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ORIGIN OF SPECIES.
BY MEANS OF NATURAL SELECTION
OR THE PRESERVATION OF FAVORED RACKS IN
THE STRUGGLE FOR LIFE
| bold
BY
CHARLES DARWIN, M. aL. Paar Re RS.
WITH ADDITIONS AND CORRECTIONS
FROM SIXTH AND LAST ENGLISH EDITION
IN TWO VOLUMES
VOLUME I
NEW YORK
D. APPLETON AND COMPANY
1889
CONTENTS.
ADDITIONS AND CORRECTIONS, TO THE SIXTH Eprrion .. Page ix
EAPO RICAT ISMECHG sa. pcg y ech oer. tyeatc aes ce cones se) OL
INTRODUCTION rr) ee ce ee es eo eo eo eo ee 1
CHAPTER I.
VARIATION UNDER DOMESTICATION.
Causes of Variability—Effects of Habit and the use or disuse of
Parts — Correlated Variation — Inheritance — Character of
Domestic Varieties—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, anciently followed, their Effects—
Methodical and Unconscious Selection—Unknown Origin of our
Domestic Productions—Circumstances. favourable to Man’s
POWER OL SClECHOM 50. emis ae: 2) sel ean nicalaniisen ena U
CHAPTER IL
VARIATION UNDER NATURE.
Variability — Individual differences— Doubtful species — Wide
: ranging, much diffused, and common species, vary most—
Species of the larger genera in each country vary more fre-
quently 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
LESIIELLO TANOCS yn eae ae pact tae se Gietyty eek Geet ee DM
vi CONTENTS.
CHAPTER III.
STRUGGLE FOR EXISTENCE.
Its bearing on natural selection—The term used in a wide sense—
Geometrical ratio of increase—Rapid increase of naturalised
animals and plants—Nature of the checks to increase—Com-
petition 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 individuals 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
Page 7d
CHAPTER IV.
NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST.
Natural Selection—its power compared with man’s selection—its
power on characters of triflimg importance—its power at all
ages and on both sexes—Sexual selection—On the generality
of intercrosses between individuals of the same species—Cir-
cumstances 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
inhabitants of any small area, and to naturalisation—Action of
Natural Selection, through divergence of Character and Ex-
tinction, on the descendants from a common parent—Explains
the grouping of all organie beings—Advance in organisation—
Low forms preserved—Convergence of Character—Indefinite
multiplication of species—Summary ... .. os « «: OF
CHAPTER V.
LAWS OF VARIATION.
Effects of changed conditions—Use and disuse, combined with
natural seiection; organs of flight and of vision—Acclimatisa-
CONTENTS. Vil
tion—Correlated variation—Compensation and economy of
growth—False correlations—Multiple, rudimentary, and lowly
organised structures variable—Parts developed in an unusual
manner are highly variable; specific characters more variable
than generic: secondary sexual characters variable—Species of
the same genus vary in an analogous manner—Reversions to
long-lost characters—Summary .. .. « « « Page 164
CHAPTER VI.
DIFFICULTIES OF THE THEORY.
Difficulties 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
perfection—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 Conditions of Existence embraced by the theory of Natural
DICESOME Cee. tue we us) teal | ee way) lew) “eur | esp tow LOG
CHAPTER VII.
MIscELLANEOUS OBJECTIONS TO THE THEORY oF NATURAL
SELECTION.
Longevity—Modifications not necessarily simultaneous—Modifica-
tions 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 functions—
Widely different organs in members of the same class,
developed from one and the same source—Reasons for dis-
believing in great and abrupt modifications .. .. .. 262
Vill
CONTENTS.
CHAPTER VIII.
INSTINCT.
Instincts comparable with habits, but different in their origin—
Instincts graduated—Aphides and ants—lInstincts variable—
Domestic 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 . oc oc e8 «sf e« oe bage dig
ADDITIONS AND CORRECTIONS
TO THE SIXTH EDITION.
NUMEROUS small corrections have been made in the last
and present editions on various subjects, according as
the evidence has become somewhat stronger or weaker.
The more important corrections and some additions in.
the present volume are tabulated on the following page,
for the convenience of those interested in the subject,
and who possess the fifth edition. The second edition
was little more than a reprint of the first. The third
edition was largely corrected and added to, and the
fourth and fifth still more largely. As copies of the
present work will be sent abroad, it may be of use if I
specify the state of the foreign editions. The third
French and second German editions were from the third
English, with some few of the additions given in the
fourth edition. A new fourth French edition has been
translated by Colonel Moulinié; of which the first half
is from the fifth English, and the latter half from the
present edition. A third German edition, under the
superintendence of Professor Victor Carus, was from the
fourth English edition ; a fifth is now preparing by the
same author from the present volume. The second
American edition was from the English second, with a
x ADDITIONS AND CORRECTIONS.
few of the additions given in the third; and a third
American edition has been printed from the fifth Eng-
lish edition. The Italian is from the third, the Dutch
and three Russian editions from the second English
edition, and the Swedish from the fifth English edition.
Fifth | Sixth
Edition. | Edition.
Page | Page
vol. i.
100 | 106 | Influence of fortuitous destruction on natural selection.
158 | 156 | On the convergence of specific forms.
220 | 221 | Account of the Ground-Woodpecker of La Plata
modified.
225 | 227 | On the modification of the eye.
230 233 | Transitions through the acceleration or retardation
of the period of reproduction.
231 | 234 | The account of the electric organ of fishes added to.
233 | 2387 | Analogical resemblance between the eyes of Cepha-
lopods and Vertebrates.
234 | 239 | Claparéde on the analogical resemblance of the hair-
claspers of the Acaridze.
248 | 254 | The probable use of the rattle to the Rattle-snake.
248 | 254 | Helmholtz on the imperfection of the human eye.
255 | 262 | The first part of this new chapter consists of portions,
in a much modified state, taken from chap. iv. of
the former editions. The latter and larger part is
new, and relates chiefly to the supposed incom-
petency of natural selection to account for the
incipient stages of useful structures. There is
also a discussion on the causes which prevent in
many cases the acquisition through natural selec-
tion of useful structures. Lastly, reasons are
given for disbelieving in great and sudden modifi-
cations. Gradations of character, often accom-
panied by changes of function, are likewise here
incidentally considered.
268 | 833 | Thé statement with respect to young cuckoos ejecting
their foster-brothers confirmed.
270 | 834 | On the cuckoo-like habits of the Molothrus.
307 9 | On fertile hybrid moths.
319 2 The discussion on the fertility of hybrids not having
been acquired through natural selection condensed
| and modified. cs
Chief Additions and Corrections.
ADDITIONS AND CORRECTIONS. Xa
Fifth Sixth
Edition. | Edition.
Page Page
Z vol. ii.
326 28
377/81
402 107
440 148
463 172
505 218
516 | 232
518 236
520 237
521 240
541 262
547 262
552 275
568 | 293
572 | 297
Chief Additions and Corrections.
On the causes of sterility of hybrids, added to and
corrected. .
Pyrgoma found in the chalk.
Extinct forms serving to connect existing groups.
On earth adhering to the feet of migratory birds.
On the wide geographical range of a species of
Galaxias, a fresh-water fish.
Discussion on analogical resemblances, enlarged and
modified.
Homological structure of the feet of certain mar-
supial animals.
On serial homologies, corrected.
Mr. E. Ray Lankester on morphology.
On the asexual reproduction of Chironomus.
On the origin of rudimentary parts, corrected.
Recapitulation on the sterility of hybrids, corrected.
Recapitulation on the absence of fossils beneath the
Cambrian system, corrected.
Natural selection not the exclusive agency in the
modification of species, as always maintained in
this work.
The belief in the separate creation of species generally
held by naturalists, until a recent period.
“But with regard to the material world, we can at least go so 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 establishment of general laws.”
WHEWELL: Bridgewater Treatise.
“The only distinct meaning of the word ‘natural’ is stuted,
fixed, or settled; since what is natural as much requires and
presupposes an intelligent agent to render it so, z.e., to effect it
continually or at stated times, as what is supernatural or miraculous
does to effect it for once.”
Butter: Analogy of Revealed Religion.
“To conclude, therefore, let no man out of a weak conceit 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 proficence in both.”
Bacon: Advancement of Learning.
Down, Beckenham, Kent,
First Edition, November 24th, 1859,
Siath Edition, Jan. 1872.
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 witt here give a brief sketch of the progress of
opinion on 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 allusions to the sub-
ject in the classical writers,* the first author who in
* Aristotle, in his ‘ Physica Auscultationes’ (lib. 2, cap. 8, s. 2),
after remarking that rain does not fall in order to make the corn
grow, any more than it falls 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 different parts [of the
body | from having this merely accidental relation in nature? as the
teeth, for example, grow by necessity, the front ones sharp, adapted
for dividing, and the grinders 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 toan end. Whereso-
ever, therefore, all things together (that is all the parts of one
whole) happened like as if they were made for the sake of some-
thing, these were preserved, having been appropriately constituted
X1V HISTORICAL SKETCH.
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.
Lamarck was the first man whose conclusions on the
subject excited much attention. This justly-celebrated
naturalist first published his views in 1801; he much
enlarged them in 1809 in his ‘ Philosophie Zoologique,’
and subsequently, in 1815, in the Introduction to his
‘Hist. Nat. des Animaux sans Vertébres.’ In these
works he upholds the doctrine that all species, including
man, are descended from other species. He first did
the eminent service of arousing attention to the pro-
bability 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 produc-
tions. 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
by an internal spontaneity ; and whatsoever things were not thus
constituted, perished, and still perish.” We here see the principle
of natural selection shadowed forth, but how little Aristotle fully
comprehended the principle, is shown by his remarks on the
formation of the teeth.
HISTORICAL SKETCH. XV
branches of trees. But he likewise believed in a law of
progressive development; 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 im 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 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 conditions 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 4 réserver
entierement a4 lavenir, supposé méme que l’avenir doive
avoir prise sur lui.” _
In 1813, Dr. W. C. Wells read before the Royal
* T have taken the date of the first publication of Lamarck from
Isid. Geoffroy Saint-Hilaire’s (‘ Hist. Nat. Générale,’ tom. 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), published in
1794. According to Isid. Geoffroy there is no doubt that Goethe
was an extreme partisan of similar views, as shown in the Intro-
duction to a work written in 1794 and 1795, but not published till
long afterwards: he has pointedly remarked (‘ Goethe als Natur-
forscher,’ von Dr. Karl Meding, s. 34) that the future question for
naturalists will be how, for instance, cattle got their horns, and not
for what they are used. It is rather a singular 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
conclusion on the origin of species, in the years 1794-5,
Xvi HISTORICAL SKETCH.
Society ‘An Account of a White female, part of whose ~
skin resembles 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 indi-
cated; but he apples it only to the races of man, and
to certain characters alone. .After remarking that
negroes and mulattoes enjoy an immunity from certain
tropical diseases, he observes, firstly, that all animals
tend to vary in some degree, and, secondly, that agri-
culturists improve their domesticated animals by selec-
tion ; 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 inhabi-
tants of the middle regions of Africa, some one would
be better fitted than the others to bear the diseases of
the country. 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
eranted, from what has been already said, would be
dark. But the same disposition to form varieties 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
¥
HISTORICAL SKETCH. XVil
climates. I am indebted 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
Manchester, in the fourth volume of the ‘ Horticultural
Transactions, 1822, and in his work on the ‘ Amaryl-
lidaceze ’ (1837, pp. 19, 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 para-
eraph in his well-known paper (‘ Edinburgh Philosophi-
cal 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 en-
larged in the present volume. Unfortunately the view
was given by Mr. Matthew very briefly in scattered
passages in an Appendix to a work on a different
subject, so that it remained unnoticed until Mr. Matthew
himself drew attention to it in the ‘ Gardener’s
Chronicle, on April 7th, 1860. The differences of Mr
XVili HISTORICAL SKETCH. —
Matthew’s view from mine are not of much importance :
he seems to consider that the world was nearly de-
populated 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.” Jam not sure that I understand
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 pe
of natural selection.
The celebrated geologist and naturalist, Von Buch,
in his excellent ‘Description Physique des Isles
Canaries’ (1836, p. 147), clearly expresses his belief
that varieties slowly become changed into permanent
species, which are no longer capable of intercrossing.
Rafinesque, in his ‘New Flora of North America,’
published in 1836, wrote (p. 6) as follows:—“ All
species might have been varieties once, and many
varieties are gradually becoming species by assuming
constant and peculiar characters;” but farther on
(p. 18) he adds, “ except the original types or ancestors
of the genus.”
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 develop-
ment and modification of species: he seems to lean
towards the side of change.
The ‘ Vestiges of Creation’ appeared 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 recent, are, under the
HISTORICAL SKETCH. aD.¢
providence of God, the results, first, of an impulse which
has been imparted to the forms of life, advancing 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 apparently 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 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, imme-
diately 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 l’Acad. Roy. Bruxelles,’ tom. xiii. p. 581)
xx HISTORICAL SKETCH.
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 ignorant.” In his Address
to the British Association, in 1858, he speaks (p. 1.) 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 dis-
tribution, 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 distinct 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, one by the other, it appears that
this eminent philosopher felt in 1858 his confidence
HISTORICAL SKETCH. xxi
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.
Wallace 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 completely deceived, as were many
others, by such expressions as “ the continuous operation
of creative power,” that I included Professor Owen with
other paleontologists as being firmly convinced of the
immutability of species; but it appears (‘ Anat. of
Vertebrates,’ vol. ii. 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 announce-
ment; but as far as it is possible to understand certain
recently published passages (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
xxii HISTORICAL SKETCH.
enunciation of the principle of natural selection is con-
cerned, 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 Résumé appeared in the
‘Revue et Mag. de Zoolog.” Jan. 1851), briefly gives
his reason for believing that specific characters “sont
fixés, pour chaque espece, tant qu'elle se perpétue au
milieu des mémes circonstances: ils se modifient, si les
circonstances ambiantes viennent a changer.” “En
résumé, l’observation des animaux sauvages démontre
déja la variabilité limitée des especes. Les expériences
sur les animaux sauvages devenus domestiques, et sur
les animaux domestiques redevenus sauvages, la démon-
trent plus clairement encore. Ces mémes expériences
prouvent, de plus, que les différences produites peuvent
étre de valeur générique.” In his ‘ Hist. Nat. Générale’
(tom. ii. p. 430, 1859) he amplifies analogous conclusions.
From a circular lately issued it appears that Dr.
Freke, in 1851 (‘ Dublin Medical Press,’ p. 322), pro-
pounded the doctrine that all organic beings have
descended from one primordial 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 Species 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 pub-
lished 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
HISTORICAL SKETCH. XxUll
remarkable skill and force. He argues from the analogy
of domestic productions, from the changes which the
embryos of many species undergo, from the difficulty
of distinguishing species and varieties, 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
acquirement of each mental power and capacity by
gradation.
In 1852 M. Naudin, a distinguished botanist, ex-
pressly stated, in an admirable paper on the Origin of
Species (‘ Revue Horticole, p. 102; since partly repub-
lished in the ‘ Nouvelles Archives du Muséum,’ 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 selection 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, “puissance mystérieuse, indéterminée ;
fatalité pour les uns; pour les autres, volonté provi-
dentielle, dont V’action incessante sur les étres vivants
détermine, a toutes les époques de l’existence du monde,
la forme, le volume, et la durée de chacun d’eux, en
raison de sa destinée dans l’ordre de choses dont il fait
partie. Ovest cette puissance qui harmonise chaque
membre a l’ensemble, en l’appropriant a la fonction qu’il
doit remplir dans lorganisme général de la nature,
fonction qui est pour lui sa raison d’étre.” *
* From references in Bronn’s ‘ Untersuchungen iiber die Eni-
wickelungs-Gesetze, it appears that the celebrated botanist
XXivV HISTORICAL SKETCH.
In 1853 a celebrated geologist, Count Keyserling
(‘ Bulletin de la Soc. Géolog.,’ 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 chemically affected by circum-
ambient 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 development 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 Géograph. Bot., tom. i. p. 250),
“On voit que nos recherches sur la fixité ou la variation
de l’espece, nous conduisent directement aux idées émises,
paleontologist Unger published, in 1852, his belief that species
undergo development and modification. Dalton, likewise, in
Pander and Dalton’s work on Fossil Sloths, expressed, in 1821, a
similar belief. Similar views have, as is well known, been main-
tained by Oken in his mystical ‘ Natur-Philosophie.’ From other
references in Godron’s work ‘Sur l’Espéce,’ it seems that Bory
St. Vincent, Burdach, Poiret, and Fries, have all admitted that new
species are continually being produced.
I may 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.
HISTORICAL SKETCH. XXV
par deux hommes justement célebres, Geoffroy Saint-
Hilaire et Gceethe.” Some other passages scattered
through M. Lecoq’s large work, make it a little
doubtful how far he extends his views on the modifica-
tion of species.
The ‘Philosophy of Creation’ has been treated in a
masterly 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 myself, in which, as stated in the intro-
ductory remarks to this volume, the theory of Natural
Selection is promulgated by Mr. Wallace with admir-
able force and clearness.
Von Baer, towards whom all zoologists feel so pro-
found a respect, expressed about the year 1859 (see
Prof. Rudolph Wagner, ‘ Zoologisch-Anthropologische
Untersuchungen, 1861, s. 51) his conviction, chiefly
erounded 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 eases, he remarks,
“Tt is difficult to comprehend 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
2
XXvVl1 HISTORICAL SKETCH.
long intervals by a distinct act of creative power; and
it is well to recollect that such an assumption -is as
unsupported 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 supposes the species living at any
time to be the result of the gradual modification of
pre-existing species a hypothesis which, though un-
proven, 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.”
In December, 1859, Dr. Hooker published his ‘ Intro-
duction to the Australian Flora.’ In the first part of
this great work he admits the truth of the descent and
modification of species, and supports this doctrine by
many original observations.
The first edition of this work was published on
November 24th, 1859, and the second edition on
January 7th, 1860.
ORIGIN OF SPECIES.
INTRODUCTION.
WHEN on board H.MLS. ‘ Beagle, as naturalist, I was
much struck with certain facts in the distribution of
the organic beings inhabiting 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 speculate 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.
2 INTRODUCTION.
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—honoured me
by thinking it advisable to publish, with Mr. Wallace’s
excellent memoir, some brief extracts from my manu-
scripts. :
This Abstract, which I now publish, must necessarily
be imperfect. I cannot here give references and au-
thorities for my several statements; and I must trust
to the reader reposing some confidence in my accuracy.
No doubt errors will have crept in, though I hope I
have always been cautious in trusting to good authorities
alone. JI 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 refer-
ences, 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 facts cannot be adduced, often
apparently leading to conclusions directly opposite to
INTRODUCTION. 3
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 satisfaction 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
conclusion that species had 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 perfec-
tion of structure and coadaptation which justly excites
our admiration. Naturalists continually refer to ex-
ternal conditions, such as climate, food, &c, 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 nourishment from certain
4 INTRODUCTION.
trees, which has seeds that must be transported 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 account for the structure of this parasite,
with its relations to several distinct organic beings, by
the effects of external conditions, or of habit, or of the
volition of the plant itself.
It is, therefore, of the highest importance to gain a
clear insight into the means of modification and co-
adaptation. At the commencement of my observations
it seemed to me probable that a careful study of domes-
ticated animals and of cultivated plants would offer the
best-chance of making out this obscure problem. 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 clue. I may
venture to express my conviction of the high value of
such studies, although they have been very commonly
neglected by naturalists.
From these considerations, I shall devote the first
chapter of this Abstract to Variation under Domesti-
cation. We shall thus see that a large amount of
hereditary modification is at least possible; and, what
is equally or more important, we shall see how great
is the power of man in accumulating by his Selection
successive slight variations. I will then pass on to
the variability of species 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, however, be
enabled to discuss what circumstances are most favour-
INTRODUCTION. 5
able to variation. In the next chapter the Struggle for
Existence amongst all organic beings throughout the
world, which inevitably follows from the high geo-
metrical ratio of their increase, will be considered.
This is the doctrine of Malthus, applied to the whole
animal and vegetable kingdoms. As many more in-
dividuals of each species are born than can possibly
survive; and as, consequently, there is a frequently
recurring 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 conditions 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 in-
evitably causes much Extinction of the less improved
forms of life, and leads to what I have called Diver-
gence of Character. In the next chapter I shall discuss
the complex 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 transitions, 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 im-
perfection of the Geological Record. In the next
chapter I shall consider the geological succession of
6 INTRODUCTION.
organic beings throughout time; in the twelfth and
thirteenth, their geographical distribution throughout
space; in the fourteenth, their classification or mutual
affinities, both when mature and in an embryonic con-
dition. In the last chapter I shall give a brief recapitu-
lation of the whole work, and a few concluding remarks.
No one ought to feel surprise at much remaining as
yet unexplained 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 an-
other allied species has a narrow rangeandisrare? 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 dispassionate judgment of which I am capable, that
the view which most naturalists until recently enter-
tained, and which I formerly entertained—namely, that
each species has been independently created—is erro-
neous. 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 de-
scendants of that species. Furthermore, I am convinced
that Natural Selection has been the most important,
but not the exclusive, means of modification.
Cuarp, LL] VARIATION UNDER DOMESTICATION. t
CHAPTER IL
VARIATION UNDER DOMESTICATION,
Causes of Variability—Effects of Habit and the use or disuse of
Parts—Correlated Variation—Inheritance—Character of Do-
mestic Varieties—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, anciently followed, their Hffects—
Methodical and Unconscious Selection—Unknown Origin of
our Domestic Productions —Circumstances favourable to Man’s
power of Selection.
Causes of Variability.
WHEN we compare the individuals of the same variety
or sub-variety of our older cultivated plants 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 variability is due to our
domestic productions having been raised under con-
ditions 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 pro-
8 VARIATION UNDER DOMESTICATION. ([Cuap. IL.
bability 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 generations to new
conditions to cause any great amount of variation; 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 wheat, still yield new varieties: our oldest do-
mesticated animals are still capable of rapid improv-
ment 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 respect to the direct action, we must
bear in mind that in every case, as Professor Weis-
mann has lately insisted, and as I have incidentally
shown in my work on ‘ Variation under Domestication,’
there are two factors: namely, the nature of the organ-
ism, and the nature of the conditions. The former seems
to be much the more important; for nearly similar vari-
ations sometimes arise under, as far as we can judge,
dissimilar conditions ; and, on the other hand, dissimilar
variations arise under conditions which appear to be
nearly uniform. ‘The effects on the offspring are either
definite or indefinite. They may be considered as defi-
nite 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 conclusion in regard to the
extent of the changes which have been thus definitely
Cuar. 1.) VARIATION UNDER DOMESTICATION. 9
induced. There can, however, be little doubt about many
sheht changes,—such as size from the amount of food,
colour from the nature of the food, thickness of the skin
and hair from climate, &e. 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, all 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
probably played a more important part in the forma-
tion of our domestic races. We see indefinite vari-
ability in the endless slight peculiarities which
distinguish the individuals of the same species, and
which cannot be accounted for by inheritance from
either parent or from some more remote ancestor.
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 pronounced 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
10 $$ VARIATION UNDER DOMESTICATION. ([Cuap. I.
as the indefinite effects of the conditions of life on each
individual organism, in nearly the same manner as the
chill affects different 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 system 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 remarked, between the
variability which follows from the crossing of distinct
species, and that which may be observed 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 difficult 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 display
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; but to show how singular the
Cuar.I.] VARIATION UNDER DOMESTICATION. 11
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 exception of
the plantigrades or bear family, which seldom produce
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 domesticated 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 re-
productive 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 producing offspring somewhat unlike
their parents. I may add, that as some organisms
breed freely under the most unnatural 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 domestica-
tion or cultivation, and vary very slightly—perhaps
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
12 VARIATION UNDER DOMESTICATION. ([Cuap. I.
on the same plant. These bud variations, as they may
be named, can be propagated by grafts, offsets, &c., and
sometimes by seed. They occur rarely under nature,
but are far from rare under culture. Asa 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 con-
ditions, have sometimes yielded nearly the same variety
—for instance, buds on peach-trees producing nec-
tarines, and buds on common roses producing moss-
roses—we clearly see that the nature of the con-
ditions 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 deter-
mining 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
period of the flowering of plants when transported from
one climate to another. With animals the increased
use or disuse 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 skeleton, 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
Cuap. I.] VARIATION UNDER DOMESTICATION. 13
and goats in countries where they are habitually
milked, in comparison with these organs in other
countries, is probably another instance of the effects of
use. Not one of our domestic 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 entail 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 this is confined to the males. Colour and
constitutional peculiarities 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 injured by certain plants,
whilst dark-coloured individuals escape: Professor Wy-
man has recently communicated to me a good illustra-
tion of this fact; on asking some farmers in Virginia
how it was that all their pigs were black, they informed
him that the pigs ate the paint-root (Lachnanthes), which
coloured their bones pink, and which caused the hoofs
of all but the black varieties to drop off; and one of the
4 VARIATION UNDER DOMESTICATION. ([Cuap. I.
“crackers” (ze. 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 peculiarity,
he will almost certainly modify unintentionally other
parts of the structure, owing to the mysterious laws of
correlation.
The results of the various, unknown, or but dimly
understood laws of variation are 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, &c. ;
and it is really surprising to note the endless points of
structure and constitution in which the varieties and
sub-varieties differ slghtly 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 lke
produces like is his fundamental belief: doubts have
been thrown on this principle only by theoretical
writers. When any deviation of structure often ap-
Cuap. 1.}] VARIATION UNDER DOMESTICATION. 15
pears, 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 com-
pels us to attribute its reappearance to inheritance.
Every one must have heard of cases of albinism,
prickly .skin, hairy bodies, &¢., 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-in-
heritance as the anomaly.
The laws governing inheritance are for the most part
unknown. No one can say why the same peculiarity
in different 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 com-
monly but not exclusively to the like sex. It is a fact
of some importance to us, that peculiarities appearing
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
16 VARIATION UNDER DOMESTICATION. ([Cuzap. I.
reappear in the offspring at a corresponding age,
though sometimes earlier. In many cases this could
not be otherwise; thus the inherited peculiarities in
the horns of cattle could appear only in the offspring
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 exten-
sion, 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 appeared in the parent. I
believe this rule to be of the highest importance in
explaining the laws of embryology. These remarks are
of course confined to the first appearance of the pe-
culiarity, 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-
horned bull, though appearing late in life, is clearly
due to the male element.
Having alluded to the subject of reversion, 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 boldy 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
Cuar. IL] VARIATION UNDER DOMESTICATION. 17
state. In many cases we do no know what the abo-
riginal stock was, and so could not tell whether or not
nearly perfect reversion had ensued. It would be
necessary, in order to prevent the effects of inter-
crossing, that only a single variety should have been
turned loose in its new home. Nevertheless, 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 experiment 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
check, by blending together, any slight deviations in
their structure, in such case, I grant that we could de-
duce 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-horned
cattle, and poultry of various breeds, and esculent
vegetables, for an unlimited number of generations,
would be opposed to all experience.
18 CHARACTER OF DOMESTIC VARIETIES. ([Cuapr. I.
Character of Domestic Varieties; difficulty of dts-
tinguishing between Varieties and Species; origin of
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 monstrous character; by which I
mean, that, although differmg 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 another, 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), domestic 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 value. It can be shown
that this statement is not correct; but naturalists differ
Caap. I.] CHARACTER OF DOMESTIC VARIETIES, 19 -
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
difference 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 bull-dog, 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 immutability of
the many closely allied natural species—for instance,
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 domesti-
cation; 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 domes-
ticated 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 do-
mestication 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 domes-
ticated productions: but how could a savage possibly
20 CHARACTER OF DOMESTIC VARIETIES. ([Cuar. I.
know, when he first tamed an animal, 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 endurance of
warmth by the reindeer, or of cold by the common
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 generations under domestication, they would
on a 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 conclusion, 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 diversity in the
breeds ; and that some of these ancient breeds closely
resemble, or are even identical with, those still existing.
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
Cuap. IL] CHARACTER OF DOMESTIC VARIETIES. 21
previous period of less advanced civilisation, during
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
probably 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
Canidz have been tamed, and that their blood, in some
cases mingled together, flows in the veins of our do-
mestic 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, constitution, and
structure of the humped Indian cattle, it is almost
certain that they are descended from a different
aboriginal 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 distinction between the humped
and common cattle, may, indeed, be looked upon ag
established by the admirable researches of Professor
Ritimeyer. With respect to horses, from reasong
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
22 CHARACTER OF DOMESTIC VARIETIES. ([Cuap. I.
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 Britam! 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, &c., but that
each of these kingdoms possesses several peculiar breeds
of cattle, sheep, &c., we must admit that many domestic
breeds must have originated in Europe; for whence
otherwise could they have been derived? So it is in
India. Even in the case of the breeds of the domestic
dog throughout the world, which I admit are descended
from several wild species, it cannot be doubted that
there has been an immense amount of inherited
variation; for who will believe that animals closely
resembling the Italian greyhound, the bloodhound, the
bull-dog, pug-dog, or Blenheim spaniel, &e.—so unlike
all wild Canide—ever existed in a state of nature? It
Cuar. I.] - DOMESTIC PIGEONS. 23
has often been loosely said that all our races of dogs
have been produced by the crossing of a few aboriginal
species ; 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 the Italian greyhound, bloodhound, bull-dog,
&e., 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 between
two pure breeds is tolerably and sometimes (as I have
found with pigeons) quite uniform in character, and
everything 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 of the Domestic Pigeon, their Differences 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. Ellot from India, and by
the Hon. ©. Murray from Persia. Many treatises in
24 DOMESTIC PIGEONS. [Cuap. I.
different languages have been published on pigeons,
and some of them are very important, as beimg of
considerable antiquity. I have associated with several
eminent fanciers, and have been permitted to jom two
of the London Pigeon Clubs. The diversity of the
breeds is something astonishing. Compare the English
carrier and the short-faced tumbler, and see the
wonderful difference in their beaks, entailing corres-
ponding 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 the nostrils, and
a wide gape of mouth. The short-faced tumbler has a
beak in outline almost lke that of a finch; and the
common tumbler has the singular inherited habit of
flying at a great height in a compact ficck, 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 expanding, slightly, the upper part of the
cesophagus. 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
Cuap. 1.] DOMESTIC PIGEONS. 25
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 all 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 develop-
ment of the bones of the face in length and breadth and
curvature ditfers 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
vertebre vary in number; as does the number of the
ribs, together with their relative breadth and the pre-
sence of processes. ‘The size and shape of the apertures
in the sternum are highly variable; so is the degree
of divergence and relative size of the 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 cesophagus; the develop-
ment 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
scutelle on the toes, the development of skin between
the toes, are all points of structure 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
YAS) DOMESTIC PIGEONS. [Cuap. I
some breeds the voice and disposition, differ remarkably.
Lastly, in certain breeds, the males and females have
come to differ in a slight degree from 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 cértainly 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,
could be shown hin.
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), in-
eluding 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 degree applicable
in other cases, I will here briefly give them. If the
several breeds are not varieties, and have not proceeded
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 possessed the characteristic
enormous crop? The supposed aboriginal 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
Cuap. I.] DOMESTIC PIGEONS. 27
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 ex-
terminated; and the common rock-pigeon, which has
the same habits with the domestic breeds, has not
been exterminated 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
cguntry ; but not one has become wild or feral, though
the dovecot-pigeon, which is the rock-pigeon in a very
shghtly altered state, has become feral in several places.
Again, all recent experience shows that it is difficult
to get wild animals to breed freely under domesti-
cation; yet on the hypothesis of the multiple origin
of our pigeons, it must be assumed that at least seven
or eight species were so thoroughly domesticated in
ancient times by half-civilised man, as to be quite
prolitic under confinement.
An argument of great weight, and applicable in
several other cases, is, that the above-specified breeds,
though agreeing generally with the wild rock-pigeon
in constitution, habits, voice, colouring, and in most
AME RIC
28 - - DOMESTIC PIGEONS. [Cuar. I.
parts of their structure, yet are certainly highly abnor-
mal in other parts; we may look in vain through the
whole great family of Columbidee for a beak lke that
of the English carrier, or that of the short-faced tumbler,
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-civiised man succeeded in thoroughly
domesticating several species, but that he intention-
ally 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
deserve 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-domestic breeds, and
some truly wild breeds, have, besides the two black
bars, the wings chequered with black. These several
marks co not occur together in any other species of
the whole family. Now, in every one of the 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. More-
over, 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 offspring
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
Cuap. I.] DOMESTIC PIGEONS. 29
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 monvrels 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! We can under-
stand these facts, on the well-known principle of
reversion to ancestra! characters, if all the domestio
breeds are descended from the rock-pigeon. But if we
deny this, we must make one of the two following
highly improbable suppositions. Fither, 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 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 aozen, or at most within a score, of generations, been
erossed 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 naturally become less and less, as in each suc-
ceeding generation there will be less of the foreign
blood; but when there has been no cross, aud there
30 : DOMESTIC PIGEONS. [Cuap. I.
is a tendency in the breed to revert to a character
which was lost during some former generation, 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 inheritance.
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 domestic
animals, this conclusion is probably quite correct, if
applied to species closely related to each other. But
to extend it so far as to suppose that species, aborigi-
nally as distinct 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 improba-
bility of man having formerly made seven or eight
supposed species of pigeons to breed freely under
domestication ;—these supposed 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
Columbide, though so like the rock-pigeon in most
respects ;—the occasional re-appearance of the blue
colour and various black marks in all the breeds, both
when kept pure and when crossed ;—and lastly, the
Cuap. I.] DOMESTIC PIGEONS. 31
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. Secondly, 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 variable, 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 earliest known record of pigeons is in the fifth
Egyptian dynasty, about 3000 Bc., 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
o2 DOMESTIC PIGEONS. [Cuar. I.
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 crossing the breeds, 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-
plaining the immense amount of variation which pigeons
have undergone, will likewise be obvious when we treat
of Selection. Weshall 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 probable 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
Cuap. I.] DOMESTIC PIGEONS. Be
has attended, are descended from so many aboriginally
distinct species. Ask, as I have asked, a celebrated
raiser of Hereford cattle, whether his cattle might not
have descended from Long-horns, 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. In-
numerable other examples could be given. The ex-
planation, I think, is simple: from long-continued
study they are strongly impressed with the differences
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 differences 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 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 parents—may they not learn a lesson
of caution, when they deride the idea of species in a
state of nature being lineal descendants of other
species ?
34 _ SELECTION BY MAN. (Cuar. 1
Principles of Selection anciently followed, and their
Lifjects.
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 at-
tributed to the direct and definite 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 domesticated 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 suddenly, or by one
step; many botanists, for mstance, 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
suddenly 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
Cuap. I.) SELECTION BY MAN. 35
compare the host of agricultural, culinary, orchard,
and flower-garden races of plants, most useful to man
at different seasons and for different purposes, or so
beautiful in his eyes, we must, I think, look further
than to mere variability. We cannot suppose that all
the 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 accumulative 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
hypothetical. It is certain that several of our eminent
breeders have, even within a single hfetime, 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 organisation as some-
thing plastic, which they can model almost as they
please. If I had space I could quote numerous pas-
sages to this effect from highly competent authorities.
Youatt, who was probably better acquainted with the
works of agriculturists than almost any other indi-
vidual, and who was himself 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 Scmerville, speaking of what breeders
have done for sheep, says :—“ It would seem as if they
36 SELECTION BY MAN. (Cuap. I.
had chalked out upon a wall a form perfect in itself,
and then had given it existence.” In Saxony 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
ordinary cases. If selection consisted merely in sepa-
rating 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 jude-
ment 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
Cuap. I.] SELECTION BY MAN. 37
natural capacity and years of practice requisite to
become 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 pro-
duced 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 florists’ flowers,
when the flowers of the present day are compared 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 animals this kind of selection is, in
fact, likewise followed; for hardly any one is so care-
less as to breed from his worst animals.
In regard to plants, there is another means of ob-
serving 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 comparison with
the leaves and flowers of the same set of varieties.
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 go0se-
58 _ METHODICAL SELECTION. (Crap. I.
berries 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—perhaps
never, the case. The law of correlated variation, the
importance 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 references to works of
high antiquity, im which the full importance of the
principle is acknowledged. In rude and barbarous
periods of English history choice animals were often
imported, and laws were passed to prevent their ex-
portation: the destruction of horses under a certain
size was ordered, and this may be compared to the
“roouing” of plants by nurserymen. The principle of
selection I find distinctly given in an ancient Chinese
encyclopedia. Explicit rules are laid down by some
of the Roman classical writers. From passages in
Genesis, it is clear that the colour of domestic animals
was at that early period attended to. Savages now
sometimes cross their dogs with wild canine animals,
Cap. 1] UNCONSCIOUS SELECTION. 39
to improve the breed, and they 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 dogs. 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 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 in-
heritance 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
naturally tries to get as good dogs as he can, and
afterwards breeds from his own best dogs, but he has no
wish or expectation 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, &c., 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
40 UNCONSCIOUS SELECTION. ([Cuar. L
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’s 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 pro-
bably 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 certainly came
from Spain, Mr. Borrow has not seen, as I am informed
by him, any native dog in Spain like our pointer.
By a similar 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 earry. 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.
Cuap. I.] UNCONSCIOUS SELECTION. — 4]
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 production 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 suspicion
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 F uego,
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 indi-
viduals, whether or not sufficiently distinct to ‘be
ranked at their first appearance as distinct varieties,
and whether or not two or more species or races have
42 UNCONSCIOUS SELECTION. [Cuap. I.
become blended together by crossing, 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. JI have seen great surprise
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 unconsciously. 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 preserved the best varieties they could anywhere
find.
A large amount of change, thus slowly and un-
consciously 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
ae:
vA
5 ere
\
Cuap. 1.] UNCONSCIOUS SELECTION. 43
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 inhabited 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 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, individuals of the same
species, having slightly different constitutions 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
selection 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
a4 UNCONSCIOUS SELECTION. [Cuap I.
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 externally visible; and indeed he rarely cares for
what is internal. 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
somewhat 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 un-
conscious 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 individuals of other and distinct breeds, in which
as many as 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 cesophagus,—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 value 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
Cuap. 1.] UNCONSCIOUS SELECTIUN. 45
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
standard 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 breeds 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
shehtly 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 valuable, 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 district than in
46 CIRCUMSTANCES FAVOURABLE TO SELECTION.
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,
favourable, or the reverse, to man’s power of selection.
A high degree of variability is obviously favourable, as
freely giving the materials for selection to work on;
not that mere individual differences are not amply
sie,
sufficient, with extreme care, to allow of the accumula- _
tion of a large amount of modification in almost any
desired direction. But as variations manifestly 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, number 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 zm 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 selection. But probably the most
important element is that the animal or plant should
CIRCUMSTANCES FAVOURABLE TO SELECTION. 47
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
ean 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 strawberry had always varied since it was
cultivated, but the slight varieties had been neglected.
As soon, however, as gardeners picked out individual
plants with slightly larger, earlier, or better fruit, and
raised seedlings from them, and again 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 propagated in.great numbers 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
4
48 CIRCUMSTANCES FAVOURABLE TO SELECTION.
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
display of distinct breeds; but the goose, under the
conditions to which it is exposed when domesticated,
seems to have a singularly inflexible organisation,
though it has varied to a slight extent, as I have else-
where 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 assert that the limit has been attained
in any one case; for almost 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 increased to
their utmost limit, could not, after remaining fixed for
many centuries, again vary under 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
CIRCUMSTANCES FAVOURABLE TO SELECTION. 49
terrestrial animal, as this will be determined by the
friction to be overcome, the weight of body to be
earried, and the power of contraction in the muscular
fibres. But what concerns us is that the domestic
varieties 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. Isidore 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 characters, Eclipse was
far fleeter, and a dray-horse is incomparably 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 regard to the fruit of the several varieties
of the plum, and still more strongly with the melon, as
well as in many other analogous 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
shallendure. 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
50 - SUMMARY OF SELECTION. (Cap. I.
be attributed to the increased use or disuse of parts.
The final result is thus rendered infinitely complex.
In some cases the intercrossing of aboriginally distinct —
species appears to have played an important part in
the origin of our breeds. When several breeds have
once been formed in any country, their occasional
intercrossing, with the aid of selection, has, no doubt,
largely aided in the formation of new sub-breeds ; but
the importance of crossing has been much exaggerated,
both in regard to animals and to those plants which
are propagated by seed. With plants which are
temporarily propagated by cuttings, 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 import-
ance 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 predominant Power.
Cuap. IL] VARIATION UNDER NATURE. 5
CHAPTER ITI.
VARIATION UNDER NATURE.
Variability —Individual differences—Doubtful species—Wide rang-
ing, 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 s: ecies of the
larger genera resemble varieties in being very closely, but un-
equally, 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 definition has satisfied all
naturalists; yet every naturalist knows vaguely what
he means when he speaks of a species. Generally the
term includes the unknown element of a distinct act of
creation. The term “variety” is almost equally
difficult to define; but here community of descent
is almost universally 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 considerable deviation of
structure, generally injurious, or not useful to the
species. Some authors use the term “variation” in a
52 VARIATION UNDER NATURE. [Cuap. IT.
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 in this case I
presume that the form would be called a variety.
It may be doubted whether sudden and considerable
deviations of structure such as we occasionally see in
our domestic productions, more especially with plants,
are ever permanently propagated in a state of nature.
Almost every part of every organic being is so beauti-
fully related to its complex conditions of life that it
seems as improbable that any part should have been
suddenly produced perfect, as that a complex 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 proboscis, and if any wild species of the
same genus had naturally 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 resembling
nermal 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 reproduction (which is not always the case),
as they occur rarely and singly, their preservation
would depend on unusually favourable circumstances.
They would, also, during the first and succeeding
Cuap. II.] INDIVIDUAL DIFFERENCES. 53
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
preservation and perpetuation of single or occasional
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 actual mould. These
individual differences are of the highest importance 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 manner
as man accumulates in any given direction individual
differences in his domesticated productions. These
individual differences generally affect what naturalists
consider unimportant 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, sometimes vary in the
individuals of the same species. I am convinced that
the most experienced naturalist would be surprised at
the number of the cases of variability, even in im-
portant parts of structure, 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
54 INDIVIDUAL DIFFERENCES. (Crap. II,
men who will laboriously examine internal and
important organs, and compare them in many specimens
of the same species. It would never have been ex-
pected that the branching of the main nerves close to
the great central 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 philosophical
naturalist, I may add, has also shown that the muscles
in the larve 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 honestly 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
“polymorphic,” in which the species present an
inordinate amount of variation. With respect 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
polymorphic genera some of the species have fixed and
definite characters. Genera which are polymorphic
in one country seem to be, with a few exceptions,
Cuap. IT.) INDIVIDUAL DIFFERENCES. d0
polymorphic in other countries, 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 inchned 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 consequently 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
females 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 Malayan archipelago, recularly
appear under two or even three conspicuously distinct
forms, not connected by intermediate varieties. Fritz
Miiller 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 differently
shaped pincers, and the other has antennz 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,
56 | DOUBTFUL SPECIES. (Cuar. 11.
describes a certain butterfly which presents in the
same island a great range of varieties connected 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 varieties. So it is, as I have myself
observed, with some dimorphic plants. It certainly at
first appears a highly remarkable fact that the same
female butterfly should have the power 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. Never-
theless 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 gradations, 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 doubtful 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
Cuap. Il.) DOUBTFUL SPECIES. 57
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 species, and the other as the variety. But cases of
great difficulty, 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 intermediate 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
suppose either that they do now somewhere exist, or
may formerly 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 expe-
rience seems the only guide to follow. We must,
however, In many cases, decide by a majority of
naturalists, for few well-marked and well-known
varieties can be named which have not been ranked as
species by at least some competent judges.
That varieties of this doubtful nature are far from
uncommon 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 con-
58 . DOUBTFUL SPECIES. [Cuar. II.
sidered 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,
_ Mz. Babington gives 251 species, whereas Mr. Bentham
gives only 112,—a difference 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! Mr. Wallace, in several valuable
papers on the various animals, especially on the
Lepidoptera, inhabiting the islands of the great
Malayan archipelago, shows that they may be classed
under four heads, namely, as variable forms, as local
forms, as geographical races or sub-species, and as true
representative species. The first or variable forms vary
much within the lhmits 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 differences are seen to be so
slight and graduated, that it is impossible to define or
describe them, though at the same time the extreme
forms are sufliciently distinct. The geographical races
or sub-species are local forms completely fixed and
isolated; but as they do not differ from each other by
Cuap. II.] DOUBTFUL SPECIES. 59
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 natural economy of each island as do the
local forms and sub-species; but as they are dis-
tinguished 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
criterion 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
compare, the birds from the closely 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 dis-
tinction 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
Ireland has a few animals, now generally regarded as
varieties, but which have been ranked as species by
same zoologists. Several experienced ornithologists
consider our British red grouse as only a strongly-
marked race of a Norwegian species, whereas the
ereater number rank it as an undoubted species
peculiar to Great Britain. A wide distance between
the homes of two doubtful forms leads many naturalists
to rank them as distinct species; but what distance, it
has been well asked, will suffice; if that between
60 DOUBTFUL SPECIES. ([Cuap. IL.
America and Europe is ample, will that between Europe
and the Azores, or Madeira, or the Canaries, or between.
the several islets of these small archipelagos, be sufficient ?
Mr. B. D. Walsh, a distinguished entomologist of the
United States, has described what he calls Phytophagic
varieties and Phytophagic species. Most vegetable-
feeding insects live on one kind of plant or on one
croup 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 to present in their
larval or mature state, or in both states, slight,
though constant differences 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 differences 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 determine 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 connecting the several
forms should now be found. The naturalist thus loses
his best guide in determining whether to rank doubtful
forms as varieties or species. This likewise necessarily
occurs with closely allied organisms, which inhabit
distinct continents or islands. When, on the other
Cuap. 11.] DOUBTFUL SPECIES. 61
hand, an animal or plant ranges over the same
continent, or inhabits 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 distant
countries. or in two geological formations, they believe
that two distinct species are hidden under the same
dress. The term species thus comes to be a mere
useless abstraction, implying and assuming a separate
act of creation. It is certain that many forms,
considered 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.
Many of the cases of strongly-marked varieties or
doubtful species well deserve consideration ; for several
interesting lines of argument, from geographical dis-
tribution, analogical variation, hybridism, &c., have
been brought to bear in the attempt to determine their
rank; but space does not here permit me to discuss
them. Close investigation, in many cases, will no
doubt bring naturalists to agree how to rank doubtful
forms. Yet it must be contessed 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
62 DOUBTFUL SPECIES. [Cuap. IL.
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
authorities 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 remarkable memoir lately
published by A. de Candolle, on the oaks of the whole
world. No one ever had more ample materials for the
discrimination of the species, or could have worked on
them with more zeal and sagacity. He first gives in
detail all the many points of structure which vary in
the several species, and estimates numerically 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 development, sometimes without any assignable
reason. Such characters 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 remarks: “They are mistaken, who
repeat that the greater part of our species are clearly
Cuap. II.) DOUBTFUL SPECIES. 63
limited, and that the doubtful species are in a feeble
minority. This seemed to be true, so long as a genus
was imperfectly known, and its species were founded
upon a few specimens, that is to say, were provisional.
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. Thus Quercus robur has twenty-
eight varieties, all of which, excepting six, are clustered
round three sub-species, namely, Q. pedunculata,
sessiliflora, 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 believes 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 paleontology, geographical 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 perplexed in determining what differences to
consider as specific, and what as varietal ; for he knows
64 , DOUBTFUL SPECIES. (Cuap. IL
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
doubtful 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 difference in the forms which he is
continually studying; and he has little general know-
ledge of analogical variation in other groups and in other
countries, by which to correct his first 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
observations be widely extended, he will im 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
intermediate links, he will be compelled to trust
almost entirely to analogy, and his difficulties will rise
to a climax.
Certainly no clear 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
Cuap. IT] DOUBTFUL SPECIES. 65
umpresses 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
shght varieties as are barely thought worth recording
in works on natural history. 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 leading 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 exposed ;
but with respect to the more important and adaptive
characters, the passage from one stage of difference to
another, 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 variety 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
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
66 DOMINANT SPECIES VARY MOST. (Cuar. IL.
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 differences, is also
apphed 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
difficulties, 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 state-
ments are fairly well established. The whole subject,
however, treated as it necessarily 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.
Cuap. I.] DOMINANT SPECIES VARY MOST. 67
Alphonse de Candolle and others have shown that
plants 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 competition (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 consideration from wide range, and to a certain
extent from commonness), 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 varieties, or, as I
consider them, incipient species. And this, perhaps,
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
species which are already dominant will be the most —
likely to yield offspring, which, though in some slight
degree modified, still inherit those advantages that
enabled their parents to become dominant over their
compatriots. In these remarks on predominance, it
should be understood that reference 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
68 SPECIES OF LARGER GENERA VARIABLE. ([Caap. IL
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.
closely allied forms be considered as independently
created species, that they have in varying assumed 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 an allied species. I have collec-
ted 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 repeat that such cases certainly
occur, and seem to me very remarkable.
I will, however, give one curious and complex ease,
not indeed as affecting any important character, but
from occurring 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,
Cuap. V.] ANALOGOUS VARIATIONS. 199
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. Thestripe
on the shoulder is sometimes double, and is very variable
in leneth 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
actually quite lost, in dark-coloured asses. The koulan
of Pallas is said to have been seen with a double shoulder-
stripe. Mr. Blyth 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 quagea, 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
England of the spinal stripe in horses of the most -
distinct breeds, and of a// 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 with a double
stripe on each shoulder and with leg-stripes; I have
myself seen a dun Devonshire pony, and a small dun
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
200 - DISTINCT SPECIES PRESENT [Cuar. V.
as purely-bred. The spine is always striped; the legs
are generally barred ; and the shoulder-stripe, which is
sometimes double and sometimes treble, is common;
the side of the face, moreover, is sometimes striped.
The stripes are often plainest in the foal; and some-
times 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 infor-
mation 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 disappeared
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 close 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 appearances are all due to
ancient crosses with the dun stock. But this view
may be safely rejected ; for it is highly improbable that
Cuap. V.] ANALOGOUS VARIATIONS. 201
the heavy Belgian cart-horse, Welsh ponies, Norwegian
cobs, the lanky Kattywar race, &c., inhabiting the most
distant 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
species of the horse-genus. Rollin 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 subsequently
produced from thé same mare by a black Arabian
sire, were much more plainly barred across the legs
than is even the pure quagga. Lastly, and this is
another most remarkable 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 occasionally 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
202 DISTINCT SPECIES PRESENT [Cuar, V.
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 tendency strong whenever a dun tint appears—
a tint which approaches to that of the general colouring
of the other species of the genus. The appearance of
the stripes is not accompanied by any change of form
or by any other new character. We see this tendency
to become striped most strongly displayed 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 tendency for the blue tint and bars
and marks to reappear in the mongrels. I have stated
that the most probable hypothesis to account for the
reappearance of very ancient characters, is—that there
is a tendency in the young of each successive generation
to produce the long-lost character, and that this
tendency, from unknown causes, sometimes prevails,
Caap, V.J ANALOGOUS VARIATIONS. 203
And we have just seen that in several species of the
horse-genus the stripes are either plainer or appear
more commonly 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 parent 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
independently 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 1t seems to me, to reject a real for an unreal,
or at least for an unknown, cause. It makes the works
of God a 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
profound. 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
=
204 . DISTINCT SPECIES PRESENT [Cuap. V.
producing the lesser differences 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 producing constitutional peculiarities and use in
strengthening and disuse in weakening and diminishing
organs, appear in many cases to have been potent in -
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
nourishment from the adjoining parts; and every part
of the structure which can be saved without detriment
will be saved. Changes of structure at an early age
may affect parts subsequently developed; and many
cases of correlated variation, the nature of which we
are unable to understand, undoubtedly occur. Multiple
parts are variable in number and in structure, perhaps
arising from such parts not having been closely special-
ised for any particular function, so that their modifica-
tions have not been closely checked by natural selection.
It follows probably from this same cause, that organic
beings low in the scale are more variable than those
standing higher in the scale, and which have their
whole. organisation 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
Cuar. V.] ANALOGOUS VARIATIONS. 205
a common parent—are more variable than generic
characters, or those which have long been 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 individual; for in a district where many
species of a genus are found—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. Secondary
sexual characters are highly variable, and such charac-
ters differ much in the species of the same group.
Variability in the same parts of the organisation has
generally 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 variable
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
206 LAWS OF VARIATION. - [Crane
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 con-
stitution from a common parent, and exposed to similar
influences, naturally tend to present analogous varia-
tions, 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
modifications will add to the beautiful and harmonious
diversity of nature.
Whatever the cause may be of each slight difference
between 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 relation to the habits of
each species.
Cuar, VI.) DIFFICULTIES OF THE THEORY. 207
CHAPTER VI.
DIFFICULTIES OF THE THEORY.
Difficulties of the theory of descent with modification—A bsence 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
perfection—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 Conditions of Existence embraced by the theory of Natural
Selection.
Lone before the reader has arrived at this part.of my
work, a crowd of difficulties 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
staggered; but, to the best of my judgment, the
greater number are only apparent, and those that are
real are not, I think, fatal to the theory.
These difficulties and objections may be classed under
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
— 208 _ ABSENCE OR RARITY (Cuar. VI.
believe that natural selection could produce, on the one
hand, an organ of trifling importance, 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 leads the bee to make cells, and which
has practically anticipated 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,
miscellaneous 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 convenient to discuss-this question in the
chapter on the Imperfection of the Geological Record ;
Cuap. VI.] OF TRANSITIONAL VARIETIES. 209
and I will here only state that I believe the answer
mainly lies in the record being incomparably 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 continent, 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 representative species often
meet and interlock ; and as the one becomes 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
absolutely 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 common 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 region, though they must have existed there, and
may be embedded there in a fossil condition. But in
the intermediate region, having intermediate conditions
of life, why do we not now find closely-linking inter-
mediate varieties? ‘This difficulty for a long time quite
210 : ABSENCE OR RARITY (Cuar. VL
confounded me. But I think it can be in large part
explained. :
In the first place we should be extremely cautious in
inferring, 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 inter-
mediate varieties existing in the intermediate zones.
By changes in the form of the land and of climate,
marine areas now continuous must often have existed
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 perfectly defined species have been formed on
strictly continuous 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 wander-
ing 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 generally narrow in comparison with the
territory proper to each. We see the same fact in
ascending mountains, and sometimes it is quite remark-
able how abruptly, as Alph. de Candolle has observed, a
common alpine species disappears. The same fact has been
noticed by E. Forbes in sounding the depths of the sea
with the dredge. To those who look at climate and the
Cuar. VI.] OF TRANSITIONAL VARIETIES. 211
physical conditions of life as the all-important elements
of distribution, these facts ought to cause surprise, as
climate and height or depth graduate away iusensibly.
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 competition; 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 lessened
numbers, will, during fluctuations in the number of its
enemies or of its prey, or in the nature of the seasons,
be extremely liable to utter extermination ; and thus its
geographical range will come to be still more sharply
defined.
As allied or representative species, when inhabiting
a, continuous area, are generally distributed in such a
manner that each has a wide range, with a compara-
tively 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
DA? : ABSENCE OR RARITY — [Cuar. VIL.
to adapt two varieties to two large areas, and a third
variety to a narrow intermediate zone. The inter-
mediate 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 varieties in
the genus Balanus. And it would appear from infor- ~
mation given me by Mr. Watson, Dr. Asa Gray, and
Mr. Wollaston, that generally, when varieties inter-
mediate between two other forms occur, they are much
rarer numerically than the forms which they connect.
Now, if we may trust these facts and inferences, and con-
clude 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 endure for very long
periods :—why, as a general rule, they should be exter-
minated 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 exter-
minated than one existing in large numbers; and in
this particular case the intermediate form would be
eminently lable 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
aistinct species, the two which exist in larger numbers,
fiom inhabiting larger areas, will havea great advantage
over the intermediate variety, which exists in smaller
Cuap. VI] OF TRANSITIONAL VARIETIES, 213
numbers in a narrow and intermediate zone. For forms
existing in larger numbers will have a better chance,
within any given period, of presenting further favour-
able 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, presentmg 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 extensive moun-
tainous 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 selec-
tion ; 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 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, without the interposition of the supplanted, inter-
mediate 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 inextricable chaos of varying and _ inter-
mediate links: first, because new varieties are very
slowly formed, for variation is a slow process, and
214 ABSENCE OR RARITY [Cuar. VI.
natural selection can do nothing until favourable in-
dividual differences or variations occur, and until a
place in the natural polity of the country can be better
filled by some modification of some one or more of its
inhabitants. And 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 modifications of
structure in some degree permanent ; and this assuredly
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 rendered sufficiently distinct to
rank as representative species. In this case, inter-
mediate varieties between the several representative
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, inter-
mediate 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 already as-
signed (namely from what we know of the actual
Cuar. Vi] OF TRANSITIONAL VARIETIES. 215
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 num-
bers 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 assuredly have existed; but the very
process of natural selection constantly tends, as has
been so often remarked, to exterminate the parent-forms
and the intermediate links. Consequently 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 imperfect
and intermittent record.
On the Origin and Transitions of Orgame 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 fee pe it is clear that each must be well
216 TRANSITIONS OF ORGANIC BEINGS. ([Cuap. VI.
adapted to its place in nature. Look at the Mustela
vison of North America, which has webbed feet, and
which resembles an otter in its fur, short legs, and form
of tail. During 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 insectivorous quadruped
could possibly have been converted into a flying bat,
the question would have been far more difficult to
answer. Yet I think such difficulties have little
weight.
Here, as on other occasions, I lie under a heavy
disadvantage, for, out of the many striking cases which
I have collected, 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 flattened, 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,
Cuapr. VI.] TRANSITIONS OF ORGANIC BEINGS. Dit
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 manner. 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 modification
being useful, each being propagated, until, by the
accumulated effects of this process of natural selection,
a perfect 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. An
extremely wide flank-membrane stretches from the
corners of the jaw to the tail, and includes the limbs
with the elongated fingers. This flank-membrane is
furnished with an extensor muscle. Although no
graduated links of structure, fitted for gliding through
the air, now connect the Galeopithecus with the other
Insectivora, yet there is no difficulty in 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 Galeopithecus might have
218 ‘TRANSITIONS OF ORGANIC BEINGS. fCuar. VE
been greatly lengthened by natural selection; 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
oliding 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 the Apteryx? Yet
the structure of each of these birds is good for it, under
the conditions of life to which it is éxposed, 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
orades 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, flying 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 perfectly winged
animals. If this had been effected, who would have
Cuar. VL] TRANSITIONS OF ORGANIC BEINGS. 219
ever Imagined that in an early transitional state they
had been the inhabitants of the open océan, 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
particular 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 selection. Fur-
thermore, 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 numbers 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 fiight 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 stage of perfection,
so as to have given them a decided advantage over
other animals in the battle for life. Hence the chance
of discovering species with transitional grades of struc:
ture in a fossil condition 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 diver-
sified 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 exclusively to one of its several
habits. it is, however, difficult to decide, and ims
220 TRANSITIONS OF ORGANIC BEINGS. ([Caap. VI
material for us, whether habits generally change first
and structure afterwards; or whether slight modifi-
cations of structure lead to changed habits; both
probably 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 exclusively on artificial substances.
Of diversified habits innumerable instances could be
given: I have often watched a tyrant flycatcher (Sauro-
phagus sulphuratus) in South America, 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 lke a kinefisher 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 te 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 seizing
insects in the chinks of the bark? Yet in North
America there are woodpeckers which feed largely on
Cuar. VI.] TRANSITIONS OF ORGANIC BEINGS. PPA
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
flicht, its close blood-relationship to our common wood-
pecker 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 certain other districts, however, this same wood-
pecker, as Mr. Hudson states, frequents trees, and bores
holes in the trunk for its nest. I may mention as
another illustration of the 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 aérial 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 flyin»
when made to take flight, would be mistaken by any
one for an auk or a grebe; nevertheless it is essentially
a petrel, but with many parts of its organisation pro-
foundly modified in relation to its new habits of life;
ae TRANSITIONS OF ORGANIC BEINGS. ([Cuap. VL
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 beneath
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 agreement. What can be plainer than
that the webbed feet of ducks and geese are formed for
swimming? Yet there are upland 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 landrail 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
Cuar. VIL] ORGANS OF EXTREME PERFECTION. 223
change 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
creation 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 acknowledge that
every organic being is constantly endeavouring 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
woodpeckers where hardly a tree grows; that there
should be diving thrushes and diving Hymenoptera,
and petrels with the habits of auks.
Organs of extreme Perfection and Complication.
To suppose that the eye with all its inimitable
contrivances for adjusting the focus to different dis-
tances, for admitting different amounts of light, and
for the correction of spherical and chromatic aberration,
~ » 228 ee
A ee
s we a Se
. a aa
*
224 ORGANS OF EXTREME PERFECTION. ([Caar. VL.
could have been formed by natural selection, seems, I
freely confess, absurd in the highest degree. 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 Voz populi,
vox Dei, as every philosopher knows, cannot be trusted
in science. Reason tells me, that if numerous gradations
from a simple and imperfect eye to one complex and
perfect can be shown to exist, each grade being useful
to its possessor, as is certainly the case; if further, the
eye ever varies and the variations be inherited, as is
likewise certainly the case; and if such variations
should be useful to any animal under changing con-
ditions 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 considered as subversive of the theory.
How a nerve comes to be sensitive to light, hardly
concerns us more than how life itself originated ; but I
may remark that, as some of the lowest organisms, in
which nerves cannot be detected, are capable of per-
ceiving light, it does not seem impossible that certain
sensitive elements in their sarcode should become
ageregated and developed into nerves, endowed with
this special sensibility.
In searching for the gradations through which an
organ in any species has been perfected, we ought to
look exclusively to its lneal 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 possible, and for the
chance of some gradations having been transmitted in
Cuar. VI.] ORGANS OF EXTREME PERFECTION. 225
an unaltered or little altered condition. But the state
of the same organ in distinct classes may incidentally
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. Jourdaim, descend even a step lower and find
ageregates of pigment-cells, apparently 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 dis-
‘tinguish 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 surface, 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-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 optical contrivance. With insects it
is now known that the numerous facets on the cornea
226 ORGANS OF EXTREME PERFECTION. ([Cuapr. VI.
of their great compound eyes form true lenses, and that
the cones include curiously modified nervous filaments.
But these organs in the Articulata are so much diver-
sified that Miller formerly made three main classes
with seven subdivisions, besides a fourth main class of
agoregated simple eyes.
When we reflect on these facts, here given much
too briefly, with respect to the wide, diversified, and
eraduated 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 difficulty ceases to
be very great in believing that natural selection may
have converted the simple apparatus of an optic nerve,
coated with pigment and invested by transparent mem-
brane, into an optical mstrument 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 extremely slight and gradual.
Different kinds of modification would, also, serve for the
Cuar. VI] ORGANS OF EXTREME PERFECTION. ai
same general purpose: as Mr. Wallace 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
regularity of curvature will be an improvement. So
the contraction 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 division of the
animal kingdom, namely, the Vertebrata, we can start
from an eye so simple, that it consists, as in the
lancelet, of a little sack of transparent skin, furnished
with a nerve and lined with pigment, but destitute of
any other apparatus. 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 difficulty 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
228 ORGANS OF EXTREME PERFECTION. ([Cuap. VI.
highest human intellects; and we naturally infer that
the eye has been formed by a somewhat analogous
process. But may not this inference be presumptuous ?
Have we any right to assume that the Creator 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 sensi-
tive to light beneath, and then suppose every part
of this layer to be continually changing slowly in
density, so as to separate into layers of different densities
and thicknesses, placed at different distances from each
other, and with the surfaces of each 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 suppose 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 slght alterations, generation will
multiply 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?
Cuap. VI.] MODES OF TRANSITION. 229
Modes of Tramsition.
Tf it could be demonstrated that any complex organ
existed, which could not possibly have been formed by
numerous, successive, slight modifications, my theory
would absolutely break down. But I can find out no
such case. No doubt many organs exist of which we
do not know the transitional 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 members of the class have been developed ;
and in order to discover the early transitional grades
through which the organ has passed, we should have to
look to very ancient ancestral forms, long since become
extinct.
We should be extremely cautious in concluding that
an organ could not have been formed by transitional
eradations 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-fly and in the fish
Cobites the alimentary canal respires, digests, and
excretes. In the Hydra, the animal may be turned
inside out, and the exterior surface will then digest and
the stomach respire. In such cases natural selection
might specialise, 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
230 MODES OF TRANSITION. (Cuap. VIL.
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
character of the species. It is, however, probable that
the two sorts of flowers borne by the same plant were
originally differentiated 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 important means of transition: to give one
instance,—there are fish with gills or branchie 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 vascular 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 aérial 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 individual. 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; and then this other organ might be modified for
some other and quite distinct purpose, or be wholly
obliterated.
The illustration of the swimbladder in fishes is a
good one, because it shows us clearly the highly
important fact that an organ originally constructed for
one purpose, namely, flotation, may be converted into
Cap, VI] MODES OF TRANSITION. Dat
one for a widely different purpose, namely, respira-
tion. The swimbladder has, also, been worked in as an
accessory to the auditory organs of certain fishes. All
physiologists admit that the swimbladder is homologous,
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 converted into lungs, or an organ used exclusively
for respiration.
According to this view it may be inferred that all
vertebrate animals with true lungs are descended by
ordinary generation from an ancient and unknown
prototype, which was furnished with a floating ap-
paratus or swimbladder. We can thus, as I infer from
Owen’s interesting description of these parts, under-
stand 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,
notwithstanding the beautiful contrivance by which the
glottis is closed. In the higher Vertebrata the branchiz
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 branchie might
have been gradually worked in by natural selection for
some distinct purpose: for instance, Landois has shown
that the wings of insects are developed from the
tracheze; 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,
D352, MODES OF TRANSITION. [CHap. VL
- 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 branchie, the whole surface of the body and of
the sack, together with the small frena, serving for
respiration. The Balanidze 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 lacune of the sack
and body, and which have been considered by all
naturalists to act as branchiez. Now I think no one
will dispute that the ovigerous frena in the one family
are strictly homologous with the branchiz of the other
family ; indeed, they graduate into 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
branchie, simply through an increase in their size and
the obliteration of their adhesive glands. [If all pedun-
culated cirripedes had become extinct, and they have
suffered far more extinction than have sessile cirripedes,
who would ever have imagined that the branchiz in this
latter family had originally existed as organs for pre-
venting 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
reproduction. 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
Cuar. VI] MODES OF TRANSITION. 233
early age, before 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 character 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 Miiller, after
maturity. Im all such cases,—and many could be
given,—if the age for reproduction were retarded, 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 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 the
mature and the old, were primordially acquired by
graduated steps.
234 DIFFICULTIES OF THE THEORY ([Cuap. VI
Special Difficulties of the Theory of Natural Selection.
Although we must be extremely cautious in con-
cluding that any organ could not have been produced
by successive, small, transitional gradations, yet un-
doubtedly serious cases of difficulty 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 surprising, 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 electrical, 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 discharge ;
and, as Dr. Radcliffe insists, “in the electrical apparatus
of the torpedo during rest, there would seem to be a
charge in every respect lixe that which is met with in
Cuap. VI] OF NATURAL SELECTION. 235
muscle and nerve during rest, and the discharge of the
torpedo, instead of being peculiar, may be only another
form of the discharge which attends upon the action of
muscle and 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 gradu-
ally developed.
These organs appear at first to offer another and far
more serious difficulty ; for they occur in about a dozen
kinds of fish, of which several are widely remote in their
affinities. 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 inheritance from a common
ancestor ; and its absence in some of the members to
loss through disuse or natural selection. 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 descend-
ants have now lost. But when we look at the subject
more closely, we find in the seyeral fishes provided with
electric organs, that these are situated in different parts
of the body,—that they differ in construction, as in the
arrangement of the plates, and, aecording to Pacini, in
the process or means by which the electricity is excited
—and lastly, in being supplied with nerves proceeding
936 DIFFICULTIES OF THE THEORY ([Cuapr. VI.
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 homologous, but only as analogous in
function. Consequently there is no reason to suppose ~
that they have been inherited from a common pro-
genitor ; for had this been the case they would have
elosely 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 difficulty ; 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,
belonging to widely different families, and which are
situated in 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 instance 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 almost as
remote as is possible amongst flowering plants; but
here again the parts are not homologous. In all cases
of beings, far removed from each other in the scale of
organisation, 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 differences between them
can always be detected. For instance, the eyes of
cephalopods or cuttle-fish and of vertebrate animals
appear wonderfully alike; and in such widely sun-
dered groups no part of this resemblance can be due
- Ree
Cuap. VI.) OF NATURAL SELECTION. Davitt
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. Beyond this
superficial resemblance, there is hardly any real simi-
larity 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 different, with an
actual inversion of the elemental parts, and with a large
nervous ganglion included within the membranes of the
eye. The relations of the muscles are as different 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 possible in the other; and
fundamental differences of structure in the visual organs
of two groups might have been anticipated, in accord-
ance 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
238 DIFFICULTIES OF THE THEORY ([Cuap. VI.
being, and taking advantage of all favourable variations,
has produced similar organs, as far as function is con-
cerned, 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 impor-
tant characters; namely in their sense organs, circula-
ting system, in the position of the tufts of hair within
their complex stomachs, and lastly in the whole
structure of the water-breathing branchiz, 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 Miller argues that this close similarity in so
many points of structure must, in accordance with the
views advanced by me, be accounted for by inheritance
from a common progenitor. But as the vast majority
of the species in the above two families, as well as most
other crustaceans, are aquatic in their habits, it 1s im-
probable in the highest degree, that their common
progenitor should have been adapted for breathing air.
Cuap. VL] OF NATURAL SELECTION. 239
Miller 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
differences are intelligible, and might even have been
expected, 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 certain extent, and in ac-
cordance with the principle that the nature of each
variation depends on two factors, viz., the nature of
the organism and that of the surrounding conditions,
their variability assuredly would not have been exactly
the same. Consequently natural selection would have
had different materials or variations to work on, in
order to arrive 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 remains unintelligible. 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
Claparéde, has argued in the same manner, and has
arrived at the same result. He shows that there are
parasitic mites (Acaride), 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
12
240 DIFFICULTIES OF THE THEORY ([Cuap. VI.
hind-legs—of the maxille or lips,—and of appendages
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 remotely allied, by organs in appearance, though
not in development, closely similar. On the other hand,
it is a common 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 butterfly, 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,—from
the long row of neatly interlocking teeth in a Nucula
to the simple ligament of a Mussel! Seeds are dis-
seminated 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 nutritious, as well as con-
spicuously 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,
Cap. VI] OF NATURAL SELECTION. 241
but such a view of nature is incredible. With plants
having separated sexes, and with those in which, though
hermaphrodites, the pollen does not spontaneously fall
on the stigma, some aid is necessary for their fertilisa-
tion. 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
inexhaustible 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 some-
times capable of neatly adapted movements through
irritability or elasticity. From such structures we may
advance till we come to such a case of extraordinary
adaptation 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, inta
which drops of almost pure water continually fall from
two secreting horns 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; within this
chamber there are curious fleshy ridges. The most
242 DIFFICULTIES OF THE THEORY [Caap. VI.
ingenious man, if he had not witnessed what takes
place, could never have imagined what purpose all
these parts serve. But Dr. Criiger 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 compelled to crawl out through the passage
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. Criiger sent me a flower in spirits of wine, with a
bee which he had lalled 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
Caap. VI.] OF NATURAL SELECTION. 243
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 antenna. This antenna,
when touched, transmits a sensation or vibration to a
certain membrane which is instantly ruptured; 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
innumerable 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 struc-
ture tends to be inherited, so that each modification
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 -
244 DIFFICULTIES OF NATURAL SELECTION. [Cuar. VI.
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
difficult even to conjecture by what transitions organs
have arrived at their present state; yet, considering
how small the proportion of living and known forms is
to the extinct and unknown, 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 ex-
aggerated, canon in natural history of “Natura non
facit saltum.” 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 innovation. Why, on the
theory of Creation, should there be so much variety
and so little real novelty 2 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
selection, we can clearly understand why she should
not; for natural selection acts only by taking ad-
vantage 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 sei by
Natural Selection.
As natural selection acts by life and tase the
survival of the fittest, and by the destruction of the
less well-fitted individuals,—I have sometimes felt
ereat difficulty in understanding the origin or forma-
tion of parts of little importance; 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 characters, 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 consti-
tutional differences or from determining the attacks
of insects, might assuredly be acted on by natural
selection. The tail of the giraffe looks like an
artificially constructed fly-flapper; and it seems at
first incredible 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 cf 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
pastures and thus gain a great advantage. It is not
that the larger quadrupeds are actually destroyed
246 ORGANS OF LITTLE IMPORTANCE [Cuap. VI.
(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 state, 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 swim-
bladders betray 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
importance 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 conditions of life,—of so-called spon-
taneous 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 correlation,
Cuar. VI.] AFFECTED BY NATURAL SELECTION. 247
compensation, of the pressure of one part on another,
&c.,—and finally of sexual selection, by which characters
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 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 selection ; 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 quadrupeds, so the spikes on
the palm may at first have been developed 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 adaptation for wallowing in putridity; and so
it may be, or it may possibly be due to the direct action
248 ORGANS OF LITTLE IMPORTANCE ([Cuap. VL
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 clean-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 between 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
constitutions would succeed best under different
climates. With cattle susceptibility to the attacks
of ilies is correlated with colour, as is the lability 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 clmate
affects the growth of the hair, and that with the hair
the horns are correlated. Mountain breeds always
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;
Cuar. VL] AFFECTED BY NATURAL SELECTION. 249
and then by the law of homologous variation, the front
limbs and the 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 together 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 great modification which the breeds of
swine have undergone. But we are far too ignorant to
speculate on the relative importance of the several
known and unknown causes of variation; and I have
made these remarks only to show that, if we are
unable to account for the characteristic 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
precise cause of the shght analogous differences between
true species.
Utilitarian Doctrine, how far 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 the Creator (but this
-
950 UTILITARIAN DOCTRINE, HOW FAR TRUE:
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 absolutely 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 great effect,
independently of any advantage thus gained. But a
still more important consideration 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 believe
that the webbed feet of the upland goose or of the
frizate-bird are of special use to these birds; we cannot
believe 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
Cuap. VI] BEAUTY, HOW ACQUIRED. 258
bones in the fin of some ancient fish-like progenitor of
the whole class. It is scarcely possible to decide 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 conclude 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 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. Were 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 diatomacez: were these created
that they might be examined and admired under 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 productions of nature; but they
252 UTILITARIAN DOCTRINE, HOW FAR TRUE:
have been rendered conspicuous in contrast 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 habitually produce two kinds of flowers; one
kind open and coloured 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 spimdle-wood tree
and the scarlet berries of the holly are beautiful objects,
—will be admitted by every one. But this beauty
serves merely as a guide to birds 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
Cuar. VI] BEAUTY, HOW ACQUIRED. 9538
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 apparently 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 pre-
sented, if we enquire 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 modi-
fication in a species exclusively for the good of another
species; though throughout nature one species in-
cessantly takes advantage 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
254 UTILITARIAN DOCTRINE, HOW FAR TRUE:
it could be proved that any part of the structure of any
one species had been formed for the exclusive good of
another species, it would annihilate my theory, for such
could not have been produced through natural selection.
Although many statements may be found 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 puff-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
structure 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
Cuap. VI.] BEAUTY, HOW ACQUIRED. 255
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 inhabitants of the same country with which it
comes into competition. And we see that this is the
standard of perfection attained under nature. The
endemic productions of New Zealand, for instance, are
perfect one compared with another; but they are now
rapidly yielding before the advancing legions of plants
and animals introduced from Europe. Natural selection
will not produce absolute perfection, nor do we always
meet, as far as we can judge, with this high standard
under nature. The correction for the aberration of light
is said by Miller 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 wonderful powers of the human eye,
adds these remarkable words: “That which we have
discovered in the way of inexactness and imperfection
in the optical machine and in the image on the retina,
is as nothing in comparison with the inconegruities
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
remove all foundation from the theory of a pre-existing
harmony 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 contrivances are less perfect.
Can we consider the sting of the bee as perfect, which,
256 UTILITARIAN DOCTRINE, HOW FAR TRUE:
when used against many kinds of enemies, cannot be
withdrawn, owing to the backward serratures, 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 instru-
ment, 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 perhaps under-
stand 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 production 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 her to destroy the young queens, her daughters,
as soon as they are born, or to perish herself in the
combat ; for undoubtedly this is for the good of the com-
munity ; and maternal 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 contrivances, by which orchids
and many other plants are fertilised through insect
agency, can we consider as equally perfect the elabora-
Cuap. VI.] SUMMARY. 257
tion of dense clouds of pollen by our fir-trees, so that a
few granules may be waited by chance on to the
ovules ?
Summary : the Law of Unity of Type and of the Con-
ditions 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 variable, and are not
linked together by a multitude of intermediate grada-
tions, partly because the process of natural selection 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 extinc-
tion of preceding and intermediate gradations. Closely
allied species, now living on a continuous area, must
often have been formed when the area was not con-
tinuous, and when the conditions of life did not insen-
sibly graduate away from one part to another. When
two varieties are formed in two districts 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 ;
consequently the two latter, during the course of
further modification, from existing in greater numbers,
will have a great advantage over the less numerous
258 SUMMARY. [Cuap. VI.
intermediate variety, and will thus generally succeed in
supplanting and exterminating it.
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 organic being is trying to live wherever it can
live, how it has arisen that there are upland geese with
webbed feet, ground woodpeckers, 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 con-
ditions 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 performed simultaneously very different
functions, and then having been in part or in whole
specialised for one function; and two distinct organs
Cuap. VI.] SUMMARY. 259
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 purpose 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.
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 structures 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, believe
that a part formerly of high importance has frequently
been retained (as the tail of an aquatic animal by its
terrestrial descendants), though it has become of such
small importance 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
260 | SUMMARY. [Cuar. VI.
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 success 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 individuals 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 necessarily lead to
absolute perfection ; nor, as far as we can judge by our
limited faculties, can absolute perfection be everywhere
predicated.
On the theory of natural selection we can clearly
understand 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 correct; 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 been formed on two great laws—Unity of Type,
and the Conditions of Existence. By unity of type is
meant that fundamental agreement in structure which
we see in organic beings of the same class, and which is
quite independent of their habits of lifee On my
theory, unity of type is explained by unity of descent,
The expression of conditions of existence, so often
insisted on by the illustrious Cuvier, is fully embraced
Cuar. VL] SUMMARY. 261
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 con-
ditions 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.
262 MISCELLANEOUS OBJECTIONS TO THE ([Caap. VIL.
CHAPTER VIL
MISCELLANEOUS OBJECTIONS TO THE THEORY OF
NATURAL SELECTION.
Longevity—Modifications not necessarily simultaneous—Modifica-
tions 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 inter-
fere with the acquisition through natural selection of useful
structures—Gradations of structure with changed functions—
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 discussions
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
Cuar. VIL] THEORY OF NATURAL SELECTION. 263
they were at any one time perfectly adapted to their con-
ditions 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
mathematical accuracy, that longevity is a great advan-
tage to all species, so that he who believes in natural
selection “must arrange his genealogical tree” in such
a manner that all the descendants have longer lives
than their progenitors! Cannot 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 selec-
tion, survive from year to year by means of its seeds or
ova? Mr. E. Ray Lankester has recently discussed this
subject, and he concludes, as far as its extreme com-
plexity 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
expenditure 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 remarked, this line of argument
proves toc 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
13
264 MISCELLANEOUS OBJECTIONS TO THE ([Caapr. VIL
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 modification 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 selec-
tion 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
circumstances.
The celebrated paleontologist, Bronn, at the close of
his German translation of this work, asks, how, on the
principle of natural selection, can a variety live side by
side with the parent species? If both have become
fitted for slightly different habits of life or conditions,
they might live together; and if we lay on one side
polymorphic species, in which the variability seems to
be of a peculiar nature, and all mere temporary varia-
tions, 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
Cuap. VIL] THEORY OF NATURAL SELECTION. 265
from each other in single characters, but in many parts;
and he asks, how it always comes that many parts
of the organisation 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 trans-
mitted all together, they would appear to us as if they
had been simultaneously developed. The best answer,
however, 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 greyhound 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 attri-
buted partly to the principle of correlated growth, and
partly to so-called spontaneous variation.
A much more serious objection has been urged by
Bronn, and recently by Broca, namely, that many cha-
racters appear to be of no service whatever to their
266 MISCELLANEOUS OBJECTIONS TO THE [Caap. VI.
possessors, and therefore cannot have been influenced
through natural selection. Bronn adduces the length
of the ears and tails in the different 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 morpho-
logical 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 dissemina-
tion, &e.
There is much force in the above objection. Never-
theless, we ought, in the first place, to be extremely
cautious in pretending to decide what structures now
are, or have formerly been, of use to each species. In
the second place, it should always be borne in mind
that when one part is modified, so will be other parts,
through certain dimly seen causes, such as an increased
or diminished flow of nutriment to a part, mutual pres-
sure, 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,
Cuar. VII] THEORY OF NATURAL SELECTION. 267
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 ap-
parently plays a quite subordinate part. Bud-variations,
such as the appearance of a moss-rose on a common rose,
or of a nectarine on a peach-tree, offer good instances of
spontaneous variations; but even in these cases, if we
bear in mind the power of a minute drop of poison in
producing complex galls, we ought not to feel too sure
that the above variaticns 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
modifications 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 selection 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 fore-
going 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
fe
=e
268 MISCELLANEOUS OBJECTIONS TO THE ([Cuar. VII
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, | may mention that, according to Dr. Schdébl, 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 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 selec-
tion. 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, one ovule holds
the former and a second ovule the latter position. These
positions seem at first purely morphological, or of no
physiological signification ; 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»
Cuar. VII] THEORY OF NATURAL SELECTION. 269
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
produce flowers of two kinds,—the one open of the
ordinary structure, the other closed and imperfect.
These two kinds of flowers sometimes differ wonder-
fully 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 benefits which
certainly are derived from this process are thus secured.
The closed and imperfect flowers are, however, mani-
festly of high importance, as they yield with the utmost
safety a large stock of seed, with the expenditure of
wonderfully 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 columne 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 perfect flowers), the sepals are reduced from
the normal number of five to three. In one section of
the Malpighiacee 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
a
270 MISCELLANEOUS OBJECTIONS TO THE [Cuapr. VIL
sixth stamen standing opposite to a petal being alone
developed; and this stamen is not present in the ordi-
nary 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 pre-
vent some of the flowers from expanding, and to reduce
the amount of pollen, when rendered by the closure of
the flowers superflous, 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
pentamerous. In many Composite and Umbelliferze
(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 reproductive organs. It is a more
curious fact, previously referred to, that the achenes
Cuar. VIL] THEORY OF NATURAL SELECTION. 271
or seeds of the circumference and centre sometimes
differ greatly in form, colour, and other characters. In
Carthamus and some other Composite the central
achenes alone are furnished with a pappus; and in
Hyoseris the same head yields achenes of three different
forms. In certain Umbellifere the exterior seeds,
according to Tausch, are orthospermous, and the central
one ccelospermous, and this is a character which was
considered by De Candolle to be in other species of the
highest systematic importance. 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 conspicuous
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 rela-
tive 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 condition, 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 gener-
ally of a highly important nature, affecting only some
of the flowers on the same plant, or occurring on dis-
tinct 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;
272 MISCELLANEOUS OBJECTIONS TO THE (Cuar. VII.
we cannot even attribute them, as in the last class of
cases, to any proximate agency, such as relative position.
I will give only afew instances. It is so common to
observe on the same plant, flowers indifferently tetra-
merous, pentamerous, &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
Candolle, 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 estivation is almost as frequently that
of the Rhinanthidee as of the Antirrhinides, to which
latter tribe the genus belongs. Aug. St. Hilaire gives
the following cases: the genus Zanthoxylon belongs to
a division of the Rutacee 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 Helianthemum the capsule has been
described as unilocular or 3-locular; and in H. mutabile,
“Une lame, plus ou moins large, s’étend entre 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
oleeformis 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, “ Voila
done dans un méme individu des loges et un style qui
se rattachent tantdt 4 un axe verticale et tantét a un
gynobase.”
Cuar. VII] THEORY OF NATURAL SELECTION. 273
We thus see that with plants many morphological
changes may be attributed to the laws of growth and
the inter-action of parts, independently of natural selec-
tion. But with respect 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 classi-
fications. 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 des-
cribed, 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 speci-
fied modifications ; but if the unknown cause were to act
almost uniformly for a leneth 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 unimpor-
tant for the welfare of the species, any slight variations
which occurred in them would not have been accumu-
lated and augmented through natural selection. A
structure which has been developed through long-con-
tinued selection, when it ceases to be of service to a
species, generally becomes variable, as we see with rudi-
mentary organs; for it will no longer be regulated by
274 MISCELLANEOUS OBJECTIONS TO THE ([Czap. VIL.
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 importance 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, whatever it may be,
which is common to many allied forms, is ranked by us
as of high systematic importance, and consequently is
often assumed to be of high vital importance to the
species. Thus; as I am inclined to believe, morpho-
logical differences, which we consider as important—
such as the arrangement 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 condi-
tions, as well as through the intercrossing of distinct
individuals, but not through natural selection; 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
species, 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 para-
doxical as it may at first appear.
Although we have no good evidence of the existence
Cuap. VII] THEORY OF NATURAL SELECTION. 275
in organic beings of an innate tendency towards pro-
gressive development, yet this necessarily follows, as I
have attempted to show in the fourth chapter, through
the continued action 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
276 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VU.
so strongly convinced of the general truth of the conclu-
sions 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,
considered in the present volume. The one new point
which appears to have struck many readers is, “that
natural selection is incompetent to account for the in-
cipient stages of useful structures.” This subject is
intimately connected with that of the gradation of cha-
racters, 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 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 beauti-
fully 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 preserving an animal’s life.
These cattle can browse 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
Cuar. VIL] THEORY OF NATURAL SELECTION. 277
has modified some of his animals, without necessarily
having attended to special points of structure, by simply
preserving 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 indi-
viduals 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 differences, 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
probable 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 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 inter-
cross, and will destroy 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
278 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VII.
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
objections. One is that the increased size of the body
would obviously require an increased supply of food,
and he considers 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 in-
creased 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 8. 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
Cuap. VII.] THEORY OF NATURAL SELECTION. 279
quadruped acquired a long neck and lofty stature, besides
the giraffe, and, in a 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 formerly 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 ungulate animals.
Why, in other quarters of the world, various animals
belonging 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 conjecture 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 at a considerable height (without climbing, for
280 MISCELLANEOUS OBJECTIONS TO THE [Cuapr. VIL
which hoofed animals are singularly ill-constructed) im-
plies 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 unparalleled 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 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 indispens-
able 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 variations 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 determined chiefly through
destruction by beasts of prey,—by external or internal
parasites, &c.,—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 obtaining food. Lastly, natural selection is a slow pro-
cess,and the same favourable conditions must long endure
in order that any marked effect should thus be produced.
Cuar. VII] THEORY OF NATURAL SELECTION. 28]
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 browsing 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, besides the general ones just indicated, have
probably interfered with the acquisition through natural
selection of structures, 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 reasons In answer, why have not seals and bats
given birth on such islands to forms fitted to live on the
land? But seals would necessarily be first converted
into terrestrial carnivorous 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. Grada-
tions of structure, with each stage beneficial to a changing
species, will be favoured only under certain peculiar
conditions. especial difficulty in this having
been effected through natural selection. But I must
pass over this preliminary difficulty. The great diffi-
culty 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
Cuap. VIII.] OF NATURAL SELECTION. 307
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. Ifa working ant or other neuter insect had 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 born with slight profitable modifications, which
were inherited by the offspring; and that these again
varied 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 modifica-
tions of structure or instinct to its progeny. It may
well be asked how is it possible to reconcile this case
with the theory of natural selection ?
First, let it be remembered that we have innumerable
instances, both in our domestic productions and in those
in a state of nature, of all sorts of differences of inherited
structure 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 differences 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 difficulty lies in understanding how such correlated
308 OBJECTIONS TO THE THEORY (Caap. VIII.
modifications of structure could have been slowly accu-
mulated by natural selection.
This difficulty, though appearing insuperable, is
lessened, or, as I believe, disappears, when it is remem-
bered that selection 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 care-
fully watching which individual bulls and cows, when
matched, produced oxen 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 varieties 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 service-
able end. Hence we may conclude that slight modi-
fications 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 trans-
Cuap. VIII.) OF NATURAL SELECTION. 359
mitted to their fertile offspring a tendency to produce
sterile members with the same modifications. This
process must have been repeated many times, until
that prodigious amount of difference between the fertile
and sterile females of the same species has been pro-
duced, which we see in many social insects.
But we have not as yet touched on the acme of the
difficulty ; 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 wonderful sort of shield on their heads, the use
of which is quite unknown: in the Mexican Myrmeco-
cystus, the workers of one caste never leave the nest;
they are fed by the workers of another caste, and they
have an enormously developed abdomen 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.
It will indeed be thought that I have an overweening
confidence 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 different from the fertile males and
females through natural selection, we may conclude
17
360 OBJECTIONS TO THE THEORY ([Cnuap. VIIL
from the analogy of ordinary variations, that the succes-
sive, 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
advantageous modification, all the neuters ultimately
came to be thus characterised. According to this view —
we ought occasionally 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 some-
times 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 few 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 care-
fully dissected several specimens of these workers, I
can affirm that the eyes are far more rudimentary 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
Cuap. VIII.) OF NATURAL SELECTION. 361
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 community, 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-
developed ocelli.
I may give one other case: so confidently did I
expect occasionally to find gradations of important struc-
tures between the different castes of neuters in the same
species, that I gladly 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 workmen 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
insensibly into each other, as does the widely-different
structure of their jaws. I speak confidently on this latter
362 OBJECTIONS TO NATURAL SELECTION. [Cuapr. VIII.
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
selection, 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 simultaneously another set of workers
of a different size and structure;—a graduated series
having first been formed, as in the case of the driver
ant, and then the extreme forms having been produced
in greater and greater numbers, through 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 Muller, of certain
Brazilian crustaceans lkewise 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
Cuapr. VIII} SUMMARY 363
organs or tools, whilst man works by acquired know-
ledge 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, therefore, 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 difficulty 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 variations, which aze 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.
Summary.
I have endeavoured 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. There-
fore there is no real difficulty, under changing conditions
of life, in natural selection accumulating to any extent
364 SUMMARY. (Cuap. VIIL
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 lable to mistakes :—that no
instinct can be shown to have been produced 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
inexplicable—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 consider-
ably different conditions of life, yet often retaining
nearly the same instincts. For instance, we can under-
stand, 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 Hornbills 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
inales 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
Cuap. VIII.) SUMMARY. 365
known bird. Finally, it may not be a logical deduction,
but to my imagination it is far more satisfactory to look
at such instincts as the young cuckoo ejecting its foster-
brothers,—ants making slaves,—the larvee of ichneu-
monidz feeding within the live bodies of caterpillars,—
not as specially endowed or created instincts, but as
small consequences 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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