevitable contingency of much extinction,
explains the arrangement of all the forms of life in groups
subordinate to groups, all within a few great classes, which
has prevailed throughout all time. This grand fact of the
grouping of all organic beings under what is called the Nat-
ural System, is utterly inexplicable on the theory of creation.
As natural selection acts solely by accumulating slight,
successive, favourable variations, it can produce no great or
sudden modifications ; it can act only by short and slow steps.
Hence, the canon of "Natura non facit saltum," which every
fresh addition to our knowledge tends to confirm, is on this
theory intelligible. We can see why throughout nature the
same general end is gained by an almost infinite diversity of
means, for every peculiarity when once acquired is long in-
herited, and structures already modified in many different
ways have to be adapted for the same general purpose. We
can, in short, see why nature is prodigal in variety, though
niggard in innovation. But why this should be a law of
nature if each species has been independently created no man
can explain.
Many other facts are, as it seems to me, explicable on
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RECAPITULATION AND CONCLUSION 511
this theory. How strange it is that a bird, under the form
of a woodpecker, should prey on insects on the ground; that
upland geese which rarely or never swim, should possess
webbed feet; that a thrush-like bird should dive and feed
on sub-aquatic insects; and that a petrel should have the
habits and structure fitting it for the life of an auk 1 and so
in endless other cases. But on the view of each species
constantly trying to increase in number, with natural selec-
tion always ready to adapt the slowly varying descendants of
each to any unoccupied or ill-occupied place in nature, these
facts cease to be strange, or might even have been antici-
pated.
We can to a certain extent understand how it is that there
is so much beauty throughout nature ; for this may be largely
attributed to the agency of selection. That beauty, accord-
ing to our sense of it^ is not universal, must be admitted by
every one who will look at some venomous snakes, at some
fishes, and at certain hideous bats with a distorted resem-
blance to the human face. Sexual selection has given the
most brilliant colours, elegant patterns, and other ornaments
to the males, and sometimes to both sexes of many birds,
butterflies, and other animals. With birds it has often ren-
dered the voice of the male musical to the female, as well as
to our ears. Flowers and fruit have been rendered con-
spicuous by brilliant colours in contrast with the green foli-
age, in order that the flowers may be easily seen, visited,
and fertilised by insects, and the seeds disseminated by birds.
How it comes that certain colours, sounds, and forms should
give pleasure to man and the lower animals, — that is, how
the sense of beauty in its simplest form was first acquired, —
we do not know any more than how certain odours and
flavours were first rendered agreeable.
As natural selection acts by competition, it adapts and
improves the inhabitants of each country only in relation to
their co-inhabitants; so that we need feel no surprise at the
species of any one country, although on the ordinary view
supposed to have been created and specially adapted for that
country, being beaten and supplanted by the naturalised pro-
ductions from another land. Nor ought we to marvel if all
the contrivances in nature be not, as far as we can judge.
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512 ORIGIN OF SPECIES
absolutely perfect, as in the case even of the human eye ; or
if some of them be abhorrent to our ideas of fitness. We
need not marvel at the sting of the bee, when used against
an enemy, causing the bee's own death; at drones being
produced in such great numbers for one single act, and being
then slaughtered by their sterile sisters; at the astonishing
waste of pollen by our fir-trees; at the instinctive hatred of
the queen-bee for her own fertile daughters; at ichneumon-
idae feeding within the living bodies of caterpillars; or at
other such cases. The wonder indeed is, on the theory of
natural selection, that more cases of the want of absolute
perfection have not been detected.
The complex and little known laws governing the produc-
tion of varieties are the same, as far as we can judge, with
the laws which have governed the production of distinct
species. In both cases physical conditions seem to have pro-
duced some direct and definite effect, but how much we can-
not say. Thus, when varieties enter any new station, they
occasionally assume some of the characters proper to the
species of that station. With both varieties and species, use
and disuse seem to have produced a considerable effect; for
it is impossible to resist this conclusion when we look, for
instance, at the logger-headed duck, which has wings in-
capable of flight, in nearly the same condition as in the do-
mestic duck; or when we look at the burrowing tucu-tucu,
which is occasionally blind, and then at certain moles, which
are habitually blind and have their eyes covered with skin;
or when we look at the blind animals inhabiting the dark
caves of America and Europe. With varieties and species,
correlated variation seems to have played an important part,
so that when one part has been modified other parts have
been necessarily modified. With both varieties and species,
reversions to long-lost characters occasionally occur. How
inexplicable on the theory of creation is the occasional ap-
pearance of stripes on the shoulders and legs of the several
species of the horse-genus and of their hybrids I How simply
is this fact explained if we believe that these species are all
descended from a striped progenitor, in the same manner as
the several domestic breeds of the pigeon are descended
from the blue and barred rock-pigeon !
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RECAPITULATION AND CONCLUSION 513
On the ordinary view of each species having been inde-
pendently created, why should specific characters, or those
by which the species of the same genus differ from each
other, be more variable than generic characters in which
they all agree? Why, for instance, should the colour of a
flower be more likely to vary in any one species of a genus,
if the other species possess differently coloured flowers, than
if all possessed the same coloured flowers? If species are
only well-marked varieties, of which the characters have be-
come in a high degree permanent, we can understand this
fact; for they have already varied since they branched off
from a common progenitor in certain characters, by which
they have comt to be specifically distinct from each other;
therefore these same characters would be more likely again
to vary than the generic characters which have been in-
herited without change for an immense period. It is inex-
plicable on the theory of creation why a part developed in a
very unusual manner in one species alone of a genus, and
therefore, as we may naturally infer, of great importance to
that species, should be eminently liable to variation; but, on
our view, this part has undergone, since the several species
branched off from a common progenitor, an unusual amount
of variability and modification, and therefore we might ex-
pect the part generally to be still variable. But a part may
be developed in the most unusual manner, like the wing of a
bat, and yet not be more variable than any other structure,
if the part be common to many subordinate forms, that is, if
it has been inherited for a very long period ; for in this case
it will have been rendered constant by long-continued natural
selection.
Glancing at instincts, marvellous as some are, they offer
no greater difficulty than do corporeal structures on the
theory of the natural selection of successive, slight, but
profitable modifications. We can thus understand why nature
moves by graduated steps in endowing different animals of
the same class with their several instincts. I have attempted
to show how much light the principle of gradation throws
on the admirable architectural powers of the hive-bee. Habit
no doubt often comes into play in modifying instincts; but
it certainly is not indispensable, as we see in the case of
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514 ORIGIN OF SPECIES
neuter insects, which leave no progeny to inherit the effects
of long-continued habit. On the view of all the species of
the same genus having descended from a common parent,
and having inherited much in common, we can understand
how it is that allied species, when placed under widely dif-
ferent conditions of life, yet follow nearly the same in-
stincts; why the thrushes of tropical and temperate South
America, for instance, line their nests with mud like our
British species. On the view of instincts having been slowly
acquired through natural selection, we need not marvel at
some instincts being not perfect and liable to mistakes, and
at many instincts causing other animals to suffer.
If species be only well-marked and permanent varieties,
we can at once see why their crossed offspring should follow
the same complex laws in their degrees and kinds of resem-
blance to their parents, — in being absorbed into each other
by successive crosses, and in other such points, — as do the
crossed offspring of acknowledged varieties. This similarity
would be a strange fact, if species had been independently
created and varieties had been produced through secondary
laws.
If we admit that the geological record is imperfect to an
extreme degree, then the facts, which the record does give,
strongly support the theory of descent with modification.
New species have come on the stage slowly and at succes-
sive intervals; and the amount of change, after equal inter-
vals of time, is widely different in different groups. The
extinction of species and of whole groups of species, which
has played so conspicuous a part in the history of the organic
world, almost inevitably follows from the principle of nat-
ural selection; for old forms are supplanted by new and
improved forms. Neither single species nor groups of
species reappear when the chain of ordinary generation is
once broken. The gradual diffusion of dominant forms, with
the slow modification of their descendants, causes the forms
of life, after long intervals of time, to appear as if they had
changed simultaneously throughout the world. The fact of
the fossil remains of each formation being in some degree
intermediate in character between the fossils in the forma-
tions above and below, is simply explained by their inter-
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RECAPITULATION AND CONCLUSION 515
mediate position in the chain of descent The grand fact
that all extinct beings can be classed with all recent beings,
naturally follows from the living and the extinct being the
offspring of common parents. As species have generally
diverged in character during their long course of descent
and modification, we can understand why it is that the more
ancient forms, or early progenitors of each group, so often
occupy a position in some degree intermediate between ex-
isting groups. Recent forms are generally looked upon as
being, on the whole, higher in the scale of organisation than
ancient forms; and they must be higher, in so far as the
later and more improved forms have conquered the older and
less improved forms in the struggle for life; they have also
generally had their organs more specialised for different
functions. This fact is perfectly compatible with numerous
beings still retaining simple and but little improved struc-
tures, fitted for simple conditions of life; it is likewise com-
patible with some forms having retrograded in organisation,
by having become at each stage of descent better fitted for
new and degraded habits of life. Lastly, the wonderful law
of the long endurance of allied forms on the same conti-
nent,— of marsupials in Australia, of edentata in America,
and other such cases, is intelligible, for within the same coun-
try the existing and the extinct will be closely allied by
descent.
Looking to geographical distribution, if we admit that
there has been during the long course of ages much migra-
tion from one part of the world to another, owing to former
climatal and geographical changes and to the many occa-
sional and unknown means of dispersal, then we can under-
stand, on the theory of descent with modification, most of
the great leading facts in Distribution. We can see why
there should be so striking a parallelism in the distribution
of organic beings throughout space, and in their geological
succession throughout time; for in both cases the beings
have been connected by the bond of ordinary generation, and
the means of modification have been the same. We see the
full meaning of the wonderful fact, which has struck every
traveller, namely, that on the same continent, under the most
diverse conditions, under heat and cold, on mountain and
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516 ORIGIN OP SPECIES
lowland, on deserts and marshes, most of the inhabitants
within each great class are plainly related; for they are the
descendants of the same progenitors and early colonists.
On this same principle of former migration, combined in
most cases with modification, we can understand, by the aid
of the Glacial period, the identity of some few plants, and
the close alliance of many others, on the most distant moun-
tains, and in the northern and southern temperate zones;
and likewise the close alliance of some of the inhabitants
of the sea in the northern and southern temperate latitudes,
though separated by the whole intertropical ocean. Al-
though two countries may present physical conditions as
closely similar as the same species ever require, we need feel
no surprise at their inhabitants being widely different, if
they have been for a long period completely sundered from
each other; for as the relation of organism to organism is
the most important of all relations, and as the two countries
will have received colonists at various periods and in differ-
ent proportions, from some other country or from each other,
the course of modification in the two areas will inevitably
have been different.
On this view of migration, with subsequent modification, we
see why oceanic islands are inhabited by only few species,
but of these, why many are peculiar or endemic forms. We
clearly see why species belonging to those groups of animals
which cannot cross wide spaces of the ocean, as frogs and
terrestrial mammals, do not inhabit oceanic islands; and
why, on the other hand, new and peculiar species of bats,
animals which can traverse the ocean, are often found on
islands far distant from any continent. Such cases as the
presence of peculiar species of bats on oceanic islands and
the absence of all other terrestrial mammals, are facts utterly
inexplicable on the theory of independent acts of creation.
The existence of closely allied or representative species
in any two areas, implies, on the theory of descent with modi-
fication, that the same parent-forms formerly inhabited both
areas: and we almost invariably find that wherever many
closely allied species inhabit two areas, some identical
species are still common to both. Wherever many closely
allied yet distinct species occur, doubtful forms and vari-
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RECAPITULAHON and conclusion 517
eties belonging to the same groups likewise occur. It is a
rule of high generality that the inhabitants of each area are
related to the inhabitants of the nearest source whence im-
migrants might have derived. We see this in the striking
relation of nearly all the plants and animals of the Gala-
pagos archipelago, of Juan Fernandez, and of the other
American islands, to the plants and animals of the neigh-
bouring American mainland; and of those of the Cape de
Verde archipelago, and of the other African islands to the
African mainland. It must be admitted that these facts
receive no explanation on the theory of creation.
The fact, as we have seen, that all past and present or-
ganic beings can be arranged within a few great classes, in
groups subordinate to groups, and with the extinct groups
often falling in between the recent groups, is intelligible on
the theory of natural selection with its contingencies of ex-
tinction and divergence of character. On these same prin-
ciples we see how it is, that the mutual affinities of the forms
within each class are so complex and circuitous. We see
why certain characters are far more serviceable than others
for classification ; — why adaptive characters, though of para-
mount importance to the beings, are of hardly any impor-
tance in classification; why characters derived from rudi-
mentary parts, though of nx> service to the beings, are often
of high classificatory value; and why embryological charac-
ters are often the most valuable of all. The real affinities
of all organic beings, in contradistinction to their adaptive
resemblances, are due to inheritance or community of de-
scent. The Natural System is a genealogical arrangement,
with the acquired grades of difference, marked by the terms,
varieties, species, genera, families, &c. ; and we have to dis-
cover the lines of descent by the most permanent characters
whatever they may be and of however slight vital impor-
tance.
The similar framework of bones in the hand of a man,
wing of a bat, fin of a porpoise, and leg of the horse, — the
same number of vertebrae forming the neck of the giraffe
and of the elephant, — ^and innumerable other such facts* at
once explain themselves on the theory of descent with slow
and slight successive modifications. The similarity of pat-
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518 ORIGIN OF SPECIES
tern in the wing and in the leg of a bat, though used for
such different purpose, — in the jaws and legs of a crab, —
in the petals, stamens, and pistils of a flower, is likewise, to
a large extent, intelligible on the view of the gradual modi-
fication of parts or organs, which were aboriginally alike in
an early progenitor in each of these classes. On the prin-
ciple of successive variations not always supervening at an
early age, and being inherited at a corresponding not early
period of life, we clearly see why the embryos of mammals,
birds, reptiles, and fishes should be so closely similar, and so
unlike the adult forms. We may cease marvelling at the
embryo of an air-breathing mammal or bird having branchial
slits and arteries running in loops, like those of a fish which
has to breathe the air dissolved in water by the aid of well-
developed branchiae.
Disuse,* aided sometimes by natural selection, will often
have reduced organs when rendered useless under changed
habits or conditions of life; and we can understand on this
view the meaning of rudimentary organs. But disuse and
selection will generally act on each creature, when it has
come to maturity and has to play its full part in the struggle
for existence, and will thus have little power on an organ
during early life; hence the organ will not be reduced or
rendered rudimentary at this early age. The calf, for in-
stance, has inherited teeth, which never cut through the
gums of the upper jaw, from an early progenitor having well-
developed teeth; and we may believe, that the teeth in the
mature animal were formerly reduced by disuse, owing to
the tongue and palate, or lips, having become excellently
fitted through natural selection to browse without their aid;
whereas in the calf, the teeth have been left unaffected, and
on the principle of inheritance at corresponding ages have
been inherited from a remote period to the present day. On
the view of each organism with all its separate parts having
been specially created, how utterly inexplicable is it that
organs bearing the plain stamp of inutility, such as the teeth
in the embryonic calf or the shrivelled wings under the sol-
dered wing-covers of many beetles, should so frequently
occur. Nature may be said to have taken pains to reveal
her scheme of modification, by means of rudimentary organs.
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RECAPITULATION AND CONCLUSION 519
of embryolog^cal and homologous structures, but we are too
blind to understand her meaning.
I have now recapitulated the facts and considerations
which have thoroughly convinced me that species have been
modified, during a long course of descent. This has been
effected chiefly through the natural selection of numerous
successive, slight, favourable variations; aided in an im-
portant manner by the inherited effects of the use and dis-
use of parts ; and in an unimportant manner, that is in rela-
tion to adaptive structures, whether past or present, by the
direct action of external conditions^ and by variations which
seem to us in our ignorance to arise spontaneously.^ It ap-
pears that I formerly underrated the frequency and value of
these latter forms of variation, as leading to permanent modi-
fications of structure independently of natural selection.
But as my conclusions have lately been much misrepre-
sented, and it has been stated that I attribute the modifica-
tion of species exclusively to natural selection, I may be per-
mitted to remark that in the first edition of this work, and
subsequently, I placed in a most conspicuous position—*
namely, at the close of the Introduction the following words :
"I am convinced that natural selection has been the main
but not the exclusive means of modification." This has been
of no avail. Great is the power of steady misrepresenta-
tion; but the history of science shows that fortunately this
power does not long endure.
It can hardly be supposed that a false theory would ex-
plain, in so satisfactory a manner as does the theory of nat-
ural selection, the several large classes of facts above speci-
fied. It has recently been objected that this is an unsafe
method of arguing; but it is a method used in judging of
the common events of life, and has often been used by the
greatest natural philosophers. The undulatory theory of
light has thus been arrived at ; and the belief in the revolu-
tion of the earth on its own axis was until lately supported
by hardly any direct evidence. It is no valid objection that
science as yet throws no light on the far higher problem of
the essence or origin of life. Who can explain what is the
essence of the attraction of gravity? No one now objects
to following out the results consequent on this unknown
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S20 ORIGIN OP SPECIES
element of attraction; notwithstanding that Leibnitz for-
merly accused Newton of introducing "occult qualities and
miracles into philosophy/'
I see no good reason why the views given in this volume
should shock the religious feelings of any one. It is satis-
factory, as showing how transient such impressions are, to
remember that the greatest discovery ever made by man,
namely, the law of the attraction of gravity, was also at-
tacked by Leibnitz, "as subversive of natural, and inferen-
tially of revealed, religion." A celebrated author and divine
has written to me that "he has gradually learnt to see that
it is just as noble a conception of the Deity to believe that
He created a few original forms capable of self-develop-
ment into other and needful forms, as to believe that He
required a fresh act of creation to supply the voids caused
by the action of His laws."
Why, it may be asked, tmtil recently did nearly all the
most eminent living naturalists and geologists disbelieve in
.the mutability of species. It cannot be asserted that organic
beings in a state of nature are subject to no variation; it
cannot be proved that the amount of variation in the course
of long ages is a limited quantity; no clear distinction has
been, or can be, drawn between species and well-marked
varieties. It cannot be maintained that species when inter-
crossed are invariably sterile, and varieties invariably
fertile; or that sterility is a special endowment and sign of
creation. The belief that species were immutable produc-
tions was almost unavoidable as long as the history of the
world was thought to be of short duration ; and now that we
have acquired some idea of the lapse of time, we are too apt
to assume, without proof, that the geological record is so
perfect that it would have afforded us plain evidence of the
mutation of species, if they had undergone mutation.
But the chief cause of our natural unwillingness to admit
that one species has given birth to other and distinct species,
is that we are always slow in admitting great changes of
which we do not see the steps. The difficulty is the same as
that felt by so many geologists, when Lyell first insisted that
long lines of inland cliffs had been formed, and great valleys
excavated, by the agencies which we see still at work. The
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RECAPITULATION AND CONCLUSION 521
mind cannot possibly grasp the full meaning of the term of
even a million years; it cannot add up and perceive the full
effects of many slight variations, accumulated during an
almost infinite number of generations.
Although I am fully convinced of the truth of the views
given in this volume under the form of an abstract, I by no
means expect to convince experienced naturalists whose
minds are stocked with a multitude of facts all viewed,
during a long course of years, from a point of view directly
opposite to mine. It is so easy to hide our ignorance under
such expressions as the "plan of creation," "unity of design,"
&c., and to think that we give an explanation when we only
re-state a fact. Any one whose disposition leads him to
attach more weight to unexplained difficulties than to the
explanation of a certain number of facts will certainly reject
the theory. A few naturalists, endowed with much flexibility
of mind, and who have already begun to doubt the immu-
tability of species, may be influenced by this volume; but I
look with confidence to the future^ — to young and rising
naturalists, who will be able to view both sides of the ques-
tion with impartiality. Whoever is led to believe that species
are mutable will do good service by conscientiously express-
ing his conviction; for thus only can the load of prejudice by
which this subject is overwhelmed be removed.
Several eminent naturalists have of late published their be«
lief that a multitude of reputed species in each genus are
not real species; but that other species are real, that is, have
been independently created. This seems to me a strange con*
elusion to arrive at. They admit that a multitude of forms,
which till lately they themselves thought were special crea-
tions, and which are still thus looked at by the majority of
naturalists, and which consequently have all the external
characteristic features of true species, — they admit that these
have been produced by variation, but they refuse to extend
the same view to other and slightly different forms. Never-
theless they do not pretend that they can define, or even con-
jecture, which are the created forms of life, and which are
those produced by secondary laws. They admit variation as
a vera causa in one case, they arbitrarily reject it in another,
without assigning any distinction in the two cases. The day
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522 ORIGIN OF SPECIES
will come when this will be given as a curious illustration of
the blindness of preconceived opinion. These authors seem
no more startled at a miraculous act of creation than at an
ordinary birth. But do they really believe that at innu-
merable periods in the earth's history certain elemental atoms
have been commanded suddenly to flash into living tissues?
Do they believe that at each supposed act of creation one
individual or many were produced? Were all the infinitely
numerous kinds of animals and plants created as eggs or
seed, or as full grown? and in the case of mammals, were
they created bearing the false marks of nourishment from
the mother's womb? Undoubtedly some of these same ques-
tions cannot be answered by those who believe in the appear*
ance or creation of only a few forms of life, or of some
one form alone. It has been maintained by several authors
that it is as easy to believe in the creation of a million beings
as of one; but Maupertuis' philosophical axiom ''of least
action" leads the mind more willingly to admit the smaller
number; and certainly we ought not to believe that innu-
merable beings within each great class have been created
with plain, but deceptive, marks of descent from a single
parent.
As a record of a former state of things, I have retained in
the foregoing paragraphs, and elsewhere, several sentences
which imply that naturalists believe in the separate creation
of each species; and I have been much censured for having
thus expressed myself. But undoubtedly this was the general
belief when the first edition of the present work appeared.
I formerly spoke to very many naturalists on the subject of
evolution, and never once met with any sympathetic agree-
ment. It 19 probable that some did then believe in evolution,
but they were either silent, or expressed themselves so am-
biguously that it was> not easy to understand their meaning.
Now things are wholly changed, and almost every naturalist
admits the great principle of evolution. There are, however,
some who still think that species have suddenly given birth,
through quite unexplained means, to new and totally differ-
ent forms: but, as I have attempted to show, weighty evi-
dence can be opposed to the admission of great and abrupt
modifications. Under a scientific point of view, and as lead-
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RECAPITULATION AND CONCLUSION 523
ing to further investigation, but little advantage is gained
by believing that new forms are suddenly developed in an
inexplicable manner from old and widely different forms,
over the old belief in the creation of species from the dust of
the earth.
It may be asked how far I extend the doctrine of the modi-
fication of species. The question is difficult to answer, be-
cause the more distinct the forms are which we consider, by
so much the arguments in favour of community of descent
become fewer in number and less in force. But some
arguments of the greatest weight extend very far. All
tjie members of whole classes are connected together by
a chain of affinities, and all can be classed on the same
principle, in groups subordinate to groups. Fossil remains
sometimes tend to fill up very wide intervals between exist-
ing orders.
Organs in a rudimentary condition plainly show that an
early progenitor had the organ in a fully developed condi-
tion; and this in some cases implies an enormous amount of
modification in the descendants. Throughout whole classes
various structures are formed on the same pattern^ and at a
very early age the embryos closely resemble each other.
Therefore I cannot doubt that the theory of descent with
modification embraces all the members of the same great
class or kingdom. I believe that animals are descended from
at most only four or five progenitors, and plants from an
equal or lesser number.
Analogy would lead me one step farther, namely, to the
belief that all animals and plants are descended from some
one prototype. But analogy may be a deceitful guide. Never-
theless all living things have much in . common, in their
chemical composition, their cellular structure, their laws of
growth, and their liability to injurious influences. We see
this even in so trifling a fact as that the same poison often
similarly affects plants and animals; or that the poison se-
creted by the gall-fly produces monstrous growths on the
wild rose or oak-tree. With all organic beings, excepting
perhaps some of the very lowest, sexual reproduction seems
to be essentially similar. With all, as far as is at present
known, the germinal vesicle is the same ; so that all organisms
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524 ORIGIN OF SPECIES
start from a common origin. If we look even to the two
main divisions — ^namely, to the animal and vegetable king-
doms— certain low forms are so far intermediate in character
that naturalists have disputed to which kingdom they should
be referred. As Professor Asa Gray has remarked; "the
spores and other reproductive bodies of many of the lower
algae may claim to have first a characteristically animal,
and then an unequivocal vegetable existence." Therefore,
on the principle of natural selection with divergence of char*
acter, it does not seem incredible that, from some such low
and intermediate form, both animals and plants may have
been developed ; and, if we admit this, we must likewise a<J-
mit that all the organic beings which have ever lived on this
earth may be descended from some one primordial form.
But this inference is chiefly grounded on analogy, and it is
immaterial whether or not it be accepted. No doubt it is
possible, as Mr. G. H. Lewes has urged, that at the first
commencement of life many different forms were evolved;
but if so, we may conclude that only a very few have left
modified descendants. For, as I have recently remarked in
regard to the members of each great kingdom, such as the
Vertebrata, Articulata, &c., we have distinct evidence in
their embryological, homologous, and rudimentary structures,
that within each kingdom all the members are descended
from a single progenitor.
When the views advanced by me in this volume, and by
Mr. Wallace, or when analogous views on the origin of spe-
cies are generally admitted, we can dimly foresee that there
will be a considerable revolution in natural history. Sys-
tematists will be able to pursue their labours as at present ;
but they will not be incessantly haunted by the shadowy
doubt whether this or that form be a true species. This, I
feel sure and I speak after experience, will be no slight re-
lief. The endless disputes whether or not some fifty species
of British brambles are good species will cease. Systematists
will have only to decide (not that this will be easy) whether
any form be sufiiciently constant and distinct from other
forms, to be capable of definition; and if definable, whether
the differences be sufficiently important to deserve a specific
name. This latter point will become a far more essential
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RECAPITULATION AND CONCLUSION 525
consideration than it is at present; for differences, however
slight, between any two forms, if not blended by interme-
diate gradations, are looked at by most naturalists as suffi-
cient to raise both forms to the rank of species.
Hereafter we shall be compelled to acknowledge that the
only distinction between species and well-marked varieties is,
that the latter are known, or believed^ to be connected at the
present day by intermediate gradations whereas species were
formerly thus connected. Hence, without rejecting the con-
sideration of the present existence of intermediate grada-
tions between any two forms, we shall be led to weigh more
carefully and to value higher the actual amount of difference
between them. It is quite possible that forms now generally
acknowledged to be merely varieties may hereafter be
thought worthy of specific names; and in this case scientific
and common language will come into accordance. In short,
we shall have to treat species in the same manner as those
naturalists treat genera, who admit that genera are merely
artificial combinations made for convenience. This may not
be a cheering prospect; but we shall at least be freed from
the vain search for the undiscovered and undiscoverable
essence of the term species.
The other and more general departments of natural history
will rise greatly in interest The terms used by naturalists,
of affinity, relationship, community of type, paternity, mor-
phology, adaptive characters, rudimentary and aborted
organs, &c, will cease to be metaphorical, and will have a
plain signification. When we no longer look at an organic
being as a savage looks at a ship, as something wholly be-
yond his comprehension; when we regard every production
of nature as one which has had a long history; when we
contemplate every complex structure and instinct as the
summing up of many contrivances, each useful to the pos-
sessor, in the same way as any great mechanical invention
is the summing up of the labour, the experience, the reason,
and even the blunders of numerous workmen; when we
thus view each organic being, how far more interesting — I
speak from experience — does the study of natural history
become !
A grand and almost untrodden field of inquiry will be
QG— HC zi
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S26 ORIGIN OF SPECIES
opened, on the causes and laws of variation, on correlation,
on the effects' of use and disuse, on the direct action of ex-
ternal conditions, and so forth. The study of domestic pro-
ductions will rise immensely in value. A new variety raised
by man will be a more important and interesting subject for
study than one more species added to the infinitude of already
recorded species. Our classifications will come to be, as far
as they can be so made, genealogies ; and will then truly give
what may be called the plan of creation. The rules for
classifying will no doubt become simpler when we have a
definite object in view. We possess no pedigrees or armorial
bearings; and we have to discover and trace the many di-
verging lines of descent in our natural genealogies, by char-
acters of any kind which have long been inherited. Rudi-
mentary organs will speak infallibly with respect to the
nature of long-lost structures. Species and groups of species
which are called aberrant, and which may fancifully be
called living fossils, will aid us in forming a picture of the
ancient forms of life. Embryology will often reveal to us
the structure, in some degree obscured, of the prototypes of
each great class.
When we can feel assured that all the individuals of the
same species, and all the closely allied species of most genera,
have within a not very remote period descended from one
parent, and have migrated from some one birth-place; and
when we better know the many means of migration, then, by
the light which geology now throws, and will continue to
throw, on former changes of climate and of the level of the
land, we shall surely be enabled to trace in an admirable
manner the former migrations of the inhabitants of the whole
world. Even at present, by comparing the differences be-
tween the inhabitants of the sea on the opposite sides of a
continent, and the nature of the various inhabitants on that
continent in relation to their apparent means of immigration,
some light can be thrown on ancient geography.
The noble science of Geology loses glory from the extreme
imperfection of the record. The crust of the earth with its
imbedded remains must not be looked at as a well-filled
museum, but as a poor collection made at hazard and at rare
intervals. The accumulation of each great fossiliferous far-
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RECAPITULATION AND CONCLUSION 527
mation will be recognised as having depended on an unusual
concurrence of favourable circumstances, and the blank in-
tervals between the successive stages as having been of vast
duration. But we shall be able to gauge with some security
the duration of these intervals by a comparison of the pre-
ceding and succeeding organic forms. We must be cautious
in attempting to correlate as strictly contemporaneous two
formations, which do not include many identical species, by
the general succession of the forms of life. As species are
produced and exterminated by slowly acting and still exist-
ing causes, and not by miraculous acts of creation; and as
the most important of all causes of organic change is one
which is almost independent of altered and perhaps sud-
denly altered physical conditions, namely, the mutual rela-
tion of organism to organism, — ^the improvement of one
organism entailing the improvement or the extermination
of others; it follows, that the amount of organic change in
the fossils of consecutive formations probably serves as a
fair measure of the relative, though not actual lapse of
time. A number of species, however, keeping in a body
might remain for a long period unchanged, whilst within
the same period, several of these species by migrating into
new countries and coming into competition with foreign
associates, might become modified; so that we must not
overrate the accuracy of organic change as a measure of
time.
In the future I see open fields for far more important re-
searches. Psychology will be securely based on ^e founda-
tion already well laid by Mr. Herbert Spencer, that of the
necessary acquirement of each mental power and capacity by
gradation. Much light will be thrown on the origin of man
and his history.
Authors of the highest eminence seem to be fully satisfied
with the view that each species has been independently cre-
ated To my mind it accords better with what we know of
the laws impressed on matter by the Creator, that the pro-
duction and extinction of the past and present inhabitants
of the world should have been due to secondary causes, like
those determining the birth and death of the individual.
When I view all beings not as special creations, but as the
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528 ORIGIN OF SPECIES
lineal descendants of some few beings which lived long be-
fore the first bed of the Cambrian system was deposited,
they seem to me to become ennobled. Judging from the past,
we may safely infer that not one living species will transmit
its unaltered likeness to a distant futurity. And of the
species now living very few will transmit progeny of any
kind to a far distant futurity; for the manner in which all
organic beings are grouped, shows that the greater number
of species in each genus, and all the species in many genera,
have left no descendants, but have become utterly extinct.
We can so far take a prophetic glance into futurity as to
foretell that it will be the common and widely-spread species,
belonging to the larger and dominant groups within each
class, which will ultimately prevail and procreate new and
dominant species. As all the living forms of life are the
lineal descendants of those which lived long before the Cam-
brian epoch, we may feel certain that the ordinary succes-
sion by generation has never once been broken, and that no
cataclysm has desolated the whole world. Hence we may
look with some confidence to a secure future of great length.
And as natural selection works solely by and for the good
of each being, all corporeal and mentsd endowments will tend
to progress towards perfection.
It is interesting to contemplate a tangled bank, clothed
with many plants of many kinds, with birds singing on the
bushes, with various insects flitting about, and with worms
crawling through the damp earth, and to reflect that these
elaborately constructed forms, so different from each other,
and dependent upon each other in so complex a manner, have
all been produced by laws acting around us. These laws,
taken in the largest sense, being Growth with Reproduction;
Inheritance which is almost implied by reproduction ; Varia-
bility from the indirect and direct action of the conditions of
life, and from use and disuse: a Ratio of Increase so high as
to lead to a Struggle for Life, and as a consequence to
Natural Selection, entailing Divergence of Character and the
Extinction of less-improved forms. Thus, from the war of
nature, from famine and death, the most exalted object
which we are capable of conceiving, namely, the production
of the higher animals, directly follows. There is grandeur in
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RECAPITULATION AND CONCLUSION 529
this view of life, with its several powers, having been origi-
nally breathed by the Creator into a few forms or into one ;
and that, whilst this planet has gone cycling on according
to the fixed law of gravity, from so simple a beginning end-
less forms most beautiful and most wonderful have been, and
are being evolved.
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GLOSSARY
OF THE
PRINCIPAL SCIENTIFIC TERMS USED IN THE
PRESENT VOLUME*
Ahtrrani — ^Ponns or groa^ of animali or pimnts which deviate in important
characters from their nearest allies, so as not to be easily included in
the same croup with them, are said to he aberrant.
Aberration iin Optics} — In the refraction of light by a convex lens the rays
passing through different parts of the lens are brought to a focus at
slightljr different distances — this is called spherical aberration; at the
same time the coloured rays are separated oy the prismatic action of
the lens and likewise brought to a focus at different distances — this
is chromatic aberration.
Abnormal — Contrary to the general rule.
Aborted — An organ is said to be aborted when its development has been
arrested at a very early stage.
Albinism — Albinos are animals in which the usual colouring matters char-
acteristic of the species have not been produced in the sldn and ita
appendages. Albinism is the state of being an albino.
Alg« — ^A class of plants including the ordinary sea- weeds and the filamentous
fresh-water weeds.
Alternation of Generations — ^This term is applied to a peculiar mode of
reproduction which prevails ^ among man^ of the lower animals, in
which the e^ produces a living form quite different from its parent,
but from which the parent-form is reproduced by a process of budding,
or by the division of the substance of the first product of the egg.
Ammonites — A group of fossil, spiral, chambered shells, allied to the exist-
ing pearly Nautilus, but having the partitions between the chambers
waved in complicated patterns at their junction with the outer wall
of the shell.
Analogy— fThe resemblance of structures which depends upon similarity of
function, as in the winn of insects and birds. Such structures are
said to be analogous^ and to be analogues of each other.
Animalcule — A minute animal: generally applied to those visible only by
the microscope.
Annelids — A class of worms in which the surface of the body exhibits a
more or less distinct division into rings or segments, generally pro-
vided with appendages for locomotion and with gills. It includes the
ordinary marine worms, the earthworms, and the leeches.
Antenntt — ^Jointed organs appended to the head in Insects, Crustacea, and
Centipedes, and not belonging to the mouth.
Anthers — ^The summits of the stamens of flowers, in which the pollen or
fertilizing dust is produced.
Apiacentalia, Aplacentata or Aplacental Mammals — See Mammalia.
Archetypal— -Of or belonging to the Archetype, or ideal primitive form upon
which all the beings of a group seem to be organized.
AriicuUaa—h great division of the Animal Kingdom characterized generally
by having the surface of the body divided into rings called segments,
a greater or less number of which are furnished with jointed legs
(such as Insects, Crustaceans, and Centipedes).
Asymmetrical — ^Having the two sides unlike.
Atrophied — ^Arrested in development at a very early stage.
* I am indebted to the kindness of Mr. W. S. Dallas for this Glossary,
which has been given because several readers have complained to me that
some of the terms used were unintelligible to them. Mr. Dallas has endeav-
oured to give the explanations of the terms in as popular a form as possible.
531
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532 GLOSSARY
Balanus-^hc genus including the common Acorn-shells which live in
abundance on the rocks of the sea-coast.
Batrachians — ^A class of animals allied to the Reptiles, but undergoing a
peculiar metamorphosis, in which the young animal is generallv
aquatic and breathes by gills. ^Examples, Frogs, Toads, and Newts.)
Boulders — ^Large transported blocks of stone generally embedded in clays or
gravels.
Brachiopoda — A class of marine Mollusca, or soft-bodied animals, furnished
with a bivalve shell, attached to submarine objects by a stalk which
passes through an aperture in one of the valves, and furnished with
fringed arms, by the action of which food is carried to the mouth.
BranchUt — Gills or organs for respiration in water.
Branchial — ^Pertaining to gills or oranchis.
Cambrian System — A series of very ancient Palaeozoic rocks, between the
Laurentian and the Silurian. Until recently these were regarded as
, the oldest fossiliferous rocks.
Camdir— The Dog-family, including the Dog, Wolf. Fox, Jackal, &c
Carapace — ^The shell enveloping the anterior part of the body in Crustaceans
generally: applied also to the hard shelly pieces of the Cirrij>edes.
Carboniferous — This term is applied to the great formation which includes,
among other rocks, the coal measures. It belongs to the oldest, or
Palaeozoic, system of formations.
Caudal— Oi or belonging to the tail.
Cepkalopods — The highest class of the Mollusca, or soft-bodied animals,
characterized by having the mouth surrounded by a greater or less
number of fleshy arms or tentacles, which, in most living species, are
furnished with sucking-cupa. {Examples, Cuttle-fish, Nautilus.)
Cetacea — An order of Mammalia, including the Whales, Dolphins. &c,
having the form of the body fish-like, the skin naked, and only the
forelimbs developed.
Chelonia — An order of Reptiles, including the Turtles, Tortoises, &c
Cirripedes — ^An order of Crustaceans including the Barnacles and Acorn-
shells. Their young resemble those of many other Crustaceans in
form; but when mature they are always attached to other objects,
either directly or by means of a stalk, and their bodies are enclosed
by a calcareous shell composed of several pieces, two of which can
open to give issue to a bunch of curled, jointed tentacles, which rep-
resent the limbs.
Coccus — The genus of Insects including the Cochineal. In these the male
is a minute, winged fly, and the female generally a motionless, berry-
like mass.
Cocoon — ^A case usually of silky material, in which insects are frequently
enveloped during the second or resting stage (pupa) of their existence.
The term " cocoon-sta^ e " is here used as eouivalent to " pupa-stage.'*
Calospermous — ^A term applied to those fruits ox the Umbelhferae which
have the seed hollowed on the inner face.
Coleoptera — Beetles, an order of Insects, having a biting mouth and the first
pair of wings more or less homy, forming sheaths for the second pair,
and usually meeting in a straight line down the middle of the back.
Column — ^A peculiar organ in the flowers of Orchids, in which the stamens,
style and stigma (or the reproductive parts) are united.
Compos^ or Compositous Plants — Plants in which the inflorescence con-
sists of numerous small flowers (florets) brought together into a dense
head, the base of which is enclosed by a common envelope. (Examples,
the Daisy, Dandelion, &c)
Conferwt— 'The filamentous weeds of fresh water.
Conglomerate — A rock made up of fragments of rock or pebbles, cemented
together by some other material.
Corollor-^The second envelope of a flower, usually composed of coloured,
leaf-like oreans (petals), which may be united by their edges either
in the basal part or throuffhout
Correlation^— 'Tht normal coincidence of one phenomenon, character, &c.,
with another.
Corymb — A bunch of flowers in which those sprineing from the lower part
of the flower stalk are supported on long stalks so as to be nearly on
a level with the upper ones.
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GLOSSARY 533
Cotyledons— Tht first or seed-leaves of plants.
Crustacgani — ^A class of articulated animals, having the skin of the body
senerally more or less hardened by the deposition of calcareous matter,
breathing bv means of gills. iBxampUs, Crab, Lobster, Shrimp. &c.)
CurctUi^— The old generic term for the Beetles known as Weevils, charac-
terized by their four-jointed feet, and by the head being produced into
a sort of beak, upon the sides of which the anteniue are inserted.
Cutaneous — Of or belonging to the sldn.
Degradation — ^The wearing down of land by the action of the sea or of
meteoric agencies.
Denudation — The wearing away of the surface of the land by water.
Devonian System or Formation — A series of Palaeozoic rocks, including the
Old Red Sandstone.
Dicotyledons or Dicotyledonous Plants^-^ class of plants characterized by
having two seed leaves, by the formation of new wood between the
bark and the old woodf (oxogenous growth), and by the reticulation
of the veins of the leaves. The parts of the flowers are generally in
multiples of five.
Differentiation — ^The separation, or discrimination of narts or organs which
in simpler forms of life are more or less united.
Dimorphic — Having two distinct forms. — Dimorphism is the condition of the
appearance of the same species under two dissimilar forms.
Dietcious — Having; the organs of the sexes upon distinct individuals.
Diorite — A peculiar form of Greenstone.
Dorsal — Of or belonging to the back.
Edentata — A peculiar order of Quadrupeds, characterized by the absence of
at least the middle incisor (front) teeth in both jaws. iExamples, the
Sloths and Armadillos.)
Elytra— The hardened fore-wings of Beetles, serving as sheaths for the mem-
branous hind-wings, which constitute the true organs of fli^t.
Embryo — ^The young animal undergoing development within the egg or
womb.
Embryoloffv— -The study of the development of the embryo.
£nd#fm'c^-Peculiar to a given locality.
Entomostrac»—A division of the class Crustacea, having all the segments
of the body usually distinct, gills attached to the feet or organs of
the mouth, and the feet fringed with fine hairs. They are generally
of small size.
Eocene— 'Th9 earliest of the three divisions of the Tertiary epoch of geolo-
gists. Rocks of this age contain a small proportion of shells identical
with species now living.
Ephemerous Insects — Insects allied to the May-fly.
Fauna — ^The totality of the animals naturally inhabiting a certain country
or region, or which have lived during a given geological period.
Felida^The Cat-family.
Feral — Having become wild from a state of cultivation or domestication.
Flora — ^The totalitv of the i>lants growing naturally in a country, or during
a given geological period.
Florets--e\owen imperfectlv developed in some respects, and collected into
a dense spike or head, as in the Grasses, the Dandelion. &c.
Fcetal — Of or belonging to the foetus, or embryo in course ot development.
Foraminifera — ^A class of animals of verv low organization, and generallv
of small size, bavins a jelly-like bodv, from tne surface of which deli-
cate filaments can Be given off and retracted for the prehension of
external objects, and naving a calcareous or sandy shell, usually
divided into chambers, and perforated with small apertures.
Fossiliferous — Containing fossils.
Fossorial — Having a faculty of digging. The Fossorial Hymenoptera are a
group of Wasp-like Insects, which burrow in sandy soil to make nests
tor their young.
Frenum (,pl, Frend) — A small band or fold of skin.
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534 GLOSSARY
Fungi isinp. Funffus) — A cimas of eellular plants, of which Mtuhrooms,
Toacutooli, and Moulds mre familiar examples.
FurcuUh— The forked bone formed by the union of the collar-bones in many
bards, such as the common Fowl.
GaUinaceoms Bird* — ^An order of Birds of which the common Fowl, Turkey,
and Pheasant are well-known examples.
Gallus — ^The genus of birds which includes the common Fowl.
Ganglion — A swelling or knot from which nerves are given off as from a
centre.
Ganoid Fish** — ^Fishes covered with peculiar enamelled bony scales. Most
of them are extinct.
GamUnal VeticU^A minute vesicle in the eggs of animals, from which the
development of the embryo proceeds.
Glacial Period — A period of great cold and of enormous extension of ice
upon the surface of the earth. It is believed that glacial periods have
occurred repeatedly during the geological historv of the earth, but
the term is generauj applied to the close of the Tertiary epoch, when
nearly the whole ox Europe was subjected to an arctic climate.
Gland— An organ which secretes or separates some peculiar product from
the blood or sap of animals or plants.
GlofH* — ^The opening of the windpipe mto the oesophagus or gullet.
Gneit* — A rock approaching granite in composition, but more or less lami-
nated, and really produced by the alteration of a sedimentary deposit
after its consolidation.
Grallator** — ^The so-called Wadin^-birds (Storks, Cranes, Snipes, ftc), which
are generally furnished with long legs, bare of feathers above the
heel, and have no membranes between the toes.
GroniU — ^A rock consisting essentially of crystals of felspar and mica in a
I of quartz.
Habitat — ^The locality In which a plant or animal naturally lives.
MtnUptera — ^An order or sub-order of Insects, characterized by the posses-
sion of a jointed beak or rostrum, and by having the ft>re-wings
homy in the basal portion and membranous at the extremity, where
they cross each other. This group includes the various species
Hermaphrodtt* — ^Possessing the organs of both sexes.
Homology — That relation between parts which results from their develop-
ment from corresponding embryonic parts, either in different animals,
as in the case of the arm of man, the fore-leg of a quadruped, and
the wing of a bird; or in the same individual, as in the case of the
fore and hind legs in quadrupeds, and the segments or rings and
their appendages of which the body of a worm, a centipede, ftc, is
composed. The latter is called *erial homology. The parts which
stand in such a relation to each other are said to be nomologou*,
and one such part or organ is called the homologue of the other. In
different plants the parts of the flower are homologous, and in general
these parts are regarded as homologous with leaves.
Homoptera — ^An order or sub-order of Insects having (like the Hemiptera)
a jointed beak, but in which the fore-winn are either whoUv mem-
branous or wholly leathery. The Cicada, Frog-hoppers, and Aphid**,
are wdl-known examples. . .
Hybrid— The offspring of the union of two distinct species.
Hymenoptora—An order of Insects possessing biting jaws and usually four
membranous wings in which there are a few veins. Bees and Wasps
are familiar examples of this group.
Hyp*rtrophi*d — Excessively developed.
Ichn*umonid^—A family of Hymenopterous insects, the members of which
lay their eggs in the bodies or eggs of other insecU.
Imago — ^The perfect (generally winged) reproductive state of an msect.
Ind^tn*— The aborigmal animal or vegeUble inhabitanto of a country or
region.
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GLOSSARY S85
InHorescenet — ^The mode of arrangement of the flowers of ftlanta.
Infusoria — ^A dau of microscopic Animal enles, to called from their having
originally been obaenred m infusions of vegetable matters. They con-
sist of a gelatinous material enclosed in a delicate membrane, the
whole or part of which is furnished with short vibrating hairs (called
dlia), by means of which the animalcules swim through the water or
convey the minute particles of their food to the orifice of the mouth.
InsecHvorou* — Feeding on Insects.
Inveriebrata, or Inverfebrate Animais^^Thote animals which do not possess
a baclcbone or spinal column.
Lac«M«— S|)ace8 left among the tissues in some of the lower animals, and
serving in place of vessels for the circulation of the fluids of the body.
Lamellated--FuTnlakcd with lamellc or little i>lates.
Larva ipL Larva) — The first condition of an insect at its issuing from the
egg, when it is usually in the form of a grub, caterpillar, or maggot.
Larynjr^-The upper part of the windpipe opening into the gullet.
Laurentian — A group of greatly altered and very ancient rocks, which is
greatly developed alonK the course of the St Laurence, whence the
name. It is in these that the earliest known traces of organic bodies
have been found.
Lsguminosa — An order of plants represented by the common Peas and
Beans, having an irregular flower in which one petal stands up like
a wing, and the stamens and pistil are enclosed in a sheath formed
bv two other petals. The fruit is a pod (or legume).
LemuriMt—>A group of four-handed animals, distinct from the Monkejrs
and approachmg the Insectivorous Quadrupeds in some of their char-
acters and habits. Its members have the nostrils curved or twisted,
and a claw instead of a nail upon the first finger of the hind hands.
Lepidoptera — An order of Insects, characterized by the possession of a
spiral proboscis, and of four large more or less scaly wings. It
includes the well-known Butterflies and Moths.
Littoral — Inhabiting the seashore.
Loess — ^A marly deposit of recent (Post-Tertiiry) date, wUch occupies a
great part of the valley of the Rhine.
Malaeostraca—Tht higher division of the Crustacea, including the ordlnatv
Crabs, Lobsters, Shrimps, ftc., together with the Wooduee and Sand-
hoppers.
Mammalia — ^The highest class of animals, including the ordinary hairy
quadrupeds, the Whale^ and Man, and characterised by the produc-
tion of living young which are nourished after birth by milk from
the teaU (Mamma, Mammary glands) of the mother. A striking dif-
ference in embryonic development has led to the division of this
class into two great groups, in one of these, when the embryo has
attained a certain stage, a vascular connection, called the placenta,
is formed between the embryo and the mother; in the other this is
wanting, and the young are produced in a very incomplete state.
The former, including the greater part of the class, are called
Placental mammals; the latter, or Aplacental mammals. Include the
Marsupials and Monotremes iOmithorhynchns).
Mammiferons — Having mamnue or teats (see Maicmai:.xa).
Mandibles, in Insects — ^The first or uppermost pair of jaws, which are
Knerally solid, homy, biting organs. In Birds the term is applied to
th jaws with their horny coverings. In Quadrupeds the mandible is
properlv the lower jaw.
Marsupials — An order of Mammalia in which the voung are bom in a very
incomplete state of development, and earned by the mother, while
sucking, in a ventral pouch (marsupium), such as the Kangaroos,
Opossums, &c (see Mammalia).
Maxilla, in Insects — ^The second or lower pair of jaws, which are composed
of several joints and furnished with peculiar jointed appendages called
palpi, or feelers.
Melanum^-The opposite of albinism; an undue development of colouring
material in the skin and its appendages.
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536 GLOSSARY
Metamorphic Rock* — Sedimentary rocks which have undergone alteration,
generally by the action of heat, subsequently to their deposition and
consolidation.
Mollusca — One of the great divisions of the Animal Kingdom, including
those animals which have a soft body, usually furnished with a shell,
and in which the nervous ganglia, or centres, present no definite gen-
eral arrangement. They are generally known under the denomination
of " shell-fish " ; the cuttle-fish, and the common snails, whelks,
oysters, mussels, and cockles, may serve as exam]>les of them.
Monocotyledons, or Monocotyledonous Plants — ^Plants in which the seed
sends up only a single seed-leaf (or cotyledon): characterized by the
absence of consecutive layers of wood in the stem (endogenous
growth), by the veins of the leaves being generally straight and
by the parts of the flowers being generally in multiples of three.
(Bxampies, Oasses, Lilies, Orchids, Palms, ftc.)
Mormnss — ^The accumulations of fragments of rock brought down by
glaciers.
Morphology — ^The law of form or structure independent of function.
My sis-stags — A stage in the development of certain Crustaceans (Prawns),
in which they closely resemble the adulu of a genus iMysis) belong-
ing to a slightly lower group.
Nascent — Commencing development
Natatory — Adapted for the purpose of swimming.
Nauplius-form — ^The earliest stage in the development of many Crustacea,
especially belonsing to the lower groups. In this ste^e the animal
has a short body, with indistinct indications of a division into seg-
ments, and three pairs of fringed limbs. This form of the common
fresh-water Cyclops was described as a distinct genus under the name
of Nauplius.
Neuration — ^The arrangement of the veins or nervures in the wings of
Insects.
Neuters — ^Imperfectly developed females of certain social insecta (such as
Anta and Bees), which perform all the labours of the community.
Hence thev are also called workers.
Nictitating Membrane — A semi-transparent membrane, which can be drawn
across the eye in Birds and Keptiles, either to moderate the effecta
of a strong light or to sweep particles of dust, &c., from the surface
of the eye.
Ocelli — ^The simple eyes or stemmata of Insects, usually situated on the
crown of the head between the great compound eyes.
CEsopkagns— The gullet.
Oolitic — ^A great series of secondary rocks, so called from the texture of
some of ita members, which appear to be made up of a mass of small
egg-like calcareous bodies.
Opercufum — A calcareous plate employed by many Mollusca to close the
• aperture of their shell. The opercular valves of Cirripedes are those
which close the aperture of the shell.
Orbit — ^The bony cavity for the reception of the eye.
Organism — ^An organized being, whether plant or animal.
Orthospermous-^A term applied to those fruits of the Umbelliferx which
have the seed straight.
Osculant — ^Forms or groups apparently intermediate between and connecting
other groups are said to be osculant
Ova — Eggs.
Ovarium or Ovary (in Plants) — ^The lower part of the pistil or female organ
of the flower, containing the ovules or incipient seeds; by growth after
the other orsans of the flower have fallen, it usually becomes con-
verted into the fruit
Ot/t^^erow^^Egg-bearins.
Ovules iof Plants)— Tht seeds in the earliest condition.
Pachyderms — ^A group of Mammalia, so called from their thick skins, and
including the Elephant, Rhinoceros, Hippopotamus, ftc
PaUsosoic — ^The oldest system of fossiliferous rocks.
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GLOSSARY 537
Palpi — ^Jointed ai^pendages to some of the organs of the mouth in Insects
and Crustacea.
Papitionaceit — An order of Plants (see LECUMiifosjB). The flowers of
these plants are called papilionaceous, or butterfly-like, from the
fancied resemblance of the expanded superior petals to the wings of
a butterfly.
Parasit€-^An animal or plant living upon or in, and at the expense of,
another organism.
Parthenogenesi* — The production of living organisms from unimpregnated
eggs or seeds.
Pedunculated — Supported upon a stem or stalk. The pedunculated oak has
its acorns borne upon a footstool.
Peloria or Pelorism — The appearance of re^laritv of structure in the
flowers of plants which normally bear irregular flowers.
Pelvis — ^The bony arch to which the hind limbs of vertebrate animals are
articulated.
Petals — ^The leaves of the corolla, or second circle of organs in a flower.
They are usually of delicate texture and brightly coloured.
PhyUodineous—VLimn% flattened, leaf-like twigs or leafaUlks instead of
true leaves.
Pigment — ^The colouring material produced generally in the superficial parts
of animals. The cells secreting it are called pigment-cells.
Ptufiatr— ^Bearing leaflets on each side of a central stalk.
Pistils — ^The female organs of a flower, which occupy a position in the centre
of the other floral organs. The pistil is generally divisible into the
ovary or germen, the style and the stigma.
Placentalia, Placentata, or Placental Mammals — See Mammalia.
/'tonfii^rad^j^— Quadrupeds which walk upon the whole sole of the foot, like
the Bears.
Plastic Period— The latest portion of the Tertiary epoch.
Plumule On Plants) — ^The minute bud between the seed-leaves of newly-
f^erminated plants.
Plutonic Rocks — Rocks supposed to have been produced by igneous action
in the deoths of the earth.
Pollen — ^The male element in flowering plants: usually a fine dust produced
§Y the anthers, which, by contact with the stigma, effects the fecunda-
on of the seeds. This impregnation is brought about by means of
tubes (pollen-tubes) which Issue from the poTlen-grains adhering to
the stigma, and penetrate through the tissues until they reach the
ovary.
Polyandrous {Flowers) — Flowers having many stamens.
Polygamous Plants — Plants in which some flowers are unisexual and others
hermaphrodite. The unisexual (male and female) flowers may be
on the same or on different plants.
Polymorphic — Presenting many forms.
Polysoary — ^The common structure formed by the cells of the Polyzoa, such
as the well-known Sea-mats.
Prehensile — Capable of grasping.
Prepotent — Having a superiori^ of power.
Primaries — ^The feathers forming the tip of the wing of a bird, and inserted
upon that part which represents the hand of man.
Processes — ^Projecting portions of bones, usually for the attachment of
muscles, ligaments, &c
Propolis — 'A resinous material collected by the Hive-Bees from the opening
buds of various trees.
Protean — Exceedingly variable.
Protozoa — ^The lowest great division of the Animal Kingdom. These animals
are composed of a gelatinous material, and show scarcely any trace of
distinct organs. The Infusoria, Foraminifera, and Sponges, with some
other forms, belong to this division.
Pupa ipl. Pupa) — ^The second stage in the development of an Insect, from
which It emerges in the perfect (winged) reproductive form. In most
insects the pupal stage is passed in perfect repose. The chrysalis is
the pupal state of butterflies.
Radicle — ^The minute root of an embryo plant
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538 GLOSSARY
Ramus— Ont'half of the lower jaw in the Mammalia. The portion which
rises to articulate with the skull is called the asctnding ramus.
Rauge—Tht extent of country over which a plant or animal is naturally
spread. Ranpe in tims expresses the distribution of a species or
group through the fossUiferous beds of the earth's crust
Rgtina — The delicate inner coat of the eye, formed br nenrous filaments
spreading from the optic nerve, and serving for the perception of the
impressions produced by light.
Rstrogrsssion — Backward development. When an animal, as it approaches
maturity, becomes less perfectly organized than might be expected
from its early stages and known relationshipa, it is said to undergo
a retrograde development or metamorphosis,
RhiMopods — A class of lowly organized animals (Protozoa), having a gelat-
inous body, the surface of which can be protruded in the form of
root-like processes or filaments, which serve for locomotion and
the prehension of food. The most important order is that of the
Foraminifera.
Rodents~^h» gnawing Mammalia, such as the Rats, Rabbits, and Squirrels.
They are especiallv characterized by the possession of a single pair
of chisel-like cutting teeth in each jaw, between which and the
grinding teeth there is a great gap.
Rutms—Tht Bramble Genus.
Rudimentary — Very imperfectly developed.
RuminanU — ^The group of Quadrupeds which ruminate or chew the cud,
such as Oxen, Sheep, and Deer. They have divided hoofs, and are
destitute of front teeth in the upper jaw.
Jocro^^Belonging to tiie sacrum, or the bone composed usually of two or
more united vertebrK to which the sides of the pelvis in vertebrate
animals are attached.
Sarcode — The gelatinous material of which the bodies of the lowest animals
(Protozoa) are composed.
ScutelkS'-^Tlke homy plates with which the feet of birds are generally more
or less covered, especially in front
Sedimentary Formations — Rocks deposited as sediments from water.
Segments— ^he traverse rings of which the body of an articulate animal
or Annelid is composed.
SePois — ^The leaves or seirments of the calyx, or outennost envelope of an
ordinary flower. They are usually green, but sometimes brightly
coloured.
Serratures— Teeth like those of a saw.
Sessite — Not supported on a stem or footstalk. ,
Silurian System — A verv ancient system of fossihferous roeks belonging to
the earlier part of the Palaeozoic series.
SpeciaiiMation—Tht setting apart of a particular organ for the performance
of a particular function.
Spinal Chord — ^The central portion of the nervous system in the Vertebrata,
whidi descends from the brain through the arches of the vertebrae,
and gives off nearly all the nerves to tiie various organs of the bodv.
Stamens — ^The male organs of flowering plants, standing in a circle withm
the petals. They usually consist of a filament and an anther, the
anther being the essential part in which the pollen, or fecundating
dust, is formed.
Sternum The breast-bone. ^ , . ., . ^
Stigma — ^The apical portion of the pistil in flowering plants.
Stipules — Small leafy organs placed at the base ot the footstalks of the
leaves in many plants.
Style — ^The middle portion of the perfect pistil, which rises like a column
from the ovary and supports the stigma at its summit
Subcuta$teous—Sita»,teA beneath the skin.
Suctorial — ^Adapted for sucking.
Sutures (tn the skull) — ^The unes of junction of the bones of which the
skull is composed.
Tarsus (pi. Tarsi) — ^The pointed feet of articulate animals, such as Insects.
Teleostean Pishes — Fishes of the kind familiar to us in the present day,
having the skeleton usually completely ossified and the scales homy.
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GLOSSARY 539
Tentacula or Tentacles — Delicate fLeahy organs of prehension or touch po»-
sessed by many of the lower animals.
Tertiary — The latest geological epoch, immediately preceding the cstablish-
ment of the present order of things.
Trachea — ^The windpipe or passage for the admission of air to the lungs.
Tridactyle — ^Three-fingered, or composed of three movable parts attached
to a common base.
Trilohites — A peculiar group of extinct Crustaceans, somewhat resembling
the Woodlice in external form, and, like some of them, capable or
rolling themselves up into a bail. Their remains are found only in
the Palaeozoic rocks, and most abundantly in those of Silurian age.
Trimorphic — Presenting three distinct forms.
Umhellifer« — ^An order of plants in which the flowers, which contain five
stamens and a pistil with two styles, are supported upon footstalks
which^ spring from the top of the flower stem and spread out like
the wires of an umbrella, so as to bring all the flowers in the same
head {umbel) nearly to the same level. {Examples, Parsley and
Carrot.;
Ungulata — ^Hoofed quadrupeds.
C/m'c£//f»/ar— Consisting of a single cell
Vascular — Containing blood-vessels.
Vermiform — ^Like a worm.
Vertebrata; or Vertebrate Animt^ — ^The highest division of the animal
kingdom, so called from the presence in most cases of a backbone
composed of numerous joints or vertebra, which constitutes the cen-
tre of the skeleton and at the same time supports and protects the
central parts of the nervous system.
Whorls — ^The circles or spiral lines in which the ports of plants are
arranged upon the axis of growth.
Workers — See Neutbss.
Zoea-stage — ^The earliest stue in the development of many of the higher
Crustacea, so called from the name of ZoSa, applied to these young
animals when they were supposed to constitute a peculiar genus.
Zooids — In man^ of the lower animals (such as the Corals, Medusae, &c.)
reproduction takes place in two wajrs. namely, by means of eggs and
by a process of budding with or without separation from the parent
ot the product of the latter, which is often very different from that
of the e^g. The individuality of the species is represented by the
whole ot the form produced between two sexual reproductions; and
these forms, which are apparently individual animals, have been
called Mooids.
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INDEX
Abeuant groups, 468.
Abyssinia, plants of, 423.
Acclimatisation, 152*
Adoxa, 335.
Affinities of extinct species, 377-
of organic beings, 467.
AgassiK, on Amblyopsis, iS^-^, ,
, on groups of speaes suddenly
appearing, 363.,
, on prophetic forms, 378.
, on embryological succession,
388.
, on the Glacial period, 4x2.
— ' — t on embryological characters,
456*
, on the latest tertiary forms,
350'
. on parallelism of embryologi-
cal development and geological
■succession, 489.
, Alex., on pedicellariae, 247.
Algse of New Zealand, 421.
Alligators, males, fighting, lox.
Alternate generations, 478.
Amblyopsis, blind fish. 152.
America, North^ productions allied
to those of Europe, 416.
, ^ boulders and glaciers
of, 4 '8.
^ South, no modern formations
on west coast, 343.
Ammonites, sudden extinction of,
372.
Anagallis, sterility of, 300.
Analogy of variations, 170.
Ancjrlus, 420.
Andaman Islands inhabited by a
toad. 435.
Animals, not domesticated from
being variable, 35.
, domestic, descended from
several stocks. 36.
, -. acclimatisation of, 154.
Animals ot Australia, 126.
with thicker fur in cold cli-
mates, 146.
, blind, in caves, 150,
extinct, of Australia, 389.
Anomma, 294.
Antarctic islands, ancient flora of,
441*
Antechinus, 462.
Ants attending aphides, 265.
, slave-making instinct^ 275,
^ neuters, structure of, 292.
Apes, not having acquired intel-
lectual powers, 234.
Aphides, attended by ants, 265.
Aphis, development of, 482.
Apteryx, 186.
Arab horses, 50.
Aralo-Caspian Sea, 389.
Archeopteryx, 356.
Archiac, M. de, on the succession
of species, 374.
Artichoke, Jerusalem, 154.
Ascension, plants of, 432.
Asdepias, pollen of, 200.
Asparagus, 406.
Aspicarpa, 455*
Asses, striped, 171.
, improved by selection, 55.
Ateuchus, X48.
Aucapitaine, on land-shells, 439.
Audubon, on habits of frigate-bird,
189.
, on variation in birds' nests,
, op heron eating seeds, 431.
Australia, animals of, 126.
, do8;s of, 269.
, extinct animals of, 388.
, European plants in, 420.*
, glaciers of, 4x8.
Azara, on flies destroying cattle,
86.
Azores, flora of, 4x0.
B
Babington, Mr., on British plants,
63.
Baer, Von, standard of Highness,
135.
, comparison of bee and fish,
386.
1 embryonic similarity of the
Vertebrata. 479.
Baker, Sir S., on the giraffe, 231.
Balancement of growth, xs8.
Baleen, 237.
Barberrv, flowers of^ ixx.
Barrande, M., on Silurian colonies.
J65.
375.
on the succession of species.
, on parallelism of palaeozoic
formations, ^^^»
, on affinities of ancient species,
379
541
HH—HCatl
Barriers, importance of, 396.
Digiti
ized by Google
542
INDEX
Bmtea, Mr., on mimetic butterflies.
465, 466.
Batrachiana on islands, 435*
Bats, how ^structure acquired, 186.
1 distribution of, 437.
Bear, catching water-insects, 188.
Beauty, how acquired, 309, 511.
Bee, sting of, 3x4.
, queen, killing rivalsp 214.
, Australian, extermmation of,
90.
Bees fertilising flowers, 88.
, hive, not sudong the red
clover, X08.
, Ligurian. zo8.
, hive^ cell-making instinct, 279,
, variation in habits, 366.
, parasitic, a7S.
— . numble, cells of, 280.
Beetles, wingless, in Maderia, 148.
- with ddident tarsi, 148.
Bentham, Mr., on British plants, 63.
, on classification, 457.
Berkeley, Mr., on seeds in salt water,
405.
Bermuda, birds of, 433.
Birds acquiring fear, 366.
— , beauty of, aia.
annually cross the Atlantic,
410.
, colour of, on continents, Xi^6.
, footsteps, and remains of, in
secondaiT rocks, 357- , „ „
, fossil, in caves of Brazil,
, of Madeira, Bermuda, and
Galapagos, 433.
Birds, song of males, xoa.
transporting seeds, 409.
— -s waders, 430.
~— , wingless, 147, 186, 187.
Bizcacha, 398.
•^— , affinities of, 469.
Bladder for swimming, in fish, 195.
Blindness of cave animals, 150.
Blyth, Mr., on distinctness of Indian
cattle, 35.
— ^-, on striped hemionus, 171.
, on crossed ffeese, 304,
Borrow, Mr., on the Spanish pointer,
49-
Bory St Vincent, on Batrachiaiu,
435.
Bosquet, M., on fossil CHithamalus,
^357.
Boulders, erratic, on the Azores, 308.
Branchiae, 196, Z97.
of crustaceans, aox.
Braun, Prof., on the seeds of Fuma-
riaceae, 226.
Brent, Mr., on house-tumblers, 26S.
Britain, mammals of, 437.
Broca, Prof., on Natural Selection,
Brpnn, Prof., on duration of specific
rious objectiona by, aaa.
forms, 247,
vanou
Brown. Robert, on classification, 453.
, S^uard, on inherited mutfla-
tions. 148.
Busk, Mr., on the Polyzoa, 248.
Butterflies, mimetic, 46^, 466.
Buzareingues, on sterility of varie-
ties, 325.
Cabbage, varieties of, crossed, ixa.
Calceolaria. 303.
Canary-birds, sterility of hybrids,
303.
Cape de Verde islands, productions
of, 440.
f plants of, on mountains^
Cape of Good Hope, plants of.
.43a.
420.
140,
Carpenter, Dr.. on foraminifera, 385.
Carthamus, 22s*
Cataaetum, 204, 461.
Cats, with blue eyes, deaf, 29.
, variation in habits of, 267.
curling tail when going to
spring, 2x3.
Cattle destroying fir-trees, 86.
destroyed by flies in Paraguay,
86.
, breeds of, locally extinct, xsi.
, fertility of Indian and Euro-
pean breeds, 304.
— — , Indian, 35, 305.
Cave, inhabitants of, blind, X50.
Ceddomjria, 478.
Celts, proving antiquity of man, 35.
Centres of Creation, 400.
Cephalopoda, structures of eyes, 200.
— — , development of, 482.
Ceroopithecus, tail of, 243.
Ceroxvlus laceratus, 236.
Cervuius, 304.
Cetacea, teeth and hair, 156.
, devdopment of the whalebone,
236.
Cetaceans. 236.
Ceylon, plants of, 420.
Chalk formation, 373.
of
, sua
Charlock, 00.
Checks to Increase, 83.
— — , mutual, 85.
Chelae of Crustaceans, 248.
Chickens, instinctive tameness
269.
Chironomus, its asexual reproduction,
478.
Chthamaliiue, 341.
Chthamalus, cretacean spedes of,
357.
Circumstances favourable to selec^
tion of domestic products, 53.
to natural selection, 1x4.
Cirripedes capable of crossing, 1x3.
, carapace aborted, 259.
Digiti
ized by Google
INIXBX
SA3
Orripedet,
190.
Qimiu
fUtnt oTVerooi tttBBf
, fonil, 357.
1 larrc of, 48X.
ClapftrMe, Prof., on the hair-clasp-
era of the Acaridc 302.
Oarke, Rev, W. B., on old gladen
in Australia, 4x8.
Qassification, 450.
Clift, Mr., on the suooession of
t3rpes, 388.
Climate, effects of, in checking in-
crease of beings, 84.
— k adaptation of, to organisms,
bing plants, 195.
, developments of, 35a.
Qover visited by bees, xxo, ixi«
Cobites, intestine of, 194.
Cockroach, 90.
Collections, pabeontological, poor.
Colour, influenced by dimate, 146.
, in relation to attack by flies,
309.
Columba livia, parent of domestic
pigeons, 39.
Coiymbetes^ 439.
Compensation of growth, Z58.
Compositse, flowera and seeds of, 157.
— , outer and inner florets of, 22$.
— — , male flowers of, 491.
Conclusion, general. 519.
Conditions, slight changes in, favour-
able to fertility, 317.
Convergence of genera, 139.
Cope, Prof., on the acceleration or
retardation of the period of repro-
duction, 197.
Coral-islands, seeds drifted to, 406.
reefs, indicating movements of
earth, 406.
Corn-crake, 190.
Correlated variation in domestic
productions, 29.
Coryanthes, 203.
Creation, single centres of, 400.
Crinum, 303.
Croll, Mr., on subaerial denudation,
339*
, on the age of our oldest for*
mations, 359.
^— , on alternate Glacial periods in
the North and South, 4x8.
Crosses, reciprocal, qo6.
Crossing of domestic animals, im-
portance in altering breeds, 36.
, advantages of, xio.
, unfavourable to selection, 113,
114.
Criiger, Dr., on Conranthes, 304.
Crustacea of New Zealand, 431.
Crustacean, blind, 150.
air-breathers, aos.
Crustaceans, their chelae, 349.
Cryptocenis, 393.
Ctenomys, Wind, iso.
Cuckoo, instinct of, 363. 370.
Cunningham, Mr., on the flight of
the logger-headed dude, 147.
Currants, mfts of, 311.
Currents of sea. rate of. 406.
Cuvier, on conditions of existence,
363, 363.
, on fossil monkeys, 356.
, Fred., on instinct^ 36a, 363.
Cydostoma, resisting salt water, 439.
Dana, Prof., on blind cave-animals,
X51.
, on relations of crustaceans of
Japan, 4x7.
, on crustaceans of New Zea-
land, 43X.
Dawson, Dr., on eozoon, 360.
De CandoUe, Aug. Pyr., on struggle
for existence, 77.
, on umbelliterae, 15 7,
, on general affinities, 469*
■, Alph., on the variability of
oaks, 07.
— ' — , on low plants, widely dis-
persed, i^6.
, on widely-ranging plants being
variable, 69.
, on naturalisation, 135.
, on winged seeds, xs8.
, on Alpine spedes suddenly be-
coming rare, 180.
, on distribution of plants with
large seeds, 407.
—*— , on vegetation of Australia,
, on xresh-water plants, 430.
, on insular plants, 4^3.
Degradation of rodcs, 330.
Denudation, rate of, 337.
of oldest rocks, 360.
of granitic areas, 345.
Devdqpment of andent forms, 384.
Devonian system, 383.
Dianthus, fertili^ of crosses, 306,
307.
Dimorphism in plants, 6x, 3x9.
Dirt on feet of birds, 409.
Dispersal, means of, 403*
durmg Gladal period, 41 x.
Distribution, geograiMiical, 395*
, meanc of, 403.
Disuse, effect of, under nature, 147.
Divergence of character, 122,
Diveraification of means for same
general purpose, 203.
Division, physiological, of labour, 135.
Dog, resemblance of jaw to that of
the Thyladnus, 463.
Dogs, hairless, with imperfect teeth,
30.
descended from several wfld
stocks, 35.
, domcitic instincts of, s68.
Digiti
ized by Google
544
INDEX
as.
Dogs, inherited civilisation of, a68.
— , fertility of breeds together,
30s.
, of crosses, 3JJ.
, proportions of body in differ-
ent breeds, when young, 484.
Domestication, variation under.
Double flowers, 292.
Downinpr, Mr., on frui^trees in
America, 98.
Dragon-flies, intestines of, 194.
Drift-timber, 407.
Driver ant. 29^.
Drones killed by other bees. 3x4.
Duck, domestic, wings of, redu<
Dndcwi
-, beak of, 237.
headed, x86.
uced^9.
>^9.
Dugong, affinities of, 453.
Dunff-beetles with dddent tarsi,
Dybscus, 429.
E
Earl. Mr. W., on the Malay Archi-
pelago, 4^7.
Ears, droopmg, in domestic animals,
*^-
f rudimentary, 494.
Earth, seeds in roots of trees, 407.
charged with seeds, 409.
Echlnodermata, their pedicellariae,
Eciton, agj.
Economy of organisation, 159.
Edentata, teeth and hair, 156.
, fossil species of, 515.
Edwards, Milne, on physiological
division of labour, 126.
, on gradations of structure,
205.
, on embryological characters,
456.
Eggs, young birds escaping from,
100.
Egypt, productions of, not modified,
220.
Electric organs, 198.
Elephant, rate of increase, 79.
9 of Glacial period, 154.
Embryology, 478.
Eozoon Canaaense, 360.
Existence, struggle for, 76.
, condition of, a 18.
Extinction, as bearing on natural
selection, 134.
— of domestic varieties, 130.
^r~' 368.
Eye, structure of. 191.
, correction tor aberration, 216.
Eyes, reduced in moles, 149.
Fabre, M., on hymenoptera fighting,
202.
— , on parasitic sphex, 275,
«— -k on Sitaris, 487, 488.
of
ad-
I, 302.
changes
in con-
Falconer, Dr., on naturalisation of
plants in India, 80.
on elephants and mastodons,
383.
and Cautley, on
sub-Himalayan beds. 389.
Falkland Islands, wolf of, 43^
Faults, 338.
Faunas, marine, ^97.
Fear, instinctive, in birds, 269.
Feet of birds, young molluscs
hering to, 429.
Fertilisation variously effected, 203,
an.
Fertility of hybrids,
, from slight
ditions, 318.
of crossed varieties, 322.
Fir-trees destroyed by cattle, 86.
, pollen of, 2 IS.
Fish, flsring, 187.
, teleostean, sudden appearance
®^» 357.
, eating seeds, 408, 430.
, fresh-water, distribution of,
4a7t 4^8.
Fishes, ganoid, now confined to
fresh water, 118.
, electric organs of, 198.
, ganoid, living in fresh water,
37a.
, of southern hemisphere, 421.
Flat-fish, their structure, 240.
Flight, powers of, how acquired,
186, 187-
Flint-tools, proving antiquity of
man, 35.
Flower, Trof., on the Urvnx, 246.
, on Halitherium, 378.
, on the resemblance between
the jaws of the dog and Thylad-
nus, 464.
, on the homology of the feet
of certain marsupials, 47^.
Flowers, structure of, in relation to
crossing, 106.
, of compositae and umbelliferc,
iS7t aas.
, beauty of, axx.
, double, 292.
Flysch formation, destitute of or-
ganic remains, 341.
Forbes, Mr. D., on glacial action in
the Andes, 418.
, E., on colours of shells, 146.
, on abrupt range of shells in
depth, 181.
. on poorness of palcontological
collections, 340.
f on continuous succession of
genera, 367.
, on continental extensions, 404,
40s.
^^, on distribution during Glacial
period, 412.
, on naraUelism in time and
space, 44&
Digiti
ized by Google
INDEX
545
Forests, changes in, in America, 88.
Formation, Devonian, 38a.
, Cambrian, 360.
Formations, thickness of, in Britain,
338.
, intermittent, 348.
Formica, rufescens, 377.
, sanguinea, 276.
, flava, neuter of, 293.
Forms, lowly organised, long endur-
ing, 136, 137. ....
Frena, OTigerous, of arripedes, 196.
Fresh-water productions, dispersal
of, 437. . . ,
Fries, on species m large genera
being closely allied to other spe-
cies, 73.
Frigate-Dird. 180.
Fross on islands, ^36.
Fruit-trees, gradual improyement of,
5x.
in United States, 08.
f varieties of, acclimatised in
United States, 154*
Fuci, crossed} 308. 314.
Fur, thicker in cold climates, 146*
Galapagos Archipelago, birds
-, productions of, 439, 440.
Galeopithecus, 185*
Game, increase of.
of,
Galaxias. its wide range, 427.
Galeopitni
une, ini
min, 84.
checked by ver-
Gartner, on sterility of hybrids, 299,
300, 305. .
, on reciprocal crosses, 308.
, on crossed maize and verbas-
cum, 325.
, on comparison of hybrids and
mongrels, ^ay, 328.
Gaudry, Prof., on intermediate gen-
era of fossil mammals in Attica,
378.
Geese, fertility when crossed, 304.
— -, upland, 189,
Geikie, Mr., on subaerial denuda-
tion, 336.
Genealogy, important in classifica-
tion, 457.
Generations, alternate, 478.
Geoffrey St. Hilaire, on balance-
ment, 158.
, on homologous organs, 47^.
, Isidore, on variability of re-
peated parts, 160.
, on correlation, in monstrosi-
ties, 29.
, on correlation, 156.
, on variable parts being often
monstrous, 265.
Geographical distribution, 395.
Geology, future progress of, 527.
527.
imperifectiott of the record.
Gervais, Prof., on Typotherinm, 378.
Giraffe, tail of, 206.
■ I structure of, 230.
Glacial period, axi.
, affecting the North and South,
4Z2L*
Glands, mammary, 244.
Gmelin, on distribution, 412.
Godwin-Austen, Mr., on the Malay
Archipelago, 352.
Goethe, on compensation of growth,
X58.
Gomphia, 227.
Gooseberry, grafts of, 3x1.
Gould, Dr. Aug. A., on land-shells,
438.
, Mr.^ on colours of birds, 146.
, on instincts of cuckoo, 273.
, on distribution of genera of
birds, 445.
Gourds, crossed, 925.
Graba, on the Una lacrymas, 105.
Grafting, capad^ of, 310, 311.
'^ '■ of denuded
Granite, areas of
ded, 345.
on asexual reproduction.
Grasses, varieties of, 124.
Gray. Dr. Asa, on the variability of
oaks, 66.
, on man not causing variabil-
ity, 93-
, on sexes of the holly, xo7.
, on trees of the United States,
XX3.
, on naturalised plants in the
United States, 125.
, on Kstivation, 226,
, on Alpine plants, 4x2.
, on rarity of intermediate va-
rieties, 182.
, Dr. J. E., on striped mule,
171.
Grebe, X89.
Grunm,
478.
Groups, aberrant, 468.
Grouse, colours of, 98.
, red, a doubtful species. 64.
Growth, compensation of, 158.
Giinther, Dr.. on flat-fish, 244.
, on prehensile tails, 244.
, on the fishes of Panama, 396.
. on the range of fresh-water
fishes, 427.
, on the limbs of Lepidosiren,
H
Haast. Dr., on glaciers of New 2^a-
land, 4io*
Habit, effect of, under domestica-
tion, 29.
, effect of, under nature, 148.
f diversified, of same species,
187.
Hackel^ Prof^ on classification and
the lines of descent, 472*
Hair and teeth, correlated, 156.
Halitherium, 378.
Digiti
ized by Google
546
INDEX
>• resistinc salt water, 439.
M., on the imperzectioii
HAroourL Mr. E. V., 00 the bird*
of Madeira, 433.
Hartung, M., on boulderi in the
Azores, 410.
Hazel-nuta, 406.
Heame, on habits of bears, 188.
Heath, changes in Tegetation. 8s.
Hector, Dr., on glaciers of New
Zealand, 4x8.
Heer, Oswald, on ancient cultivated
plants, 3«.
^ on plants of Madeira, 11 8.
Hellanthemum, 227.
Helix pomatia, 439>
i resisting salt
Helmholtz,
of the human eje, 314.
Helosdadium, 406.
Hemionus. striped. 173.
Hensen, Dr., on tue eyes of Cepha-
lopods, aoo.
Herbert, W., on struggle for exist'
encc, 77.
, on sterility of hvbrids, 30a.
Hermaphrodites crosstng, Z09, no.
Heron eatins seed, 431.
Heron, Sir K., on peacocks, xos.
Heusinser, on white animals poi-
soned by certain plants, 30.
Hewitt, Mr., on sterility of first
crosses, 3x4.
Hildebrand, Frof., on the self-steril-
ity of Corydalis, 302.
Hil^endorf, on intermediate varie-
Himaiaya, gladers of, 4x7.
, plants of, 420.
Hfppeastrum, 302.
Hippicamptts, 245.
Hofmeister, Prof., on the
ments of plants, 254.
Hooker, on plants of mountains of
Fernando Po, 420.
Hooks on palms, 208.
Holly-trees, sexes of, 107.
Hooker, Dr., on trees of New Zea-
land, XI 3.
, on acclimatisation of Hima-
layan trees, 153.
-, on flowers of umbellifene, 157.
ulei
224.
4x8.
on the position of OTules,
on glaciers of Himalaya, 4171
-, on algae of New Zealand, 420.
i on vegetation at the base of
the Himalaya, 421.
, on plants of Tierra del Fuego,
419.
, on Australian plants, 420. 44 <•
, on relations of flora of Amer-
ica, 4^3:
, on flora of the Antarctic lands,
, on the plants of the Galapagos,
434, 440.
, on glaciers of the Lebanon,
, on man not causang variabil-
ity, 93.
on seeds, on islands, 435.
. dns. Mr., on denudation, 344.
Hombill, remarkable instinct ot.
296.
Horns, rudimentary, 494.
Horse, fossil, in La Plata, 369.
, proportions of, when young,
484-
Horses destroyed by flies in Para-
guay. 86.
, stnped, X7X.
Horticulturists, selection applied by,
Huoer, on cells of bee^ 284.
, P., on reason blended with
instinct. 262.
1 on habitual nature of instincts,
263.
, on slave-making ants, 277.
— — , on Melipona domestica. 281.
Hudson, Mr., on the Ground-Wood-
pecker of La Plata, 188.
f on the Molothrus, 273, 274.
Humble-bees, cells of, 280.
Hunter, J., on secondary sexual
characters, x6x.
Hutton, Captain, on crossed geese,
304.
Huxlev, Prof., on structure of her-
maphrodites, 113.
-»— , on the affinities of the Sirenia,
, on forms connecting birds aiK*
reptiles, 379-
, on homologous organs, 477.
, on the development of aphis.
Hybrids and mongrels compared,
327.
Hybridism, 298.
Hydra, structure of, 194.
Hymenoptera, fighting, 102.
Hymenopterous insects, diving, 199*
Hyoseris, 225.
Ibla, 159.
Icebergs transporting seeds, 4x0.
Increase, rate of, 79.
Individuals, numbers favourable to
selection, XX4.
, many, whether simultaneously
created, 40a.
Inheritance, laws of, 3i<
, at corresponding ages, 3i>
lOX.
Insects, colour of, fitted for their
stations, 100. * ,
, sea-side, colours of, 146.
, blind, in caves, 149, 150-
, luminous, I99.
, their resemblance to certain
objecu, 235.
, neuter, 292.
Digiti
ized by Google
INDBX
547
Instinct. 262.
, not varying simaltaneously
with structure, 290.
Instincts, domestic, 267.
Intercrossing, advantages of, xio.
Isia
lands, oceanic, 4;
favoun
Isolation
X16,
able
to selection.
Japan, productions of, 4x7.
Java, plants of, 420.
Jones, Mr. J. M«, on the birds of
Bermuda, 433.
Jourdain. M., on the eye-spots of
star-fisoeSy 191.
Jukes, Prof., on subaerial denuda-
tion, 336.
Jnssieu, on classification, 455.
Kentucky, caves of, 150.
Kerguelen-land, flora of, 425, 441.
Kidney-bean, acclimatisation of, 155.
Kidneys of birds, 156*
denci
Kidney-bean, acclimatisation
Kidneys of birds, 156.
Kirbv, on tarsi deficient in beeties.
Knight, Andrew, on cause of varia-
4tion, 25.
Kolreuter, on Intercrossing, 109.
— , on the barberrv, in.
, on sterility of hybrids, 399,
300.
, on reciprocal crosses, 308.
, on crossed varieties of nico-
tiana, 326.
, on crossing male and her*
maphrodite flowers, 490.
Lamarck,
462.
on adaptive characters.
Lancelet, 137.
eyes of, 193
Landois, on the development of the
wings of insects, to6.
Land-shells, distribution of, 4^8.
, of Madeira, naturalised, 443.
, resisting salt water, 439.
Languages, classification of, 459.
Lankester, Mr. £. Ray, on
ity, 229.
, on homologies, 477.
Lapse, great, of time, 335.
Larvae. 480.
Laurel, nectar secreted by the
leaves, zo6.
Laurentian formation, 360.
Laws of variation. 145.
Leech, varieties of, 89.
Leguminosse, nectar secreted by
fflands, 106.
Leibnitz' attack on Newton, 520.
Lepidosiren, xx8, 380.
Lepidosiren, limbs in a nascent con-
dition, 49s.
Lewes, Mr. G. H., on species not
having changed in Egypt, 220.
, on the Salamandra atra, 401.
, on many forms of life having
been at firsf evolved, 524.
Life, struffile for, 78.
Lingula, SDurian, 350.
Linncus, aphorism of, 452.
Lion, mane of. 102.
, young of, striped, 480.
Lobelia fulf^ens, 87, in.
, sterility of crosses, 302.
Lodcwood, Mr., on the ova of the
Hippocampus, 244.
Locusts transporting seeds, 408.
Logan, Sir W., on Lanrentian for-
mation, 360.
Lowe, Rev. R. T., on locusts visit-
ing Madeira, 408.
Lowness of structure connected with
variability, z6o.
—V related to wide distribution,
Lubbock, Sir J., on the nerves of
coccus, 60.
, on secondary sexual charac-
ters, 167.
, on a diving hymenopterous
insect, 189.
, on aflmities, 352.
, on metamorpboses. 480.
Lucas, Dr. P., on inheritance, 30.
, on resemblance of child to
parent, ^29.
Lund ana Clausen, on fossils of
BraziK 388.
Lyell, Sir C, on the struggle for
existence, 77.
, on modem changes of the
earth, 100.
, Sir C, on terrestrial animals
not having been developed on
islands, 233.
, on a carboniferous land-shell,
341.
— — , on strata beneath Silurian
ssrstem, 3^0.
, on the imperfection of the geo-
logical record, 363.
1 on the appearance of species,
363.
, on Barrande's colonies, 364,
, on tertiary formations of
Europe and North America, 373*
, on parallelism of tertiary for-
mations, 377.
, on transport of seeds by ice-
bergs, 410.
, on great alterations of climate,
426.
, on the distribution of fresh-
water shells, 429.
^1 on land-shells of Madeira, A43.
Lyell and Dawson, on fosaihxcd
trees in Nova Scotia, 340.
Lythrum salicaria, trimorpl
321.
Digiti
ized by Google
548
INDEX
Macleay, on analogiGal characters,
462.
Macrancheniat 378*
M'Donnell, Dr., on electric organs.
MaSdra,
Madeira, plants of. xi8.
, beetles of, winsleas, 148,
, fossil land-shells of, 389
-, birds of, 433.
agpie tame in N(
Males fighting, 102.
M,
389.
orway, 266,
Maize, crossed, 325.
Malay Archipelago compared with
Europe, 35a.
, mammals of, 437.
Malm, on flat-fish, 341.
Malpighiaceae, small imperfect flow-
ers of, 225.
Mamnue, their development, 344.
, rudimentary, 49a
Mammals, fossil, in secondary for-
mation, 356.
-—-, insular, 435.
Man, ongm of, 527.
Manatee, rudimentary nails of, 494.
Marsupials of Australia, 126,
, structure of their feet, 473.
, fossil species of, 388.
Martens, M«, experiment on seeds,
406.
Martin, Mr. W. C, on striped mules,
173-
Masters, Dr., on Saponaria, 227,
Matteuoct, on the electric organs of
ray^ 198.
Matthiola, reciprocal crosses of, 308.
Maurandia, 253.
Means of dispersal, 40J.
Melipona domestics, a8o.
Merrell, Dr., on the American
cuckoo, 270.
Metamorphism of oldest rocks, 360.
Mice destroying bees, 88.
^*— , acclimatisation of, 153.
, tails of, 344.
Miller, Prof., on the cells of bees,
281, 285.
Mirabilis, crosses of, 308.
Missel-thrush, 90.
Mistletoe, complex relations of, 22.
Mivart, Mr., on the relation of hair
and teeth. 156.
, on the eyes of cephalopoda,
200.
, various objections to Natural
Selection, 229.
, on abrupt modifications, 258,
259.
, on the resemblance of the
mouse and antechinus, 462.
Mocking-thnish of the Galapagos,
Modification of species not abrupt,
523.
Moles, blind, i«i.
Molothrus, habits of, 273.
Mongrels, fertility and sterility of,
322.
— and hybrids compared, 327.
Monkevs, fossil, 35^
Monachanthus, 461.
Mons, Van, on the origin of fruit-
trees, 44.
Monstrosities, 58.
Moquin-Tandon, on sea-side plants,
146.
Morphology, 472.
Morren, on the leaves of Oxalis, 254.
Moths, hybrid, 304.
Mozart, musical powers of, 263.
Mud, seeds in, 429.
Mules, stnpe<L 173.
Muller, Aaolt, on the instincts of
the cuckoo, 271.
Muller, Dr. Ferdinand, on Alpine
Australian plants, 420.
Muller, Fritz, on dimorphic crus-
taceans, 61, 295.
, on the lancelet, 137.
, on air-breathing crustaceans,
20Z.
, on climbins plants, 2C3.
on the selx-steriliQr of orchids,
302,
on embryolMy in relation to*
classification, 451
, on the metamorphoses of crus-
taceans, 482, 488.
, on terrestrial and fresh-water
organisms not undergoing any
metamorphosis. 486.
Multiplication ox species not indefi-
nite, 140.
Murchison, Sir R., on the forma-
tions of Russia, 342.
, on azoic formations, 360,
^1 on extinction, 368.
Mune, Dr., on the modification of
the skull in old age, 197.
Murray, Mr. A., on cave-insects,
152.
Mustela vision, 184.
My an thus, 461.
Myrmecocystus, 292.
Myrmica, eyes of, 294.
N
Nageli, on morphological characters,
222,
Nails, rudimentary, 4^.
Nathusius, Von, on pigs, 209.
Natural history, future progress of,
5*5. , .
■— — selection, 93.
system, 452.
Naturalisation of forms distinct
from the indigenous species. 125.
Naturalisation in New Zealand, 21^.
Naudin, on analogous variations in
gourds, 168.
Digiti
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INDEX
549
Nandin, on hybrid gourds, 335.
, on reversion, 3J8.
Nautilus, Silurian, 359*
Nectar of olantSp 106.
Nectaries, now formed, io6.
Nelumbium luteum, 430.
Nests, variations in, j66, 189, 996.
Neuter insects, 393, 29^
Newman, Col., on humble-bees, 88.
New Zealand, productions of, not
perfect, 21^.
, naturalised products of, 387.
f fossil birds of, 389.
f glaciers of, 418.
, crustaceans of, 420.
, algK of, 421.
, number of plants of, 432.
, flora of, 441.
Newton, Sir I., attacked for irre-
ligion, 520.
, Prof., on earth attached to a
partridge's foot, 409; .
Nicotiana, crossed varieties of, 326.
, certain species very sterile,
Nitsche, Dr., on the Polysoa. 248.
JMoble, Mr., on fertility of Khodo-
dendron, 303.
Nodules, phosphatic, in asote rocks,
360.
> O
Oaks, variability of, 67.
Onites apelles, 148.
Ononis, small imperfect flowers of.
Orchids, fertilisation of, 204. ao«.
, the development of their
flowers, 251.
, forms of, 461.
Orchis^ pollen of, 200.
Organisation, tendency to advance,
US-
Organs of extreme perfection, 190.
, electric, of fishes, 199.
, of little importance, 205.
, homologous, 474-
, rudiments ot, and nascent,
490.
Omlthorhynchus. xi8, 454.
of.. 245.
Ostrich not capable of flight, 233.
^ lay*
habit of laying eggs together.
^74-
, American, two species of, 397.
Otter, habits of, how acquired, 184.
Ouzel, water, 189.
Owen, Prof., on birds not flying,
147.
, on vegetative repetition, 160.
, on variability of unusually
developed parts, 161.
^— , on the eyes of fishes, 193.
', on the swim-bladder of fishes.
Z96.
369.
on fossil horse of La Plata,
Owen, Prof., on generalised form,
378.
, on relation of ruminants and
pachyderms, 378.
, on fossil birds of New Zea-
land, 388.
, on succession of types, 389.
, on affinities of the dngong,
, on homologous organs, 473.
, on the metamorphosis of
cephalopoda, 482.
Pacific Ocean, faunas of, 397.
Pacini, on electric orsans, 199.
Paley, on no organ formed to give
PiSlas,' on 'the fertility of the do-
mesticated descendants of wild
stocks, 305.
Palm with hooks, 208.
Papaver bracteatum, 226,
Paraguay, cattle destroyed by flies,
86*
Parasites, 274, 275.
Partridge, with ball of earth at-
tached to foot. 409.
Parts greatly developed, variable,
x6i.
Parus major, 188.
Passiflora, 302.
Peaches in United States, 98.
Pear, grafts of.
I'ear, grafts ot, 3x1.
Pediceuaric, 247.
Pelargonium, flowers of,
. sterility of, 303.
Pelvis of women, 150.
157.
Peloria, 157.
Period, Glacial, 41 x.
Petrels, habits ot, x
Phasianus, fertility of hybrids, 304.
Pheasant, young, wild, 269.
Pictet, Prof., on groups of species
suddenly appearmg, 356.
36$.
on rate of organic change.
on continuous succession of
genera, 367. . ,
, on change in latest tertiary
forms. 350.
, on close alliance of fossils in
consecutive formations, ^8^.
1 on early transitional finks, 355.
Pierce, Mr., on varieties of wolves,
X03.
Pigeons with ftethered feet and
skin between toes, 30.
breeds described, and origin
of, 37.
, on
53-
reeds of, how produced, 52,
— ^, tumbler, not being able to get
out of em, 100.
— , reverting to blue colour, 170.
— , instinct of tumbling, 268.
Digiti
ized by Google
550
INDBX
Pigeons, young of, 485.
Pigs^ black; not affected by the
paint-root, ^o.
, modlned by want of exercise,
Pistil, rudimentary, 491.
Plants, poisonous, not affecting cer-
tain coloured animals, 30.
, selection applied to, 51.
^— , gradual improvement of, 51.
, not improved in barbarous
countries, sz.
, dimorpbie, 61.
, destroyed by insects, 84.
, in midst of range, have to
struggle with other plants, 97.
, nectar of, xo6.
, fleahvp on sea-shores, 146.
, climbing, 196, ass.
, fresh-water, distribution of,
4S9.
, low in scale, widely distrib-
uted, 446.
Pleuronectidae, their structure, 240.
Plumage, laws of change in aezea
of birds, I OS.
Plums in the United States, 98.
Pointer dog, origin of, 49.
, habits of, 269.
Poison not affecting certain col-
oured animals, 30.
, similar effect of, on animals
and plants, 533.
Pollen of fiMrees, sis.
transported by various means,
203, ao4, SIX.
Pollinia, their development, asx.
Polyzoa, their avicularia, 349.
Poole, Col., on striped hemionus,
Potamogeton, 430.
Pouchet, on the colours of flat-fish,
343.
Prestwich, Mr., on English and
French eocene formations, 377,
Proctotrupes, 189.
Proteolepas, 159.
Proteus, 153.
Psychology, future progress of, 537.
Prygoma, found in the chalk, 357.
Quagga. striped, 174.
Quatrefages, M.., on hybrid moths,
304.
Quercus, variability of, 67,
Quince, grafts of, 311.
R
Rabbits, disposition of young, 269.
Race^ domestic, characteis of, 33.
Race-horses, Arab, 50.
, English, 403.
Raddiffe, Dr., the electrical organs
of the torpedo* 198.
Ramottd, on plants of Pyrenees,
413*
Ramsay, Prof^ on subaerial denu-
dation, 337.
— 7-, on thickness of the British
formations. 338.
, on faults, ^38.
, Mr., on instincts of cuckoo,
3^3.
Rauo of increase, 79.
Rats supplanting each other, 90.
, acclimatisation of, 153.
— — •, blind, in cave, 150.
RatUe-snake, 3x3.
Reason and instinct, 363.
Recapitulatiofu general, 409.
Reciprocity of crosses, 308.
Record, geolojncal, imperfect, 333-
Rragger, on ffies destroying cattle.
Reproduction, rate of, 80.
Resemblance, protective of insects,
235.
— -- to parents in mongrels and
hybrids, 339.
Reversion, law of inheritance, 33.
, in pigeons, to blue colour,
170.
Rhododendron, sterility of, 303, 304.
Richard, Prof., on Aspicarpa, 455;
Richardson, Sir J., on structure of
squirrels, 185.
1 on fishes of the southern
hemisphere, 431.
Robinia, grafts of, 311.
Rodents, blind, 149.
Rogers, Prof., Map of N. America,
Rudimentary organs, 491.
Rudiments important for classifica-
tion, 455.
Rtttimeyer, on Indian cattle, 36,
305.
S
Salamandra atra, 491. ^
Saliva used m nests, 380.
Salvin, Mr., on the beaks of ducks.
r,*38.
Saseret, on srafts, 3x1.
Salmons, males fighting, and hooked
jaws of, 101.
Salt water, how far injurious to
seeds, 405, 406.
not destructive to land-shells.
Sajtcr, Ififr., on early death of hy-
brid embryos, 3x5.
Saurophagus sulphuratus. 187.
Schacht, Prof., on Phyllotaxy, 335.
Schiodte, on blind insects, X50.
, on flat-fish, 340.
Schlegel, on snakes, 156.
Schdbl, Dr., on the ears of mice,
333.
Scott, J... Mr., on the self-steriUty
of orchids, 303. ,
Digiti
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INDEX
551
Scott, J., Mr., on the crossing of
▼arieties of verbaacum, 326.
Sea-water, how far injurious to
seeds, 405, 406.
not destructive to land-shells,
438, 439*
Seoright, Sir J., on crossed animals,
Sedgwick, Prof., on groups of spe-
cies suddenly apnearin^, 354.
Seedlings destroyed by insects, 8j.
Seeds, nutriment in, 91.
, winged, 158.
, means of dissemination, 203,
a 1 2, 407, 408.
, power of resisting salt water,
406.
, in crops and intestines of
birds, 407, 408.
1 eaten by fish, 408, 430.
, in mud, 428.
, hooked, on islands, 415.
Selection of domestic prodfucts, 43,
44.
, principle not of recent origin,
48.
, unconscious, 49.
, natural, 93.
, sexual^ 1 01.
, objections to term. 94.
natural, has not induced steril-
ity, 312.
Sexes, relations of, loi.
SexuaJ characters variable, 166.
selection, lox.
Sheep, Merino, their selection, 46.
, two sub-breeds, unintention-
ally produced, 50.
, mountain varieties of, 89.
Shells, colours of, 246.
, hinges of, 202.
, littoral, seldom embedded, 341.
, fresh-water, long retain Uie
forms, 385.
, -- — , dis^rsal of, 428.
, of Madeira. 4^3.
, land, distribution of. 433.
• , resisting salt water,
^438. 439.
Shrew-mouse, ^62,
Silene, infertility of crosses, 307.
Silliman, Prof., on blind rat, 150.
Sirenia, their affinities, 178.
Sitaris, metamorphosis of, 488.
Skulls of young mammals, 208, 475.
Slave-making instinct, 275.
Smith, Col. Hamilton, on striped
horses, 172.
, Mr. Fred., on slave-making
ants, 276.
, on neuter ants, 294.
Smitt, Dr.. on the Polyzoa, 248.
Snake with tooth for cutting
throuffh egg-shell, 273.
Somervule, Xord, on selection of
sheep, 46.
Sorbtts, grafts of, 311.
Sorex, 463.
Spaniel^ King Charles's breed, 49.
Specialisation of organs, 135.
Species polymorphic, 60.
f dominant, 71.
, common, variable, 60.
in large Renera variable, 71.
, groups of, suddenly appearing,
354* 359. ^ «.. . ,
beneath Silurian fonnatiotis,
360.
Species successively a{>pearing, 364.
changing simultaneously
throughout the world, 373.
Spencer, Lord, on increase in sixe
of cattle, 50.
'—', Herbert. Mr., on the first
steps in differentiation, 138.
, on the tendency to an equilib-
rium in all forces, 318.
Sphex, parasitic, 275.
Spiders, development of, 482.
Sports in plante, 28.
Sprengel, C. C, on crossing, 109.
- — , on ray-florets, 157.
Squalodon, 379.
Squirrels, gradations In structure.
StaflSi
,8s.
irdshire, heath, changes in.
Stag-beetles, fighting, xoi.
Star-fishes, eyes of, 191.
f their pedicellarise, 247.
Sterility from changed conditionaof
of hybrids, ,
300.
laws of, 305.
of, ;
ty of
— — , from unfavourable conditions,
316.
not induced through natural
selection, 313.
St Helena, productions of,
St. Hilaire, Aug., on varii
certain plants, 226, 227.
. on classification, 4^6.
St. John, Mr., on habits of cats,
267.
Stins of bee. 3x4.
Stoocs, aboriginal, of domestic ani-
Strata, tnickness of, in Britain, 339.
Stripes on horses, 172.
Structure, degrees of utility of,
209.
Struggle for existence, 76.
Succession, geological, 364.
■ of types in same areas, 388.
Swallow, one species supplanting
another. 90.
Swaysland, Mr., on earth adhering
to the feet of migratory birds.
Swifts, nests of, 289.
Swim-Sl adder, I95<
Switzerland, lake-habitations of, 35,
System, natural, 45^*
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552
INDEX
Tail of giraffe, 206.
of aquatic animals, 307.
, prehensile, 244.
, rudimenury, ^94.
Tanais, dimorphic, 01.
Tarsi, deficient, 148.
Tausch, Dr., on umbeUifene, 336.
Teeth and hair correlated, 156.
, rudimentary, embryonic calf,
490, 518.
Tegetmeier, Mr., on cells of bees,
383, 387.
Temminck, on distribution aiding
classification, 45 7>
Tendrils, their development, 353.
Thompson. Sir W.. on the age of
the habitable world, 360.
, on the consolidation of the
crust of the earth, 505*
Thouin, on grafts, 311.
Thrush, aquatic species of, 189.
, mocking, of the Galapagos,
443.
, young of, spotted, 480.
, nest of, 396.
Thwaites, Mr., on acclimatisation,
153*
Thylacinus, 463.
Tierra del Fuego, dogs of, 369.
Timber, drift, 407.
Time, lapse of, 335-
by itself not causmg modifica-
tion, X14.
Titmouse, x88.
Toads on island^ 436.
Tobacco, crossed varieties of, 326.
Tomes, Mr., on the distribution of
bats. 437.
Transitions in varieties rare, x8o.
Traquair, Dr., on flat-fish, 343.
Trautschold, on intermediate varie-
ties, 346.
Trees on islands belong to peculiar
orders, 435-
wiui separated sexes, Z13.
Trifolium pretense, 87, xo8.
incamatum, 108.
Triffonia, 373.
""rile"
Trilobites, 360.
, sudden extinction of, ^72,
Trimen, Mr., on imitating-insc
467.
Trimorphism in plants, 63, 331.
Troglodytes. 396.
iCtS,
Tumbler-pigeons, habits of, heredi-
tary, 368.
Tuco-tuco, blind, 149.
* abi
ary, 3$8.
Tumbler, young of, 484.
Turkey-cock, tuft of hair on breast,
103.
, naked skin on head. 308.
, young of, instinctively wild,
369.
Turnip and cabbage, analogous vari-
ations of, x68.
Type, unity of^ 3x8.
Types, succession of, in same areas,
388.
Typotherium, 378.
U
Udders enlarged by use, 39.
, rudimentary, 400.
Ulex, jroung leaves of, 480.
Umbelliferae, flowers and seeds of,
157.
, outer and xxiner florets of,
325.
Uni^ of type, 318.
Uria lacrymans, 105.
Use, effects of, under domestica-
tion, 39.
, effects of, in a state of na-
ture, 147.
Utility, how far important in the
construction of each part, 309.
Valenciennes, on fresh-water fish,
438.
Variability of mongrels and hy-
brids, 336.
Variation under domestication, 35.
caused by reproductive system
being affected by conditions of
life, 36, 37.
under nature, 58.
— , laws of, 145.
, correlated, 39, X55, 309.
Variations appear at corresponding
ages, 30, 99. . ,. .
analogous m distinct speaes,
168.
Varieties, natural, 58.
, struggle between, 90.
, domestic, extinction of, i3X.
— , transitional, rarity of, 180.
, when crossed, fertile, 336.
, 1 sterile, 335.
, das^cation of, 460.
Verbascum, sterility of, 303.
, varieties of crossed, 335, 326.
Verlot, M., on double stocks, 303.
Verneuil, M. de, on the succession
of species. 374.
Vibrecula of tne Polyzoa, 349.
Viola, small imperfect flowers of,
334.
, tricolor, 87.
Virchow, on the structure of the
crystalline lens, 103.
Virfi^nia, pigs of.
Volcanic islands,
337*
Vulture, naked skin on head, 308.
denudation of,
W
Wading-birds, 430.
Wagner, Dr., on Cecidomyia, 478.
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INDEX
553
Wasner, Moritz, on the importance
of isolation, ii6
Wallace, Mr., on origin of species,
21.
, on the limit of variation un-
der domestication, 56.
, on dimorphic lepidoptera, 61,
295.
• . on races in the Malay Archi-
pelago, 63. ,
, on the improvement of the
eye, 193.
, on the walking-stick insect,
236.
. on laws of geographical dis-
tribution, 402.
, on the Malay Archipelago,
, on mimetic animals, 4<$7-
Walsh, Mr. B. D., on phytophagic
forms, 64.
, on equal variability, x68.
Water, fresh, productions of, 427.
Water-hen, x8o.
Waterhouse, Mr., on Australian
marsupials, 126.
. on greatly developed parts
bemg variable. x6i.
, on the cells of bees, 280.
■ , on general affinities, 468.
Watson, Mr. H. C, on range of
varieties of British plants, 63, 74.
, on acclimatisation, 153.
, on flora of Azores, 410.
J on Ali>ine plants, 413.
, on rarity 01 intermediate ra-
rieties, 282.
, on convergence, 138.
, on the indefinite multiplica-
tion of species. 139.
Weale. Mr., on locusts transporting
seecu. 4p9>
Web of feet in water-birds, 190.
Weismann, Prof., on the causes of
variability, 26.
, on rudimentary organs, 493.
West Indian Islands, mamma1n of,
437*
Westwood, on species in large
genera being closely allied to
others, 73.
, on the tarsi of Engidae, 166,
, on the antennae of hymenop-
terous insects, 454.
Whales, 236.
Wheat, varieties of, X24«
White Mountains, flora of, 412.
Whitaker, Mr., on lines of escarp-
ment, 357.
Wichura, Max, on hybrids, 31 St 328.
Wings, reduction of size, 148.
of insects homologous with
branchiae, 195.
', rudunentarv, in insects, 490.
Wolf crossed with dog, 268.
of Falkland Isles, 436.
Wollaston, Mr., on varieties of in-
sects, 64.
1 on fossil varieties of shells in
Madeira, 69.
, on colours of insects on sea-
shore, X46.
,_ on wingless beetles, 148, 149.
i on rarity of intermediate va-
rieties, 182.
, on insular insects, 432.
—V on land-shells of Madeira
naturalised, 443.
Wolves, varieties of, X03.
Woodcock with earth attached to
Woojpeoccr, habits of, x88.
f green colour of. aor.
Woodward. Mr., on the duration of
specific forms, 347.
, on Pvrgoma,, 357.
, on the continuous succession
of genera, 367-
on the succession of types.
^rfd, species changing simultane-
ously throughout, 374.
Wrens, nest of, 296.
Wright, Mr. Chauncey, on the
giraffe, 2^1.
, on abrupt modifications, 260.
Wyman, Prof., on correlation of
colour and effects of poison.
n, 30.
:, 282.
on the cells of the bee,
Youatt, Mr., on selection, 46.
, on sub-breeds of sheep, 50.
, on rudimentary homt in
young cattle, 494.
Zanthoxylon, 227,
Zebra, stripes on, xyx.
Zeuglodon, 379.
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