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Jjhe V^rONDERS o/ NATURE and the
ACHIEVEMENTS OF MAN

With an Introduction by
IRA REMSEN, Ph.D., LL.D.

LIST OF CONTRIBUTORS

CHARLES R. DARWIN' HERBERT SPENCER

THOMAS H. HUXLEY ALFRED RUSSEL WALLACE

LORD AVEBURY ERNST HEINRICH HAECKEL

RICHARD A. PROCTOR EDWARD B. TYLOR

Sir ARCHIBALD GEIKIE ADOLPHE GANOT

JOHN STUART MILL JOHN TYNDALL

SAMUEL P. LANGLEY GEORGE ILES

GEORGE M. STERNBERG LELAND O. HOWARD

ROBSON ROOSE, M.D. Sir JAMES PAGET, M.D.

HENRY DESMAREST W. STANLEY JEVONS

RAY STANNARD BAKER CLEVELAND MOFFETT
CLARENCE LUDLOW BROWNELL

AND OTHERS

ch(e^o} York

J. A. HILL AND COMPANY

^uhlishers

Copyright, 1904, by J. A. Hill & Co.
Copyright, 1906, by J. A. Hill & Co.

brigha:^ ^'Oung universitv
phovcutah

CHARLES DARWIN,

.Vv\lT*i\kC\ ?.'^.A*j\K^^3

(Bti^in of Species

BY MEANS OF NATURAL SELECTION OR THE PRESER-
VATION OF FAVORED RACES IN THE STRUGGLE FOR LIFE

By
Charles R. Darwin, M.A., LL.D., F.R.S,

popular Button

NEW YORK

J. A. HILL AND COMPANY

MCMIV

CONTENTS

Historical Sketch v

Introduction 1

CHAPTER I.

variation under domestication.

Causes of Variability — Effects of Habit and tlie use or disuse of
Parts — Correlated Variation — Inheritance — Character of Domes-
tic Varieties — Difficulty of distinguishing- betweenw' Varieties and
Species — Origin of Domestic Varieties from one or more Species —
Domestic Pigeons, their Differences and Origin — Principles of Se-
lection, anciently followed, their Effects — Methodical and Uncon-
scious Selection — Unknown Origin of our Domestic Productions —
Circumstances favourable to Man's power of Selection Page 5

CHAPTER II.

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 frequently than the species
of the smaller genera — Many of the species of the larger genera
resemble varieties in being very closely, but unequally, related to each
other, and in having restricted ranges Page 33

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 — Competition uni-
versal — Effects of Climate — Protection from the number of indi-
viduals — 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 impor-
tant of all relations Page 48

i

ii CONTENTS

CPIAPTER IV.

NATURAL SELECTION ; OR THE SURVIVAL OF THE FITTEST.

Natural Selection — its power compared with man's selection — its power
on characters of trifling importance — its power at all ages and on
both sexes — Sexual selection — On the generality of intercrosses
between individuals of the same species — Circumstances favourable
and unfavourable to the results of Natural Selection, namely, inter-
crossing, isolation, number of individuals — Slow action — Extinc-
tion caused by Natural Selection — Divergence of Character, related
to the diversity of inhabitants of any small area, and to naturalisa-
tion— Action of Natural Selection, through Divergence of Char-
acter and Extinction, on the descendants from a common parent — ■
Explains the grouping of all organic beings — Advance in organisa-
tion — Low forms preserved — Convergence of Character — Indefinite
multiplication of species — Summary Page 02

CHAPTER V.

LAWS OF VARIATION.

Effects of changed conditions — Use and disuse, combined with natural
selection ; organs of flight and of vision — Acclimatisation — Corre-
lated variation — Compensation and economy of growth — False cor-
relations — 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 100

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 — Diversi-
fied 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 per-
fect — The law of Unity of Type and of the Conditions of Existence
embraced by the theory of Natural Selection Page 133

CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION.

Longevity — Modifications not necessarily simultaneous — Modifications
apparently of no direct service — Progressive development — Char-
acters of small functional importance, the most constant — Supposed

CONTENTS iii

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 struc-
ture 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. . , Page 1G8

CHAPTER VIII.

INSTINCT.

Instincts comparable with habits, but different in their origin — Instincts
graduated — Aphides and ants — Instincts variable — Domestic in-
stincts, 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 Page 205

CHAPTER IX.

HYBRIDISM.

Distinction between the sterility of first crosses and of hybrids — Sterility
various in degree, not universal, affected by close interbreeding, re-
moved by domestication — Laws governing the sterility of hybrids —
Sterility not a special endowment, but incidental on other differences,
not accumulated by natural selection — Causes of the sterility of
first crosses and of hybrids — Parallelism between the effects of
changed conditions of life and of crossing — Dimorphism and tri-
morphism — Fertility of varieties when crossed and of their mongrel
offspring not universal — Hybrids and mongrels compared independ-
ently of their fertility — Summary. Page 236

CHAPTER X.

ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.

On the absence of intermediate varieties at the present day — On the
nature of extinct intermediate varieties ; on their number — On the
lapse of time, as inferred from the rate of denudation and of depo-
sition — On the lapse of time as estimated by years — On the poor-
ness of our palaeontological collections — On the intermittence of
geological formations — On the denudation of granitic areas — On
the absence of intermediate varieties in any one formation — On the
sudden appearance of groups of species — On their sudden appear-
ance in the lowest known fossiliferous strata — Antiquity of the
habitable earth Page 2G6

iv CONTENTS

CHAPTER XI.

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.

On the slow and s-uccessive appearance of new species — On their dif-
ferent rates of change — Species once lost do not reappear — Groups
of species follow the same general rules in their appearance and
disappearance as do single species — On extinction — On simul-
taneous changes in the forms of life throughout the world — On the
affinities of extinct species to each other and to living species — On
the state of development of ancient forms — On the succession of
the same types within the same areas — Summary of preceding and
present chapter Page 293

CHAPTER XII.

GEOGRAPHICAL DISTRIBUTION.

Present distribution cannot be accounted for by differences in physical
conditions — Importance of barriers — Affinity of the productions of
the same continent — Centres of creation — Means of dispersal by
changes of climate and of the level of the land, and by occasional
means — Dispersal during the Glacial period — Alternate Glacial
periods in the North and South Page 319

CHAPTER XIII.

GEOGRAPHICAL DISTRIBUTION Continued.

Distribution of fresh-water productions — On the inhabitants of oceanic
islands — Absence of Batrachians and of terrestrial Mammals — On
the relation of the inhabitants of islands to those of the nearest main-
land — On colonisation from the nearest source with subsequent
modification — Summary of the last and present chapter. .Page 346

CHAPTER XIV.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY: EMBRYOLOGY:
RUDIMENTARY ORGANS Page 3G6

CHAPTER XV.

RECAPITULATION AND CONCLUSION.

Recapitulation of the objections to the theory of Natural Selection —
Recapitulation of the general and special circumstances in its favour
• — Causes of the general belief in the immutability of species — How
far the theory of Natural Selection may be extended — Effects of
its adoption on the study of Natural History — Concluding Re-
marts Page 407

AK HISTORICAL SKETCH

OF THE PROGRESS OF OPINION ON THE ORIGIN OF SPECIES,

PREVIOUSLY TO THE PUBLICATION OF THE PIRST EDITION

OF THIS WORK.

I WILL 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 subject in the
classical writers,* the first author who in modern times has
treated it in a scientific spirit was Buffon. But as his opinions
fluctuated greatly at different periods, and as he does not enter
on the causes or means of the transformation of species, I need
not here enter on details.

Lamarck was the first man whose conclusions on the subject

* Aristotle, in his " Physicse Auscnltationes " (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 trans-
lated 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 to an end.
Wheresoever, therefore, all things together (that is all parts of one
whole) happened like as if thej?^ were made for the sake of something,
these were preserved, having been appropriately constituted by an internal
spontaneity ; and whatsoever things were not thus constituted, perished,
and still perish." We here see the principle of natural Belection shad-
owed forth, but how little Aristotle fully comprehended the principle, is
shown by his remarks on the formation of the teeth.

V

vi HISTORICAL SKETCH

excited mucli attention. Tliis justly-celebrated naturalist first
published his views in 1801; he much enlarged them in 1809
in his '' Philosophic Zoologique/^ and subsequently, in 1815, in
the Introduction to his '^ Hist. N'at. des Animaux sans Yerte-
bres.^^ 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 probability of
all change in the organic, as well as in the inorganic world,
being the result of law, and not of miraculous interposition.
Lamarck seems to have been chiefly led to his conclusion on the
gradual change of species by the difficulty of distinguishing
species and varieties, by the almost perfect gradation of forms in
certain groups, and by the analogy of domestic productions.
With respect to the means of modification, he attributed some-
thing 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 na-
ture;— such as the long neck of the giraffe for browsing on the
branches of trees. But he likewise believed in a law of progres-
sive 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.*

Geoffrey Saint-Hilaire, as is stated in his ^^ Life,^^ written by
his son, suspected, as early as 1795, that what we call species
are various degenerations of the same type. It was not until
1828 that he published his conviction that the same forms have

* I have taken the date of the first publication of Lamarck from Isid.
Geoffroy Saint-Hilaire's ("Hist. Nat. Generale," 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 Introduction to a work written in 1794 and 1795, but not
published till long afterwards: he has pointedly remarked ("Goethe als
Naturforscher," von Dr. Karl Meding, s. 34) that the future question for
naturalists will be 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 m Ger-
many, Dr. Darwin in England, and Geoffrey Saint-Hilaire (as we shall
immediately see) in France, came to the same conclusion on the origin
of species, in the years 1794-5,

HISTORICAL SKETCH vU

not been perpetuated since the origin of all things. GeofTroy
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 a reserver entierement a I'avenir, suppose
meme que Tavenir doive avoir prise sur lui.^^

In 1813, Dr. W. C. Wells read before the Eoyal Society ''An
Account of a Wliite female, part of whose skin resembles that
of a Kegro '^ ; 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 applies 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, sec-
ondly, that agriculturists improve their domesticated animals
by selection; and then, he adds, but what is done in this latter
case '' by art, seems to be done with equal efficacy, though more
slowly, by nature, in the formation of varieties of mankind, fitted
for the country which they inhabit. Of the accidental varieties
of man, which would occur among the first few and scattered
inhabitants 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 granted, 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 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. Well's work.

The Hon. and Rev. W. Herbert, afterward Dean of Manches-

viii HISTORICAL SKETCH

7?

ter, in tlie fourth volume of the " Horticultural Transactions,
1822, and in his work on the ^^ AmaryllidaceEe ^^ (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 ex-
tends the same view to animals. The Dean believes that single
species of each genus were created in an originally highly plastic
condition, and that these have produced, chiefly by intercrossing,
but likewise by variation, all our existing species.

In 1826 Professor Grant, in the concluding paragraph in his
well-known paper (^^ Edinburgh Philosophical Journal,^^ vol.
xiv. p. 283) on the Spongilla, clearly declares his belief that
species are descended from other species, and that they become
improved in the course of modification. This same view was
given in his 55th Lecture, published in the " Lancet ^^ in 1834.

In 1831 Mr. Patrick Matthew published his work on ^^ Naval
Timber and Arboriculture,^^ in which he gives precisely the same
view on the origin of species as that (presently to be alluded to)
propounded by Mr. Wallace and myself in the " Linnean Jour-
nal,^^ and as that enlarged 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. Matthew's view from mine are not of much
importance: he seems to consider that the world was nearly
depopulated at successive periods, and then re-stocked; and he
gives as an alternative, that new forms may be generated ^^ with-
out the presence of any mould or germ of former aggregates."
I am 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 principle 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.

Eafinesque, in his ^^ N"~ew Plora of ISTorth America," published
irt 1836, wrote (p. 6) as follows: — ^^ All species might have been

HISTORICAL SKETCH ix

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 development and modifica-
tion 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 con-
sideration is, that the several series of animated beings, from
the simplest and oldest up to the highest and most recent, are,
under the 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 difhculty
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 circum-
stances, as food, the nature of the habitat, and the meteoric
agencies, these being the ^ adaptations ^ of the natural the-
ologian.^^ 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 sub-
ject, 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 pub-

X HISTORICAL SKETCH

lislied in an excellent tliougli short paper ("Bulletins de ?Acad.
Eoy. Bmxelles/^ torn. xiii. p. 581) his opinion that it is more
probable that new species have been produced by descent with
modification than that they have been separately created: the
author first promulgated this opinion in 1831.

Professor Owen, in 1849 ("Nature of Limbs/^ p. 8G), wrote
as follows : — " The archetypal idea was manifested in the flesh
under divers 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 com-
mitted, we, as yet, are ignorant.^^ In his Address to the British
Association, in 1858, he speaks (p. li.) of "the axiom of the
continuous operation of creative power, or of the ordained
becoming of living things.''^ Farther on (p. xc), after referring
to geographical distribution, he adds, " These phenomena shake
our confidence in the conclusion that the Apteryx of New Zea-
land and the Eed 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 Eed 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 Eed 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
shaken that the Apteryx and the Eed 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 edi-
tion 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 palaeontologists as being firmly convinced of the im-

HISTORICAL SKETCH xi

mutability of species; but it appears (^^Anat. of Vertebrates/''
vol. iii. p. 796) that this was on my part a preposterous error.
In the last edition of this work I inferred, and the inference still
seems to me perfectly just, from a passage beginning with the
words "no doubt the type-form/^ &c. (Ibid. vol. i. p. xxi.),
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 evi-
dence. I also gave some extracts from a correspondence between
Professor Owen and the Editor of the " London Eeview/' from
which it appeared manifest to the Editor as well as to myself,
that Professor Owen claimed to have promulgated the theory
of natural selection before I had done so ; and I expressed my
surprise and satisfaction at this announcement ; but as far as
it is possible to understand certain recently published passages
(Ibid. vol. iii. p. 798) I have either partially or wholly again
fallen into error. It is consolatory to me that others find Pro-
fessor Owen's controversial writings as difficult to understand
and to reconcile with each other, as I do. As far as the mere
enunciation of the principle of natural selection is concerned, it
is quite immaterial whether or not Professor Owen preceded me,
for both of us, as shown in this historical sketch, were long ago
preceded by Dr. Wells and Mr. Matthews.

M. Isidore Geoffroy Saint-Hilaire, in his lectures delivered in
1850 (of which a Eesume appeared in the " Eevue et Mag. de
Zoolog.,'' Jan. 1851), briefly gives his reason for believing that
specific characters '^ sont fixes, pour chaque espece, tant qu'elle
se perpetue au milieu des memes circonstances : ils se modifient,
si les circonstances ambiantes viennent a changer.*' " En re-
sume, Vohservation des animaux sauvages demontre deja la
variabilite limitee des especes. Les experiences sur les animaux
sauvages, devenus domestiques, et sur les animaux domestiques
redevenus sauvages, la demontrent plus clairement en-
core. Ces memes experiences prouvent, de plus, que les differ-
ences produites peuvent etre de valeur gencriquef' In his " Hist.
Nat. Generale" (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), propounded the doc-
trine that all organic beings have descended from one primordial

xii HISTORICAL SKETCH

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 published in
the '' Leader/^ March, 1852, and republished in his " Essays," in
1858), has contrasted the theories of the Creation and the De-
velopment of organic beings with remarkable skill and force.
He argues from the analogy of domestic productions, from the
changes which the embryos of many species 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, expressly stated,
in an admirable paper on the Origin of Species (^"^Eevue Hor-
ticole," p. 102 ; since partly republished in the ^^ Nouvelles
Archives du Museum," tom. i. p. 171), his belief that species
are formed in an analogous manner as varieties are under culti-
vation; 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 mysterieuse, indetemiinee ;
f atalite pour les uns ; pour les autres, volonte providentielle, dont
Taction incessante sur les etres vivants determine, a toutes les
epoques de Texistence du monde, la forme, le volume, et la duree
de chacun d'eux, en raison de sa destinee dans Tordre de choses
dont il fait partie. C'est cette puissance qui harmonise chaque
membre a Fensemble, en Fappropriant a la fonction qu^il doit
remplir dans I'organisme general de la nature, fonction qui est
pour lui sa raison d'etre." *

* From references in Bronn's " Untersuchungen iiber die Entwickeliings-
Gesetze," it appears that the celebrated botanist and palaeontologist Unger
pnblished, in 1852, his belief that species undergo development and modi-
fication. 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 maintained by Oken in his mystical "Natur-philosophie."
From other references in Godron's work " Sur I'Espece," it seems that

HISTORICAL SKETCH xiii

In 1853 a celebrated geologist, Count Keyserling (^'^ Bulletin
de la Soe. Geolog./' 2nd Ser., torn, 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
circumambient molecules of a particular nature, and thus have
given rise to new forms.

In this same year, 1853, Dr. Schaaffhausen published an ex-
cellent pamphlet (" Yerhand. des Naturhist. Vereins der Preuss.
Eheinlands,^^ &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 inter-
mediate graduated forms. ^^ Thus living plants and animals are
not separated from the extinct by new creations, but are to be
regarded as their descendants through continued reproduction.'^

A well-known French botanist, M. Lecoq, writes in 1854
(*^^ Etudes sur Geograph. Bot.,'' tom. 1. p. 250), ^^ On voit que
nos recherches sur la fixite ou la variation de Fespece, nous con-
duisent directement aux idees emises, par deux hommes juste-
ment celebres, Geoffrey Saint-Hilaire et Goethe.'^ Some other
passages scattered through M. Lecoq's large work, make it a
little doubtful how far he extends his views on the modification
of species.

" The Philosophy of Creation '' has been treated in a masterly
manner by the Rev. Baden Powell, in his " Essays on the Unity
of Worlds," 1855. N'othing can be more striking than the man-
ner 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 1st, 1858, by Mr. Wallace and myself,
in which, as stated in the introductory remarks to this volume,

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.

xiv HISTORICAL SKETCH

the theory of Natural ' Selection is promulgated by Mr. Wallace
with admirable force and clearness.

Von Baer, towards whom all zoologists feel so profound a
respect, expressed about the year 1859 (see Prof. Eudolph Wag-
ner, " Zoologisch-Anthropologische Untersuchungen/^ 1861, s.
51) his conviction, chiefly grounded on the laws of geographical
distribution, that forms now perfectly distinct have descended
from a single parent-form.

In June, 1859, Professor Huxley gave a lecture before the
Koyal Institution on the " Persistent Types of Animal Lif e.^'
Eeferring to such cases, he remarks, ^^ It is difficult to compre-
hend the meaning of such facts as these, if we suppose that
each species of animal and plant, or each great type of organisa-
tion, was formed and placed upon the surface of the globe at
long intervals by a distinct act of creative power ; and it is well
to recollect that such an assumption is as unsupported by tradi-
tion 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 unproven, and sadly
damaged by some of its supporters, is yet the only one to which
physiology lends any countenance; their existence would seem
to show that the amount of modification which living beings
have undergone during geological time is but very small in rela-
tion to the whole series of changes which they have suffered.^^

In December, 1859, Dr. Hooker published his "Introduction
to the Australian Flora.'^ In the first part of this great work
he admits the truth of the descent and modification of 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.M.S. ' 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 specu-
late on the subject, and drew up some short notes; these I enlarged
in 1844 into a sketch of the conclusions, which then seemed to me
probable : from that period to the present day I have steadily
pursued the same object. I hope that I may be excused for enter-
ing on these personal details, as I give them to show that I have
not been hasty in coming to a decision.

My work is now (1859) nearly finished; but as it will take me
many more years to complete it, and as my health is far from
strong, I have been urged to publish this Abstract. I have more
especially been induced to do this, as Mr. Wallace, who is now
studying the natural history of the Malay archipelago, has arrived
at almost exactly the same general conclusions that I have on the
origin of species. In 1858 he sent me a memoir on this subject,
with a request that I would forward it to Sir Charles Lyell, who
sent it to the Linnean Society, and it is published in the third
volume of the Journal of that society. Sir C. Lyell and Dr.
Hooker, who both knew of my work — the latter having read my
sketch of 1844 — honored me by thinking it advisable to pub-
lish, with Mr. Wallace's excellent memoir, some brief extracts
from my manuscripts.

This Abstract, which I now publish, must necessarily be imper-
fect. I cannot here give references and authorities for my several

2 ORIGIN OF SPECIES

statements; and I must trust to the reader reposing some confi-
dence in my accuracy. No doubt errors will have crept in, though
I hope I have always been cautious in trusting to good authorities
alone. I can here give only the general conclusions at which I
have arrived, with a few facts in illustration, but which I hope, in
most cases, will suffice. No one can feel more sensible than I do
of the necessity of hereafter publishing in detail all the facts,
with references, on which my conclusions have been grounded;
and I hope in a future work to do this. For I am well aware
that scarcely a single point is discussed in this volume on which
facts cannot be adduced, often apparently leading to conclusions
directly opposite to those at which I have arrived. A fair result
can be obtained only by fully stating and balancing the facts and
arguments on both sides of each question; and this is here im-
possible.

I much regret that want of space prevents my having the satis-
faction of acknowledging the generous assistance which I have
received from very many naturalists, some of them personally
unknown to me. I cannot, however, let this opportunity pass with-
out 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 perfection of
structure and coadaptation which justly excites our admiration.
Naturalists continually refer to external 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 struc-
ture, 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 trees, which has seeds that must be transported
by certain birds, and which has flowers with separate sexes abso-
lutely 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

INTRODUCTION 3

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 coadaptation. At the com-
mencement of my observations it seemed to me probable that a
careful study of domesticated animals and of cultivated plants
would offer the best chance of making out this obscure 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 com-
monly neglected by naturalists.

From these considerations, I shall devote the first chapter of
this Abstract to Variation under Domestication. We shall thus
see that a large amount of hereditary modification is at least pos-
sible; and, what is equally or more important, we shall see how
great is the power of man in accumulating by his Selection suc-
cessive slight variations. I will then pass on to the variability
of species in a state of nature ; but I shall, unfortunately, be com-
pelled to treat this subject far too briefly, as it can be treated
properly only by giving long catalogues of facts. We shall, how-
ever, be enabled to discuss what circumstances are most favourable
to variation. In the next chapter the Struggle for Existence
amongst all organic beings throughout the w^orld, which inevitably
follows from the high geometrical ratio of their increase, will be
considered. This is the doctrine of Malthus, applied to the whole
animal and vegetable kingdoms. As many more individuals of
each species are born than can possibly survive; and as, conse-
quently, 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 nahwally selected. From the strong principle of inherit-
ance, any selected variety will tend to propagate its new and
modified form.

This fundamental subject of Natural Selection will be treated at
some length in the fourth chapter; and we shall then see how
Natural Selection almost inevitably causes much Extinction of
the less improved forms of life, and leads to what I have called
Divergence of Character. In the next chapter I shall discuss the
complex and little known laws of variation. In the five succeed-
ing chapters, the most apparent and gravest difiiculties in accept-
ing the theory will be given : namely, first, the difficulties of tran-

4 ORIGIN OF SPECIES

sitions, or how a simple being or a simple organ can be changed
and perfected into a highly developed being or into an elaborately
constructed organ; secondly, the subject of Instinct, or the mental
powers of animals; thirdly, Hybridism, or the infertility of
species and the fertility of varieties when intercrossed; and
fourthly, the imperfection of the Geological Record. In the next
chapter I shall consider the geological succession of organic be-
ings throughout time; in the twelfth and thirteenth, their geo-
graphical distribution throughout space; in the fourteenth, their
classification or mutual affinities, both when mature and in an
embryonic condition. In the last chapter I shall give a brief
recapitulation of the whole work, and a few concluding remarks.
No one ought to feel surprised at much remaining as yet unex-
plained in regard to the origin of species and varieties, if he make
due allowance for our profound ignorance in regard to the mutual
relations of the many beings which live around us. Who can ex-
plain why one species ranges widely and is very numerous, and
why another allied species has a narrow range and is rare? Yet
these relations are of the highest importance, for they determine
the present welfare and, as I believe, the future success and modi-
fication of every inhabitant of this Avorld. 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. Al-
though much remains obscure, and will long remain obscure, I can
entertain no doubt, after the most deliberate study and dispassion-
ate judgment of which I am capable, that the view which most
naturalists until recently entertained, and which I formerly enter-
tained— namely, that each species has been independently created
— is erroneous. I am fully convinced that species are not im-
mutable; but that those belonging to what are called the same
genera are lineal descendants of some other and generally extinct
species, in the same manner as the acknowledged varieties of any
one species are the descendants of that species. Furthermore, I
am convinced that Natural Selection has been the most important,
but not the exclusive, means of modification.

VARIATION UNDER DOMESTICATION

CIIAPTEK I.

VARIATION UNDER DOMESTICATION.

Causes of Variability — P]ffects of ITabit and Hip use or disuse of Parts —
Correlated Variation — Inheritance — Character of Domestic Vari-
eties — Difficulty of distinguishing between Varieties and Species —
Origin of Domestic Varieties from one or more Species — Domestic
IMgeons, their Differences and Origin — Principles of Selection,
anciently followed, their Effects — Methodical and Unconscious Selec-
tion — Unknown Origin of our Domestic Productions — Circumstances
favourable to Man's power of Selection.

Causes of V ariahility .

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 gen-
erally 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 culti-
vated, and which have varied during all ages under the most
diiferent climates and treatment, v*^e are driven to conclude that
this great variability is due to our domestic productions having
been raised under conditions of life not so uniform as, and some-
what different from, those to which the parent species had been
exposed under nature. There is, also, some probability in the
view propounded by Andrew Knight, that this variability may be
partly connected with excess of food. It seems clear that organic
beings must be exposed during several generations to new condi-
tions to cause any great amount of variation; and that, when the
organisation has once begun to vary, it generally continues vary-
ing for many generations. No case is on record of a variable or-
ganism ceasing to vary under cultivation. Our oldest cultivated
plants, such as wheat, still yield new varieties : our oldest domes-
ticated animals are still capable of rapid improvement or modi-
fication.

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

G ORIGIN OF SPECIES

affecting the reproductive system. With respect to the direct ac-
tion, 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 organism, and the nature of the condi-
tions. The former seems to be much the more important; for
nearly similar variations sometimes arise under, as far as we can
judge, dissimilar conditions; and, on the other hand, dissimilar
variations arise under conditions which appear to be nearly uni-
form. The effects on the offspring are either definite or indefinite.
They may be considered as definite when all or nearly all the off-
spring 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 induced. There can,
however, be little doubt about many slight changes, — such as size
from the amount of food, colour from the nature of the food,
thickness of the skin and hair from climate, &c. 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 invariably
follow from the insertion of a minute drop of poison by a gall-pro-
ducing 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 formation of our domestic races. We
see indefinite variability in the endless slight peculiarities which
distinguish the individuals of the same species, and which cannot
be accounted for by inheritance from either parent or from some
more remote ancestor. Even strongly-marked differences occasion-
ally 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 as the indefinite effects of the conditions of life
on each individual organism, in nearly the same manner as the

A^ARIATION UNDER DOMESTICATION 7

chill affects different men in an indefinite manner, according to
their state of body or constitution, causing coughs, or colds, rheu-
matism, or inflammation of various organs.

With respect to what I have called the indirect action of
changed conditions, namely, through the reproductive system 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 Kulreuter 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 con-
ditions. 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 con-
finement, even when the male and female unite. How many ani-
mals 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 vigor, 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 deter-
mine 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 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 exceptions, hardly ever
lay fertile eggs. Many exotic plants have pollen utterly worth-
less, 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 organ-
isms breed freely under the most unnatural conditions (for in-
stance, rabbits and ferrets kept in hutches), showing that their
reproductive organs are not easily affected; so will some animals

8 ORIGIN OF SPECIES

and plants withstand domestication or cultivation, and vary very
slightly — perhaps hardly more than in a state of nature.

Some naturalists have maintained that all variations are con-
nected with the act of sexual reproduction; but this is certainly
an error ; for I have given in another work a long list of " sporting
plants," as they are called by gardeners ; — that is, of plants which
have suddenly produced a single bud with a new and sometimes
widely different character from that of the other buds on the same
plant. These bud variations, as they may be named, can be prop-
agated by grafts, offsets, &c., and sometimes by seed. They occur
rarely under nature, but are far from rare under culture. As a
single bud out of the many thousands, produced year after year
on the same tree under uniform conditions, has been known sud-
denly to assume a new character; and as buds on distinct trees,
growing under different conditions, have sometimes yielded nearly
the same variety — for instance, buds on peach-trees producing
nectarines, and buds in common roses producing moss-roses — we
clearly see that the nature of the conditions is of subordinate im-
portance in comparison with the nature of the organism in de-
termining each particular form of variation ; — perhaps of not
more importance than the nature of the spark, by which a mass
of combustible matter is ignited, has in determining the nature
of the flames.

Effects of Habit and of the Use or Disuse of Parts; Correlated

Variation; Inheritance.

Changed habits produce an inherited effect, as in the 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 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

VARIATION UNDER DOMESTICATION 9

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 Geoffrey St. Hilaire's great work on this subject. Breed-
ers believe that long limbs are almost always accompanied by an
elongated head. Some instances of correlation are quite whim-
sical: 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 Ileusinger,
it appears that white sheep and pigs are injured by certain plants,
whilst dark-coloured individuals escape: Professor Wyman has
recently communicated to me a good illustration of this fact; on
asking some farmers in Virginia how it was that all their pigs
were black, they 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
" crackers " (i.e. Virginia squatters) added, " we select the black
members of a litter for raising, as they alone have a good chance
of living." Hairless dogs have imperfect teeth; long-haired and
coarse-haired animals are apt to have, as is asserted, long or
many horns; pigeons with feathered feet have skin between their
outer toes; pigeons with short beaks have small feet, and those
with long beaks large feet. Hence if man goes on selecting, and
thus augmenting, any peculiarity, he will almost certainly modify
unintentionally other parts of the structure, owing to the mys-
terious 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 struc-
ture and constitution in which the varieties and sub-varieties differ
slightly from each other. The whole organisation seems to have
become plastic, and departs in a slight degree from that of the
parental type.

Any variation which is not inherited is unimportant for us.
But the number and diversity of inheritable deviations of structure,
both those of slight and those of considerable physiological im-
portance, are enrlless. Dr. Prosper Lucas's treatise, in two large
volumes, is the fullest and the best on this subject. No breeder
doubts how strong is the tendency to inheritance; that like pro-

10 ORIGIN OF SPECIES

duces like is his fundamental belief: doubts have been thrown on
this principle only by theoretical writers. When any deviation
of structure often appears, and we see it in the father and child,
we cannot tell whether it may not be due to the same cause having
acted on both; but when amongst individuals, apparently exposed
to the samie conditions, any very rare deviation, due to some ex-
traordinary combination of circumstances, appears in the parent
— say once amongst several million individuals — and it reappears
in the child, the mere doctrine of chances almost compels us to
attribute its reappearance to inheritance. Every one must have
heard of cases of albinism, prickly skin, hairy bodies, &c., appear-
ing in several members of the same family. If strange and rare
deviations of structure are really inherited, less strange and com-
moner deviations may be freely admitted to be inheritable. Per-
haps the correct way of viewing the whole subject would be, to
look at the inheritance of every character whatever as the rule,
and non-inheritance as the anomaly.

The laws governing inheritance are for the most part unknown.
No one can say why the same peculiarity in different individuals
of the same species, or in different species, is sometimes inherited
and sometimes not so; why the child often reverts in certain char-
acters to its grandfather or grandmother or more remote ances-
tor; why a peculiarity is often transmitted from one sex to both
sexes or to one sex alone, more commonly but not exclusively to
the like sex. It is a fact of some importance to us, that peculiari-
ties 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 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 an offspring when nearly mature ; peculiarities
in the silkworm are known to appear at the corresponding caterpil-
lar or cocoon stage. But hereditary diseases and some other facts
make me believe that the rule has a wider extension, and that,
when there is no apparent reason why a peculiarity should appear
at any particular age, yet that it does tend to appear in the off-
spring 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 peculiarity, and not to the primary
cause which may have acted on the ovules or on the male element ;
in nearly the same manner as the increased length of the horns

VARIATION UNDER DOMESTICATION 11

in the offspring- from the 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 re-
vert 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 endeavored to dis-
cover on what decisive facts the above statement has so often and
so boldly been made. There would be great difficulty in proving
its truth : we may safely conclude that very many of the most
strongly marked domestic varieties could not possibly live in a
wild state. In many cases we do not know what the aboriginal
stock was, and so could not tell whether or not nearly perfect
reversion had ensued. It would be necessary, in order to prevent
the effects of intercrossing, 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 an-
cestral forms, it seems to me not improbable that if we could suc-
ceed in naturali-sing, or were to cultivate, during many genera-
tions, the several races, for instance, of the cabbage, in very poor
soil (in which case, however, some effect would have to be attrib-
uted 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
deduce nothing from domestic varieties in regard to species. But
there is not a shadow of evidence in favour of this view : to
assert that we could not breed our cart and race-horses, long and
short-horned cattle, and poultry of various breeds, and esculent
vegetables, for an unlimited number of generations, .would be
opposed to all experience.

Character of Domestic Varieties; difficulty of distinguishing
between Varieties and Species; origin of Domestic Varieties
from one or more species.

When we look to the hereditary varieties or races of our domes-
tic animals and plants, and compare them with closely allied

12 ORIGIN OF SPECIES

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 differing from each other, and from
other species of the same genus, in several trifling respects, they
often differ in an extreme degree in some one part, both when com-
pared 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 varie-
ties when crossed, — a subject hereafter to be discussed), domestic
races of the same species differ from each other in the same man-
ner as do the closely allied species of the same genus in a state of
nature, but the differences in most canes are less in degree. This
must be admitted as true, for the domestic races of many animals
and plants have been ranl^ed by some competent judges as the
descendants of aboriginally distinct species, and by other compe-
tent 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 character of
generic value. It can be shown that this statement is not correct ;
but naturalists differ much in determining what characters are of
generic value; all such valuations being at present empirical.
When it is explained how genera originate under nature, it will
be seen that we have no right to expect often to find a generic
amount of difference in our domesticated races.

In attempting to estimate the amount of structural difference
between allied domestic races, wo 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 j^resently see, that the
whole amount of difference between the several breeds of the dog
has been produced under domestication ; I believe that a small part
of the difference is due to their being descended from distinct
species. In the case of strongly marked races of some other
domesticated species, there is presumptive or even strong evidence,
that all are descended from a single wild stock.

It has often been assumed that man has chosen for domestica-

VARIATION UNDER DOMESTICATION 13

tion animals and plants having an extraordinary inherent ten-
dency to vary, and likewise to withstand diverse climates. I do
not dispute that these capacities have added largely to the value
of most of our domesticated productions : but how could a savage
possibly know, when he first tamed an 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, w^ere taken from a state of nature, and could be
made to breed for an equal number of generations under domesti-
cation, they would on an average vary as largely as the parent
species of our existing domesticated productions have varied.

In the case of most of our anciently domesticated animals and
plants, it is not possible to come to any definite conclusion,
whether they are descended from one or several wild species. The
argument mainly relied on by those who believe in the multiple
origin or 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-inhab-
itants 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 ITeer has remarked, that they
had at this early age progressed considerably in civilisation; and
this again implies a long continued previous period of less ad-
vanced 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 geolo-
gists 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 collec-
tion of all known facts, come to the conclusion that several wild
species of Canidap have been tamed, and that their blood, in some

14 ORIGIN OF SPECIES

cases mingled together, flows in the veins of our domestic breeds.
In regard to sheep and goats I can form no decided opinion.
From facts communicated to me by Mr. Blyth, on the habits, voice,
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 be-
lieve 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 as established by the
admirable researches of Professor Riitimeyer. With respect to
horses, from reasons which I cannot here give, I am doubtfully in-
clined to believe, in opposition to several authors, that all the
races belong to the same species. Having kept nearly all the
English breeds of the fowl alive, having bred and crossed them,
and examined their skeletons, it appears to me almost certain that
all are the descendants of the wild Indian fowl, Gallus bankiva;
and this is the conclusion of Mr. Blyth, and of others who have
studied this bird in India. In regard to ducks and rabbits, some
breeds of which differ much from each other, the evidence is clear
that they are all descended from the common wild duck and rabbit.
The doctrine of the origin of our several domestic races from
several aboriginal stocks, has been carried to an absurd extreme
by some authors. They believe that every race which breeds true,
let the distinctive characters be ever so slight, has had its wild
prototype. At this rate there must have existed at least a score
of species of wild cattle, as many sheep, and several goats, in
Europe alone, and several even within Great Britain. One author
believes that there formerly existed eleven wild species of sheep
peculiar to Great Britain ! When we bear in mind that Britain
has now not one peculiar mammal, and France but few distinct
from those of Germany, and so with Hungary, Spain, &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 blood-
hound, the bull-dog, pug-dog, or Blenheim spaniel, &c., — so unlike
all wild Canidffi — ever existed in a state of nature? It has often
been loosely said that all our races of dogs have been produced by
the crossing of a few aboriginal species ; but by crossing we can only

VARIATION UNDER DOMESTICATION 15

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, &c., 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 care-
ful selection of the individuals which present the desired char-
acter; but to obtain a race intermediate between two quite dis-
tinct races, would be very difficult. Sir J. Sebright expressly ex-
perimented 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 every-
thing seems simple enough; but when these mongrels are crossed
one with another for several generations, hardly two of them are
alike, and then the difficulty of the task become 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 globe,
more especially by the Hon. W. Elliot from India, and by the
Hon. C. Murray from Persia. Many treatises in different lan-
guages have been published on pigeons, and some of them are very
important, as being of considerable antiquity. I have associated
with several eminent fanciers, and have been permitted to join
two of the London Pigeon Clubs. The diversity of the breeds is
something astonishing. Compare the English carrier and the
short-faced tumbler, and see the wonderful difference in their
beaks, entailing corresponding differences in their skulls. The
carrier, more especially the male bird, is also remarkable from the
the wonderful development of the carunculated skin about the
head; and this is accompanied by greatly elongated eyelids, very
large internal orifices to the nostrils, and a wide gape of mouth.
The short-faced tumbler has a beak in outline almost like that of
a finch; and the common tumbler has the singular inherited habit
of flying at a great height in a compact flock, and tumbling in the
air head over heels. The runt is a bird of great size, with long
massive beak and large feet ; some of the sub-breeds of runts have
very long necks, others very long wings and tails, others singularly
short tails. The barb is allied to the carrier, but, instead of a
long beak, has a very short and broad one. The pouter has a

10 ORIGIN OF SPECIES

much elongated body, wings, and legs; and its enormously devel-
oped crop, which it glories in inflating, may well excite astonish-
ment 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
oesophagus. The Jacobin has the feathers so much reversed along
the back of the neck that they form a hood; and it has, propor-
tionally to its size, elongated wing and tail feathers. The trump-
eter and laugher, as their names express, utter a very different
coo from the other breeds. The fantail has thirty or even forty
tail-feathers, instead of twelve or fourteen — the normal number
in 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 development of the
bones in the face in length and breadth and curvature differs
enormously. The shape, as well as the breadth and length of the
ramus of the lower jaw, varies in a highly remarkable manner.
The caudal and sacral vertebrae vary in number; as does the num-
ber of the ribs, together with their relative breadth and the pres-
ence 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 eye-
lids, of the orifice of the nostrils, of the tongue (not always in
strict correlation with the length of beak), the size of the crop
and of the upper part of the oesophagus ; the development and
abortion of the oil-gland; the number of the primary wing and
caudal feathers; the relative length of the wing and tail to each
other and to the body; the relative length of the leg and foot; the
number of scutella? 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 man-
ner of flight, and in 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 certainly be ranked by him as well-defined species.
Moreover, I do not believe that any ornithologist would in this
case place the English carrier, the short-faced tumbler, the runt,

VARIATION UNDER DOMESTICATION 17

the barb, the pouter, and f antail 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 him.

Great as are the differences between the breeds of the pigeon, I
am fully convinced that the common opinion of naturalists is cor-
rect, namely, that all are descended from the rock-pigeon (Columba
livia), including under this term several geographical races or
sub-species, which differ from each other in the most trifling re-
spects. As several of the reasons which have led me to this be-
lief are in some degree applicable in other cases, I will here briefly
give them. If the several breeds are not varieties, and have not pro-
ceeded from the rock-pigeon, they must have descended from at
least seven or eight aboriginal stocks ; for it is impossible to make
the present domestic breeds by the crossing of any lesser number:
how, for instance, could a pouter be produced by crossing two
breeds unless one of the parent-stocks 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 species of rock pigeons are known ; and
these have not any of the characters of the domestic breeds.
Hence the supposed aboriginal stocks must either still exist in
the countries where they were originally domesticated, and yet be
unknown to ornithologists; and this, considering their size, habits,
and remarkable characters, seems improbable; or they must have
become extinct in the wild state. But birds breeding on precipices,
and good fliers, are unlikely to be exterminated; and the common
rock-pigeon, which has the same habits with the domestic breeds,
has not been 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 country; but not one has be-
come wild or feral, though the dovecot-pigeon, which is the rock-
pigeon in a very slightly altered state, has become feral in several
places. Again, all recent experience shows that it is difficult to
get wild animals to breed freely under domestication; yet on the
hypothesis of the multiple origin of our pigeons, it must be as-
sumed that at least seven or eight species were so thoroughly
domesticated in ancient times by half-civilized man, as to be quite
prolific under confinement.

An argument of great weight, and applicable in several other

18 ORIGIN OF SPECIES

cases, is, that the above-specified breeds, though agreeing generally
with the wild rock-pigeon in constitution, habits, voice, coloring,
and in most parts of their structure, yet are certainly highly ab-
normal in other parts ; we may look in vain through the whole great
family of Columbida3 for a beak like 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 -civilised man succeeded in thoroughly domesticating
several species, but that he intentionally or by chance picked out
extraordinarily abnormal species; and further, that these very
species have since all become extinct or unknown. So many strange
contingencies are improbable in the highest degree.

Some facts in regard to the colouring of pigeons well 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 do 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 con-
cur perfectly developed. Moreover, when birds belonging to two
or more distinct breeds are crossed, none of which are blue or have
any of the above-specified marks, the mongrel offspring are very
apt suddenly to acquire these characters. To give one instance
out of several which I have observed : — I crossed some white fan-
tails, which breed very true, with some black barbs — and it so
happens that blue varieties of barbs are so rare that I never heard
of an instance in England; and the mongrels were black, brown
and mottled. I also crossed a barb with a spot, which is a white
bird with a red tail and red spot on the forehead, and which no-
toriously breeds very true; the mongrels were dusky and mottled.
I then crossed one of the mongrel barb-fantails with a mongrel
barb-spot, and they produced a bird of as beautiful a blue colour,
with the white loins, double black wing-bar, and barred and white-
edged tail-feathers, as any wild-rock pigeon! We can under-
stand these facts, on the well-known principle of reversion to an-
cestral characters, if all the domestic breeds are descended from
the rock-pigeon. But if we deny this, we must make one of the
two following highly improbable suppositions. Either, first, that
all the several imagined aboriginal stocks were coloured and

VARIATION UNDER DOMESTICATION ID

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 mark-
ings. Or, secondly, that each breed, even the purest, has within
a dozen, or at most within a score, of generations, been crossed
by the rock-pigeon : I say within a dozen or twenty generations, for
no instance is known of crossed descendants reverting to an an-
cestor of foreign blood, removed by a greater number of genera-
tions. 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 succeeding generation there will
be less of the foreign blood ; but when there has been no cross, and
there is a tendency in the breed to revert to a character which was
lost during some former 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 obser-
vations, 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 prob-
ably quite correct, if applied to species closely related to each other.
But to extend it so far as to suppose that species, aboriginally as
distinct as carriers, tumblers, pouters, and fantails, now are, should
yield offspring perfectly fertile wier se, would be rash in the ex-
treme.

From these several reasons, namely, — the improbability of man
having formerly made seven or eight supposed species of pigeons
to breed freely under domestication ; — these supposed species being
quite unknown in a wild state, and their not having become any-
where feral ; — these species presenting certain very abnormal char-
acters, as compared with all other Columbidse, though so like the
rock-pigeon in most respects ; — the occasional re-appearance of the
blue colour and various black marks in all the breeds, both when
kept pure and when crossed ; — and lastly, the mongrel offspring
being perfectly fertile ; — from these several reasons taken together,
we may safely conclude that all our domestic breeds are descended
from the rock-pigeon or Columba livia with its geographical sub-
species.

20 ORIGIN OF 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;
arid 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 short-
ness 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 b. c, as was pointed out to me by
Professor Lepsius; but ]\Ir. Birch informs me that pigeons are
given in a bill of fare in the previous dynasty. In the time of
the Romans, as we hear from Pliny, immense prices were given
for pigeons ; " nay, they are come to this pass, that they can
reckon up their pedigree and race." Pigeons were much valued
by Akber Khan in India, about the year 1600; never less than
20,000 pigeons were taken with the court. " The monarchs of Iran
and Turan sent him some very rare birds;" and, continues the
courtly historian, " His Majesty by crossing the breeds, which
method was never practised before, has improved them aston-
ishingly." About this same period the Dutch were as eager about
pigeons as were the old Romans. The paramount importance of
these considerations in explaining the immense amount of varia-
tion which pigeons have undergone, will likewise be obvious
when we treat of Selection. We shall then, also, see how it is
that the several breeds so often have a somewhat monstrous char-
acter. It is also a most favourable circumstance for the produc-
tion 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 com-

VARIATION UNDER DOMESTICATION 21

mon parent, as any naturalist could in coming to a similar con-
clusion in regard to the many species of finches, or other groups
of birds, in nature. One circumstance has struck me much ; name-
ly, that nearly all the breeders of the various domestic animals
and the cultivators of plants, with whom I have conversed, or
whose treatises I have read, are firmly convinced that the several
breeds to which each has attended, are descended from so many
aboriginally distinct species. Ask, as I have asked, a celebrated
raiser of 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 Kibston-pippin or
Codlin-apple, could ever have proceeded from the seeds of the
same tree. Innumerable other examples could be given. The
explanation, I think, is simple : from long-continued study
they are strongly impressed with the differences between the sev-
eral races; and though they well know that each race varies
slightly, for they win their prizes by selecting such slight differ-
ences, 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 les-
son of caution, when they deride the idea of species in a state
of nature being lineal descendants of other species?

Principles of Selection anciently followed, and their Effects.

Let us now briefly consider the steps by which domestic races
have been produced, either from one or from several allied species.
Some effect may be attributed to the direct and 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 differ-
ences between a dray- and race-horse, a greyhound and blood-
hound, a carrier and tumbler pigeon. One of the most remark-
able 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 prob-
ably arisen suddenly, or by one step; many botanists, for in-

22 ORIGIN OF SPECIES

stance, believe that the fuller's teasel, with its hooks, which cannot
be rivalled by any mechanical contrivance, is only a variety of
the wild Dipsacus; and this amount of change may have sud-
denly arisen in a seedling. So it has probably been with the
turnspit dog; and this is known to have been the case with the
ancon sheep. But when we compare the dray-horse and race-
horse, the dromedary and camel, the various breeds of sheep fitted
either for cultivated land or mountain pasture, with the wool of
one breed good for one purpose, and that of another breed for
another purpose; when we compare the many breeds of dogs, each
good for man in different ways; when we compare the game-cock,
so pertinacious in battle, with other breeds so little quarrelsome,
with " everlasting layers " which never desire to sit, and with the
bantam so small and elegant; when we compare the host of agri-
cultural, culinary, orchard, and flower-garden races of plants,
most useful to man at different seasons and for different pur-
poses, 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 hypothet-
ical. It is certain that several of our eminent breeders have, even
within a single lifetime, modified to a large extent their breeds of
cattle and sheep. In order fully to realise what they have done, it
is almost necessary to read several of the many treatises devoted
to this subject, and to inspect the animals. Breeders habitually
speak of an animal's organisation as something plastic, which
they can model almost as they please. If I had space I could
quote numerous passages to this effect from highly competent
authorities. Youatt, who was probably better acquainted with
the works of agriculturists than almost any other individual, and
who was himself a very good judge of animals, speaks of the prin-
ciple of selection as " that which enables the agriculturist, not
only to modify the character of his flock, but to change it alto-
gether. It is the magician's wand, by means of which he may
summon into life whatever form and mould he pleases." Lord
Somerville, speaking of what breeders have done for sheep, says:
• — " It would seem as if they had chalked out upon a wall a form
perfect in itself, and then had given it existence." In Saxony the
importance of the principle of selection in regard to merino sheejf

VARIATION UNDER DOMESTICATION 23

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 ulti-
mately 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 differ-
ent 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 in-
dispensable even than in ordinary cases. If selection consisted
merely in separating some very distinct variety, and breeding from
it, the principle would be so obvious as hardly to be worth notice;
but its importance consists in the great effect produced by the ac-
cumulation in one direction, during successive generations, of
differences absolutely inappreciable by an uneducated eye — dif-
ferences which I for one have vainly attempted to appreciate. Not
one man in a thousand has accuracy of eye and judgment suffi-
cient to become an eminent breeder. If gifted with these qual-
ities, and he studies his subject for years, and devotes his life-
time to it with indomitable perseverance, he will succeed, and may
make great improvements; if he wants any of these qualities, he
will assuredly fail. Few would readily believe in the natural
capacity and years of practice requisite to 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 produced by a single variation
from the aboriginal stock. We have proofs that this has not
been so in several cases in which exact records have been kept;
thus, to give a very trifling instance, the steadily-increasing size
of the common gooseberry may be quoted. We see an astonishing
improvement in many 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 es-
tablished, the seed-raisers do not pick out the best plants, but
merely go over their seed-beds, and pull up the " rogues," as they
call the plants that deviate from the proper standard. With ani-
mals this kind of selection is, in fact, likewise followed; for
hardly any one is so careless as to breed from his worst animals.

In regard to plants, there is another means of observing the ac-
cumulated effects of selection — namely, by comparing the di-

24 ORIGIN OF SPECIES

versity of flowers in the different varieties of the same species in
the flower-garden ; the diversity of leaves, pods, or tubers, or what-
ever 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 un-
like the flowers of the heartsease are, and how alike the leaves;
how much the fruit of the different kinds of gooseberries differ in
size, colour, shape, and hairiness, and yet the flowers present very
slight differences. It is not that the varieties which differ largely
in some one point do not differ at all in other points; that 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-quar-
ters 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 im-
portant. But it is very far from true that the principle is a
modern discovery. I could give several references to works of
high antiquity, in 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 pre-
vent their exportation : the destruction of horses under a certain
size was ordered, and this may be compared to the " roguing "
of plants by nurserymen. The principle of selection I find dis-
tinctly given in an ancient Chinese encyclopaedia. Explicit rules
are laid down by some of the Koman classical writers. From
passages in Genesis, it is clear that the colour of domestic ani-
mals was at that early period attended to. Savages now some-
times cross their dogs with wild canine animals, 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

VARIATION UNDER DOMESTICATION 25

attended to in ancient times, and is now attended to by the lowest
savages. It would, indeed, have been a strange fact, had attention
not been paid to breeding, for the inheritance of good and bad
qualities is so obvious.

Unconscious Selection.

At the present time, eminent breeders try by methodical se-
lection, 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 Un-
conscious, 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 dur-
ing their lifetimes, the forms and qualities of their cattle. Slow
and insensible changes of this kind can never be recognised unless
actual measurements or careful drawings of the breeds in ques-
tion have been made long ago, which may serve for comparison.
In some cases, however, unchanged, or but little changed indi-
viduals 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 com-
petent authorities are convinced that the setter is directly derived
from the spaniel, and has probably been slowly altered from it.
It is known that the English pointer has been greatly changed
within the last century, and in this case the change has, it is be-
lieved, been chiefly effected by crosses with the foxhound; but
what concerns us is, that the change has been effected uncon-
sciously 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, Eng-
lish race-horses have come to surpass in fleetness and size the
parent Arabs, so that the latter, by the regulations for the Good-
wood Races, are favoured in the weights which they carry. Lord
Spencer and others have shown how the cattle of England have

26 ORIGIN OF SPECIES

increased in weight and in early maturity, compared with the
stock formerly kept in this country. By comparing the accounts
given in various old treatises of the former and present state of
carrier and tumbler pigeons in Britain, India, and Persia, we
can trace the stages through which they have insensibly passed,
and come to differ so greatly from the rock-pigeon.

Youatt gives an excellent illustration of the effects of a course
of selection, which may be considered as unconscious, in so far
that the breeders could never have expected, or even wished, to
produce the result which ensued — namely, the 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 in-
herited character of the offspring of their domestic animals, yet
any one animal particularly useful to them, for any special pur-
pose, would be carefully preserved during famines and other ac-
cidents, 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 selec-
tion going on. We see the value set on animals even by the bar-
barians of Tierra del Fuego, by their killing and devouring their
old women, in times of dearth, as of less value than their dogs.

In plants the same gradual process of improvement, through
the occasional preservation of the best individuals, 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 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 hearts-
ease or dahlia from the seed of a wild plant. No one would expect
to raise a first-rate melting pear from the seed of the wild pear,
though he might succeed from a poor seedling growing wild, if
it had come from a garden-stock. The pear though cultivated in
classical times, appears, from Pliny's description, to have been a
fruit of very inferior quality. I have seen great surprise ex-

VARIATION UNDER DOMESTICATION 27

pressed in horticultural works at the wonderful skill of gardeners,
in having produced such splendid results from such poor ma-
terials; but the art has been simple, and, as far as the final re-
sult is concerned, has been followed almost unconsciously. It
has consisted in always cultivating the best known variety, sow-
ing 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 unconsciously ac-
cumulated, 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 cul-
tivated in our flower and kitchen gardens. If it has taken cen-
turies 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 re-
marked 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 under-
stand the frequently abnormal character of our domestic races,
and likewise their differences being so great in external char-
acters, and relatively so slight in internal parts or organs. Man

28 ORIGIN OF SPECIES

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 incor-
rect. The man who first selected a pigeon with a slightly larger
tail, never dreamed what the descendants of that pigeon would
become through long-continued, partly unconscious and partly
methodical, selection. Perhaps the parent -bird of all fantails had
only fourteen tail-feathers somewhat expanded, like the present
Java fantail, or like 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 i)art of its oesophagus, — 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 ex-
tremely 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 differ-
ences in the individuals of the same species, be judged of by the
value which is now set on them, after several breeds have fairly
been established. It is known that with pigeons many slight
variations now occasionally appear, but these are rejected as faults
or deviations from the 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 exliibited as dis-
tinct at our poultry-shows.

These views appear to explain what has sometimes been noticed
— namely, that we know hardly anything about the origin or his-
tory 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 ani-
mals slowly spread in the immediate neighborhood. But they

VARIATION UNDER DOMESTICATION 29

will as yet hardly have a distinct name, and from being only
slightly valued, their history will have been disregarded. When
further improved by the same slow and gradual process, they will
spread more widely, and will be recognised as something distinct
and valuable, and will then probably first receive a provincial
name. In semi-civilised countries, with little free communica-
tion, the spreading of a new sub-breed would be a slow process.
As soon as the points of value are once acknowledged, the prin-
ciple, 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
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 rec-
ord 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 varia-
bility is obviously favourable, as freely giving the materials for
selection to work on; not that mere individual differences are not
amply sufiicient, with extreme care, to allow of the accumulation
of a large amount of medification 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 prin-
ciple Marshall formerly remarked, with respect to the sheep of
parts of Yorkshire, " as they generally belong to poor people, and
are mostly in small lots, they never can be improved." On the
other hand, nurserymen, from keeping large stocks of the same
plant, are generally far more successful than amateurs in raising
new and valuable varieties. A large number of individuals of
an animal or plant can be reared only where the conditions for its
propagation are favourable. When the individuals are scanty, all
will be allowed to breed, whatever their quality may be, and this
will effectually prevent selection. But probably the most im-
portant element is that the animal or plant should be so highly
valued by man, that the closest attention is paid to even the
slightest deviations in its qualities or structure. Unless such at-
tention be paid nothing can be effected. I have seen it gravely re-
marked, that it was most fortunate that the strawberry began to

30 ORIGIN OF SFP^CIES

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 en-
closure of the land plays a part. Wandering savages or the in-
habitants 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 almost always imported from some other coun-
try. 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 breed-
ing; 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 do-
mesticated, seems to have a singularly inflexible organisation,
though it has varied to a slight extent, as I have elsewhere de-
scribed.

Some authors have maintained that the amount of variation
in our domestic productions is soon reached, and can never after-
wards be exceeded. It would be somewhat rash to assert that

VARIATION UNDER DOMESTICATION 31

the limit has been attained in any one case; for ahnost 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 ut-
most limit, could not, after remaining fixed for many centuries,
again vary under new conditions of life. No doubt, as Mr. Wal-
lace has remarked with much truth, a limit will be at last reached.
For instance, there must be a limit to the fleetness of any ter-
restrial animal, as this will be determined by the friction to be
overcome, the weight of body to be carried, and the power of
contraction in the 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.
Isidor Geoffrey St. Hilaire has proved this in regard to size,
and so it is with colour and probably with the length of hair.
With respect to fleetness, which depends on many bodily char-
acters. Eclipse was far fleeter, and a dray-horse is incompara-
bly 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 shall endure. Varia-
bility is governed by many unknown laws, of which correlated
growth is probably the most important. Something, but how
much we do not know, may be attributed to the definite action of
the conditions of life. Some, perhaps a great, effect may be at-
tributed to the increased use or disuse of parts. The final re-
sult is thus rendered infinitely complex. In some cases the inter-
crossing 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 in-
tercrossing, with the aid of selection, has, no doubt, largely aided
in the formation of new sub-breeds; but the importance of cross-
ing has been much exaggerated, both in regard to animals and to

32 ORIGIN OF SPECIES

those plants which are propagated by seed. WUh plants which
are temporarily propagated by cuttings, buds, &c., ihe importance
of crossing is immense; for the cultivator may here disregard the
extreme variability both of hybrids and of mongrels, and the steril-
ity of hybrids; but plants not propagated by seed are of little im-
portance 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.

VARIATION UNDER NATURE 33

CHAPTER 11.

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 frequently than the species of the
smaller genera — Many of the species of the larger genera resemble
varieties in being very closely, but unequally, related to each other,
and in having restricted ranges.

BEFORE applying the principles arrived at in the last chap-
ter 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 nat-
uralists; yet every naturalist knows vaguely what he means when
he speaks of a si^ecies. Generally the term includes the unknown
element of a distinct act of creation. The term " variety " is al-
most 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 consider-
able deviation of structure, generally injurious, or not useful to
the species. Some authors use the term " variation '' in a tech-
nical sense, as implying a modification directly due to the phys-
ical conditions of life ; and " variations " in this sense are sup-
posed not to be inherited; but who can say that the dwarfed con-
dition 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 produc-
tions, more especially with plants, are ever permanently propagated
in a state of nature. Almost every part of every organic being
is so beautifully related to its complex conditions of life that it

34 ORIGIN OF SPECIES

seems as improbable that any part should have been suddenly pro-
duced perfect, as that a complex machine should have been in-
vented by man in a perfect state. Under domestication mon-
strosities 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
normal structures in nearly allied forms, and these alone bear
on the question. If monstrous forms of this kind ever do appear
in a state of nature and are capable of reproduction (which is
not always the case), as they occur rarely and singularly, their
preservation would depend on unusually favourable circumstances.
They would, also, during the first and succeeding generations
cross with the ordinary form, and thus their abnormal character
would almost inevitably be lost. But I shall have to return in a
future chapter to the 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 dif-
ferences 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 indi-
vidual differences in his domesticated productions. These indi-
vidual 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 important 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 char-
acters, and that there are not many men who will laboriously
examine internal and important organs, and compare them in

VARIATION UNDER NATURE 35

many specimens of the same species. It would never have been
expected 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 lar\'8e 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 as-
suredly 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 Eubus, 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 poly-
morphic in one country seem to be, with a few exceptions, poly-
morphic 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 inclined to suspect that we see, at
least in some of these polymorphic genera, variations which are
of no service or disservice to the species, and which 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 varia-
tion, 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, regularly appear under
two or even three conspicuously distinct forms, not connected by

36 ORIGIN OF SPECIES

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 antennae much more abundantly fur-
nished with smelling-hairs. Although in most of these cases, the
two or three forms, both with animals and plants, are not now
connected by intermediate gradations, it is probable that they
were once thus connected. Mr. Wallace, for instance, describes
a certain butterfly which presents in the same island a great
range of varieties connected by intermediate links, and the ex-
treme 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 hermaph-
rodite plant should produce from the same seed-capsule three dis-
tinct hermaphrodite forms, bearing three different kinds of females
and three or even six different kinds of males. Nevertheless
these cases are only exaggerations of the common fact that the
female produces offspring of two sexes which sometimes differ
from each other in a wonderful manner.

Doubtful Species,

The forms which possess in some considerable degree the char-
acter of species, but which are so closely similar to other forms, or
are so closely linked to them by intermediate gradations, that nat-
uralists do not like to rank them as distinct species, are in several
respects the most important for us. We have every reason to be-
lieve 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. Prac-
tically, when a naturalist can unite by means of intermediate
links any two forms, he treats the one as a variety of the other;
ranking the most common, but sometimes the one first described,
as the 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

VARIATION UNDER NATURE 37

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 inter-
mediate 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 judg-
ment and wide experience 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 considered as varieties, but which have all been ranked
by botanists as species; and in making this list he has omitted
many trifling varieties, but which nevertheless have been ranked
by some botanists as species, and he has entirely omitted several
highly polymorphic genera. Under genera, including the most
polymorphic forms, Mr. Babington gives 251 species, whereas Mr.
Bentham gives only 112, — 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 undovibted species, and by another as
varieties, or, as they are often called, geographical races! Mr.
Wallace, in several valuable papers on the various animals, es-
pecially 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 limits of the same island.
The local forms are moderately constant and distinct in each
separate island; but when all from the several islands are com-

38 ORIGIN OF SPECIES

pared together, the differences are seen to be so slight and grad-
uated, that it is impossible to define or describe them, though at
the same time the extreme forms are sufficiently distinct. The
geographical races or sub-species are local forms completely fixed
and isolated ; but as they do not differ from each other by strongly
marked and important characters, " there is no possible test but
individual opinion to determine which of them shall be considered
as species and which as varieties." Lastly, representative species
fill the same place in the natural economy of each island as do the
local forms and sub-species; but as they are distinguished from
each other by a greater amount of difference than that between
the local forms and sub-species, they are almost universally
ranked by naturalists as true species. Nevertheless, no certain
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 distinction between species and varieties. On the islets
of the little Madeira group there are many insects which are char-
acterised 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
some zoologists. Several experienced ornithologists consider our
British red grouse as only a strongly-marked race of a Nor-
wegian species, whereas the greater number rank it as an un-
doubted species peculiar to Great Britain. A wide distance be-
tween 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 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 group of plants; some feed indiscrim-
inately on many kinds, but do not in consequence vary. In sev-
eral 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

VARIATION UNDER NATURE 39

the males alone, in other instances both males and females, have
been observed thus to differ in a slight degree. When the differ-
ences are rather more strongly marked, and when both sexes and all
ages are affected, the forms are ranked by all entomologists as good
species. But no observer can determine for another, even if he can
do so for himself, v/hich 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 api:)ear to have lost this power as species. As the differ-
ences depend on the insects having long fed on distinct plants, it
cannot be exioected 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 spe-
cies. This likewise necessarily occurs with closely allied organisms,
which inhabit distinct continents or islands. When, on the other
hand, an animal or plant ranges over the same continent, or inhab-
its 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 dif-
ference 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 abstrac-
tion, 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 distribution, analogical variation,
hybridism, &c., have been brought to bear in the attempt to de-
termine 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 confessed that it is in the best known countries that we find
the greatest number of them. I have been struck with the fact,
that if any animal or plant in a state of nature be highly useful

40 ORIGIN OF SPECIES

to man, or from any cause closely attracts his attention, varie-
ties of it will almost universally be found recorded. These varie-
ties, 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 fre-
quency 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 assign-
able 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 difl^er by characters never varying on the same
tree, and never found connected by intermediate states. After
this discussion, the result of so much labour, he emphatically re-
marks : " They are mistaken, who repeat that the greater part of
our species are clearly limited, and that the doubtful 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 varie-
ties and sub-varieties. Thus Quercus robur has twenty-eight
varieties, all of which, excepting six, are clustered round three
sub-species, namely, Q. pedunculata, sessili-flora, and pubescens.
The forms which connect these three sub-species are compara-
tively 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

VARIATION UNDER NATURE 41

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 cre-
ations, but concludes that the derivative theory is the most
natural one, " and the most accordant with the known facts in
palaeontology, 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 nothing of the amount and kind of varia-
tion to which the group is subject; and this shows, at least, how
very generally there is some variation. But if he confine his at-
tention 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 im-
pressed, just like the pigeon or poultry fancier before alluded to,
with the amount of difference in the forms which he is continu-
ally studying; and he has little general knowledge of analogical
variation in other groups and in other countries, by which to
correct his first impressions. As he extends the range of his ob-
servations, he will meet with more cases of difiiculty; for he will
encounter a greater number' of closely-allied forms. But if his
observations be widely extended, he will in the end generally be
able to make up his own mind: but he will succeed in this at
the expense of admitting much variation, — and the truth of
this admission will often be disputed by other Naturalists. When
he comes to study allied forms brought from countries not now
continuous, in which case he cannot hope to find 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 indi-
vidual differences. These differences blend into each other by an
insensible series; and a series impresses the mind with the idea
of an actual passage.

Hence I look at individual differences, though of small interest
to the systematist, as of the highest importance for us, as being
the first steps towards such slight varieties as are barely thought
worth recording in works on natural history. And I look at varie-

42 ORIGIN OF SPECIES

ties 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 ex-
posed; but with respect to the more important and adaptive char-
acters, 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 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 applied arbi-
trarily, for convenience' sake.

Wide-ranging, much diffused, and common Species vary most.

Guided by theoretical considerations, I thought that some inter-
esting results might be obtained in regard to the nature and rela-
tions of the species which vary most, by tabulating all the varie-
ties 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 difiiculties, as did subsequently Dr. Hooker,
even in stronger terms. I shall reserve for a future work the dis-
cussion of these difficulties, and the tables of the proportional
numbers of the varying species. Dr. Hooker permits me to add

VARIATION UNDER NATURE 43

that after having carefully read my manuscript, and examined
the tables, he thinks that the following statements are fairly well
established. The whole subject, however, treated as it necessarily
here is with much brevity, is rather perplexing, and allusions can-
not be avoided to the " struggle for existence," " divergence of
character," and other questions, hereafter to be discussed.

Alphonse de CandoUe and others have shown that plants which
have very wide ranges generally present varieties; and this might
have been expected, as they are exposed to diverse physical condi-
tions, and as they come into competition (which, as we shall here-
after see, is an equally or more important circumstance) with dif-
ferent 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 indi-
viduals or commonness of species, the comparison of course re-
lates only to the members of the same group. One of the higher
plants may be said to be dominant if it be more numerous in
individuals and more widely diffused than the other plants of the
same country, which live under nearly the same conditions. A
plant of this kind is not the less dominant because some conferva
inhabiting the water or some parasitic fungus is infinitely more
numerous in individuals and more widely diffused. But if the
conferva or parasitic fungus exceeds its allies in the above re-
spects, it will then be dominant within its own class.

44 ORIGIN OF SPECIES

Species of the Larger Genera in each Country vary more fre-
quently than the Species of the Smaller Genera.

If the plants inhabiting a country, as described in any Flora,
be divided into two equal masses, all those in the larger genera
(i. e., those including many species) being placed on one side,
and all those in the smaller genera on the other side, the former
will be found to include a somewhat larger number of the very
yommon and much diffused or dominant species. This might
have been anticipated; for the mere fact of many species of the
fiame genus inhabiting any country, shows that there is something
in the organic or inorganic conditions of that country favourable
to the genus; and, consequently, we might have expected to have
found in the larger genera or those including many species, a
larger proportional number of dominant species. But so many
causes tend to obscure this result, that I am surprised that my
tables show even a small majority on the side of the larger genera.
I will here allude to only two causes of obscurity. Fresh-water
and salt-loving plants generally have very wide ranges and are
much diffused, but this seems to be connected with the nature
of the stations inhabited by them, and has little or no relation
to the size of the genera to which the species belong. Again,
plants low in the scale of organisation are generally much more
widely diffused than plants higher in the scale; and here again
there is no close relation to the size of the genera. The cause
of lowly-organised plants ranging widely will be discussed in our
chapter on Geographical Distribution.

From looking at species as only strongly-marked and well-de-
fined varieties, I was led to anticipate that the species of the
larger genera in each country would oftener present varieties,
than the species of the smaller genera; for wherever many closely
related species (i. e., species of the same genus) have been formed,
many varieties or incipient species ought, as a general rule, to be
now forming. Where many large trees grow, we expect to find
saplings. Where many species of a genus have been formed
through variation, circumstances have been favourable for varia-
tion ; and hence we might expect that the circumstances would
generally be still favourable to variation. On the other hand,
if we look at each species as a special act of creation, there is no
apparent reason why more varieties should occur in a group
having many species, than in one having few.

To test the truth of this anticipation I have arranged the
plants of twelve countries, and the coleopterous insects of two
districts, into two nearly equal masses, the species of the larger

VARIATION UNDER NATURE 45

genera on one side, and those of the smaller genera on the other
side, and it has invariably proved to be the case that a larger
proportion of the species on the side of the larger genera pre-
sented varieties, than on the side of the smaller genera. More-
over, the species of the large genera v/hich present any varieties,
invariably present a larger average number of varieties than do
the species of the small genera. Both these results follow when
another division is made, and when all the least genera, with from
only one to four species, are altogether excluded from the tables.
These facts are of plain signification on the view that species are
only strongly-marked and permanent varieties; for wherever
many species of the same genus have been formed, or where, if
we may use the expression, the manufactory of species has been
active, we ought generally to find the manufactory still in ac-
tion, more especially as we have every reason to believe the
process of manufacturing new species to be a slow one. And this
certainly holds true, if varieties be looked at as incipient species;
for my tables clearly show as a general rule that, wherever many
species of a genus have been formed, the species of that genus
present a number of varieties, that is of incipient species, beyond
the average. It is not that all large genera are now varying much,
and are thus increasing in the number of their species, or that no
small genera are now varying and increasing; for if this had been
so, it would have been fatal to my theory; inasmuch as geology
plainly tells us that small genera have in the lapse of time often
increased greatly in size ; and that large genera have often come to
their maxima, declined and disappeared. All that we want to show
is, that, where many species of a genus have been formed, on an
average many are still forming; and this certainly holds good.

Many of the Species included ivitliin the Larger Genera resemble
Varieties in heing very closely, hut unequally, related to each
other, and in having restricted ranges.

There are other relations between the species of large genera
and their recorded varieties which deserve notice. We have seen
that there is no infallible criterion by which to distinguish species
and well-marked varieties; and when intermediate links have not
been found between doubtful forms, naturalists are compelled to
come to a determination by the amount of difference between them,
judging by analogy whether or not the amount suffices to raise one
or both to the rank of species. Hence the amount of difference is
one very important criterion in settling whether two forms should
be ranked as species or varieties. Now Fries has remarked in re-

46 ORIGIN OF SPECIES

gard to plants, and Westwood in regard to insects, that in large
genera the amount of difference between the species is often ex-
ceedingly small. I have endeavoured to test this numerically by
averages, and, as far as my imperfect results go, they confirm the
view. I have also consulted some sagacious and experienced ob-
servers, and, after deliberation, they concur in this view. In this
respect, therefore, the species of the larger genera resemble varieties,
more than do the species of the smaller genera. Or the case may
be put in another way, and it may be said, that in the larger
genera, in which a number of varieties or incipient species greater
than the average are now manufacturing, many of the species
already manufactured still to a certain extent resemble varieties,
for they differ from each other by less than the usual amount of
difference.

Moreover, the species of the larger genera are related to each
other, in the same manner as the varieties of any one species are re-
lated to each other. No naturalist pretends that all the species of a
genus are equally distinct from each other ; they may generally be di-
vided into sub-genera, or sections, or lesser groups. As Fries has well
remarked, little groups of species are generally clustered like sat-
ellites around other species. And what are varieties but groups
of forms, unequally related to each other, and clustered around
certain forms — that is, round their parent-species. Undoubtedly
there is one most important point of difference between varieties
and species; namely, that the amount of difference between varie-
ties, when compared with each other or with their parent-species,
is much less than that between the species of the same genus.
But when we come to discuss the principle, as I call it, of Diver-
gence of Character, we shall see how this may be explained, and
how the lesser differences between varieties tend to increase into
the greater differences between species.

There is one other point which is worth notice. Varieties gen-
erally have much restricted ranges : this statement is indeed
scarcely more than a truism, for, if a variety were found to have
a wider range than that of its supposed parent-species, their
denominations would be reversed. But there is reason to believe
that the species which are very closely allied to other species, and
in so far resemble varieties, often have much restricted ranges.
For instance, Mr. H. C. Watson has marked for me in the well-
sifted London Catalogue of plants (4th edition) 63 plants which
are +herein ranked as species, but which he considers as so closely
allied to other species as to be of doubtful value : these 63 reputed
species range on an average over 6.9 of the provinces into which
Mr. Watson has divided Great Britain. Now, in this same Cata-

»

VARIATION UNDER NATURE 47

logue, 53 acknowledged varieties are recorded, and these range
over 7.7 provinces; whereas, the species to which these varieties
belong range over 14.3 provinces. So that the acknowledged varie-
ties have nearly the same restricted average range, as have the
closely allied forms, marked for me by Mr. Watson as doubtful
species, but which are almost universally ranked by British bota-
nists as good and true species.

8ammary.

Finally, varieties cannot be distinguished from species, — except
first, by the discovery of intermediate linking forms ; and, secondly,
by a certain indefinite amount of difference between them; for
two forms, if differing very little, are generally ranked as varie-
ties, notwithstanding that they cannot be closely connected; but
the amount of difference considered necessary to give to any
two forms the rank of species cannot be defined. In genera having
more than the average number of species in any country, the
species of these genera have more than the average number of
varieties. In large genera the species are apt to be closely, but
unequally, allied together, forming little clusters round other
species. Species very closely allied to other species apparently
have restricted ranges. In all these respects the species of large
genera present a strong analogy with varieties. And we can
hardly understand these analogies, if species once existed as
varieties, and thus originated ; whereas, these analogies are utterly
inexplicable if species are independent creations.

We have, also, seen that it is the most flourishing or dominant
species of the larger genera within each class which on an average
yield the greatest number of varieties; and varieties, as we shall
hereafter see, tend to become converted into new and distinct
species. Thus the larger genera tend to become larger; and
throughout nature the forms of life which are now dominant tend
to become still more dominant by leaving many modified and domi-
nant descendants. But by steps hereafter to be explained, the
larger genera also tend to break up into smaller genera. And
thus, the forms of life throughout the universe become divided
into groups subordinate to groups.

48 ORIGIN OF SPECIES

CHAPTEK 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 — Competition uni-
versal — Effects of Climate — Protection from the number of indi-
viduals — 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.

BEFORE entering on the subject of this chapter, I must make
a few preliminary remarks, to show how the struggle for ex-
istence bears on Natural Selection. It has been seen in the
last chapter that amongst organic beings in a state of nature there
is some individual variability : indeed I am not aware that this has
ever been disputed. It is immaterial for us whether a multitude of
doubtful forms be called species or sub-species or varieties; what
rank, for instance, the two or three hundred doubtful forms of
British plants are entitled to hold, if the existence of any well-
marked varieties be admitted. But the mere existence of indi-
vidual variability and of some few well-marked varieties, though
necessary as the foundation for the work, helps us but little in un-
derstanding how species arise in nature. How have all those ex-
quisite adaptations of one part of the organisation to another part,
and to the conditions of life, and of one organic being to another
being, been perfected? We see these beautiful co-adaptations most
plainly in the woodpecker and the mistletoe ; and only a little less
plainly in the humblest parasite which clings to the hairs of a
quadruped or feathers of a bird; in the structure of the beetle
which dives through the water ; in the plumed seed which is wafted
by the gentlest breeze; in short, we see beautiful adaptations
everywhere and in every part of the organic world.

Again, it may be asked, how is it that varieties, which I have
called incipient species, become ultimately converted into good
and distinct species which in most cases obviously differ from
each other far more than do the varieties of the same species? How
do those groups of species which constitute what are called distinct

\.

STRUGGLE FOR EXISTENCE 49

genera, and which differ from each other more than do the species
of the same genus, arise? All these results, as we shall more fully
see in the next chapter, follow from the struggle for life. Owing
to this struggle, variations, however slight and from whatever
cause proceeding, if they be in any degree profitable to the in-
dividuals of a species, in their infinite-ly complex relations to
other organic beings and to their physical conditions of life,
will tend to the preservation of such individuals, and will gen-
erally be inherited by the offspring. The offspring, also, will
thus have a better chance of surviving, for, of the many indi-
viduals of any species which are periodically born, but a small
number can survive. I have called this principle, by which each
slight variation, if useful, is preserved, by the term Natural Se-
lection, in order to mark its relation to man's power of selec-
tion. But the expression often used by Mr. Herbert Spencer
of the Survival of the Fittest is more accurate, and is some-
times equally convenient. We have seen that man by selection
can certainly produce great results, and can adapt organic beings
to his own uses, through the accumulation of slight but useful
variations, given to him by the hand of Nature. But Natural
Selection, as we shall hereafter see, is a power incessantly ready
for action, and is as immeasurably superior to man's feeble efforts,
as the works of Nature are to those of Art.

We will now discuss in a little more detail the struggle for ex-
istence. In my future work this subject will be treated, as it well
deserves, at greater length. The elder De Candolle and Lyell
have largely and philosophically shown that all organic beings
are exposed to severe competition. In regard to plants, no one has
treated this subject with more spirit and ability than W. Herbert,
Dean of Manchester, evidently the result of his great horticultural
knowledge. Nothing is easier than to admit in words the truth
of the universal struggle for life, or more difficult — at least I
have found it so — than constantly to bear this conclusion in
mind. Yet unless it be thoroughly engrained in the mind, the
whole economy of nature, with every fact on distribution, rarity,
abundance, extinction, and variation, will be dimly seen or quite
misunderstood. We behold the face of nature bright with glad-
ness, we often see superabundance of food; we do not see or we
forget, that the birds which are idly singing round us mostly live
on insects or seeds, and are thus constantly destroying life; or we
forget how largely these songsters, or their eggs, or their nestlings,
are destroyed by birds and beasts of prey; we do not always bear
in mind, that, though food may be now superabundant, it is not
so at all seasons of each recurring year.

50 ORIGIN OP SPECIES

The Term, Struggle for Existence, used in a large sense.

I should premise that I use this term in a large and metaphori-
cal sense including dependence of one being on another, and in-
cluding (which is more important) not only the life of the individ-
ual, but success in leaving progeny. Two canine animals, in a
time of dearth, may be truly said to struggle with each other
which shall get food and live. But a plant on the edge of a
desert is said to struggle for life against the drought, though
more properly it should be said to be dependent on the moisture.
A plant which annually produces a thousand seeds, of which only
one of an average comes to maturity, may be more truly said to
struggle with the plants of the same and other kinds which already
clothe the ground. The mistletoe is dependent on the apple and a
few other trees, but can only in a far-fetched sense be said to
struggle with these trees, for, if too many of these parasites grow
on the same tree, it languishes and dies. But several seedling
mistletoes, growing close together on the same branch, may more
truly be said to struggle with each other. As the mistletoe is dis-
seminated by birds, its existence depends on them; and it may
metaphorically be said to struggle with other fruit-bearing plants,
in tempting the birds to devour and thus disseminate its seeds.
In these several senses, which pass into each other, I use for con-
venience' sake the general term of Struggle for Existence.

Geometrical Ratio of Increase.

A struggle for existence inevitably follows from the high rate
at which all organic beings tend to increase. Every being, which
during its natural lifetime produces several eggs or seeds, must
suffer destruction during some period of its life, and during some
season or occasional year, otherwise, on the principle of geometri-
cal increase, its numbers would quickly become so inordinately
great that no country could support the product. Hence, as
more individuals are produced than can possibly survive, there
must in every case be a struggle for existence, either one individual
with another of the same species, or with the individuals of dis-
tinct species, or with the physical conditions of life. It is the
doctrine of Malthus applied with manifold force to the whole ani-
mal and vegetable kingdoms ; for in this case there can be no arti-
ficial increase of food, and no prudential restraint from marriage.
Although some species may be now increasing, more or less rapid-
ly, in numbers, all cannot do so, for the world would not hold
them.

STRUGGLE FOR EXISTENCE 51

There is no exception to the rule that every organic being
naturally increases at so high a rate, that, if not destroyed, the
earth would soon be covered by the progeny of a single pair.
Even slow-breeding man has doubled in twenty-five years, and at
this rate, in less than a thousand years, there would literally not
be standing-room for his progeny. Linnaeus has calculated that if
an annual plant produced only two seeds — and there is no plant
so unproductive as this — and their seedlings next year produced
two, and so on, then in twenty years there should be a million
plants. The elephant is reckoned the slowest breeder of all known
animals, and I have taken some pains to estimate its probable
minimum rate of natural increase ; it will be safest to assume that
it begins breeding when thirty years old, and goes on breeding till
ninety years old, bringing forth six young in the interval, and sur-
viving till one hundred years old; if this be so, after a period of
from 740 to 750 years there would be nearly nineteen million
elephants alive, descended from the first pair.

But we have better evidence on this subject than mere theoretical
calculations, namely, the numerous recorded cases of the astonish-
ingly rapid increase of various animals in a state of nature, when
circumstances have been favourable to them during two or three
following seasons. Still more striking is the evidence from our
domestic animals of many kinds which have run wild in several
parts of the world; if the statements of the rate of increase of
slow-breeding cattle and horses in South America, and latterly in
Australia, had not been well authenticated, they would have been
incredible. So it is with plants; cases could be given of intro-
duced plants which have become common throughout whole islands
in a period of less than ten years. Several of the plants, such as
the cardoon and a tali thistle, which are now the commonest over
the whole plains of La Plata, clothing square leagues of surface
almost to the exclusion of every other plant, have been introduced
from Europe; and there are plants which now range in India, as
I hear from Dr. Falconer, from Cape Comorin to the Himalaya,
which have been imported from America since its discovery. In
such cases, and endless others could be given, no one supposes, that
the fertility of the animals or plants has been suddenly and tem-
porarily increased in any sensible degree. The obvious explana-
tion is that the conditions of life have been highly favourable, and
that there has consequently been less destruction of the old and
young, and that nearly all of the young have been enabled to
breed. Their geometrical ratio of increase, the result of which
never fails to be surprising, simply explains their extraordinarily
rapid increase and wide diffusion in their new homes.

52 ORIGIN OF SPECIES

In a state of nature almost every full-grown plant annually
produces seed, and amongst animals there are very few which do
not annually pair. Hence we may confidently assert, that all
plants and animals are tending to increase at a geometrical ratio,
— that all would rapidly stock every station in which they could
anyhow exist, — and that this geometrical tendency to increase
must be checked by destruction at some period of life. Our
familiarity with the larger domestic animals tends, I think, to
mislead us: we see no great destruction falling on them, but we
do not keep in mind that thousands are annually slaughtered for
food, and that in a state of nature an equal number would have
somehow to be disposed of.

The only difference between organisms which annually produce
eggs or seeds by the thousand, and those which produce extremely
few, is, that the slow-breeders would require a few more years to
people, under favourable conditions, a whole district, let it be ever
so large. The condor lays a couple of eggs and the ostrich a
score, and yet in the same country the condor may be the more
numerous of the two; the Fulmar petrel lays but one egg, yet it
is believed to be the most numerous bird in the world. One fly
deposits hundreds of eggs, and another, like the hippobosca, a
single one ; but this difference does not determine how many indi-
viduals of the two species can be supported in a district. A large
number of eggs is of some importance to those species which de-
pend on a fluctuating amount of food, for it allows them rapidly to
increase in number. But the real importance of a large number
of eggs or seeds is to make up for such destruction at some period
of life; and this period in the great majority of cases is an early
one. If an animal can in any way protect its own eggs or young,
a small number may be produced, and yet the average stock be
fully kept up ; but if many eggs or young are destroyed, many
must be produced, or the species will become extinct. It would
suffice to keep up the full number of a tree, which lived on an
average for a thousand years, if a single seed were produced once
in a thousand years, supposing that this seed were never destroyed,
and could be ensured to germinate in a fitting place. So that,
in all cases, the average number of any animal or plant depends
only directly on the number of its eggs or seeds.

In looking at Nature, it is most necessary to keep the foregoing
considerations always in mind — never to forget that every single
organic being may be said to be striving to the utmost to increase
in numbers; that each lives by a struggle at some period of its
life; that heavy destruction inevitably falls either on the young
or old, during each generation or at recurrent intervals. Lighten

STRUGGLE FOR EXISTENCE 53

any check, mitigate the destruction ever so little, and the number
of the species will almost instantaneously increase to any amount.

Nature of the Checks to Increase.

The causes which check the natural tendency of each species
to increase are most obscure. Look at the most vigorous species;
by as much as it swarms in numbers, by so much will it tend to
increase still further. We know not exactly what the checks are
even in a single instance. Nor will this surprise any one who re-
flects how ignorant we are on this head, even in regard to man-
kind, although so incomparably better known than any other
animal. This subject of the checks to increase has been ably
treated by several authors, and I hope in a future work to discuss
it at considerable length, more especially in regard to the feral
animals of South America. Here I will make only a few remarks,
just to recall to the reader's mind some of the chief points. Eggs
or very young animals seem generally to suffer most, but this is
not invariably the case. With plants there is a vast destruction
of seeds, but, from some observations which I have made it ap-
pears that the seedlings suffer most from germinating in ground
already thickly stocked with other plants. Seedlings, also, are
destroyed in vast numbers by various enemies ; for instance, on
a piece of ground three feet long and two wide, dug and cleared,
and where there could be no choking from other plants, I marked
all the seedlings of our native weeds as they came up, and out of
357 no less than 295 were destroyed, chiefly by slugs and insects.
If turf which has long been mown, and the case would be the same
with turf closely browsed by quadrupeds, be let to grow, the more
vigorous plants gradually kill the less vigorous, though fully
grown plants; thus out of twenty species growing on a little plot
of mown turf (three feet by four) nine species perished, from
the other species being allowed to grow up freely.

The amount of food for each species of course gives the extreme
limit to which each can increase ; but very frequently it is not the
obtaining food, but the serving as prey to other animals, which
determines the average numbers of a species. Thus, there seems
to be little doubt that the stock of partridges, grouse, and hares
on any large estate depends chiefly on the destruction of vermin.
If not one head of game were shot during the next twenty years
in England, and, at the same time, if no vermin were destroyed^
there would, in all probability, be less game than at present,
although hundreds of thousands of game animals are now annu-
ally shot. On the other hand, in some cases, as with the elephant,

54 ORIGIN OF SPECIES

none are destroyed by beasts of prey; for even the tiger in India
most rarely dares to attack a young elephant protected by its dam.

Climate plays an important part in determining the average
number of a species, and periodical seasons of extreme cold or
drought seem to be the most effective of all checks. I estimated
(chiefly from the greatly reduced numbers of nests in the spring)
that the winter of 1854-5 destroyed four-fifths of the birds in my
own grounds; and this is a tremendous destruction, when we
remember that ten per cent, is an extraordinarily severe mortality
from epidemics with man. The action of climate seems at first
sight to be quite independent of the struggle for existence; but
in so far as climate chiefly acts in reducing food, it brings on the
most severe struggle between the individuals, whether of the same
or of distinct species, which subsist on the same kind of food.
Even when climate, for instance, extreme cold, acts directly, it
will be the least vigorous individuals, or those which have got
least food through the advancing winter, which will suffer most.
When we travel from south to north, or from a damp region to a
dry, we invariably see some species gradually getting rarer and
rarer, and finally disappearing; and the change of climate being
conspicuous, we are tempted to attribute the whole effect to its
direct action. But this is a false view; we forget that each
species, even where it most abounds, is constantly suffering enor-
mous destruction at some period of its life, from enemies or from
competitors for the same place and food; and if these enemies or
competitors be in the least degree favoured by any slight change
of climate, they will increase in numbers; and as each area is
already fully stocked with inhabitants, the other species must de-
crease. When we travel southward and see a species decreasing
in numbers, we may feel sure that the cause lies quite as much in
other species being favoured, as in this one being hurt. So it is
when we travel northward, but in a somewhat lesser degree, for
the number of species of all kinds, and therefore of competitors,
decreases northwards; hence in going northwards, or in ascending
a mountain, we far oftener meet with stunted forms, due to the
directly injurious action of climate, than we do in proceeding
southwards or in descending a mountain. When we reach the
Arctic regions, or snow-capped summits, or absolute deserts, the
struggle for life is almost exclusively with the elements.

That climate acts in main part indirectly by favouring other
species, we clearly see in the prodigious number of plants which in
our gardens can perfectly well endure our climate, but which
never become naturalised, for they cannot compete with our native
plants nor resist destruction by our native animals.

STRUGGLE FOR EXISTENCE 53

When a species, owing to highly favourable circumstances, in-
creases inordinately in numbers in a small tract, epidemics — at
least, this seems generally to occur with our game animals — often
ensue; and here we have a limiting check independent of the
struggle for life. But even some of these so-called epidemics
appear to be due to parasitic worms, which have from some cause,
possibly in part through facility of diffusion amongst the crowded
animals, been disx:)roportionately favoured : and here comes in a
sort of struggle between the parasite and its prey.

On the other hand, in many cases, a large stock of individuals
of the same species, relatively to the numbers of its enemies, is
absolutely necessary for its preservation. Thus we can easily
raise plenty of corn and rape-seed, &c.. in our fields, because the
seeds are in great excess compared with the number of birds which
feed on them; nor can the birds, though having a superabundance
of food at this one season, increase in number proportionally to
the supply of seed, as their numbers are checked during the winter ;
but any one who has tried, knows how troublesome it is to get seed
from a few wheat or other such plants in a garden : I have in this
case lost every single seed. This view of the necessity of a large
stock of the same species for its preservation, explains, I believe,
some singular facts in nature such as that of very rare plants be-
ing sometimes extremely abundant, in the few spots where they do
exist; and that of some social jdants being social, that is abound-
ing in individuals, even on the extreme verge of their range.
For in such cases, we may believe, that a plant could exist only
where the conditions of its life were so favourable that many
could exist together, and thus save the species from utter destruc-
tion. I should add that the good effects of intercrossing, and the
ill effects of close interbreeding, no doubt come into play in many
of these cases; but I will not here enlarge on this subject.

Complex Relations of all Animals and Plants to each other in the

Struggle for Existence.

Many cases are on record showing how complex and unexpected
are the checks and relations between organic beings, which have
to struggle together in the same country. I will give only a sin-
gle instance, which, though a simple one, interested me. In Staf-
fordshire, on the estate of a relation, where I had ample means
of investigation, there was a large and extremely barren heath,
which had never been touched by the hand of man ; but several
hundred acres of exactly the same nature had been enclosed
twenty-five years previously and planted with Scotch fir. The

56 ORIGIN OF SPECIES

change in the native vegetation of the planted part of the heath
was most remarkable, more than is generally seen in passing from
one quite different soil to another : not only the proportional num-
bers of the heath-plants were wholly changed, but twelve species
of plants (not counting grasses and carices) flourished in the
plantations, which could not be found on the heath. The effect
on the insects must have been still greater, for six insectivorous
birds were very common in the plantations, which were not to be
seen on the heath; and the heath was frequented by two or three
distinct insectivorous birds. Here we see how potent has been the
effect of the introduction of a single tree, nothing whatever else
having been done, with the exception of the land having been en-
closed, so that cattle could not enter. But how important an ele-
ment enclosure is, I plainly saw near Farnham, in Surrey. Here
there are extensive heaths, with a few clumps of old Scotch firs on
the distant hill-tops: within the last ten years large spaces have
been enclosed, and self-sown firs are now springing up in multitudes,
so close together that all cannot live. When I ascertained that
these young trees had not been sown or planted, I was so much
surprised at their numbers that I went to several points of view,
whence I could examine hundreds of acres of the unenclosed heath,
and literally I could not see a single Scotch fir, except the old
planted clumps. But on looking closely between the stems of the
heath, I found a multitude of seedlings and little trees which had
been perpetually browsed down by the cattle. In one square yard,
at a point some hundred yards distant from one of the old clumps,
I counted thirty-two little trees ; and one of them, with twenty-six
rings of growth, had, during many years tried to raise its head
above the stems of the heath, and had failed. No wonder that,
as soon as the land was enclosed, it became thickly clothed with
vigorously growing young firs. Yet the heath was so extremely
barren and so extensive that no one would ever have imagined
that cattle would have so closely and effectually searched it for
food.

Here we see that cattle absolutely determine the existence of the
Scotch fir; but in several parts of the world insects determine
the existence of cattle. Perhaps Paraguay offers the most curious
instance of this; for here neither cattle nor horses nor dogs have
ever run wild, though they swarm southward and northward in a
feral state; and Azara and Rengger have shown that this is caused
by the greater number in Paraguay of a certain fly, which lays its
eggs in the navels of these animals when first born. The increase
of these flies, numerous as they are, must be habitually checked by
some means, probably by other parasitic insects. Hence, if cer-

STRUGGLE FOR EXISTENCE 57

tain insectivorous birds were to decrease in Paraguay, the parasitic
insects would probably increase; and this would lessen the num-
ber of the navel-frequenting flies — then cattle and horses would
become feral, and this would certainly greatly alter (as indeed I
have observed in parts of South America) the vegetation: this
again would largely affect the insects; and this, as we have just
seen in Staffordshire, the insectivorous birds, and so onwards in
ever-increasing circles of comj^lexity. Not that under nature the
relations will ever be as simple as this. Battle within battle must
be continually recurring with varying success ; and yet in the long-
run the forces are so nicely balanced, that the face of nature re-
mains for long periods of time uniform, though assuredly the
merest trifle would give the victory to one organic being over
another. Nevertheless, so profound is our ignorance, and so high
our presumption, that we marvel when we hear of the extinction of
an organic being; and as we do not see the cause, we invoke cata-
clysms to desolate the world, or invent laws on the duration of the
forms of life!

I am tempted to give one more instance showing how plants
and animals remote in the scale of nature, arc bound together
by a web of complex relations. I shall hereafter have occasion
to show that the exotic Lobelia fulgens is never visited in my
garden by insects, and consequently, from its peculiar structure,
never sets a seed. Nearly all our orchidaceous plants absolutely
require the visits of insects to remove their pollen-masses and thus
to fertilise them. I find from experiments that humble-bees are
almost indispensable to the fertilisation of the heartsease (Violo
tricolor), for other bees do not visit this flower. I have also found
that the visits of bees are necessary for the fertilisation of some
kinds of clover; for instance, 20 beads of Dutch clover (Trifolium
repens) yielded 2,290 seeds, but 20 other heads protected from bees
produced not one. Again, 100 heads of red clover (T. pratense)
produced 2,700 seeds, but the same number of protected heads pro-
duced not a single seed. Humble-bees alone visit red clover, as
other bees cannot reach the nectar. It has been suggested that
moths may fertilise the clovers; but I doubt whether they could
do so in the case of the red clover, from their weight not being
sufficient to depress the wing petals. Hence we may infer as
highly probable that, if the whole genus of humble-bees became
extinct or very rare in England, the heartsease and red clover
would become very rare, or wholly disappear. The number of
humble-bees in any district depends in a great measure upon the
number of field-mice, which destroy their combs and nests; and
Col. Newman, who has long attended to the habits of humble-

58 ORIGIN OF SPECIES

bees, believes that " more than two-thirds of them are thus de-
stroyed all over England." Now the number of mice is largely
dependent, as every one knows, on the number of cats; and Col.
Newman says, " Near villages and small towns I have found the
nests of humble-bees more numerous than elsewhere, which I at-
tribute to the number of cats that destroy the mice." Hence it
is quite credible that the presence of a feline animal in large num-
bers in a district might determine, through the intervention first
of mice and then of bees, the frequency of certain flowers in that
district !

In the case of every species, many different checks, acting at
different periods of life, and during different seasons of years, prob-
ably come into play; some one check or some few being generally
the most potent; but all will concur in determining the average
number or even the existence of the species. In some cases it
can be shown that widely-different checks act on the same species
in different districts. When we look at the plants and bushes
clothing an entangled bank, we are tempted to attribute their pro-
portional numbers and kinds to what we call chance. But how
false a view is this ! Every one has heard that when an American
forest is cut down a very different vegetation springs up; but it
has been observed that ancient Indian ruins in the Southern
United States, which must formerly have been cleared of trees,
now display the same beautiful diversity and proportion of kinds
as in the surrounding virgin forest. What a struggle must have
gone on during long centuries between the several kinds of trees
each annually scattering its seeds by the thousand; what war
between insect and insect — between insects, snails, and other
animals with birds and beasts of prey — all striving to increase,
all feeding on each other, or on the trees, their seeds and seedlings,
or on the other plants which first clothed the ground and thus
checked the growth of the trees ! Throw up a handful of feathers,
and all fall to the ground according to definite laws; but how sim-
ple is the problem where each shall fall compared to that of the
action and reaction of the innumerable plants and animals which
have determined, in the course of centuries, the proportional num-
bers and kinds of trees now growing on the old Indian ruins!

The dependency of one organic being on another, as of a para-
site on its prey, lies generally between beings remote in the scale of
nature. This is likewise sometimes the case with those which
may be strictly said to struggle with each other for existence, as
in the case of locusts and grass-feeding quadrupeds. But the
struggle will almost invariably be most severe between the individ-
uals of the same species, for they frequent the same districts, re-

STRUGGLE FOR EXISTENCE 5!)

quire the same food, and are exposed to the i^ame dangers. In the
case of varieties of the same species, the struggle will generally be
almost equally severe, and we sometimes see the contest soon de-
cided : for instance, if several varieties of wheat be sown together,
and the mixed seed be resown, some of the varieties which best
suit the soil or climate, or are naturally the most fertile, will beat
the others and so yield more seed, and will consequently in a few
years supplant the other varieties. To keep up a mixed stock of
even such extremely close varieties as the variously-coloured sweet
peas, they must be each year harvested separately, and the seed
then mixed in due proportion, otherwise the weaker kinds will
steadily decrease in number and disappear. So again with the
varieties of sheep; it has been asserted that certain mountain
varieties will starve out other mountain-varieties, so that they
cannot be kept together. The same result has followed from keep-
ing together different varieties of the medicinal leech. It may
even be doubted whether the varieties of any of our domestic
plants or animals have so exactly the same strength, habits, and
constitution, that the original proportions of a mixed stock (cross-
ing being prevented) could be kept up for half a dozen genera-
tions, if they were allowed to struggle together, in the same man-
ner as beings in a state of nature, and if the seed or young were
not annually preserved in due proportion.

Struggle for Life most severe hetween Individuals and Varie-
ties of the same Species.

As the species of the same genus usually have, though by no
means invariably, much similarity in habits and constitution, and
always in structure, the struggle will generally be more severe be-
tween them, if they come into competition with each other, than
between the species of distinct genera. We see this in the recent
extension over parts of the United States of one species of swal-
low having caused the decrease of another species. The recent
increase of the missel-thrush in parts of Scotland has caused
the decrease of the song-thrush. How frequently we hear of one
species of rat taking the place of another species under the most
different climates! In Russia the small Asiatic cock-roach has
everywhere driven before it its great congener. In Australia the
imported hive-bee is rapidly exterminating the small, stingless
native bee. One species of charlock has been known to supplant
another species; and so in other cases. We can dimly see why
the competition should be most severe between allied forms, which
fill nearly the same place in the economy of nature; but probably

60 ORIGIN OF SPECIES

in no one case could we precisely say why one species lias been
victorious over another in the great battle of life.

A corollary of the highest importance may be deduced from
the foregoing remarks, namely, that the structure of every organic
being is related, in the most essential yet often hidden manner,
to that of all the other organic beings, with which it comes into
competition for food or residence, or from which it has to escape,
or on which it preys. This is obvious in the structure of the teeth
and talons of the tiger; and in that of the legs and claws of the
parasite which clings to the hair on the tiger's body. But in the
beautifully plumed seed of the dandelion, and in the flattened
and fringed legs of the water-beetle, the relation seems at first
confined to the elements of air and water. Yet the advantage of
plumed seeds no doubt stands in the closest relation to the land
being already thickly clothed with other plants; so that the seeds
may be widely distributed and fall on unoccupied ground. In the
water-beetle, the structure of its legs, so well adapted for diving,
allows it to compete with other aquatic insects, to hunt for its
own prey, and to escape serving as prey to other animals.

The store of nutriment laid up within the seeds of many plants
seems at first sight to have no sort of relation to other plants. But
from the strong growth of young plants produced from such seeds,
as peas and beans, when sown in the midst of long grass, it may be
suspected that the chief use of the nutriment in the seeds is to
favour the growth of the seedlings, whilst struggling with other
plants growing vigorously all around.

Look at a plant in the midst of its range, why does it not double
or quadruple its numbers? We know that it can perfectly well
withstand a little more heat or cold, dampness or dryness, for
elsewhere it ranges into slightly hotter or colder, damper or drier
districts. In this case we can clearly see that if we wish in imagi-
nation to give the plant the power of increasing in number, we
should have to give it some advantage over its competitors, or over
the animals which prey on it. On the confines of its geographical
range, a change of constitution with respect to climate would
clearly be an advantage to our plant; but we have reason to be-
lieve that only a few plants or animals range so far, that they
are destroyed exclusively by the rigour of the climate. Not until
we reach the extreme confines of life, in the Arctic regions or on
the borders of an utter desert, will competition cease. The land
may be extremely cold or dry, yet there will be competition be-
tween some few species, or between the individuals of the same
species, for the warmest or dampest spots.

Hence we can see that when a plant or animal is placed in a

STRUGGLE FOR EXISTENCE 61

new country amongst new competitors, the conditions of its life
will generally be changed in an essential manner, although the cli-
mate may be exactly the same as in its former home. If its average
numbers are to increase in its new home, we should have to modify
it in a diiferent way to what we should have had to do in its na-
tive country; for we should have to give it some advantage over
a different set of competitors or enemies.

It is good thus to try in imagination to give to any one species
an advantage over another. Probably in no single instance should
we know what to do. This ought to convince us of our ignorance
on the mutual relations of all organic beings; a conviction as ne-
cessary, as it is difficult to acquire. All that we can do, is to keep
steadily in mind that each organic being is striving to increase
in a geometrical ratio; that each at some period of its life, during
some season of the year, during each generation or at intervals,
has to struggle for life and to suffer great destruction. When we
reflect on this struggle, we may console ourselves with the full
belief, that the war of nature is not incessant, that no fear is felt,
that death is generally prompt, and that the vigorous, the healthy,
and the happy survive and multiply.

6is UUIGIN OF SPECIES

CHAPTER IV

NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST.

Natural Selection — its power compared with man's selection — its
power on characters of trifling importance — its power at all ages and
on both sexes — Sexual Selection — On the generality of intercrosses
between individuals of the same species — Circumstances favourable
and unfavourable to the results of Natural Selection, namely, inter-
crossing, 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
Extinction, on the descendants from a common parent — Explains
the grouping of all organic beings — Advance in organisation — Low
forms preserved • — Convergence of Character — Indefinite multiplica-
tion of species — Summary.

HOW will the struggle for existence, briefly discussed in the
last chapter, act in regard to variation? Can the prin-
ciple of selection, which we have seen is so potent in
the hands of man, apply under nature? I think we shall see
that it can act most efficiently. Let the endless number of
slight variations and individual differences occurring in our
domestic productions, and, in a lesser degree, in those under
nature, be borne in mind; as well as the strength of the hereditary
tendency. Under domestication, it may be truly said that the
whole organisation becomes in some degree plastic. But the
variability, which we almost universally meet with in our do-
mestic productions, is not directly produced, as Hooker and
Asa Gray have well remarked, by man; he can neither originate
varieties, nor prevent their occurrence; he can preserve and ac-
cumulate such as do occur. Unintentionally he exposes organic
beings to new and changing conditions of life, and variability
ensues; but similar changes of conditions might and do occur
under nature. Let it also be borne in mind how infinitely complex
and close-fitting are the mutual relations of all organic beings to
each other and to their physical conditions of life; and conse-
quently what infinitely varied diversities of structure might be of
use to each being under changing conditions of life. Can it, then,
be thought improbable, seeing that variations, \jseful to niari have

Natural selection, etc. 63

undoubtedly occurred, that other variations useful in some way to
each being in the great and complex battle of life, should occur
in the course of many successive generations? If such do occur,
can we doubt (remembering that many more individuals are born
than can possibly survive) that individuals having any advantage,
however slight, over others, would have the best chance of surviv-
ing and of procreating their kind ? On the other hand, we may feel
sure that any variation in the least degree injurious would be
rigidly destroyed. This preservation of favourable individual dif-
ferences and variations, and the destruction of those which are
injurious, I have called Natural Selection, or the Survival of the
Fittest. Variations neither useful nor injurious would not be
affected by natural selection, and would be left either a fluctuating
element, as perhaps we see in certain polymorphic species, or would
ultimately become fixed, owing to the nature of the organism
and the nature of the conditions.

Several writers have misapprehended or objected to the term
Natural Selection. Some have even imagined that natural se-
lection induces variability, whereas it implies only the preserva-
tion of such variations as arise and are beneficial to the being
under its conditions of life. No one objects to agriculturists
speaking of the potent effects of man's selection ; and in this case
the individual differences given by nature, which man for some
object selects, must of necessity first occur. Others have objected
that the term selection implies conscious choice in the animals
which become modified ; and it has even been urged that, as plants
have no volition, natural selection is not applicable to them! In
the literal sense of the word, no doubt, natural selection is a false
term; but who ever objected to chemists speaking of the elective
affinities of the various elements ? — and yet an acid cannot
strictly be said to elect the base with which it in preference com-
bines. It has been said that I speak of natural selection as an
active power or Deity; but who objects to an author speaking of
the attraction of gravity as ruling the movements of the planets?
Every one knows what is meant and is implied by such metaphor-
ical expressions; and they are almost necessary for brevity. So
again it is difficult to avoid personifying the word Nature; but
I mean by Nature, only the aggregate action and product of many
natural laws, and by laws the sequence of events as ascertained by
us. With a little familiarity such superficial objections will be
forgotten.

We shall best understand the probable course of natural selec-
tion by taking the case of a country undergoing some slight physi-
cal change, for instance, of climate. The proportional numbers

G4 ORIGIN OF SPECIES

of its inhabitants will almost immediately undergo a change, and
some species will probably become extinct. We may conclude,
from what we have seen of the intimate and complex manner in
which the inhabitants of each country are bound together, that
any change in the numerical proportions of the inhabitants, in-
dependently of the change of climate itself, would seriously affect
the others. If the country were open on its borders, new forms
would certainly immigrate, and this would likewise seriouslj'' dis-
turb the relations of some of the former inhabitants. Let it be
remembered how powerful the influence of a single introduced
tree or mammal has been shown to be. But in the case of an
island, or of a country partly surrounded by barriers, into which
new and better adapted forms could not freely enter, we should
then have places in the economy of nature which would assuredly
be better filled up, if some of the original inhabitants were in some
manner modified; for, had the area been open to immigration,
these same places would have been seized on by intruders. In such
cases, slight modifications, which in any way favoured the indi-
viduals of any species, by better adapting them to their altered
conditions, would tend to be preserved; and natural selection would
have free scope for the work of improvement.

We have good reason to believe, as shown in the first chapter,
that changes in the conditions of life give a tendency to increased
variability ; and in the foregoing cases the conditions have changed,
and this would manifestly be favourable to natural selection, by
affording a better chance of the occurrence of profitable variations.
Unless such occur, natural selection can do nothing. Under the
term of " variations," it must never be forgotten that mere indi-
vidual differences are included. As man can produce a great re-
sult with his domestic animals and plants by adding up in any
given direction, individual differences, so could natural selection,
but far more easily from having incomparably longer time for
action. Nor do I believe that any great physical change, as of
climate, or any unusual degree of isolation to check immigration,
is necessary in order that new and unoccupied places should be
left, for natural selection to fill up by improving some of the vary-
ing inhabitants. For as all the inhabitants of each country are
struggling together with nicely balanced forces, extremely slight
modifications in the structure or habits of one species would often
give it an advantage over others; and still further modifications
of the same kind would often still further increase the advantage,
as long as the species continued under the same conditions of life
and profited by similar means of subsistence and defence. No
country can be named in which all the native inhabitants are now

NATURAL SELECTION, ETC. 65

so perfectly adapted to each other and to the physical conditions
under which they live, that none of them could bo still better
adapted or improved; for in all countries, the natives have been
so far conquered by naturalised productions, that they have al-
lowed some foreigners to take firm possession of the land. And as
foreigners have thus in every country beaten some of the natives,
we may safely conclude that the natives might have been modified
with advantage, so as to have better resisted the intruders.

As man can produce, and certainly has produced, a great re-
sult by his methodical and unconscious means of selection, what
may not natural selection effect? Man can act only on external
and visible characters: Nature, if I may be allowed to personify
the natural preservation or survival of the fittest, cares nothing
for appearances, except in so far as they are useful to any being.
She can act on every internal organ, on every shade of constitu-
tional difference, on the whole machinery of life. Man selects only
for his own good: Nature only for that of the being which she
tends. Every selected character is fully exercised by her, as is im-
plied by the fact of their selection. Man keeps the natives of
many climates in the same country; he seldom exercises each se-
lected character in some peculiar and fitting manner; he feeds a
long and a short beaked pigeon on the same food ; he does not exer-
cise a long-backed or long-legged quadruped in any peculiar man-
ner; he exposes sheep with long and short wool to the same cli-
mate. He does not allow the most vigorous males to struggle for
the females. He does not rigidly destroy all inferior animals, but
protects during each varying season, as far as lies in his power,
all his productions. He often begins his selection by some half-
monstrous form; or at' least by some modification prominent enough
to catch the eye or to be plainly useful to him. Under nature,
the slightest differences of structure or constitution may well turn
the nicely-balanced scale in the struggle for life, and so be pre-
served. How fleeting are the wishes and efforts of man! how
short his time ! and consequently how poor will be his results, com-
pared with those accumulated by Nature during whole geological
periods! Can we wonder, then, that Nature's productions should
be far "truer'' in character than man's productions; that they
should be infinitely better adapted to the most complex conditions
of life, and should plainly bear the stamp of far higher workman-
sliip ?

It may metaphorically be said that natural selection is daily
cud hourly scrutinising, throughout the world, the slightest varia-
tions; rejecting those that are bad, preserving and adding np all
tliat are good; silently and insensibly working, ivhenever and wher-

G6 ORIGIN OF SrECIES

ever opportunity offers, at the improvement of each organic being
in relation to its organic and inorganic conditions of life. We see
nothing of these slow changes in progress, until the hand of time
has marked the lapse of ages, and then so imperfect is our view
into long-past geological ages, that we see only that the forms of
life are now different from what they formerly were.

In order that any great amount of modification should be ef-
fected in a species, a variety when once formed must again,
perhaps after a long interval of time, vary or present individual
differences of the same favourable nature as before; and these
must be again preserved, and so onwards step by step. Seeing that
individual differences of the same kind perpetually recur, this can
hardly be considered as an unwarrantable assumption. But
whether it is true, we can judge only by seeing how far the hy-
pothesis accords with and explains the general phenomena of na-
ture. On the other hand, the ordinary belief that the amount of
possible variation is a strictly limited quantity is likewise a sim-
ple assumption.

Although natural selection can act only through and for the
good of each being, yet characters and structures, which we are
apt to consider as of very trifling importance, may thus be acted
on. When we see leaf -eating insects green, and bark-feeders mot-
tled-grey; the alpine ptarmigan white in winter, the red-grouse the
colour of heather, we must believe that these tints are of service
to these birds and insects in preserving them from danger. Grouse,
if not destroyed at some period of their lives, would increase in
countless numbers; they are known to suffer largely from birds
of prey ; and hawks are guided by eyesight to their prey — so much
so, that on parts of the Continent persons are warned not to keep
white pigeons, as being the most liable to destruction. Hence
natural selection might be effective in giving the proper colour to
each kind of grouse, and in keeping that colour, when once ac-
quired, true and constant. Nor ought we to think that the occa-
sional destruction of an animal of any particular colour would
produce little effect : we should remember how essential it is in a
flock of white sheep to destroy a lamb with the faintest trace of
black. We have seen how the colour of the hogs, which feed on
the " paint-root " in Virginia, determines whether they shall live
or die. In plants, the down on the fruit and the colour of the
flesh are considered by botanists as characters of the most trifling
importance : yet we hear from an excellent horticulturist, Downing,
that in the United States, smooth-skinned fruits suffer far more
from a beetle, a Curculio, than those with down; that purple plums
suffer far more from a certain disease than yellow plums; whereas

I

NATURAL SELECTION, ETC. 67

another disease attacks yellow-fleshed peaches far more than those
with other coloured flesh. If, with all the aids of art, these slight
differences make a great difference in cultivating the several varie-
ties, assuredly, in a state of nature, where the trees would have to
struggle with other trees, and with a host of enemies, such dif-
ferences would effectually settle which variety, whether a smooth
or downy, a yellow or purple fleshed fruit, should succeed.

In looking at many small points of difference between species,
which, as far as our ignorance permits us to judge, seem quite
unimportant, we must not forget that climate, food, &c., have no
doubt produced some direct effect. It is also necessary to bear
in mind that, owing to the law of correlation, when one part varies,
and the variations are accumulated through natural selection, other
modifications, often of the most unexpected nature, will ensue.

As we see that those variations which, under domestication, ap*
pear at any particular period of life, tend to reappear in the
offspring at the same period ; — for instance, in the shape, size,
and flavour of the seeds of the many varieties of our culinary and
agricultural plants; in the caterpillar and cocoon stages of the
varieties of the silk-worm ; in the eggs of poultry, and in the colour
of the down of their chickens; in the horns of our sheep and cat-
tle when nearly adult ; — so in a state of nature natural selection
will be enabled to act on and modify organic beings at any age,
by the accumulation of variations profltable at that age, and by
their inheritance at a corresponding age. If it profit a plant to
have its seeds more and more widely disseminated by the wind, I
can see no greater difficulty in this being effected through natural
selection, than in the cotton-planter increasing and improving by
selection the down in the pods on his cotton-trees. Natural se-
lection may modify and adapt the larva of an insect to a score of
contingencies, wholly different from those which concern the
mature insect ; and these modifications may affect, through cor-
relation, the structure of the adult. So, conversely, modifications
in the adult may affect the structure of the larva ; but in all cases
natural selection will ensure that they shall not be injurious: for
if they were so, the species would become extinct.

Natural selection will modify the structure of the young in re-
lation to the parent, and of the parent in relation to the young.
In social animals it will adapt the structure of each individual for
the benefit of the whole community; if the community profits by
the selected change. What natural selection cannot do, is to mod-
ify the structure of one species, without giving it any advantage,
for the good of another species; and though statements to this
effect may be found in works of natural history, I cannot find

68 ORIGIN OF SPECIES

one case which will bear investigation. A structure used only
once in an animal's life, if of high importance to it, might be modi-
fied to any extent by natural selection; for instance, the great
jaws possessed by certain insects, used exclusively for opening the
cocoon — or the hard tip to the beak of unhatched birds, used for
breaking the egg. It has been asserted, that of the best short-
beaked tumbler-pigeons a greater number perish in the egg than
are able to get out of it ; so that fanciers assist in the act of hatch-
ing. Now if nature had to make the beak of a full-grown pigeon
very short for the bird's own advantage, the process of modifica-
tion would be very slow, and there would be simultaneously the
most rigorous selection of all the young birds within the egg, which
had the most powerful and hardest beaks, for all with weak beaks
would inevitably perish; or, more delicate and more easily broken
shells might be selected, the thickness of the shell being known to
vary like every other structure.

It may be well here to remark that with all beings there must
be much fortuitous destruction, which can have little or no in-
fluence on the course of natural selection. For instance a vast
number of eggs or seeds are annually devoured, and these could
be modified through natural selection only if they varied in some
manner which protected them from their enemies. Yet many of
these eggs or seeds would perhaps, if not destroyed, have yielded
individuals better adapted to their conditions of life than any
of those which happened to survive. So again a vast number of
mature animals and plants, whether or not they be the best
adapted to their conditions, must be annually destroyed by acci-
dental causes, which would not be in the least degree mitigated
by certain changes of structure or constitution which would in
other ways be beneficial to the species. But let the destruction
of the adults be ever so heavy, if the number which can exist in any
district be not wholly kept down by such causes, — or again let the
destruction of eggs or seeds be so great that only a hundredth or
thousandth part are developed, — yet of those which do survive, the
best adapted individuals, supposing that there is any variability
in a favourable direction, will tend to propagate their kind in
larger numbers than the less well adapted. If the numbers be
wholly kept down by the causes just indicated, as will often have
been the case, natural selection will be powerless in certain bene-
ficial directions; but this is no valid objection to its efficiency at
other times and in other ways; for we are far from having any
reason to suppose that many species ever undergo modification
and improvement at the same time in the same area.

NATURAL SELECTION, ETC. G9

Sexual Selection,

Inasmuch as peculiarities often appear under domestication in
one sex and become hereditarily attached to that sex, so no doubt
it will be under nature. Thus it is rendered possible for the two
sexes to be modified through natural selection in relation to dif-
ferent habits of life, as is sometimes the case; or for one sex to
be modified in relation to the other sex, as commonly occurs.
This leads me to say a few words on what I have called Sexual
Selection. This form of selection depends, not on a struggle for
existence in relation to other organic beings or to external con-
ditions, but on a struggle between the individuals of one sex,
generally the males, for the possession of the other sex. The result
is not death to the unsuccessful competitor, but few or no off-
spring. Sexual selection is, therefore, less rigorous than natural
selection. Generally, the most vigorous males, those which are
best fitted for their places in nature, will leave most progeny. But
in many cases, victory depends not so much on general vigor,
as on having special weapons, confined to the male sex. A hornless
stag or spurless cock would have a poor chance of leaving numerous
offspring. Sexual selection, by always allowing the victor to
breed, might surely give indomitable courage, length to the spur,
and strength to the wing to strike in the spurred leg, in nearly
the same manner as does the brutal cockfighter by the careful
selection of his best cocks. How low in the scale of nature the
law of battle descends, I know not; male alligators have been de-
scribed as fighting, bellowing, and whirling round, like Indians in
a war-dance, for the possession of the females; male salmons have
been observed fighting all day long; male stag-beetles sometimes
bear wounds from the huge mandibles of other males; the males
of certain hymenopterous insects have been frequently seen by
that inimitable observer, M. Fabre, fighting for a particular fe-
male who sits by, an apparently unconcerned beholder of the
struggle, and then retires with the conqueror. The war is, per-
haps, severest between the males of polygamous animals, and these
seem oftenest provided with special weapons. The males of carniv-
orous animals are already well armed ; though .to them and to
others, special means of defence may be given through means of
sexual selection, as the mane of the lion, and the hooked jaw to
the male salmon; for the shield may be as important for victory,
as the sword or spear.

Amongst birds, the contest is often of a more peaceful charac-
ter. All those who have attended to the subject, believe that
there is the severest rivalry between the males of many species

70 ORIGIN OF SPECIES

to attract, by singing-, the females. The rock-thrush of Guiana,
birds of paradise, and some others, congregate; and successive
males display with the most elaborate care, and show off in the
best manner, their gorgeous plumage; they likewise perform
strange antics before the females, which, standing by as spectators,
at last choose the most attractive partner. Those who have closely
attended to birds in confinement well know that they often take
individual preferences and dislikes: thus Sir R. Heron has de-
scribed how a pied peacock was eminently attractive to all his
hen birds. I cannot here enter on the necessary details; but if
man can in a short time give beauty and an elegant carriage to
his bantams, according to his standard of beauty, I can see no
good reason to doubt that female birds, by selecting, during thou-
sands of generations, the most melodious or beautiful males, ac-
cording to their standard of beauty, might produce a marked
effect. Some well-known laws, with respect to the plumage of male
and female birds, in comparison with the plumage of the young,
can partly be explained through the action of sexual selection on
variations occurring at different ages, and transmitted to the males
alone or to both sexes at corresponding ages ; but I have not space
here to enter on this subject.

Thus it is, as I believe, that when the males and females of
any animal have the same general habits of life, but differ in
structure, colour, or ornament, such differences have been mainly
caused by sexual selection : that is, by individual males having
had, in successive generations, some slight advantage over other
males, in their weapons, means of defence, or charms, which they
have transmitted to their male offspring alone. Yet, I would not
wish to attribute all sexual differences to this agency: for we
see in our domestic animals peculiarities arising and becoming
attached to the male sex, which apparently have not been aug-
mented through selection by man. The tuft of hair on the breast
of the wild turkey-cock cannot be of any use, and it is doubtful
whether it can be ornamental in the eyes of the female bird; —
indeed, had the tuft appeared under domestication, it would have
been called a monstrosity.

Illustrations of the Action of Natural Selection, or the
Survival of the Fittest.

In order to make it clear how, as I believe, natural selection
acts, I must beg permission to give one or two imaginary illustra-
tions. Let us take the case of a wolf, which preys on various ani-
mals, securing some by craft, some by strength, and some by

NATURAL SELECTION, ETC. 71

fleetness; and let us suppose that the fleetest prey, a deer for
instance, had from any change in the country increased in num-
bers, or that other prey had decreased in numbers, during that
season of the year when the wolf was hardest pressed for food.
Under such circumstances the swiftest and slimmest wolves would
have the best chance of surviving and so be preserved or selected,
— provided always that they retained strength to master their
prey at this or some other period of the year, when they were com-
pelled to prey on other animals. I can see no more reason to
doubt that this would be the result, than that man should be able
to improve the fleetness of his greyhounds by careful and method-
ical selection, or by that kind of unconscious selection which fol-
lows from each man trying to keep the best dogs without any
thought of modifying the breed. I may add, that according to
Mr. Pierce, there are two varieties of the wolf inhabiting the
Catskill Mountains, in the United States, one with a light grey-
hound-like form, which pursues deer, and the other more bulky,
wdth shorter legs, which more frequently attacks the shepherd's
flocks.

It should be observed that, in the above illustration, I speak of
the slimmest individual wolves, and not of any single strongly-
marked variation having been preserved. In former editions of
this work I sometimes spoke as if this latter alternative had fre-
quently occurred. I saw the great importance of individual
differences, and this led me fully to discuss the results of uncon-
scious selection by man, which depends on the preservation of
all the more or less valuable individuals, and on the destruction
of the worst. I saw, also, that the preservation in a state of
nature of any occasional deviation of structure, such as a monstros-
ity, would be a rare event ; and that, if at first preserved, it would
generally be lost by subsequent intercrossing with ordinary indi-
viduals. Nevertheless, until reading an able and valuable article
in the ^ ISTorth British Keview ' (1867), I did not appreciate how
rarely single variations, whether slight or strongly-marked, could
be perpetuated. The author takes the case of a pair of animals,
producing during their lifetime two hundred offspring, of which,
from various causes of destruction, only two on an average sur~
vive to pro-create their kind. This is rather an extreme estimate
for most of the higher animals, but by no means so for many of
the lower organisms. He then shows that if a single individual
"were born, which varied in some manner, giving it twice as good
a chance of life as that of the other individuals, yet the chances
would be strongly against its survival. Supposing it to survive
and to breed, and that half its young inherited the favourable

72 ORIGIN OF SPECIES

variation; still, as the Keviewer goes on to show, the young would
have only a slightly better chance of surviving and breeding; and
this chance would go on decreasing in the succeeding genera-
tions. The justice of these remarks cannot, I think, be disputed.
If, for instance, a bird of some kind could procure its food more
easily by having its beak curved, and if one were born with its
beak strongly curved, and which consequently flourished, never-
theless there would be a very poor chance of this one individual
perpetuating its kind to the exclusion of the common form; but
there can hardly be a doubt, judging by what we see taking place
under domestication, that this result would follow from the preser-
vation during many generations of a large number of individuals
with more or less strongly curved beaks, and from the destruction
of a still larger number with the straightest beaks.

It should not, however, be overlooked that certain rather strong-
ly marked variations^ which no one would rank as mere indi-
vidual differences, frequently recur owing to a similar organisation
being similarly acted on — of which fact numerous instances could
be given with our domestic productions. In such cases, if the
varying individual did not actually transmit to its offspring its
newly-acquired character, it would undoubtedly transmit to them,
as long as the existing conditions remained the same, a still
stronger tendency to vary in the same manner. There can also be
little doubt that the tendency to vary in the same manner has
often been so strong that all the individuals of the same species
have been similarly modified without the aid of any form of se-
lection. Or only a third, fifth, or tenth part of the individuals
may have been thus affected, of which fact several instances could
be given. Thus Graba estimates that about one-fifth of the guille-
mots in the Faroe Islands consist of a variety so well marked, that
it was formerly ranked as a distinct species under the name of
Uria lacrymans. In cases of this kind, if the variation were of a
beneficial nature, the original form would soon be supplanted by
the modified form, through the survival of the fittest.

To the effects of intercrossing in eliminating variations of all
kinds, I shall have to recur ; but it may be here remarked that most
animals and plants keep to their proper homes, and do not need-
lessly wander about ; we see this even with migratory birds, which
almost always return to the same spot. Consequently each newly-
formed variety would generally be at first local, as seems to be the
common rule with varieties in a state of nature; so that similarly
modified individuals would soon exist in a small body together,
and would often breed together. If the new variety were success-
ful in its battle for life, it would slowly spread from a centra'

NATUKAL SELECTION, ETC. 73

district, competing with and conquering the unchanged individuals
on the margins of an ever-increasing circle.

It may be worth while to give another and more complex illus-
tration of the action of natural selection. Certain plants excrete
sweet juice, apparently for the sake of eliminating something in-
jurious from the sap : this is effected, for instance, by glands at
the base of the stipules in some Leguminosse, and at the backs
of the leaves of the common laurel. This juice, though small
in quantity, is greedily sought by insects ; but their visits do not in
any way benefit the plant. Now, let us suppose that the juice or
nectar was excreted from the inside of the flowers of a certain
number of plants of any species. Insects in seeking the nectar
would get dusted with pollen, and would often transport it from
one flower to another. The flowers of two distinct individuals of
the same species would thus get crossed; and the act of crossing,
as can be fully proved, gives rise to vigorous seedlings which con-
sequently would have the best chance of flourishing and surviving.
The plants which produced flowers with the largest glands or nec-
taries, excreting most nectar, would oftenest be visited by insects,
and would oftenest be crossed ; and so in the long-run would gain
the upper hand and form a local variety. The flowers, also, which
had their stamens and pistils placed, in relation to the size and
habits of the particular insects which visited them, so as to favour
in any degree the transportal of the pollen, would likewise be
favoured. We might have taken the case of insects visiting flowers
for the sake of collecting pollen instead of nectar; and as pollen
is formed for the sole purpose of fertilisation, its destruction ap-
pears to be a simple loss to the plant; yet if a little pollen were
carried, at first occasionally and then habitually, by the pollen-
devouring insects from flower to flower, and a cross thus effected,
although nine-tenths of the pollen were destroyed it might still be
a great gain to the plant to be thus robbed; and the individuals
which produced more and more pollen, and had larger anthers,
would be selected.

When our plant, by the above process long continued, had been
rendered highly attractive to insects, they would, unintentionally
on their part, regularly carry pollen from flower to flower ; and that
they do this effectually, I could easily show by many striking
facts. I will give only one, as likewise illustrating one step in
the separation of the sexes of plants. Some holly-trees bear only
male flowers, which have four stamens producing a rather small
quantity of pollen, and a rudimentary pistil ; other holly-trees bear
only female flowers ; these have a full-sized pistil, and four stamens
with shrivelled anthers, in which not a grain of pollen can be de-

74 ORIGIN OF SPECIES

tected. Having found a female tree exactly sixty yards from a
male tree, I put the stigmas of twenty flowers, taken from dif-
ferent branches, under the microscope, and on all, without excep-
tion, there were a few pollen-grains, and on some a profusion. As
the wind had set for several days from the female to the male tree,
the pollen could not thus have been carried. The weather had
been cold and boisterous, and therefore not favourable to bees,
nevertheless every female flower which I examined had been ef-
fectually fertilised by the bees, which had flown from tree to tree
in search of nectar. But to return to our imaginary case : as soon
as the plant had been rendered so highly attractive to insects that
pollen was regularly carried from flower to flower, another process
might commence. No naturalist doubts the advantage of what
has been called the " physiological division of labour ;" hence we
may believe that it would be advantageous to a plant to produce
stamens alone in one flower or on one whole plant, and pistils
alone in another flower or on another plant. In plants under
culture and placed under new conditions of life, sometimes the
male organs and sometimes the female organs become more or
less impotent; now if we suppose this to occur in ever so slight
a degree under nature, then, as pollen is already carried regularly
from flower to flower, and as a more complete separation of the
sexes of our plant would be advantageous on the principle of the
division of labour, individuals with this tendency more and more
increased, would be continually favoured or selected, until at
last a complete separation of the sexes might be effected. It
would take up too much space to show the various steps, through
dimorphism and other means, by which the separation of the sexes
in plants of various kinds is apparently now in progress; but I
may add that some of the species of holly in North America, are,
according to Asa Gray, in an exactly intermediate condition,
or, as he expresses it, are more or less dioeciously polygamous.

Let us now turn to the nectar-feeding insects; we may suppose
the plant, of which we have been slowly increasing the nectar by
continued selection, to be a common plant; and that certain in-
sects depended in main part on its nectar for food. I could give
many facts showing how anxious bees are to save time : for in-
stance, their habit of cutting holes and sucking the nectar at the
bases of certain flowers, which, with a very little more trouble,
they can enter by the mouth. Bearing such facts in mind, it may
be believed that under certain circumstances individual differences
in the curvature or length of the proboscis, &c., too slight to be
appreciated by us, might profit a bee or other insect, so that certain
individuals would be able to obtain their food more quickly than

NATURAL SELECTION, ETC. 75

others; and thus the communities to which they belonged would
flourish and throw off many swarms inheriting the same peculiari-
ties. The tubes of the corolla of the common red and incarnate
clovers (Trifolium pratense and incarnatum) do not on a hasty
glance appear to differ in length ; yet the hive-bee can easily suck
the nectar out of the incarnate clover, but not out of the common
red clover, which is visited by humble-bees alone; so that whole
fields of red clover offer in vain an abundant supply of precious
nectar to the hive-bee. Tliat this nectar is much liked by the
hive-bee is certain; for I have repeatedly seen, but only in the
autumn, many hive-bees sucking the flowers through holes bitten
in the base of the tube by humble-bees. The difference in the
length of the corolla in the two kinds of clover, which determines
the visits of the hive-bee, must be very trifling; for I have been
assured that when red clover has been mown, the flowers of the
second crop are somewhat smaller, and that these are visited by
many hive-bees. I do not know whether this statement is accurate ;
nor whether another published statement can be trusted, namely,
that the Ligurian bee which is generally considered a mere variety
of the common hive-bee, and which freely crosses with it, is able to
reach and suck the nectar of the red clover. Thus, in a country
where this kind of clover abounded, it might be a great advantage
to the hive-bee to have a slightly longer or differently constructed
proboscis. On the other hand, as the fertility of this clover abso-
lutely depends on bees visiting the flowers, if humble-bees were
to become rare in any country, it might be a great advantage to
the plant to have a shorter or more deeply divided corolla, so that
the hive-bees, could be enabled to suck its flowers. Thus I can
understand how a flower and a bee might slowly become, either
simultaneously or one after the other, modified and adapted to
each other in the most perfect manner, by the continued preserva-
tion of all the individuals which presented slight deviations of
structure mutually favourable to each other.

I am well aware that this doctrine of natural selection, exem-
plified in the above imaginary instances, is open to the same
objections which were first urged against Sir Charles Lyell's noble
views on " the modern changes of the earth, as illustrative of
geology ; " but we now seldom hear the agencies which we see still
at work, spoken of as trifling or insignificant, when used in ex-
plaining the excavation of the deepest valleys or the formation of
long lines of inland cliffs. ^Natural selection acts only by the pres-
ervation and accumulation of small inherited modifications, each
profitable to the preserved being; and as modern geology has al-
most banished such views as the excavation of a great valley by a

76 ORIGIN OF SPECIES

single diluvial wave, so will natural selection banish the belief of
the continued creation of new organic beings, or of any great and
sudden modification in their structure.

On the Intercrossing of Individuals,

I must here introduce a short digression. In the case of ani-
mals and plants with separated sexes, it is of course obvious that
two individuals must always (with the exception of the curious
and not well understood cases of parthenogenesis) unite for each
birth ; but in the case of hermaphrodites this is far from obvious.
Nevertheless there is reason to believe that with all hermaphrodites
two individuals, either occasionally or habitually, concur for the
reproduction of their kind. This view was long ago doubtfully
suggested by Sprengel, Knight and Kolreuter. We shall presently
see its importance ; but I must here treat the subject with extreme
brevity, though I have the materials prepared for an ample dis-
cussion. All vertebrate animals, all insects, and some other large
groups of animals, pair for each birth. Modern research has
much diminished the number of supposed hermaphrodites, and of
real hermaphrodites a large number pair; that is, two individuals
regularly unite for reproduction, which is all that concerns us.
But still there are many hermaphrodite animals which certainly
do not habitually pair, and a vast majority of plants are her-
maphrodites. What reason, it may be asked, is there for supposing
in these cases that two individuals ever concur in reproduction?
As it is impossible here to enter on details, I must trust to some
general considerations alone.

In the first place, I have collected so large a body of facts, and
made so many experiments, showing, in accordance with the almost
universal belief of breeders, that with animals and plants a cross
between different varieties, or between individuals of the same
variety but of another strain, gives vigour and fertility to the off-
spring; and on the other hand, that close interbreeding diminishes
vigour and fertility; that these facts alone incline me to believe
that it is a general law of nature that no organic being fertilises
itself for a perpetuity of generations ; but that a cross with another
individual is occasionally — perhaps at long intervals of time —
indispensable.

On the belief that this is a law of nature, we can, I think, under-
stand several large classes of facts, such as the following, which
on any other view are inexplicable. Every hybridizer knows how
unfavourable exposure to wet is to the fertilisation of a flower, yet
what a multitude of flowers have their anthers and stigmas fully

NATURAL SELECTION, ETC. 77

exposed to the weather! If an occasional cross be indispensable,
notwithstanding that the plant's own anthers and pistil stand so
near each other as almost to insure self-fertilisation, the fullest
freedom for the entrance of pollen from another individual will
explain the above state of exposure of the organs. Many flowers,
on the other hand, have their organs of fructification closely en-
closed, as in the great papilionaceous or i)ea-family; but these
almost invariably present beautiful and curious adaptations in
relation to the visits of insects. So necessary are the visits of bees
to many papilionaceous flowers, that their fertility is greatly di-
minished if these visits be prevented. Now, it is scarcely possible
for insects to fly from flower to flower, and not to carry pollen
from one to the other, to the great good of the plant. Insects act
like a camel-hair pencil, and it is suflicient, to ensure fertilisation,
just to touch with the same brush the anthers of one flower and
then the stigma of another; but it must not be supposed that bees
would thus produce a multitude of hybrids between distinct
species; for if a plant's own pollen and that from another species
are placed on the same stigma, the former is so prepotent that
it invariably and completely destroys, as has been shown by
Gartner, the influence of the foreign pollen.

When the stamens of a flower suddenly spring towards the
pistil, or slowly move one after the other towards it, the con-
trivance seems adapted solely to ensure self-fertilisation; and no
doubt it is useful for this end : but the agency of insects is often
required to cause the stamens to spring forward as Kolreuter has
shown to be the case with the barberry; and in this very genus,
which seems to have a special contrivance for self-fertilisation,
it is well-known that, if closely-allied forms or varieties are
planted near each other, it is hardly possible to raise pure seedlings
so largely do they naturally cross. In numerous other cases, far
from self-fertilisation being favoured, there are special contriv-
ances which effectually prevent the stigma receiving pollen from
its own flower, as I could show from the works of Sprengel arid
others, as well as from my own observations : for instance, in
Lobelia fulgens, there is a really beautiful and elaborate contriv-
ance by which all the infinitely numerous pollen-granules are
swept out of the conjoined anthers of each flower, before the
stigma of that individual flower is ready to receive them; and as
this flower is never visited, at least in my garden, by insects, it
never sets a seed, though by placing pollen from one flower on the
stigma of another, I raise plenty of seedlings. Another species of
Lobelia which is visited by bees seeds freely in my garden. In
very many other cases, though there is no special mechanical con-

78 ORIGIN OF SPECIES

trivance to prevent the stigma receiving pollen from the same
flower, yet, as Sprengel, and more recently Hildebrand, and
others, have shown, and as I can confirm, either the anthers burst
before the stigma is ready for fertilisation, or the stigma is ready
before the pollen of that flower is ready, so that these so-named
dichogamous plants have in fact separated sexes, and must habitu-
ally be crossed. So it is with the reciprocally dimorphic and tri-
morphic plants previously alluded to. How strange are these facts !
How strange that the pollen and stigmatic surface of the same
flower, though placed so close together, as if for the very purpose
of self-fertilisation, should be in so many cases mutually useless
to each other? How simply are these facts explained on the view
of an occasional cross with a distinct individual being advanta-
geous or indispensable!

If several varieties of the cabbage, radish, onion, and of some
other plants, be allowed to seed near each other, a large majority of
the seedlings thus raised turn out, as I have found, mongrels: for
instance, I raised 233 seedling cabbages from some plants of dif-
ferent varieties growing near each other, and of these only 78 were
true to their kind, and some even of these were not perfectly true.
Yet the pistil of each cabbage-flower is surrounded not only by its
own six stamens but by those of the many other flowers on the
same plant; and the pollen of each flower readily gets on its own
stigma without insect agency; for I have found that plants care-
fully protected from insects produce the full number of pods.
How, then, comes it that such a vast number of the seedlings are
mongrelized? It must arise from the pollen of a distinct variety
having a prepotent effect over the flower's own pollen ; and that
this is part of the general law of good being derived from the
intercrossing of distinct individuals of the same species. When
distinct species are crossed the case is reversed, for a plant's own
pollen is almost always prepotent over foreign pollen; but to this
subject we shall return in a future chapter.

In the case of a large tree covered with innumerable flowers,
it may be objected that pollen could seldom be carried from tree
to tree, and at most only from flower to flower on the same tree;
and flowers on the same tree can be considered as distinct indi-
viduals only in a limited sense. I believe this objection to be
valid, but that nature has largely provided against it by giving to
trees a strong tendency to bear flowers with separated sexes. When
the sexes are separated, although the male and female flowers may
be produced on the same tree, pollen must be regularly carried
from flower to flower ; and this will give a better chance of pollen
being occasionally carried from tree to tree. That trees belonging

I

NATURAL SELECTION, ETC. 79

to all Orders have their sexes more often separated than other
plants, I find to be the case in this country; and at my request Dr.
Hooker tabulated the trees of New Zealand, and Dr. Asa Gray
those of the United States, and the result was as I anticipated. On
the other hand, Dr. Hooker informs me that the rule does not
hold good in Australia: but if most of the Australian trees are
dichogamous, the same result would follow as if they bore flowers
with separated sexes. I have made these few remarks on trees
simply to call attention to the subject.

Turning for a brief space to animals : various terrestrial species
are hermaphrodites, such as the land-mollusca and earth-worms;
but these all pair. As yet I have not found a single terrestrial
animal which can fertilise itself. This remarkable fact, which
offers so strong a contrast with terrestrial plants, is intelligible on
the view of an occasional cross being indispensable ; for owing to the
nature of the fertilising element there are no means, analogous
to the action of insects and of the wind with plants, by which an
occasional cross could be effected with terrestrial animals without
the concurrence of two individuals. Of aquatic animals, there
are many self- fertilising hermaphrodites; but here the currents of
water offer an obvious means for an occasional cross. As in the
case of flowers, I have as yet failed, after consultation with one of
the highest authorities, namely, Professor Huxley, to discover a
single hermaphrodite animal with the organs of reproduction so
perfectly enclosed that access from without, and the occasional
influence of a distinct individual, can be shown to be physically
impossible. Cirripedes long appeared to me to present, under
this point of view, a case of great difiiculty; but I have been en-
abled, by a fortunate chance, to prove that two individuals,
though both are self-fertilising hermaphrodites, do sometimes
cross.

It must have struck most naturalists as a strange anomaly that,
both with animals and plants, some species of the same family and
even of the same genus, though agreeing closely with each other
in their whole organisation are hermaphrodites, and some unisex-
ual. But if, in fact, all hermaphrodites do occasionally intercross,
the difference between them and unisexual species is, as far as
function is concerned, very small.

From these several considerations and from the many special
facts which I have collected, but which I am unable here to
give, it appears that with animals and plants an occasional inter-
cross between distinct individuals is a very general, if not univer-
sal, law of nature.

80 ORIGIN OF SPECIES

Circumstances favourable for the production of new forms through

Natural Selection.

This is an extremely intricate subject. A great amount of
variability, under which term individual differences are always
included, will evidently be favourable. A large number of indi-
viduals, by giving a better chance within any given jieriod for
the appearance of profitable variations, will compensate for a
lesser amount of variability in each individual, and is, I believe, a
highly important element of success. Though Nature grants
long periods of time for the work of natural selection, she does
not grant an indefinite period; for as all organic beings are striv-
ing to seize on each place in the economy of nature, if any one
species does not become modified and improved in a corresponding
degree with its competitors, it will be exterminated. Unless fa-
vourable variations be inherited by some at least of the offspring,
nothing can be effected by natural selection. The tendency to
reversion may often check or prevent the work; but as this tend-
ency has not prevented man from forming by selection numerous
domestic races, why should it prevail against natural selection?

In the case of methodical selection, a breeder selects for some
definite object, and if the individuals be allowed freely to inter-
cross, his work will completely fail. But when many men, with-
out intending to alter the breed, have a nearly common standard
of perfection, and all try to procure and breed from the best ani-
mals, improvement surely but slowly follows from this uncon-
scious process of selection, notwithstanding that there is no sep-
aration of selected individuals. Thus it will be under nature; for
within a confined area, with some place in the natural polity not
perfectly occupied, all the individuals varying in the right direc-
tion, though in different degrees, will tend to be preserved. But if
the area be large, its several districts will almost certainly present
different conditions of life ; and then, if the same species under-
goes modification in different districts, the newly-formed varieties
will intercross on the confines of each. But we shall see in the
sixth chapter that intermediate varieties, inhabiting intermediate
districts, will in the long run generally be supplanted by one of
the adjoining varieties. Intercrossing will chiefly affect those
animals which unite for each birth and wander much, and which
do not breed at a very quick rate. Hence with animals of this
nature, for instance, birds, varieties will generally be confined
to separate countries; and this I find to be the case. With herm-
aphrodite organisms which cross only occasionally, and likewise
xvith animals which unite for each birth, but which wander little

NATTKAL SELECTION, KTC. 81

and can increase at a rapid rate, a new and improved variety ini.^lit
be qnickly formed on any one spot, and might there maintain
itself in a body and afterwards spread, so that the individuals of
the new variety would chiefly cross together. On this principle,
nnrserymen always prefer saving seed from a large body of plants,
as the chance of intercrossing is thus lessened.

Even with animals which unite for each birth, and which do
not propagate rapidly, we must not assume that free intercrossing
would always eliminate the effects of natural selection ; for I can
bring forward a considerable body of facts showing that within
the same area, two varieties of the same animal may long remain
distinct, from haunting different stations, from breeding at slight-
ly different seasons, or from the individuals of each variety pre-
ferring to pair together.

Intercrossing plays a very important part in nature by keep-
ing the individuals of the same species, or of the same variety,
true and luiiform in character. It will obviously thus act far
more efficiently with those animals which unite for each birth ; but,
as already stated, we have reason to believe that occasional inter-
crosses take place with all animals and plants. Even if these
take place only at long intervals of time, the young thus produced
will gain so much in vigour and fertility over the offspring from
long-continued self- fertilisation, that they will have a better chance
of surviving and propagating their kind; and thus in the long
run the influence of crosses, even at rare intervals, will be great.
With respect to organic beings extremely low in the scale, which
do not propagate sexually, nor conjugate, and which cannot pos-
sibly intercross, uniformity of character can be retained by them
under the same conditions of life, only through the principle of
inheritance, and through natural selection which will destroy any
individuals departing from the i^roper type. If the conditions
of life change and the form undergoes modification, uniformity
of character can be given to the modified offspring, solely by
natural selection preserving similar favourable variations.

Isolation, also, is an important element in the modification of
species through natural selection. In a confined or isolated area,
if not very large, the organic and inorganic conditions of life will
generally be almost uniform; so that natural selection will tend
to modify all the varying individuals of the same species in the
same manner. Intercrossing with the inhabitants of the sur-
rounding districts will, also, be thus prevented. Moritz Wagner
has lately published an interesting essay on this subject, and has
shown that the service rendered by isolation in preventing crosses
Wtween newly-formed varieties is probably greater even than I

82 ORIGIN OF SPECIES

supposed. But from reasons already assigned I can by no means
agree with this naturalist, that migration and isolation are neces-
sary elements for the formation of new species. The importance
of isolation is likewise great in preventing, after any physical
change in the conditions, such as of climate, elevation of the land,
&c., the immigration of better adapted organisms; and thus new
places in the natural economy of the district will be left open to
be filled up by the modification of the old inhabitants. Lastly,
isolation will give time for a new variety to be improved at a slow
rate; and this may sometimes be of much importance. If, how-
ever, an isolated area be very small, either from being surrounded
by barriers, or from having very peculiar physical conditions, the
total number of the inhabitants will be small ; and this will retard
the production of new species, through n- "^ural selection, by de-
creasing the chances of favourable variatic 3 arising.

The mere lapse of time by itself does nothing, either for or
against natural selection. I state this because it has been err-
oneously asserted that the element of time has been assum.ed
by me to play an all-important part in modifying species, as if
all the forms of life were necessarily undergoing change through
some innate law. Lapse of time is only so far important, and
its importance in this respect is great, that it gives a better chance
of beneficial variations arising and of their being selected, ac-
cumulated, and fixed. It likewise tends to increase the direct
action of the physical conditions of life, in relation to the constitu-
tion of each organism.

If we turn to nature to test the truth of these remarks, and look
at any small isolated area, such as an oceanic island, although the
number of species inhabiting it is small, as we shall see in our
chapter on Geographical Distribution; yet of these species a very
large proportion are endemic, — that is, have been produced there
and nowhere else in the world. Hence an oceanic island at first
sight seems to have been highly favourable for the production of
new species. But we may thus deceive ourselves, for to ascertain
whether a small isolated area, or a large open area like a continent,
has been most favourable for the production of new organic forms,
we ought to make the comparison within equal times; and this we
are incapable of doing.

Although isolation is of great importance in the production of
new species, on the whole I am inclined to believe that largeness
of area is still more important, especially for the production of
species which shall prove capable of enduring for a long period,
and of spreading widely. Throughout a great and open area, not
only will there be a better chance of favourable variations, arising

NATURAL SELECTION, ETC. 83

from the large number of individuals of the same species there sup-
ported, but the conditions of life are much more complex from
the large number of already existing species; and if some of these
many species become modified and improved, others will have to
be improved in a corresponding degree, or they will be exter-
minated. Each new form, also, as soon as it has been improved,
will be able to spread over the open and continuous area, and will
thus come into competition with many other forms. Moreover,
great areas, though now continuous, will often, owing to former
oscillations of level, have existed in a broken condition; so that
the good effects of isolation will generally, to a certain extent,
have concurred. Finally, I conclude that, although small isolated
areas have been in some respects highly favourable for the pro-
duction of new spe s, yet that the course of modification will
generally have been more rapid on large areas; and what is more
important, that the new forms produced on large areas, which al-
ready have been victorious over many competitors, will be those
that will spread most widely, and will give rise to the greatest
number of new varieties and species. They will thus play a more
important part in the changing history of the organic world.

In accordance with this view, we can, perhaps, understand some
facts which will be again alluded to in our chapter on Geographical
Distribution; for instance, the fact of the productions of the
smaller continent of Australia now yielding before those of the
larger Europseo-Asiatic area. Thus, also, it is that continental pro-
ductions have everywhere become so largely naturalised on islands.
On a small island, the race for life will have been less severe, and
there will have been less modification and less extermination.
Hence, we can understand how it is that the flora of Madeira, ac-
cording to Oswald Heer, resembles to a certain extent the extinct
tertiary flora of Europe. All fresh-water basins, taken together,
make a small area compared with that of the sea or of the land.
Consequently, the competition between fresh-water productions will
have been less severe than elsewhere ; new forms will have been there
more slowly produced, and old forms more slowly exterminated. And
it is in fresh-water basins that we find seven genera of Ganoid
fishes, remnants of a once preponderant order : and in fresh water
we find some of the most anomalous forms now known in the world
as the Ornithorhynchus and Lepidosiren which, like fossils, con-
nect to a certain extent orders at present widely sundered in the
natural scale. These anomalous forms may be called living fos-
sils; they have endured to the present day, from having inhabited
a confined area, and from having been exposed to less varied, and
therefore less severe competition.

84 ORIGIN OP SPECIES

To sum up, as far as the extreme intricacy of 'the subject per-
mits, the circumstances favourable and unfavourable for the pro-
duction of new species through natural selection. I conclude that
for terrestrial productions a large continental area, which has
undergone many oscillations of level, will have been the most
favourable for the production of many new forms of life, fitted
to endure for a long time and to spread widely. Whilst tlie area
existed as a continent, the inhabitants will have been numerous
in individuals and kinds, and will have been subjected to severe
competition. When converted by subsidence into large separate
islands, there will still have existed many individuals of the same
species on each island: intercrossing on the confines of the range
of each new species will have been checked : after physical changes
of any kind, immigration will have been prevented, so that new
places in the polity of each island will have had to be filled up by
the modification of the old inhabitants; and time will have been
allowed for the varieties in each to becomie well modified and per-
fected. When, by renewed elevation, the islands were reconverted
into a continental area, there will again have been very severe com-
petition : the most favoured or improved varieties will have been
enabled to spread : there will have been much extinction of the
less improved forms, and the relative proportional numbers of
the various inhabitants of the reunited continent will again have
been changed; and again there will have been a fair field for
natural selection to improve still further the inhabitants, and
thus to produce new species.

That natural selection generally acts with extreme slowness I
fully admit. It can act only when there are places in the natural
polity of a district which can be better occupied by the modification
of some of its existing inhabitants. The occurrence of such places
will often depend on physical changes which generally take place
very slowly, and on the immigration of better adapted forms being
prevented. As some few of the old inhabitants become modified,
the mutual relations of others will often be disturbed; and this
will create new places, ready to be fdled up by better adapted
forms, but all this will take place very slowly. Although all the
individuals of the same species differ in some slight degree from
each other, it would often be long before differences of the right
nature in various parts of the organisation might occur. The
result would often be greatly retarded by free intercrossing. Many
will exclaim that these several causes are amply sufficient to neu-
tralise the power of natural selection. I do not believe so. But
I do believe that natural selection will genernlly act very slowly,
only at long intervals of time, and only on a few of the inhabitants

NATl'ltAL SELECTION, ETC. 85

of the same region. I further believe that these slow, intermittent
results accord well with what geology tells us of the rate and man-
ner at which the inhabitants of the world have changed.

Slow though tlie process of selection may be, if feeble man can
do much by artificial selection, I can see no limit to the amount
of change, to the beauty and complexity of the coadaptations be-
tween all organic beings, one with another and with their physical
conditions of life, which may have been effected in the long course
of time through nature's power of selection, that is by the survival
of the fittest.

Extinction caused hy Natural Selection.

This subject will be more fully discussed in our chapter on
Geology; but it must here be alluded to from being intimately
connected with natural selection. Natural selection acts solely
throug}\ the preservation of variations in some way advantageous,
which consequently endure. Owing to the high geometrical rate
of increase of all organic beings, each area is already fully stocked
with inhabitants; and it follows from this, that as the favoured
forms increase in number, so, generally, will the less favoured de-
crease and become rare. Rarity, as geology tells us, is the
precursor to extinction. We can see that any form which is repre-
sented by few individuals will run a good chance of utter ex-
tinction, during great fluctuations in the nature of the seasons, or
from a temporary increase in the number of its enemies. But
we may go further than this; for, as new forms are produced,
unless we admit that specific forms can go on indefinitely in-
creasing in number, many old forms must become extinct. That
the number of specific forms has not indefinitely increased,
geology plainly tells us; and we shall presently attempt to show
why it is that the number of species throughout the world has not
become immeasurably great.

We have seen that the species which are most numerous in indi-
viduals have the best chance of producing favourable variations
within any given period. We have evidence of this, in the facts
stated in the second chapter showing tliat it is the common and
diffused or dominant species which offer the greatest number of
recorded varieties. Hence, rare species will be less quickly mod-
ified or improved within any given period; they will consequently
be beaten in the race for life by the modified and improved de-
scendants of the commoner species.

From these several considerations I think it inevitably follows,
that as new species in the course of time are formed through

86 ORIGIN OF SPECIES

natural selection, others will become rarer and rarer, and finally
extinct. The forms which stand in closest competition with those
undergoing modification and improvement will naturally suffer
most. And we have seen in the chapter on the Struggle for Ex-
istence that it is the most closely-allied forms, — varieties of the
same species, and species of the same genus or of related genera, — -
which, from having nearly the same structure, constitution, and
habits, generally come into the severest competition with each
other; consequently, each new variety or species, during the prog-
ress of its formation, will generally press hardest on its nearest
kindred, and tend to exterminate them. We see the same process
of extermination amongst our domesticated productions, through
the selection of improved forms by man. Many curious instances
could be given showing how quickly new breeds of cattle, sheep,
and other animals, and varieties of flowers, take the place of older
and inferior kinds. In Yorkshire, it is historically known that
the ancient black cattle were displaced by the long-horns, and
that these " were swept away by the short-horns " (I quote the
words of an agricultural writer) " as if by some murderous pesti-
lence."

Divergence of Character.

The principle, which I have designated by this term, is of high
importance, and explains, as I believe, several important facts. In
the first place, varieties, e\en strongly-marked ones, though having
somewhat of the character of species — as is shown by the hope-
less doubts in many cases how to rank them — yet certainly difier
far less from each other than do good and distinct species. Never-
theless, according to my view, varieties are species in the process
of formation, or are, as I have called them, incipient species. How,
then, does the lesser difference between varieties become augmented
into the greater differences between species? That this does habit-
ually happen, we must infer from most of the innumerable species
throughout nature presenting well-marked differences; whereas
varieties, the supposed prototypes and parents of future well-marked
species, present slight and ill-defined differences. Mere chance,
as we may call it, might cause one variety to differ in some char-
acter from its parents, and the offspring of this variety again to
differ from its parent in the very same character and in a greater
degree; but this alone would never account for so habitual and
large a degree of difference as that between the species of the
same genus.

As has always been my practice. I have sought light on this head

NATURAL SELECTION, ETC. 87

from our domestic productions. We shall here find something
analogous. It will be admitted that the production of races so
different as short-horn and Hereford cattle, race and cart horses,
the several breeds of pigeons, &c., could never have been effected
by the mere chance accumulation of similar variations during
many successive generations. In practice, a fancier is, for in-
stance, struck by a pigeon having a slightly shorter beak; another
fancier is struck by a pigeon having a rather longer beak; and
on the acknowledged principle that " fanciers do not and will not
admire a medium standard, but like extremes," they both go on
(as has actually occurred with the sub-breeds of the tumbler-
pigeon) choosing and breeding from birds with longer and longer
beaks, or with shorter and shorter beaks. Again, we may suppose
that at an early period of history, the men of one nation or district
required swifter horses, whilst those of another required stronger
and bulkier horses. The early differences would be very slight ; but,
in the course of time, from the continued selection of swifter
horses in the one case, and of stronger ones in the other, the dif-
ferences would become greater, and would be noted as forming two
sub-breeds. Ultimately, after the lapse of centuries, these sub-
breeds would become converted into two well-established and dis-
tinct breeds. As the differences become greater, the inferior ani-
mals with intermediate characters, being neither very swift nor
very strong, would not have been used for breeding, and will thus
have tended to disappear. Here, then, we see in man's productions
the action of what may be called the principle of divergence, caus-
ing differences, at first barely appreciable, steadily to increase, and
the breeds to diverge in character, both from each other and
from their common parent.

But how, it may be asked, can any analogous principle apply
in nature ? I believe it can and does apply most efficiently (though
it was a long time before I saw how), from the simple circum-
stance that the more diversified the descendants from any one
species become in structure, constitution, and habits, by so much
will they be better enabled to seize on many and widely diversified
places in the polity of nature, and so be enabled to increase in
numbers.

We can clearly discern this in the case of animals with simple
habits. Take the case of a carnivorous quadruped, of which the
number that can be supported in any country has long ago arrived
at its full average. If its natural power of increase be allowed to
act, it can succeed in increasing (the country not undergoing any
change in conditions) only by its varying descendants seizing on
places at present occupied by other animals : some of them, for in-

88 OKIGIN OF SPECIES

i:>tance, bciuj;' enabled to feed on new kinds of i)rey,. either dead
or alive; some inhabiting new stations, climbing trees, frequenting
water, and some perhaps becoming less carnivorous. The more
diversified in habits and structure the descendants of our carnivo-
rous animals become, the more places they will be enabled to occupy.
What applies to one animal will apply throughout all time to all
animals — that is, if they vary — for otherwise natural selection
can affect nothing. So it will be with plants. It has been exper-
imentally proved, that if a plot of ground be sown with one
species of grass, and a similar plot be sown with several distinct
genera of gTasses, a greater number of plants and a greater weight
of dry herbage can be raised in the latter than in the former case.
The same has been found to hold good when one variety and
several mixed varieties of wheat have been sown on equal spaces of
ground. Hence, if any one species of grass were to go on varying,
and the varieties were continually selected which differed from
each other in the same manner, though in a very sliglit degree, as
do the distinct species and genera of grasses, a greater number of
individual plants of this species, including its modified descend-
ants, would succeed in living on the same piece of ground. And
we know that each species and each variety of grass is annually
sowing almost countless seeds; and is thus striving, as it may be
said, to the utmost to increase in number. Consequently, in the
course of many thousand generations, the most distinct varieties
of any one species of grass would have the best chance of succeed-
ing and of increasing in numbers, and thus of supplanting the
less distinct varieties; and varieties, when rendered very distinct
from each other, take the rank of species.

The truth of the principle that the gieatest amount of life can
be supported by great diversification of structure, is seen under
many natural circumstances. In an extremely small area, es-
]iecially if freely open to immigration, and where the contest be-
tween individual and individual must be very severe, we always
find great diversity in its inhabitants. For instance, I found that
a piece of turf, three feet by four in size, which had been ex-
posed for many years to exactly the same conditions, supported
twenty species of plants, and these belonged to eighteen genera
and to eight orders, which shows how much these plants differed
from each other. So it is with the plants and insects on small and
uniform islets: also in small ponds of fresh water. Farmers find
that they can raise most food by a rotation of plants belonging to
the most different orders : nature follows what may be called a
simultaneous rotation. Most of the animals and plants which live
close round any small piece of ground, could live on it (suppos-

NATURAL SELECTION, ETC. 89

iiig its nature not to be In any way peculiar), and may be said to
be striving- to the utmost to live there; but, it is seen, that where
they come into the closest competition, the advantages of diversifi-
cation of structure, with the accompanying differences of habit and
constitution, determine that the inhabitants, which thus jostle each
other most closely, shall, as a general rule, belong to what we call
different genera and orders.

The same principle is seen in the naturalisation of plants through
man's agency in foreign lands. It might have been expected that
the plants which would succeed in becoming naturalised in any
land would generally have been closely allied to the indigenes;
for these are commonly looked at as specially created and adapted
for their owni country. It might also, perhai^s, have been expected
that naturalised plants would have belonged to a few groups more
especially adapted to certain stations in their new homes. But the
case is very different; and Alph. De Candolle has well remarked,
in his great and admirable work, that floras gain by naturalisation,
proportionally with the number of the native genera and species
far more in new genera than in new species. To give a single in-
stance : in the last edition of Dr. Asa Gray's ^ Manual of the Flora
of the Northern United States,' 2G0 naturalised plants are enu-
merated, and these belong to 162 genera. We thus see that tlu^se
naturalised plants are of a highly diversified nature. They dif-
fer, moreover, to a large extent, from the indigenes, for out of the
162 naturalised genera, no less than 100 genera are not there in-
digenous, and thus a large proportional addition is made to the
genera now living in the United States.

By considering the nature of the plants or animals which have
in any country struggled successfully with the indigenes and have
there become naturalised, we may gain some crude idea in wdiat
manner some of the natives would have to be modified, in order
to gain an advantage over their compatriots; and w^e may at least
infer that diversification of structure, amounting to new generic
differences, would be profitable to them.

The advantage of diversification of structure in the inhabitants
of the same region is, in fact, the same as that of the physiological
division of labour in the organs of the same individual body — a
sidjject so well elucidated by Milne Edv/ards. No physiologist
doubts that a stomach adapted to digest vegetable matter alone,
or flesh alone, draws most nutriment from these substances. So
in the general economy of any land, the more widely and perfectly
the animals and ]dants are diversified for different habits of life,
so will a greater number of individuals be capable of there sup-
porting themselves. A set of animals, with their organisation but

90 ORIGIN OF SPECIES

little diversified, could hardly compete with a set more perfectly
diversified in structure. It may be doubted, for instance, whether
the Australian marsupials, which are divided into groups differing
but little from each other, and feebly representing, as Mr. Water-
house and others have remarked, our carnivorous, ruminant, and
rodent mammals, could successfully compete with these well-
developed orders. In the Australian mammals, we see the process
of diversification in an early and incomplete stage of development.

The Prohahle Effects of the Action of Natural Selection through
Divergence of Character and Extinction, on, the Descendants
of a Common Ancestor.

After the foregoing discussion, which has been much compressed,
we may assume that the modified descendants of any one species
will succeed so much the better as they become more diversified in
structure, and are thus enabled to encroach on places occupied by
other beings. Now let us see how this principle of benefit being
derived from divergence of character, combined with the princi-
ples of natural selection and of extinction, tends to act.

The accompanying diagram will aid us in understanding this
rather perplexing subject. Let A to L represent the species of a
genus large in its own country; these species are supposed to re-
semble each other in unequal degrees, as is so generally the case
in nature, and as is represented in the diagram by the letters
standing at unequal distances. I have said a large genus, because
as we saw in the second chapter, on an average more species vary
in large genera than in small genera ; and the varying species of
the large genera present a greater number of varieties. We have,
also, seen that the species, which are the commonest and the most
widely diffused, vary more than do the rare and restricted species.
Let (A) be a common, widely-diffused, and varying species, belong-
ing to a genus large in its own country. The branching and diverg-
ing dotted lines of unequal lengths proceeding from (A), may
represent its varying offspring. The variations are supposed to be
extremely slight, but of the most diversified nature; they are not
supposed all to appear simultaneously, but often after long in-
tervals of time; nor are they all supposed to endure for equal
periods. Only those variations which are in some way profitable
will be preserved or naturally selected. And here the importance
of the principle of benefit derived from divergence of character
comes in; for this will generally lead to the most different or di-
vergent variations (represented by the outer dotted lines) being
preserved and accumulated by natural selection. When a dotted

NATURAL SELECTION, ETC. 91

line reaches one of the horizontal lines, and is there marked hy
a small numbered letter, a sufficient amount of variation is sup-
posed to have been accumulated to form it into a fairly well-
marked variety, such as would be thought worthy of record in a
systematic work.

The intervals between the horizontal lines in the diagram, may
represent each a thousand or more generations. After a thousand
generations, species (A) is supposed to have produced two fairly
well-marked varieties, namely a^ and m\ These two varieties will
generally still be exposed to the same conditions which made their
parents variable, and the tendency to variability is in itself hered-
itary; consequently they will likev/ise tend to vary, and commonly
in nearly the same manner as did their parents. Moreover, these
two varieties, being only slightly modified forms, will tend to in-
herit those advantages which made their parent (A) more numerous
than most of the other inhabitants of the same country; they will
also partake of those more general advantages which made the
genus to which the parent-species belonged, a large genus in its
own country. And all these circumstances are favourable to the
production of new varieties.

If, then, these two varieties be variable, the most divergent of
their variations will generally be preserved during the next thou-
sand generations. And after this interval, variety a^ is supposed
in the diagram to have produced variety a^, which will, owing to
the principle of divergence, differ more from (A) than did variety
a\ Variety m^ is supposed to have produced two varieties, namely
m^ and s^, differing from each other, and more considerably from
their common parent (A). We may continue the process by sim-
ilar steps for any length of time ; some of the varieties, after each
thousand generations, producing only a single variety, but in a
more and more modified condition, some producing two or three
varieties, and some failing to produce any. Thus the varieties or
modified descendants of the common parent (A), will generally go
on increasing in number and diverging in character. In the dia-
gram the process is represented up to the ten-thousandth genera-
tion, and under a condensed and simplified form up to the four-
teen-thousandth generation.

But I must here remark that I do not suppose that the process
ever goes on so regularly as is represented in the diagram, though
in itself made somewhat irregular, nor that it goes on continuously;
it is far more probable that each form remains for long periods un-
altered, and then again undergoes modification. Nor do I suppose
that the most divergent varieties are invariably preserved : a
medium form may often long endure, and may or may not produce

92 ORIGIN OF SPECIES

more than one modified descendant; for natural selection will al-
ways act according to tlie nature of the places which are either
"unoccupied or not perfectly occupied by other beings; and this
will depend on infinitely complex relations. But as a general rule,
the more diversified in structure the descendants from any one
species can be rendered, the more places they will be enabled to
seize on, and the more their modified progeny will increase. In our
diagram the line of succession is broken at regular intervals by
small numbered letters marking the successive forms wliicli have
become sufficiently distinct to be recorded as varieties. But these
breaks are imaginary, and might have been inserted anywhere, after
intervals long enough to allow the accumulation of a considerable
amount of divergent variation.

As all the modified descendants from a common and widely-
diffused species, belonging to a large genus, will tend to partake
of the same advantages which made their parent successful in life,
they will generally go on multiplying in number as well as diverg-
ing in character: this is represented in the diagram by the several
divergent branches proceeding from (A). The modified offspring
from the later and more highly improved branches in the lines
of descent, will, it is probable, often take the place of, and so de-
stroy, the earlier and less improved branches: this is represented
in the diagram by some of the lower branches not reaching to the
upper horizontal lines. In some cases no doubt the process of
modification will be confined to a single line of descent, and the
number of modified descendants will not be increased; although
the amount of divergent modification may have been augmented.
This case would be represented in the diagram, if all the lines pro-
ceeding from (A) were removed, excepting that from a^ to a^".
In the same way the English race-horse and English pointer have
apparently both gone on slowly diverging in character from their
original stocks, without either having given off any fresh branches
or races.

After ten thousand generations, species (A) is supposed to have
produced three forms, n^, f'\ and m^'^, which, from having di-
verged in character during the successive generations, will have
come to differ largely, but perhaps unequally, from each other
and from their common parent. If we suppose the amount of
change between each horizontal line in our diagram to be exces-
sively small, these three forms may still be only well-marked
varieties; but we have only to suppose the steps in the process of
modification to be more numerous or greater in amount, to convert
these three forms into doubtful or at last into well-defined species.
Thus the diagram illustrates the steps by which the small differ-

NATL'liAL SELECTION, ETC. 93

ences (listin^2,uisliing" varieties are increased into the larger dilTer-
erices distinguishing- species. By continuing the same process
for a greater nuuibcr of generations (as sliown in the diagram in
a condensed and simplified manner), we get eight species, marked
by the letters between a/* and m^\ all descended from (A). Thus, as
1 believe, species are multiplied and genera are formed.

hi a large genus it is i^robable that more than one species wouhl
vary. In the diagram I have assumed that a second species (1)
has produced, by analogous steps, after ten thousand generations,
either two well-marked varieties (w^*^ and 2") or two species, accord-
ing to the amount of change supposed to be representcMl between
the horizontal lines. After fourteen thousand generations, six new
species, marked by the letters n'\ to z^^, are supposed to have been
produced. In any genus, the species which arc already very dif-
ferent in character from each other, will generally tend to produce
the greatest number of modified descendants; for these will have
the best chance of seizing on new and widely different places in
the polity of nature : hence in the diagram I have chosen the ex-
treme species (A), and the nearly extreme species (I), as those
which have largely varied, and have given rise to new varieties
and sj^ecies. The other nine species (marked by capital letters)
of our original genus, may for long but unequal periods continue
to transmit unaltered descendants; and this is shown in the dia-
gram by the dotted lines unequally prolonged upwards.

But during the process of modification, represented in the dia-
gram, another of our principles, namely that of extinction, will
have played an important part. As in each fully stocked country
natural selection necessarily acts by the selected form having some
advantage in the struggle for life over other forms, there will be
a constant tendency in the improved descendants of any one species
to supplant and exterminate in each stage of descent their pred-
ecessors and their original progenitor. For it should be remem-
bered that the competition will generally be most severe between
those forms which are most nearly related to each other in habits,
constitution, and structure. Hence all the intermediate forms be-
tween the earlier and later states, that is between the less and
more improved states of the same species, as well as the original
parent-species itself, will generally tend to become extinct. So
it probably will be with many whole collateral lines of descent,
which will be conquered by later and improved lines. If, however,
the modified offspring of a species get into some distinct country,
or become quickly adapted to some quite new station, in which off-
spring and progenitor do not come into competition, both may
continue to exist.

94 OrUGIN OF SPECIES

If, then, our diagram be assumed to represent a considerable
amount of modification, species (A) and all the earlier varieties
will have become extinct, being replaced by eight new species (a^*
to m") ; and species (I) will be replaced by six {n^ to 2") new
species.

But we may go further than this. The original species of our
genus were supposed to resemble each other in unequal degrees, as
is so generally the case in nature; species (A) being more nearly
related to B, C, and D, than to the other species; and species (I)
more to G, H, K, L, than to the others. These two species (A)
and (I) were also supposed to be very common and widely diffused
species, so that they must originally have had some advantage over
most of the other species of the genus. Their modified descend-
ants, fourteen in number at the fourteen-thousandth generation,
will probably have inherited some of the same advantages : they
have also been modified and improved in a diversified manner at
each stage of descent, so as to have become adapted to many re-
lated places in the natural economy of their country. It seems,
therefore, extremely probable that they will have taken the places
of, and thus exterminated not only their parents (A) and (I),
but likewise some of the original species which were most nearly
related to their parents. Hence very few of the original species
will have transmitted offspring to the fourteen-thousandth genera-
tion. We may suppose that only one, (F), of the two species (E
and F) which were least closely related to the other nine original
species, has transmitted descendants to this late stage of descent.

The new species in our diagram descended from the original
eleven species, will now be fifteen in number. Owing to the di-
vergent tendency of natural selection, the extreme amount of dif-
ference in character between species a" and z^^ will be much greater
than that between the most distinct of the original eleven species.
The new species, moreover, will be allied to each other in a widely
different manner. Of the eight descendants from (A) the three
marked a", g", p"? will be nearly related from having recently
branched off from a^; ?>", and f*, from having diverged at an
earlier period from a^ will be in some degree distinct from the
three first-named species; and lastly, 0", e^*, and m", will be nearly
related one to the other, but, from having diverged at the first com-
mencement of the process of modification, will be widely different
from the other five species, and may constitute a sub-genus or a
distinct genus.

The six descendants from (I) will form two sub-genera or genera.
But as the original species (I) differed largely from (A), standing
nearly at the extreme end of the original genus, the six descend-

"Natural selection, etc. 95

ants from. (I) will, owing to inheritance alone, differ considerably
from the eight descendants from (A) ; the two groups, moreover,
are supposed to have gone on diverging in different directions.
The intermediate species, also (and this is a very important con-
sideration), which connected the original species (A) and (I),
have all become, excepting (F), extinct, and have left no descend-
ants. Hence the six new species descended from (I), and the eight
descendants from (A), will have to be ranked as very distinct
genera, or even as distinct sub-families.

Thus it is, as I believe, that two or more genera are produced by
descent with modification, from two or more species of the same
genus. And the two or more parent-species are supposed to be
descended from some one species of an earlier genus. In our dia-
gram, this is indicated by the broken lines, beneath the capital
letters, converging in sub-branches downward towards a single
point; this point represents a species, the supposed progenitor of
our several new sub-genera and genera.

It is worth while to reflect for a moment on the character of
the new species f^*, which is supposed not to have diverged much in
character, but to have retained the form of (F), either unaltered or
altered only in a slight degree. In this case, its affinities to the
other fourteen new species will be of a curious and circuitous
nature. Being descended from a form which stood between the
parent-species (A) and (I), now supposed to be extinct and un-
known, it will be in some degree intermediate in character between
the two groups descended from these two species. But as these two
groups have gone on diverging in character from the type of their
parents, the new species (f") will not be directly intermediate be-
tween them, but rather between types of the two groups ; and every
naturalist will be able to call such cases before his mind.

In the diagram, each horizontal line has hitherto been supposed
to represent a thousand generations, but each may represent a mil-
lion or more generations; it may also represent a section of the
successive strata of the earth's crust including extinct remains.
We shall, when we come to our chapter on Geology, have to refer
again to this subject, and I think we shall then see that the dia-
gram throws light on the afiinities of extinct beings, which, though
generally belonging to the same orders, families, or genera, with
those now living, yet are often, in some degree, intermediate in
character between existing groups; and we can understand this
fact, for the extinct species lived at various remote epochs when
the branching lines of descent had diverged less.

I see no reason to limit the process of modification, as now ex-
plained, to the formation of genera alone. If, in the diagram, we

96 ORIGIN OF SPECIES

suppose the amount of change, represented by each successive
group of diverging dotted lines to be great, the forms marked a*
to p^\ those marlved V^ and f", and those marked o'' to
ni^, will form three very distinct genera. We shall also have two
very distinct genera descended from (1), differing widely from the
descendants of (A). These two groups of genera will thus form
two distinct families, or orders, according to the amount of di-
vergent modification supposed to be represented in the diagram.
And the two new families, or orders, are descended from two species
of the original genus, and these are supposed to be descended from
some still more ancient and uiiknown form.

We have seen that in each country it is the species belonging
to the larger genera which oftenest present varieties or incipient
species. This, indeed, might have been expected; for, as natural
selection acts through one form having some advantage over other
forms in the strugjii^ie for existence, it will chiefiy act on those
T/hich already have some advantage; and the largeness of any
ij-roup shows that it;s si)ecies have inherited from a common an-
fp-sror some advanL.i.t-e in common. Ilcnce, the struggle for the
production of new and modified descendants will mainly lie be-
tween the larger groups which are all trying to increase in num-
ber. One large group will slowly conquer another large group,
reduce its numbers, and thus lessen its chance of further varia-
tion and improvement. Within the same large group, the later and
more highly perfected sub-groups, from branching out and seiz-
ing on many new places in the polity of Nature, will constantly
tend to supplant and destroy the earlier and less improved sub-
groups. Small and broken groups and sub-groups will finally dis-
appear. Looking to the future, we can predict that the groups of
organic beings which are now large and triumphant, and whic'i
are least broken up, that is, which have as yet suffered least ex-
tinction, will, for a long period, continue to increase. But wliie!i
groups will ultimately prevail, no man can predict; for we know
that many groups formerly most extensively developed, have now
become extinct. Looking still more remotely to the future, we
may predict that, owing to the continued and steady increase of
the larger groups, a multitude of smaller groups will become ut-
terly extinct, and leave no modified descendants; and consequently
that, of the species living at any one period, extremely few will
transmit descendants to a remote futurity. I shall have to re-
turn to this subject in the chapter on Classification, but I may
add that as, according to this view, extremely few of the more
ancient species have transmitted descendants to the present day.
and, as all the descendants of the same species form a class, we

I

NATURAL SELECTION, ETC. 07

can understand how it is that there exist so few classes in each
main division of the animal and vegetable kingdoms. Although
few of the most ancient species have left modified descendants, yet,
at remote geological periods, the earth may have been almost as
well peopled with species of many genera, families, orders, and
classes, as at the present time.

On the Degree to which Organisation tends to advance.

Natural Selection acts exclusively by the preservation and ac-
cumulation of variations, which are beneficial under the organic and
inorganic conditions to which each creature is exposed at all pe-
riods of life. The ultimate result is that each creature tends to
become more and more improved in relation to its conditions. This
improvement inevitably leads to the gradual advancement of the
organisation of the greater number of living beings throughout
the world. But here we enter on a very intricate subject, for nat-
uralists have not defined to each other's satisfaction what is meant
by an advance in organisation. Amongst the vertebrata the de-
gree of intellect and an approach in structure to luan clearly come
into play. It might be thought that the amount of change which
the various parts and organs pass through in their development
from the embryo to maturity would suffice as a standard of com-
parison; but there are cases, as with certain parasitic crustaceans,
in which several parts of the structure become less perfect, so
that the mature animal cannot be called higher than its larva.
Von Baer's standard seems the most widely applicable and the best,
namely, the amount of differentiation of the parts of the same
organic being, in the adult state as I should be inclined to add,
and their specialisation for different functions; or, as Milne Ed-
wards would express it, the completeness of the division of physio-
logical labour. But we shall see how obscure this subject is if we
look, for instance, to fishes, amongst which some naturalists rank
those as highest which, like the sharks, approach nearest to amphib-
ians; whilst other naturalists rank the common bony or teleostean
fishes as the highest, inasmuch as they are most strictly fish-like,
and differ most from the other vertebrate classes. We see still
more plainly the obscurity of the subject by turning to plants,
amongst which the standard of intellect is of course quite ex-
cluded ; and here some botanists rank those plants as highest which
have every organ, as sepals, petals, stamens, and pistils, fully de-
veloped in each flower ; whereas other botanists, probably with more
truth, look at the plants which have their several organs much
modified and reduced in number as the highest.

98 ORIGIN OF SPECIES

If we take as the standard of high organisation, the amount of
differentiation and specialisation of the several organs in each be-
ing when adult (and this will include the advancement of the brain
for intellectual purposes), natural selection clearly leads towards
this standard : for all physiologists admit that the specialisation of
organs, inasmuch as in this state they perform their functions
better, is an advantage to each being; and hence the accumulation
of variations tending towards specialisation is within the scope of
natural selection. On the other hand, we can see, bearing in mind
that all organic beings are striving, to increase at a high ratio and
to seize on every unoccupied or less well occupied place in the
economy of nature, that it is quite possible for natural selection
gradually to fit a being to a situation in which several organs
would be superfluous or useless : in such cases there would be retro-
gression in the scale of organisation. Whether organisation on
the whole has actually advanced from the remotest geological
periods to the present day will be more conveniently discussed in
our chapter on Geological Succession.

But it may be objected that if all organic beings thus tend to
rise in the scale, how is it that throughout the world a multitude
of the lowest forms still exist; and how is it that in each great
class some forms are far more highly developed than others ? Why
have not the more highly developed forms everywhere supplanted
and exterminated the lower? Lamarck, who believed in an innate
and inevitable tendency towards perfection in all organic beings,
seems to have felt this difficulty so strongly, that he was led to
suppose that new and simple forms are continually being produced
by spontaneous generation. Science has not as yet proved the
truth of this belief, whatever the future may reveal. On our
theory the continued existence of lowly organisms offers no diffi-
culty; for natural selection, or the survival of the fittest, does
not necessarily include progressive development — it only takes
advantage of such variations as arise and are beneficial to each
creature under its complex relations of life. And it may be asked
what advantage, as far as we can see, would it be to an infusorian
animalcule — to an intestinal worm — or even to an earthworm,
to be highly organised. If it were no advantage, these forms would
be left, by natural selection, unimproved or but little improved,
and might remain for indefinite ages in their present lowly con-
dition. And geology tells us that some of the lowest forms, as the
infusoria and rhizopods, have remained for an enormous period
in nearly their present state. But to suppose that most of the many
now existing low forms have not in the least advanced since the
first dawn of life would be extremely rash; for every naturalist

NATURAL SELECTION, ETC. 99

who has dissected some of the beings now ranked as very low in
the scale, must have been struck with their really wondrous and
beautiful organisation.

Nearly the same remarks are applicable if we look to the differ-
ent grades of organisation within the same great group; for in-
stance, in the vertebrata, to the co-existence of mammals and fish
— amongst mammalia, to the co-existence of man and the ornitho-
rhynchus — amongst fishes, to the co-existence of the shark and the
lancelet (Amphioxus), which latter fish in the extreme simplicity
of its structure approaches the invertebrate classes. But mam-
mals and fish hardly come into competition with each other; the
advancement of the whole class of mammals, or of certain mem-
bers in this class, to the highest grade would not lead to their
taking the place of fishes. Physiologists believe that the brain
must be bathed by warm blood to be highly active, and this re-
quires aerial respiration; so that warm-blooded mammals when
inhabiting the water lie under a disadvantage in having to come
continually to the surface to breathe. With fishes, members of the
shark family would not tend to supplant the lancelet ; for the lance-
let, as I hear from Fritz Miiller, has as sole companion and com-
petitor on the barren sandy shore of South Brazil, an anomalous
annelid. The three lowest orders of mammals, namely, marsupials,
edentata, and rodents, co-exist in South America in the same region
with numerous monkeys, and probably interfere little with each
other. Although organisation, on the whole, may have advanced
and be still advancing throughout the world, yet the scale will al-
ways present many degrees of perfection; for the high advancement
of certain whole classes, or of certain members of each class, does
not at all necessarily lead to the extinction of those groups with
which they do not enter into close competition. In some cases,
as we shall hereafter see, lowly organised forms appear to have
been preserved to the present day, from inhabiting confined or pe-
culiar stations, where they have been subjected to less severe com-
petition, and where their scanty numbers have retarded the chance
of favourable variations arising.

Finally, I believe that many lowly organised forms now exist
throughout the world, from various causes. In some cases varia-
tions or individual differences of a favourable nature may never
have arisen for natural selection to act on and accumulate. In no
case, probably, has time sufficed for the utmost possible amount of
development. In some few cases there has been what we must call
retrogression of organisation. But the main cause lies in the fact
that under very simple conditions of life a high organisation
would be of no service, — possibly would be of actual disservice, as

100 ORIGIN OF SPECIES

being of a more delicate nature, and more liable to be put out of
order and injured.

Looking- to the first dawn of life, when all organic beings, as
we may believe, presented the simplest structure, how, it has been
asked, could the first steps in the advancement or difi'erentiation
of parts have arisen? Mr. Herbert Spencer would probably an-
swer that, as soon as simple unicellular organism came by growth
or division to be compounded of several cells, or became attached
to any supporting surface, his law " that homologous units of any
order become differentiated in proportion as their relations to in-
cident forces become different " would come into action. But as
we have no facts to guide us, speculation on the subject is almost
useless. It is, however, an error to suppose that there would be
no struggle for existence, and, consequently, no natural selection,
until many forms had been produced : variations in a single species
inhabiting an isolated station might be beneficial, and thus the
whole mass of individuals might be modified, or two distinct forms
might arise. But, as I remarked towards the close of the Intro-
duction, no one ought to feel surprise at much remaining as yet
unexplained on the origin of species, if we make due allowance
for our profound ignorance on the mutual relations of the inhabi-
tants of the world at the present time, and still more so during
past ages.

Convergence of Character,

Mr. H. C. Watson thinks that I have overrated the importance
of divergence of character (in which, however, he apparently be-
lieves), and that convergence, as it may be called, has likewise
l)layed a part. If two species, belonging to two distinct though
allied genera, had both produced a large number of new and
divergent forms, it is conceivable that these might approach each
other so closely that they would have all to be classed under the
same genus; and thus the descendants of two distinct genera
would converge into one. But it would in most cases be ex-
tremely rash to attribute to convergence a close and general simi-
larity of structure in the modified descendants of widely distinct
forms. The shape of a crystal is determined solely by the molec-
ular forces, and it is not surprising that dissimilar substances
should sometimes assume the same form; but with organic beings
we should bear in mind that the form of each depends on an
infinitude of complex relations, namely on the variations which
have arisen, these being due to causes far too intricate to be fol-
lowed out, — on the nature of the variations which have been pre-

NATURAL SELECTION, ETC. 101

served or selected, and this depends on the surrounding physical
conditions, and in a still higher degree on the surrounding organ-
isms with which each being has come into competition, — and
lastly, on inheritance (in itself a fluctuating element) from in-
numerable progenitors, all of which have had their forms deter-
mined through equally complex relations. It is incredible that
the descendants of two organisms, which had originally differed in
a marked manner, should ever afterwards converge so closely as to
lead to a near approach to identity throughout their whole or-
ganisation. If this had occurred, we should meet with the same
form, independently of genetic connection, recurring in widely
separated geological formations; and the balance of evidence is
opposed to any such an admission.

Mr. Watson has also objected that the continued action of nat-
ural selection, together with divergence of character, would tend
to make an indefinite number of specific forms. As far as mere
inorganic conditions are concerned, it seems probable that a suffi-
cient number of species v/ould soon become adapted to all consid-
erable diversities of heat, moisture, &c. ; but I fully admit that the
mutual relations of organic beings are more important ; and as the
number of species in any country goes on increasing, the organic
conditions of life must become more and more complex. Conse-
quently there seems at first sight no limit to the amount of profit-
able diversification of structure, and therefore no limit to the
number of species which might be produced. We do not know
that even the most prolific area is fully stocked with specific
forms: at the Cape of Good Hope and in Australia, which sup-
port such an astonishing number of species, many European plants
have become naturalised. But geology shows us, that from an
early part of the tertiary period the number of species of shells,
and that from the middle part of this same period the number
of mammals, has not greatly or at all increased. What then
checks an indefinite increase in the number of species? The
amount of life (I do not mean the number of specific forms) sup-
ported on an area must have a limit, depending so largely as it does
on physical conditions; therefore, if an area be inhabited by very
many species, each or nearly each species will be represented by
few individuals; and such species will be liable to extermination
from accidental fluctuations in the nature of the seasons or in the
number of their enemies. The process of extermination in such
cases would be rapid, whereas the production of new species must
always be slow. Imagine the extreme case of as many species as
individuals in England, and the first severe winter or very dry
summer would exterminate thousands on thousands of species.

102 ORIGIN OF SPECIES

Rare species, and each species will become rare if the number of
species in any country becomes indefinitely increased, will, on
the principle often explained, present within a given period few
favourable variations; consequently, the process of giving birth to
new specific forms would thus be retarded. When any species be-
comes very rare, close interbreeding will help to exterminate it;
authors have thought that this comes into play in accounting for
the deterioration of the Aurochs in Lithuania, of Ked Deer in
Scotland, and of Bears in Norway, &c. Lastly, and this I am in-
clined to think is the most important element, a dominant species,
which has already beaten many competitors in its own home, will
tend to spread and supplant many others. Alph. de Candolle has
shown that those species which spread widely, tend generally to
spread very widely; consequently, they will tend to supplant and
exterminate several species in several areas, and thus check the
inordinate increase of specific forms throughout the world. Dr.
Hooker has recently shown that in the S.E. corner of Australia,
where, apparently, there are many invaders from different quar-
ters of the globe, the endemic Australian species have been greatly
reduced in number. How much weight to attribute to these sev-
eral considerations I will not pretend to say; but conjointly they
must limit in each country the tendency to an indefinite aug-
mentation of specific forms.

Summary of Chapter,

If under changing conditions of life organic beings present in-
dividual differences in almost every part of their structure, and
this cannot be disputed; if there be, owing to their geometrical
rate of increase, a severe struggle for life at some age, season, or
year, and this certainly cannot be disputed; then, considering the
infinite complexity of the relations of all organic beings to each
otlier and to their conditions of life, causing an infinite diversity
in structure, constitution, and habits, to be advantageous to them,
it would be a most extraordinary fact if no variations had ever
occurred useful to each being's own welfare, in the same manner
as so many variations have occurred useful to man. But if varia-
tions useful to any organic being ever do occur, assuredly indi-
viduals thus characterised will have the best chance of being
preserved in the struggle for life; and from the strong principle
of inheritance, these will tend to produce offspring similarly char-
acterised. This principle of preservation, or the survival of the
fittest, I have called Natural Selection. It leads to the improve-
ment of each creature in relation to its organic and inorganic con-

NATURAL SELECTION, ETC. 103

ditions of life; and consequently, in most cases, to what must be
regarded as an advance in organisation. Nevertheless, low and
simple forms will long endure if well fitted for their simple con-
ditions of life.

Natural selection, on the principle of qualities being inherited
at corresponding ages, can modify the egg, seed, or young, as
easily as the adult. Amongst many animals, sexual selection will
have given its aid to ordinary selection, by assuring to the most
vigorous and best adapted males the greatest number of offspring.
Sexual selection will also give characters useful to the males
alone, in their struggles or rivalry with other males; and these
characters will be transmitted to one sex or to both sexes, accord-
ing to the form of inheritance which prevails.

Whether natural selection has really thus acted in adapting the
various forms of life to their several conditions and stations, must
be judged by the general tenor and balance of evidence given in
the following chapters. But we have already seen how it entails
extinction; and how largely extinction has acted in the world's
history, geology plainly declares. Natural selection, also, leads
to divergence of character; for the more organic beings diverge
in structure, habits, and constitution, by so much the more can a
large number be supported on the area, — of which we see proof by
looking to the inhabitants of any small spot, and to the produc-
tions naturalised in foreign lands. Therefore, during the modi-
fication of the descendants of any one species, and during the
incessant struggle of all species to increase in numbers, the more
diversified the descendants become, the better will be their chance
of success in the battle for life. Thus the small differences distin-
guishing varieties of the same species, steadily tend to increase,
till they equal the greater differences between species of the same
genus, or even of distinct genera.

We have seen that it is the common, the widely-diffused and
widely-ranging species, belonging to the larger genera within each
class, which vary most; and these tend to transmit to their modi-
fied offspring that superiority which nOw makes them dominant
in their own countries. Natural selection, as has just been re-
marked, leads to divergence of character and to much extinction
of the less improved and intermediate forms of life. On these
principles, the nature of the affinities, and the generally well-
defined distinctions between the innumerable organic beings in
each class throughout the world, may be explained. It is a truly
wonderful fact — the wonder of which we are apt to overlook from
familiarity — that all animals and all plants throughout all time
and space should be related to each other in groups, subordinate

104 ORIGIN OF SPECIES

to groups, in the manner whicli we everywhere behold — namely,
varieties of the same species most closely related, species of the
same genus less closely and unequally related, forming sections
and sub-genera, species of distinct genera much less closely re-
lated, and genera related in different degrees, forming sub-fami-
lies, families, orders, sub-classes and classes. The several subor-
dinate groups in any class cannot be ranked in a single file, but
seem clustered round points, and these round other points, and so
on in almost endless cycles. If species had been independently
created, no explanation would have been possible of this kind of
classification; but it is explained through inheritance and the
complex action of natural selection, entailing extinction and di-
vergence of character, as we have seen illustrated in the diagram.

The afiinities of all the beings of the same class have sometimes
been represented by a great tree. I believe this simile largely
speaks the truth. The green and budding twigs may represent
existing species; and those produced during former years may
represent the long succession of extinct species. At each period
of growth all the growing twigs have tried to branch out on all
sides, and to overtop and kill the surrounding twigs and branches,
in the same manner as species and groups of species have at all
times overmastered other species in the great battle for life. The
limbs divided into great branches, and these into lesser and lesser
branches, were themselves once, when the tree was young, budding
twigs; and this connection of the former and present buds by
ramifying branches may well represent the classification of all
extinct and living species in groups subordinate to groups. Of the
many twigs which flourished when the tree was a mere bush, only
two or three, now grown into great branches, yet survive and bear
the other branches; so with the species which lived during long-
past geological periods, very few have left living and modified
descendants. From the first growth of the tree, many a limb and
branch has decayed and dropped off; and these fallen branches of
various sizes may represent those whole orders, families, and
genera which have now no living representatives, and which ar/*
known to us only in a fossil state. As we here and there set a
thin straggling branch springing from a fork low down in a tree,
and which by some chance has been favoured and is still alive on
its summit, so we occasionally see an animal like the Ornitho-
rhynchus or Lepidosiren, which in some small degree connects by
its afiinities two large branches of life, and which has apparently
been saved from fatal competition by having inhabited a pro-
tected station. As buds give rise by growth to fresh buds, and
these, if vigorous, branch out and overtop on all sides many a

NATURAL SELECTION, ETC. 105

feebler oranch, so by generation I believe it lias been with the
great Tree of Life, which fills with its dead and broken branches
the cnist of the earth, and covers the surface with its ever-branch-
ing and beautiful ramifications.

106 ORIGIN OF SPECIES

CHAPTER Y.

LAWS OF VARIATION.

Effects of changed conditions — Use and disuse, combined with natural
selection ; organs of flight and of vision — Acclimatisation — Correlated
variation — Compensation and economj^ 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 sexral characters
variable — Species of the same genus vary in an analogous manner

— Reversions to long-lost characters — Summary.

1HAVE hitherto sometimes spoken as if tlie variations — so com-
mon and multiform with organic beings under domestication,
and in a lesser degree with those Tuider nature — were due to
chance. This, of course, is a wholly incorrect exi^ression, but it
serves to acknowledge plainly our ignorance of the cause of each
particular variation. Some authors believe it to be as much the
function of the reproductive system to produce individual diifer-
ences, or slight deviations of structure, as to make the child like
its parents. But the fact of variations and monstrosities occurring
much more frequently under domestication than under nature, and
the greater variability of species having wide ranges than of
those with restricted ranges, lead to the conclusion that variability
is generally related to the conditions of life to which each species
has been exposed during several successive generations. In the
first chapter I attempted to show that changed conditions act in
two ways, directly on the whole organisation or on certain parts
alone, and indirectly through the reproductive system. In all cases
there are two factors, the nature of the organism, which is much
the most important of the two, and the nature of the conditions.
The direct action of changed conditions leads to definite or in-
definite results. In the latter case the organisation seems to
become plastic, and we have much fluctuating variability. In the
former case the nature of the organism is such that it yields read-
ily, when subjected to certain conditions, and all, or nearly all
the individuals become modified in the same way.

It is very difficult to decide how far changed conditions, such
as of climate, food, &c., have acted in a definite manner. There

LAWS OF VARIATION 107

is reason to believe that in the course of time the effects have
been greater than can be proved by clear evidence. But we may
safely conclude that the innumerable complex co-adaptations of
structure, which we see throughout nature between various organic
beings, cannot be attributed simply to such action. In the fol-
lowing cases the conditions seem to have produced some slight
definite effect: E. Forbes asserts that shells at their southern
limit, and when living in shallow water, are more brightly coloured
than those of the same species from further north or from a
greater depth; but this certainly does not always hold good. Mr.
Gould believes that birds of the same species are more brightly
coloured under a clear atmosphere, than when living near the
coast or on islands, and Wollaston is convinced that residence
near the sea affects the colours of insects. Moquin-Tandon gives
a list of plants which, when growing near the sea-shore, have their
leaves in some degree fleshy, though not elsewhere fleshy. These
slightly varying organisms are interesting in as far as they present
characters analogous to those possessed by the species which are
confined to similar conditions.

When a variation is of the slightest use to any being, we cannot
tell how much to attribute to the accumulative action of natural
selection, and how much to the definite action of the conditions
of life. Thus, it is well known to furriers that animals of the
same species have thicker and better fur the further north they
live; but who can tell how much of this difference may be due
to the warmest-clad individuals having been favoured and pre-
served during many generations, and how much to the action of
the severe climate? for it would appear that climate has some
direct action on the hair of our domestic quadrupeds.

Instances could be given of similar varieties being produced
from the same species under external conditions of life as differ-
ent as can well be conceived; and, on the other hand, of dissimilar
varieties being produced under apparently the same external con-
ditions. Again, innumerable instances are known to every nat-
uralist, of species keeping true, or not varying at all, although
living under the most opposite climates. Such considerations as
these incline me to lay less weight on the direct action of the sur-
rounding conditions, than on a tendency to vary, due to causes of
which we are quite ignorant.

In one sense the conditions of life may be said, not only to cause
variability, either directly or indirectly, but likewise to include
natural selection, for the conditions determine whether this or that
variety shall survive. But when man is the selecting agent, we
clearly see that the two elements of change are distinct; varia-

108 ORIGIN OF SPECIES

bility is in some manner excited, but it is the will of man which
accumulates the variations in certain directions; and it is this
latter agency which answers to the survival of the fittest under
nature.

Eifects of the increased Use and Disuse of Parts, as controlled hy

Natural Selection.

From the facts alluded to in the first chapter, I think there can
be no doubt that use in our domestic animals has strengthened and
enlarged certain parts, and disuse diminished them ; and that such
modifications are inherited. Under free nature, we have no
standard of comparison, by which to judge of the effects of long-
continued use or disuse, for we know not the parent-forms ; but
many animals possess structures which can be best explained by
the effects of disuse. As Professor Owen has remarked, there is
no greater anomaly in nature than a bird that cannot fly; yet
there are several in this state. The logger-headed duck of South
America can only flap along the surface of the water, and has its
wings in nearly the same condition as the domestic Aylesbury
duck: it is a remarkable fact that the young birds, according to
Mr. Cunningham, can fly, while the adults have lost this power.
As the larger ground-feeding birds seldom take flight except to
escape danger, it is probable that the nearly wingless condition
of several birds, now inhabiting or which lately inhabited several
oceanic islands, tenanted by no beast of prey, has been caused by
disuse. The ostrich indeed inhabits continents, and is exposed to
danger from which it cannot escape by flight, but it can defend
itself by kicking its enemies, as efiiciently as many quadrupeds.
We may believe that the progenitor of the ostrich genus had
habits like those of the bustard, and that, as the size and weight
of its body were increased during successive generations, its legs
were used more, and its wings less, until they became incapable of
flight.

Kirby has remarked (and I have observed the same fact) that
the anterior tarsi, or feet, of many male dung-feeding beetles are
often broken off; he examined seventeen specimens in his own
collection, and not one had even a relic left. In the Onites
apelles the tarsi are so habitually lost, that the insect has been
described as not having them. In some other genera they are
present, but in a rudimentary condition. In the Ateuchus or
sacred beetle of the Egyptians, they are totally deficient. The
evidence that accidental mutilations can be inherited is at present
not decisive; but the remarkable cases observed by Brown-Sequara

LAWS OF VARIATION 100

in guinea-pigs, of the inherited effects of operations, should make
us cautious in denying this tendency. Hence it will perhaps be
safest to look at the entire absence of the anterior tarsi in Ateu-
chus, and their rudimentary condition in some other genera, not
as cases of inherited mutilations, but as due to the effects of long-
continued disuse; for as many dung-feeding beetles are generally
found with their tarsi lost, this must happen early in life; there-
fore the tarsi cannot be of much importance or be much used by
these insects.

In some cases we might easily put down to disuse modifications
of structure which are wholly, or mainly, due to natural selec-
tion. Mr. Wollaston has discovered the remarkable fact that 200
beetles, out of the 550 species (but more are now known) in-
habiting Madeira, are go far deficient in wings that they cannot
fly; and that, of the twenty-nine endemic genera, no less than
twenty-three have all their species in this condition ! Several
facts, — namely, that beetles in many parts of the world are fre-
quently blown to sea and perish; that the beetles in Madeira, as
observed by Mr. Wollaston, lie much concealed, until the wind
lulls and the sun shines ; that the proportion of wingless beetles is
larger on the exposed Desertas than in Madeira itself; and espe-
cially the extraordinary fact, so strongly insisted on by Mr.
Wollaston, that certain large groups of beetles, elsewhere exces-
sively numerous, which absolutely require the use of their wings,
are here almost entirely absent ; — these several considerations
make me believe that the wingless condition of so many Madeira
beetles is mainly due to the action of natural selection, combined
probably with disuse. For during many successive generations
each individual beetle which flew least, either from its wings hav-
ing been ever so little less perfectly developed or from indolent
habit, will have had the best chance of surviving from not being
blown out to sea ; and, on the other hand, those beetles which most
readily took to flight would oftenest have been blown to sea, and
thus destroyed.

The insects in Madeira which are not ground-feeders, and
which, as certain flower-feeding coleoptera and lepidoptera, must
habitually use their wings to gain their subsistence, have, as Mr.
Wollaston suspects, their v^ings not at all reduced, but even en-
larged. This is quite compatible with the action of natural selec-
tion. For when a new insect first arrived on the island, the
tendency of natural selection to enlarge or to reduce the wings,
would depend on whether a greater number of individuals were
saved by successfully battling with the winds, or by giving up the
attempt and rarely or never flying. As with mariners shipwrecked

no ORIGIN OF SPECIES

near a coast, it would have been better for the good swimmers if
they had been able to swim still further, whereas it would have
been better for the bad swimmers if they had not been able to swim
at all and had stuck to the wreck.

The eyes of moles and some burrowing rodents are rudimen-
tary in size, and in some cases are quite covered by skin and fur.
This state of the eyes is probably due to gradual reduction from
disuse, but aided perhaps by natural selection. In South Amer-
ica, a burrowing rodent, the tuco-tuco, or Ctenomys, is even more
subterranean in its habits than the mole; and I was assured by a
Spaniard, who had often caught them, that they were frequently
blind. One which I kept alive was certainly in this condition, the
cause, as appeared on dissection, having been inflammation of the
nictitating membrane. As frequent inflammation of the eyes must
be injurious to any animal, and as eyes are certainly not necessary
to animals having subterranean habits, a reduction in their size,
with the adhesion of the eyelids and growth of fur over them,
might in such case be an advantage; and if so, natural selection
would aid the effects of disuse.

It is well known that several animals, belonging to the most
different classes, which inhabit the caves of Carniola and of Ken-
tucky, are blind. In some of the crabs the foot-stalk for the
eye remains, though the eye is gone ; — the stand for the telescope
is there, though the telescope with its glasses has been lost. As
it is difficult to imagine that eyes, though useless, could be in any
way injurious to animals living in darkness, their loss may be
attributed to disuse. In one of the blind animals, namely, the
cave-rat (Neotoma), two of which were captured by Professor
Silliman at above half a mile distance from the mouth of the
cave, and therefore not in the profoundest depths, the eyes were
lustrous and of large size; and these animals, as I am informed
by Professor Silliman, after having been exposed for about a
month to a graduated light, acquired a dim perception of objects.

It is difficult to imagine conditions of life more similar than
deep limestone caverns under a nearly similar climate; so that, in
accordance with the old view of the blind animals having been
separately created for the American and European caverns, very
close similarity in their organisation and affinities might have
been expected. This is certainly not the case if we look at the
two whole faunas; and with respect to the insects alone, Schiodte
has remarked, " We are accordingly prevented from considering
the entire phenomenon in any other light than something purely
local, and the similarity which is exhibited in a few forms be-
tween the Mammoth cave (in Kentucky) and the caves in Car-

LAWS OF VARIATION 111

iiiola, otherwise than as a very phiiii expression of that analogy
which subsists generally between the fauna of Europe and of
North America/' On my view we must suppose that American
animals, having in most cases ordinary powers of vision, slowly
migrated by successive generations from the outer world into the
deeper and deeper recesses of the Kentucky caves, as did European
animals into the caves of Europe. We have some evidence of this
gradation of habit ; for, as Schiodte remarks, " We accordingly
look upon the subterranean faunas as small ramifications which
have penetrated into the earth from the geographically limited
faunas of the adjacent tracts, and which, as they extended them-
selves into darkness, have been accommodated to surrounding cir-
cumstances. Animals not far remote from ordinary forms, prepare
the transition from light to darkness. Next follow those that are
constructed for twilight; and, last of all, those destined for total
darkness, and whose formation is quite peculiar." These remarks
of Schiodte's, it should be understood, apply not to the same, but
to distinct species. By the time that an animal had reached,
after numberless generations, the deepest recesses, disuse will on
this view have more or less perfectly obliterated its eyes, and
natural selection will often have effected other changes, such as
an increase in the length of the antennae or palpi, as a compensa-
tion for blindness. Notwithstanding such modifications, we might
expect still to see in the cave-animals of America, afiinities to the
other inhabitants of that continent, and in those of Europe to the
inhabitants of the European continent. And this is the case with
some of the American cave-animals, as I hear from Professor
Dana; and some of the European cave-insects are very closely al-
lied to those of the surrounding country. It would be difficult to
give any rational explanation of the affinities of the blind cave-
animals to the other inhabitants of the two continents on the
ordinary view of their independent creation. That several of the
inhabitants of the caves of the Old and New Worlds should be
closely related, we might expect from the well-known relationship
of most of their other productions. As a blind species of Bathy-
scia is found in abundance on shady rocks far from caves, the
loss of vision in the cave-species of this one genus has probably
had no relation to its dark habitation ; for it is natural that an
insect already deprived of vision should readily become adapted to
dark caverns. Another blind genus (Anophthalmus) offers this
remarkable peculiarity, that the species, as Mr. Murray observes,
have not as yet been found anywhere except in caves; yet those
which inhabit the several caves of Europe and America are dis-
tinct; but it is possible that the progenitors of these several

112 ORIGIN OF SPECIES

species, whilst they were furnished with eyes, may formerly have
ranged over both continents, and then have become extinct, ex-
cepting in their present secluded abodes. Far from feeling sur-
prise that some of the cave-animals should be very anomalous, as
Agassiz has remarked in regard to the blind fish, the Amblyopsis,
and as is the case with the blind Proteus with reference to the
reptiles of Europe, I am only surprised that more wrecks of an-
cient life have not been preserved, owing to the less severe com-
petition to which the scanty inhabitants of these dark abodes will
have been exposed.

Acclimatisation.

Habit is hereditary with plants, as in the period of flowering, in
the time of sleep, in the amount of rain requisite for seeds to
germinate, &c., and this leads me to say a few words on ac-
climatisation. As it is extremely common for distinct species
belonging to the same genus to inhabit hot and cold countries, if
it be true that all the species of the same genus are descended
from a single parent-form, acclimatisation must be readily effected
during a long course of descent. It is notorious that each species
is adapted to the climate of its own home: species from an arctic
or even from a temperate region cannot endure a tropical climate,
or conversely. So again, many succulent plants cannot endure a
damp climate. But the degree of adaptation of species to the
climates under which they live is often overrated. We may infer
this from our frequent inability to predict whether or not an im-
ported plant will endure our climate, and from the number of
plants and animals brought from different countries which are
here perfectly healthy. "We have reason to believe that species in
a state of nature are closely limited in their ranges by the com-
petition of other organic beings quite as much as, or more than,
by adaptation to particular climates. But whether or not this
adaptation is in most cases very close, we have evidence with some
few plants, of their becoming, to a certain extent, naturally
habituated to different temperatures; that is, they become ac-
climatised: thus the pines and rhododendrons, raised from seed
collected by Dr. Hooker from the same species growing at differ-
ent heights on the Himalaya, were found to possess in this country
different constitutional powers of resisting cold. Mr. Thwaites in-
forms me that he has observed similar facts in Ceylon ; analogous
observations have been made by Mr. H. C. Watson on European
species of plants brought from the Azores to England ; and I could
give other cases. In regard to animals, several authentic instances

LAWS OF VARIATION 113

could be adduced of species having largely extended, within his-
torical times, their range from warmer to cooler latitudes, and
conversely; but we do not positively know that these animals were
strictly adapted to their native climate, though in all ordinary
cases we assume such to be the case; nor do we Imow that they
have subsequently become specially acclimatised to their new
homes, so as to be better fitted for them than they were at first.

As w^e may infer that our domestic animals were originally
chosen by uncivilised man because they were useful and because
they bred readily under confinement, and not because they were
subsequently found capable of far-extended transportation, the
common and extraordinary capacity in our domestic animals of
not only withstanding the most different climates, but of being
perfectly fertile (a far severer test) under them, may be used as
an argument that a large proportion of other animals now in a
state of nature could easily be brought to bear widely different cli-
mates. We must not, however, push the foregoing" argument too
far, on account of the probable origin of some of our domestic
animals from several wild stocks; the blood, for instance, of a
tropical and arctic wolf may perhaps be mingled in our domestic
breeds. The rat and mouse cannot be considered as domestic ani-
mals, but they have been transported by man to many parts of the
world, and now have a far wider range than any other rodent ; for
they live under the cold climate of Faroe in the north and of the
Falklands in the south, and on many an island in the torrid zones.
Ilence adaptation to any special climate may be looked at as a
quality readily grafted on an innate wide flexibility of constitu-
tion, common to most animals. On this view, the capacity of
enduring the most different climates by man himself and by his
domestic animals, and the fact of the extinct elephant and rhinoc-
eros having formerly endured a glacial climate, whereas the living
species are now all tropical or sub-tropical in their habits, ought
not to be looked at as anomalies, but as examples of a very com-
mon flexibility of constitution, brought, under peculiar circum-
stances, into action.

How much of the acclimatisation of species to any peculiar cli-
mate is due to mere habit, and how much to the natural selection
of varieties having different innate constitutions, and how much
to both means combined, is an obscure question. That habit or
custom has some influence, I must believe, both from analogy and
from the incessant advice given in agricultural works, even in the
ancient Encyclopaedias of China, to be very cautious in transport-
ing animals from one district to another. And as it is not likely
that man should have succeeded in selecting so many breeds and

114 ORIGIN OF SPECIES

sub-breeds with constitutions specially fitted for their own dis-
tricts, the result must, I think, be due to habit. On the other
hand, natural selection would inevitably tend to preserve those in-
dividuals which were born with constitutions best adapted to any
country which they inhabited. In treatises on many kinds of
cultivated plants, certain varieties are said to withstand certain
climates better than others; this is strikingly shown in works on
fruit-trees published in the United States, in which certain varie-
ties are habitually recommended for the northern and others for
the southern States; and as most of these varieties are of recent
origin, they cannot owe their constitutional differences to habit.
The case of the Jerusalem artichoke, which is never propagated
in England by seed, and of which consequently new varieties have
not been produced, has even been advanced, as proving that ac-
climatisation cannot be effected, for it is novv^ as tender as ever it
was! The case, also, of the kidney-bean has been often cited for
a similar purpose, and with much greater weight ; but until some-
one will sow, during a score of generations, his kidney-beans so
early that a very large proportion are destroyed by frost, and then
collect seed from the few survivors, with care to prevent acci-
dental crosses, and then again get seed from these seedlings, with
the same precautions, the experiment cannot be said to have been
tried. Nor let it be supposed that differences in the constitution
of seedling kidney-beans never appear, for an account has been
published how much more hardy some seedlings are than others;
and of this fact I have myself observed striking instances.

On the whole, we may conclude that habit, or use and disuse,
have, in some cases, played a considerable part in the modification
of the constitution and structure; but that the effects have often
been largely combined with, and sometimes overmastered by, the
natural selection of innate variations.

Correlated Variation,

I mean by this expression that the whole organisation is so
tied together during its growth and development, that when slight
variations in any one part occur, and are accumulated through
natural selection, other parts become modified. This is a very
important subject, most imperfectly understood, and no doubt
wholly different classes of facts may be here easily confounded
together. We shall presently see that simple inheritance often
gives the false appearance of correlation. One of the most obvi-
ous real cases is, that variations of structure arising in the young
or larvae naturally tend to affect the structure of the mature

DAWS OF VAIUATION "5

ar.;mal. The several parts of the body -l^i^^'no'TlTnltTueture^
which, at an early embryomc period, are 'd«"*'^«^^ ;^. ^*™"^^*^,'^
and which are necessarily exposed to similar ««"di tions seem
eminently liable to vary in a like manner: -'l'^^^''^^^^;.
rio-ht and left sides of the body varying m the same manner,
Ci" he fron and hind legs, and even in the jaws and 1-bs varying

o<4ther for the lower jaw is believed by some ^/^tomists to be
horaolooous with the limbs. These tendencies, I do not doubt,
Sr^rstered more or 1- — -1. '^^^^l^jX
Lj"ft,-f S\r oTty' gtaVr tf the bU it might
nrobably have been rendered permanent by selection.
'Homologous parts, as has been remarked ^^ -^ ^ J^^;,* ^J
to cohere- this is often seen in monstrous plants, and nothing
Tore c'ommon than the union of homologous Pfs in norm

tructures. as in the union of thepetals mo a tube Hard parts

So^Zr inLnces .y P— ^^^^^

L^et :i swi^ilSfminf ;he position and form of several

of the most important viscera. ., , ^ ivT T«

irlVtte ^uter ^o^,. or between the presence o mo.e orjess

'r Z ?sVur^e'ragJn"«laS^^^^^^^ *^ ^-%-^
^et'h th natd^TuSisirdog, though here no doubt homology
comes into'play? With respect to this latter -- of -re U tio"
T think it can hardly be accidental, that the two orders oi
Lmm'ls which are most abnormal in their dermal covering, viz.,
OptTc^a (whales) and Edentata (armadilloes. scaly ant-eaters,
STre SS on the whole the --bnonnal in their .ej;
but there are so many exceptions to this rule, as
Vinq remarked, that it has little value. , . ^ ^f +1,^

1 know of no case better adapted to show t^^^ |™Pf ^"f,?. f *^
laws of correlation and variation, independently of utility and

116 ORIGIxX OF SPECIES

therefore of natural selection, than that of the difference bctvv^een
the outer and inner flowers in some Compositous and Umbellif-
erous plants. Every one is familiar with the difference between
the ray and central florets of, for instance, the daisy, and this
difference is often accompanied with the partial or complete
abortion of the reproductive organs. But in some of these plants,
the seeds also differ in shape and structure. These differences
have sometimes been attributed to the pressure of the involucra
on the florets, or to their mutual pressure, and the shape of the
seeds in the ray-florets of some Compositae countenances this idea;
but with the Umbelliferse, it is by no means, as Dr. Hooker
informs me, the species with the densest heads which most fre-
quently differ in their inner and outer flowers. It might have
been thought that the development of the ray-petals by drawing
nourishment from the reproductive organs causes their abortion;
but this can hardly be the sole cause, for in some Composit83 the
seeds of the outer and inner florets differ, without any difference
in the corolla. Possibly these several differences may be con-
nected with the different flow of nutriment towards the central
and external flowers : we know, at least, that with irregular
flowers, those nearest to the axis are most subject to peloria, that is
to become abnormally symmetrical. I may add, as an instance
of this fact, and as a striking case of correlation, that in many
pelargoniums, the two upper petals in the central flower of the
truss often lose their patches of darker colour; and when this
occurs, the adherent nectary is quite aborted; the central flower
thus becoming peloric or regular. When the colour is absent
from only one of the two upper petals, the nectary is not quite
aborted but is much shortened.

With respect to the development of the corolla, Sprengel's idea
that the ray-florets serve to attract insects, whose agency is highly
advantageous or necessary for the fertilisation of these plants,
is highly probable; and if so, natural selection may have come
into play. But with respect to the seeds, it seems impossible
that their differences in shape, which are not always correlated
with any difference in the corolla, can be in any way beneficial:
yet in the Umbelliferse these differences are of such apparent
importance — the seeds being sometimes orthospermous in the
exterior flowers and coelospermous in the central flowers, — that the
elder De Candolle founded his main divisions in the order on
such characters. Hence modifications of structure, viewed by
systematists as of high value, may be wholly due to the laws
of variation and correlation, without being, as far as we can
judge, of the slightest service to the species.

LAWS OF VARIATION 117

We may often falsely attribute to correlated variation structures
which are common to whole groups of species, and which in
truth are simply due to inheritance; for an ancient progenitor
may have acquired through natural selection some one modification
in structure, and, after thousands of generations, some other and
independent modification; and these two modifications, having
been transmitted to a whole group of descendants with diverse
habits, would naturally be thought to be in some necessary manner
correlated. Some other correlations are apparently due to the
manner in which natural selection can alone act. For instance,
Alph. de Candolle has remarked that winged seeds are never found
in fruits which do not open; I should explain this rule by the
impossibility of seeds gradually becoming winged through natural
selection, unless the capsules were open; for in this case alone
could the seeds, which were a little better adapted to be wafted
by the wind, gain an advantage over others less well fitted for
wide dispersal.

Compensation and Economy of Growth,

The elder Geoffrey and Goethe propounded, at about the same
time, their law of compensation or balancement of growth; or,
as Goethe expressed it, " in order to spend on one side, nature
is forced to economise on the other side." I think this holds
true to a certain extent with our domestic productions : if nourish-
ment flows to one part or organ in excess, it rarely flows, at least in
excess, to another part; thus it is difficult to get a cow to give
much milk and to fatten readily. The same varieties of the
cabbage do not yield abundant and nutritious foliage and a
copious supply of oil-bearing seeds. When the seeds in our
fruits become atrophied, the fruit itself gains largely in size
and quality. In our poultry, a large tuft of feathers on the
head is generally accompanied by a diminished comb, and a
large beard by diminished wattles. With species in a state of
nature it can hardly be maintained that the law is of universal
application; but many good observers, more especially botanists,
believe in its truth. I will not, however, here give any instances,
for I see hardly any way of distinguishing between the effects,
on the one hand, of a part being largely developed through natural
selection and another and adjoining part being reduced by this
same process or by disuse, and, on the other hand, the actual
withdrawal of nutriment from one part owing to the excess of
growth in another and adjoining part.

I suspect, also, that some of the cases of compensation which

118 ORIGIN OP SPECIES

have been advanced, and likewise some other facts, may be
merged under a more general principle, namely, that natural
selection is continually trying to economise every part of the
organisation. If under changed conditions of life a structure,
before useful, becomes less useful, its diminution will be favoured,
for it will profit the individual not to have its nutriment wasted
in building up an useless structure. I can thus only understand
a fact with which I was much struck when examining cirripedes,
and of which many analogous instances could be given : namely,
that when a cirripede is parasitic within another cirripede and
is thus protected, it loses more or less completely its own shell
or carapace. This is the case with the male Ibla, and in a truly
extraordinary manner with the Proteolepas : for the carapace in
all other cirripedes consists of the three highly-important anterior
segments of the head enormously developed, and furnished with
great nerves and muscles; but in the parasitic and protected
Proteolepas, the whole anterior part of the head is reduced to the
merest rudiment attached to the bases of the prehensile antennse.
Now the saving of a large and complex structure, when rendered
superfluous, would be a decided advantage to each successive
individual of the species; for in the struggle for life to which
every animal is exposed, each would have a better chance of
supporting itself, by less nutriment being wasted.

Thus, as I believe, natural selection will tend in the long run
to reduce any part of the organization, as soon as it becomes,
through changed habits, superfluous, without by any means caus-
ing some other part to be largely developed in a corresponding
degree. And, conversely, that natural selection may perfectly
well succeed in largely developing an organ without requiring as
a necessary compensation the reduction of some adjoining part.

Multiple, Rudimentary, and Lowly-organised Structures are

Variable.

It seems to be a rule, as remarked by Is. Geoffrey St. Hilaire,
both with varieties and species, that when any part or organ is
repeated many times in the same individual (as the vertebrae in
snakes, and the stamens in polyandrous flowers) the number is
variable; whereas the same part or organ, when it occurs in lesser
numbers, is constant. The same author as well as some botanists
have further remarked that multiple parts are extremely liable to
vary in structure. As " vegetative repetition," to use Prof. Owen's
expression, is a sign of low organisation, the foregoing statements
accord with the common opinion of naturalists, that beings which

LAWS OF VARIATION 119

stand low in the scale of nature are more variable than those which
are higher. I presume that lowness here means that the several
parts of the organisation have been but little specialised for
particular functions; and as long as the same part has to perform
diversified work, we can perhaps see why it should remain
variable, that is, why natural selection should not have preserved
or rejected each little deviation of form so carefully as when the
part has to serve for some one special purpose. In the same way
that a knife which has to cut all sorts of things may be of almost
any shape; whilst a tool for some particular purpose must be of
some particular shape. Natural selection, it should never be
forgotten, can act solely through and for the advantage of each
being.

Rudimentary parts, as it is generally admitted, are apt to be
highly variable. We shall have to recur to this subject; and I
will here only add that their variability seems to result from
their usefulness, and consequently from natural selection having
had no power to check deviations in their structure.

A Part developed m any Species in an extraordinary degree or
manner, in comparison with the same Part in allied Species,
tends to he highly variable.

Several years ago I was much struck by a remark, to the above
effect, made by Mr. Waterhouse. Professor Owen, also, seems to
have come to a nearly similar conclusion. It is hopeless to
attempt to convince any one of the truth of the above propo-
sition without giving the long array of facts which I have
collected, and which cannot possibly be here introduced. I can
only state my conviction that it is a rule of high generality.
I am aware of several causes of error, but I hope that I have
made due allowance for them. It should be understood that the
rule by no means applies to any part, however unusually developed,
unless it be unusually developed in one species or in a few
species in comparison with the same part in many closely allied
species. Thus, the wing of a bat is a most abnormal structure
in the class of mammals, but the rule would not apply here,
because the whole group of bats possesses wings; it would apply
only if some one species had wings developed in a remarkable
manner in comparison with the other species of the same genus.
The rule applies very strongly in the case of secondary sexual
characters, when displayed in any unusual mf«\ner. The term,
secondary sexual characters, used by Hun+er, relates to characters
which are attached to one sex, but are not directly connected

120 ORIGIN OF SPECIES

with the act of reproduction. The rule applies to males and
females; but more rarely to the females, as they seldom offer
remarkable secondary sexual characters. The rule being so plainly
applicable in the case of secondary sexual characters, may be
due to the great variability of these characters, whether or not
displayed in any unusual manner — of which fact I think there
can be little doubt. But that our rule is not confined to secondary
sexual characters is clearly shown in the case of hermaphrodite
cirripedes; I particularly attended to Mr. Waterhouse's remark,
whilst investigating this Order, and I am fully convinced that
the rule almost always holds good. I shall, in a future work,
give a list of all the more remarkable cases ; I will here give only
one, as it illustrates the rule in its largest application. The
opercular valves of sessile cirripedes (rock barnacles) are, in
every sense of the word, very important structures, and they
differ extremely little even in distinct genera; but in the several
species of one genus, Pyrgoma, these valves present a marvellous
amount of diversification; the homologous valves in the different
species being sometimes wholly unlike in shape; and the amount
of variation in the individuals of the same species is so great, that
it is no exaggeration to state that the varieties of the same species
differ more from each other in the characters derived from these
important organs, than do the species belonging to other distinct
genera.

As with birds the individuals of the same species, inhabiting the
same country, vary extremely little, I have particularly attended
to them; and the rule certainly seems to hold good in this class.
I cannot make out that it applies to plants, and this would have
seriously shaken my belief in its truth, had not the great varia-
bility in plants made it particularly difficult to compare their
relative degrees of variability.

When we see any part or organ developed in a remarkable degree
or manner in a species, the fair presumption is that it is of high
importance to that species : nevertheless it is in this case eminently
liable to variation. Why should this be so? On the view that
each species has been independently created, with all its parts as
we now see them, I can see no explanation. But on the view that
groups of species are descended from some other species, and have
been modified through natural selection, I think we can obtain
some light. First let me make some preliminary remarks. If,
in our domestic animals, any part or the whole animal be neglected,
and no selection be applied, that part (for instance, the comb in
the Dorking fowl) or the whole breed will cease to have a uniform
oh^racter; and the breed may be said to be degenerating. In

LAWS OP VARIATION 121

rudimentary organs, and in those which have been but little spe-
cialised for any particular purpose, and perhaps in x>olymorphic
groups, we see a nearly i)arallel case; for in such cases natural
selection either has not or cannot have come into full play, and
thus the organisation is left in a fluctuating condition. But what
here more i~»articularly concerns us is, that those points in our
domestic animals, which at the present time are undergoing rapid
change by continued selection, are also eminently liable to varia-
tion. Look at the individuals of the same breed of the pigeon,
and see what a prodigious amount of difference there is in the
beaks of tumblers, in the beaks and wattle of carriers, in the car-
riage and tail of fantails, &c., these being the points now mainly
attended to by English fanciers. Even in the same sub-breed, as
in that of the short-faced tumbler, it is notoriously difficult to
breed nearly perfect birds, many departing widely from the
standard. There may truly be said to be a constant struggle going
on between, on the one hand, the tendency to reversion to a less
perfect state, as well as an innate tendency to new variations, and,
on the other hand, the power of steady selection to keep the breed
true. In the long run selection gains the day, and we do not ex-
pect to fail so completely as to breed a bird as coarse as a com-
mon tumbler pigeon from a good short-faced strain. But as long
as selection is rapidly going on, much variability in the parts un-
dergoing modification may always be expected.

Now let us turn to nature. When a part has been developed in
an extraordinary manner in any one species, compared with the
other species of the same genus, we may conclude that this part
has undergone an extraordinary amount of modification since the
period when the several species branched off from the common
progenitor of the genus. This period will seldom be remote in
any extreme degree, as species rarely endure for more than one
geological period. An extraordinary amount of modification im-
plies an unusually large and long-continued amount of variability,
which has continually been accumulated by natural selection for
the benefit of the species. But as the variability of the extraor-
dinarily developed part or organ has been so great and long-
continued within a period not excessively remote, we might, as a
general rule, still expect to find more variability in such parts than
in other parts of the organisation which have remained for a much
longer period nearly constant. And this, I am convinced, is the
case. That the struggle between natural selection on the one
hand, and the tendency to reversion and variability on the other
hand, will in the course of time cease; and that the most ab-
normally developed organs may be made constant, I see no reason

122 ORIGIN OF SPECIES

to doubt. Hence, when an organ, however abnormal it may be,
has been transmitted in approximately the same condition to many
modified descendants, as in the case of the wing of the bat, it must
have existed, according to our theory, for an immense period in
nearly the same state ; and thus it has come not to be more variable
than any other structure. It is only in those cases in which the
modification has been comparatively recent and extraordinarily
great that we ought to find the generative varialnlity , as it may
be called, still present in a high degree. For in this case the
variability will seldom as yet have been fixed by the continued
selection of the individuals varying in the required manner and
degree, and by the continued rejection of those tending to revert
to a former and less-modified condition.

Specific Characters more Yaridhle than Generic Characters.

The i:)rinciple discussed under the last heading may be applied
to our present subject. It is notorious that specific characters are
more variable than generic. To explain by a simple example what
is meant : if in a large genus of plants some species had blue
flowers and some had red;, the colour would be only a specific char-
acter, and no one would be surprised at one of the blue species
varying into red, or conversely; but if all the species had blue
flowers, the colour would become a generic character, and its
variation would be a more unusual circumstance. I have chosen
this example because the explanation which most naturalists would
advance is not here applicable, namely, that specific characters
are more variable than generic, because they are taken from parts
of less physiological importance than those commonly used for
classing genera. I believe this explanation is partly, yet only in-
directly, true; I shall, however, have to return to this point in the
chapter on Classification. It would be almost superfluous to ad-
duce evidence in support of the statement, that ordinary specific
characters are more variable than generic; but with respect to im-
portant characters, I have repeatedly noticed in works on natural
history, that when an author remarks with surprise that some im-
portant organ or part, which is generally very constant throughout
a large group of species, differs considerably in closely-allied spe-
cies, it is often variahle in the individuals of the same species.
And this fact shows that a character, which is generally of generic
value, when it sinks in value and becomes only of specific value,
often becomes variable, though its physiological importance may
remain the same. Something of the same kind applies to mon-
strosities: at least Is. Geoffroy St. Hilaire apparently entertains no

LAWS OF VARIATION 123

doubt, that the more an organ normally differs in the different
species of the same group, the more subject it is to anomalies in
the individuals.

On the ordinary view of each species having been independently
created, why should that part of the structure, which differs from
the same part in other independently-created species of the same
genus, be more variable than those parts which are closely alike in
the several species? I do not see that any explanation can be
given. But on the view that species are only strongly marked and
fixed varieties, we might expect often to find them still continuing
to vary in those parts of their structure which have varied within
a moderately recent period, and which have thus come to differ.
Or to state the case in another manner : — the points in which all
the species of a genus resemble each other, and in which they
differ from allied genera, are called generic characters; and these
characters may be attributed to inheritance from a common
progenitor, for it can rarely have happened that natural selection
will have modified several distinct species, fitted to more or less
widely-different habits, in exactly the same manner: and as these
so-called generic characters have been inherited from before the
period when the several species first branched off from their com-
mon progenitor, and subsequently have not varied or come to differ
in any degree, or only in a slight degree, it is not probable that
they should vary at the present day. On the other hand, the
points in which species differ from other species of the same genus
are called specific characters; and as these specific characters have
varied and come to differ since the period when the species
branched off from a common progenitor, it is probable that they
should still often be in some degree variable, — at least more varia-
ble than those parts of the organisation which have for a very long
period remained constant.

Secondary Sexual Characters Variahle. — I think it will be ad-
mitted by naturalists, without m.y entering on details, that sec-
ondary sexual characters are highly variable. It will also be ad-
mitted that species of the same group differ from each other more
widely in their secondary sexual characters, than in other parts
of their organisation : compare, for instance, the amount of differ-
ence between the males of gallinaceous birds, in which secondary
sexual characters are strongly displayed, with the amount of dif-
ference between the females. The cause of the original variability
of these characters is not manifest; but w^e can see why they
should not have been rendered as constant and uniform as others,
for they are accumulated by sexual selection, which is less rigid
in its action than ordinary selection, as it does not entail death,

124 ORIGIN OF SPECIES

but only gives fewer offspring to the less favoured males. What-
ever the cause may be of the variability of secondary sexual char-
acters, as they are highly variable, sexual selection will have had
a wide scope for action, and may thus have succeeded in giving to
the species of the same group a greater amount of difference in
these than in other respects.

It is a remarkable fact, that the secondary differences between
the two sexes of the same species are generally displayed in the
very same parts of the organisation in which the si^ecies of the
same genus differ from each other. Of this fact I will give in
illustration the two first instances which happen to stand on my
list; and as the differences in these cases are of a very unusual
nature, the relation can hardly be accidental. The same number
of joints in the tarsi is a character common to very large groups
of beetles, but in the Engidss, as Westwood has remarked, the num-
ber varies greatly; and the number likewise differs in the two
sexes of the same species. Again in the fossorial hymenoptera,
the neuration of the wings is a character of the highest im-
portance, because common to large groups ; but in certain genera
the neuration differs in the different species, and likewise in the
two sexes of the same species. Sir J. Lubbock has recently re-
marked, that several minute crustaceans offer excellent illustra-
tions of this law. " In Pontella, for instance, the sexual charac-
ters are afforded mainly by the anterior antennce and by the fifth
pair of legs : the specific differences also are principally given by
these organs." This relation has a clear meaning on my view:
I look at all the species of the same genus as having as certainly
descended from a common progenitor, as have the two sexes of
any one species. Consequently, whatever part of the structure of
the common progenitor, or of its early descendants, became varia-
ble, variations of this part would, it is highly probable, be taken
advantage of by natural and sexual selection, in order to fit the
several species to their several places in the economy of nature,
and likewise to fit the two sexes of the same species to each other,
or to fit the males to struggle with other males for the possession
of the females.

Finally, then, I conclude that the greater variability of specific
characters, or those which distinguish species from species, than
of generic characters, or those which are possessed by all the spe-
cies ; — that the frequent extreme variability of any part which is
developed in a species in an extraordinary manner in comparison
with the same part in its congeners ; and the slight degree of varia-
bility in a part, however extraordinarily it may be developed, if it

LAWS OF VARIATION 125

be common to a whole group of species ; — that the great varia-
bility of secondary sexual characters, and their great difference in
closely allied species ; — that secondary sexual and ordinary speci-
fic differences are generally displayed in the same parts of the
organisation, — are all principles closely connected together. All
being mainly due to the species of the same group being the
descendants of a common progenitor, from whom they have in-
herited much in common, — to parts which have recently and
largely varied being more likely still to go on varying than parts
which have long been inherited and have not varied — to natural
selection having more or less completely, according to the lapse of
time, overmastered the tendency to reversion and to further varia-
bility,— to sexual selection being less rigid than ordinary selection,
— and to variations in the same parts having been accumulated
by natural and sexual selection, and having been thus adapted for
secondary sexual, and for ordinary purposes.

Distinct Species present analogous Variations, so that a Variety
of one Species often assumes a Character proper to an allied Spe-
cies, or reverts to some of the Characters of an early Progenitor. —
These propositions will be most readily understood by looking to
our domestic races. The most distinct breeds of the pigeon, in
countries widely apart, present sub-varieties with reversed feathers
on the head, and with feathers on the feet, — characters not pos-
sessed by the aboriginal rock-pigeon; these then are analogous
variations in two or more distinct races. The frequent presence
of fourteen or even sixteen tail-feathers in the pouter may be
considered as a variation representing the normal structure of an-
other race, the fantail. I presume that no one will doubt that all
such analogous variations are due to the several races of the pigeon
having inherited from a common parent the same constitution and
tendency to variation, when acted on by similar unknown influ-
ences. In the vegetable kingdom we have a case of analogous
variation, in the enlarged stems, or as commonly called roots, of
the Swedish turnip and Ruta baga, plants which several botanists
rank as varieties produced by cultivation from a common parent :
if this be not so, the case will then be one of analogous variation
in two so-called distinct species ; and to these a third may be added,
namely, the common turnip. According to the ordinary view of
each species having been independently created, we should have
to attribute this similarity in the enlarged stems of these three
plants, not to the vera causa of community of descent, and a con-
sequent tendency to vary in a like manner, but to three separate
yet closely related acts of creation. Many similar cases of analo-
gous variation have been observed by Naudin in the great gourd-

126 ORIGIN OF SFECIES

family, and by various authors in our cereals. Similar eases
occurring with insects under natural conditions have lately been
discussed with much ability by Mr. Walsh, who has grouped them
under his law of Equable Variability.

With pigeons, however, we have another case, namely, the occa-
sional appearance in all the breeds, of slaty-blue birds with two
black bars on the wings, white loins, a bar at the end of the tail,
with the outer feathers externally edged near their basis with white.
As all these marks are characteristic of the parent rock-pigeon, I
presume that no one will doubt that this is a case of reversion, and
not of a new yet analogous variation appearing in the several
breeds. We may, I think, confidently come to this conclusion,
because, as we have seen, these coloured marks are eminently
liable to appear in the crossed offspring of two distinct and dif-
ferently coloured breeds ; and in this case there is nothing in the
external conditions of life to cause the reappearance of the slaty-
blue, with the several marks, beyond the influence of the mere act
of crossing on the laws of inheritance.

No doubt it is a very surprising fact that characters should
reappear after having been lost for many, probably for hundreds
of generations. But when a breed has been crossed only once by
some other breed, the offspring occasionally show for many genera-
tions a tendency to revert in character to the foreign breed — some
say, for a dozen or even a score of generations. After twelve
generations, the proportion of blood, to use a common expression,
from one ancestor, is only 1 in 2048 ; and yet, as we see, it is gen-
erally believed that a tendency to reversion is retained by this
remnant of foreign blood. In a breed which has not been crossed,
but in which both parents have lost some character which their
progenitor possessed, the tendency, whether strong or weak, to re-
produce the lost character might, as was formerly remarked, for
all that we can see to the contrary, be transmitted for almost any
number of generations. When a character which has been lost in a
breed, reappears after a great number of generations, the most
probable hypothesis is, not that one individual suddenly takes after
an ancestor removed by some hundred generations, but that in
each successive generation the character in question has been lying
latent, and at last, under unknown favourable conditions, is de-
veloped. With the barb-pigeon, for instance, which very rarely
produces a blue bird, it is probable that there is a latent tendency
in each generation to produce blue plumage. The abstract im-
probability of such a tendency being transmitted through a vast
number of generations, is not greater than that of quite useless
or rudimentary organs being similarly transmitted. A mere

Lx\WS OF VARIATION 127

tendency to produce a rudiment is indeed sometimes thus in-
herited.

As all the species of the same genus are supposed to be de-
scended from a common progenitor, it might be expected that they
would occasionally vary in an analogous manner; so that the
varieties of two or more species would resemble each other, or that
a variety of one species would resemble in certain characters an-
other and distinct species, — this other species being, according to
our view, only a well-marked and permanent variety. But charac-
ters exclusively due to analogous variation would probably be oi
an unimportant nature, for the preservation of all functionally
important characters will have been determined through natural
selection, in accordance with the different habits of the species.
It might further be expected that the species of the same genus
would occasionally exhibit reversions to long lost characters. As,
however, we do not know the common ancestor of any natural
group, we cannot distinguish between reversionary and analogous
characters. If, for instance, we did not know that the parent rock-
pigeon was not feather-footed or turn-crowned, we could not have
told, whether such characters in our domestic breeds were rever-
sions or only analogous variations; but we might have inferred
that the blue colour was a case of reversion from the number of
the markings, which are correlated with this tint, and which would
not probably have all appeared together from simple variation.
More especially we might have inferred this, from the blue colour
and the several marks so often appearing when differently coloured
breeds are crossed. Hence, although under nature it must gener-
ally be left doubtful, what cases are reversions to formerly existing
characters, and what are new but analogous variations, yet we
ought, on our theory, sometimes to find the varying offspring of a
species assuming characters which are already present in other
members of the same group. And this undoubtedly is the case.

The difficulty in distinguishing variable species is largely due
to the varieties mocking, as it were, other species of the same
genus. A considerable catalogue, also, could be given of forms
intermediate between two other forms, which themselves can only
doubtfully be ranked as species; and this shows, unless all these
closely allied forms be considered as independently created species,
that they have in varying 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 collected a long
list of such cases; but here, as before, I lie under the great disad-

128 ORIGIN OF SPECIES

vantage 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 case, not indeed
as affecting any important character, but from occurring in sev-
eral species of the same genus, partly under domestication and
partly under nature. It is a case almost certainly of reversion.
The ass sometimes has very distinct transverse bars on its legs,
like those on the legs of the zebra : it has been asserted that these
are plainest in the foal, and, from inquiries which I have made,
I believe this to be true. The stripe on the shoulder is sometimes
double, and is very variable in length and outline. A white ass,
but not an albino^ has been described without either spinal or
shoulder stripe : and these stripes are sometimes very obscure, or
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 quagga, though so
plainly barred like a zebra over the body, is without bars on the
legs; but Dr. Gray has figured one specimen with very distinct
zebra-like bars on the hocks.

With respect to the horse, I have collected cases in England of
the spinal stripe in horses of the most distinct breeds, and of all
colours : transverse bars on the legs are not rare in duns, mouse-
duns, and in one instance in a chestnut : a faint shoulder-stripe
may sometimes be seen in duns, and I have seen a trace in a bay
horse. My son made a careful examination and sketch for me of
a dun Belgian cart-horse 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 ex-
amined this breed for the Indian Government, a horse without
stripes is not considered as purely-bred. The spine is always
striped; the legs are generally barred; and the shoulder-stripe,
which is sometimes double and sometimes treble, is common; the
side of the face, moreover, is sometimes striped. The stripes are
often plainest in the foal; and sometimes quite disappear in old
horses. Colonel Poole has seen both gray and bay Kattywar
horses striped when first foaled. I have also reason to suspect,
from information given me by Mr. W. W. Edwards, that with the
English race-horse the spinal stripe is much commoner in the

LAWS OF VARIATION 129

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. With-
out here entering on further details, I may state that I have col-
lected 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 in-
cluded, 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 strijjed; 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 the heavy Belgian
cart-horse, Welsh ponies, JSTorwegian 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. Kollin asserts, that the common mule from
the ass and horse is particularly apt to have bars on its legs; ac-
cording to Mr. Gosse, in certain parts of the United States about
nine out of ten mules have striped legs. I once saw a mule with
its legs so much striped that any one might have thought that it
was a hybrid-zebra ; and Mr. W. C. Martin, in his excellent treatise
on the horse, has given a figure of a similar mule. In four
coloured drawings, which I have seen, of hybrids between the ass
and zebra, the legs were much more plainly barred than the rest
of the body; and in one of them there was a double shoulder-
stripe. In Lord Morton's famous hybrid, from a chestnut mare
and male quagga, the hybrid, and even the pure offspring subse-
quently produced from the same mare by a black Arabian sire,
were much more plainly barred across the legs than is even the
pure quagga. 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 its legs
and the hemionus has none and has not even a shoulder-stripe,
nevertheless had all four legs barred, and had three short shoulder-

130 ORIGIN OP SPECIES

stripes, like those on the dun Devonshire and Welsh ponies, and
even had some zebra-like stripes on the sides of its face. With
respect to this last fact, I was so. convinced that not even a stripe
of colour appears from what is commonly called chance, that I
was led solely from the occurrence of the face-stripes on this
hybrid from the ass and hemionus to ask Colonel Poole whether
such face-stripes ever occurred in the eminently striped Kattywar
breed of horses, and was, as we have seen, answered in the affirma-
tive.

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 un-
known causes, sometimes prevails. 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 spe-
cies 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 con-
structed, 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 domestica-

LAWS OF VARIATION 131

tion, 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 dis-
tant quarters of the world, to produce hybrids resembling in their
stripes, not their own parents, but other species of the genus. To
admit this view is, as it seems to me, to reject a real for an unreal,
or at least for an unknown, cause. It makes the works of God a
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 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 fluctuat-
ing variability, but sometimes they cause direct and definite ef-
fects; 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 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 detri-
ment 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, un-
doubtedly occur. Multiple parts are variable in number and in
structure, perhaps arising from such parts not having been closely
specialised for any particular function, so that their modifications
have not been closely checked by natural 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. Rudimen-
tary organs, from being useless, are not regulated by natural selec-
tion, and hence are variable. Specific characters — that is, the
characters which have come to differ since the several species of
the same genus branched off from a common parent — are more
variable than generic characters, or those which have long been

132 ORIGIN OF SPECIES

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 spe-
cies of a genus are found — that is, where there has been much
former variation and diiferentiation, 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 char-
acters 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, xlny 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 be-
come the parent of many modified descendants — which on our
view must be a very slow process, requiring a long lapse of time —
in this case, natural selection has succeeded in giving a fixed char-
acter to the organ, in however extraordinary a manner it may have
been developed. Species inheriting nearly the same constitution
from a common parent, and exposed to similar influences, naturally
tend to present analogous variations, or these same species may
occasionally revert to some of the characters of their ancient pro-
genitors. 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 im-
portant modifications of structure in relation to the habits of each
species.

DIFFICULTIES OF THE THEORY 133

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 Selection.

LONG 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 fol-
lowing 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 modi-
fication of some other animal with widely different habits and
structure? Can we believe that natural selection could produce,
on the one hand, an organ of trifling importance, such as the tail
of a giraffe, which serves as a fly-flapper, and, on the other hand,
an organ so wonderful ls 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 discov-
eries 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.

134 ORIGIN OF SPECIES

On the Absence or Rarity of Transitional Varieties. — As nat-
ural selection acts solely by the preservation of profitable modifica-
tions, 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 va-
rieties 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 ; 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 nat-
ural collections have been imperfectly made, and only at long in-
tervals 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 represenlative 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 x>i"ocess of modification, each has become
adapted to the conditions of life of its own region, and has sup-
planted 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 ex-
isted 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 intermediate varieties?
This difficulty for a long time quite confounded me. But I think
it can be in large part explained.

In the first place we should be extremely cautious in inferring,

DIFFICULTIES OF THE THEORY 135

because an area is now continuous, that it has been continuous
during a long period. Geology would lead us to believe that most
continents have been broken up into islands even during the later
tertiary periods; and in such islands distinct species might have
been separately formed without the possibility of intermediate
varieties existing in the 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 contin
nous 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
wandering animals.

In looking at species as they are now distributed over a wide
area, we generally find them tolerably numerous over a large terri-
tory, 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 com-
parison with the territory proper to each. We see the same fact
in ascending mountains, and sometimes it is quite remarkable how
abruptly, as Alph. de Candolle has 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 physical conditions of life as the all-
important elements of distribution, these facts ought to cause sur-
prise, as climate and height or depth graduate away insensibly.
But when we bear in mind that almost every species, even in its
metropolis, would increase immensely in numbers, were it not for
other competing species; that nearly all either prey on or serve as
prey for others; in short, that each organic being is either directly
or indirectly related in the most important manner to other or-
ganic 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 grada-
tions, 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 numi-
bers, will, during fluctuations in the number of its enemies or of
its prey, or in the nature of the seasons, be extremely liable to utte^

13G ORIGIN OF SPECIES

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 comjDaratively narrow neutral territory be-
tween them, in which they become rather suddenly rarer and rarer ;
then, as varieties do not essentially differ from species, the same
rule will probably apply to both; and if we take a varying species
inhabiting a very large area, we shall have to adapt two varieties
to two large areas, and a third variety to a narrow intermediate
zone. The intermediate 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 information
given me by Mr. Watson, Dr. Asa Gray, and Mr. Wollaston, that
generally, when varieties intermediate 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
conclude that varieties linking two other varieties together gener-
ally have existed in lesser numbers than the forms which they con-
nect, then we can understand why intermediate varieties should
not endure for very long periods : — why, as a general rule, they
should be exterminated and disappear, sooner than the forms which
they originally linked together.

For any form existing in lesser numbers would, as already re-
marked, run a greater chance of being exterminated than one ex-
isting in large numbers; and in this particular case the inter-
mediate form would be eminently liable to the inroads of
closely-allied forms existing on both sides of it. But it is a far
more important consideration, that during the process of further
modification, by which two varieties are supposed to be converted
and perfected into two distinct species, the two which exist in
larger numbers, from inhabiting larger areas, will have a great
advantage over the intermediate variety, which exists in smaller
numbers in a narrow and intermediate zone. For forms existing
in larger numbers will have a better chance, within any given
period, of presenting further favourable variations for natural
selection to seize on, than will the rarer forms which exist in lesser
numbers. Hence, the more common forms, in the race for life,
will tend to beat and supplant the less common forms, for these
will be more slowly modified and improved. It is the same prin-
ciple which, as I believe, accounts for the common species in each

DIFFICULTIES OF THE THEORY 137

country, as shown in the second chapter, presenting on an average
a greater number of well-marked varieties than do the rarer species.
I may illustrate what I mean by supposing three varieties of sheep
to be kept, one adapted to an extensive mountainous region; a
second to a comparatively narrow, hilly tract; and a third to the
wide plains at the base; and that the inhabitants are all trying
with equal steadiness and skill to improve their stocks by 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, intermediate hill variety.

To sum up, I believe that species come to be tolerably well-
defined objects, and do not at any one period present an inextric-
able chaos of varying and intermediate links : first, because new
varieties are very slowly formed, for variation is a slow progress,
and natural selection can do nothing until favourable individual
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 immigra-
tion 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 as-
suredly we do see.

Secondly, areas now continuous must often have existed within
the recent period as isolated portions, in which many forms, more
especially amongst the classes which unite for each birth and wan-
der much, may have separately been rendered sufficiently distinct
to rank as representative species. In this case, intermediate va-
rieties 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, intermediate varie-
ties will, it is probable, at first have been formed in the inter-

138 ORIGIN OF SPECIES

mediate zones, but they will generally have had a short duration.
For these intermediate varieties will, from reasons already assigned
(namely from what we know of the actual distribution of closely
allied or representative species, and likewise of acknowledged
varieties), exist in the intermediate zones in lesser numbers than
the varieties which they tend to connect. From this cause alone
the intermediate varieties will be liable to accidental extermina-
tion; and during the process of further modification through nat-
ural selection, they will almost certainly be beaten and sup-
planted by the forms which they connect; for these from existing
in greater numbers will, in the aggregate, present more varieties,
and thus be further improved through natural selection and gain
further advantages.

Lastly, looking not to any one time, but to all time, if my
theory be true, numberless intermediate varieties, linking closely
together all the species of the same group, must 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 Organic Beings with peculiar
Habits and Structure. — It has been asked by the opponents of such
views as I hold, how, for instance, could a land carnivorous ani-
mal have been converted into one with aquatic habits; for how
could the animal in its transitional state have subsisted? It
would be easy to show that there now exist carnivorous animals
presenting close intermediate grades from strictly terrestrial to
aquatic habits; and as each exists by a struggle for life, it is
clear that each must be well adapted to its place in nature.
Look at the Mustela vison of North America, which has webbed
feet, and which 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 difiicult 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
only give one or two instances of transitional habits and struc-
tures in allied species; and of diversified habits, either constant

DIFFICULTIES OF THE THEORY 139

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 squirrrels ; 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 pos-
terior part of their bodies rather wide, and with the skin on
their flanks rather full, to the so-called flying squirrels; and
flying squirrels have their limbs and even the base of the tail
united by a broad expanse of skin, which serves as a parachute
and allows them to glide through the air to an astonishing
distance from tree to tree. We cannot doubt that each structure
is of use to each kind of squirrel in its own country, by enabling
it to escape birds or beasts of prey, to collect food more quickly,
or, as there is reason to believe, to lessen the danger from occa-
sional falls. But it does not follow from this fact that the
structure of each squirrel is the best that it is possible to con-
ceive under all possible conditions. Let the climate and vegetation
change, let other competing rodents or new beasts of prey immi-
grate, 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 modi-
fied and improved in structure in a corresponding manner. There-
fore, 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 struc-
ture, fitted for gliding through the air, now connect the Gale-
opithecus with the other Insectivora, yet there is no difficulty in
supposing that such links formerly existed, and that each was de-
veloped in the same manner as with the less perfectly gliding squir-
rels; 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 been greatly lengthened by natural selection; and
this, as far as the organs of flight are concerned, would have

140 ORIGIN OF SPECIES

converted the animal into a bat. In certain bats in which the
wing-membrane extends from the top of the shoulder to the tail
and includes the hind-legs, we perhaps see traces of an apparatus
originally fitted for gliding through the air rather than for
flight.

If about a dozen genera of birds were to become extinct,
who would have ventured to surmise that birds might have existed
which used their wings solely as flappers, like the logger-headed
duck (Micropterus of Eyton) ; as fms 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 condi-
tions of life to which it is exposed, for each has to live by a
struggle; but it is not necessarily the best possible under all
possible conditions. It must not be inferred from these remarks
that any of the grades of wing-structure here alluded to, which
perhaps may all be the result of disuse, indicate the steps by
which birds actually acquired their perfect power of flight; but
they serve to show what diversified means of transition are at least
possible.

Seeing that a few members of such water-breathing classes
as the Crustacea and Mollusca are adapted to live on the land;
and seeing that we have flying birds and mammals, 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 ever imagined that in
an early transitional state they had been the inhabitants of
the open ocean, and had used their incipient organs of flight
exclusively, as far as we know, to escape being devoured by other
fish?

When we see any structure highly perfected for any 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 ren-
dered more perfect through natural selection. Furthermore, we
may conclude that transitional states between structures fitted for
very different habits of life will rarely have been developed at
an early period in great 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
flight would have been developed under many subordinate forms.

DIFFICULTIES OF THE THEORY 14}

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 structure in a
fossil condition will always be less, from their having existed
in lesser numbers, than in the case of species with fully devel-
oped structures.

I will now give two or three instances both of diversified
and of changed habits in the individuals of the same species.
In either case it would be easy for natural selection to adapt
the structure of the animal to its changed habits, or exclusively
to one of its several habits. It is, however, difficult to decide,
and immaterial for us, whether habits generally change first
and structure afterwards; or whether slight modifications of
structure lead to changed habits; both 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 (Saurophagus 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 like a kingfisher
at a fish. In our own country the larger titmouse (Parus
major) may be seen climbing branches, almost like a creeper;
it sometimes, like a shrike, kills small birds by blows on the
head; and I have many times seen and heard it hammering the
seeds of the yew on a branch, and thus breaking them like a
nuthatch. In North America the black bear was seen by Hearne
swimming for hours with widely open mouth, thus catching,
almost like a whale, insects in the water.

As we sometimes see individuals following habits different from
those proper to their species and to the other species of the same
genus, we might expect that such individuals would occasionally
give rise to new species, having anomalous habits, and with their
structure either slightly or considerably modified from that of
their type. And such instances occur in nature. Can a more
striking instance of adaptation be given than that of a wood-
pecker for climbing trees and seizing insects in the chinks of
the bark? Yet in North America there are woodpeckers which
feed largely on fruit, and others with elongated wings which chase
insects on the wing. On the plains of La Plata, where hardly
a tree grows, there is a woodpecker (Colaptes campestris) which

142 ORIGIN OF SPECIES

has two toes before and two behind, a long pointed tongue,
pointed tail-feathers, sufficiently stiff to support the bird in a
vertical position on a post, but not so stiff as in the typical
woodpeckers, and a straight strong beak. The beak, however, is
not so straight or so strong as in the typical woodpeckers, but
it is strong enough to bore into wood. Hence this Colaptes in all
the essential parts of its structure is a woodpecker. Even in
such trifling characters as the colouring, the harsh tone of the
voice, and undulatory flight, its close blood-relationship to our
common woodpecker is plainly declared; yet, as I can assert,
not only from my own observations, but from those of the accurate
Azara, in certain large districts it does not climb trees, and it
makes its nest in holes in banks ! In certain other districts,
however, this same woodpecker, as Mr. Hudson states, frequents
trees, and bores holes in the trunk for its nest. I may mention
as another illustration of the varied habits of this genus, that
a Mexican Colaptes has been described by De Saussure as boring
holes into hard wood in order to lay up a store of acorns.

Petrels are the most aerial and oceanic of birds, but in the
quiet sounds of Tierra del Fuego, the Puffinuria berardi, in its
general habits, in its astonishing power of diving, in its manner
of swimming and of flying when made to take flight, would be
mistaken by any one for an auk or a grebe; nevertheless it is
essentially a petrel, but with many parts of its organisation pro-
foundly modified in relation to its new habits of life; whereas
the woodpecker of La Plata has had its structure only slightly
modified. In the case of the water-ouzel, the acutest observer
by examining its dead body would never have suspected its sub-
aquatic habits ; yet this bird, which is allied to the thrush family,
subsists by diving — using its wings under water, and grasping
stones at its feet. All the members of the great order of
Hymenopterous insects are terrestrial, excepting the genus Procto-
trupes, 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

DIFFICULTIES OF THE THEORY 143

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 Gralla-
tores 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
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 mem-
brane 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. Plence it
will cause him no surprise that there should be geese and frigate-
birds with webbed feet, living on the dry land and rarely alighting
on the water, that there should be long-toed corncrakes, living
in meadows instead of in swamps; that there should be wood-
peckers where hardly a tree grows; that there should be 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 distances, for admitting different
amounts of light, and for the correction of spherical and chro-
matic aberration, 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 Vox 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

144 ORIGIN OF SPECIES

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" conditions of life, then the difficulty of
believing that a perfect and complex eye could be formed by
natural selection, though insuperable by our imagination, should
not be 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 perceiving light, it does not seem impossible that certain sensi-
tive elements in their sarcode should become aggregated and de-
veloped 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
lineal progenitors ; but this is scarcely ever possible, and we are
forced to look to other species and genera of the same group,
that is to the collateral descendants from the same parent-form,
in order to see what gradations are possible, and for the chance
of some gradations having been transmitted in an unaltered or
little altered condition. But the state of the same organ in
distinct classes may 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 translu-
cent skin, but without any lens or other refractive body. We may,
however, according to M. Jourdain, descend even a step lower
and find aggregates of pigment-cells, 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 distinguish 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 con-
centrate 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

DIFFICULTIES OF THE THEORY 145

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 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 Miiller formerly made three main classes with seven
subdivisions, besides a fourth main class of aggregated simple eyes.

When w^e reflect on these facts, here given much too briefly,
v/ith respect to the wide, diversifled, and graduated range of
structure in the eyes of the lower animals; and when we bear
in mind how small the number of all living forms must be in
comparison with those which have become extinct, the difliculty
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 membrane, into an
optical instrument as perfect as is possessed by any member of
the Articulate Class.

Pie 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 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 king-

14G ORIGIN OF SPECIES

dom, 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 indis-
pensable 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 highest human intellects; and
we naturally infer that the eye has been formed by a somewhat
analogous process. But niay not this inference be presumptuous?
Have we any right to assume that the Creator works by intellec-
tual powers like those of man? If we must compare the eye to
an optical instrument, we ought in imagination to take a thick
layer of transparent tissue, with spaces filled with fluid, and
with a nerve sensitive to light 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 surface
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 altera-
tion in the transparent layers; and carefully preserving each
which, under varied circumstances, in any way or in any degree,
tends to produce a distinct 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 slight alterations, generation will multiply them almost in-
finitely, 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

DIFFICULTIES OF THE THEORY 147

be formed as superior to one of glass, as the works of the Creator
are to those of man?

Modes of Transition.

If it could be demonstrated that any complex organ existed,
which could not possibly have been formed by numerous, succes-
sive, 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 gradations of some
kind. Numerous cases could be given amongst the lower animals
of the same organ performing at the same time wholly distinct
functions; thus in the larva of the dragon-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 ext^^rior
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 same time differently con-
structed 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 fol-
lowed in some few cases.

Again, two distinct organs, or the same organ under two very
different forms, may simultaneously perform in the same individ-
ual the same function, and this is an extremely important means
of t-ransition : to give one instance, — there are fish with gills or
branchiae that breathe the air dissolved in the water, at the same
time that they breathe free air in their swimbladders, this latter
organ being divided by highly vascular partitions and having a

148 ORIGIN OF SPECIES

ductus p-neumaticus for the supply of air. To give another
instance from the vegetable kingdom : i)lants climb by three dis-
tinct means, by spirally twining, by clasping a support with their
sensitive tendrils, and by the emission of aerial rootlets; these
three means are usually found in distinct groups, but some few
species exhibit two of the meanS;, or even all three, combined in
the same 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 one for a widely different purpose, namely,
respiration. The swimbladder has, also, been worked in as an
accessory to the auditory organs of certain fishes. All physiolo-
gists admit that the swimbladder is homologous, or " ideally sim-
ilar " 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 apparatus 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 con-
trivance by which the glottis is closed. In the higher Vertebrata
the branchiae have wholly disappeared — but in the embryo the
slits on the sides of the neck and the loop -like course of the
arteries still mark their former position. But it is conceivable
that the now utterly lost branchiae might have been gradually
worked in by natural selection for some distinct purpose : for
instance, Landois has shown that the wings of insects are developed
from the tracheae; it is therefore highly probable that in this great
class organs which once served for respiration have been actually
converted into organs for flight.

In considering transitions of organs, it is so important to bear
in mind the probability of conversion from one function to
another, that I will give another instance. Pedunculated cirri-
pedes have two minute folds of skin, called by me the ovigerous

DIFFICULTIES OF THE THEORY 149

freiia, which serve, through the means of a sticky secretion,
to retain the eggs until they are hatched within..the sack. These
cirripedes have no branchite, the whole surface of the body and
of the sack, together with the small frena, serving for respiration.
The Balanidse or sessile cirripedes, on the other hand, have no
ovigerous frena, the eggs lying loose at the bottom of the sack,
within the well-enclosed shell; but they have, in the same relative
position with the frena, large, much-folded membranes, which
freely communicate with the circulatory lacunae of the sack and
body, and which have been considered by all naturalists to act
as branchiae. Now I think no one will dispute that the ovigerous
frena in the one family are strictly homologous with the branchiae
of the other family ; indeed, they graduate into each other. There-
fore it need not be doubted that the two little folds of skin,
which originally served as ovigerous frena, but which, likewise,
very slightly aided in the act of respiration, have been gradually
converted by natural selection into branchiae, simply through an
increase in their size and the obliteration of their adhesive glands.
If all pedunculated cirripedes had become extinct, and they have
suffered far more extinction than have sessile cirripedes, who
would ever have imagined that the branchiae in this latter family
had originally existed as organs for preventing the ova from
being washed out of the sack?

There is another possible mode of transition, namely, through
the acceleration or retardation of the period of 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 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. In all such cases, — and many

150 ORIGIN OP SPECIES

could be given, — if the age for reproduction were retarded, tlie
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.

Special Difficulties of the Theory of Natural Selection.

Although we must be extremely cautious in concluding that
any organ could not have been produced by successive, small,
transitional gradations, yet undoubtedly serious cases of 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 Mat-
teucci, an analogous organ in the tail manifests but little elec-
tricity, 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 toi*pedo
during rest, there would seem to be a charge in every respect
iike that which is met with in muscle and nerve during rest,
and the discharge of the torpedo, instead of being peculiar, may
be only another form of the discharge which depends 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

DIFFICULTIES OF THE THEORY 151

about the uses of these organs, and as we know nothing about the
habits and structure of the progenitors of the existing electric
fishes, it would be extremely bold to maintain that no serviceable
transitions are possible by which these organs might have been
gradually developed.

These organs appear at first to offer another and far more
serious 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 descendants have now lost.
But when we look at the subject more closely, we find in the
several fishes provided with electric organs, that these are situated
in different parts of the body, — that they differ in construction,
as in the a-rrangement of the plates, and, according to Pacini, in
the process or means by which the electricity is excited — and
lastly, in being supplied with nerves proceeding from different
sources, and this is perhaps the most important of all the differ-
ences. Hence in the several fishesi 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 progenitor; for had this
been the case they would have closely resembled each other in
all respects. Thus the difficulty of an organ, apparently the same,
arising in several remotely allied species, disappears, leaving only
the lesser yet still great 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

152 ORIGIN OF SPECIES

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 verte-
brate animals appear wonderfully alike; and in such widely
sundered groups no part of this resemblance can be due to
inheritance from a common progenitor. Mr. Mivart has advanced
this case as one of special difficulty, but I am unable to see the
force of his argument. An organ for vision must be formed of
transparent tissue, and must include some sort of lens for throwing
an image at the back of a darkened chamber. Beyond this super-
ficial resemblance, there is hardly any real similarity between the
eyes of cuttle-fish and vertebrates, as may be seen by consulting
Ilensen'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 riot
a little difficult to decide how far even the same terms ought to
be employed in describing the eyes of the Cephalopoda and Verte-
brata. 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 accordance with this view of their
manner of formation. As two men have sometimes independently
hit on the same invention, so in the several foregoing cases it
appears that natural selection, working for the good of each
being, and taking advantage of all favourable variations, has
produced similar organs, as far as function is concerned, in dis-
tinct 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

DIFFICULTIES OF THE THEORY 153

out of the water. In two of these families, which were more
especially examined by Ivliiller, and which are nearly related to
each other, the species agree most closely in all important
characters; namely, in their sense organs, circulating system,
in the position of the tufts of hair within their complex stomachs,
and lastly in the whole structure of the water-breathing branchiae,
even to the microscopical hooks by which they are cleansed.
Hence it might have been expected that in the few species
belonging to both families which live on the land, the equally-
important air-breathing apparatus would have been the same;
for why should this one apparatus, given for the same purpose,
have been made to differ, whilst all the other important organs
were closely similar or rather identical?

Fritz Miiller argues that this close similarity in so many
points of structure must, in accordance with the views advanced
by me, be accounted for by inheritance from a common progeni-
tor. 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 is improbable in the highest degree, that their common
progenitor should have been adapted for breathing air. Miiller
was thus led carefully to examine the apparatus in the air-
breathing species; and he found it to differ in each in several
important points, as in the position of the orifices, in the manner
in which they are opened and closed, and in some accessory
details. Now such 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 accordance with the principle that the nature of
each variation depends on two factors, viz., the nature of the
organism and that of the surrounding 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 jeparate 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 Claparede,
has argued in the same manner, and has arrived at the same
result. He shows that there are parasitic mites (Acaridse), be-
long:ing to distinct sub-families and families, which are furnished

154 ORIGIN OB" SPECIES

with hair-claspers. These organs must have been independently
developed, as they could not have been inherited from a common
progenitor; and in the several groups they are formed by the
modification of the fore-legs, — of the hind legs, — of the maxillae
or lips, — and of 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 through-
out 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 of 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 dissem-
inated 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 conspicuously coloured, so as to attract and be devoured
by birds, — by having hooks and grapnels of many kinds and
serrated awns, so as to adhere to the fur of quadrupeds, — and
by being furnished with wings and plumes, as different in shape
as they are elegant in structure, so as to be wafted by every
breeze. I will give one other instance; for this subject of the
same end being gained by the most diversified means well deserves
attention. Some authors maintain that organic beings have been
formed in many ways for the sake of mere variety, almost like
toys in a shop, but such a view of nature is incredible. With
plants having separated sexes, and with those in which, though
hermaphrodites, the pollen does not spontaneously fall on the
stigma, some aid is necessary for their fertilisation. With several
kinds this is effected by the pollen-grains, which are light and
incoherent, being blown by the wind through niere 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

DIFFICULTIES OF THE THEORY 155

number of contrivances, all for the same purpose and effected in
essentially the same manner, but entailing changes in every part
of the flower. The nectar may be stored in variously shaped
receptacles, with the stamens and pistils modified in many ways,
sometimes forming trap-like contrivances, and sometimes capable
of neatly adapted 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 Ooryanthes. This orchid has part of its labellum or lower
lip hollowed out into a great bucket, into which drops of almost
pure water continually fall from two secreting 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 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. Oriiger saw a
" continual procession " of bees thus crawling out of their in-
voluntary 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 killed before it had quite crawled out with a pollen-mass
still fastened to its back. When the bee, thus provided, flies to
another flower, or to the same flower a second time, and is pushed
by its comrades into the bucket and then crawls out by the passage,
the pollen-mass necessarily comes first into contact with the
viscid stigma, and adheres to it, and the flower is fertilised.
Now at last we see the full use of every part of the flower, of the
water-secreting horns, of the bucket half full of water, which
prevents the bees from flying away, and forces them to crawl
out through the spout, and rub against the properly placed viscid
pollen-masses and the viscid stigma.

The construction of the flower in another closely allied orchid,

156 ORIGIN OF SPECIES

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, fertilisa-
tion is effected.

How, it may be asked, in the foregoing and in innumerable
other instances, can we understand the graduated scale of com-
plexity and the multifarious means for gaining the same end.
The answer no doubt is, as already remarked, that when two
forms vary, which already differ from each other in some slight
degree, the variability will not be of the same exact nature, and
consequently the results obtained through natural selection for
the same general purpose will not be the same. We should also
bear in mind that every highly developed organism has passed
through many changes; and that each modified structure tends
to be inherited, so that each 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 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
l^resent 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 exaggerated, canon in natural history of
" Natura non facit saltum." We meet with this admission in
the writings of almost every experienced naturalist; or as Mihie
Edwards has well expressed it, ISTature 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? Why

DIFFICULTIES OF THE THEORY 157

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 advantage of slight successive variations; she can never
take a great and sudden leap, but must advance by short and sure,
though slow steps.

Organs of little apparent Importance, as affected hy Natural

Selection.

As natural selection acts by life and death, — by the survival
of the fittest, and by the destruction of the less well-fitted indi-
viduals,— I have sometimes felt great difficulty in understanding
the origin or formation of parts of little importance; almost
as great, though of a very difi^erent 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 of cattle and
other animals in South America absolutely depend on their power
of resisting the attacks of insects : so that individuals which could
by any means defend themselves from these small enemies, would
be able to range into new pastures and thus gain a great advantage.
It is not that the larger quadrupeds are actually destroyed (except
in some rare cases) by flies, but they are incessantly harassed and
their strength reduced, so that they are more subject to disease,
or not so well enabled in a coming dearth to search for food,
or to escape from beasts of prey.

Organs now of trifling importance have probably in some cases
been of high importance to an early progenitor, and, after having

158 ORIGIN OF SPECIES

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
swimbladders 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 spontaneous variations, which seem to depend in a quite
subordinate degree on the nature of the conditions, — of the ten-
dency to reversion to long-lost characters, — of the complex laws
of growth, such as of correlation, compensation, of the pressure
of one part on another, &c., — and finally of sexual selection, by
which characters of use to one sex arc 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 con-
ditions 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 adap-
tation 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

DIFFICULTIES OF THE THEORY 159

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 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 parturi-
tion, 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 coun-
tries 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
flies is correlated with colour, as is the liability to be poisoned
by certain plants; so that even colour would be thus subjected
to the action of natural selection. Some observers are convinced
that a damp climate affects the growth of the hair, and that with
the hair the horns are correlated. Mountain breeds 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; 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 labor-
ious 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 exer-
cise together with abundant food on the whole organisation is
probably still more important; and this, as H. von ISTathusius 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 rela-

1(50 ORIGIN OF SPECIES

live importance of the several known and unknown causes oi
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 slight analogous differences
between true species.

Utilitarian Doctrine, liow 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 latter point is beyond the scope of scientihc 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 progeni-
tors; 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 con-
sideration is that the chief part of the organisation of every living
creature is due to inheritance; and consequently, though each
being assuredly is well fitted for its place in nature, many struc-
tures 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 frigate-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; but we may further venture to
believe that the several bones in the limbs of the monkey, horse,
and bat, were originally developed, on the principle of utility,
probably through the reduction of more numerous bones in the

DIFFICULTIES OF THE THEORY 161

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 con-
ditions, 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 cab-
inet? Few objects are more beautiful than the minute siliceous
cases of the diatomacese: 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 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 in-
variable 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 at-
tract 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 straw-
berry or cherry is as pleasing to the eye as to the palate, —
that the gaily-coloured fruit of the spindle-wood tree and the
scarlet berries of the holly are beautiful objects, — will be ad-

162 ORIGIN OF SPECIES

mitted 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 matured seeds disseminated: I infer that this is the case
from having as yet found no exception to the rule that seeds
are always thus disseminated when embedded within a fruit of
any kind (that is within a fleshy or pulpy envelope), if it be
coloured of any brilliant tint, or rendered conspicuous by being
white or black.

On the other hand, I willingly admit that a great number of
male animals, as all our most gorgeous birds, some fishes, reptiles,
and mammals, and a host of magnificently coloured butterflies,
have been rendered beautiful for beauty's sake; but this has
been effected through sexual selection, that is, by the more beauti-
ful 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 presented, 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 modification in
a species exclusively for the good of another species; though
throughout nature one species incessantly 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 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

DIFFICULTIES OF THE THEORY 163

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 rattle-
snake 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 prin-
ciple 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 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 Miiller 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
incongruities which we have just come across in the domain of
the sensations. One might say that nature has taken delight in
accumulating contradictions in order to remove all foundation

164 ORIGIN OF SPECIES

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, 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 instrument, like that in
so many members of the same great order, and that it has since
been modified but not perfected for its present purpose, with
the poison originally adapted for some other object, such as to
produce galls, since intensified, we can perhaps understand how
it is that the use of the sting should so often cause the insect's
own death : for if on the whole the power of stinging be useful
to the social community, it will fulfil all the requirements of
natural selection, though it may cause the death of some few
members. If we admire the truly wonderful power of scent by
which the males of many insects find their females, can we ad-
mire 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 community; 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 elaboration of dense clouds of
pollen by our fir-trees, so that a few granules may be wafted
by chance on to the ovules?

Summary: the Law of Unity of Type and of the Conditions of
Existence embraced hy 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

DIFFICULTIES OF TllF THEORY 1G5

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 gradations, 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 extinction of preceding and intermediate gradations. Closely
allied species, now living on a continuous area, must often have
been formed when the area was not continuous, and when the
conditions of life did not insensibly graduate away from one part
to another. When two varieties are formed in two 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
intermediate variety, and will thus generally succeed in sup-
planting 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 conditions of life, there is no logical impossibility
in the acquirement of any conceivable degree of perfection through
natural selection. In the cases in which we know of no inter-
mediate 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

166 ORIGIN OF SPECIES

then having" been in part or in whole specialised for one function ;
and two distinct organs having performed at the same time the
same function, the one having been perfected whilst aided by the
other, must often have largely facilitated transitions.

We have seen that in two beings widely remote from each other
in the natural scale, organs serving for the same 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 varia-
tion 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 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 com-
petition will have been severer, and thus the standard of perfec-
tion 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 every-
where predicated.

DIFFICULTIES OF THE THEORY 1G7

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 in-
habitants 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 Con-
ditions of Existence. By unity of type is meant that funda-
mental agreement in structure which we see in organic beings
of the same class, and which is quite independent of their
habits of life. On my theory, unity of type is explained by
unity of descent. The expression of conditions of existence,
so often insisted on by the illustrious Cuvier, is fully embraced
by the principle of natural selection. For natural selection acts
by either now adapting the varying parts of each being to its
organic and inorganic conditions of life; or by having adapted
them during past periods of time : the adaptations being aided
in many cases by the increased use or disuse of parts, being
affected by the direct action of the external conditions of life,
and subjected in all cases to the several laws of growth and
variation. Hence, in fact, the law of the Conditions of Existence
is the higher law; as it includes, through the inheritance of
former variations and adaptations, that of Unity of Type.

168 ORIGIN OF SPECIES

CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION.

Longevity — Modifications not necessarily simultaneous — Modifications
apparently of no direct service — Progressive development — Char-
acters 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 struc-
ture 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 mis-
cellaneous objections v^hich 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 con-
sider all organic beings as imperfect : what I have really said
is, that all are not as perfect as they might have been in relation
to their conditions; and this is shown to be the case by so
many native forms in many quarters of the world having yielded
their places to intruding foreigners. Nor can organic beings,
even if they were at any one time perfectly adapted to their
conditions of life, have remained so, when their conditions
changed, unless they themselves likewise changed; and no one
will dispute that the physical conditions of each country, as
well as the numbers and kinds of its inhabitants, have undergone
many mutations.

A critic has lately insisted, with some parade of mathematical
accuracy, that longevity is a great advantage 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 selection, survive
from year to year by means of it^ seeds or ova? Mr, E. Ray

MISCELLANEOUS OBJECTIONS, ETC. 169

Lankester has recently discussed this subject, and he concludes,
as far as its extreme complexity allows him. to form a judgment,
that longevity is generally related to the standard of each species
in the scale of organisation, as well as to the amount of ex-
Ijenditure 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. II. Lewes has remarked,
l»iis line of argument proves too much, for the ancient domestic
r?.ces figured on the Egyptian monuments, or embalmed, are
closely similar or even identical with those now living; yet all
naturalists admit that such races have been produced through the
modification of their original tj^pes. The many animals which
have remained unchanged since the commencement of the glacial
period, would have been an incomparably stronger case, for these
have been exposed to great changes of climate and have migrated
over great distances; whereas, in Egypt, during the last several
thousand years, the conditions of life, as far as we know, have
remained absolutely uniform. The fact of little or no modifi-
cation having been effected since the glacial period would have
been of some avail against those who believe in an innate and
necessary law of development, but is powerless against the doctrine
of natural selection or the survival of the fittest, which implies
that when variations or individual differences of a beneficial
nature happen to arise, these will be preserved; but this will
be effected only under certain favourable circumstances.

The celebrated palssontologist, Bronn, at the close of his Ger-
man 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 variations, such
as size, albinism, &c., the more permanent varieties are generally
found, as far as I can discover, inhabiting distinct stations, —
such as high land or low land, dry or moist districts. Moreover,
in the case of animals which wander much about and cross freely,
their varieties seem to be generally confined to distinct regions.

Bronn also insists that distinct species never differ from each
other in single characters, but in many parts; and he asks^
how it always comes that many parts of the organisation should

170 ORIGIN OP SPECIES

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 varia-
tions, if slight, first in one part and then in another; and as
they would be transmitted all together, they would appear to us
as if they had been simultaneously 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 attributed 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 characters appear to be
of no service whatever to their possessors, and therefore cannot
have been influenced through natural selection. Bronn adduces
the length of the ears and tails in the 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 Niigeli 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 morphological characters, which appear to be quite un-
important 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 nu-
merical 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, &c.

There is much force in the above objection. Nevertheless, we

MISCELLANEOUS Q-BJECTLOXS, ETC. 171

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 increas"ed or di-
minished flow of nutriment to a part, mutual pressure, an early
developed part affecting one subsequently developed, and so forth,
— as well as through other causes which lead to the many mys-
terious cases of correlation, which we do not in the least under-
stand. These agencies may be all grouped together, for the sake
of brevity, under the expression of the laws of growth. In the
third place, we have to allow for the direct and definite action of
changed conditions of life, and for so-called spontaneous varia-
tions, in which the nature of the conditions apparently plays a
quite subordinate part. Bud-variations, such as the appearance
of a moss-rose on a common rose, or of a 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 variations are not the effect of some local change
in the nature of the sap, due to some change in the conditions.
There must be some efiicient 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 per-
sistently, 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 under-
stood, excited so much surprise in the minds of the older natural-
ists, can thus be explained.

It may be worth while to illustrate some of the foregoing re-
marks. With respect to the assumed inutility of various parts
and organs, it is hardly necessary to observe that even in the
higher and best-known animals many structures exist, which
are so highly developed that no one doubts that they are of
importance, yet their use has not been, or has only recently been,
ascertained. As Bronn gives the length of the ears and tail in
the several species of mice as instances, though trifling ones, of
differences in structure which can be of no special use, I may

172 ORIGIN OF SPECIES

mention that, according to Dr. SchobI, 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 struc-
tures, 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 selection. No one until lately would
have imagined that in dimorphic and trimorphic plants the dif-
ferent 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 positio'ns seems at first purely morpho-
logical, 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
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 selec-
tion 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 some-
times differ wonderfully in structure, yet may be seen to graduate
intQ 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, manifestly 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 im-
perfect flowers almost always consist of mere rudiments, and the

MISCELLANEOUS OBJECTIONS, ETC. 173

* pollen-grains are reduced in diameter. In Ononis columnaB 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 Malpighiacese the closed flowers, according to
A. de Jussieu, are still further modified, for the five stamens which
stand opposite to the sepals are all aborted, a sixth stamen
standing opposite to a petal being alone developed; and this
stamen is not present in the ordinary flowers of these species;
the style is aborted; and the ovaria are reduced from three to
two. Now although natural selection may well have had the
power to prevent some of the flowers from expanding, and to
reduce the amount of pollen, when rendered by the closure of
the flowers superfluous, yet hardly any of the above special modi-
fications 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 Compositse and Umbelliferse (and in some
other plants) the circumferential flowers have their corollas much
more developed than those of the centre; and this seems often
connected with the abortion of the reproductive organs. It is
a more curious fact, previously referred to, that the achenes or
seeds of the circumference and centre sometimes differ greatly
in form, colour, and other characters. In Carthamus and some
other Compositge the central achenes alone are furnished with
a pappus; and in Hyoseris the same head yields achenes of three
different forms. In certain Umbelliferse the exterior seeds, ac-

174 ORIGIN OF SPECIES

cording to Tausch, are orthospermous, and the central one coelo- •
spermous, and this is a character which was considered by De
Candolle to be in other species of the highest systematic im-
portance. Prof. Braun mentions a Fumariaceous genus, in which
the flowers in the lower part of the spike bear oval, ribbed, one-
seeded nutlets; and in the upper part of the spike, lanceolate,
two-valved, and two-seeded siliques. In these several cases, with
the exception of that of the well developed ray-florets, which are
of service in making the flowers 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 relative position and inter-action of the parts;
and it can hardly be doubted that if all the flowers and leaves
on the same plant had been subjected to the same external and
internal condition, as are the flowers and leaves in certain posi-
tions, all would have been modified in the same manner.

In numerous other cases we find modifications of structure,
which are considered by botanists to be generally of a highly
important nature, affecting only some of the flowers on the same
plant, or occurring on distinct plants, which grow close together
under the same conditions. As these variations seem of no
special use to the plants, they cannot have been influenced by
natural selection. Of their cause we are quite ignorant; we
cannot even attribute them, as in the last class of cases, to any
proximate agency, such as relative position. I will give only a
few instances. It is so common to observe on the same plant,
flowers indifferently tetramerous, 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 mor-
phological character; but Professor Asa Gray states that with
some species of Minulus, the aestivation is almost as frequently
that of the Rhinanthidese as of the Antirrhinidese, to which latter
tribe the genus belongs. Aug. St. Ililaire gives the following
cases: the genus Zanthoxylon belongs to a division of the Puta-
cese 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'etend entre le pericarpe et le placenta." In
the flowers of Saponaria officinalis. Dr. Masters has observed

MISCELLANEOUS OBJECTIONS, ETC. 175

instances of both marginal and free central placentation. Lastly,
St. Hilaire found towards the southern extreme of the range of
Gomphia oleseformis two forms which he did not at first doubt
were distinct species, but he subsequently saw them growing on
the same bush ; and he tiien adds, " Voila done dans un meme
individu des logos et un style qui se rattachent tantot a un
axe verticale et tantot a un gynobase."

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 selection. 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 pro-
nounced 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 classifications. The acquisition of a useless part can
hardly be said to raise an organism in the natural scale; and in
the case of the imperfect, closed flowers above described, if any
new principle has to be invoked, it must be one of retrogression
rather than of progression; and so it must be with many parasitic
and degraded animals. We are ignorant of the exciting cause of
the above specified modifications; but if the unknown cause
were to act almost uniformly for a length of time, we may infer
that the result would be almost uniform; and in this case all
the individuals of the species would be modified in the same
manner.

From the fact of the above characters being unimportant for
the welfare of the species, any slight variations which occurred
in them would not have been accumulated and augmented through
natural selection. A structure which has been developed through
long-continued selection, when it ceases to be of service to a
species, generally becomes variable, as we see with rudimentary
organs; for it will no longer be regulated by this same power
of selection. But when, from the nature of the organism and
of the conditions, modifications have been induced which are
unimportant for the welfare of the species, they may be, and
apparently often have been, transmitted in nearly the same
state to numerous, otherwise modified, descendants. It cannot
have been of much importance to the greater number of mam-
mals, birds, or reptiles, whether they were clothed with hair,
feathers, or scales; yet hair has been transmitted to almost all

176 ORIGIN OP SPECIES

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, morphological
differences, which we consider as important — such as the arrange-
men!: 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 con-
ditions, 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 accumlated
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 class-
ification, this is by no means so paradoxical as it may at first
appear.

Although we have no good evidence of the existence in organic
beings of an innate tendency towards progressive development,
yet this necessarily follows, as I have attempted to show in the
fourth chapter, through the continued action 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 per-
form 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

MISCELLANEOUS OBJECTIONS, ETC. 177

attribute nothing to variation, independently of natural selection,
whereas in the work just referred to I have collected a greater
number of well-established cases than can be found in any other
work known to me. My judgment may not be trustworthy, but
after reading with care Mr. Mivart's book, and comparing each
section with what I have said on the same head, I never before
felt so strongly convinced of the general truth of the conclusions
here arrived at, subject, of course, in so intricate a subject, to
much partial error.

All Mr. Mivart's objections will be, or have been, considered
in the present volume. The one new point which appears to
have struck many readers is, " that natural selection is incom-
petent to account for the incipient stages of useful structures."
This subject is intimately connected with that of the gradation
of characters, often accompanied by a change of function, — for
instance, the conversion of a swim-bladder into lungs, — points
which were discussed in the last chapter under two headings.
Nevertheless, I will here consider in some detail several of the
cases advanced by Mr. Mivart, selecting those which are the most
illustrative, as want of space prevents me from considering all.

The giraffe, by its lofty stature, much elongated neck, fore-
legs, head and tongue, has its whole frame beautifully adapted for
browsing on the higher branches of trees. It can thus obtain
food beyond the reach of the other Ungulata or hoofed animals
inhabiting the same country; and this must be a great advantage
to it during dearths. The Niata cattle in S. America show us
how a small difference in structure may make, during such peri-
ods, a great difference in preserving an animal's life. These
cattle can browse as well as others on grass, but from the pro-
jection of the lower jaw they cannot, during the often recurrent
droughts, browse on the twigs of trees, reeds, &c., to which food
the common cattle and horses are then driven; so that at these
times the Niatas perish, if not fed by their owners. Before
coming to Mr. Mivart's objections, it may be well to explain
once again how natural selection will act in all ordinary cases.
Man has modified some of his animals, without necessarily having
attended to special points of structure, by simply 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 individuals of the same

178 ORIGIN OF SPECIES

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 dif-
ferences, due to the laws of growth and variation, are not of the
slightest use or imi^ortance 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,
wpuld 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 selec-
tion will preserve and thus separate all the superior individuals,
allowing them freely to intercross, and will destroy all the inferior
individuals. By this process long-continued, which exactly corre-
sponds with what I have called unconscious selection by man,
combined no doubt in a m.ost important manner with the inherited
effects of the increased use of parts, it seems to me almost certain
that an ordinary hoofed quadruped raight 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 prob-
lematical whether the disadvantages thence arising would not,
in times of scarcity, more than counterbalance the advantages."
But as the giraffe does actually exist in large numbers in S.
Africa, and as some of the largest antelopes in the world, taller
than an ox, abound there, why should we doubt that, as far as
size is concerned, intermediate gradations could formerly have
existed there, subjected as now to severe dearths. Assuredly the
being able to reach, at each stage of increased size, to a supply
of food, left untouched by the other hoofed quadrupeds of the
country, would have been of some advantage to the nascent
giraffe. Nor must we overlook the fact, that increased bulk
would act as a protection against almost all beasts of prey except-
ing the lion ; and against this animal, its tall neck, — and the
taller the better, — would, as Mr. Chauncey Wright has remarked,
serve as a watch-tower. It is from this cause, as Sir S. Baker
remarks, that no animal is more difficult to stalk than the giraffe.
This animal also uses its long neck as a means of offence or
defence, by violently swinging his head armed with stump-like

MISCELLANEOUS OBJECTIONS, ETC. 170

horns. The preservation of each species can rarely be determined
by any one advantage, buL by the union of all, great and small.

Mr. Mivart then asks (and this is his second objection), if
natural selection be so potent, and if high browsing be so great
an advantage, why has not any other hoofed quadruped 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 un-
reasonable 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 pro-
boscis. To reach the foliage at a considerable height (without
climbing, for which hoofed animals are singularly ill-constructed)
implies greatly increased bulk of body; and we know that some
areas support singularly few large quadrupeds, for instance S.
America, though it is so luxuriant; whilst S. Africa abounds
with them to an 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.

180 ORIGIN OP SPECIES

In order than an animal should acquire some structure specially
and largely developed, it is almost indispensable that several other
parts should be modified and co-adapted. Although every part of
the body varies slightly, it does not follow that the necessary
parts should always vary in the right direction and to the right
degree. With the different species of our domesticated animals
we know that the parts vary in a different manner and degree ; and
that some species are much more variable than others. Even if
the fitting 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 process, and the same
favourable conditions must long endure in order that any marked
effect should thus be produced. Except by assigning such general
and vague reasons, we cannot explain why, in many quarters of
the world, hoofed quadrupeds have not acquired much elongated
necks or other means for 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 b© 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 in-
habited 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
colonize and abound on most oceanic islands. Gradations of
structure, with each stage beneficial to a changing species, will

MISCELLANEOUS OBJECTIONS, ETC. 181

be favoured only under certain peculiar conditions. A strictly
terrestrial animal, by occasionally hunting for food in shallow
water, then in streams or lakes, might at last be converted into
an animal so thoroughly aquatic as to brave the open ocean. But
seals would not find on oceanic islands the conditions favour-
able to their gradual reconversion into a terrestrial form. Bats,
as formerly shown, probably acquired their wings by at first
gliding through the air from tree to tree, like the so-called flying
squirrels, for the sake of escaping from their enemies, or for
avoiding falls; but when the power of true flight had once been
acquired, it would never be reconverted back, at least for the
above purposes, into the less eflicient power of gliding through the
air. Bats might, indeed, like many birds, have had their wings
greatly reduced in size, or completely lost, through disuse; but
in this case it would be necessary that they should first have
acquired the power of running quickly on the ground, by the aid
of their hind legs alone, so as to compete with birds or other
ground animals; and for such a change a bat seems singularly
ill-fitted. These conjectural remarks have been made merely to
show that a transition of structure, with each step beneficial,
is a highly complex affair; and that there is nothing strange in
a transition not having occurred in any particular case.

Lastly, more than one writer has asked, why have some animals
had their mental powers more highly developed than others, as
such development would be advantageous to all? Why have not
apes acquired the intellectual powers of man? Various causes
could be assigned; but as they are conjectural, and their relative
probability cannot be weighed, it would be useless to give them.
A definite answer to the latter question ought not to be expected,
seeing that no one can solve the simpler problem why, of two
races of savages, one has risen higher in the scale of civilisation
than the other; and this apparently implies increased brain-power.

We will return to Mr. Mivart's other objections. Insects often
resemble for the sake of protection various objects, such as green
or decayed leaves, dead twigs, bits of lichen, flowers, spines, excre-
ment of birds, and living insects; but to this latter point I shall
hereafter recur. The resemblance is often wonderfully close,
and is not confined to colour, but extends to form, and even to
the manner in which the insects hold themselves. The caterpillars
which project motionless like dead twigs from the bushes on
which they feed, offer an excellent instance of a resemblance of
this kind. The cases of the imitation of such objects as the
excrement of birds, are rare and exceptional. On this head, Mr.
Mivart remarks, "As, according to Mr. Darwin's theory, there

182 ORIGIN OF SPECIES

is a constant tendency to indefinite variation, and as the minute
incipient variations will be in all directioris, they must tend to
neutralise each other, and at first to form such unstable modifica-
tions that it is difiicult, if not impossible, to see h>w such in-
definite oscillations of infinitesimal beginnings can ever build up
a sufiiciently appreciable resemblance to a leaf, bamboo, or other
object, for Natural Selection to seize upon and perpetuate."

But in all the foregoing cases the insects in their original
state no doubt presented some rude and accidental resemblance
to an object commonly found in the stations frequented by
them. Nor is this at all improbable, considering the almost in-
finite number of surrounding objects and the diversity in form
and colour of the hosts of insects which exist. As some rude
resemblance is necessary for the first start, we can understand
how it is that the larger and higher animals do not (with the
exception, as far as I know, of one fish) resemble for the sake
of protection special objects, but only the surface which commonly
surrounds them, and this chiefly in colour. Assuming that an
insect originally happened to resemble in some degree a dead
twig or a decayed leaf, and that it varied slightly in many ways,
then all the variations which rendered the insect at all more
like any such object, and thus favoured its escape, would be
preserved, whilst other variations would be neglected and ulti-
mately lost; or, if they rendered the insect at all less like the
imitated object, they would be eliminated. There would indeed
be force in Mr. Mivart's objection, if we were to attempt to
account for the above resemblances, independently of natural
selection, through mere fluctuating variability; but as the case
stands there is none.

Nor can I see any force in Mr. Mivart's difficulty with respect
to " the last touches of perfection in the mimicry " ; as in the
case given by Mr. Wallace, of a walking-stick insect (Ceroxylus
laceratus), which resembles " a stick grown over by a creeping moss
or jungermannia." So close was this resemblance, that a native
Dyak maintained that the foliaceous excrescences were really
moss. Insects are preyed on by birds and other enemies, whose
sight is probably sharper than ours, and every grade in resem-
blance which aided an insect to escape notice or detection, would
tend towards its preservation ; and the more perfect the resem-
blance so much the better for the insect. Considering the nature
of the differences between the species in the group which includes
the above Ceroxylus, there is nothing improbable in this insect
having varied in the irregularities on its Gurface, and in these
having become more or less green-coloured; for in every group

MISCELLANEOUS OBJECTIONS, ETC. 183

the characters which differ in the several species are the most
apt to vary, whilst the generic characters, or those common to
all the species, are the most constant.

The Greenland whale is one of the most wonderful animals
in the world, and the baleen, or whale-bone, one of its greatest
peculiarities. The baleen consists of a row, on each side, of the
upper jaw, of about 300 plates or laminse, which stand close
together transversely to the longer axis of the mouth. Within
the main row there are some subsidiary rows. The extremities and
inner margins of all the plates are frayed into stiff bristles,
which clothe the whole gigantic palate, and serve to strain or sift
the water, and thus to secure the minute prey on which these
great animals subsist. I'he middle and longest lamina in the
Greenland whale is ten, twelve, or even fifteen feet in length;
but in the different species of Cetaceans there are gradations in
length; the middle lamina being in one species, according to
Scoresby, four feet, in another three, in another eighteen inches,
and in the Balsenoptera rostrata only about nine inches in length.
The quality of the whale-bone also differs in the different species.

With respect to the baleen, Mr. Mivart remarks that if it " had
once attained such a size and development as to be at all useful,
then its preservation and augmentation within serviceable limits
would be promoted by natural selection alone. But how to obtain
the beginning of such useful development ? " In answer, it may
be asked, why should not the early progenitors of the whales with
baleen have possessed a mouth constructed something like the
lamellated beak of a duck? Ducks, like whales, subsist by sifting
the mud and water; and the family has sometimes been called
Crihlatores, or sifters. I hope that I may not be misconstrued
into saying that the progenitors of whales did actually possess
mouths lamellated like the beak of a duck. I wish only to show
that this is not incredible, and that the immense plates of baleen
in the Greenland whale might have been developed from such
lamellae by finely graduated steps, each of service to its possessor.

The beak of a shoveller-duck (Spatula clypeata) is a more
beautiful and complex structure than the mouth of a whale.
The upper mandible is furnished on each side (in the specimen
examined by me) with a row or comb formed of 188 thin, elastic
lamellae, obliquely bevelled so as to be pointed, and placed trans-
versely to the longer axis of the mouth. They arise from the
palate, and are attached by flexible membrane to the sides of the
mandible. Those standing towards the middle are the longest,
being about one-third of an inch in length, and they project .14

184 ORIGIN OF SPECIES

of an inch beneath the edge. At their bases there is a short
subsidiary row of obliquely transverse lamellae. In these several
respects they resemble the plates of baleen in the mouth of a
whale. But towards the extremity of the beak they differ much,
as they project inwards, instead of straight downwards. The
entire head of the shoveller, though incomparably less bulky, is
about one-eighteenth of the length of the head of a moderately
large Balsenoptera rostrata, in which species the baleen is only
nine inches long; so that if we were to make the head of the
shoveller as long as that of the Balsenoptera, the lamellae would
be six inches in length, — that is, two-thirds of the length of
the baleen in this species of whale. The lower mandible of the
shoveller-duck is furnished with lamellae of equal length with
those above, but finer; and in being thus furnished it differs
conspicuously from the lower jaw of a whale, which is destitute
of baleen. On the other hand the extremities of these lower
lamellae are frayed into fine bristly points, so that they thus
curiously resemble the plates of baleen. In the genus Prion, a
member of the distinct family of the Petrels, the upper mandible
alone is furnished with lamellae, which are well developed and
project beneath the margin; so that the beak of this bird re-
sembles in this respect the mouth of a whale.

From the highly developed structure of the shoveller's beak
we may proceed (as I have learnt from information and speci-
mens sent to me by Mr. Salvin), without any great break, as far
as fitness for sifting is concerned, through the beak of the
Merganetta armata, and in some respects through that of the
Aix sponsa, to the beak of the common duck. In this latter
species, the lamellae are m.uch coarser than in the shoveller, and
are firmly attached to the sides of the mandible; they are only
about 50 in number on each side, and do not project at all
beneath, the margin. They are square-topped, and are edged with
translucent hardish tissue, as if for crushing food. The edges
of the lower mandible are crossed by numerous fine ridges, which
project very little. Although the beak is thus very inferior as a
sifter to that of the shoveller, yet this bird, as every one knows,
constantly uses it for this purpose. There are other species, as
I hear from Mr. Salvin, in which the lamellae are considerably
less developed than in the common duck; but I do not know
whether they use their beaks for sifting the water.

Turning to another group of the same family. In the Egyptian
goose (Chenalopex) the beak closely resembles that of the common
duck; but the lamellae are not so numerous, nor so distinct from
each other, nor do they project so much inwards; yet this gogse,

MISCELLANEOUS OBJECTIONS, ETC. 185

as I am informed by Mr. E. Bartlett, " uses its bill like a duck
by throwing the water out at the corners." Its chief food, how-
ever, is grass, which it crops like the common goose. In this
latter bird, the lamellse of the upper mandible are much coarser
than in the common duck, almost confluent, about 27 in number
on each side, and terminating upwards in teeth-like knobs. The
palate is also covered with hard rounded knobs. The edges of the
lower mandible are serrated with teeth much more in-ominent,
coarser, and sharper than in the duck. The common goose does
not sift the water, but uses its beak exclusively for tearing or
cutting herbage, for which purpose it is so well fitted, that it
can crop grass closer than almost any other animal. There are
other species of geese, as I hear from Mr. Bartlett, in which the
lamellae are less developed than in the common goose.

We thus see that a member of the duck family, with a beak
constructed like that of the common goose and adapted solely
for grazing, or even a member with a beak having less well-
developed lamellae, might be converted by small changes into a
species like the Egyptian goose, — this into one like the common
duck, — and, lastly, into one like the shoveller, provided with a
beak almost exclusively adapted for sifting the water ; for this bird
could hardly use any part of its beak, except the hooked tip, for
seizing or tearing solid food. The beak of a goose, as I may add,
might also be converted by small changes into one provided with
prominent, recurved teeth, like those of the Merganser (a member
of the same family), serving for the widely different purpose of
securing live fish.

Returning to the whales. The Hyperoodon bidens is destitute
of true teeth in an efficient condition, but its palate is roughened,
according to Lacepede, with small, unequal, hard points of horn.
There is, therefore, nothing improbable in supposing that some
early Cetacean form was provided with similar points of horn
on the palate, but rather more regularly placed, and which, like
the knobs on the beak of the goose, aided it in seizing or tearing
its food. If so, it will hardly be denied that the points might
have been converted through variation and natural selection into
lamellae as well-developed as those of the Egyptian goose, in
which case they would have been used both for seizing objects and
for sifting the water ; then into lamellae like those of the domestic
duck; and so onwards, until they became as well constructed as
those of the shoveller, in which case they would have served
exclusively as a sifting apparatus. Erom this stage, in which
the lamellae w^ould be two-thirds of the length of the plates of
baleen in the Balaenoptera rostrata, gradations, which may be

186 ORIGIN OF SPECIES

observed in still-existing Cetaceans, lead us onwards to the enor-
mous plates of baleen in the Greenland whale. Nor is there the
least reason to doubt that each step in this scale might have been
as serviceable to certain ancient Cetaceans, with the functions of
the parts slowly changing during the progress of development,
as are the gradations in the beaks of the different existing mem-
bers of the duck-family. We should bear in mind that each
species of duck is subjected to a severe struggle for existence,
and that the structure of every part of its frame must be well
adapted to its conditions of life.

The Pleuronectidae, or Flat-fish, are remarkable for their asym-
metrical bodies. They rest on one side, — in the greater number
of species on the left, but in some on the right side; and occa-
sionally reversed adult specimens occur. The lower, or resting-
surface, resembles at first sight the ventral surface of an ordinary
fish: it is of a white colour, less developed in many ways than the
upper side, with the lateral fins often of smaller size. But the
eyes offer the most remarkable peculiarity; for they are both
placed on the upper side of the head. During early youth, how-
ever, they stand opposite to each other, and the whole body is
then symmetrical, with both sides equally coloured. Soon the
eye proper to the lower side begins to glide slowly round the
head to the upper side; but does not pass right through the skull,
as was formerly thought to be the case. It is obvious that unless
the lower eye did thus travel round, it could not be used by the
fish whilst lying in its habitual position on one side. The lower
eye would, also, have been liable to be abraded by the sandy bot-
tom. That the Pleuronectidse are admirably adapted by their
flattened and asymmetrical structure for their habits of life, is
manifest from several species, such as soles, flounders, &c., being
extremely common. The chief advantages thus gained seem to
be protection from their enemies, and facility for feeding on
the ground. The different members, however, of the family pres-
ent, as Schiodte remarks, " a long series of forms exhibiting a
gradual transition from Hippoglossus iDinguis, which does not
in any considerable degree alter the shape in which it leaves the
ovum, to the soles, which are entirely thrown to one side."

Mr. Mivart has taken up this case, and remarks that a sudden
spontaneous transformation in the position of the eyes is hardly
conceivable, in which I quite agree with him. He then adds :
" if the transit was gradual, then how such transit of one eye
a minute fraction of the journey towards the other side of the
head could benefit the individual is, indeed, far from clear. It
seems, even, that such an incipient transformation must rather

MISCELLANEOUS OBJECTIONS, ETC. 187

have been injurious." But he might have found an answer to
this objection in the excellent observations published in 1867 by
Malm. The Pleuronectida}, whilst very young and still symmet-
rical, with their eyes standing on opposite sides of the head, cannot
long retain a vertical position, owing to the excessive depth of
their bodies, the small size of their lateral fins, and to their
being destitute of a swimbladder. Hence soon growing tired,
they fall to the bottom on one side. Whilst thus at rest they
often twist, as Malm observed, the lower eye upwards, to see
above them; and they do this so vigorously that the eye is
pressed hard against the upper part of the orbit. The forehead
between the eyes consequently becomes, as could be plainly seen,
temporarily contracted in breadth. On one occasion Malm saw
a young fish raise and dei)ress the lower eye through an angular
distance of about seventy degrees.

Wo should remember that the skull at this early age is carti-
laginous and flexible, so that it readily yields to muscular action.
It is also known with the higher animals, even after early youth,
that the skull yields and is altered in shape, if the skin or muscles
be permanently contracted through disease or some accident.
With long-eared rabbits, if one ear lops forwards and downwards,
its weight drags forward all the bones of the skull on the same
side, of which I have given a figure. Malm states that the newly-
hatched young of perches, salmon, and several other symmetrical
fishes, have the habit of occasionally resting on one side at the
bottom; and he has observed that they often then strain their
lower eyes so as to look upwards; and their skulls are thus
rendered rather crooked. These fishes, however, are soon able
to hold themselves in a vertical position, and no permanent effect
is thus produced. With the Pleuronectidre, on the other hand,
the older they grow the more habitually they rest on one side,
owing to the increasing flatness of their bodies, and a permanent
effect is thus produced on the form of the head, and on the posi-
tion of the eyes. Judging from analogy, the tendency to distor-
tion would no doubt be increased through the principle of in-
heritance. Schiodte believes, in opposition to some other natural-
ists, that the Pleuronectidse are not quite symmetrical even in the
embryo; and if this be so, we could understand how it is that
certain species, whilst young, habitually fall over and rest on the
left side, and other species on the right side. Malm adds, in
confirmation of the above view, that the adult Trachypterus
arcticus, which is not a member of the Pleuronectidse, rests on
its left side at the bottom, and swims diagonally through the
water; and in this fish, the two sides of the head are said to be

188 ORIGIN OP SPECIES

somewhat dissimilar. Our great authority on Fishes, Dr. Giin-
ther, concludes his abstract on Malm's paper, by remarking that
" the author gives a very simple explanation of the abnormal con-
dition of the Pleuronectoids."

We thus see that the first stages of the transit of the eye from
one side of the head to the other, which Mr. Mivart considers
would be injurious, may be attributed to the habit, no doubt
beneficial to the individual and to the species, of endeavouring to
look upwards with both eyes, whilst resting on one side at the
bottom. We may also attribute to the inherited effects of use the
fact of the mouth in several kinds of flat-fish being bent towards
the lower surface, with the jaw bones stronger and more effective
on this, the eyeless side of the head, than on the other, for the
sake, as Dr. Traquair supposes, of feeding with ease on the ground.
Disuse, on the other hand, will account for the less developed
condition of the whole inferior half of the body, including the
lateral fins; though Yarrell thinks that the reduced size of these
fins is advantageous to the fish, as " there is so much less room
for their action, than with the larger fins above." Perhaps the
lesser number of teeth in the proportion of four to seven in the
upper halves of the two jaws of the plaice, to twenty-five to thirty
in the lower halves, may likewise be accounted for by disuse.
From the colourless state of the ventral surface of most fishes
and of many other animals, we may reasonably suppose that the
absence of colour in flat-fish on the side, whether it be the right
or left, which is undermost, is due to the exclusion of light.
But it cannot be supposed that the peculiar speckled appearance
of the upper side of the sole, so like the sandy bed of the sea,
or the power in some species, as recently shown by Pouchet, of
changing their colour in accordance with the surrounding surface,
or the presence of bony tubercles on the upper side of the turbot,
are due to the action of the light. Here natural selection has
probably come into play, as well as in adapting the general shape
of the body of these fishes, and many other peculiarities, to their
habits of life. We should keep in mind, as I have before insisted,
that the inherited effects of the increased use of parts, and per-
haps of their disuse, will be strengthened by natural selection.
For all spontaneous variations in the right direction will thus
be preserved ; as will those individuals which inherit in the highest
degree the effects of the increased and beneficial use of any part.
How much to attribute in each particular case to the effects of
use, and how much to natural selection, it seems impossible to
decide.

I may give another instance of a structure which apparently

MISCELLANEOUS OBJECTIONS, ETC. 189

owes its origin exclusively to use or habit. The extremity of
the tail in some American monkgys has been converted into a
wonderfully perfect prehensile organ, and serves as a fifth hand.
A reviewer who agrees with Mr. Mivart in every detail, remarks
on this structure : " It is impossible to believe that in any num-
ber of ages the first slight incipient tendency to grasp could
preserve the lives of the individuals possessing it, or favour their
chance of having and of rearing offspring." But there is no
necessity for any such belief. Habit, and this almost implies
that some benefit great or small is thus derived, would in all
probability suffice for the work. Brehm saw the young of an
African monkey (Cercopithecus) clinging to the under surface
of their mother by their hands, and at the same time they hooked
their little tails round that of their mother. Professor Henslow
kept in confinement some harvest mice (Mus messorius) which do
not possess a structurally prehensile tail; but he frequently ob-
served that they curled their tails round the branches of a bush
placed in the cage, and thus aided themselves in climbing. I have
received an analogous account from Dr. Giinther, who has seen
a mouse thus suspend itself. If the harvest mouse had been
more strictly arboreal, it would perhaps have had its tail rendered
structurally prehensile, as is the case with some members of the
same order. Why Cercopithecus, considering its habits whilst
young, has not become thus provided, it would be difficult to say.
It is, however, possible that the long tail of this monkey may be
of more service to it as a balancing organ in making its pro-
digious leaps, than as a prehensile organ.

The mammary glands are common to the whole class of mam-
mals, and are indispensable for their existence; they must, there-
fore, have been developed at an extremely remote period, and
we can know nothing positively about their manner of de-
velopment. Mr. Mivart asks : " Is it conceivable that the young
of any animal was ever saved from destruction by accidentally
sucking a drop of scarcely nutritious fluid from an accidentally
hypertrophied cutaneous gland of its mother? And even if one
was so, what chance was there of the perpetuation of such a
variation ? " But the case is not here put fairly. It is admitted
by most evolutionists that mammals are descended from a marsu-
pial form ; and if so, the mammary glands will have been at first
developed within the marsupial sack. In the case of the fish
(Hippocampus) the eggs are hatched, and the young are reared
for a time, within a sack of this nature; and an American natu-
ralist, Mr. Lockwood, believes from what he has seen of the

190 ORIGIN OF SPECIES

development of the young, that they are nourished by a secretion
from the cutaneous glands of the sack. Now with the early
progenitors of mammals, almost before they deserved to be thus
designated, is it not at least possible that the young might have
been similarly nourished? And in this case, the individuals
which secreted a fluid, in some degree or manner the most nutri-
tious, so as to partake of the nature of milk, would in the long
run have reared a larger number of well-nourished offspring, than
would the individuals which secreted a poorer fluid; and thus
the cutaneous glands, which are the homologues of the mammary
glands, would have been improved or rendered more effective.
It accords with the widely extended principle of specialisation,
that the glands over a certain space of the sack should have
become more highly developed than the remainder ; and they would
then have formed a breast, but at first without a nipple, as we
see in the Ornithorhyncus, at the base of the mammalian series.
Through what agency the glands over a certain space became
more highly specialised than the others, I will not pretend to
decide, whether in part through compensation of growth, the
effects of use, or of natural selection.

The development of the mammary glands would have been
of no service, and could not have been effected through natural
selection, unless the young at the same time were able to partake
of the secretion. There is no greater difficulty in understanding
how young mammals have instinctively learnt to suck the breast,
than in understanding how unhatched chickens have learnt to
break the egg-shell by tapping against it with their specially
adapted beaks; or how a few hours after leaving the shell they
have learnt to pick up grains of food. In such cases the most
probable solution seems to be, that the habit was at first acquired
by practice at a more advanced age, and afterwards transmitted
to the offspring at an earlier age. But the young kangaroo is
said not to suck, only to cling to the nipple of its mother, who
has the power of injecting milk into the mouth of her helpless,
half -formed offspring. On this head, Mr. Mivart remarks : " Did
no special provision exist, the young one must infallibly be
choked by the intrusion of the milk into the windpipe. But
there is a special provision. The larynx is so elongated that it
rises up into the posterior end of the nasal passage, and is thus
enabled to give free entrance to the air for the lungs, while the
milk passes harmlessly on each side of this elongated larynx, and
so safely attains the gullet behind it." Mr. Mivart then asks
how did natural selection remove in the adult kangaroo (and in
most other mammals, on the assumption that they are descended

MISCELLANEOUS OBJECTIONS, ETC. 191

from a marsupial form), "this at least perfectly innocent and
harmless structure ? " It may be suggested in answer that the
voice, which is certainly of high importance to many animals,
could hardly have been used with full force as long as the larynx
entered the nasal passage; and Professor Flower has suggested
to me that this structure would have greatly interfered with an
animal swallowing solid food.

We will now turn for a short space to the lower divisions of
the animal kingdom. The Echinodermata (star-fishes, sea-
urchins, &c.) are furnished with remarkable organs, called pedicel-
lariae, which consist, when well developed, of a tridactyle forceps
— that is, of one formed of three serrated arms, neatly fitting
together and placed on the summit of a flexible stem, moved by
muscles. These forceps can seize firmly hold of any object;
and Alexander Agassiz has seen an Echinus or sea-urchin rapidly
passing particles of excrement from forceps to forceps down
certain lines of its body, in order that its shell should not be
fouled. But there is no doubt that besides removing dirt of all
kinds, they subserve other functions; and one of these apparently
is defence.

With respect to these organs, Mr. Mivart, as on so many pre-
vious occasions, asks : " What would be the utility of the first
rudimentary heginnings of such structures, and how could such
incipient buddings have ever preserved the life of a single Echi-
nus ? " He adds, " not even the sudden development of the snap-
ping action could have been beneficial without the freely move-
able stalk, nor could the latter have been efficient without the
snapping jaws, yet no minute merely indefinite variations could
simultaneously evolve these complex co-ordinations of structure;
to deny this seems to do no less than to affirm a startling para-
dox." Paradoxical as this may appear to Mr. Mivart, tridactyle
forcepses, immovably fixed at the base, but capable of a snapping
action, certainly exist on some star-fishes; and this is intelligible
if they serve, at least in part, as a means of defence. Mr. Agassiz,
to whose great kindness I am indebted for much information
on the subject, informs me that there are other star-fishes, in
which one of the three arms of the forceps is reduced to a sup-
port for the other two ; and again, other genera in which the
third arm is completely lost. In Echinoneus, the shell is de-
scribed by M. Perrier as bearing two kinds of pedicellarise, one
resembling those of Echinus, and the other those of Spatangus;
and such cases are always interesting as affording the means of
apparently sudden transitions, through the abortion of one of
the two states of an organ.

192 ORIGIN OF SPECIES

With respect to the steps by which these curious organs have
been evolved, Mr. Agassiz infers from his own researches and those
of Miiller, that both in ytar-fishes and sea-urchins the pedicellarise
must undoubtedly be looked at as modified spines. This may be
inferred from their manner of development in the individual, as
well as from a long and perfect series of gradations in different
species and genera, from simple granules to ordinary spines, to
perfect tridactyle pedicellaria?. The gradations extend even to
the manner in which ordinary spines and pedicellarise with their
supporting calcareous rods are articulated to the shell. In certain
genera of star-fishes, " the very combinations needed to show that
the pedicellariae are only modified branching spines " may be
found. Thus we have fixed spines, with three equi-distant, ser-
rated, moveable branches, articulated to near their bases; and
higher up, on the same spine, three other moveable branches.
Now when the latter arise from the summit of a spine they form
in fact a rude tridactyle pedicellaria, and such may be seen on
the same spine together with the three lower branches. In this
case the identity in nature between the arms of the pedicellarise
and the moveable branches of a spine, is unmistakable. It is
generally admitted that the ordinary spines serve as a protection;
and if so, there can be no reason to doubt that those furnished
with serrated and moveable branches likewise serve for the same
purpose; and they would thus serve still more effectively as soon
as by meeting together they acted as a prehensible or snapping
apparatus. Thus every gradation, from an ordinary fixed spine to
a fixed pedicellaria, would be of service.

In certain genera of star-fishes these organs, instead of being
fixed or borne on an immovable support, are placed on the summit
of a flexible and muscular, though short, stem ; and in this case
they probably subserve some additional function besides defence.
In the sea-urchins the steps can be followed by which a fixed
spine becomes articulated to the shell, and is thus rendered move-
able. I wish I had space here to give a fuller abstract of Mr.
Agassiz's interesting observations on the development of the
pedicellarise. All possible gradations, as he adds, may likewise be
found between the pedicellarise of the star-fishes and the hooks of
the Ophiurians, another group of Echinodermata ; and again be-
tween the pedicellarise of sea-urchins and the anchors of the Holo-
thurise, also belonging to the same great class.

Certain compound animals, or zoophytes as they have been
termed, namely the Polyzoa, are provided with curious organs
called avicularia. These differ much in structure in the different

MISCELLANEOUS OBJECTIONS, ETC. 193

species. In their most perfect condition, they curiously resemble
the head and beak of a vulture in miniature, seated on a neck and
capable of movement, as is likewise the lower jaw or mandible.
In one species observed by me all the avicularia on the same
branch often moved simultaneously backwards and forwards, with
the lower jaw widely open, through an angle of about 90°, in the
course of five seconds; and their movement caused the whole poly-
zoary to tremble. When the jaws are touched with a needle they
seize it so firmly that the branch can thus be shaken.

Mr. Mivart adduces this case, chiefly on account of the sup-
posed difficulty of organs, namely the avicularia of the Polyzoa
and the pedicellarise of the Echinodermata, which he considers as
^^ essentially similar," having been developed through natural se-
lection in widely distinct divisions of the animal kingdom. But,
as far as structure is concerned, I can see no similarity between
tridactyle pedicellarise and avicularia. The latter resemble some-
what more closely the chelae or pincers of Crustaceans; and Mr.
Mivart might have adduced with equal appropriateness this re-
semblance as a special difficulty; or even their resemblance to
the head and beak of a bird. The avicularia are believed by Mr.
Busk, Dr. Smitt, and Dr. ISTitsche — naturalists who have care-
fully studied this group — to be homologous with the zooids and
their cells which compose the zoophyte; the moveable lip or lid
of the cell corresponding with the lower and moveable mandible
of the avicularium. Mr. Busk, however, does not know of any
gradations now existing between a zooid and an avicularium.
It is therefore impossible to conjecture by what serviceable grada-
tions the one could have been converted into the other: but it
by no means follows from this that such gradations have not ex-
isted.

As the chelae of Crustaceans resemble in some degree the avicu-
laria of Polyzoa, both serving as pincers, it may be worth while
to show that with the former a long series of serviceable grada-
tions still exists. In the first and simplest stage, the terminal
segment of a limb shuts down either on the square summit of the
broad penultimate segment, or against one whole side; and is thus
enabled to catch hold of an object; but the limb still serves as an
organ of locomotion. We next find one corner of the broad penul-
timate segment slightly prominent, sometimes furnished with
irregular teeth; and against these the terminal segment shuts
down. By an increase in the size of this projection, with its
shape, as well as that of the terminal segment, slightly modified
and improved, the pincers are rendered more and more perfect,^

194 ORIGIN OP SPECIES

■until we Iiave at last an instrument as efficient as the chelae of a
lobster; and all these gradations can be actually traced.

Besides the avicularia, the Polyzoa possess curious organs called
vibracula. These generally consist of long bristles, capable of
movement and easily excited. In one species examined by me
the vibracula were slightly curved and serrated along the outer
margin; and all of them on the same polyzoary often moved
simultaneously ; so that, acting like 'long oars, they swept a branch
rapidly across the object-glass of my microscope. When a branch
was placed on its face, the vibracula became entangled, and they
made violent efforts to free themselves. They are supposed to
serve as a defence, and may be seen, as Mr. Busk remarks, " to
sweep slowly and carefully over the surface of the polyzoary, re-
moving what might be noxious to the delicate inhabitants of the
cells when their tentacula are protruded." The avicularia, like
the vibracula, probably serve for defence, but they also catch and
kill small living animals, which it is believed are afterwards
swept by the currents within reach of the tentacula of the zooids.
Some species are provided with avicularia and vibracula; some
with avicularia alone, and a few with vibracula alone.

It is not easy to imagine two objects more widely different in
appearance than a bristle or vibraculum, and an avicularium
like the head of a bird; yet they are almost certainly homologous
and have been developed from the same common source, namely
a zooid with its cell. Hence we can understand how it is that
these organs graduate in some cases, as I am informed by Mr.
Busk, into each other. Thus with the avicularia of several species
of Lepralia, the moveable mandible is so much produced and is
so like a bristle, that the presence of the upper or fixed beak
alone serves to determine its avicularian nature. The vibracula
may have been directly developed from the lips of the cells, with-
out having passed through the avicularian stage; but it seems
more probable that they have passed through this stage, as during
the early stages of the transformation, the other parts of the cell
with the included zooid could hardly have disappeared at once.
In many cases the vibracula have a grooved support at the base,
which seems to represent the fixed beak; though this support in
some species is quite absent. This view of the development of
the vibracula, if trustworthy, is interesting; for supposing that
all the species provided with avicularia had become extinct, no
one with the most vivid imagination would ever have thought that
the vibracula had originally existed as part of an organ, resem-
bling a bird's head or an irregular box or hood. It is interesting
to see two such widely different organs developed from a common

MISCELLANEOUS OBJECTIONS, ETC. 195

origin; and as the moveable lip of the cell serves as a protection
to the zooid, there is no difficulty in believing that all the grada-
tions, by which the lip became converted first into the lower
mandible of an avicularium and then into an elongated bristle,
likewise served as a protection in different ways and under dif-
ferent circumstances.*

In the vegetable kingdom Mr. Mivart only alludes to two cases,
namely the structure of the flowers of orchids, and the n*iove-
ments of climbing plants. With respect to the former, he says,
" the explanation of their origin is deemed thoroughly unsatisfac-
tory— utterly insufficient to explain the incipient, infinitesimal
beginnings of structures which are of utility only when they are
considerably developed." As I have fully treated this subject in
another work, I will here give only a few details on one alone of
the most striking peculiarities of the flowers of orchids, namely
their pollinia. A pollinium when highly developed consists of a
mass of pollen-grains, affixed to an elastic foot-stalk or caudicle,
and this to a little mass of extremely viscid matter. The pollinia
are by this means transported by insects from one flower to the
stigma of another. In some orchids there is no caudicle to the
pollen-masses, and the grains are merely tied together by fine
threads ; but as these are not confined to orchids, they need not
here be considered; yet I may mention that at the base of the
orchidaceous series, in Cypripedium, we can see how the threads
were probably first developed. In other orchids the threads
cohere at one end of the pollen-masses; and this forms the first or
nascent trace of a caudicle. That this is the origin of the cau-
dicle, even when of considerable length and highly developed, we
have good evidence in the aborted pollen-grains which can some-
times be detected embedded within the central and solid parts.

With respect to the second chief peculiarity, namely the little
mass of viscid matter attached to the end of the caudicle, a long
series of gradations can be specified, each of plain service to the
plant. In most flowers belonging to other orders the stigma se-
cretes a little viscid matter. Now in certain orchids similar viscid
matter is secreted, but in much larger quantities by one alone of
the three stigmas; and this stigma, perhaps in consequence of the
copious secretion, is rendered sterile. When an insect visits a
flower of this kind, it rubs off some of the viscid matter and thus
at the same time drags away some of the pollen-grains. From
this simple condition, which differs but little from that of a multi-
tude of common flowers, there are endless gradations, — to species

* Mr. Darwin's views on this interesting feature of Natural Selection
have been strongly supported by more recent observation,

196 ORIGIN OF SPECIEB

in which the pollen-tnass terminates in a very short, free caudicle,
— to others in which the caudicle becomes firmly attached to the
viscid matter, with the sterile stigma itself much modified. In
this latter case we have a pollinium in its most highly developed
and perfect condition. He who will carefully examine the flowers
of orchids for himself will not deny the existence of the above series
of gradations — from a mass of pollen-grains merely tied together
by threads, with the stigma differing but little from that of an
ordinary flower, to a highly complex pollinium, admirably adapted
for transportal by insects ; nor will he deny that all the gradations
in the several species are admirably adapted in relation to the
general structure of each flower for its fertilisation by different
insects. In this, and in almost every other case, the enquiry may
be pushed further backwards; and it may be asked how did the
stigma of an ordinary flower become viscid, but as we do not
know the full history of any one group of beings, it is as useless
to ask, as it is hopeless to attempt answering, such questions.

We will now turn to climbing plants. These can be arranged
in a long series, from those which simply twine round a support,
to those which I have called leaf-climbers, and to those provided
with tendrils. In these two latter classes the stems have gener-
ally, but not always, lost the power of twining, though they retain
the power of revolving, which the tendrils likewise possess. The
gradations from leaf-climbers to tendril-bearers are wonderfully
close, and certain plants may be indifferently placed in either
class. But in ascending the series from simple twiners to leaf-
climbers, an important quality is added, namely sensitiveness to a
touch, by which means the foot-stalks of the leaves or flowers, or
these modified and converted into tendrils, are excited to bend
round and clasp the touching object. He who will read my
memoir on these plants will, I think, admit that all the many
gradations in function and structure between simple twiners and
tendril-bearers are in each case beneficial in a high degree to the
species. For instance, it is clearly a great advantage to a twin-
ing plant to become a leaf -climber ; and it is probable that every
twiner which possessed leaves with long foot-stalks would have
been developed into a leaf-climber, if the foot-stalks had pos-
sessed in any slight degree the requisite sensitiveness to a touch.

As twining is the simplest means of ascending a support, and
forms the basis of our series, it may naturally be asked how did
plants acquire this power in an incipient degree, afterwards to be
improved and increased through natural selection. The power of
twining depends, firstly, on the stems whilst young being ex-
tremely flexible (but this is a character common to many plants

MISCELLANEOUS OBJECTIONS, ETC. 197

which are not climbers) ; and, secondly, on their continually bend-
ing to all points of the compass, one after the other in succession,
in the same order. By this movement the stems are inclined to
all sides, and are made to move round and round. As soon as tho
lower part of a stem strikes against any object and is stopped, the
upper part still goes on bending and revolving, and thus neces-
sarily twines round and up the support. The revolving move-
ment ceases after the early growth of each shoot. As in many
widely separated families of plants, single species and single
genera possess the power of revolving, and have thus become
twiners, they must have independently acquired it, and cannot
have inherited it from a common progenitor. Hence I was led
to predict that some slight tendency to a movement of this kind
would be found to be far from uncommon with plants which did
not climb; and that this had afforded the basis for natural selec-
tion to work on and improve. When I made this prediction, I
knew of only one imperfect case, namely, of the young flower-
peduncles of a Maurandia which revolved slightly and irregularly,
like the stems of twining plants, but without making any use of
this habit. Soon afterwards Fritz Miiller discovered that the
young stems of an Alisma and of a Linum, — plants which do not
climb and are widely separated in the natural system, — revolved
plainly, though irregularly; and he states that he has reason to
suspect that this occurs with some other plants. These slight
movements appear to be of no service to the plants in question;
anyhow, they are not of the least use in the way of climbing,
which is the point that concerns us. Nevertheless we can see that
if the stems of these plants had been flexible, and if under the
conditions to which they are exposed it had profited them to
ascend to a height, then the habit of slightly and irregularly re-
volving might have been increased and utilised through natural
selection, until they had become converted into well-developed
twining species.

With respect to the sensitiveness of the foot-stalks of the leaves
and flowers, and of tendrils, nearly the same remarks are ap-
plicable as in the case of the revolving movements of twining
plants. As a vast number of species, belonging to widely dis-
tinct groups, are endowed with this kind of sensitiveness, it ought
to be found in a nascent condition in many plants which have
not become climbers. This is the case : I observed that the
young flower-peduncles of the above Maurandia curved themselves
a little towards the side which was touched. Morren found in
several species of Oxalis that the leaves and their foot-stalks
moved, especially after exposure to a hot sun, when they were

198 ORIGIN OF SPECIES

gently and repeatedly touched, or when the plant was shaken. I
repeated these observations on some other species of Oxalis with
the same result; in some of them the movement was distinct, but
was best seen in the young leaves; in others it was extremely
slight. It is a more important fact that according to the high
authority of Hofmeister, the young shoots and leaves of all plants
move after being shaken; and with climbing plants it is, as we
know, only during the early stages of growth that the foot-stalks
and tendrils are sensitive.

It is scarcely possible that the above slight movements, due to
a touch or shake, in the young and growing organs of plants, can
be of any functional importance to them. But plants possess, in
obedience to various stimuli, powers of movement, which are of
manifest importance to them; for instance, towards and more
rarely from the light, — in opposition to, and more rarely in the
direction of, the attraction of gravity. When the nerves and
muscles of an animal are excited by galvanism or by the absorp-
tion of strychnine, the consequent movements may be called an
incidental result, for the nerves and muscles have not been ren-
dered specially sensitive to these stimuli. So with plants it ap-
pears that, from having the power of movement in obedience
to certain stimuli, they are excited in an incidental manner by a
touch, or by being shaken. Hence there is no great difficulty in
admitting that in the case of leaf-climbers and tendril-bearers, it
is this tendency which has been taken advantage of and increased
through natural selection. It is, however, probable, from reasons
which I have assigned in my memoir, that this will have occurred
only with plants which had already acquired the power of revolv-
ing, and had thus become twiners.

I have already endeavoured to explain how plants became
twiners, namely, by the increase of a tendency to slight and ir-
regular revolving movements, which were at first of no use to
them; this movement, as well as that due to a touch or shake,
being the incidental result of the power of moving, gained for
other and beneficial purposes. Whether, during the gradual de-
velopment of climbing plants, natural selection has been aided by
the inherited effects of use, I will not pretend to decide; but we
know that certain periodical movements, for instance the so-called
sleep of plants, are governed by habit.

I have now considered enough, perhaps more than enough, of
the cases, selected with care by a skilful naturalist, to prove that
natural selection is incompetent to account for the incipient
stages of useful structures ; and I have shown, as I hope, that there

MISCELLANEOUS OBJECTIONS, ETC. 199

is no great difficulty on this head. A good opportunity has thus
been afforded for enlarging a little on gradations of structure,
often associated with changed functions, — an important subject,
which was not treated at sufficient length in the former editions of
this work. I will now briefly recapitulate the foregoing cases.

With the giraffe, the continued preservation of the individuals
of some extinct high-reaching ruminant, which had the longest
necks, legs, &c., and could browse a little above the average height,
and the continued destruction of those which could not browse
so high, would have sufficed for the production of this remarkable
quadruped; but the prolonged use of all the parts together with
inheritance will have aided in an important manner in their co-
ordination. With the many insects which imitate various ob-
jects, there is no improbability in the belief that an accidental
resemblance to some common object was in each case the founda-
tion for the work of natural selection, since perfected through the
occasional preservation of slight variations which made the re-
semblance at all closer; and this will have been carried on as
long as the insect continued to vary, and as long as a more and
more perfect resemblance led to its escape from sharp-sighted
enemies. In certain species of whales there is a tendency to the
formation of irregular little points of horn on the palate; and it
seems to be quite within the scope of natural selection to preserve
all favourable variations, until the points were converted first into
lamellated knobs or teeth, like those on the beak of a goose, — then
into short lamellae, like those of the domestic ducks, — and then
into lamellae, as perfect as those of the shoveller-duck, — and finally
into the gigantic plates of baleen, as in the mouth of the Green-
land whale. In the family of the ducks, the lamellae are first
used as teeth, then partly as teeth, and partly as a sifting appara-
tus, and at last almost exclusively for this latter purpose.

With such structures as the above lamellae of horn or whalebone,
habit or use can have done little or nothing, as far as we can
judge, towards their development. On the other hand, the trans-
portal of the lower eye of a flat-fish to the upper side of the head,
and the formation of a prehensile tail, may be attributed almost
wholly to continued use, together with inheritance. With respect
to the mammae of the higher animals, the most probable con-
jecture is that primordially the cutaneous glands over the whole
surface of a marsupial sack secreted a nutritious fluid; and that
these glands were improved in function through natural selection,
and concentrated into a confined area, in which case they would
have formed a mamma. There is no more difficulty in under-
standing how the branched spines of some ancient Echinoderm,

200 ORIGIN OF SPECIES

which served as a defence, became developed through natural selec-
tion into tridactyle pedicellariee, than in understanding the de-
velopment of the pincers of crustaceans, through slight, serviceable
modifications in the ultimate and penultimate segments of a limb,
which was at first used solely for locomotion. In the avicularia
and vibracula of the Polyzoa we have organs widely different in
appearance developed from the same source; and with the vibrac-
ula we can understand how the successive gradations might have
been of service. With the pollinia of orchids, the threads which
originally served to tie together the pollen-grains, can be traced
cohering into caudicles; and the steps can likewise be followed
by which viscid matter, such as that secreted by the stigmas of
ordinary flowers, and still subserving nearly but not quite the
same purpose, became attached to the free ends of the caudicles;
— all these gradations being of manifest benefit to the plants
in question. With respect to climbing plants, I need not repeat
what has been so lately said.

It has often been asked, if natural selection be so potent, why
has not this or that structure been gained by certain species, to
which it would apparently have been advantageous? But it is
unreasonable to expect a precise answer to such questions, con-
sidering our ignorance of the past history of each species, and of
the conditions which at the present day determine its numbers
and range. In most cases only general reasons, but in some few
cases special reasons, can be assigned. Thus to adapt a species
to new habits of life, many co-ordinated modifications are almost
indispensable, and it may often have happened that the requisite
parts did not vary in the right manner or to the right degree.
Many species must have been prevented from increasing in num-
bers through destructive agencies, which stood in no relation to
certain structures, which we imagine would have been gained
through natural selection from appearing to ns advantageous to
the species. In this case, as the struggle for life did not depend
on such structures, they could not have been acquired through
natural selection. In many cases complex and long-enduring
conditions, often of a peculiar nature, are necessary for the de-
velopment of a structure; and the requisite conditions may seldom
have concurred. The belief that any given structure, which we
think, often erroneously, would have been beneficial to a species,
would have been gained nnder all circumstances through natural
selection, is opposed to what we can understand of its manner of
action. Mr. Mivart does not deny that natural selection has ef-
fected something ; but he considers it as " demonstrably insuffi-
cient " to account for the phenomena which I explain by its

MISCELLANEOUS OBJECTIONS, ETC. 201

agency. Ilis chief arguments have now been considered, a id the
others will hereafter be considered. They seem to lac t.- partake
little of the character of demonstration, ai.d *■(,. • lit..!', weight

in comparison with those in favour of the . tnrai selec-

tion, aided by the other agencies often specj led. ^ a.n bound to
add, that some of the facts and arguments here used by me, have
been advanced for the same purpose in an able article lately pub-
lished in the ' Medico-Chirurgical Review.'

At the present day almost all naturalists admit evolution under
some form. Mr. Mivart believes that species change through " an
internal force or tendency," about which it is not pretended that
anything is known. That species have a capacity for change will
be admitted by all evolutionists; but there is no need, as it seems
to me, to invoke any internal force beyond the tendency to or-
dinary variability, which through the aid of selection by man has
given rise to many well-adapted domestic races, and which through
the aid of natural selection would equally well give rise by grad-
uated steps to natural races or species. The final result will gen-
erally have been, as already explained, an advance, but in some
few cases a retrogression, in organisation.

Mr. Mivart is further inclined to believe, and some naturalists
agree with him, that new species manifest themselves " with sud-
denness and by modifications appearing at once." For instance,
he supposes that the difi^erences between the extinct three-toed
Hipparion and the horse arose suddenly. He thinks it difiicult
to believe that the wing of a bird " was developed in any other
way than by a comparatively sudden modification of a marked
and important kind ;" and apparently he would extend the same
view to the wings of bats and pterodactyles. This conclusion,
which implies great breaks or discontinuity in the series, appears
to me improbable in the highest degree.

Every one who believes in slow and gradual evolution, will of
course admit that specific changes may have been as abrupt and
as great as any single variation which we meet with under nature,
or even under domestication. But as species are more variable
when domesticated or cultivated than under their natural con-
ditions, it is not probable that such great and abrupt variations
have often occurred under nature, as are known occasionally to
arise under domestication. Of these latter variations several may
be attributed to reversion; and the characters which thus reappear
were, it is probable, in many cases at first gained in a gradual
manner. A still greater number must be called monstrosities,
such as six-fingered men, porcupine men, Ancon sheep, Niata cat-
tle, &c. ; and as they are widely different in character from natural

202 ORIGIN OF SPECIES

species, they throw very little light on our subject. Excluding
such cases of abrupt variations, the few which remain would at
best constitute, if found in a state of nature, doubtful species,
closely related to their parental types.

My reasons for doubting whether natural species have changed
as abruptly as have occasionally domestic races, and for entirely
disbelieving that they have changed in the wonderful manner
indicated by Mr. Mivart, are as follows. According to our ex-
perience, abrupt and strongly marked variations occur in our
domesticated productions, singly and at rather long intervals of
time. If such occurred under nature, they would be liable, as
formerly explained, to be lost by accidental causes of destruction
and by subsequent inter-crossing; and so it is known to be under
domestication, unless abrupt variations of this kind are specially
preserved and separated by the care of man. Hence in order that
a new species should suddenly appear in the manner supposed by
Mr. Mivart, it is almost necessary to believe, in opposition to all
analogy, that several wonderfully changed individuals appeared
simultaneously within the same district. This difficulty, as in the
case of unconscious selection by man, is avoided on the theory of
gradual evolution, through the preservation of a large number of
individuals, which varied more or less in any favourable direc-
tion, and of the destruction of a large number which varied in
an opposite manner.

That many species have been evolved in an extremely gradual
manner, there can hardly be a doubt. The species and even the
genera of many large natural families are so closely allied to-
gether, that it is difficult to distinguish not a few of them. On
every continent in proceeding from north to south, from lowland
to upland, &c., we meet with a host of closely related or representa-
tive species; as we likewise do on certain distinct continents, which
we have reason to believe were formerly connected. But in mak-
ing these and the following remarks, I am compelled to allude
to subjects hereafter to be discussed. Look at the many outlying
islands round a continent, and see how many of their inhabitants
can be raised only to the rank of doubtful species. So it is if
we look to past times, and compare the species which have just
passed away with those still living within the same areas ; or if we
compare the fossil species embedded in the sub-stages of the same
geological formation. It is indeed manifest that multitudes of
species are related in the closest manner to other species that still
exist, or have lately existed ; and it will hardly be maintained that
such species have been developed in an abrupt or sudden manner.
Nor should it be forgotten, when we look to the special parts of

MISCELLANEOUS OBJECTIONS, ETC. 203

allied species, instead of to distinct species, that numerous and
wonderfully fine gradations can be traced, connecting together
widely different structures.

Many large groups of facts are intelligible only on the principle
that species have been evolved by very small steps. For instance,
the fact that the species included in the larger genera are more
closely related to each other, and present a greater number of
varieties than do the species in the smaller genera. The former
are also grouped in little clusters, like varieties round species, and
they present other analogies with varieties, as was shown in our
second chapter. On this same principle we can understand how
it is that specific characters are more variable than generic char-
acters; and how the parts which are developed in an extraordinary
degree or manner are more variable than other parts of the same
species. Many analogous facts, all pointing in the same direction,
could be added.

Although very many species have almost certainly been pro-
duced by steps not greater than those separating fine varieties ; yet
it may be maintained that some have been developed in a different
and abrupt manner. Such an admission, however, ought not to
be made without strong evidence being assigned. The vague and
in some respects false analogies, as they have been shown to be
by Mr. Chauncey Wright, which have been advanced in favour
of this view, such as the sudden crystallisation of inorganic sub-
stances, or the falling of a facetted spheroid from one facet to
another, hardly deserve consideration. One class of facts, how-
ever, namely, the sudden appearance of new and distinct forms of
life in our geological formations supports at first sight the belief
in abrupt development. But the value of this evidence depends
entirely on the perfection of the geological record, in relation to
periods remote in the history of the world. If the record is as
fragmentary as many geologists strenuously assert, there is noth-
ing strange in new forms appearing as if suddenly developed.

Unless we admit transformations as prodigious as those advo-
cated by Mr. Mivart, such as the sudden development of the wings
of birds or bats, or the sudden conversion of a Hipparion into a
horse, hardly any light is thrown by the belief in abrupt modifica-
tions on the deficiency of connecting links in our geological
formations. But against the belief in such abrupt changes, em-
bryology enters a strong protest. It is notorious that the wings
of birds and bats, and the legs of horses or other quadrupeds, are
undistinguishable at an early embryonic period, and that they be-
come differentiated by insensibly fine steps. Embryological re-
semblances of all kinds can be accounted for, as we shall hereafter

204 ORIGIN OF SPECIES

see, by the progenitors of our existing species having varied after
early youth, and having transmitted their newly acquired charac-
ters to their offspring, at a corresponding age. The embryo is
thus left almost unaffected, and serves as a record of the past con-
dition of the species. Hence it is that existing species during the
early stages of their development so often resemble ancient and
extinct forms belonging to the same class. On this view of the
meaning of embryological resemblances, and indeed on any view,
it is incredible that an animal should have undergone such mo-
mentous and abrupt transformations, as those above indicated;
and yet should not bear even a trace in its embryonic condition
of any sudden modification ; every detail in its structure being de-
veloped by insensibly fine steps.

He who believes that some ancient form was transformed sud-
denly through an internal force or tendency into, for instance, one
furnished with wings, will be almost compelled to assume, in op-
position to all analogy, that many individuals varied simultane-
ously. It cannot be denied that such abrupt and great changes of
structure are widely different from those which most species ap-
parently have undergone. Hfe will further be compelled to believe
that many structures beautifidly adapted to all the other parts of
the same creature and to the surrounding conditions, have been sud-
denly produced; and of such complex and wonderful co-adapta-
tions, he will not be able to assign a shadow of an explanation.
He will be forced to admit that these great and sudden trans-
formations have left no trace of their action on the embryo. To
admit all this is, as it seems to me, to enter into the realms of
miracle, and to leave those of Science.

iNfeTlNCT 205

CHAPTEK VIII.

INSTINCT.

Instincts comparable with liabits, but different in their origin — Instincts
graduated — Aphides and ants — Instincts variable — Domestic in-
stincts, their origin — Natural instincts of the cuckoo, molothrus,
ostrich, and parasitic bees — Slave-making ants — Hive-bee, its cell-
making instinct — Changes of instinct and structure not necessarily
simultaneous — Difficulties of the theory of the Natural Selection of
instincts — Neuter or sterile insects — Summary.

MANY instincts are so wonderful that their development will
probably appear to the reader a difficulty sufficient to
overthrow my whole theory. I may here premise that I
have nothing to do with the origin of the mental powers, any more
than I have with that of life itself. We are concerned only with
the diversities of instinct and of the other mental faculties in ani-
mals of the same class.

I will not attempt any definition of instinct. It would be easy
to show that several distinct mental actions are commonly em-
braced by this term; but every one understands what is meant,
when it is said that instinct impels the cuckoo to migrate and to
lay her eggs in other birds' nests. An action, which we ourselves
require experience to enable us to perform, when performed by an
animal, more especially by a very young one, without experience,
and when performed by many individuals in the same way, with-
out their knowing for what purpose it is performed, is usually
said to be instinctive. But I could show that none of these char-
acters are universal. A little dose of judgment or reason, as
Pierre Huber expresses it, often comes into play, even with ani-
mals low in the scale of nature.

Frederick Cuvier and several of the older metaphysicians have
compared instinct with habit. This comparison gives, I think,
an accurate notion of the frame of mind under which an in-
stinctive action is performed, but not necessarily of its origin.
How unconsciously many habitual actions are performed, indeed
not rarely in direct opposition to our conscious will! yet they may
be modified by the will or reason. Habits easily become associate^

206 ORIGIN OF SPECIES

with other habits, with certain periods of time, and states of the
body. When once acquired, they often remain constant through-
out life. Several other jjoints of resemblance between instincts
and habits could be pointed out. As in repeating a well-known
song, so in instincts, one action follows another by a sort of
rhythm; if a person be interrupted in a song, or in repeating any-
thing by rote, he is generally forced to go back to recover the
habitual train of thought ; so P. Huber found it was with a cater-
pillar, which makes a very complicated hammock; for if he took
a caterpillar which had completed its hammock up to, say, the
sixth stage of construction, and put it into a hammock completed
up only to the third stage, the caterpillar simply re-performed the
fourth, fifth, and sixth stages of construction. If, however, a
caterpillar were taken out of a hammock made up, for instance,
to the third stage, and were put into one finished up to the sixth
stage, so that much of its work was already done for it, far from
deriving any benefit from this, it was much embarrassed, and in
order to complete its hammock, seemed forced to start from the
third stage, where it had left off, and thus tried to complete the
already finished work.

If we suppose any habitual action to become inherited — and
it can be shown that this does sometimes happen — then the re-
semblance between what originally was a habit and an instinct
becomes so close as not to be distinguished. If Mozart, instead
of playing the pianoforte at three years old with wonderfully lit-
tle practice, had played a tune with no practice at all, he might
truly be said to have done so instinctively. But it would be a
serious error to suppose that the greater number of instincts have
been acquired by habit in one generation, and then transmitted
by inheritance to succeeding generations. It can be clearly shown
that the most wonderful instincts with which we are acquainted,
namely, those of the hive-bee and of many ants, could not possibly
have been acquired by habit.

It will be universally admitted that instincts are as important
as corporeal structures for the welfare of each species, under its
present conditions of life. Under changed conditions of life, it
is at least possible that slight modifications of instinct might be
profitable to a species; and if it can be shown that instincts do
vary ever so little, then I can see no difficulty in natural selection
preserving and continually accumulating variations of instinct to
any extent that was profitable. It is thus, as I believe, that all
the most complex and wonderful instincts have originated. As
modifications of corporeal structure arise from, and are increased
by, use or habit, and are diminished or lost by disuse, so I do not

INSTINCT 207

doubt it has been with instincts. But I believe that the effects of
habit are in many cases of subordinate importance to the effects
of the natural selection of what may be called spontaneous varia-
tions of instincts; — that is of variations produced by the same
unknown causes which produce slight deviations of bodily struc-
ture.

No complex instinct can possibly be produced through natural
selection, except by the slow and gradual accumulation of numer-
ous slight, yet profitable, variations. Hence, as in the case of
corporeal structures, we ought to find in nature, not the actual
transitional gradations by which each complex instinct has been
acquired — for these could be found only in the lineal ancestors
of each species — but we ought to find in the collateral lines of
descent some evidence of such gradations; or we ought at least
to be able to show that gradations of some kind are possible; and
this we certainly can do. I have been surprised to find, making
allowance for the instincts of animals having been but little ob-
served except in Europe and North America, and for no instinct
being known amongst extinct species, how very generally grada-
tions, leading to the most complex instincts, can be discovered.
Changes of instinct may sometimes be facilitated by the same spe-
cies having different instincts at different periods of life, or at
different seasons of the year, or when placed under different cir-
cumstances, &c. ; in which case either the one or the other instinct
might be preserved by natural selection. And such instances of
diversity of instinct in the same species can be shown to occur in
nature.

Again, as in the case of corporeal structure, and conformably
to my theory, the instinct of each species is good for itself, but
has never, as far as we can judge, been produced for the exclu-
sive good of others. One of the strongest instances of an animal
apparently performing an action for the sole good of another, with
which I am acquainted, is that of aphides voluntarily yielding, as
was first observed by Huber, their sweet excretion to ants : that
they do so voluntarily, the following facts show. I removed all
the ants from a group of about a dozen aphides on a dock-plant,
and prevented their attendance during several hours. After this
interval, I felt sure that the aphides would want to excrete. I
watched them for some time through a lens, but not one excreted;
I then tickled and stroked them with a hair in the same manner,
as well as I could, as the ants do with their antennae; but not one
excreted. Afterwards I allowed an ant to visit them, and it im-
mediately seemed, by its eager way of running about, to be well
aware what a rich flock it had discovered; it then began to play

208 ORIGI^' OF SPECIES

with its antennae on the abdomen first of one aphis and then of an-
other; and each, as soon as it felt the antennae, immediately lifted
up its abdomen and excreted a limpid drop of sweet juice, which
was eagerly devoured by the ant. Even the quite young aphides
behaved in this manner, showing that the action was instinctive,
and not the result of experience. It is certain, from the observa-
tions of Huber, that the aphides show no dislike to the ants: if
the latter be not present they are at last compelled to eject their
excretion. But as the excretion is extremely viscid, it is no doubt
a convenience to the aphides to have it removed; therefore prob-
ably they do not excrete solely for the good of the ants. Although
there is no evidence that any animal performs an action for the
exclusive good of another species, yet each tries to take advan-
tage of the instincts of others, as each takes advantage of the
weaker bodily structure of other species. So again certain in-
stincts cannot be considered as absolutely perfect; but as details
on this and other such points are not indispensable, they may be
here passed over.

As some degree of variation in instincts under a state of nature,
and the inheritance of such variations, are indispensable for the
action of natural selection, as many instances as possible ought
to be given; but want of space prevents me. I can only assert
that instincts certainly do vary — for instance, the migratory in-
stinct, both in extent and direction, and in its total loss. So it is
with the nests of birds, which vary partly in dependence on the
situations chosen, and on the nature and temperature of the coun-
try inhabited, but often from causes wholly unknown to us :
Audubon has given several remarkable cases of differences in the
nests of the same species in the northern and southern United
States. Why, it has been asked, if instinct be variable, has it not
granted to the bee " the ability to use some other material when
wax was deficient"? But what other natural material could bees
use? They will work, as I have seen, with wax hardened with
vermilion or softened with lard. Andrew Knight observed that
his bees, instead of laboriously collecting propolis, used a cement
of wax and turpentine, with which he had covered decorticated
trees. It has lately been shown that bees, instead of searching for
pollen, will gladly use a very different substance, namely oatmeal.
Tear of any particular enemy is certainly an instinctive quality,
as may be seen in nestling birds, though it is strengthened by ex-
perience, and by the sight of fear of the same enemy in other
animals. The fear of man is slowly acquired, as I have elsewhere
shown, by the various animals which inhabit desert islands; and
we see an instance of this even in England, in the greater wild-

INSTINCT 209

ness of all our large birds in comparison with our small birds; for
the large birds have been most persecuted by man. We may safely
attribute tlie greater wildness of our large birds to this cause; for
in uninhabited islands large birds are not more fearful than
small; and the magpie, so wary in England, is tame in Norway,
as is the hooded crow in Egyi^t.

That the mental qualities of animals of the same kind, born in
a state of nature, vary much, could be shown by many facts.
Several cases could also be adduced of occasional and strange
habits in wild animals, which, if advantageous to the species,
might have given rise, through natural selection, to new instincts.
But I am well aware that these general statements, without the
facts in detail, will produce but a feeble effect on the reader's
mind. I can only repeat my assurance, that I do not speak with-
out good evidence.

Inherited Changes of Habit or Instinct in Domesticated Animals.

The possibility, or even probability, of inherited variations of
instinct in a state of nature will be strengthened by briefly con-
sidering a few cases under domestication. We shall thus be ena-
bled to see the part which habit and the selection of so-called spon-
taneous variations have played in modifying the mental qualities
of our domestic animals. It is notorious how much domestic
animals vary in their mental qualities. With cats, for instance,
one naturally takes to catching rats, and another mice, and these
tendencies are known to be inherited. One cat, according to Mr.
St. John, always brought home game-birds, another hares or rab-
bits, and another hunted on marshy ground and almost nightly
caught woodcocks or snipes. A number of curious and authentic
instances could be given of various shades of disposition and of
taste, and likewise of the oddest tricks, associated with certain
frames of mind or periods of time, being inherited. But let us
look to the familiar case of the breeds of the dogs: it cannot be
doubted that young pointers (I have myself seen a striking in-
stance) will sometimes point and even back other dogs the very
first time that they are taken out; retrieving is certainly in some
degree inherited by retrievers; and a tendency to run round, in-
stead of at, a flock of sheep, by shepherd dogs. I cannot see that
these actions, performed without experience by the young, and in
nearly the same manner by each individual, performed with eager
delight by each breed, and without the end being known — for the
young pointer can no more know that he points to aid his master,
than the white butterfly knows why she lays her eggs on the leaf

210 ORIGIN OF SPECIES

of the cabbage — I cannot see that these actions differ essentially
from true instincts. If we were to behold one kind of wolf, when
young and without any training, as soon as it scented its prey,
stand motionless like a statue, and then slowly crawl forward with
a peculiar gait; and another kind of wolf rushing round, instead
of at, a herd of deer, and driving them to a distant point, we
should assuredly call these actions instinctive. Domestic in-
stincts, as they may be called, are certainly far less fixed than
natural instincts; but they have been acted on by far less rigorous
selection, and have been transmitted for an incomparably shorter
period, under less fixed conditions of life.

How strongly these domestic instincts, habits, and dispositions
are inherited, and how curiously they become mingled, is well
shown when different breeds of dogs are crossed. Thus it is known
that a cross with a bull-dog has affected for many generations the
courage and obstinacy of greyhounds; and a cross with a grey-
hound has given to a whole family of shepherd-dogs a tendency to
hunt hares. These domestic instincts, when thus tested by cross-
ing, resemble natural instincts, which in a like manner become
curiously blended together, and for a long period exhibit traces of
the instincts of either parent: for example, Le Roy describes a
dog, whose great-grandfather was a wolf, and this dog showed
a trace of its wild parentage only in one way, by not coming in a
straight line to his master, when called.

Domestic instincts are sometimes spoken of as actions which
have become inherited solely from long-continued and compulsory
habit; but this is not true. No one would ever have thought of
teaching, or probably could have taught, the tumbler-pigeon to
tumble, — an action which, as I have witnessed, is performed by
young birds, that have never seen a pigeon tumble. We may be-
lieve that some one pigeon showed a slight tendency to this
strange habit, and that the long-continued selection of the best
individuals in successive generations made tumblers what they
now are; and near Glasgow there are house-.tumblers, as I hear
from Mr. Brent, which cannot fly eighteen inches high without
going head over heels. It may be doubted whether any one would
have thought of training a dog to point, had not some one dog
naturally shown a tendency in this line; and this is known occa-
sionally to happen, as I once saw, in a pure terrier: the act of
pointing is probably, as many have thought, only the exaggerated
pause of an animal preparing to spring on its prey. When the
first tendency to point was once displayed, methodical selection
and the inherited effects of compulsory training in each suc-
cessive generation would soon complete the work; and unconscious

INSTINCT 211

selection is. still in progress, as each man tries to procure, without
intending to improve the breed, dogs whicli stand and hunt best.
On the other hand, habit alone in some cases has sufficed; hardly
any animal is more difficult to tame than the young of the wild
rabbit; scarcely any animal is tamer than the young of the tame
rabbit; but I can hardly suppose that domestic rabbits have often
been selected for tameness alone; so that we must attribute at
least the greater i^art of the inherited change from extreme wild-
ness to extreme tameness, to habit and long-continued close con-
finement.

Natural instincts are lost under domestication : a remarkable
instance of this is seen In those breeds of fowls which very rarely
or never become " broody," that is, never wish to sit on their eggs.
Familiarity alone prevents our seeing how largely and how perma-
nently the minds of our domestic animals have been modified.
It is scarcely possible to doubt that the love of man has become
instinctive in the dog. All wolves, foxes, jackals, and species of
the cat genus, when kept tame, are most eager to attack poultry,
sheep, and pigs; and this tendency has been found incurable in
dogs which have been brought home as puppies from countries
such as Tierra del Fuego and Australia, where the savages do not
keep these domestic animals. How rarely, on the other hand, do
our civilised dogs, even when quite young, require to be taught
not to attack poultry, sheep, and pigs! No doubt they occasion-
ally do make an attack, and are then beaten; and if not cured,
they are destroyed; so that habit and some degree of selection
have probably concurred in civilising by inheritance our dogs.
On the other hand, young chickens have lost, wholly by habit,
that fear of the dog and cat which no doubt was originally in-
stinctive in them; for I am informed by Captain Hutton that the
young chickens of the parent-stock, the G alius bankiva, when
reared in India under a hen, are at first excessively wild. So it
is with young pheasants reared in England under a hen. It is
not that chickens have lost all fear, but fear only of dogs and
cats, for if the hen gives the danger-chuckle, they will run (more
especially young turkeys) from inider her, and conceal themselves
in the surrounding grass or thickets; and this is evidently done
for the instinctive purpose of allowing, as we see in wild ground-
birds, their mother to fly away. But this instinct retained by our
chickens has become useless under domestication, for the mother-
hen has almost lost by disuse the power of flight.

Hence, we may conclude, that under domestication instincts
have been acquired, and natural instincts have been lost, partly
by habit, and partly by man selecting and accumulating, during

212 ORIGIN OF SPECIES

successive generations, peculiar mental habits and actions, which
at first appeared from what we must in our ignorance call an acci-
dent. In some cases compulsory habit alone has sufficed to pro-
duce inherited mental changes; in other cases, compulsory habit
has done nothing, and all has been the result of selection, pursued
both methodically and unconsciously: but in most cases habit and
selection have probably concurred.

Special Instincts.

We shall, perhaps, best understand how instincts in a state of
nature have become modified by selection by considering a few
cases. I will select only three, — namely, the instinct which leads
the cuckoo to lay her eggs in other birds' nests; the slave-making
instinct of certain ants; and the cell-making power of the hive-
bee. These two latter instincts have generally and justly been
ranked by naturalists as the most wonderful of all known in-
stincts.

Instincts of the Cuckoo. — It is supposed by some naturalists
that the more immediate cause of the instinct of the cuckoo is,
that she lays her eggs, not daily, but at intervals of two or three
days ; so that, if she were to make her own nest and sit on her own
eggs, those first laid would have to be left for some time unincu-
bated, or there would be eggs and young birds of different ages
in the same nest. If this were the case, the process of laying and
hatching might be inconveniently long, more especially as she mi-
grates at a very early period; and the first hatched young would
probably have to be fed by the male alone. But the American
cuckoo is in this predicament ; for she makes her own nest, and has
eggs and young successively hatched, all at the same time. It has
been both asserted and denied that the American cuckoo occa-
sionally lays her eggs in other birds' nests ; but I have lately heard
from Dr. Merrell, of Iowa, that he once found in Illinois a young
cuckoo together with a young jay in the nest of a Blue jay (Gar-
rulus cristatus) ; and as both were nearly full feathered, there
could be no mistake in their identification. I could also give sev-
eral instances of various birds which have been known occasionally
to lay their eggs in other birds' nests. Now let us suppose that
the ancient progenitor of our European cuckoo had the habits of
the American cuckoo, and that she occasionally laid an egg in
another bird's nest. If the old bird profited by this occasional
habit through being enabled to migrate earlier or through any
other cause; or if the young were made more vigorous by advan-
fage being taken of the mistaken instinct of another species than

INSTINCT 213

when reared by their own mother, encumbered as she could hardly
fail to be by having eggs and young of different ages at the same
time; then the old birds or the fostered young would gain an ad-
vantage. And analogy would lead us to believe, that the young
thus reared would be apt to follow by inheritance the occasional
and aberrant habit of their mother, and in their turn would be
apt to lay their eggs in other birds' nests, and thus be more suc-
cessful in rearing their young. By a continued process of this
nature, I believe that the strange instinct of our cuckoo has been
generated. It has, also, recently been ascertained on sufficient
evidence, by Adolf Miiller, that the cuckoo occasionally lays her
eggs on the bare ground, sits on them, and feeds her young. This
rare event is probably a case of reversion to the long-lost, aborigi-
nal instinct of nidification.

It has been objected that I have not noticed other related in-
stincts and adaptations of structure in the cuckoo, which are
spoken of as necessarily co-ordinated. But in all cases, specula-
tion on an instinct known to us only in a single species, is useless,
for we have hitherto had no facts to guide us. Until recently
the instincts of the European and of the non-parasitic American
cuckoo alone were known; now, owing to Mr. Kamsay's observa-
tions, we have learnt something about three Australian species,
which lay their eggs in other birds' nests. The chief points to be
referred to are three: first, that the common cuckoo, with rare ex-
ceptions, lays only one egg in a nest, so that the large and vora-
cious young bird receives ample food. Secondly, that the eggs
are remarkably small, not exceeding those of the skylark, — a bird
about one-fourth as large as the cuckoo. That the small size of
the egg is a real case of adaptation we may infer from the fact of
the non-parasitic American cuckoo laying full-sized eggs. Third-
ly, that the young cuckoo, soon after birth, has the instinct, the
strength, and a properly shaped back for ejecting its foster-
brothers, which then perish from cold and hunger. This has been
boldly called a beneficent arrangement, in order that the young
cuckoo may get sufficient food, and that its foster-brothers may
perish before they had acquired much feeling!

Turning now to the Australian species ; though these birds gen-
erally lay only one egg in a nest, it is not rare to find two and
even three eggs in the same nest. In the Bronze cuckoo the eggs
vary greatly in size, from eight to ten lines in length. ISTow if it
had been an advantage to this species to have laid eggs even
smaller than those now laid, so as to have deceived certain foster-
parents, or, as is more probable, to have been hatched within a
shorter period (for it is asserted that there is a relation between

214 ORIGIN OF SPECIES

the size of eggs and the period of their incubation), then there is
no difficulty in believing that a race or species might liave been
formed which would have laid smaller and smaller eggs ; for these
would have been more safely hatched and reared. Mr. Ramsay
remarks that two of the Australian cuckoos, when they lay their
eggs in an open nest, manifest a decided preference for nests con-
taining eggs similar in colour to their own. The European spe-
cies apparently manifests some tendency towards a similar in-
stinct, but not rarely departs from it, as is shown by her laying
her dull and pale-coloured eggs in the nest of the Hedge-warbler
with bright greenish-blue eggs. Had our cuckoo invariably dis-
played the above instinct, it would assuredly have been added to
those which it is assumed must all have been acquired together.
The eggs of the Australian Bronze cuckoo vary, according to Mr.
Ramsay, to an extraordinary degree in colour; so that in this re-
spect, as well as in size, natural selection might have secured and
fixed any advantageous variation.

In the case of the European cuckoo, the offspring of the foster-
parents are commonly ejected from the nest within three days
after the cuckoo is hatched; and as the latter at this age is in a
most helpless condition, Mr. Gould was formerly inclined to be-
lieve that the act of ejection was performed by the foster-parents
themselves. But he has now received a trustworthy account of a
young cuckoo which was actually seen, whilst still blind and not
able even to hold up its own head, in the act of ejecting its foster-
brothers. One of these was replaced in the nest by the observer,
and was again thrown out. With respect to the means by which
this strange and odious instinct was acquired, if it were of great
importance for the young cuckoo, as is probably the case, to re-
ceive as much food as possible soon after birth, I can see no special
difficulty in its having gradually acquired, during successive gen-
erations, the blind desire, the strength, and structure necessary for
the work of ejection; for those young cuckoos which had such
habits and structure best developed would be the most securely
reared. The first step towards the acquisition of the proper in-
stinct might have been mere unintentional restlessness on the part
of the young bird, when somewhat advanced in age and strength;
the habit having been afterwards improved, and transmitted to
an earlier age. I can see no more difficulty in this, than in the
unhatched young of other birds acquiring the instinct to break
through their own shells ; — or than in young snakes acquiring in
their upper jaws, as Owen has remarked, a transitory sharp tooth
for cutting through the tough egg-shell. Eor if each part is liable
to individual variations at all ages, and the variations tend to

INSTINCT 215

be inherited at a corresponding or earlier age, — propositions which
cannot be disputed, — then the instincts and structure of the young
could be slowly modified as surely as those of the adult; and both
cases must stand or fall together with the whole theory of natural
selection.

Some species of Molothrus, a widely distinct genus of Ameri-
can birds, allied to our starlings, have parasitic habits like those
of the cuckoo ; and the species present an interesting gradation in
the perfection of their instincts. The sexes of Molothrus badius
are stated by an excellent observer, Mr. Hudson, sometimes to live
promiscuously together in flocks, and sometimes to pair. They
either build a nest of their own, or seize on one belonging to some
other bird, occasionally throwing out the nestlings of the stranger.
They either lay their eggs in the nest thus appropriated, or oddly
enough build one for themselves on the top of it. They usually
sit on their own eggs and rear their own young; but Mr.
Hudson says it is probable that they are occasionally parasitic,
for he has seen the young of this species following old birds of a
distinct kind and clamouring to be fed by them. The parasitic
habits of another species of Molothrus, the M. bonariensis, are
much more highly developed than those of the last, but are still
far from perfect. This bird, as far as it is known, invariably
lays its eggs in the nests of strangers; but it is remarkable that
several together sometimes commence to build an irregular untidy
nest of their own, placed in singularly ill-adapted situations, as
on the leaves of a large thistle. They never, however, as far as
Mr. Hudson has ascertained, complete a nest for themselves. They
often lay so many eggs — from fifteen to twenty — in the same
foster-nest, that few or none can possibly be hatched. They have,
moreover, the extraordinary habit of pecking holes in the eggs,
whether of their own species or of their foster-parents, which they
find in the appropriated nests. They drop also many eggs on the
bare ground, which are thus wasted. A third species, the M.
pecoris of North America, has acquired instincts as perfect as
those of the cuckoo, for it never lays more than one egg in a
foster-nest, so that the young bird is securely reared. Mr. Hud-
son is a strong disbeliever in evolution, but he appears to have been
so much struck by the imperfect instincts of the Molothrus
bonariensis that he quotes my words, and asks, " Must we con-
sider these habits, not as especially endowed or created instincts,
but as small consequences of one general law, namely, transi-
tion?"

Various birds, as has already been remarked, occasionally lay
their eggs in the nests of other birds. This habit is not very un-

216 ORIGIN OF SPECIES

common with the GallinaceaB, and throws some light on the sin-
gular instinct of the ostrich. In this family several hen-birds
unite and lay first a few eggs in one nest and then in another ; and
these are hatched by the males. This instinct may probably be
accounted for by the fact of the hens laying a large number of
eggs, but, as with the cuckoo, at intervals of two or three days.
The instinct, however, of the American ostrich, as in the case of
the Molothrus bonariensis, has not as yet been perfected; for a
surprising number of eggs lie strewed over the plains, so that in
one day's hunting I picked up no less than twenty lost and wasted
eggs.

Many bees are parasitic, and regularly lay their eggs in the nests
of other kinds of bees. This case is more remarkable than that
of the cuckoo ; for these bees have not only had their instincts but
their structure modified in accordance with their parasitic habits;
for they do not possess the pollen-collecting apparatus which
would have been indispensable if they had stored up food for their
own young. Some species of Sphegidse (wasp-like insects) are
likewise parasitic; and M. Fabre has lately shown good reason for
believing that, although the Tachytes nigra generally makes its
own burrow and stores it with paralysed prey for its own larvai,
yet that, when this insect finds a burrow already made and stored
by another sphex, it takes advantage of the prize, and becomes
for the occasion parasitic. In this case, as with that of the Molo-
thrus or cuckoo, I can see no difficulty in natural selection mak-
ing an occasional habit permanent, if of advantage to the species,
and if the insect whose nest and stored food are feloniously ap-
propriated, be not thus exterminated.

Slave-making instinct. — This remarkable instinct was first dis-
covered in the Formica (Polyerges) rufescens by Pierre Huber, a
better observer even than his celebrated father. This ant is ab-
solutely dependent on its slaves; without their aid, the species
would certainly become extinct in a single year. The males and
fertile females do no work of any kind, and the workers or sterile
females, though most energetic and courageous in capturing slaves,
do no other work. They are incapable of making their own nests,
or of feeding their own larvae. When the old nest is found incon-
venient, and they have to migrate, it is the slaves which determine
the migration, and actually carry their masters in their jaws. So
utterly helpless are the masters, that when Huber shut up thirty
of them without a slave, but with plenty of the food which they
like best, and with their own larvae and pupae to stimulate them
to work, they did nothing; they could not even feed them.selves.
and many perished of hunger. Huber then introduced a single

INSTINCT 217

slave (F. fusca), and slie instantly set to work, fed and savsrl the
survivors; made some cells and tended the larva3, and put all to
rights. What can be more extraordinary than these well-ascer-
tained facts? If we had not known of any other slave-making
ant, it would have been hopeless to speculate how so wonderful an
instinct could have been perfected.

Another species, Formica sanguinea, was likewise first discov-
ered by P. Huber to be a slave-making ant. This species is found
in the southern parts of England, and its habits have been at-
tended to by Mr. F. Smith, of the British Museum, to whom I am
much indebted for information on this and other subjects. Al-
though fully trusting to the statements of Huber and Mr. Smith,
I tried to approach the subject in a sceptical frame of mind, as
any one may well be excused for doubting the existence of so ex-
traordinary an instinct as that of making slaves. Hence, I will
give the observations which I made in some little detail. I opened
fourteen nests of F. sanguinea, and found a few slaves in all.
Males and fertile females of the slave species (F. fuscr.) are found
only in their own proper communities, and have never been ob-
served in the nests of F. sanguinea. The slaves are black and
not above half the size of their red masters, so that the contrast
in their appearance is great. When the nest is slightly disturbed,
the slaves occasionally come out, and like their masters are much
agitated and defend the nest : when the nest is much disturbed,
and the larvae and pupse are exposed, the slaves work energetically
together with their masters in carrying them away to a place of
safety. Hence, it is clear, that the slaves feel quite at home.
During the months of June and July, on three successive years, I
watched for many hours several nests in Surrey and Sussex, and
never saw a slave either leave or enter a nest. As, during these
months, the slaves are very few in number, I thought that they
might behave differently when more numerous; but Mr. Smith
informs me that he has watched the nests at various hours during
May, June, and August, both in Surrey and Hampshire, and has
never seen the slaves, though present in large numbers in August,
either leave or enter the nest. Hence he considers them as strictly
household slaves. The masters, on the other hand, may be con-
stantly seen bringing in materials for the nest, and food of all
kinds. During the year 1860, however, in the month of July, I
came across a community with an unusually large stock of slaves,
and I observed a few slaves mingled with their masters leaving
the nest, and marching along the same road to a tall Scotch-fir-
tree, twenty-five yards distant, which they ascended together, prob-
ably in search of aphides or cocci. According to Huber, who had

218 ORIGIN OF SPECIES

ample opportunities for observation, the slaves in Switzerland
habitually work with their masters in making the nest, and they
alone open and close the doors in the morning and evening; and,
as Huber expressly states, their principal office is to search for
aphides. This difference in the usual habits of the masters and
slaves in the two countries, probably depends merely on the slaves
being captured in greater numbers in Switzerland than in Eng-
land.

One day I fortunately witnessed a migration of F. sanguinea
from one nest to another, and it was a most interesting spectacle
to behold the masters carefully carrying their slaves in their jaws
instead of being carried by them, as in the case of F. rufescens.
Another day my attention was struck by about a score of the slave-
makers haunting the same spot, and evidently not in search of
food; they approached and were vigorously repulsed by an inde-
pendent community of the slave-species (F. fusca) ; sometimes as
many as three of these ants clinging to the legs of the slave-
making F. sanguinea. The latter ruthlessly killed their small op-
ponents, and carried their dead bodies as food to their nest, twenty-
nine yards distant; but they were prevented from getting any
pupae to rear as slaves. I then dug up a small parcel of the pupae
of F. fusca from another nest, and put them down on a bare spot
near the place of combat; they were eagerly seized and carried off
by the tyrants, who perhaps fancied that, after all, they had been
victorious in their late combat.

At the same time I laid on the same place a small parcel of
the pupse of another species, F. flava, with a few of these little
yellow ants still clinging to the fragments of their nest. This
species is sometimes, though rarely, made into slaves, as has been
described by Mr. Smith. Although so small a species, it is very
courageous, and I have seen it ferociously attack other ants. In
one instance I found to my surprise an independent community
of F. flava under a stone beneath a nest of the slave-making F.
sanguinea; and when I had accidentally disturbed both nests, the
little ants attacked their big neighbours with surprising courage.
Now I was curious to ascertain whether F. sanguinea could dis-
tinguish the pupae of F. fusca, which they habitually make into
slaves, from those of the little and furious F. flava, which they
rarely capture, and it was evident that they did at once distin-
guish them; for we have seen that they eagerly and instantly
seized the pupae of F. fusca, whereas they were much terrified when
they came across the pupae, or even the earth from the nest, of F.
flava, and quickly ran away; but in about a quarter of an hour,

INSTINCT 219

shortly after all the little yellow ants had crawled away, they took
heart and carried off the pupae.

One evening I visited another community of F. sanguinea, and
found a number of these ants returning home and entering their
nests, carrying the dead bodies of F. fusca (showing that it was
not a migration) and numerous pupae. I traced a long file of ants
burthened with booty, for about forty yards back, to a very thick
clump of heath, whence I saw the last individual of F. sanguinea
emerge, carrying a pupa; but I was not able to find the desolated
nest in the thick heath. The nest, however, must have been close
at hand, for two or three individuals of F. fusca were rushing
about in the greatest agitation, and one was perched motionless
with its own pupa in its mouth on the top of a spray of heath, an
image of despair over its ravaged home.

Such are the facts, though they did not need confirmation by
me, in regard to the wonderful instinct of making slaves. Let
it be observed what a contrast the instinctive habits of F. san-
guinea present with those of the continental F. rufescens. The
latter does not build its own nest, does not determine its own
migrations, does not collect food for itself or its young, and can-
not even feed itself: it is absolutely dependent on its numerous
slaves. Formica sanguinea, on the other hand, possesses much
fewer slaves, and in the early part of the summer extremely few:
the masters determine when and where a new nest shall be formed,
and when they migrate, the masters carry the slaves. Both in
Switzerland and England the slaves seem to have the exclusive
care of the larvae, and the masters alone go on slave-making ex-
peditions. In Switzerland the slaves and masters work together,
making and bringing materials for the nest; both, but chiefly the
slaves, tend, and milk, as it may be called their aphides; and thus
both collect food for the community. In England the masters
alone usually leave the nest to collect building materials and food
for themselves, their slaves and larvae. So that the masters in this
country receive much less service from their slaves than they do
in Switzerland.

By what steps the instinct of F. sanguinea originated I will
not pretend to conjecture. But as ants which are not slave-
makers will, as I have seen, carry off the pupae of other species, if
scattered near their nests, it is possible that such pupae originally
stored as food might become developed ; and the foreign ants thus
unintentionally reared would then follow their proper instincts,
and do what work they could. If their presence proved useful to
the species which had seized them — if it were more advantageous
to this species to capture workers than to procreate them — the

220 ORIGIN OF SPECIES

habit of collecting pupae, originally for food, might by natural
selection be strengthened and rendered permanent for the very
different purpose of raising slaves. When the instinct was once
acquired, if carried out to a much less extent even than in our
British F. sanguinea, which, as we have seen, is less aided by its
slaves than the same species in Switzerland, natural selection
might increase and modify the instinct — always supposing each
modification to be of use to the species — until an ant was formed
as abjectly dependent on its slaves as is the Formica rufescens.

Cell-making instinct of the Hive-Bee. — I will not here enter
on minute details on this subject, but will merely give an outline
of the conclusions at which I have arrived. He must be a dull
man who can examine the exquisite structure of a comb, so beau-
tifully adapted to its end, without enthusiastic admiration. We
hear from mathematicians that bees have practically solved a rec-
ondite problem, and have made their cells of the proper shape to
hold the greatest possible amount of honey, with the least possible
consumption of precious wax in their construction. It has been
remarked that a skilful workman with fitting tools and measures,
would find it very difficult to make cells of wax of the true form,
though this is effected by a crowd of bees working in a dark hive.
Granting whatever instincts you please, it seems at first quite in-
conceivable how they can make all the necessary angles and
planes, or even perceive when they are correctly made. But the
difficulty is not nearly so great as it at first appears: all this beau-
tiful work can be shown, I think, to follow from a few simple in-
stincts.

I was led to investigate this subject by Mr. Waterhouse, who
has shown that the form of the cell stands in close relation to the
presence of adjoining cells ; and the following view may, perhaps, be
considered only as a modification of his theory. Let us look to
the great principle of gradation, and see whether Nature does not
reveal to us her method of work. At one end of a short series we
have humble-bees, which use their old cocoons to hold honey,
sometimes adding to them short tubes of wax, and likewise making
separate and very irregular rounded cells of wax. At the other
end of the series we have the cells of the hive-bee, placed in a
double layer: each cell, as is well known, is an hexagonal prism,
with the basal edges of its six sides bevelled so as to join an in-
verted pyramid, of three rhombs. These rhombs have certain
angles, and the three which form the pyramidal base of a single
cell on one side of the comb enter into the composition of the
bases of three adjoining cells on the opposite side. In the
series between the extreme perfection of the cells of the hive-

INSTINCT 221

bee and the simplicity of those of the humble-bee we have
the cells of the Mexican Melipona domestica, carefully described
and figured by Pierre Pluber. The Melipona itself is interme-
diate in structure between the hive and humble-bee, but more
nearly related to the latter; it forms a nearly regular waxen
comb of cylindrical cells, in which the young are hatched, and,
in addition, some large cells of wax for holding honey. These
latter cells are nearly spherical and of nearly equal sizes, and
are aggregated into an irregular mass. But the important point
to notice is, that these cells are always made at that degree of
nearness to each other that they would have intersected or broken
into each other if the spheres had been completed; but this is
never permitted, the bees building perfectly flat walls of wax
between the spheres which thus tend to intersect. Hence, each
cell consists of an outer spherical portion, and of two, three, or
more flat surfaces, according as the cell adjoins two, three, or
more other cells. When one cell rests on three other cells, which,
from the spheres being nearly of the same size, is very frequently
and necessarily the case, the three flat surfaces are united into
a pyramid; and this pyramid, as Tluber has remarked, is mani-
festly a gross imitation of the three-sided pyramidal base of the
cell of the hive-bee. As in the cells of the hive-bee, so here,
the three plane surfaces in any one cell necessarily enter into the
construction of three adjoining cells. It is obvious that the
Melipona saves wax, and what is more important, labour, by this
manner of building; for the flat walls between the adjoining
cells are not double, but are of the same thickness as the outer
spherical portions, and yet each flat portion forms a part of two
cells.

Reflecting on this case, it occurred to me that if the Meli-
pona had made its spheres at some given distance from each
other, and had made them of equal sizes and had arranged
them symmetrically in a double layer, the resulting structure
would have been as perfect as the comb of the hive-bee. Accord-
ingly I wrote to Professor Miller of Cambridge, and this geometer
has kindly read over the following statement, drawn up from
his information, and tells me that it is strictly correct : —

If a number of equal spheres be described with their centres
placed in two parallel layers; with the centre of each sphere
at the distance of radius X i^ 2, or radius X 1-41421 (or at
some lesser distance), from the centres of the six surrounding
spheres in the same layer; and at the same distance from the
centres of the adjoining spheres in the other and parallel layer;
then, if planes of intersection between the several spheres in

222 ORIGIN OF SPECIES

both layers be formed, there will result a double layer of hex-
agonal prisms united together by pyramidal bases formed of
three rhombs; and the rhombs and the sides of the hexagonal
prisms will have every angle identically the same with the
best measurements which have been made of the cells of the
hive-bee. But I hear from Prof. Wyman, who has made numer-
ous careful measurements, that the accuracy of the workmanship
of the bee has been greatly exaggerated; so much so, that what-
ever the typical form of the cell may be, it is rarely, if ever,
realised.

Hence we may safely conclude that, if we could slightly modify
the instincts already possessed by the Melipona, and in themselves
not very wonderful, this bee would make a structure as wonder-
fully perfect as that of the hive-bee. We must suppose that
Melipona to have the power of forming her cells truly spherical,
and of equal sizes; and this would not be very surprising, seeing
that she already does so to a certain extent, and seeing what
perfectly cylindrical burrows many insects make in wood, appar-
ently by curning round on a fixed point. We must suppose the
Melipona to arrange her cells in level layers, as she already does
her cylindrical cells; and we must further suppose, and this is
the greatest difficulty, that she can somehow judge accurately at
what distance to stand from her fellow-laborers when several are
making their spheres; but she is already so far enabled to judge
of distance, that she always describes her spheres so as to inter-
sect to a certain extent; and then she unites the points of
intersection by perfectly flat surfaces. By such modifications
of instincts which in themselves are not very wonderful, — hardly
more wonderful than those which guide a bird to make its nest, —
I believe that the hive-bee has acquired, through natural selection,
her inimitable architectural i^owers.

But this theory can be tested by experiment. Following the
example of Mr. Tegetmeier, I separated two combs, and put
between them a long, thick, rectangular strip of wax; the bees
instantly began to excavate minute circular pits in it ; and as they
deepened these little pits, they made them wider and wider until
they were converted into shallow basins, appearing to the eye
perfectly true or parts of a sphere, and of about the diameter of a
cell. It was most interesting to observe that, wherever several bees
had begun to excavate these basins near together, they had
begun their work at such a distance from each other, that by the
time the basins had acquired the above-stated width (i. e. about
the width of an ordinary cell), and were in depth about one-sixth
of the diameter of the sphere of which they formed a part, the

INSTINCT 223

rims of the basins intersected or broke into each other. As soon
as this occurred, the bees ceased to excavate, and began to build
up flat walls of wax on the lines of intersection between the
basins, so that each hexagonal prism was built upon the Scal-
loped edge of a smooth basin, instead of on the straight edges of
a three-sided pyramid as in the case of ordinary cells.

I then put into the hive, instead of a thick, rectangular piece
of wax, a thin and narrow, knife-edged ridge, colored with ver-
milion. The bees instantly began on both sides to excavate little
basins near to each other, in the same way as before; but the
ridge of wax was so thin, that the bottoms of the basins, if they
had been excavated to the same depth as in the former experiment,
would have broken into each other from the opposite sides. The
bees, however, did not suffer this to happen, and they stopped their
excavations in due time; so that the basins, as soon as they had
been a little deepened, came to have flat bases; and these flat
bases, formed by thin little plates of the vermilion wax left
ungnawed, were situated, as far as the eye could judge, exactly
along the planes of imagii.ary intersection between the basins on
the opposite sides of the ridge of wax. In some parts, only small
portions, in other parts, large portions of a rhombic plate were
thus left between the opposed basins, but the work, from the un-
natural state of things, had not been neatly performed. The bees
must have worked at very nearly the same rate in circularly
gnawing away and deepening the basins on both sides of the ridge
of vermilion wax, in order to have thus succeeded in leaving
flat plates between the basins, by stopping work at the planes
of intersection.

Considering how flexible thin wax is, I do not see that there
is any difficulty in the bees, whilst at work on the two sides of
a strip of wax, perceiving when they have gnawed the wax away
to the proper thinness, and then stopping their work. In ordi-
nary combs it has appeared to me that the bees do not always suc-
ceed in working at exactly the same rate from the opposite sides;
for I have noticed half-completed rhombs at the base of a
just commenced cell, which were slightly concave on one side,
where I suppose that the bees had excavated too quickly, and
convex on the opposed side where the bees had worked less quickly.
In one well marked instance, I put the comb back into the hive,
and allowed the bees to go on working for a short time, and
again examined the cell, and I found that the rhombic plate had
been completed, and had become perfectly flat: it was absolutely
impossible, from the extreme thinness of the little plate, that
they could have effected this by gnawing away the convex side;

224 ORIGIN OF SPECIES

and I suspect that the bees in such cases stand on opposite sides
and push and bend the ductile and warm wax (which as I have
tried is easily done) into its proper intermediate plane, and thus
flatten it.

From the experiment of the ridge of vermilion wax we can
see that, if the bees were to build for themselves a thin wall of
wax, they could make their cells of the proper shape, by standing
at the proper distance from each other, by excavating at the same
rate, and by endeavoring to make equal spherical hollows, but never
allowiiig the spheres to break into each other. Now bees, as
may be clearly seen by examining the edge of a growing comb,
do make a rough, circumferential wall or rim all round the
comb; and they gnaw this way from the opposite sides, always
working circularly as they deepen each cell. They do not make
the whole three-sided pyramidal base of any one cell at the
same time, but only that one rhombic plate which stands on
the extreme growing margin, or the two plates, as the case
may be; and they never complete the upper edges of the rhombic
plates, until the hexagonal walls are commenced. Some of these
statements differ from those made by the justly celebrated elder
Huber, but I am convinced of their accuracy; and if I had space,
I would show that they are conformable with my theory.

Huber's statement that the very first cell is excavated out
of a little parallel-sided wall of wax, is not, as far as I have
seen, strictly correct; the first commencement having always been
a little hood of wax; but I will not here enter on details. We
see how important a part excavation plays in the construction
of the cells; but it would be a great error to suppose that the
bees cannot build up a rough wall of wax in the proper position —
that is, along the plane of intersection between two adjoining
spheres. I have several specimens showing clearly that they can
do this. Even in the rude circumferential rim or wall of wax
round a growing comb, flexures may sometimes be observed,
corresponding in position to the planes of the rhombic basal plates
of future cells. But the rough wall of wax has in every case
to be finished off, by being largely gnawed away on both sides.
The manner in which the bees build is curious; they always
make the first rough wall from ten to twenty times thicker than
the excessively thin finished wall of the cell, which will ultimately
be left. We shall understand how they work, by supposing masons
first to pile up a broad ridge of cement, and then to begin cutting
it away equally on both sides near the ground, till a smooth,
very thin wall is left in the middle; the masons always piling
up the cut-away cement, and adding fresh cement on the summit

INSTINCT 225

of the ridge. We shall thus have a thin wall steadily growing
upward but always crowned by a gigantic coping. From all
the cells, both those just connnenced and those completed, being
thus crowned by a strong coping of wax, the bees can cluster
and crawl over the comb without injuring the delicate hexagonal
walls. These walls, as Professor Miller has kindly ascertained
for me, vary greatly in thickness; being, on an average of twelve
measurements made near the border of the comb, 352 of an inch
in thickness; whereas the basal rhomboidal plates are thicker,
nearly in the proportion of three to two, having a mean thickness,
from twenty-one measurements, of -Aw of an inch. By the above
singular manner of building, strength is continually given to the
comb, wdth the utmost ultimate economy of wax.

It seems at first to add to the difficulty of understanding how
the cells are made, that a multitude of bees all work together;
one bee after working a short time at one cell going to another,
so that, as Huber has stated, a score of individuals work even at
the commencement of the first cell. I was able practically to
show this fact, by covering the edges of the hexagonal walls of a
single cell, or the extreme margin of the circumferential rim of
a growing comb, with an extremely thin layer of melted vermilion
wax; and I invariably found that the colour was most delicately
diffused by the bees — as delicately as a painter could have done
it with his brush — by atoms of the coloured wax having been
taken from the spot on which it liad been placed, and worked into
the growing edges of the cells all round. The work of construc-
tion seems to be a sort of balance struck between many bees,
all instinctively standing at the same relative distance from each
other, all trying to sweep equal spheres, and then building up,
or leaving ungnawed, the planes of intersection between these
spheres. It was really curious to note in cases of difficulty, as
when two pieces of comb met at an angle, how often the bees
would pull down and rebuild in different ways the same cell,
sometimes recurring to a shape which they had at first rejected.

When bees have a place on which they can stand in their
proper positions for working, — for instance, on a slip of wood,
placed directly under the middle of a comb growing downwards,
so that the comb has to be built over one face of the slip — in
this case the bees can lay the foundations of one wall of a new
hexagon, in its strictly proper place, projecting beyond the other
completed cells. It suffices that the bees should be enabled to
stand at their proper relative distances from each other and from
the walls of the last completed cells, and then, by striking
imaginary spheres, they can build up a wall intermediate be-

226 ORIGIN OF SPECIES

tween two adjoining spheres; but, as far as I have seen, they
never gnaw away and finish off the angles of a cell till a large
part both of that cell and of the adjoining cells has been built.
This capacity in bees of laying down under certain circumstances
a rough wall in its proper place between two just-commenced
cells, is important, as it bears on a fact, which seems at first
subversive of the foregoing theory; namely, that the cells on the
extreme margin of wasp-combs are sometimes strictly hexagonal;
but I have not space here to enter on this subject. Nor does
there seem to me any great difficulty in a single insect (as in the
case of a queen-wasp) making hexagonal cells, if she were
to work alternately on the inside and outside of two or three
cells commenced at the same time, always standing at the proper
relative distance from the parts of the cells just begun, sweeping
spheres or cylinders, and building up intermediate planes.

As natural selection acts only by the accumulation of slight
modifications of structure or instinct, each profitable to the in-
dividual under its conditions of life, it may reasonably be asked,
how a long and graduated succession of modified architectural
instincts, all tending towards the present perfect plan of con-
struction, could have profited the progenitors of the hive-bee? I
think the answer is not difficult : cells constructed like those of
the bee or the wasp gain strength, and save much in labour and
space, and in the materials of which they are constructed. With
respect to the formation of wax, it is known that bees are often
hard pressed to get sufficient nectar, and I am informed by Mr.
Tegetmeier that it has been experimentally proved that from
twelve to fifteen pounds of dry sugar are consumed by a hive
of bees for the secretion of a pound of wax; so that a prodigious
quantity of fluid nectar must be collected and consumed by the
bees in a hive for the secretion of the wax necessary for the
construction of their combs. Moreover, many bees have to re-
main idle for many days during the process of secretion. A
large store of honey is indispensable to support a large stock
of bees during the winter; and the security of the hive is known
mainly to depend on a large number of bees being supported.
Hence the saving of wax by largely saving honey and the time
consumed in collecting the honey must be an important element
of success to any family of bees. Of course the success of the
species may be dependent on the number of its enemies, or para-
sites, or on quite distinct causes, and so be altogether independ-
ent of the quantity of honey which the bees can collect. But let us
suppose that this latter circumstance determined, as it probably
often has determined, whether a bee allied to our humble-bees

INSTINCT 227

could exist in large numbers in any country; and let us further
suppose that the community lived through the winter, and con-
sequently required a store of honey: there can in this case be no
doubt that it would be an advantage to our imaginary humble-
bee if a slight modification in her instincts led her to make
her waxen cells near together, so as to intersect a little; for
a wall in common even to two adjoining cells would save some
little labour and wax. Hence it would continually be more and
more advantageous to our humble-bees, if they were to make
their cells more and more regular, nearer together, and aggregated
into a mass, like the cells of the Melipona; for in this case a
large part of the bounding surface of each cell would serve to
bound the adjoining cells, and much labour and wax would
be saved. Again, from the same cause, it would be advanta-
geous to the Melipona, if she were to make her cells closer to-
gether, and more regular in every way than at present; for then,
as we have seen, the spherical surfaces would wholly disappear
and be replaced by plane surfaces; :and the Melipona would make
a comb as perfect as that of the hive-bee. Beyond this stage of
perfection in architecture, natural selection could not lead ; for
the comb of the hive-bee, as far as w^e can see, is absolutely
perfect in economising labour and wax.

Thus, as I believe, the most wonderful of all known instincts,
that of the hive-bee, can be explained by natural selection having
taken advantage of numerous successive, slight modifications of
simpler instincts; natural selection having, by slow degrees, more
and more perfectly led the bees to sweep equal spheres at a
given distance from each other in a double layer, and to build up
and excavate the wax along the planes of intersection; the bees,
of course, no more knowing that they swept their spheres at one
particular distance from each other, than they know what are
the several angles of the hexagonal prisms and of the basal
rhombic plates; the motive power of the process of natural selec-
tion having been the construction of cells of due strength and of
the proper size and shape for the larva), this being effected with
the greatest possible economy of labour and wax; that individual
swarm which thus made the best cells with least labour, and
least waste of honey in the secretion of wax, having succeeded
best, and having transmitted their newly-acquired economical
instincts to new swarms, which in their turn will have had the
best chance of succeeding in the struggle for existence.

228 ORIGIN OF SrECIES

Objections to the Theory of Natural Selection as applied to
Instincts: Neuter and Sterile Insects.

It has been objected to the foregoing view of the origin of
instincts that " the variations of structure and of instinct must
have been simultaneous and accurately adjusted to each other,
as a modification in the one without an immediate corresponding
change in the other would have been fatal." The force of this
objection rests entirely on the assumption that the changes in
the instincts and structure are abrupt. To take as an illustration
the case of the larger titmouse (Parus major) alluded to in a
previous chapter; this bird often holds the seeds of the yew be-
tween its feet on a branch, and hammers with its beak till it
gets at the kernel. Now what special difficulty would there be in
natural selection preserving all the slight individual variations in
the shape of the beak, which were better and better adapted to
break open the seeds, until a beak was formed, as well con-
structed for this purpose as that of the nuthatch, at the same
time that habit, or compulsion, or spontaneous variations of
taste, led the bird to become more and more of a seed-eater?
In this case the beak is supposed to be slowly modified by natural
selection, subsequently to, but in accordance with, slowly changing
habits or taste; but let the feet of the titmouse vary and grow
larger from correlation with the beak, or from any other un-
known cause, and it is not improbable that such larger feet
would lead the bird to climb more and more until it acquired
the remarkable climbing instinct and power of the nuthatch. In
this case a gradual change of structure is supposed to lead to
changed instinctive habits. To take one more case : few instincts
are more remarkable than that which leads the swift of the
Eastern Islands to make its nest wholly of inspissated saliva.
Some birds build their nests of mud, believed to be moistened
with saliva; and one of the swifts of North America makes
its nest (as I have seen) of sticks agglutinated with saliva, and
even with flakes of this substance. Is it then very improbable that
the natural selection of individual swifts, which secreted more,
and more saliva, should at last produce a species with instincts
leading it to neglect other materials, and to make its nest exclus-
ively of inspissated saliva ? And so in other cases. It must,
however, be admitted that in many instances we cannot conjec-
ture whether it was instinct or structure which first varied.

No doubt many instincts of very difficult explanation could be
opposed to the theory of natural selection — cases, in which we
cannot see how an instinct could have originated; cases, in which

INSTINCT . 220

no intermediate gradations are known to exist; cases of instincts
of such trifling importance, that they could hardly have ^been acted
on by natural selection; cases of instincts almost identically the
same in animals so remote in the scale of nature, that we cannot
account for their similarity by inheritance from a common pro-
genitor, and consequently must believe that they were independ-
ently acquired through natural selection. I will not here enter
on these several cases, but will confine myself to one special
difficulty, which at first appeared to me insuperable, and actually
fatal to the whole theory. I allude to the neuters or sterile
females in insect-communities; for these neuters often differ
widely in instinct and in structure from both the males and
fertile females, and yet, from being sterile, they cannot propagate
their kind.

The subject well deserves to be discussed at great length,
but I will here take only a single case, that of working or sterile
ants. How the workers have been rendered sterile is a difficulty;
but not much greater than that of any other striking modification
of structure; for it can be shown that some insects and other
articulate animals in a state of nature occasionally become ster-
ile ; and if such insects had been social, and it had been profitable
to the community that a number should have been annually
born capable of work, but incapable of procreation, I can see
no especial difficulty in this having been effected through natural
selection. But I must pass over this preliminary difficulty. The
great difficulty lies in the working ants differing widely from
both the males and the fertile females in structure, as in the
shape of the thorax, and in being destitute of wings and some-
times of eyes, and in instinct. As far as instinct alone is con-
cerned, the wonderful difference in this respect between the
workers and the perfect females, would have been better exempli-
fied by the hive-bee. If a 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 off-
spring; and that these again varied and again were selected, and
30 onwards. But with the working ant we have an insect differ-
ing greatly from its parents, yet absolutely sterile; so that it
could never have transmitted successively acquired modifications
of structure or instinct to its progeny. It may well be asked
how is it possible to reconcile this case with the theory of natural
selection ?

First, let it be remembered that we have innumerable in-

230 . ORIGIN OF SPECIES

stances, 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. AVe have
differences correlated not only with one sex, Wt 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 modifica-
tions of structure could have been slowly accumulated by natural
selection.

This difficulty, though appearing insuperable, is lessened, or,
as I believe, disappears, when it is remembered that selection
may b© 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 char-
acterised has been slaughtered, but the breeder has gone with
confidence to the same stock and has succeeded. Such faith may
be placed in the power of selection, that a breed of cattle, always
yielding oxen with extraordinarily long horns, could, it is probable,
be formed by carefully watching which individual bulls and cows,
when matched, produced oxen with the longest horns; and yet
no 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 ser-
viceable end. Hence we may conclude that slight modifications of
structure or of instinct, correlated with the sterile condition
of certain members of the community, have proved advantageous :
consequently the fertile males and females have flourished, and
transmitted to their fertile offspring a tendency to produce ster-
ile members with the same modifications. This process must have

INSTINCT 231

been repeated many times, until that prodigious amount of differ-
ence between the fertile and sterile females of the same species
has been produced, which we see in many social insects.

But we have not as yet touched on the acme of the difficulty;
namely, the fact that the neuters of several ants differ, not only
from the fertile females and males, but from each other, some-
times to an almost incredible degree, and are thus divided into
tw^o or even three castes. The castes, moreover, do not com-
monly 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 Myrmecocystus, the workers of one caste never leave the
nest; they are fed by the workers of another caste, and they
have an enormously developed 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 con-
fidence in the principle of natural selection, when I do not admit
that such wonderful and well-established facts at once annihil-
ate the theory. lii 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 con-
clude from the analogy of ordinary variations, that the succes-
sive, slight, profitable modificaUons 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
mxost neuters having the advantageous modification, all the neu-
ters ultimately came to be thus characterised. According to this
view we ought occasionally to find in the same nest neuter in-
sects, presenting gradations of structure; and this we do find,
even not rarely, considering how few neuter insects out of
Europe have been carefully examined. Mr. F. Smith has shown
that the neuters of several British ants differ surprisingly from
each other in size and sometimes in colour; and that the extreme
forms can be linked together by individuals taken out of the
same nest : I have myself compared perfect gradations of this
kind. It sometimes happens that the larger or the smaller sized
workers are the most numerous ; or that both large and siuall
are numerous, whilst those of an intermediate size are scanty in

232 ORIGIN OF SPECIES

numbers. Formica flava lias 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 carefully
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 in-
termediate condition. So that here we have two bodies of sterile
workers in the same nest, differing not only in size, but in their
organs of vision, yet connected by some few members in an
intermediate condition. I may digress by adding, that if the
smaller workers had been the most useful to the 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 rudi-
ments 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 occa-
sionally to find gradations of important structures 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, more-
over, of the working ants of the several sizes differed wonder-
fully 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 insen-
sibly into each other, as does the widely-different structure of
their jaws. I speak confidently on this latter point, as Sir J.
Lubbock made drawings for me, with the camera lucida, of the
jaws which I dissected from the workers of the several sizes.

INSTINCT 233

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 gen-
erated 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 Miiller, of certain Brazilian crustaceans likewise ap-
pearing 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 prin-
ciple that the division of labour is useful to civilised man. Ants,
however, work by inherited instincts and by inherited organs or
tools, whilst man works by acquired knowledge and manufactured
instruments. But I must confess, that, with all my faith in
natural selection, I should never have anticipated that this prin-
ciple 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 diffi-
culty which my theory has encountered. The case, also, is very
interesting, as it proves thai with animals, as with plants, any
amount of modification may be effected by the accumulation of
numerous, slight, spontaneous variations, which are in any way
profitable, without exercise or habit having been brought into
play. For peculiar habits confined to the workers or sterile
females, however long they might be followed, could not possibly
affect the males and fertile females, which alone leave descendants.
I am surprised that no one has hitherto advanced this demon-

234 OlilGIN OF SPECIES

strative 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. Therefore there is no real difficulty, under changing con-
ditions of life, in natural selection accumulating to any extent
slight modifications of instinct which are in any way useful.
In many cases habit or use and disuse have probably come into
play. I do not_ pretend that the facts given in this chapter
strengthen in any great degree my theory; but none of the cases
of difficulty, to the best of my judgment, annihilate it. On the
other hand, the fact that instincts are not always absolutely
perfect and are liable 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 " ISTatura non f acit saltum," is
applicable to instincts as well as to corporeal structure, and is
plainly explicable on the foregoing views, but is otherwise inexpli-
cable — all tend to corroborate the theory of natural selection.

This theory is also strengthened by some few other facts in
regard to instincts; as by that common case of closely allied, but
distinct species, when inhabiting distant parts of the world and
living under considerably different conditions of life, yet often
retaining ijearly 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
Tlornbills of Africa and India have the same extraordinary in-
stinct of plastering up and imprisoning the females in a hole in
a tree, with only a small hole left in the plaster through which
the males feed them and their young when hatched; how it is
that the male wrens (Troglodytes) of North America build
" cock-nests," to roost in, like the males of our Kitty-wrens, —
a habit wholly unlike that of any other known bird. Finally, it
may not be a logical deduction, but to my imagination it is far
more satisfactory to look at such instincts as the young cuckoo
ejecting its foster-brothers, — ants making slaves, — the larvae of
ichneumonidse feeding within the live bodies of caterpillars, — •

INSTINCT 235

not as specially endowed or created instincts, but as small conse-
quences of one general law leading to the advancement of all
organic beings, — namely, multiply, vary, let the strongest live
and the weakest die.

236 ORIGIN OF SPECIES

CHAPTEK IX.

HYBRIDISM.

Distinction between the sterility of first crosses and of hybrids — Sterility
various in degree, not universal, affected by close interbreeding, removed
by domestication — Laws governing the sterility of hybrids — Sterility
not a special endowment, but incidental on other differences, not
accumulated by natural selection — Causes of the sterility of first
crosses and of hybrids — Parallelism between the effects of changed
conditions of life and of crossing — Dimorphism and trimorphism —
Fertility of varieties when crossed and of their mongrel offspring not
universal — Plybrids and mongrels compared independently of their
fertility — Summary.

THE view cominonly entertained by naturalists is that species,
when intercrossed, have been specially endowed with steril-
ity, in order to prevent their confusion. This view cer-
tainly seems at first highly probable, for species living together
could hardly have been kept distinct had they been capable of
freely crossing. The subject is in many ways important for us,
more especially as the sterility of species when first crossed, and
that of their hybrid offspring, cannot have been acquired, as I
shall show, by the preservation of successive profitable degrees
of sterility. It is an incidental result of differences in the re-
productive systems of the parent-species.

In treating this subject, two classes of facts, to a large extent
fundamentally different, have generally been confounded ; namely,
the sterility of species when first crosssed, and the sterility of
the hybrids produced from them.

Pure species have of course their organs of reproduction in a
perfect condition, yet when intercrossed they produce either few
or no offspring. PTybrids, on the other hand, have their repro-
ductive organs functionally impotent, as may be clearly seen in
the state of the male element in both plants and animals; though
the formative organs themselves are perfect in structure, as far
as the microscope reveals. In the first case the two sexual ele-
ments which go to form the embryo are perfect; in the second
case they are either not at all developed, or are imperfectly de-

HYBRIDISM 237

veloped. This distinction is important, when the cause of the ster-
ility, which is common to the two cases, has to be considered.
The distinction probably has been slurred over, owing to the
sterility in both cases being looked on as a special endowment,
beyond the province of our reasoning powers.

The fertility of varieties, that is of the forms known or be-
lieved to be descended from common parents, when crossed, and
likewise the fertility of their mongrel offspring, is, with reference
to my theory, of equal importance with the sterility of species ; for
it seems to make a broad and clear distinction between varieties
and species.

Degrees of Sterility. — First, for the sterility of species when
crossed and of their hybrid offspring. It is impossible to study
the several memoirs and works of those two conscientious and
admirable observers, Kolreuter and Gartner, who almost devoted
their lives to this subject, without being deeply impressed with the
high generality of some degree of sterility. Kolreuter makes the
rule universal; but then he cuts the knot, for in ten cases in
which he found two forms, considered by most authors as distinct
species, quite fertile together, he unhesitatingly ranks them as
varieties. Gartner, also, makes the rule equally universal; and
he disputes the entire fertility of Kolreuter's ten cases. But in
these and in many other cases, Gartner is obliged carefully to
count the seeds, in order to show that there is any degree of
sterility. He always compares the maximum number of seeds
produced by two species when first crossed, and the maximum pro-
duced by their hybrid offspring, with the average number pro-
duced by both pure parent-species in a state of nature. But
causes of serious error here intervene : a plant, to be hybridised,
must be castrated, and, what is often more important, must be
secluded in order to prevent pollen being brought to it by insects
from other plants. Nearly all the plants experimented on by
Gartner were potted, and were kept in a chamber in his house.
That these processes are often injurious to the fertility of a
plant cannot be doubted; for Gartner gives in his table about a
score of cases of plants which he castrated, and artificially fertil-
ised with their own pollen, and (excluding all cases such as the
Leguminos^, in which there is an acknowledged difficulty in the
manipulation) half of these twenty plants had their fertility in
some degree impaired. Moreover, as Gartner repeatedly crossed
some forms, such as the common red and blue pimpernels (Anag-
allis arvensis and coerulea), which the best botanists rank as
varieties, and found them absolutely sterile, we may doubt whether

238 ORIGIN OP SPECIES

many species are really so sterile, when intercrossed, as he be-
lieved.

It is certain, on the one hand, that the sterility of various
species when crossed is so different in degree and graduates away
so insensibly, and, on the other hand, that the fertility of pure
species is so easily affected by various circumstances, that for all
practical purposes it is most difficult to say where perfect fertility
ends and sterility begins. I think no better evidence of this can
be required than that the two most experienced observers who have
ever lived, namely Kolreuter and Gartner, arrived at diametrically
opposite conclusions in regard to some of the very same forms.
It is also most instructive to compare — but I have not space
here to enter on details — the evidence advanced by our best
botanists on the question whether certain doubtful forms should
be ranked as species or varieties, with the evidence from fertility
adduced by different hybridisers, or by the same observer from
experiments made during different years. It can thus be shown
that neither sterility nor fertility affords any certain distinction
between species and varieties. The evidence from this source
graduates away, and is doubtful in the same degree as is the
evidence derived from other constitutional and structural differ-
ences.

In regard to the sterility of hybrids in successive generations;
though Gartner was enabled to rear some hybrids, carefully guard-
ing them from a cross with either pure parent, for six or seven, and
in one case for ten generations, yet he asserts positively that their
fertility never increases, but generally decreases greatly and
suddenly. With respect to this decrease, it may first be noticed
that when any deviation in structure or constitution is common to
both parents, this is often transmitted in an augmented degree
to the offspring; and both sexual elements in hybrid plants are
already affected in some degree. But I believe that their fer-
tility has been diminished in nearly all these cases by an inde-
pendent cause, namely, by too close interbreeding. I have made
so many experiments and collected so many facts, showing on
the one hand that an occasional cross with a distinct individual
or variety increases the vigour and fertility of the offspring,
and on the other hand that very close interbreeding lessens their
vigour and fertility, that I cannot doubt the correctness of this
conclusion. Hybrids are seldom raised by experimentalists in
great numbers; and as the parent-species, or other allied hybrids,
generally grow in the same garden, the visits of insects must be
carefully prevented during the flowering season : hence hybrids,
jf left to themselves, will generally be fertilised during each gen-

HYBRIDISM 239

eration by pollen from the same flower; and this would probably
be injurious to their fertility, already lessened by their hybrid
origin. I am strengthened in this conviction by a remarkable
statement repeatedly made by Gartner, namely, that if even the
less fertile hybrids be artificially fertilised with hybrid pollen of
the same kind, their fertility, notwithstanding the frequent ill
effects from manipulation, sometimes decidedly increases, and goes
on increasing. Now, in the process of artificial fertilisation,
pollen is as often taken by chance (as I know from my own
experience) from the anthers of another flower, as from the
anthers of the flower itself which is to be fertilised; so that a
cross between two flowers, though probably often on the same
plant, would be thus effected. Moreover, whenever complicated
experiments are in progress, so careful an observer as Gartner
would have castrated his hybrids, and this would have ensured
in each generation a cross with pollen from a distinct flower,
either from the same plant or from another plant of the same
hybrid nature. And thus, the strange fact of an increase of
fertility in the successive generations of artificially fertilised
hybrids, in contrast with those spontaneously self-fertilised, may,
as I believe, be accounted for by too close interbreeding having
been avoided.

Now let us turn to the results arrived at by a third most
experienced hybridiser, namely, the Hon. and Rev. W. Herbert.
He is as emphatic in his conclusion that some hybrids are perfectly
fertile — as fertile as the pure parent-species — as are Kolreuter
and Gartner that some degree of sterility between distinct species
is a universal law of nature. He experimented on some of the
very same species as did Gartner. The difference in their results
may, I think, be in part accounted for by Herbert's great horti-
cultural skill, and by his having hot-houses at his command. Of
his many important statements I will here give only a single one as
an example, namely, that " every ovule in a pod of Crinum ca-
pense fertilised by C. revolutum produced a plant, which I never
saw to occur in a case of its natural fecundation." So that
there we have perfect or even more than commonly perfect fer-
tility, in a first cross between two distinct species.

This case of the Crinum leads me to refer to a singular fact,
namely, that individual plants of certain species of Lobelia, Ver-
bascum and Passiflora, can easily be fertilised by pollen from a
distinct species, but not by pollen from the same plant, though
this pollen can be proved to be perfectly sound by fertilising other
plants or species. In the genus Hippeastrum, in Corydalis as
shown by Professor Hildebrand, in various orchids as shown by

240 ORIGll^ OI^' SrliJCIliiC]

Mr. Scott and Fritz Miiller, all the individuals are in ims peculiar
condition. So that with some species, certain abnormal individ-
uals, and in other species all the individuals, can actually be
hybridised much more readily than they can be fertilised by pollen
from the same individual plant! To give one instance, a bulb
of Hippeastrum aulicum produced four flowers; three were fer-
tilised by Herbert with their own pollen, and the fourth was
subsequently fertilised by the pollen of a compound hybrid de-
scended from three distinct species : the result was that " the ova-
ries of the three first flowers soon ceased to grow, and after a
few days perished entirely, whereas the pod impregnated by the
pollen of the hybrid made vigorous growth and rapid progress to
maturity, and bore good seed, which vegctaied freely/' Mr. Her-
bert tried similar experiments during many years, and always
with the same result. These cases serve to show on what slight and
mysterious causes the lesser or greater fertility of a species some-
times depends.

The practical experiments of horticulturists, though not made
with scientific precision, deserve some notice. It is notorious
in how complicated a manner the species of Pelargonium, Fuch-
sia, Calceolaria, Petunia, Rhododendron, &c., have been crossed, yet
many of these hybrids seed freely. For instance, Herbert as-
serts that a hybrid from Calceolaria integrifolia and plantaginea,
species most widely dissimilar in general habit, " reproduces it-
self as perfectly as if it had been a natural species from the
mountains of Chili." I have taken some pains to ascertain the
degree of fertility of some of the complex crosses of Rhododen-
drons, and I am assured that many of them are perfectly fertile.
Mr. C. Noble, for instance, informs me that he raises stocks for
grafting from a hybrid between Rhod. ponticum and catawbiense,
and that this hybrid " seeds as freely as it is possible to imagine."
Had hybrids when fairly treated, always gone on decreasing in fer-
tility in each successive generation, as Gartner believed to be the
case, the fact would have been notorious to nurserymen. Horticul-
turists raise large beds of the same hybrid, and such alone are
fairly treated, for by insect agency the several individuals are al-
lowed to cross freely with each other, and the injurious influence
of close interbreeding is thus prevented. Any one may readily con-
vince himself of the efliciency of insect-agency by examining the
flowers of the more sterile kinds of hybrid Rhododendrons, which
produce no pollen, for he will find on their stigmas plenty of
pollen brought from other flowers.

In regard to animals, much fewer experiments have been care-
fully tried than with plants. If our systematic arrangements can

HYBRIDISM 241

be trusted, that is, if the genera of animals are as distinct from
each other as are the genera of phmts, then we may infer that
animals more widely distinct in the scale of nature can be crossed
more easily than in the case of plants; but the hybrids themselves
are, I think, more sterile. It should, however, be borne in mind,
that, owing to few animals breeding freely under confinement,
few experiments have been fairly tried : for instance, the canary-
bird has been crossed with nine distinct species of finches, but,
as not one of these breeds freely in confinement, we have no right
to expect that the first crosses between them and the canary, or
that their hybrids, should be perfectly fertile. Again, with re-
spect to the fertility in successive generations of the more fertile
hybrid animals, I hardly know of an instance in which two fami-
lies of the same hybrid have been raised at the same time from
different parents, so as to avoid the ill effects of close interbreed-
ing. On the contrary, brothers and sisters have usually been
crossed in each successive generation, in opposition to the con-
stantly repeated admonition of every breeder. And in this case,
it is not at all surprising that the inherent sterility in the hybrids
should have gone on increasing.

Although I know of hardly any thoroughly well-authenticated
cases of perfectly fertile hybrid animals, I have reason to believe
that the hybrids from Cervulus vaginalis and Keevesii, and from
Phasianus colchicus with P. torquatus, are perfectly fertile. M.
Quatrefages states that the hybrids from two moths (Bombyx
cynthia and arrindia) were proved in Paris to be fertile inter' se
for eight generations. It has lately been asserted that two such
distinct species as the hare and rabbit, when they can be got to
breed together, produce offspring, which are highly fertile when
crossed with one of the parent-species. The hybrids from the
common and Chinese geese (A. cygnoides), species which are
so different that they are generally ranked in distinct genera, have
often bred in this country with either pure parent, and in one
single instance they have bred inter' se. This was effected by
Mr. Eyton, who raised two hybrids from the same parents, but from
different hatches; and from these two birds he raised no less than
eight hybrids (grandchildren of the pure geese) from one nest.
In India, however, these cross-bred geese must be far more fer-
tile; for I am assured by two eminently capable judges, namely
Mr. Blyth and Capt. Tlutton, that whole flocks of these crossed
geese are kept in various parts of the country; and as they are
kept for profit, where neither pure parent-species exists, they must
certainly be highly or perfectly fertile.

With our domesticated animals, the various races when crossed

242 ORIGIN OF SPECIES

together are quite fertile; yet in many cases they are descended
from two or more wild species. From this fact we must conclude
either that the aboriginal parent-species at first produced perfectly
fertile hybrids, or that the hybrids subsequently reared under
domestication became quite fertile. This latter alternative, which
was first propounded by Pallas, seems by far the most probable,
and can, indeed, hardly be doubted. It is, for instance, almost
certain that our dogs are descended from several wild stocks; yet,
with i^erhaps the exception of certain indigenous domestic dogs of
South America, all are quite fertile together; but analogy makes
me greatly doubt, whether the several aboriginal species would
at first have freely bred together and have produced quite fertile
hybrids. So again I have lately acquired decisive evidence that
the crossed offspring from the Indian humped and common cattle
are inter se perfectly fertile; and from the observations by Riiti-
meyer on their important osteological differences, as well as from
those by Mr. Blyth on their differences in habits, voice, consti-
tution, &c., these two forms must be regarded as good and distinct
species. The same remarks may be extended to the two chief
races of the pig. We must, therefore, either give up the belief
of the universal sterility of species when crossed; or we must
look at this sterility in animals, not as an indelible characteristic,
but as one capable of being removed by domestication.

Finally, considering all the ascertained facts on the intercross-
ing of plants and animals, it may be concluded that some degree
of sterility, both in first crosses and in hybrids, is an extremely
general result ; but that it cannot, under our present state of knowl-
edge, be considered as absolutely universal.

Laws governing the Sterility of first Crosses and of Hyhrids.

We will now consider a little more in detail the laws governing
the sterility of first crosses and of hybrids. Our chief object
will be to see whether or not these laws indicate that species have
been specially endowed with this quality, in order to prevent their
crossing and blending together in utter confusion. The follow-
ing conclusions are drawn up chiefly from Gartner's admirable
work on the hybridisation of plants. I have taken much pains
to ascertain how far they apply to animals, and, considering how
scanty our knowledge is in regard to hybrid animals, I have been
surprised to find how generally the same rules apply to both king-
doms.

It has been already remarked, that the degree of fertility,
both of first crosses and of hybrids, graduates from zero to per-

HYBRIDISM 243

feet fertility. It is surprising in how many curious ways this
gradation can be shown; but only the barest outline of the facts
can here be given. When pollen from a plant of one family
is placed on the stigma of a plant- of a distinct family, it exerts
no more influence than so much inorganic dust. From this abso-
lute zero of fertility, the pollen of different species applied to the
stigma of some one species of the same genus, yields a perfect
gradation in the number of seeds produced, up to nearly complete
or even quite complete fertility; and, as we have seen, in certain
abnormal cases, even to an excess of fertility, beyond that which
the plant's own j^ollen produces. So in hybrids themselves, there
are some which never have produced, and probably never would
produce, even with the pollen of the pure parents, a single fertile
seed: but in some of these cases a first trace of fertility may be
detected, by the pollen of one of the pure parent-species causing
the flower of the hybrid to wither earlier than it otherwise would
have done; and the early withering of the flower is well known to
be a sign of incipient fertilisation. From this extreme degree of
sterility we have self-fertilised hybrids producing a greater and
greater number of seeds up to perfect fertility.

The hybrids raised from two species which are very diflicult to
cross, and which rarely produce any offspring, are generally very
sterile; but the parallelism between the difficulty of making a
first cross, and the sterility of the hybrids thus produced — two
classes of facts which are generally confounded together — is by no
means strict. There are many cases, in which two pure species, as
in the genus Yerbascum, can be united with unusual facility,
and produce numerous hybrid offspring, yet these hybrids are re-
markably sterile. On the other hand, there are species which can
be crossed very rarely, or with extreme difficulty, but the hybrids,
when at last produced, are very fertile. Even within the limits
of the same genus, for instance in Dianthus, these two opposite
cases occur.

The fertility, both of first crosses and of hybrids, is more
easily affected by unfavourable conditions, than is that of pure
species. But the fertility of first crosses is likewise innately
variable; for it is not always the same in degree when the same
two species are crossed under the same circumstances; it depends
in part upon the constitution of the individuals which happen
to have been chosen for the experiment. So it is with hybrids,
for their degree of fertility is often found to differ greatly in
the several individuals raised from seed out of the same capsule
and exposed to the same conditions.

By the term systematic affinity is meantj the general resem-

244 ORIGIN OF SPECIES

blance between species in structure and constitution. Now the
fertility of first crosses, and of the hybrids produced from them,
is largely governed by their systematic affinity. This is clearly
shown by hybrids never having been raised between species ranked
by systematists in distinct families; and on the other hand,
by very closely allied species generally uniting with facility. But
the correspondence between systematic affinity and the facility of
crossing is by no means strict. A multitude of cases could be
given of very closely allied species which will not unite, or only
with extreme difficulty; and on the other hand of very distinct
species which unite with the utmost facility. In the same family
there may be a genus, as Dianthus, in which very many species
can most readily be crossed ; and another genus, as Silene, in which
the most persevering efforts have failed to produce between ex-
tremely close species a single hybrid. Even within the limits of
the same genus, we meet with this same difference ; for instance,
the many species of Nicotiana have been more largely crossed
than the species of almost any other genus; but Gartner found
that N. acuminata, which is not a particularly distinct species,
obstinately failed to fertilise, or to be fertilised by no less than
eight other species of Nicotiana. Many analogous facts could be
given.

No one has been able to point out what kind 6v what amount
of difference, in any recognisable character, is sufficient to prevent
two species crossing. It can be shown that i:>lants most widely
different in habit and general appearance, and having strongly
marked differences in every part of the flower, even in the pollen,
in the fruit, and in the cotyledons, can be crossed. Annual and
perennial plants, deciduous and evergreen trees, plants inhabiting
different stations and fitted for extremely different climates, can
often be crossed with ease.

By a reciprocal cross between two species, I mean the case, for
instance, of a female-ass being first crossed by a stallion, and
then a mare by a male-ass; these two species may then be said to
have been reciprocally crossed. There is often the widest possible
difference in the facility of making reciprocal crosses. Such cases
are highly important, for they prove that the capacity in any
two species to cross is often completely independent of their sys-
tematic affinity, that is of any difference in their structure or
constitution, excepting in their reproductive systems. The di-
versity of the result in reciprocal crosses between the same two
species was long ago observed by Kr'dreuter. To give an instance :
Mirabilis jalapa can easily be fertilised by the pollen of M. longi-
flora, and the hybrids thus produced are sufficiently fertile; but

HYBRIDISM 245

Kolreuter tried more than two hundred times, during eight follow-
ing years, to fertilise reciprocally M. longiflora with the pollen of
M. jalapa, and utterly failed. Several other equally striking cases
could be given. Thuret has observed the same fact with certain
sea-weeds or Fuci. Gartner, moreover, found that this difference
of facility in making reciprocal crosses is extremely common in
a lesser degree. He has observed it even between closely related
forms (as Matthiola annua and gilabra) which many botanists
rank only as varieties. It is also a remarkable fact, that hybrids
raised from reciprocal crosses, though of course compounded of
the very same two species, the one species having first been used
as the father and then as the mother, though they rarely differ
in external characters, yet generally differ in fertility in a small,
and occasionally in a high degree.

Several other singular rules could be given from Gartner: for
instance, some species have a remarkable power of crossing with
other species; other species of the same genus have a remarkable
power of impressing their likeness on their hybrid offspring;
but these two powers do not at all necessarily go together. There
are certain hybrids which, instead of having, as is usual, an
intermediate character between their two parents, always closely
resemble one of them; and such hybrids, though externally so
like one of their pure parent-species, are with rare exceptions
extremely sterile. So again amongst hybrids which are usually
intermediate in structure between their parents, exceptional and
abnormal individuals sometimes are born, which closely resemble
one of their pure parents; and these hybrids are almost always
utterly sterile, even when the other hybrids raised from seed
from the same capsule have a considerable degree of fertility.
These facts show how completely the fertility of a hybrid may be
independent of its external resemblance to either pure parent.

Considering the several rules now given, which govern the
fertility of first crosses and of hybrids, we see that when forms,
which must be considered as good and distinct species, are united,
their fertility graduates from zero to perfect fertility, or even
to fertility under certain conditions in excess ; that their fertility,
besides being eminently susceptible to favourable and unfavour-
able conditions, is innately variable ; that it is by no means always
the same in degree in the first cross and in the hybrids produced
from this cross; that the fertility of hybrids is not related to the
degree in which they resemble in external appearance either parent ;
and lastly, that the facility of making a first cross betw^een any two
species is not always governed by their systematic affinity or degree
of resemblance to each other. This latter statement is clearly

246 ORIGIN OF SPECIES

proved by the difference in the result of reciprocal crosses between
the same two species, for, according as the one species or the
other is used as the father or the mother, there is generally some
difference, and occasionally the widest possible difference, in the
facility of effecting an union. The hybrids, moreover, produced
from reciprocal crosses often differ in fertility.

Now do these complex and singular rules indicate that species
have been endowed with sterility simply to prevent their becoming
confounded in nature ? I think not. For why should the sterility
be so extremely different in degree, when various species are
crossed, all of which we must suppose it would be equally im-
portant to keep from blending together? Why should the degree
of sterility be innately variable in the individuals of the same
species? Why should some species cross with facility, and yet
produce very sterile hybrids; and other species cross with extreme
difficulty, and yet produce fairly fertile hybrids? Why should
there often be so great a difference in the result of a reciprocal
cross between the same two species? Why, it may even be asked,
has the production of hybrids been permitted ? To grant to species
the special power of producing hybrids, and then to stop their
further propagation by different degrees of sterility, not strictly
related to the facility of the first union between their parents,
seems a strange arrangement.

The foregoing rules and facts, on the other hand, appear to
me clearly to indicate that the sterility both of first crosses and
of hybrids is simply incidental or dependent on unknown differ-
ences in their reproductive systems; the differences being of so pe-
culiar and limited a nature, that, in reciprocal crosses between the
same two species, the male sexual element of the one will often
freely act on the female sexual element of the other, but not
in a reversed direction. It will be advisable to explain a little
more fully by an example what I mean by sterility being incidental
on other differences, and not a specially endowed quality. As the
capacity of one plant to be grafted or budded on another is
unimportant for their welfare in a state of nature, I presume that
no one will suppose that this capacity is a specially endowed qual-
ity, but will admit that it is incidental on differences in the laws
of growth of the two plants. We can sometimes see the reason why
one tree will not take on another, from differences in their rate of
growth, in the hardness of their wood, in the period of the flow
or nature of their sap, &c. ; but in a multitude of cases we can
assign no reason whatever. Great diversity in the size of two
plants, one being woody and the other herbaceous, one being eve?-
green and the other deciduous, and adaptation to widely different

HYBRIDISM 247

climates, do not always prevent the two grafting together. As
in hybridisation, so with grafting, the capacity is limited by
systematic affinity, for no one has been able to graft together
trees belonging to quite distinct families; and, on the other hand,
closely allied species, and varieties of the same species, can usually,
but not invariably, be grafted with ease. But this capacity, as in
hybridisation, is by no means absolutely governed by systematic
affinity. Although many distinct genera within the same family
have been grafted together, in other cases species of the same
genus will not take on each other. The pear can be grafted
far more readily on the quince, which is ranked as a distinct
genus, than on the apple, which is a member of the same genus.
Even different varieties of the pear take with different degrees of
facility on the quince; so do different varieties of the apricot
and peach on certain varieties of the plum.

As Gartner found that there was sometimes an innate differ-
ence in different individuals of the same two species in crossing;
so Sageret believes this to be the case with different individuals of
the same two species in being grafted together. As in reciprocal
crosses, the facility of effecting an union is often very far from
equal, so it sometimes is in grafting; the common gooseberry,
for instance, cannot be grafted on the currant, whereas the currant
will take, though with difficulty, on the gooseberry.

We have seen that the sterility of hybrids, which have their
reproductive organs in an imperfect condition, is a different case
from the difficulty of uniting two pure species, which have their
reproductive organs perfect; yet these two distinct classes of
cases run to a large extent parallel. Something analogous occurs
in grafting ; for Thouin found that three species of Robinia, which
seeded freely on their own roots, and which could be grafted
with no great difficulty on a fourth species, when thus grafted
were rendered barren. On the other hand, certain species of
Sorbus, when grafted on other species yielded twice as much
fruit as when on their own roots. We are reminded by this latter
fact of the extraordinary cases of Hippeastrum, Passiflora, &c.,
which seed much more freely when fertilised with the pollen of
a distinct species, than when fertilised with pollen from the same
plant.

We thus see, that, although there is a clear and great difference
between the mere adhesion of grafted stocks, and the union of
the male and female elements in the act of reproduction, yet that
there is a rude degree of parallelism in the results of grafting and
of crossing distinct species. And as we must look at the curious
and complex laws governing the facility with which trees can

248 ORIGIN OF SPECIES

be grafted on each other as incidental on unknown differences
in their vegetative i^ystems, so I believe that the still more complex
laws governing the facility of first crosses are incidental on un-
known differences in their reproductive systems. These differences
in both cases follow to a certain extent, as might have been
expected, systematic affinity, by which term every kind of resem-
blance and dissimilarity between organic beings is attempted to
be expressed. The facts by no means seem to indicate that the
greater or lesser difficulty of either grafting or crossing various
species has been a special endowment; although in the case of
crossing, the difficulty is as important for the endurance and
stability of specific forms, as in the case of grafting it is unim-
portant for their welfare.

Origin and Causes of the Sterility of first Crosses and of Hybrids.

At one time it appeared to me probable, as it has to others,
that the sterility of first crosses and of hybrids might have been
slowly acquired through the natural selection of slightly lessened
degrees of fertility, which, like any other variation, spontaneously
appeared in certain individuals of one variety when crossed with
those of another variety. For it would clearly be advantageous
to two varieties or incipient species, if they could be kept from
blending, on the same principle that, when man is selecting at
the same time two varieties, it is necessary that he should keep
them separate. In the first place, it may be remarked that species
inhabiting distinct regions are often sterile when crossed; now
it could clearly have been of no advantage to such separated
species to have been rendered mutually sterile, and consequently
this could not have been effected through natural selection; but
it may perhaps be argued, that, if a species was rendered sterile
with some one comi^atriot, sterility with other species would fol-
low as a necessary contingency. In the second place, it is almost
as much opposed to the theory of natural selection as to that of
special creation, that in reciprocal crosses the male element
of one form should have been rendered utterly impotent on a
second form, whilst at the same time the male element of this
second form is enabled freely to fertilise the first form; for this
peculiar state of the reproductive system could hardly have been
advantageous to either species.

In considering the probability of natural selection having come
into action, in rendering species mutually sterile, the greatest
difficulty will be found to lie in the existence of many graduated
steps from slightly lessened fertility to absolute sterility. It

HYBRIDISM 249

may be admitted that it would profit an incipient species, if it
were rendered in some slight degree sterile when crossed with its
parent form or with some other variety; for thus fewer bastardised
and deteriorated offspring would be produced to commingle their
blood with the new species in process of formation. But he who
will take the trouble to reflect on the steps by which this first
degree of sterility could be increased through natural selection
to that high degree which is common with so many species, and
which is universal with species which have been differentiated to
a generic or family rank, will find the subject extraordinarily
complex. After mature reflection it seems to me that this could
not have been effected through natural selection. Take the case
,of any two species which, when crossed, produce few and sterile
offspring; now, what is there which could favour the survival of
those individuals which happened to be endowed in a slightly
higher degree with mutual infertility, and which thus approach
by one small step towards absolute sterility? Yet an advance of
this kind, if the theory of natural selection be brought to bear,
must have incessantly occurred with many species, for a multi-
tude are mutually quite barren. With sterile neuter insects we
have reason to believe that modifications in their structure and
fertility have been slowly accumulated by natural selection, from
an advantage having been thus indirectly given to the community
to which they belonged over other communities of the same species;
but an individual animal not belonging to a social community,
if rendered slightly sterile when crossed with some other variety
would not thus itself gain any advantage or indirectly give any
advantage to the other individuals of the same variety, thus
leading to their iDreservation.

But it would be superfluous to discuss this question in detail;
for with plants we have conclusive evidence that the sterility of
crossed species must be due to some principle, quite independent
of natural selection. Both Gartner and Kolreuter have proved
that in genera including numerous species, a series can be formed
from species which when crossed yield fewer and fewer seeds,
to species which never produce a single seed, but yet are affected
by the pollen of certain other species, for the germen swells.
It is here manifestly impossible to select the more sterile individ-
uals, which have already ceased to yield seeds; so that this acme
of sterility, when the germen alone is affected, cannot have been
gained through selection ; and from the laws governing the va-
rious grades of sterility being so uniform throughout the animal
and vegetable kingdoms, we may infer that the cause, whatever
it may be, is the same or nearly the same in all cases.

250 ORIGIN OF SPECIES

We will now look a little closer at the probable nature o^ the
differences between species which induce sterility in first crosses
and in hybrids. In the case of first crosses, the greater or less
difficulty in effecting an union and in obtaining offspring appar-
ently depends on several distinct causes. There must sometimes
be a physical impossibility in the male element reaching the ovule,
as would be the case with a plant having a pistil too long for
the pollen-tubes to reach the ovarium. It has also been observed
that when the pollen of one species is placed on the stigma of
a distantly allied species, though the pollen-tubes protrude, they
do not penetrate the stigmatic surface. Again, the male element
may reach the female element but be incapable of causing an
embryo to be developed, as seems to have been the case with some
of Thuret's experiments on Fuci. No explanation can be given
of these facts, any more than why certain trees cannot be grafted
on others. Lastly, an embryo may be developed, and then perish
at an early period. This latter alternative has not been sufficiently
attended to; but I believe, from observations communicated to
me by Mr. Hewitt, who has had great experience in hybridising
pheasants and fowls, that the early death of the embryo is a very
frequent cause of sterility in first crosses. Mr. Salter has recently
given the results of an examination of about 500 eggs produced
from various crosses between three species of Gallus and their
hybrids; the majority of these eggs had been fertilised; and in
the majority of the fertilised eggs, the embryos had either been
partially developed and had then perished, or had become nearly
mature, but the young chickens had been unable to break through
the shell. Of the chickens which were born, more than four-
fifths died within the first few days, or at latest weeks, " without
any obvious cause, apparently from mere inability to live;" so
that from the 500 eggs only twelve chickens were reared. With
plants, hybridised embryos probably often perish in a like man-
ner; at least it is known that hybrids raised from every distinct
species are sometimes weak and dwarfed, and perish at an early
age; of which fact Max Wichura has recently given some striking
cases with hybrid willows. It may be here worth noticing that
in some cases of parthenogenesis, the embryos within the eggs of
silk moths which had not been fertilised, pass through their early
stages of development and then perish like the embryos produced
by a cross between distinct species. Until becoming acquainted
with these facts, I was unwilling to believe in the frequent early
death of hybrid embryos; for hybrids, when once born, are
generally healthy and long-lived, as we see in the case of the
common mule. Hybrids, however, are differently circumstanced

HYBRIDISM 251

before and after birth: wlien born and living in a country where
their two parents live, they are generally placed under suitable
conditions of life. But a hybrid partakes of only half of the
nature and constitution of its mother; it may therefore before
birth, as long as it is nourished within its mother's womb, or
within the egg or seed produced by the mother, be exposed to
conditions in some degree unsuitable, and consequently be liable
to perish at an early period; more especially as all very young
beings are eminently sensitive to injurious or unnatural conditions
of life. But after all, the cause more probably lies in some
imperfection in the original act of impregnation, causing the
embryo to be imperfectly developed, rather than in the conditions
to which it is subsequently exposed.

In regard to the sterility of hybrids, in which the sexual ele-
ments are imperfectly developed, the case is somewhat different.
I have more than once alluded to a large body of facts showing
that, when animals and plants are removed from their natural
conditions, they are extremely liable to have their reproductive
systems seriously affected. This, in fact, is the great bar to the
domestication of animals. Between the sterility thus superinduced
and that of hybrids, there are many points of similarity. In
both cases the sterility is independent of general health, and is
often accompanied by excess of size or great luxuriance. In
both cases the sterility occurs in various degrees; in both, the
male element is the most liable to be affected; but sometimes the
female more than the male. In both, the tendency goes to a
certain extent with systematic affinity, for whole groups of animals
and plants are rendered impotent by the same unnatural condi-
tions ; and whole groups of species tend to produce sterile hybrids.
On the other hand, one species in a group will sometimes resist
great changes of conditions with unimpaired fertility; and certain
species in a group will produce unusually fertile hybrids. No
one can tell, till he tries, whether any particular animal will
breed under confinement, or any exotic plant seed freely under
culture; nor can he tell till he tries, whether any two species of
a genus will produce more or less sterile hybrids! Lastly, when
organic beings are placed during several generations under condi-
tions not natural to them, they are extremely liable to vary, which
seems to be partly due to their reproductive systems having been
specially affected, though in a lesser degree than when sterility
ensues. So it is with hybrids, for their offspring in successive
generations are eminently liable to vary, as every experimentalist
has observed.

Thus we see that when organic beings are placed under new

252 ORIGIN OF SPECIES

and unnatural conditions, and when hybrids are produced by the
unnatural crossing of two species, the reproductive system, inde-
pendently of the general state of health, is aliected in a very
similar manner. In the one case, the conditions of life have been
disturbed, though often in so slight a degree as to be inappre-
ciable by us; in the other case, or that of hybrids, the external
conditions have remained the same, but the organisation has
been disturbed by two distinct structures and constitutions, in-
cluding of course the reproductive systems, having been blended
into one. For it is scarcely possible that two organisations should
be compounded into one, without some disturbance occurring in the
development, or periodical action, or mutual relations of the
different parts and organs one to another or to the conditions
of life. When hybrids are able to breed inter se, they transmit
to their offspring from generation to generation the same com-
pounded organisation, and hence we need not be suri:)rised that
their sterility, though in some degree variable, does not diminish;
it is even apt to increase, this being generally the result, as before
explained, of too close interbreeding. The above view of the
sterility of hybrids being caused by two constitutions being
compounded into one has been strongly maintained by Max
Wichura.

It must, however, be owned that we cannot understand, on the
above or any other view, several facts with respect to the sterility
of hybrids; for instance, the unequal fertility of hybrids pro-
duced from reciprocal crosses; or the increased sterility in those
hybrids which occasionally and exceptionally resemble closely
either pure parent. Nor do I pretend that the foregoing remarks
go to the root of the matter; no explanation is offered why an
organism, when placed under unnatural conditions, is rendered
sterile. All that I have attempted to show is, that in two cases,
in some respects allied, sterility is the common result, — in the
one case from the conditions of life having been disturbed, in the
other case from the organisation having been disturbed by two
organisations being compounded into one.

A similar parallelism holds good with an allied yet very different
class of facts. It is an old and almost universal belief founded
on a considerable body of evidence, which I have elsewhere given,
that slight changes in the conditions of life are beneficial to all
living things. We see this acted on by farmers and gardeners
in their frequent exchanges of seed, tubers, &c., from one soil
or climate to another, and back again. During the convalescence
of animals, great benefit is derived from almost any change in
their habits of life. Again, both with plants and animals, there is

HYBRIDISM 253

the clearest evidence that a cross between individuals of the same
species, which differ to a certain extent, gives vigour and fer-
tility to the offspring; and that close interbreeding continued
during several generations between the nearest relations, if these
be kept under the same conditions of life, almost always leads
to decreased size, weakness, or sterility.

Hence it seems that, on the one hand, slight changes in the
conditions of life benefit all organic beings, and on the other
hand, that slight crosses, that is crosses between the males and
females of the same species, which have been subjected to slightly
different conditions, or which have slightly varied, give vigour and
fertility to the offspring. But, as we have seen, organic beings
long habituated to certain uniform conditions under a state of
nature, when subjected, as under confinement, to a considerable
change in their conditions, very frequently are rendered more
or less sterile; and we know that a cross between two forms,
that have become widely or specifically different, produces hybrids
which are almost always in some degree sterile. I am fully
persuaded that this double parallelism is by no means an accident
or an illusion. Pie who is able to explain why the elephant and
a multitude of other animals are incapable of breeding when
kept under only i)artial confinement in their native country, will
be able to explain the primary cause of hybrids being so generally
sterile. He wall at the same time be able to explain how it is
that the races of some of our domesticated animals, which have
often been subjected to new and not uniform conditions, are
quite fertile together, although they are descended from distinct
species, which would probably have been sterile if aboriginally
crossed. The above two parallel series of facts seem to be con-
nected together by some common but unknown bond, which is
essentially related to the principle of life; this principle, accord-
ing to Mr. Herbert Spencer, being that life depends on, or consists
in, the incessant action and reaction of various forces, which, as
throughout nature, are always tending towards an equilibrium;
and when this tendency is slightly disturbed by any change, the
vital forces gain in power.

Reciprocal Dimorphism and Trimorphism.

This subject may be here briefly discussed, and will be found
to throw some light on hybridism. Several plants belonging to
distinct orders present two forms, which exist in about equal
numbers and which differ in no respect except in their reproductive
organs; one form having a long pistil with short stamens, the

254 ORIGIN OP SPECIES

other a short pistil with long stamens; the two having differently
sized pollen-grains. With trimorphic plants there are three forms
likewise differing in the lengths of their pistils and stamens, in
the size and colour of the pollen-grains, and in some other respects ;
and as in each of the three forms there are two sets of stamens,
the three forms possess altogether six sets of stamens and three
kinds of pistils. These organs are so proportioned in length to
each other, that half the stamens in two of the forms stand on a
level with the stigma of the third form. Now I have shown,
and the result has been confirmed by other observers, that, in
order to obtain full fertility with these plants, it is necessary
that the stigma of the one form should be fertilised by pollen
taken from the stamens of corresponding height in another form.
So that with dimorphic species two unions, which may be called
legitimate, are fully fertile; and two, which may be called ille-
gitimate, are more or less infertile. With trimorphic Species six
unions are legitimate, or fully fertile, — and twelve are illegiti-
mate, or more or less infertile.

The infertility which may be observed in various dimorphic
and trimorphic plants, when they are illegitimately fertilised,
that is by pollen taken from stamens not corresponding in height
with the pistil, differs much in degree, up to absolute and utter
sterility; just in the same manner as occurs in crossing distinct
species. As the degree of sterility in the latter case depends in
an eminent degree on the conditions of life being more or less
favourable, so I have found it with illegitimate unions. It is well
known that if pollen of a distinct species be placed on the stigma
of a flower, and its own pollen be afterwards, even after a con-
siderable interval of time, placed on the same stigma, its action is
so strongly prepotent that it generally annihilates the effect of the
foreign pollen; so it is with the pollen of the several forms of the
same species, for legitimate pollen is strongly prepotent over ille-
gitimate pollen, when both are placed on the same stigma. I
ascertained this by fertilising several flowers, first illegitimately,
and twenty-four hours afterwards legitimately with the pollen
taken from a peculiarly coloured variety, and all the seedlings were
similarly coloured; this shows that the legitimate pollen, though
applied twenty-four hours subsequently, had wholly destroyed or
prevented the action of the previously applied illegitimate pollen.
Again, as in making reciprocal crosses between the same two spe-
cies, there is occasionally a great difference in the result, so the
same thing occurs with trimorphic plants; for instance, the mid-
styled form of Lythrum salicaria was illegitimately fertilised with
the greatest ease by pollen from the longer stamens of the short-

HYBRIDISM 255

styled form, and yielded many seeds; but the latter form did not
yield a single seed when fertilised by the longer stamens of the
mid-styled form.

In all these respects, and in others which might be added, the
forms of the same undoubted species when illegitimately united
behave in exactly the same manner as do two distinct species
when crossed. This led me carefully to observe during four years
many seedlings, raised from several illegitimate unions. The chief
result is that these illegitimate plants, as they may be called, are
not fully fertile. It is possible to raise from dimorphic species,
both long-styled and short-styled illegitimate plants, and from
trimorphic plants all three illegitimate forms. These can then be
properly united in a legitimate manner. When this is done, there
is no apparent reason why they should not yield as many seeds as
did their parents when legitimately fertilised. But such is not
the case. They are all infertile, in various degrees; some being
so utterly and incurably sterile that they did not yield during four
seasons a single seed or even seed-capsule. The sterility of these
illegitimate plants, when united with each other in a legitimate
manner, may be strictly compared with that of hybrids when
crossed i7iter se. If, on the other hand, a hybrid is crossed with
either pure parent-species, the sterility is usually much lessened:
and so it is when an illegitimate plant is fertilised by a legitimate
plant. In the same manner as the sterility of hybrids does not
always run parallel with the difficulty of making the first cross
between the two parent-species, so the sterility of certain illegitimate
plants was unusually great, whilst the sterility of the unjon from
which they were derived was by no means great. With hybrids
raised from the same seed-capsule the degree of sterility is in-
nately variable, so it is in a marked manner with illegitimate
plants. Lastly, many hybrids are profuse and persistent flower-
ers, whilst' other and more sterile hybrids produce few flowers, and
are weak, miserable dwarfs; exactly similar cases occur with the
illegitimate offspring of various dimorphic and trimorphic plants.

Altogether there is the closest identity in character and be-
haviour between illegitimate plants and hybrids. It is hardly an
exaggeration to maintain that illegitimate plants are hybrids, pro-
duced within the limits of the same species by the improper
union of certain forms, whilst ordinary hybrids are produced from
an improper union between so-called distinct species. We have
also already seen that there is the closest similarity in all respects
between first illegitimate unions and first crosses between distinct
species. This will perhaps be made more fully apparent by an
illustration; we may suppose that a botanist found two well-

256 ORIGIN OF SPECIES

marked varieties (and such occur) of the long-styled form of the
trimorphic Lythrum salicaria, and that he determined to try by
crossing whether they were specifically distinct. He would find
that they yielded only about one-fifth of the proper number of
seeds, and that they behaved in all the other above specified re-
spects as if they had been two distinct species. But to make the
case sure, he would raise plants from his supposed hybridised
seed, and he would find that the seedlings were miserably dwarfed
and utterly sterile, and that they behaved in all other respects like
ordinary hybrids. He might then maintain that he had actually
proved, in accordance with the common view, that his two varie-
ties were as good and as distinct species as any in the world; but
he would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are
important, because they show us, first, that the physiological test
of lessened fertility, both in first crosses and in hybrids, is no
safe criterion of specific distinction; secondly, because we may
conclude that there is some unknown bond which connects the in-
fertility of illegitimate unions with that of their illegitimate off-
spring, and we are led to extend the same view to first crosses and
hybrids ; thirdly, because we find, and this seems to me of especial
importance, that two or three forms of the same species may exist
and may differ in no respect whatever, either in structure or in
constitution, relatively to external conditions, and yet be sterile
when united in certain ways. For we must remember that it is
the union of the sexual elements of individuals of the same form,
for instance, of two long-styled forms, which results in sterility;
whilst it is the union of the sexual elements proper to two distinct
forms which is fertile. Hence the case appears at first sight ex-
actly the reverse of what occurs, in the ordinary unions of the
individuals of the same species and with crosses between distinct
species. It is, however, doubtful whether this is really so; but I
will not enlarge on this obscure subject.

We may, however, infer as probable from the consideration of
dimorphic and trimorphic plants, that the sterility of distinct spe-
cies when crossed and of their hybrid progeny, depends exclusively
on the nature of their sexual elements, and not on any difference
in their structure or general constitution. We are also led to this
same conclusion by considering reciprocal crosses, in which the
male of one species cannot be united, or can be united with great
difficulty, with the female of a second species, whilst the converse
cross can be effected with perfect facility. That excellent ob-
server, Gartner, likewise concluded that species when crossed are

HYBRIDISM 257

sterile owing to differences confined to their reproductive sys-
tems.

Fertility of Varieties when Crossed, and of their Mongrel Off-
spring, not universal.

It may be urged, as an overwhelming argument, that there must
be some essential distinction between species and varieties, inas-
much as the latter, however much they may differ from each
other in external appearance, cross with perfect facility, and
yield perfectly fertile offspring. With some exceptions, presently
to be given, I fully admit that this is the rule. But the subject is
surrounded by difficulties, for, looking to varieties produced under
nature, if two forms hitherto . reputed to be varieties be found in
any degree sterile together, they are at once ranked by most nat-
uralists as species. For instance, the blue and red pimpernel,
which are considered by most botanists as varieties, are said by
Gartner to be quite sterile when crossed, and he subsequently ranks
them as undoubted species. If we thus argue in a circle, the fer-
tility of all varieties produced under nature will assuredly have to
be granted.

If we turn to varieties, produced, or supposed to have been pro-
duced, under domestication, we are still involved in some doubt.
For when it is stated, for instance, that certain South American
indigenous domestic dogs do not readily unite with European dogs,
the explanation which will occur to every one, and probably the
true one, is that they are descended from aboriginally distinct
species. Nevertheless the perfect fertility of so many domestic
races, differing widely from each other in appearance, for instance
those of the pigeon, or of the cabbage, is a remarkable fact; more
especially when we reflect how many species there are, which,
though resembling each other most closely, are utterly sterile when
intercrossed. Several considerations, however, render the fertility
of domestic varieties less remarkable. In the first place, it may
be observed that the amount of external difference between two
species is no sure guide to their degree of mutual sterility, so that
similar differences in the case of varieties would be no sure guide.
It is certain that with species the cause lies exclusively in differ-
ences in their sexual constitution. Now the varying conditions
to which domesticated animals and cultivated plants have been
subjected, have had so little tendency towards modifying the re-
productive system in a manner leading to mutual sterility, that
we have good grounds for admitting the directly opposite doctrine
of Pallas, namely, that such conditions generally eliminate this

258 ORIGIN OF SPECIES

tendency; so that the domesticated descendants of species, which
in their natural state probably would have been in some degree
sterile when crossed, become perfectly fertile together. With
plants, so far is cultivation from giving a tendency towards
sterility between distinct species, that in several well-authenticated
cases already alluded to, certain plants have been affected in an
opposite manner, for they have become self-impotent whilst still
retaining the capacity of fertilising, and being fertilised by, other
species. If the Pallasian doctrine of the elimination of sterility
through long-continued domestication be admitted, and it can
hardly be rejected, it becomes in the highest degree improbable
that similar conditions long-continued should likewise induce this
tendency; though in certain cases, with species having a peculiar
constitution, sterility might occasionally be thus caused. Thus,
as I believe, we can understand why with domesticated animals
varieties have not been produced which are mutually sterile; and
why with plants only a few such cases, immediately to be given,
have been observed.

The real difficulty in our present subject is not, as it appears to
me, why domestic varieties have not become mutually infertile
when crossed, but why this has so generally occurred with nat-
ural varieties, as soon as they have been permanently modified in
a sufficient degree to take rank as species. We are far from pre-
cisely knowing the cause; nor is this surprising, seeing how pro-
foundly ignorant we are in regard to the normal and abnormal
action of the reproductive system. But we can see that species,
owing to their struggle for existence with numerous competitors,
will have been exposed during long periods of time to more uni-
form conditions, than have domestic varieties; and this may well
make a wide difference in the result. For we know how commonly
wild animals and plants, when taken from their natural conditions
and subjected to captivity, are rendered sterile; and the repro-
ductive functions of organic beings which have always lived under
natural conditions would probably in like manner be eminently
sensitive to the influence of an unnatural cross. Domesticated
productions, on the other hand, which, as shown by the mere fact
of their domestication, were not originally highly sensitive to
changes in their conditions of life, and which can now generally
resist with undiminished fertility repeated changes of conditions,
might be expected to produce varieties, which would be little
liable to have their reproductive powers injuriously affected by the
act of crossing with other varieties which had originated in a like
manner.

I have as yet spoken as if the varieties of the same species wer^

HYBRIDISM 259

invariably fertile when intercrossed. But it is impossible to re-
sist the evidence of the existence of a certain amount of sterility
in the few following cases, which I will briefly abstract. The evi-
dence is at least as good as that from which we believe in the
sterility of a multitude of species. The evidence is, also, derived
from hostile witnesses, who in all other cases consider fertility and
sterility as safe criterions of specific distinction. Gartner kept
during several years a dwarf kind of maize with yellow seeds, and
a tall variety with red seeds growing near each other in his garden ;
and although these plants have separated sexes, they never nat-
urally crossed. He then fertilised thirteen flowers of the one kind
with pollen of the other; but only a single head produced any
seed, and this one head produced only five grains. Manipulation
in this case could not have been injurious, as the plants have
separated sexes. No one, I believe, has suspected that these varie-
ties of maize are distinct species ; and it is important to notice that
the hybrid plants thus raised were themselves, perfectly fertile; so
that even Gartner did not venture to consider the two varieties as
specifically distinct.

Girou de Buzareingues crossed three varieties of gourd, which
like the maize has separated sexes, and he asserts that their mu-
tual fertilisation is by so much the less easy as their differences
are greater. How far these experiments may be trusted, I know
not; but the forms experimented on are ranked by Sageret, who
mainly founds his classification by the test of infertility, as varie-
ties, and Naudin has come to the same conclusion.

The following case is far more remarkable, and seems at first
incredible; but it is the result of an astonishing number of ex-
periments made during many years on nine species of Verbascum,
by so good an observer and so hostile a witness as Gartner : namely
that the yellow and white varieties when crossed produce less seed
than the similarly coloured varieties of the same species. More-
over, he asserts that, when yellow and white varieties of one species
are crossed with yellow and white varieties of a distinct species,
more seed is produced by the crosses between the similarly coloured
flowers, than between those which are differently coloured. Mr.
Scott also has experimented on the species and varieties of Ver-
bascum; and although unable to confirm Gartner's results on the
crossing of the distinct species, he finds that the dissimilarly col-
oured varieties of the same species yield fewer seeds, in the propor-
tion of 86 to 100, than the similarly coloured varieties. Yet these
varieties differ in no respect except in the colour of their flowers;
and one variety can sometimes be raised from the seed of an-
other.

260 ORIGIN OF SPECIES

Kolreuter, whose accuracy has been confirmed by every subse-
quent observer, has proved the remarkable fact, that one particular
variety of the common tobacco was more fertile than the other
varieties, when crossed with a widely distinct species. He experi-
mented on five forms which are commonly reputed to be varieties,
and which he tested by the severest trial, namely, by reciprocal
crosses, and he found their mongrel offspring perfectly fertile. But
one of these five varieties, when used either as the father or mother,
and crossed with the Nicotiana glutinosa, always yielded hybrids
not so sterile as those which were produced from the four other
varieties when crossed with N. glutinosa. Hence the reproductive
system of this one variety must have been in some manner and in
some degree modified.

From these facts it can no longer be maintained that varieties
when crossed are invariably quite fertile. From the great diffi-
culty of ascertaining the infertility of varieties in a state of
nature, for a supposed variety, if proved to be infertile in any
degree, would almost universally be ranked as a species ; — from
man attending only to external characters in his domestic varie-
ties, and from such varieties not having been exposed for -very
long periods to uniform conditions of life ; — from these several
considerations we may conclude that fertility does not constitute
a fundamental distinction between varieties and species when
crossed. The general sterility of crossed species may safely be
looked at, not as a special acquirement or endowment, but as
incidental on changes of an unknown nature in their sexual ele-
ments.

Hyhrids and Mongrels compared^ independently of their fertility.

Independently of the question of fertility, the offspring of spe-
cies and of varieties when crossed may be compared in several
other respects. Gartner, whose strong wish it was to draw a dis-
tinct line between species and varieties, could find very few, and,
as it seems to me, quite unimportant differences between the so-
called hybrid offspring of species, and the so-called mongrel off-
spring of varieties. And, on the other hand, they agree most
closely in many important respects.

I shall here discuss this subject with extreme brevity. The most
important distinction is, that in the first generation mongrels are
more variable than hybrids; but Gartner admits that hybrids from
species which have long been cultivated are often variable in the
first generation; and I have myself seen striking instances of this
fact. Gartner further admits that hybrids between very closely

HYBRIDISM 2G1

allied species are more variable than those from very distinct spe-
cies; and this shows that the difference in the degree of variability
graduates away. When mongrels and the more fertile hybrids are
propagated for several generations, an extreme amount of varia-
bility in the offspring in both cases is notorious; but some few
instances of both hybrids and mongrels long retaining a uni-
form character could be given. The variability, however, in the
successive generations of mongrels is, perhaps, greater than in
hybrids.

This greater variability in mongrels than in hybrids does not
seem at all surprising. For the parents of mongrels are varieties,
and mostly domestic varieties (very few experiments having been
tried on natural varieties), and this implies that there has been
recent variability, which would often continue and would augment
that arising from the act of crossing. The slight variability of
hybrids in the first generation, in contrast with that in the suc-
ceeding generations, is a curious fact and deserves attention. For
it bears on the view which I have taken of one of the causes of
ordinary variability; namely, that the reproductive system from
being eminently sensitive to changed conditions of life, fails under
these circumstances to perform is proper function of producing off-
spring closely similar in all respects to the parent-form. Now
hybrids in the first generation are descended from species (exclud-
ing those long-cultivated) which have not had their reproductive
systems in any way affected, and they are not variable ; but hybrids
themselves have their reproductive systems seriously affected, and
their descendants are highly variable.

But to return to our comparison of mongrels and hybrids: Gart-
ner states that mongrels are more liable than hybrids to revert to
either parent-form; but this, if it be true, is certainly only a dif-
ference in degree. Moreover, Gartner expressly states that hybrids
from long cultivated plants are more subject to reversion than
hybrids from species in their natural state; and this probably
explains the singular difference in the results arrived at by differ-
ent observers: thus Max Wichura doubts whether hybrids ever
revert to their parent-forms, and he experimented on uncultivated
species of willows ; whilst Naudin, on the other hand, insists in the
strongest terms on the almost universal tendency to reversion in
hybrids, and he experimented chiefly on cultivated plants. Gart-
ner further states that when any two species, although most closely
allied to each other, are crossed with a third species, the hybrids
are widely different from each other; whereas if two very distinct
varieties of one species are crossed with another species, the hybrids
do not differ much. But this conclusion, as far as I can make out.

2G2 ORIGIN OF SPECIES

is founded on a single experiment; and seems directly opposed to
the results of several experiments made by Kolreuter.

Such alone are the unimportant differences which Gartner is
able to point out between hybrid and mongrel plants. On the
other hand, the degrees and kinds of resemblance in mongrels and
in hybrids to their respective parents, more especially in hybrids
produced from nearly related species, follow according to Gartner
the same laws. When two species are crossed, one has sometimes
a prepotent power of impressing its likeness on the hybrid. So I
believe it to be with varieties of plants; and with animals one
variety certainly often has this prepotent power over another var-
iety. Hybrid plants produced from a reciprocal cross, generally
resemble each other closely; and so it is with mongrel plants from
a reciprocal cross. Both hybrids and mongrels can be reduced to
either pure parent-form, by repeated crosses in successive genera-
tions with either parent.

These several remarks are apparently applicable to animals; but
the subject is here much complicated, partly owing to the existence
of secondary sexual characters; but more especially owing to pre-
potency in transmitting likeness running more strongly in one sex
than in the other, both when one species is crossed with another,
and when one variety is crossed with another variety. For in-
stance, I think those authors are right who maintain that the ass
has a prepotent power over the horse, so that both the mule and
the hinny resemble more closely the ass than the horse; but that
the prepotency runs more strongly in the male than in the female
ass, so that the mule, which is the offspring of the male ass and
mare, is more like an ass, than is the hinny, which is the offspring
of the female ass and stallion.

Much stress has been laid by some authors on the supposed fact,
that it is only with mongrels that the offspring are not inter-
mediate in character, but closely resemble one of their parents ; but
this does sometimes occur with hybrids, yet I grant much less fre-
quently than with mongrels. Looking to the cases which I have
collected of cross-bred animals closely resembling one parent, the
resemblances seem chiefly confined to characters almost monstrous
in their nature, and which have suddenly appeared — such as al-
binism, melanism, deficiency of tail or horns, or additional fingers
and toes; and do not relate to characters which have been slowly
acquired through selection. A tendency to sudden reversions to
the perfect character of either parent would, also, be much more
likely to occur with mongrels, which are descended from varieties
often suddenly produced and semi-monstrous in character, than
with hybrids, which are descended from species slowly and nat-

HYBRIDISM 263

urally produced. On the whole, I entirely agree with Dr. Prosper
Lucas, who, after arranging an enormous body of facts with re-
spect to animals, comes to the conclusion that the laws of resem-
blance of the child to its parents are the same, whether the two
parents differ little or much from each other, namely, in the union
of individuals of the same variety, or of different varieties, or of
distinct species.

Independently of the question of fertility and sterility, in all
other respects there seems to be a general and close similarity in
the offspring of crossed species, and of crossed varieties. If we
look at species as having been specially created, and at varieties
as having been produced by secondary laws, this similarity would
be an astonishing fact. But it harmonises perfectly with the
view that there is no essential distinction between species and
varieties.

Summary of Chapter.

First crosses between forms, sufficiently distinct to be ranked as
species, and their hybrids, are very generally, but not universally,
sterile. The sterility is cf all degrees, and is often so slight that
the most careful experimentalists have arrived at diametrically op-
posite conclusions in ranking forms by this test. The sterility is
innately variable in individuals of the same species, and is emi-
nently susceptible to the action of favourable and unfavourable
conditions. The degree of sterility does not strictly follow sys-
tematic affinity, but is governed by several curious and complex
laws. It is generally different, and sometimes widely different in
reciprocal crosses between the same two species. It is not always
equal in degree in a first cross and in the hybrids produced from
this cross.

In the same manner as in grafting trees, the capacity in one
species or variety to take on another, is incidental on differences,
generally of an unknown nature, in their vegetative systems, so in
crossing, the greater or less facility of one species to unite with an-
other is incidental on unknown differences in their reproductive
systems. There is no more reason to think that species have been
specially endowed with various degrees of sterility to prevent their
crossing and blending in nature, than to think that trees have been
specially endowed with various and somewhat analogous degrees of
difficulty in being grafted together in order to prevent their inarch-
ing in our forests.

The sterility of first crosses and of their hybrid progeny has not
been acquired through natural selection. In the case of first

264 ORIGIN OP SPECIES

crosses it seems to depend on several circumstances; in some in-
stances in chief part on the early death of the embryo. In the
case of hybrids, it apparently depends on their whole organisation
having been disturbed by being compounded from two distinct
forms; the sterility being closely allied to that which so frequently
affects pure species, when exposed to new and unnatural condi-
tions of life. He who will explain these latter cases will be able to
explain the sterility of hybrids. This view is strongly supported
by a parallelism of another kind: namely, that, firstly, slight
changes in the conditions of life add to the vigour and fertility of
all organic beings; and secondly, that the crossing of forms, which
have been exposed to slightly different conditions of life or which
have varied, favours the size, vigour, and fertility of their off-
spring. The facts given on the sterility of the illegitimate unions
of dimorphic and trimorphic plants and of their illegitimate pro-
geny, perhaps render it probable that some unknown bond in all
eases connects the degree of fertility of first unions with that of
their offspring. The consideration of these facts on dimorphism,
as well as of the results of reciprocal crosses, clearly leads to the
conclusion that the primary cause of the sterility of crossed spe-
cies is confined to differences in their sexual elements. But why,
in the case of distinct species, the sexual elements should so gen-
erally have become more or less modified, leading to their mutual
infertility, we do not know; but it seems to stand in some close re-
lation to species having been exposed for long periods of time to
nearly uniform conditions of life.

It is not surprising that the difficulty in crossing any two species,
and the sterility of their hybrid offspring, should in most cases
correspond, even if due to distinct causes: for both depend on the
amount of difference between the species which are crossed. Nor
is it surprising that the facility of effecting a first cross, and the
fertility of the hybrids thus produced, and the capacity of being
grafted together — though this latter capacity evidently depends on
widely different circumstances — should all run, to a certain ex-
tent, parallel with the systematic affinity of the forms subjected
to experiment; for systematic affinity includes resemblances of all
kinds.

First crosses between forms known to be varieties, or sufficiently
alike to be considered as varieties, and their mongrel offspring, are
very generally, but not, as is so often stated, invariably fertile.
Nor is this almost universal and perfect fertility surprising, when
it is remembered how liable we are to argue in a circle with re-
spect to varieties in a state of nature ; and when we remember that
the greater number of varieties have been produced under domesti-

HYBRIDISM 2G5

cation by the selection of mere external differences, and tliat they
have not been long exposed to uniform conditions of life. It
should also be especially kept in mind, that long-continued domes-
tication tends to eliminate sterility, and is therefore little likely
to induce this same quality. Independently of the question of
fertility, in all other respects there is the closest general resem-
blance between hybrids and mongrels, — in their variability, in
their power of absorbing each other by repeated crosses, and in
their inheritance of characters from both parent-forms. Finally,
then, although we are as ignorant of the precise cause of the
sterility of first crosses and of hybrids as we are why animals and
plants removed from their natural conditions become sterile, yet
the facts given in this chapter do not seem to me opposed to the
belief that species aboriginally existed as varieties.

206 ORIGIN OF SPECIES

CHAPTEK X.

ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.

On the abse-uce of intermediate varieties at the present day — On the
nature of extinct intermediate varieties ; " on their number — On the
lapse of time, as inferred from the rate of denudation and of depo-
sition — On the lapse of time as estimated by years — On the poorness
of our palaeontological collections — On the intermittence of geological
formations — On the denudation of granitic areas — On the absence
of intemiediate varieties in any one formation — On the sudden appear-
ance of groups of species — On their sudden appearance in the lowest
known fossiliferous strata — Antiquity of the habitable earth.

IN the sixth chapter I enumerated the chief objections which
might be justly urged against the views maintained in this
volume. Most of them have now been discussed. One, name-
ly the distinctness of specific forms, and their not being blended
together by innumerable transitional links, is a very obvious diffi-
culty. I assigned reasons why such links do not commonly occur
at the present day under the circumstances apparently most favour-
able for their presence, namely, on an extensive and continuous
area with graduated physical conditions. I endeavoured to show,
that the life of each species depends in a more important manner
on the presence of other already defined organic forms, than on
climate, and, therefore, that the really governing conditions of life
do not graduate away quite insensibly like heat or moisture. I
endeavoured, also, to show that intermediate varieties, from ex-
isting in lesser numbers than the forms which they connect, will
generally be beaten out and exterminated during the course of
further modification and improvement. The main cause, how-
ever, of innumerable intermediate links not now occurring every-
where throughout nature, depends on the very process of natural
selection, through which new varieties continually take the places
of and supplant their parent-forms. But just in proportion as this
process of extermination has acted on an enormous scale, so must
the number of intermediate varieties, which have formerly ex-
isted, be truly enormous. Why then is not every geological forma-
tion and every stratum full of such intermediate links? Geology
assuredly does not reveal any such finely-graduated organic chain ;

IMPERFECTION OF THE GEOLOGICAL RECORD 2G7

and this, perhaps, is the most obvious and serious objection which
can be urged against the theory. The explanation lies, as I be-
lieve, in the extreme imperfection of the geological record.

In the first place, it should always be borne in mind what sort of
intermediate forms must, on the theory, have formerly existed. I
have found it difficult, when looking at any two species, to avoid
picturing to myself forms directly intermediate between them.
But this is a wholly false view; we should always look for forms
intermediate between each species and a common but unknown
progenitor; and the progenitor will generally have differed in some
respects from all its modified descendants. To give a simple illus-
tration : the fantail and pouter pigeons are both descended from
the rock-pigeon; if we possessed all the intermediate varieties
which have ever existed, we should have an extremely close series
between both and the rock-pigeon ; but we should have no varieties
directly intermediate between the fantail and pouter; none, for
instance, combining a tail somewhat expanded with a crop some-
what enlarged, the characteristic features of these two breeds.
These two breeds, moreover, have become so much modified, that,
if we had no historical or indirect evidence regarding their origin,
it would not have been possible to have determined, from a mere
comparison of their structure with that of the rock-pigeon, C.
livia, whether they had descended from this species or from some
other allied form, such as C. oenas.

So, with natural species, if we look to forms very distinct, for
instance to the horse and tapir, we have no reason to suppose that
links directly intermediate between them ever existed, but between
each and an unknown common parent. The common parent will
have had in its whole organisation much general resemblance to
the tapir and to the horse; but in some points of structure may
have differed considerably from both, even perhaps more than they
differ from each other. Hence, in all such cases, we should be
unable to recognise the parent-form of any two or more species,
even if we closely compared the structure of the parent with that
of its modified descendants, unless at the same time we had a
nearly perfect chain of the intermediate links.

It is just possible by the theory, that one of two living forms
might have descended from the other; for instance, a horse from
a tapir ; and in this case direct intermediate links will have existed
between them. But such a case would imply that one form had
remained for a very long period unaltered, whilst its descendants
had undergone a vast amount of change; and the principle of
competition between organism and organism, between child and
parent, will render this a very rare event ; for in all cases the new

2G8 ORIGIN OF SPECIES

and improved forms of life tend to supplant the old and unim-
proved forms.

By the theory of natural selection all living species have been
connected with the parent-species of each genus, by differences not
greater than we see between the natural and domestic varieties of
the same species at the present day; and these parent-species, now
generally extinct, have in their turn been similarly connected with
more ancient forms; and so on backwards, always converging
to the common ancestor of each great class. So that the number
of intermediate and transitional links, between all living and ex-
tinct species, must have been inconceivably great. But assuredly,
if this theory be true, such have lived upon the earth.

On the Lapse of Time, as inferred from the rate of Deposition
and extent of Denudation,

Independently of our not finding fossil remains of such infinitely
numerous connecting links, it may be objected that time cannot
have sufficed for so great an amount of organic change, all changes
having been effected slowly. It is hardly possible for me to recall
to the reader who is not a practical geologist, the facts leading the
mind feebly to comprehend the lapse of time. He who can read
Sir Charles Lyell's grand work on the Principles of Geology, which
the future historian will recognise as having produced a revolu-
tion in natural science, and yet does not admit how vast have been
the past periods of time, luay at once close this volume. Not that
it suffices to study the Principles of Geology, or to read special
treatises by different observers on separate formations, and to mark
how each author attempts to give an inadequate idea of the dura-
tion of each formation, or even of each stratum. We can best
gain some idea of past time by knowing the agencies at work, and
learning how deeply the surface of the land has been denuded, and
how much sediment has been deposited. As Lyell has well re-
marked, the extent and thickness of our sedimentary formations
are the result and the measure of the denudation which the earth's
crust has elsewhere undergone. Therefore a man should examine
for himself the great piles of super-imposed strata, and watch
the rivulets bringing down mud, and the waves wearing away
the sea-cliffs, in order to comprehend something about the dura-
tion of past time, the monuments of which we see all around us.

It is good to wander along the coast, when formed of moderately
hard rocks, and mark the process of degradation. The tides in
most cases reach the cliffs only for a short time twice a day, and
the waves eat into them only when they are charged with sand

IMPERFECTION OP THE GEOLOGICAL RECORD 269

or pebbles ; for there is good evidence that pure water effects noth-
ing in wearing away rock. At last the base of the cliff is under-
mined, huge fragments fall down, and these, remaining fixed, have
to be worn away atom by atom, until after being reduced in size
they can be rolled about by the waves, and then they are more
quickly ground into pebbles, sand, or mud. But how often do we
see along the bases of retreating cliffs rounded boulders, all thickly
clothed by marine productions, showing how little they are abraded
and how seldom they are rolled about! Moreover, if we follow
for a few miles any line of rocky cliff, which is undergoing degra-
dation, we find that it is only here and there, along a short length
or round a promontory, that the cliffs are at the present time
suffering. The appearance of the surface and the vegetation
show that elsewhere years have elapsed since the waters washed
their base.

We have, however, recently learnt from the observations of Ram-
say, in the van of many excellent observers — of Jukes, Geikie,
Croll, and others, that subaerial degradation is a much more im-
portant agency than coast-action, or the power of the waves. The
whole surface of the land is exposed to the chemical action of the
air and of the rain-water with its dissolved carbonic acid, and in
colder countries to frost; the disintegrated matter is carried down
even gentle slopes during heavy rain, and to a greater extent than
might be supposed, especially in arid districts, by the wind; it
is then transported by the streams and rivers, which when rapid
deepen their channels, and triturate the fragments. On a rainy
day, even in a gently undulating country, we see the effects of
subaerial degradation in the muddy rills which flow down every
slope. Messrs. Kamsay and Whitaker have shown, and the ob-
servation is a most striking one, that the great lines of escarpment
in the Wealden district and those ranging across England, which
formerly were looked at as ancient sea-coasts, cannot have been
thus formed, for each line is composed of one and the same forma-
tion, whilst our sea-cliffs are everywhere formed by the intersec-
tion of various formations. This being the case, we are compelled
to admit that the escarpments owe their origin in chief part to the
rocks of which they are composed having resisted subaerial denuda-
tion better than the surrounding surface ; this surface consequently
has been gradually lowered, with the lines of harder rock left
projecting. ISTothing impresses the mind with the vast duration
of time, according to our ideas of time, more forcibly than the
conviction thus gained that subaerial agencies which apparently
have so little power, and which seem to work so slowly, have pro-
duced great results.

270 ORIGIN OF SPECIES

When thus impressed with the slow rate at which the land is
worn away through subaerial and littoral action, it is good, in
order to appreciate the past duration of time, to consider, on the
one hand, the masses of rock which have been removed over many
extensive areas, and on the other hand the thickness of our sedi-
mentary formations. I remember having been much struck when
viewing volcanic islands, which have been worn by the waves and
pared all round into perpendicular cliffs of one or two thousand
feet in height; for the gentle slope of the lava-streams, due to
their formerly liquid state, showed at a glance how far the hard,
rocky beds had once extended into the open ocean. The same
story is told still more plainly by faults, — those great cracks along
which the strata have been upheaved on one side, or thrown down
on the other, to the height or depth of thousands of feet; for since
the crust cracked, and it makes no great difference whether the
upheaval was sudden, or, as most geologists now believe, was slow
and effected by many starts, the surface of the land has been so
completely planed down that no trace of these vast dislocations is
externally visible. The Craven fault, for instance, extends for
upwards of 30 miles, and along this line the vertical displacement
of the strata varies from 600 to 3000 feet. Professor Ramsay has
published an account of a downthrow in Anglesea of 2300 feet;
and he informs me that he fully believes that there is one in
Merionethshire of 12,000 feet; yet in these cases there is nothing
on the surface of the land to show such prodigious movements;
the pile of rocks on either side of the crack having been smoothly
swept away.

On the other hand, in all parts of the world the piles of sedi-
mentary strata are of wonderful thickness. In the Cordillera I
estimated one mass of conglomerate at ten thousand feet; and al-
though conglomerates have probably been accumulated at a quicker
rate than finer sediments, yet from being formed of worn and
rounded pebbles, each of which bears the stamp of time, they are
good to show how slowly the mass must have been heaped to-
gether. Professor Ramsay has given me the maximum thick-
ness, from actual measurement in most cases, of the successive
formations in different parts of Great Britain; and this is the re-
sult : — T^ .

Feet.

Palaeozoic strata (not including igneous beds) 57,154

Secondary strata 13,100

Tertiary strata 2,240

— making altogether 72,584 feet ; that is, very nearly thirteen and
three-quarters British miles. Some of the formations, which are

IMPERFECTION OF THE GEOLOGICAL RECORD 271

represented in England by tliin beds, are thousands of feet in
thickness on the Continent. Moreover, between each successive
formation, we have, in the opinion of most geologists, blank periods
of enormous length. So that the lofty pile of sedimentary rocks
in Britain gives but an inadequate idea of the time which has
elapsed during their accumulation. The consideration of these
various facts impresses the mind almost in the same manner as
does the vain endeavour to grapple with the idea of eternity.

Nevertheless this impression is partly false. Mr. Croll, in an
interesting paper, remarks that we do not err " in forming too
great a conception of the length of geological periods," but in esti-
mating them by years. When geologists look at large and com-
plicated phenomena, and then at the figures representing several
million years, the two produce a totally different effect on the
mind, and the figures are at once pronounced too small. In regard
to subaerial denudation, Mr. Croll shows, by calculating the known
amount of sediment annually brought down by certain rivers,
relatively to their areas of drainage, that 1000 feet of solid rock,
as it became gradually disintegrated, would thus be removed from
the mean level of the whole area in the course of six million years.
This seems an astonishing result, and some considerations lead
to the suspicion that it may be too large, but even if halved or
quartered it is still very surprising. Few of us, however, know
what a million really means : Mr. Croll gives the following illus-
tration : take a narrow strip of paper, 83 feet 4 inches in length,
and stretch it along the wall of a large hall; then mark off at one
end the tenth of an inch. This tenth of an inch will represent
one hundred years, and the entire strip a million years. But let it
be borne in mind, in relation to the subject of this work, what a
hundred years implies, represented as it is by a measure utterly
insignificant in a hall of the above dimensions. Several eminent
breeders, during a single lifetime, have so largely modified some
of the higher animals which propagate their kind much more
slowly than most of the lower animals, that they have formed what
well deserves to be called a new sub-breed. Few men have at-
tended with due care to any one strain for more than half a
century, so that a hundred years represents the work of two breed-
ers in succession. It is not to be supposed that species in a state of
nature ever change so quickly as domestic animals under the
guidance of methodical selection. The comparison would be in
every way fairer with the effects which follow from unconscious
selection, that is the preservation of the most useful or beautiful
animals, with no intention of modifying the breed ; but by this

272 ORIGIN OP SPECIES

process of unconscious selection, various breeds have been sensibly
changed in the course of two or three centuries.

Species, however, probably change much more slowly, and within
the same country only a few change at the same time. This slow-
ness follows from all the inhabitants of the same country being
already so well adapted to each other, that new places in the
polity of nature do not occur until after long intervals, due to the
occurrence of physical changes of some kind, or through the im-
migration of new forms. Moreover variations or individual dif-
ferences of the right nature, by which some of the inhabitants
might be better fitted to their new places under the altered circum-
stances, would not always occur at once. Unfortunately we have
no means of determining, according to the standard of years, how
long a period it takes to modify a snecies; but to the subject of
time we must return.

On the Poorness of Palceontological Collections.

Now let us turn to our richest geological museums, and what a
paltry display we behold! That our collections are imperfect is
admitted by every one. The remark of that admirable palaeon-
tologist, Edward Forbes, should never be forgotten, namely, that
very many fossil species are known and named from single and
often broken specimens, or from a few specimens collected on
some one spot. Only a small portion of the surface of the earth
has been geologically explored, and no part with sufficient care,
as the important discoveries made every year in Europe prove.
No organism wholly soft can be preserved. Shells and bones decay
and disappear when left on the bottom of the sea, where sediment
is not accumulating. We probably take a quite erroneous view,
when we assume that sediment is being deposited over nearly the
whole bed of the sea, at a rate sufficiently quick to embed and
preserve fossil remains. Throughout an enormously large pro-
portion of the ocean, the bright blue tint of the water bespeaks its
purity. The many cases on record of a formation conformably
covered, after an immense interval of time, by another and later
formation, without the underlying bed having suffered in the in-
terval any wear and tear, seem explicable only on the view of the
bottom of the sea not rarely lying for ages in an unaltered con-
dition. The remains which do become embedded, if in sand or
gravel, will, when the beds are upraised, generally be dissolved by
the percolation of rain-water charged with carbonic acid. Some
of the many kinds of animals which live on the beach between
high and low water mark seem to be rarely preserved. Eor in-

IMPERFECTION OP THE GEOLOGICAL RECORD 273

stance, the several species of the Chthamalinae (a sub-family of
sessile cirripedes) coat the rocks all over the world in infinite
numbers: they are all strictly littoral, with the exception of a sin-
gle Mediterranean species, which inhabits deep water, and this has
been found fossil in Sicily, whereas not one other species has
hitherto been found in any tertiary formation : yet it is known that
the genus Chthamalus existed during the Chalk period. Lastly,
many great deposits requiring a vast length of time for their ac-
cumulation, are entirely destitute of organic remains, without
our being able to assign any reason : one of the most striking in-
stances is that of the Flysch formation, which consists of shale and
sandstone, several thousand, occasionally even six thousand feet in
thickness, and extending for at least 3000 miles from Vienna to
Switzerland; and although this great mass has been most care-
fully searched, no fossils, except a few vegetable remains, have
been found.

With respect to the terrestrial productions which lived during
the Secondary and Palaeozoic periods, it is superfluous to state that
our evidence is fragmentary in an extreme degree. For instance,
until recently not a land-shell was known belonging to either of
these vast periods, with the exception of one species discovered by
Sir C. Lyell and Dr. Dawson in the carboniferous strata of North
America ; but now land-shells have been found in the lias. In re-
gard to mammiferous remains, a glance at the historical table
published in Lyell's Manual will bring home the truth, how acci-
dental and rare is their preservation, far better than pages of
detail. Nor is their rarity surprising, when we remember how
large a proportion of the bones of tertiary mammals have been
discovered either in caves or in lacustrine deposits; and that not a
cave or true lacustrine bed is known belonging to the age of our
secondary or palaeozoic formations.

But the imperfection in the geological record largely results
from another and more important cause than any of the fore-
going; namely, from the several formations being separated from
each other by wide intervals of time. This doctrine has been em-
phatically admitted by many geologists and palseontologists, who,
like E. Forbes, entirely disbelieve in the change of species. When
we see the formations tabulated in written works, or when we fol-
low them in nature, it is difficult to avoid believing that they are
closely consecutive. But we know, for instance, from Sir R.
Murchison's great work on Russia, what wide gaps there are in that
country between the superimposed formations; so it is in North
America, and in many other parts of the world. The most skilful
geologist, if his attention had been confined exclusively to these

274 ORIGIN OF SPECIES

large territories, would never have suspected that, during the
periods which were blank and barren in his own country, great
piles of sediment, charged with new and peculiar forms of life,
had elsewhere been accumulated. And if, in each separate terri-
tory, hardly any idea can be formed of the length of time which
has elapsed between the consecutive formations, we may infer that
this could nowhere be ascertained. The frequent and great
changes in the mineralogical composition of consecutive forma-
tions, generally implying great changes in the geography of the
surrounding lands, whence the sediment was derived, accord with
the belief of vast intervals of time having elapsed between each
formation.

We can, I think, see why the geological formations of each
region are almost invariably intermittent; that is, have not fol-
lowed each other in close sequence. Scarcely any fact struck me
more when examining many hundred miles of the South Ameri-
can coasts, which have been upraised several hundred feet within
the recent period, than the absence of any recent deposits suffi-
ciently extensive to last for even a short geological period. Along
the whole west coast, which is inhabited by a peculiar marine
fauna, tertiary beds are so poorly developed, that no record of sev-
eral successive and peculiar marine faunas will probably be pre-
served to a distant age. A little reflection will explain why, along
the rising coast of the western side of South America, no exten-
sive formations with recent or tertiary remains can anywhere be
found, though the supply of sediment must for ages have been
great, from the enormous degradation of the coast-rocks and from
muddy streams entering the sea. The explanation, no doubt, is,
that the littoral and sub-littoral deposits are continually worn
away, as soon as they are brought up by the slow and gradual
rising of the land within the grinding action of the coast-waves.

We may, I think, conclude that sediment must be accumulated in
extremely thick, solid, or extensive masses, in order to withstand
the incessant action of the waves, when first upraised and during
successive oscillations of level as well as the subsequent subaerial
degradation. Such thick and extensive accumulations of sediment
may be formed in two ways; either in profound depths of the sea,
in which case the bottom will not be inhabited by so many and
such varied forms of life, as the more shallow seas; and the mass
when upraised will give an imperfect record of the organisms
which existed in the neighbourhood during the period of its ac-
cumulation. Or, sediment may be deposited to any thickness and
extent over a shallow bottom, if it continue slowly to subside. In
this latter case, as long as the rate of subsidence and the supply of

IMPERFECTION OF THE GEOLOGICAL RECORD 275

sediment nearly balance each other, the sea will remain shallow
and favourable for many and varied forms, and thus a rich fos-
siliferous formation, thick enough, when upraised, to resist a large
amount of denudation, may be formed.

I am convinced that nearly all our ancient formations, which
are throughout the greater part of their thickness Hc/i in fossils,
have thus been formed during subsidence. Since publishing my
views on this subject in 1845, I have watched the progress of
Geology, and have been surprised to note how author after author,
in treating of this or that great formation, has come to the con-
clusion that it was accumulated during subsidence. I may add,
that the only ancient tertiary formation on the west coast of South
America, which has been bulky enough to resist such degradation
as it has as yet suffered, but which will hardly last to a distant
geological age, was deposited during a downward oscillation of
level, and thus gained considerable thickness.

All geological facts tell us plainly that each area has undergone
numerous slow oscillations of level, and apparently these oscilla-
tions have affected wide spaces. Consequently, formations rich in
fossils and sufficiently thick and extensive to resist subsequent
degradation, will have been formed over wide spaces during pe-
riods of subsidence, but only where the supply of sediment was
sufficient to keep the sea shallow and to embed and preserve the
remains before they had time to decay. On the other hand, as
long as the bed of the sea remains stationary, thich deposits can-
not have been accumulated in the shallow parts, which are the
most favourable to life. Still less can this have happened during
the alternate periods of elevation; or, to speak more accurately,
the beds which were then accumulated will generally have been de-
stroyed by being upraised and brought within the limits of the
coast-action.

These remarks apply chiefly to littoral and sub-littoral deposits.
In the case of an extensive and shallow sea, such as that within
a large part of the Malay Archipelago, where the depth varies from
30 or 40 to 60 fathoms, a widely extended formation might be
formed during a period of elevation, and yet not suffer excessively
from denudation during its slow upheaval; but the thickness of
the formation could not be great, for owing to the elevatory move-
ment it would be less than the depth in which it was formed; nor
would the deposit be much consolidated, nor be capped by over-
lying formations, so that it would run a good chance of being worn
away by atmospheric degradation and by the action of the sea dur-
ing subsequent oscillations of level. It has, however, been sug-
gested by Mr. Hopkins, that if one part of the area, after rising

276 ORIGIN OF SPECIES

and before being denuded, subsided, the deposit formed during
the rising movement, though not thick, might afterwards become
protected by fresh accumulations, and thus be preserved for a long
period.

Mr. Hopkins also expresses his belief that sedimentary beds of
considerable horizontal extent have rarely been completely de-
stroyed. But all geologists, excepting the few who believe that
our present metamorphic schists and plutonic rocks once formed
the primordial nucleus of the globe, will admit that these latter
rocks have been stript of their covering to an enormous extent.
For it is scarcely possible that such rocks could have been solidified
and crystallized whilst uncovered; but if thfe metamorphic action
occurred at profound depths of the ocean, the former protecting
mantle of rock may not have been very thick. Admitting then
that gneiss, mica-schist, granite, diorite, &c., were once necessarily
covered up, how can we account for the naked and extensive areas
of such rocks in many parts of the world, except on the belief that
they have subsequently been completely denuded of all overlying
strata ? That such extensive areas do exist cannot be doubted : the
granite region of Parime is described by Humboldt as being at
least nineteen times as large as Switzerland. South of the Ama-
zon, Boue colours an area composed of rocks of this nature as
equal to that of Spain, Erance, Italy, part of Germany, and the
British Islands, all conjoined. This region has not been care-
fully explored, but from the concurrent testimony of travellers, the
granitic area is very large : thus, Von Eschwege gives a detailed
section of these rocks, stretching from Rio de Janeiro for 260
geographical miles inland in a straight line; and I travelled for
150 miles in another direction, and saw nothing but granitic
rocks. Numerous specimens, collected along the whole coast from
near Rio Janeiro to the mouth of the Plata, a distance of 1100
geographical miles, were examined by me, and they all belonged
to this class. Inland, along the whole northern bank of the Plata
I saw, besides modern tertiary beds, only one small patch of slightly
metamorphosed rock, which alone could have formed a part of the
original capping of the granitic series. Turning to a well-
known region, namely, to the United States and Canada, as shown
in Professor H. D. Rogers's beautiful map, I have estimated the
areas by cutting out and weighing the paper, and I find that the
metamorphic (excluding '' the semi-metamorphic ") and granitic
rocks exceed, in the proportion of 19 to 12.5, the whole of the newer
Palaeozoic formations. In many regions the metamorphic and
granitic rocks would be found much more widely extended than
they appear to be, if all the sedimentary beds were removed which

IMPERFECTION OF THE GEOLOGICAL RECOtlD 277

rest unconformably on them, and which could not have formed
part of the original mantle under which they were crystallized.
Hence it is probable that in some parts of the world whole forma-
tions have been completely denuded, with not a wreck left be-
hind.

One remark is here worth a passing notice. During periods of
elevation the area of the land and of the adjoining shoal parts of
the sea will be increased, and new stations will often be formed:
— all circumstances favourable, as previously explained, for the
formation of new varieties and species; but during such periods
there will generally be a blank in the geological record. On the
other hand, during subsidence, the inhabited area and number of
inhabitants will decrease (excepting on the shores of a continent
when first broken up into an archipelago), and consequently dur-
ing subsidence, though there will be much extinction, few new
varieties or species will be formed; and it is during these very
periods of subsidence, that the deposits which are richest in fos-
sils have been accumulated.

On the Absence of Numerous Intermediate Varieties in any Sin-
gle Formation.

From these several considerations, it cannot be doubted that the
geological record, viewed as a whole, is extremely imperfect ; but if
we confine our attention to any one formation, it becomes much
more difficult to understand why we do not therein find closely
graduated varieties between the allied species which lived at its
commencement and at its close. Several cases are on record of
the same species presenting varieties in the upper and lower parts
of the same formation; thus, Trautschold gives a number of in-
stances with Ammonites ; and Hilgendorf has described a most curi-
ous case of ten graduated forms of Planorbis multiformis in the
successive beds of a fresh-water formation in Switzerland. Al-
though each formation has indisputably required a vast number
of years for its deposition, several reasons can be given why each
should not commonly include a graduated series of links be-
tween the species which lived at its commencement and close;
but I cannot assign due proportional weight to the following
considerations.

Although each formation may mark a very long lapse of
years, each probably is short compared with the period requisite
to change one species into another. I am aware that two palaeon-
tologists, whose opinions are worthy of much deference, namely
Bronn and Woodward, have concluded that the average duration

278 ORIGIN OF SPECIES

of each formation is twice or thrice as long as the average duration
of specific forms. But insuperable difficulties, as it seems to me,
prevent us from coming to any just conclusion on this head.
When we see a species first appearing in the middle of any
formation, it would be rash in the extreme to infer that it had not
elsewhere previously existed. So again when we find a species
disappearing before the last layers have been deposited, it would
be equally rash to suppose that it then became extinct. We forget
how small the area of Europe is compared with the rest of the
world; nor have the several stages of the same formation through-
out Europe been correlated with perfect accuracy.

We may safely infer that with marine animals of all kinds
there has been a large amount of migration due to climatal and
other changes; and when we see a species first appearing in any
formation, the probability is that it only then first immigrated into
that area. It is well-known, for instance, that several species
appear somewhat earlier in the palaeozoic beds of North America
than in those of Europe; time having apparently been required
for their migration from the American to the European seas. In
examining the latest deposits in various quarters of the world, it
has everywhere been noted, that some few still existing species are
common in the deposit, but have become extinct in the imme-
diately surrounding sea; or, conversely, that some are now abun-
dant in the neighbouring sea, but are rare or absent in this
particular deposit. It is an excellent lesson to reflect on the ascer-
tained amount of migration of the inhabitants of Europe during
the glacial epoch, which forms only a part of one whole geological
period; and likewise to reflect on the changes of level, on the
extreme change of climate, and on the great lapse of time, all
included within this same glacial period. Yet it may be doubted
whether, in any quarter of the world, sedimentary deposits, in-
cluding fossil remains, have gone on accumulating within the
same area during the whole of this period. It is not, for instance,
probable that sediment was deposited during the whole of the gla-
cial period near the mouth of the Mississippi, within that limit of
depth at which marine animals can best flourish : for we know
that great geographical changes occurred in other parts of Amer-
ica during this space of time. When such beds as were deposited
in shallow water near the mouth of the Mississippi during some
part of the glacial period shall have been upraised, organic re-
mains will probably first appear and disappear at different levels,
owing to the migrations of species and to geographical changes.
And in the distant future, a geologist, examining these beds, would
be tempted to conclude that the average duration of life of the

IMPERFECTION OF THE GEOLOGICAL RECORD 279

embedded fossils had been less than that of the glacial period,
instead of having been really far greater, that is, extending
from before the glacial epoch to the present day.

In order to get a perfect gradation between two forms in the
upper and lower parts of the same formation, the deposit must have
gone on continuously accumulating during a long period, sufficient
for the slow process of modification; hence the deposit must be
a very thick one; and the species undergoing change must have
lived in the same district throughout the whole time. But we
have seen that a thick formation, fossiliferous throughout its
entire thickness, can accumulate only during a period of sub-
sidence; and to keep the depth approximately the same, which is
necessary that the same marine species may live on the same
space, the supply of sediment must nearly counterbalance the
amount of subsidence. But this same movement of subsidence will
tend to submerge the area whence the sediment is derived, and
thus diminish the supply, whilst the downward movement con-
tinues. In fact, this nearly exact balancing between the supply
of sediment and the amount of subsidence is probably a rare
contingency; for it has been observed by more than one palaeon-
tologist, that very thick deposits are usually barren of organic
remains, except near their upper or lower limits.

It would seem that each separate formation, like the whole
pile of formations in any country, has generally been intermit-
tent in its accumulation. When we see, as is so often the
case, a formation composed of beds of widely different mineral-
ogical composition, we may reasonably suspect that the process
of deposition has been more or less interrupted. Nor will the
closest inspection of a formation give us any idea of the length
of time which its deposition may have consumed. Many instances
could be given of beds only a few feet in thickness, represent-
ing formations, which are elsewhere thousands of feet in thickness,
and which must have required an enormous period for their
accumulation; yet no one ignorant of this fact woiild have even
suspected the vast lapse of time represented by the thinner forma-
tion. Many cases could be given of the lower beds of a forma-
tion having been upraised, denuded, submerged, and then re-cov-
ered by the upper beds of the same formation, — facts showing
what wide, yet easily overlooked, intervals have occurred in its
accumulation. In other cases we have the plainest evidence in
great fossilised trees, still standing upright as they grew, of many
long intervals of time and changes of level during the process of
deposition, w^hich would not have been suspected, had not the
trees been preserved: thus Sir C. Lyell and Dr. Dawson found

280 ORIGIN OF SPECIES

carboniferous beds 1400 feet thick in Nova Scotia, with ancient
root-bearing strata, one above the other at no less than sixty-
eight different levels. Hence, when the same species occurs at the
bottom, middle, and top of a formation, the probability is that
it has not lived on the same spot during the whole period of
deposition, but has disappeared and reappeared, perhaps many
times, during the same geological period. Consequently if it
were to undergo a considerable amount of modification during
the deposition of any one geological formation, a section would
not include all the fine intermediate gradations which must on
our theory have existed, but abrupt, though perhaps slight, changes
of form.

It is all-important to remember that naturalists have no golden
rule by which to distinguish species and varieties; they grant
some little variability to each species, but when they meet
with a somewhat greater amount of difference between any two
forms, they rank both as species, unless they are enabled to
connect them together by the closest intermediate gradations;
and this, from the reasons just assigned, we can seldom hope to
effect in any one geological section. Supposing B and C to be
two species, and a third. A, to be found in an older and under-
lying bed; even if A were strictly intermediate between B and C
it would simply be ranked as a third and distinct species, unless at
the same time it could be closely connected by intermediate varie-
ties with either one or both forms. Nor should it be forgotten,
as before explained, that A might be the actual progenitor of B
and C, and yet would not necessarily be strictly intermediate
between them in all respects. So that we might obtain the parent-
species and its several modified descendants from the lower and
upper beds of the same formation, and unless we obtained nu-
merous transitional gradations, we should not recognise their
blood-relationship, and should consequently rank them as distinct
species.

It is notorious on what excessively slight differences many pa-
laeontologists have founded their species; and they do this the
more readily if the specimens come from different sub-stages of
the same formation. Some experienced conchologists are now
sinking many of the very fine species of D'Orbigny and others into
the rank of varieties; and on this view we do find the kind
of evidence of change which on the theory we ought to find.
Look again at the later tertiary deposits, which include many
shells believed by the majority of naturalists to be identical with
existing species; but some excellent naturalists, as Agassiz and
Pictet, maintain that all these tertiary species are specifically

IMPERFECTION OF THE GEOLOGICAL RECORD 281

distinct, though the distinction is admitted to be very slight;
so that here, unless we believe that these eminent naturalists
have been misled by their imaginations, and that these late ter-
tiary species really present no difference whatever from their liv-
ing representatives, or unless we admit, in opposition to the judg-
ment of most naturalists, that these tertiary species are all truly
distinct from the recent, we have evidence of the frequent oc-
currence of slight modifications of the kind required. If we look
to rather wider intervals of time, namely, to distinct but con-
secutive stages of the same great formation, we find that the
embedded fossils, though universally ranked as specifically differ-
ent, yet are far more closely related to each other than are the spe-
cies found in more widely separated formations ; so that here again
we have undoubted evidence of change in the direction required
by the theory; but to this latter subject I shall return in the
following chapter.

With animals and plants that propagate rapidly and do not
wander much, there is reason to suspect, as we have formerly seen,
that their varieties are generally at first local ; and that such
local varieties do not spread widely and supplant their parent-forms
until they have been modified and perfected in some considerable
degree. According to this view, the chance of discovering in
a formation in any one country all the early stages of transition
between any two forms, is small, for the successive changes are
supposed to have been local or confined to some one spot. Most
marine animals have a wide range; and we have seen that with
plants it is those which have the widest range, that oftenest pre-
sent varieties; so that, with shells and other marine animals, it
is probable that those which had the widest range, far exceeding
the limits of the known geological formations in Europe, have
oftenest given rise; first to local varieties and ultimately to new
species; and this again would greatly lessen the chance of our
being able to trace the stages of transition in any one geological
formation.

It is a more important consideration, leading to the same re-
sult, as lately insisted on by Dr. Falconer, namely, that the period
during which each species underwent modification, though long
as measured by years, was probably short in comparison with that
during which it remained without undergoing any change.

It should not be forgotten, that at the present day, with perfect
specimens for examination, two forms can seldom be connected
by intermediate varieties, and thus proved to be the same species,
until many specimens are collected from many places; and with
fossil species this can rarely be done. We shall, perhaps, best

282 ORIGIN OF SPECIES

perceive the improbability of our being enabled to connect species
by numerous, fine, intermediate, fossil links, by asking ourselves
whether, for instance, geologists at some future i)eriod will be able
to prove that our different breeds of cattle, sheep, horses, and
dogs are descended from a single stock or from several aboriginal
stocks; or, again, whether certain sea-shells inhabiting the shores
of North America, which are ranked by some conchologists as dis-
tinct species from their European representatives, and by other
conchologists as only varieties, are really varieties, or are, as it is
called, specifically distinct. This could be effected by the future
geologist only by his discovering in a fossil state numerous in-
termediate gradations; and such success is improbable in the
highest degree.

It has been asserted over and over again, by writers who be-
lieve in the immutability of species, that geology yields no linking
forms. This assertion, as we shall see in the next chapter, is
certainly erroneous. As Sir J. Lubbock has remarked, " Every
species is a link between other allied forms." If we take a genus
having a score of species, recent and extinct, and destroy four-
fifths of them, no one doubts that the remainder will stand much
more distinct from each other. If the extreme forms in the
genus happen to have been thus destroyed, the genus itself will
stand more distinct from other allied genera. What geological
research has not revealed, is the former existence of infinitely
numerous gradations, as fine as existing varieties, connecting to-
gether nearly all existing and extinct species. But this ought not
to be expected; yet this has been repeatedly advanced as a most
serious objection against my views.

It may be worth while to sum up the foregoing remarks on the
causes of the imperfection of the geological record under an
imaginary illustration. The Malay Archipelago is about the size
of Europe from the North Cape to the Mediterranean, and from
Britain to Russia; and therefore equals all the geological forma-
tions which have been examined with any accuracy, excepting
those of the United States of America. I fully agree with Mr.
Godwin-Austen, that the present condition of the Malay Archi-
pelago, with its numerous large islands separated by wide and
shallow seas, probably represents the former state of Europe,
whilst most of our formations were accumulating. The Malay
Archipelago is one of the richest regions in organic beings; yet
if all the species were to be collected which have ever lived there,
how imperfectly would they represent the natural history of the
world !

But we have every reason to believe that the terrestrial pro-

IMPERFECTION OF THE GEOLOGICAL RECORD 283

ductions of the archipelago would be preserved in an extremely
imperfect manner in the formations which we suppose to be there
accumulating. Not many of the strictly littoral animals, or of
those which lived on naked submarine rocks, would be embedded;
and those embedded in gravel or sand would not endure to a
distant epoch. Wherever sediment did not accumulate on the
bed of the sea, or where it did not accumulate at a sufficient
rate to protect organic bodies from decay, no remains could be
preserved.

Formations rich in fossils of many kinds, and of thickness suffi-
cient, to last to an age as distant in futurity as the secondary
formations lie in the past, would generally be formed in the
archipelago only during periods of subsidence. These periods of
subsidence would be separated from each other by immense inter-
vals of time, during which the area would be either stationary or
rising; whilst rising, the fossiliferous formations on the steeper
shores would be destroyed, almost as soon as accumulated, by the
incessant coast-action, as we now see on the shores of South
America. Even throughout the extensive and shallow seas within
the archipelago, sedimentary beds could hardly be accumulated
of great thickness during the periods of elevation, or become
capped and protected by subsequent deposits, so as to have a
good chance of enduring to a very distant future. During the
periods of subsidence, there would probably be much extinction
of life; during the periods of elevation, there would be much
variation, but the geological record would then be less perfect.

It may be doubted whether the duration of any one great
period of subsidence over the whole or part of the archipelago,
together with a contemporaneous accumulation of sediment, would
exceed the average duration of the same specific forms; and these
contingencies are indispensable for the preservation of all the
transitional gradations between any two or more species. If such
gradations were not all fully preserved, transitional varieties would
merely appear as so many new, though closely allied species. It
is also probable that each great period of subsidence would be inter-
rupted by oscillations of level, and that slight climatal changes
would intervene during such lengthy periods; and in these cases
the inhabitants of the archipelago would migrate, and no closely
consecutive record of their modifications could be preserved in any
one formation.

Very many of the marine inhabitants of the archipelago now
range thousands of miles beyond its confines; and analogy plainly
leads to the belief that it would be chiefly these far-ranging species,
though only some of them, which would oftenest produce new varie-

284 ORIGIN OF SPECIES

ties; and the varieties would at first be local or confined to one
place, but if possessed of any decided advantage, or when further
modified and improved, they would slowly spread and supplant
their parent-forms. When such varieties returned to their an-
cient homes, as they would differ from their former state in a
nearly uniform, though perhaps extremely slight degree, and as
they would be found embedded in slightly different sub-stages of
the same formation, they would, according to the principles fol-
lowed by many palaeontologists, be ranked as new and distinct
species.

If then there be some degree of truth in these remarks, we
have no right to expect to find, in our geological formations, an
infinite number of those fine transitional forms which, on our
theory, have connected all the past and present species of the
same group into one long and branching chain of life. We ought
only to look for a few links, and such assuredly we do find —
some more distantly, some more closely, related to each other;
and these links, let them be ever so close, if found in different
stages of the same formation, would, by many palaeontologists, be
ranked as distinct species. But I do not pretend that I should ever
have suspected how poor was the record in the best preserved
geological sections, had not the absence of innumerable transi-
tional links between the species which lived at the commence-
ment and close of each formation, pressed so hardly on my
theory.

On the sudden Appearance of whole Groups of allied Species.

The abrupt manner in which whole groups of species suddenly
appear in certain formations, has been urged by several palaeontol-
ogists — for instance, by Agassiz, Pictet, and Sedgwick — as a
fatal objection to the belief in the transmutation of species. If
numerous species, belonging to the same genera or families, have
really started into life at once, the fact would be fatal to the
theory of evolution through natural selection. For the development
by this means of a group of forms, all of which are descended
from some one progenitor, must have been an extremely slow
process; and the progenitors must have lived long before their
modified descendants. But we continually overrate the perfection
of the geological record, and falsely infer, because certain genera
or families have not been found beneath a certain stage, that
they did not exist before that stage. In all cases positive palseonto-
logical evidence may be implicitly trusted; negative evidence is
worthless, as experience has so often shown. We continually for-

IMPERFECTION OF THE GEOLOGICAL RECORD 285

get how large the world is, compared with the area over which
our geological formations have been carefully examined ; we forget
that groups of species may elsewhere have long existed, and
have slowly multiplied, before they invaded the ancient archipela-
goes of Europe and the United States. We do not make due al-
lowance for the intervals of time which have elapsed between
our consecutive formations, — longer perhaps in many cases than
the time required for the accumulation of each formation. These
intervals will have given time for the multiplication of species
from some one parent-form : and in the succeeding formation, such
groups or species will appear as if suddenly created.

I may here recall a remark formerly made, namely, that it
might require a long succession of ages to adapt an organism to
some new and peculiar line of life, for instance, to fly through the
air; and consequently that the transitional forms would often
long remain confined to some one region; but that, when this
adaptation had once been effected, and a few species had thus
acquired a great advantage over other organisms, a comparatively
short time would be necessary to produce many divergent forms,
which would spread rapidly and widely, throughout the world.
Professor Pictet, in his excellent Review of this work, in com-
menting on early transitional forms, and taking birds as an illus-
tration, cannot see how the successive modifications of the an-
terior limbs of a supposed prototype could possibly have been of
any advantage. But look at the penguins of the Southern Ocean;
have not these birds their front limbs in this precise intermediate
state of " neither true arms nor true wings " ? Yet these birds hold
their place victoriously in the battle for life; for they exist in in-
finite numbers and of many kinds. I do not suppose that we here
see the real transitional grades through which the wings of birds
have passed; but what special difiiculty is there in believing that
it might profit the modified descendants of the penguin, first to
be<iome enabled to flap along the surface of the sea like tlie
logger-headed duck, and ultimately to rise from its surface and
glide through the air?

I will now give a few examples to illustrate the foregoing
remarks, and to show how liable we are to error in supposing
that whole groups of species have suddenly been produced. Even
in so short an interval as that between the first and second editions
of Pictet's great work on Palaeontology, published in 1844-46 and
in 1853-57, the conclusions on the first appearance and disap-
pearance of several groups of animals have been considerably
modified; and a third edition would require still further changes.
I may recall the well-known fact that in geological treatises,

281) ORIGIN OP SPECIES

published not many years ago, mammals were always spoken of
as having abruptly come in at the commencement of the tertiary
series. And now one of the richest known accumulations of
fossil mammals belongs to the middle of the secondary series; and
true mammals have been discovered in the new red sandstone
at nearly the commencement of this great series. Cuvier used to
urge that no monkey occurred in any tertiary stratum; but now
extinct species have been discovered in India, South America and
in Europe, as far back as the miocene stage. Had it not been for
the rare accident of the preservation of footsteps in the new red
sandstone of the United States, who would have ventured to sup-
pose that no less than at least thirty different bird-like animals,
some of gigantic size, existed during that period ? Not a fragment
of bone has been discovered in these beds. Not long ago, palaeon-
tologists maintained that the whole class of birds came suddenly
into existence during the eocene period; but now w^e know, on
the authority of Professor Owen, that a bird certainly lived during
the deposition of the upper greensand; and still more recently,
that strange bird, the Archeopteryx, with a long lizard-like tail,
bearing a pair of feathers on each joint, and with its wings fur-
nished with two free claws, has been discovered in the oolitic
slates of Solenhofen. Hardly any recent discovery shows more
forcibly than this, how little we as yet know of the former
inhabitants of the world.

I may give another instance, which, from having passed under
my own eyes, has much struck me. In a memoir on Fossil Sessile
Cirripedes, I stated that, from the large number of existing and
extinct tertiary species; from the extraordinary abundance of the
individuals of many species all over the world, from the Arctic
regions to the equator, inhabiting various zones of depths from
the upper tidal limits to 50 fathoms ; from the perfect manner in
which specimens are preserved in the oldest tertiary beds; from
the ease with which even a fragment of a valve can be recog-
nised; from all these circumstances, I inferred that, had sessile
cirripedes existed during the secondary periods, they would cer-
tainly have been preserved and discovered; and as not one species
had then been discovered in beds of this age, I concluded that this
great group had been suddenly developed at the commencement of
the tertiary series. This was a sore trouble to me, adding as I
then thought one more instance of the abrupt appearance of a
great group of species. But my work had hardly been published,
when a skilful palseontologist, M. Bosquet, sent me a drawing of
a perfect specimen of an unmistakable sessile cirripede, which
he had himself extracted from the chalk of Belgium. And, aa

IMPERFECTION OF THE GEOLOGICAL RECORD 287

if to make the case as striking as possible, this cirripede was a
Chthamalus, a very common, large, and ubiquitous genus, of
which not one species has as yet been found even in any tertiary
stratum. Still more recently, a Pyrgoma, a member of a distinct
sub-family of sessile cirripedes, has been discovered by Mr. Wood-
ward in the upper chalk; so that we now have abundant evidence
of the existence of this group of animals during the secondary
period.

The case most frequently insisted on by palaeontologists of
the apparently sudden appearance of a whole group of species, is
that of the teleostean fishes, low down, according to Agassiz, in
the Chalk period. This group includes the large majority of
existing species. But certain Jurassic and Triassic forms are now
commonly admitted to be teleostean; and even some palaeozoic
forms have thus been classed by one high authority. If the teleo-
steans had really appeared suddenly in the northern hemisphere
at the commencement of the chalk formation the fact would have
been highly remarkable; but it would not have formed an insuper-
able difficulty, unless it could likewise have been shown that at the
same period the species were suddenly and simultaneously devel-
oped in other quarters of the world. It is almost superfluous
to remark that hardly any fossil-fish are known from south of the
equator; and by running through Pictet's Palaeontology it will
be seen that very few species are known from several formations
in Europe. Some few families of fish now have a confined range;
the teleostean fishes might formerly have had a similarly confined
range, and after having been largely developed in some one sea,
have spread widely. Nor have we any right to suppose that the
seas of the world have always been so freely open from south to
north as they are at present. Even at this day, if the Malay Arch-
ipelago were converted into land, the tropical parts of the Indian
Ocean would form a large and perfectly enclosed basin, in which
any great group of marine animals might be multiplied; and here
they would remain confined, until some of the species became
adapted to a cooler climate, and were enabled to double the South-
ern capes of Africa or Australia, and thus reach other and distant
seas.

From these considerations, from our ignorance of the geology
of other countries beyond the confines of Europe and the United
States, and from the revolution in our palaeontological knowledge
effected by the discoveries of the last dozen years, it seems to me
to be about as rash to dogmatize on the succession of organic forms
throughout the world, as it would be for a naturalist to land for

288 ORIGIN OF SPECIES

five minutes on a barren point in Australia, and then to discuss
the number and range of its productions.

On the sudden Appearance of Groups of allied Species in the
lowest known Fossiliferous Strata.

There is another and allied difficulty, which is much more serious.
I allude to the manner in which species belonging to several
of the main divisions of the animal kingdom suddenly appear in
the lowest known fossiliferous rocks. Most of the arguments
which have convinced me that all the existing species of the same
group are descended from a single progenitor, apply with equal
force to the earliest known species. For instance, it cannot be
doubted that all the Cambrian and Silurian trilobites are de-
scended from some one crustacean, which must have lived long
before the Cambrian age, and which probably differed greatly
from any known animal. Some of the most ancient animals,
as the Nautilus, Lingula, &c., do not differ much from living
species; and it cannot on our theory be supposed, that these
old species were the progenitors of all the species belonging to the
same groups which have subsequently appeared, for they are not
in any degree intermediate in character.

Consequently, if the theory be true, it is indisputable that
before the lowest Cambrian stratum was deposited long periods
elapsed, as long as, or probably far longer than, the whole interval
from the Cambrian age to the present day; and that during, these
vast periods the world swarmed with living creatures. Here we
encounter a formidable objection ; for it seems doubtful whether
the earth, in a fit state for the habitation of living creatures, has
lasted long enough. Sir W. Thompson concludes that the con-
.solidation of the crust can hardly have occurred less than 20 or
more than 400 million years ago, but probably not less than 98 or
more than 200 million years. These very wide limits show how
doubtful the data are; and other elements may have hereafter
to be introduced into the problem. Mr. Croll estimates that about
60 million years have elapsed since the Cambrian period, but
this. Judging from the small amount of organic change since the
commencement of the Glacial epoch, appears a very short time
for the many and great mutations of life, which have certainly
occurred since the Cambrian formation; and the previous 140
million years can hardly be considered as sufficient for the develop-
ment of the varied forms of life which already existed during
the Cambrian period. It is, however, probable, as Sir William
Thompson insists, that the world at a very early period was sub-

IMPERFECTION OF THE GEOLOGICAL RECORD 289

jected to more rapid and violent changes in its physical condi-
tions than those now occurring; and such changes would have
tended to induce changes at a corresponding rate in the organ-
isms which then existed.

To the question why we do not find rich fossiliferous deposits
belonging to these assumed earliest periods prior to the Cambrian
system, I can give no satisfactory answer. Several eminent geolo-
gists, with Sir R. Murchison at their head, were until recently
convinced that we beheld in the organic remains of the lowest
Silurian stratum the first dawn of life. Other highly competent
judges, as Lyell and E. Forbes, have disputed this conclusion.
We should not forget that only a small portion of the world
is known with accuracy. Not very long ago M. Barrande added
another and lower stage, abounding with new and peculiar species,
beneath the then known Silurian system ; and now, still lower down
in the Lower Cambrian formation, Mr. Hicks has found in South
Wales beds rich in trilobites, and containing various molluscs and
annelids. The presence of phosphatic nodules and bituminous
matter, even in some of the lowest azoic rocks, probably indicates
life at these periods; and the existence of the Eozoon in the Lau-
rentian formation of Canada is generally admitted. There are
three great series of strata beneath the Silurian system in Canada,
in the lowest of which the Eozoon is found. Sir W. Logan states
that their " united thickness may possibly far surpass that of
all the succeeding rocks, from the base of the palaeozoic series to
the present time. We are thus carried back to a period so remote,
that the appearance of the so-called Primordial fauna (of Bar-
rande) may by some be considered as a comparatively modern
event." The Eozoon belongs to the most lowly organised of all
classes of animals, but is highly organised for its class; it existed
in countless numbers, and, as Dr. Dawson has remarked, certainly
preyed on other minute organic beings, which must have lived
in great numbers. Thus the words, which I wrote in 1859, about
the existence of living beings long before the Cambrian period, and
which are almost the same with those since used by Sir W. Logan,
have proved true. Nevertheless, the difficulty of assigning any
good reason for the absence of vast piles of strata rich in fossils
beneath the Cambrian system is very great. It does not seem
probable that the most ancient beds have been quite worn away
by denudation, or that their fossils have been wholly obliterated
by metamorphic action, for if this had been the case we should
have found only small remnants of the formations next succeed-
ing them in age, and these would always have existed in a partially
metamorphosed condition. But the descriptions which we possess

290 ORIGIN OF SPECIES

of the Silurian deposits over immense territories in Russia and
in North America, do not support the view, that the older a forma-
tion is, the more invariably it has suffered extreme denudation
and metamorphism.

The case at present must remain inexplicable; and may be
truly urged as a valid argument against the views here entertained.
To show that it may hereafter receive some explanation, I will
give the following hypothesis. From the nature of the organic
remains which do not appear to have inhabited profound depths,
in the several formations of Europe and of the United States;
and from the amount of sediment, miles in thickness, of which the
formations are composed, we may infer that from first to last
large islands or tracts of land, whence the sediment was derived,
occurred in the neighbourhood of the now existing continents of
Europe and North America. This same view has since been
maintained by Agassiz and others. But we do not know what
was the state of things in the intervals between the several suc-
cessive formations; whether Europe and the United States during
these intervals existed as dry land, or as a submarine surface near
land, on which sediment was not deposited, or as the bed of an
open and unfathomable sea.

Looking to the existing oceans, which are thrice as extensive
as the land, we see them studded with many islands ; but hardly
one truly oceanic island (with the exception of New Zealand, if
this can be called a truly oceanic island) is as yet known to afford
even a remnant of any palaeozoic or secondary formation. Hence
we may perhaps infer, that during the palaeozoic and secondary
periods, neither continents nor continental islands existed where
our oceans now extend; for had they existed, palaeozoic and sec-
ondary formations would in all probability have been accumu-
lated from sediment derived from their wear and tear; and these
would have been at least partially upheaved by the oscillations of
level, which must have intervened during these enormously long
periods. If then we may infer anything from these facts, we may
infer that, where our oceans now extend, oceans have extended
from the remotest period of which we have any record; and on
the other hand, that where continents now exist, large tracts of
land have existed, subjected no doubt to great oscillations of level,
since the Cambrian period. The coloured map appended to my
volume on Coral Reefs, led me to conclude that the great oceans
are still mainly areas of subsidence, the great archipelagoes still
areas of oscillations of level, and the continents areas of eleva-
tion. But we have no reason to assume that things have thus
remained from the beginning of the world. Our continents seem

IMPERFECTION OF THE GEOLOGICAL RECORD 291

to have been formed by a preponderance, during many oscilla-
tions of level, of the force of elevation; but may not the areas
of preponderant movement have changed in the lapse of ages ? At
a period long antecedent to the Cambrian epoch, continents may
have existed where oceans are now spread out; and clear and
open oceans may have existed where our continents now stand.
Nor should we be justified in assuming that if, for instance, the
bed of the Pacific Ocean were now converted into a continent
we should there find sedimentary formations in a recognisable
condition older than the Cambrian strata, supposing such to have
been formerly deposited; for it might well happen that strata
which had subsided some miles nearer to the centre of the earth,
and which had been pressed on by an enormous weight of superin-
cumbent water, might have undergone far more metamorphic ac-
tion than strata which have always remained nearer to the surface.
The immense areas in some parts of the world, for instance in
South America, of naked metamorphic rocks, which must have
been heated under great pressure, have always seemed to me to
require some special explanation ; and we may perhaps believe that
we see in these large areas, the many formations long anterior
to the Cambrian epoch in a completely metamorphosed and de-
nuded condition.

The several difficulties here discussed, namely — that, though
we find in' our geological formations many links between the species
which now exist and which formerly existed, we do not find
infinitely numerous fine transitional forms closely joining them
all together ; — the sudden manner in which several groups of
species first appear in our European formations ; — the almost
entire absence, as at present known, of formations rich in fossils
beneath the Cambrian strata, — are all undoubtedly of the most
serious nature. We see this in the fact that the most eminent
palaeontologists, namely, Cuvier, Agassiz, Barrande, Pictet, Fal-
coner, E. Forbes, &c., and all our greatest geologists, as Lyell,
Murchison, Sedgwick, &c., have unanimously, often vehemently,
maintained the immutability of species. But Sir Charles Lyell
now gives the support of his high authority to the opposite side;
and most geologists and palaeontologists are much shaken in their
former belief. Those who believe that the geological record is
in any degree perfect, will undoubtedly at once reject the theory.
For my part, following out Lyell's metaphor, I look at the geo-
volume alone, relating only to two or three countries. Of this
logical record as a history of the world imperfectly kept, and
written in a changing dialect; of this history we possess the last
volume, only here and there a short chapter has been preserved;

292 ORIGIN OF SPECIES

and of each page, only here and there a few lines. Each word
of the slowly-changing language, more or less different in the
successive chapters, may represent the forms of life, which are
entombed in our consecutive formations, and which falsely appear
to have been abruptly introduced. On this view, the difficulties
above discussed are greatly diminished, or even disappear.

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 293

CHAPTER XI.

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.

On the slow and successive appearance of new species — On their
different rates of change — Species once lost do not reappear — Groups
of species follow the same general rules in their appearance and
disappearance as do single species — On extinction — On simultaneous
changes in the forms of life throughout the world — On the affinities
of extinct species to each other and to living species — On the state
of development of ancient forms — On the succession of the same types
within the same areas — Summary of preceding and present chapter.

LET us now see whether the several facts and laws relating
to the geological succession of organic beings accord best
with the common view of the immutability of species, or
with that of their slow and gradual modification, through variation
and natural selection.

New species have appeared very slowly, one after another, both
on the land and in the waters. Lyell has shown that it is hardly
possible to resist the evidence on this head in the case of the
several tertiary stages; and every year tends to fill up the blanks
between the stages, and to make the proportion between the lost
and existing forms more gradual. In some of the most recent
beds, though undoubtedly of high antiquity if measured by years,
only one or two species are extinct, and only one or two are
new, having appeared there for the first time, either locally, or, as
far as we know, on the face of the earth. The secondary forma-
tions are more broken; but, as Bronn has remarked, neither the
appearance nor disappearance of the many species embedded in
each formation has been simultaneous.

Species belonging to different genera and classes have not
changed at the same rate, or in the same degree. In the older
tertiary beds a few living shells may still be found in the
midst of a multitude of extinct forms. Ealconer has given a strik-
ing instance of a similar fact, for an existing crocodile is asso-
ciated with*many lost mammals and reptiles in the sub-Himalayan
deposits. The Silurian Lingula differs but little from the living
species of this genus; whereas most of the other Silurian Mol-
luscs and all the Crusta<?eans have changed greatly. The pro-

294 ORIGIN OF SPECIES

ductioiiG of the land seem to have changed at a quicker rate than
those of the sea, of which a striking instance has been observed
in Switzerland. There is some reason to believe that organisms
high in the scale, change more quickly than those that are low:
though there are exceptions to this rule. The amount of organic
change, as Pictet has remarked, is not the same in each succes-
sive so-called formation. Yet if we compare any but the most
closely related formations, all the species will be found to have
undergone some change. When a species has once disappeared
from the face of the earth, we have no reason to believe that
the same identical form ever reappears. The strongest apparent
exception to this latter rule is that of the so-called " colonies "
of M. Barrande, which intrude for a period in the midst of an
older formation, and then allow the pre-existing fauna to reap-
pear ; but Lyell's explanation, namely, that it is a case of temporary
migration from a distinct geographical province, seems satisfac-
tory.

These several facts accord well with our theory, which includes
no fixed law of development, causing all the inhabitants of an
area to change abruptly, or simultaneously, or to an equal degree.
The process of modification must be slow, and will generally
effect only a few species at the same time; for the variability of
each species is independent of that of all others. Whether such
variations or individual differences as may arise will be accumu-
lated through natural selection in a greater or less degree, thus
causing a greater or less amount of permanent modification, will
depend on many complex contingencies — on the variations being
of a beneficial nature, on the freedom of intercrossing, on the
slowly changing physical conditions of the country, on the immi-
gration of new colonists, and on the nature of the other inhabi-
tants with which the varying species come into competition.
Hence it is by no means surprising that one species should retain
the same identical form much longer than others; or, if changing,
should change in a less degree. We find similar relations be-
tween the existing inhabitants of distinct countries; for instance,
the land-shells and coleopterous insects of Madeira have come
to differ considerably from their nearest allies on the continent
of Europe, whereas the marine shells and birds have remained un-
altered. We can perhaps understand the apparently quicker rate
of change in terrestrial and in more highly organised productions
compared with marine and lower i)roductions, by the more com-
plex relations of the higher beings to their organic and inor-
ganic conditions of life, as explained in a former chapter. When
many of the inhabitants of any area have become modified and

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 295

improved, we can understand, on the principle of competition,
and from the all-important relations of organism to organism
in the struggle for life, that any form which did not become in
some degree modified and improved, would be liable to exter-
mination. Hence we see why all the species in the same region
do at last, if we look to long enough intervals of time, become
modified, for otherwise they would become extinct.

In members of the same class the average amount of change,
during long and equal periods of time, may, perhaps, be nearly
the same; but as the accumulation of enduring formations, rich
in fossils, depends on great masses of sediment being deposited
on subsiding areas, our formations have been almost necessarily
accumulated at wide and irregularly intermittent intervals of
time ; consequently the amount of organic change exhibited by the
fossils embedded in consecutive formations is not equal. Each
formation, on this view, does not mark a new and complete act
of creation, but only an occasional scene, taken almost at haz-
ard, in an ever slowly changing drama.

We can clearly understand why a species when once lost should
never reappear, even if the very same conditions of life, organic
and inorganic, should recur. For though the offspring of one spe-
cies might be adapted (and no doubt this has occurred in innu-
merable instances) to fill the place of another species in the
economy of nature, and thus supplant it ; yet the two forms — •
the old and the new — would not be identically the same ; for both
would almost certainly inherit different characters from, their
distinct progenitors ; and organisms already differing would vary in
a different manner. For instance, it is possible, if all our fantail
pigeons were destroyed, that fanciers might make a new breed
hardly distinguishable from the present breed; but if the parent
rock-pigeon were likewise destroyed, and under nature we have
every reason to believe that parent-forms are generally supplanted
and exterminated by their improved offspring, it is incredible that
a fantail, identical with the existing breed, could be raised from
any other species of pigeon, or even from any other well-estab-
lished race of the domestic pigeon, for the successive variations
would almost certainly be in some degree different, and the newly-
formed variety would probably inherit from its progenitor some
characteristic differences.

Groups of species, that is, genera and families, follow the
same general rules in their appearance and disappearance as
do single species, changing more or less quickly, and in a greater
or lesser degree. A group, when it has once disappeared, never
reappears; that is, its existence, as long as it lasts, is continuous.

296 ORIGIN OF SPECIES

I am aware that there are some apparent exceptions to this rule,
but the exceptions are surprisingly few, so few that E. Forbes,
Pictet, and Woodward (though all strongly opposed to such views
as I maintain) admit its truth; and the rule strictly accords with
the theory. For all the species of the same group, however long it
may have lasted, are the modified descendants one from the other,
and all from a common progenitor. In the genus Lingula, for
instance, the species which have successively appeared at all ages
must have been connected by an unbroken series of generations,
from the lowest Silurian stratum to the present day.

We have seen in the last chapter that whole groups of species
sometimes falsely appear to have been abruptly developed; and
I have attempted to give an explanation of this fact, which if true
would be fatal to my views. But such cases are certainly excep-
tional; the general rule being a gradual increase in number, until
the group reaches its maximum, and then, sooner or later, a
gradual decrease. If the number of the species included within
a genus, or the number of the genera within a family, be repre-
sented by a vertical line of varying thickness, ascending through
the successive geological formations, in which the species are
found, the line will sometimes falsely appear to begin at its lower
end, not in a sharp point, but abruptly; it then gradually thickens
upwards, often keeping of equal thickness for a space, and ulti-
mately thins out in the upper beds, marking the decrease and final
extinction of the species. This gradual increase in number of the
species of a group is strictly conformable with the theory, for
the species of the same genus, and the genera of the same
family, can increase only slowly and progressively; the process
of modification and the production of a number of allied forms
necessarily being a slow and gradual process, — one species first
giving rise to two or three varieties, these being slowly converted
into species, which in their turn produce by equally slow steps
other varieties and species, and so on, like the branching of a
great tree from a single stem, till the group becomes large.

On Extinction.

We have as yet only spoken incidentally of the disappearance
of species and of groups of species. On the theory of natural
selection, the extinction of old forms and the production of new
and improved forms are intimately connected together. The old
notion of all the inhabitants of the earth having been swept away
by catastrophes at successive periods is very generally given up,
even by those geologists, as Elie de Beaumont, Murchison, Bar-

GEOLOGICAL SUCCESSION OF ORGxiNIC BEINGS 297

rande, &c., whose general views would naturally lead them to
this conclusion. On the contrary, we have every reason to be-
lieve, from the study of the tertiary formations, that species
and groups of species gradually disappear, one after another, first
from one spot, then from another, and finally from the world. In
some few cases, however, as by the breaking of an isthmus and
the consequent irruption of a multitude of new inhabitants into an
adjoining sea, or by the final subsidence of an island, the process
of extinction may have been rapid. Both single species and
whole groups of species last for very unequal periods; some
groups, as we have seen, have endured from the earliest known
dawn of life to the present day; some have disappeared before
the close of the palaeozoic period. No fixed law seems to deter-
mine the length of time during which any single species or any
single genus endures. There is reason to believe that the extinc-
tion of a whole group of species is generally a slower process than
their production : if their appearance and disappearance be rep-
resented, as before, by a vertical line of varying thickness the
line is found to taper more gradually at its upper end, which marks
the progress of extermination, than at its lower end, which marks
the first appearance and the early increase in number of the spe-
cies. In some cases, however, the extermination of whole groups,
as of ammonites, towards the close of the secondary period, has
been wonderfully sudden.

The extinction of species has been involved in the most gratu-
itous mystery. Some authors have even supposed that, as the
individual has a definite length of life, so have species a definite
duration. ~Mo one can have marvelled more than I have done
at the extinction of species. When I found in La Plata the tooth
of a horse embedded with the remains of Mastodon, Megatherium,
Toxodon, and other extinct monsters, which all co-existed with
still living shells at a very late geological period, I was filled with
astonishment; for, seeing that the horse, since its introduction by
the Spaniards into South America, has run wild over the whole
country and has increased in numbers at an unparalleled rate,
I asked myself what could so recently have exterminated the
former horse under conditions of life apparently so favourable.
But my astonishment was groundless. Professor Owen soon per-
ceived that the tooth, though so like that of the existing horse,
belonged to an extinct species. Had this horse been still living,
but in some degree rare, no naturalist would have felt the least
surprise at its rarity; for rarity is the attribute of a vast number
of species of all classes, in all countries. If we ask ourselves
why this or that species is rare, we answer that something is un-

298 ORIGIN OF SPECIES

favourable in its conditions of life; but what that something
is we can hardly ever tell. On the supposition of the fossil
horse still existing as a rare species, we might have felt certain,
from the analogy of all other mammals, even of the slow-breeding
elephant, and from the history of the naturalisation of the domes-
tic horse in South America, that under more favourable conditions
it would in a very few years have stocked the whole continent.
But we could not have told what the unfavourable conditions were
which checked its increase, whether some one or several contin-
gencies, and at what period of the horse's life, and in what de-
gree they severally acted. If the conditions had gone on, however
slowly, becoming less and less favourable, we assuredly should
not have perceived the fact, yet the fossil horse would certainly
have become rarer and rarer, and finally extinct ; — its place
being seized on by some more successful competitor.

It is most difficult always to remember that the increase of
every creature is constantly being checked by unperceived hostile
agencies; and that these same unperceived agencies are amply
sufiicient to cause rarity, and finally extinction. So little is
this s.ubject understood, that I have heard surprise repeatedly ex-
pressed at such great monsters as the Mastodon and the more
ancient Dinosaurians having become extinct; as if mere bodily
strength gave victory in the battle of life. Mere size, on the con-
trary, would in some cases determine, as has been remarked by
Owen, quicker extermination from the greater amount of requisite
food. Before man inhabited India or Africa, some cause must
have checked the continued increase of the existing elephant. A
highly capable judge. Dr. Falconer, believes that it is chiefly in-
sects which, from incessantly harassing and weakening the ele-
phant in India, check its increase; and this was Bruce's conclu-
sion with respect to the African elephant in Abyssinia. It is
certain that insects and blood-sucking bats determine the exist-
ence of the larger naturalised quadrupeds in several parts of
S. America.

We see in many cases in the more recent tertiary formations,
that rarity precedes extinction ; and we know that this has been the
progress of events with those animals which have been exter-
minated, either locally or wholly, through man's agency. I may
repeat what I published in 1845, namely, that to admit that spe-
cies generally become rare before they become extinct — to feel
no surprise at the rarity of a species, and yet to marvel greatly
when the species ceases to exist, is much the same as to admit
that sickness in the individual is the forerunner of death — to

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 290

feel no surprise at sickness, but, when the sick man dies, to wonder
and to suspect that he died by some deed of violence.

The theory of natural selection is grounded on the belief that
each new variety and ultimately each new species, is produced
and maintained by having some advantage over those with which
it comes into competition; and the consequent extinction of the
less-favoured forms almost inevitably follows. It is the same with
our domestic productions; when a new and slightly improved
variety has been raised, it at first supplants the less improved
varieties in the same neighbourhood ; when much improved it is
transported far and near, like our short-horn cattle, and takes
the place of other breeds in other countries. Thus the appear-
ance of new forms and the disappearance of old forms, both those
naturally and those artificially produced, are bound together. In
flourishing groups, the number of new specific forms which
have been produced within a given time has at some periods prob-
ably been greater than the number of the old specific forms
which have been exterminated; but we know that species have
not gone on indefinitely increasing, at least during the later
geological epochs, so that, looking to later times, we may believe
that the production of new forms has caused the extinction of
about the same number of old forms.

The competition will generally be most severe, as formerly
explained and illustrated by examples, between the forms which
are most like each other in all respects. Hence the improved
and modified descendants of a species will generally cause the
extermination of the parent-species; and if many new forms have
been developed from any one species, the nearest allies of that
species, i. e. the species of the same genus, will be the most
liable to extermination. Thus, as I believe, a number of new
species descended from one species, that is a new genus, comes
to supplant an old genus, belonging to the same family. But it
must often have* happened that a new species belonging to some
one group has^seized on the place occupied by a species belonging
to a distinct' group, and thus have caused its extermination. If
many allied forms be developed from the successful intruder,
many will have to yield their places ; and it will generally be the
allied forms, which will suffer from some inherited inferiority
in common. But whether it be species belonging to the same
or to a distinct class, which have yielded their places to other
modified and improved species, a few of the sufferers may often
be preserved for a long time, from being fitted to some peculiar
line of life, or from inhabiting some distant and isolated station,
where they will have escaped severe competition. For instance.

300 ORIGIN OF SPECIES

some species of Trigonia, a great genus of shells in the secondary
formations, survive in the Australian seas; and a few members
of the great and almost extinct group of Ganoid fishes still
inhabit our fresh waters. Therefore the utter extinction of a
group is generally, as we have seen, a slower process than its
production.

With respect to the apparently sudden extermination .of whole
families or orders, as of Trilobites at the close of the palaeozoic
period and of Ammonites at the close of the secondary period, we
must remember what has been already said on the probable wide
intervals of time between our consecutive formations ; and in these
intervals there may have been much slow extermination. More-
over, when, by sudden immigration or by unusually rapid develop-
ment, many species of a new group have taken possession of
an area, many of the older species will have been exterminated
in a correspondingly rapid manner; and the forms which thus
yield their places will commonly be allied, for they will partake
of the same inferiority in common.

Thus, as it seems to me, the manner in which single species
and whole groups of species become extinct accords well with
the theory of natural selection. We need not marvel at extinction ;
if we must marvel, let it be at our own presumption in imagining
for a moment that we understand the many complex contin-
gencies on which the existence of each species depends. If we
forget for an instant that each species tends to increase inordi-
nately, and that some check is always in action, yet seldom per-
ceived by us, the whole economy of nature will be utterly obscured.
Whenever we can precisely say why this species is more abundant
in individuals than that; why this species and not another can be
naturalised in a given country; then, and not until then, we
may justly feel surprise why we cannot account for the extinc-
tion of any particular species or group of species.

On the Forms of Life changing almost simultaneously throughout

the World.

Scarcely any palseontological discovery is more striking than
the fact that the forms of life change almost simultaneously
throughout the world. Thus our European Chalk formation can
be recognised in many distant regions, under the most different
climates, where not a fragment of the mineral chalk itself can
be found; namely in North America, in equatorial South America,
in Tierra del Fuego, at the Cape of Good Hope, and in the
peninsula of India. For at these distant points, the organic re-

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 301

mains in certain beds present an unmistakeable resemblance to
those of the Chalk. It is not that the same species are met
with; for in some cases not one species is identically the same,
but they belong to the same families, genera, and sections of
genera, and sometimes are similarly characterised in such trifling
points as mere superficial sculpture. Moreover, other forms, which
are not found in the Chalk of Europe, but which occur in the
formations either above or below, occur in the same order at these
distant points of the world. In the several successive palaeozoic
formations of Russia, Western Europe, and North America, a
similar parallelism in the forms of life has been observed by
several authors; so it is, according to Lyell, with the European
and North American tertiary deposits. Even if the few fossil
species which are common to the Old and New Worlds were kept
wholly out of view, the general parallelism in the successive forms
of life, in the palaeozoic and tertiary stages, would still be manifest,
and the several formations could be easily correlated.

These observations, however, relate to the marine inhabitants of
the world: we haj^e not sufficient data to judge whether the
productions of the land and of fresh water at distant points change
in the same parallel manner. We may doubt whether they have
thus changed: if the Megatherium, Mylodon, Macrauchenia, and
Toxodon had been brought to Europe from La Plata, without
any information in regard to their geological position, no one would
have suspected that they had co-existed with sea-shells all still
living; but as these anomalous monsters co-existed with the Mas-
todon and Horse, it might at least have been inferred that they
had lived during one of the later tertiary stages.

When the marine forms of life are spoken of as having changed
simultaneously throughout the world, it must not be supposed
that this expression relates to the same year, or to the same
century, or even that it has a very strict geological sense; for if
all the marine animals now living in Europe, and all those that
lived in Europe during the pleistocene period (a very remote
period as measured by years, including the whole glacial epoch)
were compared with those now existing in South America or in
Australia, the most skilful naturalist would hardly be able to
say whether the present or the pleistocene inhabitants of Europe
resembled most closely those of the southern hemisphere. So,
again, several highly competent observers maintain that the exist-
ing productions of the United States are more closely related to
those which lived in Europe during certain late tertiary stages,
than to the present inhabitants of Europe; and if this be so, it is
evident that fossiliferous beds now deposited on the shores of North

302 ORIGIN OF SPECIES

America would hereafter be liable to be classed with somewhat
older European beds. Nevertheless, looking to a remotely future
epoch, there can be little doubt that all the more modern marine
formations, namely, the upper pliocene, the pleistocene and strictly
modern beds of Europe, North and South America, and Australia,
from containing fossil remains in some degree allied, and from
not including those forms which are found only in the older
underlying deposits, would be correctly ranked as simultaneous in
a geological sense.

The fact of the forms of life changing simultaneously, in the
above large sense, at distant parts of the world, has greatly struck
these admirable observers, MM. de Verneuil and d'Archiac. After
referring to the parallelism of the palaeozoic forms of life in
various parts of Europe, they add, " If, struck by this strange
sequence, we turn our attention to North America, and there
discover a series of analogous phenomena, it will appear certain
that all these modifications of species, their extinction, and the
introduction of new ones, cannot be owing to mere changes in
marine currents or other causes more or less local and temporary,
but depend on general laws which govern the whole animal king-
dom." M. Barrande has made forcible remarks to precisely the
some effect. It is, indeed, quite futile to look to changes of
currents, climate, or other physical conditions, as the cause of these
great mutations in the forms of life throughout the world, under
the most different climates. We must, as Barrande has remarked,
look to some special law. We shall see this more clearly when
we treat of the present distribution of organic beings, and find
how slight is the relation between the physical conditions of
various countries and the nature of their inhabitants.

This great fact of the parallel succession of the forms of life
throughout the world, is explicable on the theory of natural selec-
tion. New species are formed by having some advantage over
older forms ; and the forms, which are already dominant, or
have some advantage over the other forms in their own country,
give birth to the greatest number of new varieties or incipient
species. We have distinct evidence on this head, in the plants
which are dominant, that is, which are commonest and most
widely diffused, producing the greatest number of new varieties.
It is also natural that the dominant, varying, and far-spreading
species, which have already invaded to a certain extent the terri-
tories of other species, should be those which would have the best
chance of spreading still further, and of giving rise in new
countries to other new varieties and species. The process of
diffusion would often be very slow, depending on climatal and

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 803

geegraphical changes, on strange accidents, and on the gradual
acclimatisation of new species to the various climates through
which they might have to pass, but in the course of time the
dominant forms would generally succeed in spreading and would
ultimately prevail. The diffusion would, it is probable, be slower
with the terrestrial inhabitants of distinct continents than with
the marine inhabitants of the continuous sea. We might there-
fore expect to find, as we do find, a less strict degree of paral-
lelism in the succession of the productions of the land than with
those of the sea.

Thus, as it seems to me, the parallel, and, taken in a large
sense, simultaneous, succession of the same forms of life through-
out the world, accords well with the principle'of new species having
been formed by dominant species spreading widely and varying;
the new species thus produced being themselves dominant, owing
to their having had some advantage over their already dominant
parents, as well as over other species, and again spreading, vary-
ing, and producing new forms. The old forms which are beaten
and which yield their places to the new and victorious forms,
will generally be allied in groups, from inheriting some inferiority
in common; and therefore, as new and improved groups spread
throughout the world, old groups disappear from the world; and
the succession of forms everywhere tends to correspond both in
their first appearance and final disappearance.

There is one other remark connected with this subject worth
making. I have given my reasons for believing that most of
our great formations, rich in fossils, were deposited during periods
of subsidence; and that blank intervals of vast duration, as far
as fossils are concerned, occurred during the periods when the
bed of the sea was either stationary or rising, and likewise when
sediment was not thrown down quickly enough to embed and
preserve organic remains. During these long and blank intervals
I suppose that the inhabitants of each region underwent a con-
siderable amount of modification and extinction, and that there
was much migration from other parts of the world. As we have
reason to believe that large areas are affected by the same move-
ment, it is probable that strictly contemporaneus formations have
often been accumulated over very wide spaces in the same quarter
of the world; but we are very far from having any right to
conclude that this has invariably been the case, and that large areas
have invariably been affected by the same movements. When
two formations have been deposited in two regions during nearly,
but not exactly, the same period, we should find in both, from
the causes explained in the foregoing paragraphs, the same general

304 ORIGIN OF SPECIES

succession in the forms of life; but the species would not exactly
correspond; for there will have been a little more time in the one
region, than in the other for modification, extinction, and immi-
gration.

I suspect that cases of this nature occur in Europe. Mr.
Prestwich, in his admirable Memoirs on the eocene deposits of
England and France, is able to draw a close general parallelism be-
tween the successive stages in the two countries; but when he
compares certain stages in England with those in France,, although
he finds in both a curious accordance in the numbers of the species
belonging to the same genera, yet the species themselves differ
in a manner very difficult to account for^ considering the proximity
of the two areas, — unless, indeed, it be assumed that an isthmus
separated two seas inhabited by distinct, but contemporaneous,
faunas. Lyell has made similar observations on some of the later
tertiary formations. Barrande, also, shows that there is a strik-
ing general parallelism in the successive Silurian deposits of
Bohemia and Scandinavia; nevertheless he finds a surprising
amount of difference in the species. If the several formations in
these regions have not been deposited during the same exact
periods, — a formation in one region often corresponding with
a blank interval in the other, — and if in both regions the species
have gone on slowly changing during the accumulation of the
several formations and during the long intervals of time between
them; in this case the several formations in the two regions could
be arranged in the same order, in accordance with the general
succession of the forms of life, and the order would falsely appear
to be strictly parallel; nevertheless the species would not be all
the same in the apparently corresponding stages in the two regions.

On the Affinities of Extinct Species to each other, and to Living

Forms.

Let us now look to the mutual affinities of extinct and living
species. All fall into a few grand classes; and this fact is at
once explained on the principle of descent. The more ancient
any form is, the more, as a general rule, it differs from living
forms. But, as Buckland long ago remarked, extinct species can
all be classed either in still existing groups, or between them.
That the extinct forms of life help to fill up the intervals between
existing genera, families, and orders, is certainly true; but as this
statement has often been ignored or even denied, it may be well
to make some remarks on this subject, and to give some instances.
If we confine our attention either to the living or to the extinct

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 305

species of the. same class, the series is far less perfect than if
we combine both into one general system. In the writings of
Professor Owen we continually meet with the expression of gener-
alised forms, as applied to extinct animals; and in the writings
of Agassiz, of prophetic or synthetic types ; and those terms imply
that such forms are in fact intermediate or connecting links.
Another distinguished palaeontologist, M. Gaudry, has shown in
the most striking manner that many of the fossil mammals dis-
covered by him in Attica serve to break down the intervals between
existing genera. Cuvier ranked the Ruminants and Pachyderms
as two of the most distinct orders of mammals : but so many
fossil links have been disentombed that Owen has had to alter
the whole classification, and has placed certain pachyderms in the
same sub-order with ruminants; for example, he dissolves by gra-
dations the apparently wide interval between the pig and the
camel. The Ungulata or hoofed quadrupeds are now divided into
the even-toed or odd-toed divisions; but the Macrauchenia of S.
America connects to a certain extent these two grand divisions.
No one will deny that the Hipparion is intermediate between the
existing horse and certain older ungulate forms. What a wonder-
ful connecting link in the chain of mammals is the Tyi^otherium
from S. America, as the name given to it by Professor Gervais
expresses, and which cannot be placed in any existing order.
The Sirenia form a very distinct group of mammals, and one of
the most remarkable peculiarities in the existing dugong and
lamentin is the entire absence of hind limbs without even
a rudiment being left ; but the extinct Halitherium had, according
to Professor Flower, an ossified thigh-bone " articulated to a well-
defined acetabulum in the pelvis," and it thus makes some approach
to ordinary hoofed quadrupeds, to which the Sirenia are in other
respects allied. The cetaceans or whales are" widely different
from all other mammals, but the tertiary Zeuglodon and Squalo-
don, which have been placed by some naturalists in an order by
themselves, are considered by Professor Huxley to be undoubtedly
cetaceans, " and to constitute connecting links with the aquatic
carnivora."

Even the wide interval between birds and reptiles has been
shown by the naturalist just quoted to be partially bridged over
in the most unexpected manner, on the one hand, by the ostrich
and extinct Archeopteryx, and on the other hand, by the Comp-
sognathus, one of the Dinosaurians — that group which includes
the most gigantic of all terrestrial reptiles. Turning to the
Invertebrata, Barrande asserts, and a higher authority could not
be named, that he is every day taught that, although palEeozoic

306 ORIGIN OF SPECIES

animals can certainly be classed under existing groups, yet that at
this ancient period the groups were not so distinctly separated
from each other as they now are.

Some writers have objected to any extinct species, or group of
species, being considered as intermediate between any two living
species, or groups of species. If by this term it is meant that an
extinct form is directly intermediate in all its characters between
two living forms or groups, the objection is probably valid. But
in a natural classification many fossil species certainly stand
between living species, and some extinct genera between living
genera, even between genera belonging to distinct families. The
most common case, especially with respect to very distinct groups,
such as fish and reptiles, seems to be, that, supposing them to be
distinguished at the present day by a score of characters, the
ancient members are separated by a somewhat lesser number of
characters; so that the two groups formerly made a somewhat
nearer approach to each other than they now do.

It is a common belief that the more ancient a form is, by so
much the more it tends to connect by some of its characters groups
now widely separated from each other. This remark no doubt
must be restricted to those groups which have undergone much
change in the course of geological ages; and it would be difficult
to prove the truth of the proposition, for every now and then
even a living animal, as the Lepidosiren, is discovered having
affinities directed towards very distinct groups. Yet if we com-
pare the older Keptiles and Batrachians, the older Fish, the older
Cephalopods, and the eocene Mammals, with the more recent mem-
bers of the same classes, we must admit that there is truth in
the remark.

Let us see how far these several facts and inferences accord
with the theory of descent with modification. As the subject
is somewhat complex, I must request the reader to turn to the
diagram in the fourth chapter. We may suppose that the num-
bered letters in italics represent genera; and the dotted lines
diverging from them the species in each genus. The diagram is
much too simple, too few genera and too few species being given,
but this is unimportant for us. The horizontal lines may rep-
resent successive geological formations, and all the forms beneath
the uppermost line may be considered as extinct. The three exist-
ing genera a^*, q^^, p", will form a small family ; ?>^* and f^ a closely
allied family or sub-family; and o^*, e^*, m^^ a third family.
These three families, together with the many extinct genera on
the several lines of descent diverging from the parent-form (A)
will form an order, for all will have inherited something in common

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 307

from tlieir ancient progenitor. On the principle of the continued
tendency to divergence of character, which was formerly illustrated
by this diagram, the more recent any form is, the more it will
generally differ from its ancient progenitor. Hence we can
understand the rule that the most ancient fossils differ most
from existing forms. We must not, however, assume that di-
vergence of character is a necessary contingency; it depends
solely on the descendants from a species being thus enabled to
seize on many and different places in the economy of nature.
Therefore it is quite possible, as we have seen in the case of some
Silurian forms, that a species might go on being slightly modified
in relation to its slightly altered conditions of life, and yet retain
throughout a vast period the same general characteristics. This
is represented in the diagram by the letter f^*.

All the many forms, extinct and recent, descended from (A),
make, as before remarked, one order; and this order, from the
continued effects of extinction and divergence of character, has
become divided into several sub-families and families, some of
which are supposed to have perished at different periods, and some
to have endured to the present day.

By looking at the diagram we can see that if many of the
extinct forms supposed to be imbedded in the successive forma-
tions, were discovered at several points low down in the series, the
three existing families on the uppermost line would be rendered
less distinct from each other. If, for instance, the genera a\ a,
a^", fy m, m, m, were disinterred, these three families would be
so closely linked together that they probably would have to be
united into one great family, in nearly the same manner as has
occurred with ruminants and certain pachyderms. Yet he who
objected to consider as intermediate the extinct genera, which thus
link together the living genera of three families, would be partly
ju^^tified, for they are intermediate, not directly, but only by a
long and circuitous course through many widely different forms.
If many extinct forms were to be discovered above one of the
middle horizontal lines or geological formations — for instance,
above No. VI. — -but none from beneath this line, then only two
of the families (those on the left hand, a", &c., and V^, &c.)
would have to be united into one; and there would remain two
families, which would be less distinct from each other than they
were before the discovery of the fossils. So again if the three
families formed of eight genera (a" to m"), on the uppermost
line, be supposed to differ from each other by half-a-dozen im-
portant characters, then the families which existed at the period
marked VI. would certainly have differed from each other by a less

308 ORIGIN OF SPECIES

number of characters; for they would at this early stage of
descent have diverged in a less degree from their common pro-
genitor. Thus it comes that ancient and extinct genera are often
in a greater or less degree intermediate in character betv^een
their modified descendants, or between their collateral relations.

Under nature the process will be far more complicated than
is represented in the diagram; for the groups will have been
more numerous; they will have endured for extremely unequal
lengths of time, and will have been modified in various degrees.
As we possess only the last volume of the geological record, and
that in a very broken condition, we have no right to expect, except
in rare cases, to fill up the wide intervals in the natural system,
and thus to unite distinct families or orders. All that we have
a right to expect is, that those groups which have, within known
geological periods, undergone much modification, should in the
older formations make some slight approach to each other; so
that the older members should differ less from each other in
some of their characters than do the existing members of the
same groups; and this by the concurrent evidence of our best
palasontologists is frequently the case.

Thus, on the theory of descent with modification, the main
facts with respect to the mutual afiinities of the extinct forms
of life to each other and to living forms, are explained in a
satisfactory manner. And they are wholly inexplicable on any
other view.

On this same theory, it is evident that the fauna during any one
great period in the earth's history will be intermediate in general
character between that which preceded and that which succeeded
it. Thus the species which lived at the sixth great stage of
descent in the diagram are the modified offspring of those which
lived at the fifth age, and are the parents of those which became
still more modified at the seventh stage; hence they could hardly
fail to be nearly intermediate in character between the forms
of life above and below. We must, however, allow for the entire
extinction of some preceding forms, and in any one region for
the immigration of new forms from other regions, and for a
large amount of modification during the long and blank intervals
between the successive formations. Subject to these allowances,
the fauna of each geological period undoubtedly is intermediate
in character, between the preceding and succeeding faunas. I
need give only one instance, namely, the manner in which the
fossils of the Devonian system, when this system was first dis-
covered, were at once recognised by palaeontologists as inter-
mediate in character between those of the overlying carboniferous,

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 309

and underlying Silurian systems. But each fauna is not neces-
sarily exactly intermediate, as unequal intervals of time have
elapsed between consecutive formationsi.

It is no real objection to the truth of the statement that the
fauna of each period as a whole is nearly intermediate in charac-
ter between the preceding and succeeding faunas, that certain
genera offer exceptions to the rule. For instance, the species of
mastodons and elephants, when arranged by Dr. Falconer in two
series, — in the first place according to their mutual affinities,
and in the second place according to their periods of existence,
— do not accord in arrangement. The species extreme in character
are not the oldest or the most recent; nor are those which are
intermediate in character, intermediate in age. But supposing
for an instant, in this and other such cases, that the record
of the first appearance and disappearance of the species was
complete, which is far from the case, we have no reason to believe
that forms successively produced necessarily endure for corre-
sponding lengths of time. A very ancient form may occasionally
have lasted much longer than a form elsewhere subsequently
produced, especially in the case of terrestrial productions inhabit-
ing separated districts. To compare small things with great;
if the principal living and extinct races of the domestic pigeon
were arranged in serial affinity, this arrangement would not
closely accord with the order in time of their production, and
even less with the order of their disappearance; for the parent
rock-pigeon still lives; and many varieties between the rock-
pigeon and the carrier have become extinct ; and carriers which are
extreme in the important character of length of beak originated
earlier than short-beaked tumblers, which are at the opposite end
of the series in this respect.

Closely connected with the statement, that the organic remains
from an intermediate formation are in some degree intermediate
in character, is the fact, insisted on by all palaeontologists, that
fossils from two consecutive formations are far more closely re-
lated to each other, than are the fossils from two remote forma-
tions. Pictet gives as a well-known instance, the general resem-
blance of the organic remains from the several stages of the
Chalk formation, though the species are distinct in each stage.
This fact alone, from its generality, seems to have shaken Pro-
fessor Pictet in his belief in the immutability of species. He who
is acquainted with the distribution of existing species over the
globe, will not attempt to account for the close resemblance of
distinct species in closely consecutive formations, by the physical
conditions of the ancient areas having remained nearly the same.

310 ORIGIN OF SPECIES

Let it be remembered that the forms of life, at least those inhabit-
ing the sea, have changed almost simultaneously throughout the
world, and therefore under the most different climates and condi-
tions. Consider the prodigious vicissitudes of climate during
the pleistocene period, which includes the whole glacial epoch,
and note how little the specific forms of the inhabitants of the
sea have been affected.

On the theory of descent, the full meaning of the fossil remains
from closely consecutive formations being closely related, though
ranked as distinct species, is obvious. As the accumulation of
each formation has often been interrupted, and as long blank
intervals have intervened between successive formations, we ought
not to expect to find, as I attempted to show in the last chapter,
in any one or in any two formations, all the intermediate varieties
between the species which appeared at the commencement and
close of these periods : but we ought to find after intervals, very
long as measured by years, but only moderately long as measured
geologically, closely allied forms, or, as they have been called
by some authors, representative species; and these assuredly we do
find. We find, in short, such evidence of the slow and scarcely
sensible mutations of specific forms, as we have the right to expect.

On the State of Development of Ancient compared with Living

Forms.

We have seen in the fourth chapter that the degree of differen-
tiation and specialisation of the parts in organic beings, when
arrived at maturity, is the best standard, as yet suggested, of their
degree of perfection or highness. We have also seen that, as
the specialisation of parts is an advantage to each being, so
natural selection will tend to render the organisation of each
being more specialised and perfect, and in this sense higher; not
but that it may leave many creatures with simple and unimproved
structures fitted for simple conditions of life, and in some cases
will even degrade or simplify the organisation, yet leaving such
degraded beings better fitted for their new walks of life. In
another and more general manner, new species become superior
to their predecessors; for they have to beat in the struggle for life
all the older forms, with which they come into close competition.
We may therefore conclude that if under a nearly similar climate
the eocene inhabitants of the world could be put into competition
with the existing inhabitants, the former would be beaten and
exterminated by the latter, as would the secondary by the eocene,
and the palseozoic by the secondary forms. So that by this funda-

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 311

mental test of victory in the battle for life, as well as by the
standard of the specialisation of organs, modern forms ought, on
the theory of natural selection, to stand higher than ancient
forms. Is this the case? A large majority of palaeontologists
would answer in the affirmative; and it seems that this answer
must be admitted as true, though difficult of proof.

It is no valid objection to this conclusion, that certain Brachio-
pods have been but slightly modified from an extremely remote
geological epoch; and that certain land and fresh-water shells
have remained nearly the same, from the time when, as far as is
known, they first appeared. It is not an insuperable difficulty that
Foraminifera have not, as insisted on by Dr. Carpenter, progressed
in organisation since even the Laurentian epoch; for some organ-
isms would have to remain fitted for simple conditions of life,
and what could be better fitted for this end than these lowly
organised Protozoa? Such objections as the above would be
fatal to my view, if it included advance in organisation as a neces-
sary contingent. They would likewise be fatal, if the above Fora-
minifera, for instance, could be proved to have first come into
existence during the Laurentian epoch, or the above Brachiopods
during the Cambrian formation ; for in this case, there would not
have been time sufficient for the development of these organisms
up to the standard which they had then reached. When advanced
up to any given point, there is no necessity, on the theory of
natural selection, for their further continued progress; though
they will, during each successive age, have to be slightly modified,
so as to hold their places in relation to slight changes in their
conditions. The foregoing objections hinge on the question whether
we really know how old the world is, and at what period the
various forms of life first appeared ; and this may well be disputed.

The problem whether organisation on the whole has advanced
is in many ways excessively intricate. The geological record, at
all times imperfect, does not extend far enough back, to show with
unmistakeable clearness that within the known history of the
world organisation has largely advanced. Even at the present
day, looking to members of. the same class, naturalists are not
unanimous wdiich forms ought to be ranked as highest : thus,
some look at the selaceans or sharks, from their approach in some
important points of structure to reptiles, as the highest fish ; others
look at the teleosteans as the highest. The ganoids stand inter-
mediate between the selaceans and teleosteans ; the latter at the
present day are largely preponderant in number; but formerly
selaceans and ganoids alone existed ; and in this case, according to
the standard of highness chosen, so will it be said that fishes have

312 ORIGIN OF SPECIES

advanced or retrograded in organisation. To attempt to compare
members of distinct types in the scale of highness seems hopeless;
who will decide whether a cuttle-fish be higher than a bee — that
insect which the great Von Baer believed to be " in fact more
highly organised than a fish, although upon another type " ? In
the complex struggle for life it is quite credible that crustaceans,
not very high in their own class, might beat cephalopods, the
highest molluscs; and such crustaceans, though not highly de-
veloped, would stand very high in the scale of invertebrate ani-
mals, if Judged by the most decisive of all trials — the law of
battle. Besides these inherent difficulties in deciding which forms
are the most advanced in organisation, we ought not solely to
compare the highest members of a class at any two periods —
though undoubtedly this is one and perhaps the most important
element in striking a balance — but we ought to compare all the
members, high and low, at the two periods. At an ancient epoch
the highest and lowest molluscoidal animals, namely, cephalopods
and brachiopods, swarmed in numbers; at the present time both
groups are greatly reduced, whilst others, intermediate in organisa-
tion, have largely increased; consequently some naturalists main-
tain that molluscs were formerly more highly developed than at
present; but a stronger case can be made out on the opposite
side, by considering the vast reduction of brachiopods, and the
fact that our existing cephalopods, though few in number, are,
more highly organised than their ancient representatives. We ought
also to compare the relative proportional numbers at any two
periods of the high and low classes throughout the world; if, for
instance, at the present day fifty thousand kinds of vertebrate
animals exist, and if we knew that at some former period only ten
thousand kinds existed, we ought to look at this increase in num-
ber in the highest class, which implies a great displacement of
lower forms, as a decided advance in the organisation of the
world. We thus see how hopelessly difficult it is to compare with
perfect fairness under such extremely complex relations, the stand-
ard of organisation of the imperfectly-known faunas of successive
periods.

We shall appreciate this difficulty more clearly, by looking to
certain existing faunas and floras. From the extraordinary man-
ner in which European productions have recently spread over
New Zealand, and have seized on places which must have been
previously occupied by the indigenes, we must believe, that if all
the animals and plants of Great Britain were set free in New
Zealand, a multitude of British forms would in the course of
time become thoroughly naturalised there, and would exterminate

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 313

many of the natives. On the other hand, from the fact that hardly
a single inhabitant of the southern hemisphere has become wild
in any part of Europe, we may well doubt whether, if all the
productions of New Zealand were set free in Great Britain, any
considerable number would be enabled to seize on places now
occupied by our native plants and animals. Under this point of
view, the productions of Great Britain stand much higher in
the scale than those of New Zealand. Yet the most skilful
naturalist, from an examination of the species of the two coun-
tries, could not have foreseen this result.

Agassiz and several other highly competent judges insist that
ancient animals resemble to a certain extent the embryos of recent
animals belonging to the same classes; and that the geological
succession of extinct forms is nearly parallel with the embryo-
logical development of existing forms. This view accords ad-
mirably well with our theory. In a future chapter I shall attempt
to show that the adult differs from its embryo, owing to variations
having supervened at a not early age, and having been inherited
at a corresponding age. This process, whilst it leaves the embryo
almost unaltered, continually adds, in the course of successive
generations, more and more difference to the adult. Thus the
embryo comes to be left as a sort of picture, preserved by nature,
of the former and less modified condition of the species. This
view may be true, and yet may never be capable of proof. Seeing
for instance, that the oldest known mammals, reptiles, and fishes
strictly belong to their proper classes, though some of these old
forms are in a slight degree less distinct from each other than
are the typical members of the same groups at the present day, it
would be vain to look for animals having the common embryolog-
ical character of the Vertebrata, until beds rich in fossils are
discovered far beneath the lowest Cambrian strata — a discovery of
which the chance is small.

On the Succession of the same Types within the same Areas,
during the later Tertiary periods.

Mr. Clift many years ago showed that the fossil mammals
from the Australian caves were closely allied to the living marsu-
pials of that continent. In South America a similar relationship
is manifest, even to an uneducated eye, in the gigantic pieces
of armour, like those of the armadillo, found in several parts
of La Plata ; and Professor Owen has shown in the most striking
manner that most of the fossil mammals, buried there in such
numbers, are related to South American types. This relationship

314 ORIGIN OF SPECIES

is even more clearly seen in tlie wonderful collection of fossil bones
made by MM. Lund and Clausen in the caves of Brazil. I v^as
so much impressed with these facts that I strongly insisted, in
1839 and 1845, on this " law of the succession of types," — on
" this wonderful relationship in the same continent between the
dead and the living." Professor Owen has subsequently extended
the same generalisation to the mammals of the Old World. We
see the same law in this author's restorations of the extinct and
gigantic birds of New Zealand. We see it also in the birds of the
caves of Brazil. Mr. Woodward has shown that the same law
holds good with sea-shells, but, from the wide distribution of
most molluscs, it is not well displayed by them. Other cases could
be added, as the relation between the extinct and living land-shells
of Madeira; and between the extinct and living brackish water-
shells of the Aralo-Caspian Sea.

Now what does this remarkable law of the succession of the
same types within the same areas mean? He would be a bold
man who, after comparing the present climate of Australia and
of parts of South America, under the same latitude, would attempt
to account, on the one hand through dissimilar physical condi-
tions, for the dissimilarity of the inhabitants of these two con-
tinents; and, on the other hand through similarity of conditions,
for the uniformity of the same types in each continent during
the later tertiary periods. Nor can it be pretended that it is an
immutable law that marsupials should have been chiefly or solely
produced in Australia; or that Edentata and other American
types should have been solely produced in South America. For
we know that Europe in ancient times was peopled by numerous
marsupials ; and I have shown in the publications above alluded to,
that in America the law of distribution of terrestrial mammals
was formerly different from what it now is. North America
formerly partook strongly of the present character of the southern
half the continent; and the southern half was formerly more
closely allied, than it is at present, to the northern half. In a
similar manner we know, from Falconer and Cautley's discoveries,
that Northern India was formerly more closely related in its
mammals to Africa than it is at the present time. Analogous
facts could be given in relation to the distribution of marine
animals.

On the theory of descent with modification, the great law
of the long enduring, but not immutable, succession of the
same types within the same areas, is at once explained; for the
inhabitants of each quarter of the world will obviously tend to
leave in that quarter, during the next succeeding period of time,

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 315

closely allied though in some degree modified descendants. If
the inhabitants of one continent formerly differed greatly from
those of another continent, so will their modified descendants
still differ in nearly the same manner and degree. But after very
long intervals of time, and after great geographical changes, per-
mitting much intermigration, the feebler will yield to the more
dominant forms, and there will be nothing immutable in the dis-
tribution of organic beings.

It may be asked in ridicule, whether I suppose that the mega-
therium and other allied huge monsters, which formerly lived
in South America, have left behind them the sloth, armadillo,
and anteater, as their degenerate descendants. This cannot for
an instant be admitted. These huge animals have become wholly
extinct, and have left no progeny. But in the caves of Brazil,
there are many extinct species which are closely allied in size
and in all other characters to the species still living in South
America ; and some of these fossils may have been the actual pro-
genitors of the living species. It must not be forgotten that, on
our theory, all the species of the same genus are the descendants of
some one species; so that, if six genera, each having eight species,
be found in one geological formation, and in a succeeding forma-
tion there be six other allied or representative genera each with
the same number of species, then we may conclude that generally
only one species of each of the older genera has left modified
descendants, which constitute the new genera containing the
several species; the other seven species of each old genus having
died out and left no progeny. Or, and this will be a far commoner
case, two or three species in two or three alone of the six older
genera will be the parents of the new genera : the other species and
the other old genera having become utterly extinct. In failing
orders, with the genera and species decreasing in numbers as is
the case with the Edentata of South America, still fewer genera
and species will leave modified blood-descendants.

Summary of the preceding and present Chapters,

I have attempted to show that the geological record is extremely
imperfect; that only a small portion of the globe has been geolog-
ically explored with care; that only certain classes of organic
beings have been largely preserved in a fossil state; that the
number both of specimens and of species, preserved in our muse-
ums, is absolutely as nothing compared with the number of gen-
erations which must have passed away even during a single forma-
tion; that, owing to subsidence being almost necessary for the

31G ORIGIN OP SPECIES

accumulation of deposits rich in fossil species of many kinds, and
thick enough to outlast future degradation, great intervals of
time must have elapsed between most of our successive formations ;
that there has probably been more extinction during the periods
of subsidence, and more variation during the periods of elevation,
and during the latter the record will have been less perfectly
kept; that each single formation has not been continuously de-
posited; that the duration of each formation is probably short
compared with the average duration of specific forms; that mi-
gration has played an important part in the first appearance of
new forms in any one area and formation; that widely ranging
species are those which have varied most frequently, and have
oftenest given rise to new species; that varieties have at first
been local; and lastly, although each species must have passed
through numerous transitional stages, it is probable that the
periods, during which each underwent modification, though many
and long as measured by years, have been short in comparison
with the periods during which each remained in an unchanged
condition. These causes, taken conjointly, will to a large extent
explain why — though we do find many links — we do not find
interminable varieties, connecting together all extinct and existing
forms by the finest graduated steps. It should also be constantly
borne in mind that any linking variety between two forms, which
might be found, would be ranked, unless the whole chain could
be perfectly restored, as a new and distinct species; for it is not
pretended that we have any sure criterion by which species and
varieties can be discriminated.

He who rejects this view of the imperfection of the geological
record, will rightly reject the whole theory. For he may ask in
vain where are the numberless transitional links which must
formerly have connected the closely allied or representative spe-
cies, found in the successive stages of the same great formation?
He may disbelieve in the immense intervals of time which must
have elapsed between our consecutive formations; he may overlook
how important a part migration has played, when the formations
of any one great region, as those of Europe, are considered ; he may
urge the apparent, but often falsely apparent, sudden coming in
of whole groups of species. He may ask where are the remains
of those infinitely numerous organisms which must have existed
long before the Cambrian system was deposited? We now know
that at least one animal did then exist; but I can answer this last
question only by supposing that where our oceans now extend they
have extended for an enormous period, and where our oscillating
continents now stand they have stood since the commencement

GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 317

of the Cambrian system ; but that, long before the epoch, the
world presented a widely different aspect; and that the older con-
tinents formed of formations older than any known to "us, exist
now only as remnants in a metamorphosed condition, or lie still
buried under the ocean.

Passing from these difiiculties, the other great leading facts
in palaeontology agree admirably with the theory of descent with
modification through variation and natural selection. We can thus
understand how it is that new species come in slowly and succes-
sively; how species of different classes do not necessarily change
together, or at the same rate, or in the same degree; yet in the
long run that all undergo modification to some extent. The
extinction of old forms is the almost inevitable consequence of
the production of new forms. We can understand why, when a
species has once disappeared, it never reappears. Groups of spe-
cies increase in numbers slowly, and endure for unequal periods
of time; for the process of modification is necessarily slow, and
depends on many complex contingencies. The dominant species
belonging to large and dominant groups tend to leave many modi-
fied descendants, which form new sub-groups and groups. As
these are formed, the species of the less vigorous groups, from
their inferiority inherited from a common progenitor, tend to be-
come extinct together, and to leave no modified offspring on the
face of the earth. But the utter extinction of a whole group of
species has sometimes been a slow process, from the survival of a
few descendants, lingering in protected and isolated situations.
When a group has once wholly disappeared, it does not reappear;
for the link of generation has been broken.

We can understand how it is that dominant forms which spread
widely and yield the greatest number of varieties tend to people
the world with allied, but modified, descendants; and these will
generally succeed in displacing the groups which are their inferiors
in the struggle for existence. Hence, after long intervals of time,
the productions of the world appear to have changed simultane-
ously.

We can understand how it is that all the forms of life, ancient
and recent, make together a few grand classes. We can under-
stand, from the continued tendency to divergence of character,
why the more ancient a form is, the more it generally differs from
those now living; why ancient and extinct forms often tend to fill
up gaps between existing forms, sometimes blending two groups,
previously classed as distinct, into one; but more commonly bring-
ing them only a little closer together. The more ancient a form is,
the more often it stands in some degree intermediate between

318 ORIGIN OP SPECIES

groups now distinct; for the more ancient a form is, the more
nearly it will be related to, and consequently resemble, the common
progenitor of groups, since become widely divergent. Extinct
forms are seldom directly intermediate between existing forms;
but are intermediate only by a long and circuitous course through
other extinct and different forms. We can clearly see why the or-
ganic remains of closely consecutive formations are closely allied:,
for they are closely linked together by generation. We can clearly
see why the remains of an intermediate formation are intermediate
in character.

The inhabitants of the world at each successive period in its
history have beaten their i:»redecessors in the race for life, and are,
in so far, higher in the scale, and their structure has generally be-
come more specialised; and this may account for the common be-
lief held by so many palaeontologists, that organisation on the
whole has progressed. Extinct and ancient animals resemble to
a certain extent the embryos of the more recent animals belonging
to the same classes, and this wonderful fact receives a simple ex-
planation according to our views. The succession of the same
types of structure within the same areas during the later geological
periods ceases to be mysterious, and is intelligible on the principle
of inheritance.

If then the geological record be as imperfect as many believe, and
it may at least be asserted that the record cannot be proved to be
much more perfect, the main objections to the theory of natural
selection are greatly diminished or disappear. On the other hand,
all the chief laws of palseontology plainly proclaim, as it seems
to me, that species have been produced by ordinary generation :
old forms having been supplanted by new and improved forms of
life, the products of Variation and the Survival of the Fittest.

GEOGRAPHICAL DISTRIBUTION 319

OHAPTEE XII.

GEOGRAPHICAL DISTRIBUTION.

Present distribution cannot be accounted for by differences in physical
conditions — Importance of barriers — Affinity of the productions of
the same continent — Centres of creation — Means of dispersal by
changes of climate and of the level of the land, and by occasional
means — Dispersal during the Glacial period — Alternate Glacial
periods in the North and South.

IN considering the distribution of organic beings over the face
of the globe, the first great fact which strikes us is, that
neither the similarity nor the dissimilarity of the inhabitants
of various regions can be wholly accounted for by climatal and
other physical conditions. Of late, almost every author who has
studied the subject has come to this conclusion. The case of
America alone would almost suffice to prove its truth; for if we
exclude the arctic and northern temperate parts, all authors agree
that one of the most fundamental divisions in geographical dis-
tribution is that between the New and Old Worlds; yet if we
travel over the vast American continent, from the central parts of
the United States to its extreme southern point, we meet with the
most diversified conditions; humid districts, arid deserts, lofty
mountains, grassy plains, forests, marshes, lakes, and great rivers,
under almost every temperature. There is hardly a climate or
condition in the Old World which cannot be paralleled in the New
— at least as closely as the same species generally require. No
doubt small areas can be pointed out in the Old World hotter than
any in the New World; but these are not inhabited by a fauna
different from that of the surrounding districts; for it is rare to
find a group of organisms confined to a small area, of which the
conditions are peculiar in only a slight degree. Notwithstanding
this general parallelism in the conditions of the Old and New
Worlds, how widely different are their living productions!

In the southern hemisphere, if we compare large tracts of land
in Australia, South Africa, and western South America, between
latitudes 25° and 35°, we shall find parts extremely similar in all
their conditions, yet it would not be possible to point out three
faunas and floras more utterly dissimilar. Or, again, we may

320 ORIGIN OF SPECIES

compare the productions of South America south of lat. 35° with
those north of 25°, which consequently are separated by a space of
ten degrees of latitude, and are exposed to considerably different
conditions; yet they are incomparably more closely related to each
other than they are to the productions of Australia or Africa
under nearly the same climate. Analogous facts could be given
with respect to the inhabitants of the sea.

A second great fact which strikes us in our general review is,
that barriers of any kind, or obstacles to free migration, are re-
lated in a close and important manner to the differences between
the productions of various regions. We see this in the great dif-
ference in nearly all the terrestrial productions of the New and
Old Worlds, excepting in the northern parts, where the land almost
joins, and where, under a slightly different climate, there might
have been free migration for the- northern temperate forms, as
there now is for the strictly arctic productions. We see the same
fact in the great difference between the inhabitants of Australia,
Africa, and South America under the same latitude; for these
countries are almost as much isolated from each other as is pos-
sible. On each continent, also, we see the same fact; for on the
opposite sides of lofty and continuous mountain-ranges, of great
deserts and even of large rivers, we find different productions;
though as mountain-chains, deserts, &c., are not as impassable, or
likely to have endured so long, as the oceans separating continents,
the differences are very inferior in degree to those characteristic
of distinct continents.

Turning to the sea, we find the same law. The marine in-
habitants of the eastern and western shores of South America are
very distinct, with extremely few shells, Crustacea, or echinoder-
mata in common; but Dr. Giinther has recently shown that about
thirty per cent, of the fishes are the same on the opposite sides of
the isthmus of Panama ; and this fact has led naturalists to believe
that the isthmus was formerly open. Westward of the shores of
America, a wide space of open ocean extends, with not an island as
a halting-place for emigrants; here we have a barrier of another
kind, and as soon as this is passed we meet in the eastern islands
of the Pacific with another and totally distinct fauna. So that
three marine faunas range far northward and southward in parallel
lines not far from each other, under corresponding climates; but
from being separated from each other by impassable barriers, either
of land or open sea, they are almost wholly distinct. On the other
hand, proceeding still farther westward from the eastern islands
of the tropical parts of the Pacific, we encounter no impassable
barriers, and we have innumerable islands as halting-places, or

GEOGRAPHICAL DISTRIBUTION 321

continuous coasts, until, after travelling over a hemisphere, we
come to the shores of Africa; and over this vast space we meet
with no well-defined and distinct marine faunas. Although so few
marine animals are common to the above-named three approximate
faunas of Eastern and Western America and the Eastern Pacific
islands, yet many fishes range from the Pacific into the Indian
Ocean, and many shells are common to the eastern islands of the
Pacific and the eastern shores of Africa on almost exactly opposite
meridians of longitude.

A third great fact partly included in the foregoing statement,
is the affinity of the productions of the same continent or of the
same sea, though the species themselves are distinct at different
points and stations. It is a law of the widest generality, and every
continent offers innumerable instances. Nevertheless the natural-
ist, in travelling, for instance, from north to south, never fails to
be struck by the manner in which successive groups of beings,
specifically distinct, though nearly related, replace each other. He
hears from closely allied, yet distinct kinds of birds, notes nearly
similar, and sees their nests similarly constructed, but not quite
alike, with eggs coloured in nearly the same manner. The plains
near the Straits of Magellan are inhabited by one species of Rhea
(American ostrich) and northward the plains of La Plata by an-
other species of the same genus ; and not by a true ostrich or emu,
like those inhabiting Africa and Australia under the same latitude.
On these same plains of La Plata we see the agouti and bizcacha,
animals having nearly the same habits as our hares and rabbits,
and belonging to the same order of Rodents, but they plainly dis-
play an American type of structure. We ascend the lofty peaks
of the Cordillera, and we find an alpine species of bizcacha; we
look to the waters, and we do not find the beaver or musk-rat, but
the coypu and capybara, rodents of the S. American tyije. Innu-
merable other instances could be given. If we look to the islands
off the American shore, however much they may differ in geological
structure, the inhabitants are essentially American, though they
may be all peculiar species. We may look back to past ages, as
shown in the last chapter, and we find American types then prevail-
ing on the American continent and in the American seas. We
see in these facts some deep organic bond, throughout space and
time, over the same areas of land and water, independently of
physical conditions. The naturalist must be dull who is not led
to enquire what this bond is.

The bond is simply inheritance, that cause which alone, as far
as we positively know, produces organisms quite like each other,
or, as we see in the case cf varieties, nearly alike. The dissimilar-

322 ORIGIN OF SPECIES

ity of the inhabitants of different regions may be attributed to
modification through variation and natural selection, and probably
in a subordinate degree to the definite influence of different phys-
ical conditions. The degrees of dissimilarity will depend on the
migration of the m,ore dominant forms of life from one region into
another having been more or less effectually prevented, at periods
more or less remote ; — on the nature and number of the former
immigrants ; — and on the action of the inhabitants on each othei
in leading to the preservation of different modifications; the rela-
tion of organism to organism in the struggle for life being, as I
have already often remarked, the most important of all relations.
Thus the high importance of barriers comes into play by checking
migration; as does time for the slow process of modification
through natural selection. Widely-ranging species, abounding in
individuals, which have already triumphed over many competitors
in their own widely-extended homes, will have the best chance of
seizing on new places, when they spread into new countries. In
their new homes they will be exposed to new conditions, and will
frequently undergo further modification and improvement; and
thus they will become still further victorious, and will produce
groups of modified descendants. On this principle of inheritance
with modification we can understand how it is that sections of
genera, whole genera, and even families, are confined to the same
areas, as is so commonly and notoriously the case.

There is no evidence, as was remarked in the last chapter, of the
existence of any law of necessary development. As the variability
of each species is an independent property, and will be taken ad-
vantage of by natural selection, only so far as it profits each indi-
vidual in its complex struggle for life, so the amount of modifica-
tion in different species will be no uniform quantity. If a number
of species, after having long competed with each other in their old
home, were to migrate in a body into a new and afterwards isolated
country, they would be little liable to modification; for neither
migration nor isolation in themselves effect anything. These prin-
ciples come into play only by bringing organisms into new rela-
tions with each other and in a lesser degree with the surrounding
physical conditions. As we have seen in the last chapter that
some forms have retained nearly the same character from an
enormously remote geological period, so certain species have mi-
grated over vast spaces, and have not become greatly or at all
modified.

According to these views, it is obvious that the several species
of the same genus, though inhabiting the most distant quarters of
the world, must originally have proceeded from the same source,

GEOGRAPHICAL DISTRIBUTION 323

as they are descended from the same progenitor. In the case of
those species which have undergone during whole geological pe-
riods little modification, there is not much difficulty in believing
that they have migrated from the same region ; for during the vast
geographical and climatal changes which have supervened since
ancient times, almost any amount of migration is possible. But
in many other cases, in which we have reason to believe, that the
species of a genus have been produced within comparatively recent
times, there is great difficulty on this head. It is also obvious that
the individuals of the same species, though now inhabiting distant
and isolated regions, must have proceeded from one spot, where
their parents were first produced: for, as has been explained, it is
incredible that individuals identically the same should have been
produced from parents specifically distinct.

Single Centres of supposed Creation. — We are thus brought to
the question which has been largely discussed by naturalists, name-
ly, whether species have been created at one or more points of the
earth's surface. Undoubtedly there are many cases of extreme
difficulty in understanding how the same species could possibly
have migrated from some one point to the several distant and
isolated points where now found. Nevertheless the simplicity of
the view that each species was first produced within a single region
captivates the mind. He who rejects it, rejects the vera causa of
ordinary generation with subsequent migration, and calls in the
agency of a miracle. It is universally admitted, that in most cases
the area inhabited by a species is continuous; and that when a
plant or animal inhabits two points so distant from each other, or
with an interval of such a nature, that the space could not have
been easily passed ove^* by migration, the fact is given as some-
thing remarkable and exceptional. The incapacity of migrating
across a wide sea is more clear in the case of terrestrial mammalv5
than perhaps with any other organic beings; and, accordingly, we
find no inexplicable instances of the same mammals inhabiting
distant points of the world. No geologist feels any difficulty in
Great Britain possessing the same quadrupeds with the rest of Eu-
rope, for they were no doubt once united. But if the same species
can be produced at two separate points, why do we not find a
single mammal common to Europe and Australia or South Amer-
ica ? The conditions of life are nearly the same, so that a multi-
tude of European animals and plants have become naturalised in
America and Australia ; and some of the aboriginal plants are
identically the same at these distant points of the northern and
southern hemispheres ? The answer, as I believe, is, that mammals
have not been able to migrate, whereas some plants, from their

324 ORIGIN OF SPECIES

varied means of dispersal, have migrated across the wide and
broken interspaces. The great and striking influence of barriers of
all kinds, is intelligible only on the view that the great majority
of species have been produced on one side, and have not been able
to migrate to the opposite side. Some few families, many sub-
families, very many genera, and a still greater number of sections
of genera, are confined to a single region ; and it has been observed
by several naturalists that the most natural genera, or those
genera in which the species are most closely related to each other,
are generally confined to the same country, or if they have a wide
range that their range is continuous. What a strange anomaly
it would be, if a directly opposite rule were to prevail, when we go
down one step lower in the series, namely, to the individuals of the
same species, and these had not been, at least at first, confined to
some one region !

Hence it seems to me, as it has to many other naturalists, that
the view of each species having been produced in one area alone,
and having subsequently migrated from that area as far as its
powers of migration and subsistence under past and present con-
ditions permitted, is the most probable. Undoubtedly many cases
occur, in which we cannot explain how the same species could have
passed from one point to the other. But the geographical and
climatal changes which have certainly occurred within recent geo-
logical times, must have rendered discontinuous the formerly con-
tinuous range of many species. So that we are reduced to consider
whether the exceptions to continuity of range are so numerous and
of so grave a nature, that we ought to give up the belief, rendered
probable by general considerations, that each species has been pro-
duced within one area, and has migrated thence as far as it could.
It would be hopelessly tedious to discuss all the exceptional cases
of the same species, now living at distant and separated points, nor
do I for a moment pretend that any explanation could be offered
of many instances. But, after some preliminary remarks, I will
discuss a few of the most striking classes of facts; namely, the
existence of the same species on the summits of distant mountain
ranges, and at distant points in the arctic and antarctic regions;
and secondly (in the following chapter), the wide distribution of
freshwater productions; and thirdly, the occurrence of the same
terrestrial species on islands and on the nearest mainland, though
separated by hundreds of miles of open sea. If the existence of
the same species at distant and isolated points of the earth's sur-
face, can in many instances be explained on the view of each spe-
cies having migrated from a single birthplace; then, considering
our ignorance with respect to former climatal and geographical

GEOGRAPHICAL DISTPaBUTION 325

changes and to the various occasional means of transport, the be-
lief that a single birthplace is the law, seems to me incomparably
the safest.

In discussing this subject, we shall be enabled at the same time
to consider a point equally important for us, namely, whether the
several species of a genus which must on our theory all be de-
scended from a common progenitor, can have migrated, undergoing
modification during their migration, from some one area. If,
when most of the species inhabiting one region are different from
those of another region, though closely allied to them, it can be
shown that migration from the one region to the other has probably
occurred at some former period, our general view will be much
strengthened; for the explanation is obvious on the principle of
descent with modification. A volcanic island, for instance, up-
heaved and formed at the distance of a few hundreds of miles from
a continent, would probably receive from it in the course of time a
few colonists, and their descendants, though modified, would still
be related by inheritance to the inhabitants of that continent.
Cases of this nature are common, and are, as we shall hereafter
see, inexplicable on the theory of independent creation. This view
of the relation of the species of one region to those of another,
does not differ much from that advanced by Mr. Wallace, who
concludes that " every species has come into existence coincident
both in space and time with a pre-existing closely allied species."
And it is now well known that he attributes this coincidence to
descent with modification.

The question of single or multiple centres of creation differs
from another though allied question, — namely, whether all the in-
dividuals of the same species are descended from a single pair, or
single hermaphrodite, or whether, as some authors suppose, from
many individuals simultaneously created. With organic beings
which never intercross, if such exist, each species must be de-
scended from a succession of modified varieties, that have sup-
planted each other, but have never blended with other individuals
or varieties of the same species; so that, at each successive stage
of modification, all the individuals of the same form will be de-
scended from a single parent. But in the great majority of cases,
namely, with all organisms which habitually unite for each birth,
or which occasionally intercross, the individuals of the same spe-
cies inhabiting the same area will be kept nearly uniform by inter-
crossing; so that many individuals will go on simultaneously
changing, and the whole amount of modification at each stage will
not be due to descent from a single parent. To illustrate what I
mean : our English race-horses differ from the horses of every other

326 ORIGIN OF SPECIES

breed; but they do not owe their difference and superiority to
descent from any single pair, but to continued care in the selecting
and training of many individuals during each generation.

Before discussing the three classes of facts, which I have selected
as presenting the greatest amount of difficulty on the theory of
" single centres of creation," I must say a few words on the means
of dispersal.

Means of Dispersal.

Sir C. Lyell and other authors have ably treated this subject. I
can give here only the briefest abstract of the more important
facts. Change of climate must have had a powerful influence on
migration. A region now impassable to certain organisms from
the nature of its climate, might have been a high road for migra-
tion, when the climate was different. I shall, however, presently
have to discuss this branch of the subject in some detail. Changes
of level in the land must also have been highly influential: a nar-
row isthmus now separates two marine faunas; submerge it, or let
it formerly have been submerged, and the two faunas will now
blend together, or may formerly have blended. Where the sea now
extends, land may at a former period have connected islands or pos-
sibly even continents together, and thus have allowed terrestrial
productions to pass from one to the other. No geologist disputes
that great mutations of level have occurred within the period of
existing organisms. Edward Forbes insisted that all the islands in
the Atlantic must have been recently connected with Europe or
Africa, and Europe likewise with America. Other authors have
thus hypothetically bridged over every ocean, and united almost
every island with some mainland. If indeed the arguments used
by Forbes are to be trusted, it must be admitted that scarcely a
single island exists which has not recently been united to some con-
tinent. This view cuts the Gordian knot of the dispersal of the
same species to the more distant points, and removes many a diffi-
culty; but to the best of my judgment we are not authorised in
admitting such enormous geographical changes within the period of
existing species. It seems to me that we have abundant evidence
of great oscillations in the level of the land or sea; but not of such
vast changes in the position and extension of our continents, as to
have united them within the recent period to each other and to the
several intervening oceanic islands. I freely admit the former ex-
istence of many islands, now buried beneath the sea, which may
have served as halting-places for plants and for many animals dur-
ing their migration. In the coral-producing oceans such sunken

GEOGRAPHICAL DISTRIBUTION 327

islands are now marked by rings of coral or atolls standing over
them. Whenever it is fully admitted, as it will some day be, that
each species has proceeded from a single birthplace, and when in
the course of time we know something definite about the means of
distribution, we shall be enabled to speculate with security on the
former extension of the land. But I do not believe that it will
ever be proved that within the recent period most of our contineuLs
which now stand quite separate have been continuously, or almost
continuously united with each other, and with the many existing
oceanic islands. Several facts in distribution, — such as the great
difference in the marine faunas on the opposite sides of almost
every continent, — the close relation of the tertiary inhabitants
of several lands and even seas to their present inhabitants, — the
degree of affinity between the mammals inhabiting islands with
those of the nearest continent, being in part determined (as we
shall hereafter see) by the depth of the intervening ocean, — these
and other such facts are opposed to the admission of such pro-
digious geographical revolutions within the recent period, as are
necessary on the view advanced by Forbes and admitted by his fol-
lowers. The nature and relative proportions of the inhabitants of
oceanic islands are likewise opposed to the belief of their former
continuity with continents. Nor does the almost universally vol-
canic composition of such islands favour the admission that they
are the wrecks of sunken continents ; — if they had originally ex-
isted as continental mountain ranges, some at least of the islands
would have been formed, like other mountain summits, of granite,
metamorphic schists, old fossiliferous and other rocks, instead of
consisting of mere piles of volcanic matter.

I must now say a few words on what are called accidental means,
but which more properly should be called occasional means of dis-
tribution. I shall here confine myself to plants. In botanic;-)!
works, this or that plant is often stated to be ill adapted for wide
dissemination ; but the greater or less facilities for transport across
the sea may be said to be almost wholly unknown. Until I tried,
with Mr. Berkeley's aid, a few experiments, it was not even known
how far seeds could resist the injurious action of sea-water. To
my surprise I found that out of 87 kinds, 64 germinated after an
immersion of 28 days, and a few survived an immersion of 137
days. It deserves notice that certain orders were far more injured
than others : nine Leguminosae were tried, and, with one exception,
they resisted the salt-water badly; seven species of the allied or-
ders, Hydrophyllacese and Polemoniacese, were all killed by a
month's immersion. For convenience' sake I chiefly tried small
seeds without the capsule or fruit; and as all of these sanl; in a

328 ORIGIN OF SPECIES

few days they could not have been floated across wide spaces of the
sea, whether or not they were injured by the salt-water. After-
wards I tried some larger fruits, capsules, &c., and some of these
floated for a long time. It is well known what a difference there
is in the buoyancy of green and seasoned timber; and it occurred
to me that floods would often wash into the sea dried plants or
branches with seed-capsules or fruit attached to them. Hence I
was led to dry the stems and branches of 94 plants with ripe fruit,
and to place them on sea- water. The majority sank rapidly, but
some which, whilst green, floated for a short time, when dried
floated much longer; for instance, ripe hazelnuts sank immediate-
ly, but when dried they floated for 90 days, and afterwards when
planted germinated; an asparagus-plant with ripe berries floated
for 23 days, when dried it floated for 85 days, and the seeds after-
wards germinated; the ripe seeds of Helosciadium sank in two
days, when dried they floated for above 90 days, and afterwards
germinated. Altogether, out of the 94 dried plants, 18 floated for
above 28 days ; and some of the 18 floated for a very much longer
period. So that as fy kinds of seeds germinated after an immersion
of 28 days ; and as i| distinct species with ripe fruit (but not all
the same species as in the foregoing experiment) floated, after
being dried, for above 28 days, we may conclude, as far as any-
thing can be inferred from these scanty facts, that the seeds of t/o"
kinds of plants of any country might be floated by sea-currents dur-
ing 28 days, and would retain their power of germination. In
Johnston's Physical Atlas, the average rate of the several Atlantic
currents is 33 miles per diem (some currents running at the rate
of 60 miles per diem) ; on this average, the seeds of iVo plants be-
longing to one country might be floated across 924 miles of sea to
another country, and when stranded, if blown by an inland gale to
a favourable spot, would germinate.

Subsequently to my experiments, M. Martens tried similar ones,
but in a much better manner, for he placed the seeds in a box in
the actual sea, so that they were alternately wet and exposed to the
air like really floating plants. He tried 98 seeds, mostly different
from mine ; but he chose many large fruits and likewise seeds from
pk.nts which live near the sea; and this would have favoured both
the average length of their flotation and their resistance to the in-
jurious action of the salt-water. On the other hand, he did not
previously dry the plants or branches with the fruit; and this, as
we have seen, would have caused some of them to have floated much
longer. The result was that if of his seeds of different kinds
floated for 42 days, and were then capable of germination. But I
do not doubt that plants exposed to the waves would float for a less

GEOGRAPHICAL DISTRIBUTION 329

time than those protected from violent movement as in our experi-
ments. Therefore it would perhaps be safer to assume that the
seeds of about tVo plants of a flora, after having been dried, could
be floated across a space of sea 900 miles in width, and would then
germinate. The fact of the larger fruits often floating longer than
the small, is interesting; as plants with large seeds or fruit which,
as Alph. de Candolle has shown, generally have restricted ranges,
could hardly be transported by any other means.

Seeds may be occasionally transported in another manner.
Drift timber is thrown up on most islands, even on those in the
midst of the widest oceans; and the natives of the coral-islands in
the Pacific procure stones for their tools, solely from the roots of
drifted trees, these stones being a valuable royal tax. I find that
when irregularly shaped stones are embedded in the roots of trees,
small parcels of earth are frequently enclosed in their interstices
and behind them, — so perfectly that not a particle could be washed
away during the longest transport : out of one small portion of
earth thus completely enclosed by the roots of an oak about 50
years old, three dicotyledonous plants germinated : I am certain
of the accuracy of this observation. Again, I can show that the
carcases of birds, when floating on the sea, sometimes escape being
immediately devoured: and many kinds of seeds in the crops of
floating birds long retain their vitality: peas and vetches, for in-
stance, are killed by even a few days' immersion in sea-water; but
some taken out of the crop of a pigeon, which had floated on
artificial sea-water for 30 days, to my surprise nearly all ger-
minated.

Living birds can hardly fail to be highly effective agents in the
transportation of seeds. I could give many facts showing how
frequently birds of many kinds are blown by gales to vast distances
across the ocean. We may safely assume that under such circum-
stances their rate of flight would often be 35 miles an hour; and
some authors have given a far higher estimate. I have never seen
an instance of nutritious seeds passing through the intestines of a
bird; but hard seeds of fruit pass uninjured through even the di-
gestive organs of a turkey. In the course of two months, I picked
up in my garden 12 kinds of seeds, out of the excrement of small
birds, and these seemed perfect, and some of them, which were
tried, germinated. But the following fact is more important : the
crops of birds do not secrete gastric juice, and do not, as I know
by trial, injure in the least the germination of seeds; now, after a
bird has found and devoured a large supply of food, it is positively
asserted that all the grains do not pass into the gizzard for twelve
or even eighteen hours. A bird in this interval might easily bQ

330 ORIGIN OF SPECIES

blown to the distance of 500 miles, and hawks are known to look
out for tired birds, and the contents of their torn crops might thus
readily get scattered. Some hawks and owls bolt their prey whole,
and, after an interval of from twelve to twenty hours, disgorge
pellets, which, as I know from experiments made in the Zoological
Gardens, include seeds capable of germination. Some seeds of the
oat, wheat, millet, canary, hemp, clover, and beet germinated after
having been from twelve to twenty-one hours in the stomachs of
different birds of prey; and two seeds of beet grew after having
been thus retained for two days and fourteen hours. Fresh-water
fish, I find, eat seeds of many land and water plants; fish are fre-
quently devoured by birds, and thus the seeds might be transported
from place to place. I forced many kinds of seeds into the stom-
achs of dead fish, and then gave their bodies to fishing-eagles,
storks, and pelicans; these birds, after an interval of many hours,
either rejected the seeds in pellets or passed them in their excre-
ment; and several of these seeds retained the power of germina-
tion. Certain seeds, however, were always killed by this process.

Locusts are sometimes blown to great distances from the land ; I
myself caught one 370 miles from the coast of Africa, and have
heard of others caught at greater distances. The Rev. R. T. Lowe
informed Sir C. Lyell that in November 1844 swarms of locusts
visited the island of Madeira. They were in countless numbers, as
thick as the flakes of snow in the heaviest snowstorm, and extended
upwards as far as could be seen with a telescope. During two or
three days they slowly careered round and round in an immense
ellipse, at least five or six miles in diameter, and at night alighted
on the taller trees, which were completely coated with them. They
then disappeared over the sea, as suddenly as they had appeared,
and have not since visited the island. Now, in parts of Natal it is
believed by some farmers, though on insufficient evidence, that
injurious seeds are introduced into their grass-land in the dung
left by the great flights of locusts which often visit that country.
In consequence of this belief Mr. Weale sent me in a letter a small
packet of the dried pellets, out of which I extracted under the
microscope several seeds, and raised from them seven grass plants,
belonging to two species, of two genera. Hence a swarm of lo-
custs, such as that which visited Madeira, might readily be the
means of introducing several kinds of plants into an island lying
far from the mainland.

Although the beaks and feet of birds are generally clean, earth
sometimes adheres to them : in one case I removed sixty-one grains,
and in another case twenty-two grains of dry argillaceous earth
from the foot of a partridge, and in the earth there was a pebble

GEOGRAPHICAL DISTRIBUTION ^31

as large as the seed of a vetch. Here is a better case: the leg
of a woodcock was sent to me by a friend, with a little cake of dry
earth attached to the shank, weighing only nine grains; and this
contained a seed of the toad-rush (Juncus bufonius) which germi=
nated and flowered. Mr. Swaysland, of Brighton, who during the
last forty years has paid close attention to our migratory birds, in-
forms me that he has often shot wagtails (Motacillse), wheatears,
and whinchats (Saxicola^), on their first arrival on our shores, be-
fore they had alighted ; and he has several times noticed little cakes
of earth attached to their feet. Many facts could be given show-
ing how generally soil is charged with seeds. For instance. Prof.
ISTewton sent me the leg of a red-legged partridge (Caccabis rufa)
which had been wounded and could not fly, with a ball of hard
earth adhering to it, and weighing six and a half ounces. The
earth had been kept for three years, but when broken, watered and
placed under a bell glass, no less than 82 plants sprung from it :
these consisted of 12 monocotyledons, including the common oat,
and at least one kind of grass, and of 70 dicotyledons, which con-
sisted, judging from the young leaves, of at least three distinct
species. With such facts before us, can we doubt that the many
birds which are annually blown by gales across great spaces of
ocean, and which annually migrate — for instance, the millions of
quails across the Mediterranean — must occasionally transport a
few seeds embedded in dirt adhering to their feet or beaks? But
I shall have to recur to this subject.

As icebergs are known to be sometimes loaded with earth and
stones, and have even carried brushwood, bones, and the nest of a
land-bird, it can hardly be doubted that they must occasionally,
as suggested by Lyell, have transported seeds from one part to an-
other of the arctic and antarctic regions; and during the Glacial
period from one part of the now temperate regions to another. In
the Azores, from the large number of plants common to Europe,
in comparison with the species on the other islands of the Atlantic,
which stand nearer to the mainland, and (as remarked by Mr.
H. 0. Watson) from their somewhat northern character in com-
parison with the latitude, I suspected that these islands had been
partly stocked by ice-borne seeds, during the Glacial epoch. At
my request Sir C. Lyell wrote to M. Hartung to inquire whether
he had observed erratic boulders on these islands, and he answered
that he had found large fragments of granite and other rocks,
which do not occur in the archipelago. Hence we may safely infer
that icebergs formerly landed their rocky burthens on the shores of
these mid-ocean islands, and it is at least possible that they may
have brought thither some few seeds of northern plants.

332 ORIGIN OP SPECIES

Considering that these several means of transport, and that other
means, which without doubt remain to be discovered, have been in
action year after year for tens of thousands of years, it would, I
think, be a marvellous fact if many plants had not thus become
widely transported. These means of transport are sometimes
called accidental, but this is not strictly correct; the currents of
the sea are not accidental, nor is the direction of prevalent gales
of wind. It should be observed that scarcely any means of
transport would carry seeds for very great distances: for seeds do
not retain their vitality when exposed for a great length of
time to the action of sea-water; nor could they be long carried
in the crops or intestines of birds. These means, however, would
suffice for occasional transport across tracts of sea some hundred
miles in breadth, or from island to island, or from a continent
to a neighbouring island, but not from one distant continent to
another. The floras of distant continents would not by such
means become mingled ; but would remain as distinct as they now
are. The currents, from their course, would never bring seeds
from North America to Britain, though they might and do bring
seeds from the West Indies to our western shores, where, if not
killed by their very long immersion in salt water, they could
not endure our climate. Almost every year, one or two land-
birds are blown across the whole Atlantic Ocean, from North
America to the western shores of Ireland and England; but
seeds could be transported by these rare wanderers only by one
means, namely, by dirt adhering to their feet or beaks, which
is in itself a rare accident. Even in this case, how small would
be the chance of a seed falling on favourable soil, and coming
to maturity ! But it would be a great error to argue that because
a well-stocked island, like Great Britain, has not, as far as
is known (and it would be very difficult to prove this), received
within the last few centuries, through occasional means of trans-
port, immigrants from Europe or any other continent, that a
poorly-stocked island, though standing more remote from the
mainland, would not receive colonists by similar means. Out of
a hundred kinds of seeds or animals transported to an island,
even if far less well-stocked than Britain, perhaps not more
than one would be so well fitted to its new home as to
become naturalised. But this is no valid argument against what
would be effected by occasional means of transport, during the
long lapse of geological time, whilst the island was being up-
heaved, and before it had become fully stocked with inhabitants.
On almost bare land, with few or no destructive insects or birds

GEOGRAPHICAL DISTRIBUTION 333

living there, nearly every seed which chanced to arrive, if fitted for
the climate, would germinate and survive.

Dispersal during the Glacial Period.

The identity of many plants and animals, on mountain-sum-
mits, separated from each other by hundreds of miles of lowlands,
where Alpine species could not possibly exist, is one of the most
striking cases known of the same species living at distant points,
without the apparent possibility of their having migrated from one
point to the other. It is indeed a remarkable fact^ to see so
many plants of the same species living on the snowy regions of
the Alps or Pyrenees, and in the extreme northern parts of
Europe ; but it is far more remarkable, that the plants on the White
Mountains, in the United States of America, are all the same with
those of Labrador, and nearly all the same, as we hear from Asa
Gray, with those on the loftiest mountains of Europe. Even as
long ago as 1747, such facts led Gmelin to conclude that the
same species must have been independently created at many dis-
tinct points ; and we might have remained in this same belief, had
not Agassiz and others called vivid attention to the Glacial
period, which, as we shall immediately see, affords a simple ex-
planation of these facts. We have evidence of almost every
conceivable kind, organic and inorganic, that, within a very recent
geological period, central Europe and North America suffered
under an arctic climate. The ruins of a house burnt by fire do
not tell their tale more plainly than do the mountains of Scot-
land and Wales, with their scored flanks, polished surfaces, and
perched boulders, of the icy streams with which their valleys
were lately filled. So greatly has the climate of Europe changed,
that in Northern Italy, gigantic moraines, left by old glaciers,
are now clothed by the vine and maize. Throughout a large
part of the United States, erratic boulders and scored rocks
plainly reveal a former cold period.

The former influence of the glacial climate on the distribu-
tion of the inhabitants of Europe, as explained by Edward Forbes,
is substantially as follows. But we shall follow the changes
more readily, by supposing a new glacial period slowly to come
on, and then pass away, as formerly occurred. As the cold came
on, and as each more southern zone became fitted for the inhab-
itants of the north, these would take the places of the former
inhabitants of the temperate regions. The latter, at the same
time, would travel further and further southward, unless they
were stopped by barriers, in which case they would perish. The

S34 ORIGIN OF SPECIES

mountains would become covered with snow and ice, and their
former Alpine inhabitants would descend to the plains. By the
time that the cold had reached its maximum, we should have
an arctic fauna and flora, covering the central parts of Europe,
as far south as the Alps and Pyrenees, and even stretching into
Spain. The now temperate regions of the United States would
likewise be covered by arctic plants and animals and these would
be nearly the same with those of Europe; for the present cir-
cumpolar inhabitants, which we suppose to have everywhere trav-
elled southward, are remarkably uniform round the world.

As the warmth returned, the arctic forms would retreat north-
ward, closely followed up in their retreat by the productions of
the more temperate regions. And as the snow melted from the
bases of the mountains, the arctic forms would seize on the
cleared and thawed ground, always ascending, as the warmth in-
creased and the snow still further disappeared, higher and higher,
whilst their brethren were pursuing their northern journey.
Hence, when the warmth had fully returned, the same species,
which had lately lived together on the European and North
American lowlands, would again be found in the arctic regions
of the Old and New Worlds, and on many isolated mountain-
summits far distant from each other.

Thus we can understand the identity of many plants at points
so immensely remote as the mountains of the United States
and those of Europe. We can thus also understand the fact that
the Alpine plants of each mountain-range are more especially
related to the arctic forms living due north or nearly due north
of them : for the first migration when the cold came on, and the
re-migration on the returning warmth, would generally have been
due south and north. The Alpine plants, for example, of Scotland,
as remarked by Mr. PI. C. Watson, and those of the Pyrenees, as
remarked by Pamond, are more especially allied to the plants of
northern Scandinavia; those of the United States to Labrador;
those of the mountains of Siberia to the arctic regions of that
country. These views, grounded as they are on the perfectly
well-ascertained occurrence of a former Glacial period, seem to me
to explain in so satisfactory a manner the present distribution
of the Alpine and Arctic productions of Europe and America,
that when in other regions we find the same species on distant
mountain-summits, we may almost conclude, without other evi-
dence, that a colder climate formerly permitted their migration
across the intervening lowlands, now become too warm for their
existence.

As the arctic forms moved first southward and afterwards

GEOGRAPHICAL DISTRIBUTION 335

backwards to the north, in unison with the changing climate,
they will not have been exposed during their long migrations to
any great diversity of temperature; and as they all migrated
in a body together, their mutual relations will not have been
much disturbed. Hence, in accordance with the principles in-
culcated in this volume, these forms will not have been liable
to much modification. But with the Alpine productions, left
isolated from the moment of the returning warmth, first at the
bases and ultimately on the summits of the mountains, the case
will have been somewhat different; for it is not likely that all
the same arctic species will have been left on mountain-ranges
far distant from each other, and have survived there ever since;
they will also in all probability, have become mingled with ancient
Alpine species, which must have existed on the mountains before
the commencement of the Glacial epoch, and which during the
coldest period will have been temporarily driven down to the
plains ; they will, also, have been subsequently exposed to somewhat
different climatal influences. Their mutual relations will thus
have been in some degree disturbed; consequently they will have
been liable to modification ; and they have been modified ; for if we
compare the present Alpine plants and animals of the several great
European mountain-ranges one with another, though many of
the species remain identically the same, some exist as varieties,
some as doubtful forms or sub-species, and some as distinct yet
closely allied species representing each other on the several ranges.
In the foregoing illustration I have assumed that at the com-
mencement of our imaginary Glacial period, the arctic produc-
tions were as uniform round the polar regions as they are at the
present day. But it is also necessary to assume that many sub-
arctic and some few temperate forms were the same round the
world, for some of the species which now exist on the lower moun-
tain-slopes and on the plains of North America and Europe are
the same; and it may be asked how I account for this degree
of uniformity in the sub-arctic and temperate forms round the
world, at the commencement of the real Glacial period. At the
present day, the sub-arctic and northern temperate productions
of the Old and New Worlds are separated from each other by
the whole Atlantic Ocean and by the northern part of the Pacific.
During the Glacial period, when the inhabitants of the Old and
New Worlds lived farther southwards than they do at present,
they must have been still more completely separated from each
other by wider spaces of ocean; so that it may well be asked how
the same species could then or previously have entered the two
continents. The explanation, I believe, lies in the nature of the

336 ORIGIN OP SPECIES

climate before the commencement of the Glacial period. At this,
the newer Pliocene period, the majority of the inhabitants of the
world were specifically the same as now, and we have good reason
to believe that the climate was warmer than at the present day.
Hence we may suppose that the organisms which now live under
latitude 60°, lived during the Pliocene period farther north under
the Polar Circle, in latitude 66°-67° ; and that the present arctic
productions then lived on the broken land still nearer to the pole.
Now, if we look at a terrestrial globe, we see under the Polar
Circle that there is almost continuous land from western Europe,
through Siberia, to eastern America. And this continuity of the
circumpolar land, with the consequent freedom under a more
favourable climate for intermigration, will account for the sup-
posed uniformity of the sub-arctic and temperate productions of
the Old and New Worlds, at a period anterior to the Glacial
epoch.

Believing, from reasons before alluded to; that our continents
have long remained in nearly the same relative position, though
subjected to great oscillations of level, I am strongly inclined
to extend the above view, and to infer that during some still
earlier and still warmer period, such as the older Pliocene period,
a large number of the same plants and animals inhabited the
almost continuous circumpolar land; and that these plants and
animals, both in the Old and New Worlds, began slowly to mi-
grate southwards as the climate became less warm, long before
the commencement of the Glacial period. We now see, as I
believe, their descendants, mostly in a modified condition, in the
central parts of Europe and the United States. On this view we
can understand the relationship with very little identity, between
the productions of North America and Europe, — a relationship
which is highly remarkable, considering the distance of the two
areas, and their separation by the whole Atlantic Ocean. We can
further understand the singular fact remarked on by several
observers that the productions of Europe and America during
the later tertiary stages were more closely related to each other
than they are at the present time ; for during these warmer
periods the northern parts of the Old and New Worlds will have
been almost continuously united by land, serving as a bridge,
since rendered impassable by cold, for the intermigration of their
inhabitants.

During the slowly decreasing warmth of the Pliocene period
as soon as the species in common, which inhabited the New and
Old Worlds, migrated south of the Polar Circle, they will have been

GEOGRAnilCAL DISTRIBUTION 337

completely cut off from each other. This separation, as far as
the more temperate productions are concerned, must have taken
place long ages ago. As the plants and animals migrated south-
ward, they will have become mingled in the one great region
Vi'ith the native American productions, and would have had to
compete with them; and in the other great region, with those
of the Old World. Consequently we have here everything fa-
vourable for much modification, — for far more modification than
with the Alpine productions, left isolated, within a much more
recent period, on the several ruountain-ranges and on the arctic
lands of Europe and N. America. Hence it has come, that when
we compare the now living productions of the temperate regions
of the New and Old Worlds, we find very few identical species
(though Asa Gray has lately shown that more plants are identical
than was formerly supposed), but we find in every great class
many forms, which some naturalists rank as geographical races,
and others as distinct species; and a host of closely allied or
representative forms which are ranked by all naturalists as spe-
cifically distinct.

As on the land, so in the waters of the sea, a slow southern
migration of a marine fauna, which, during the Pliocene or
even a somewhat earlier period, was nearly uniform along the con-
tinuous shores of the Polar Circle, will account, on the theory of
modification, for many closely allied forms now living in marine
areas completely sundered. Thus, I think, we can understand
the presence of some closely allied, still existing and extinct
tertiary forms, on the eastern and western shores of temperate
North America; and the still more striking fact of many closely
allied crustaceans (as described in Dana's admirable work), some
fish and other marine animals, inhabiting the Mediterranean and
the seas of Japan, — these two areas being now completely sep-
arated by the breadth of a whole continent and by wide spaces
of ocean.

These cases of close relationship in species either now or for-
merely inhabiting the seas on the eastern and western shores of
North America, the Mediterranean and Japan, and the temperate
lands of North America and Europe, are inexplicable on the
theory of creation. We cannot maintain that such species have
been created alike, in correspondence with the nearly similar phys-
ical conditions of the areas; for if we compare, for instance,
certain parts of South America with parts of South Africa or
Australia, we see countries closely similar in all their physical
conditions, with their inhabitants utterly dissimilar.

338 ORIGIN OF SPECIES

Alternate Glacial Periods in the North and South.

But we must return to our more immediate subject. I am
convinced that Forbes's view may be largely extended. In Europe
we meet with the plainest evidence of the Glacial period, from
the western shores of Britain to the Oural range, and south-
ward to the Pyrenees. We may infer from the frozen mammals
and nature of the mountain vegetation, that Siberia was simi-
larly affected. In the Lebanon, according to Dr. Hooker, per-
petual snow formerly covered the central axis, and fed glaciers
which rolled 400 feet down the valleys. The same observer has
recently found great moraines at a low level on the Atlas range
in N. Africa. Along the Himalaya, at points 900 miles apart,
glaciers have left the marks of their former low descent; and
in Sikkim, Dr. Hooker saw maize growing on ancient and gigantic
moraines. Southward of the Asiatic continent, on the opposite
side of the equator, we know, from the excellent researches of
Dr. J. Haast and Dr. Hector, that in New Zealand immense gla-
ciers formerly descended to a low level ; and the same plants found
by Dr. Hooker on widely separated mountains in this island
tell the same story of a former cold period. From facts com-
municated to me by the Rev. W. B. Clarke, it appears also that
there are traces of former glacial action on the mountains of the
south-eastern corner of Australia.

Looking to America; in the northern half, ice-borne fragments
of rock have been observed on the eastern side of the continent, as
far south as lat. 36°-37°, and on the shores of the Pacific, where
the climate is now so different, as far south as lat. .46°. Erratic
boulders have, also, been noticed on the Bocky Mountains. In
the Cordillera of South America, nearly under the equator, glaciers
once extended far below their present level. In Central Chile I
examined a vast mound of detritus with great boulders, crossing the
Portillo valley, which there can hardly be a doubt once formed a
huge moraine; and Mr. D. Forbes informs me that he found in
various parts of the Cordillera, from lat. 13° to 30° S., at about the
height of 12,000 feet, deeply-furrowed rocks, resembling those
with which he was familiar in Norway, and likewise great masses
of detritus, including grooved pebbles. Along this whole space of
the Cordillera true glaciers do not now exist even at much more
considerable heights. Farther south on both sides of the continent,
from lat. 41° to the southernmost extremity, we have the clearest
evidence of former glacial action, in numerous immense boulders
transported far from their parent source.

From these several facts, namely from the glacial action hav-

GEOGRAnilCAL DISTRIBUTION 339

ing extended all round the northern and southern hemispheres —
from the period having been in a geological sense recent in both
hemispheres — from its having lasted in both during a great
length of time, as may be inferred from the amount of work
effected — and lastly from glaciers having recently descended to a
low level along the whole line of the Cordillera, it at one time
appeared to me that we could not avoid the conclusion that the
temperature of the whole world had been simultaneously lowered
during the Glacial period. But now Mr. Croll, in a series of
admirable memoirs, has attempted to show that a glacial condi-
tion of climate is the result of various physical causes, brought
into operation by an increase in the eccentricity of the earth's
orbit. All these causes tend towards the same end; but the most
powerful appears to be the indirect influence of the eccentricity
of the orbit upon oceanic currents. According to Mr. Croll, cold
periods regularly recur every ten or fifteen thousand years;
and these at long intervals are extremely severe, owing to cer-
tain contingencies, of which the most important, as Sir C. Lyell
has shown, is the relative position of the land and water. Mr.
Croll believes that the last great Glacial period occurred about
240,000 years ago, and endured with slight alterations of climate
for about 160,000 years. With respect to more ancient Glacial
periods, several geologists arc convinced from direct evidence that
such occurred during the Miocene and Eocene formations, not to
mention still more ancient formations. But the most important
result for us, arrived at by Mr. Croll, is that whenever the north-
ern hemisphere passes through a cold period the temperature of
the southern hemisphere is actually raised, with the winters ren-
dered much milder, chiefly through changes in the direction of
the ocean-currents. So conversely it will be with the northern
hemisphere, whilst the southern passes through a Glacial period.
This conclusion throws so nmcli light on geographical distribution
that I am strongly inclined to trust in it; but I will first give the
facts, which demand an explanation.

In South America, Dr. Hooker has shown that besides many
closely allied species, between forty and fifty of the flowering
plants of Tierra del Fuego, forming no inconsiderable part of its
scanty flora, are common to North America and Europe, enor-
mously remote as these areas in opposite hemispheres are from
each other. On the lofty mountains of equatorial America a
host of peculiar species belonging to European genera occur. On
the Organ mountains of Brazil, some few temperate European,
some Antarctic, and some Andean genera were found by Gardner,
which do not exist in the low intervening hot countries. On the

340 ORIGIN OF SPECIES

Silla of Caraccas, the illustrious Humboldt long ago found spe-
cies belonging to genera characteristic of the Cordillera.

In Africa, several forms characteristic of Europe and some few
representatives of the flora of the Cape of Good Hope occur on
the mountains of Abyssinia. At the Cape of Good Hope a very
few European species, believed not to have been introduced by
man, and on the mountains several representative European forms
are found, which have not been discovered in the inter-tropical
parts of Africa. Dr. Hooker has also lately shown that several
of the plants living on the upper parts of the lofty island of Fer-
nando Po and on the neighbouring Cameroon mountains, in the
Gulf of Guinea, are closely related to those on the mountains cf
Abyssinia, and likewise to those of temperate Europe. It now
also appears, as I hear from Dr. Hooker, that some of these same
temperate plants have been discovered by the Rev. R. T. Lowe
on the mountains of the Cape Verde islands. This extension of
the same temperate forms, almost under the equator, across the
whole continent of Africa and to the mountains of the Cape Verde
archipelago, is one of the most astonishing facts ever recorded
in the distribution of plants.

On the Himalaya, and on the isolated mountain-ranges of the
peninsula of India, on the heights of Ceylon, and on the volcanic
cones of Java, many plants occur, either identically the same
or representing each other, and at the same time representing
plants of Europe, not found in the intervening hot lowlands. A
list of the genera of plants collected on the loftier peaks of Java,
raises a picture of a collection made on a hillock in Europe ! Still
more striking is the fact that peculiar Australian forms are rep-
»*esented by certain plants growing on the summits of the moun-
tains of Borneo. Some of these Australian forms, as I hear from
Dr. Hooker, extend along the heights of the peninsula of Malacca,
and are thinly scattered on the one hand over India, and on the
other hand as far north as Japan.

On the southern mountains of Australia, Dr. E. Miiller has
discovered several European species; other species, not introduced
by man, occur on the lowlands; and a long list can be given, as
I am informed by Dr. Hooker, of European genera, found in
Australia, but not in the intermediate torrid regions. In the
admirable ^ Introduction to the Elora of New Zealand,' by Dr.
Hooker, analogous and striking facts are given in regard to the
plants of that large island. Hence we see that certain plants
growing on the more lofty mountains of the tropics in all parts of
the world, and on the temperate plains of the north and south,
are either the same species or varieties of the same species. It

GEOGRAPHICAL DISTRIBUTION S41

should, however, be observed that these plants are not strictly
arctic forms ; for, as Mr. II. C Watson has remarked, " in re-
ceding from polar towards equatorial latitudes, the Alpine or
mountain floras really become less and less Arctic." Besides these
identical and closely allied forms, many species inhabiting' the same
widely sundered areas, belong to genera not now found in the
intermediate tropical lowlands.

These brief remarks apply to plants alone; but some few anal-
ogous facts could be given in regard to terrestrial animals. In
marine productions, similar cases likewise occur; as an example,
I may quote a statement by the highest authority, Prof. Dana,
that " it is certainly a wonderful fact that New Zealand should
have a closer resemblance in its Crustacea to Great Britain, its
antipode, than to any other part of the world." Sir J. Richard-
son, also, speaks of the reappearance on the shores of New Zea-
land, Tasmania, &c., of northern forms of fish. Dr. Hooker
informs me that twenty-five species of Algae are common to New
Zealand and to Europe, but have not been found in the interme-
diate tropical seas.

From the foregoing facts, namely, the presence of temperate
forms on the highlands across the whole of equatorial Africa, and
along the Peninsula of India, to Ceylon and the Malay Archipel-
ago, and in a less well-marked manner across the wide expanse
of tropical South America, it appears almost certain that at
some former period, no doubt during the most severe part of
a Glacial period, the lowlands of these great continents were
everywhere tenanted under the equator by a considerable number
of temperate forms. At this period the equatorial climate at
the level of the sea was probably about the same with that now
experienced at the height of from five to six thousand feet under
the same latitude, or perhaps even rather cooler. During this, the
coldest period, the lowlands under the equator must have been
clothed with a mingled tropical and temperate vegetation, like that
described by Hooker as growing luxuriantly at the height of from
four to five thousand feet on the lower slopes of the Himalaya,
but with perhaps a still greater preponderance of temperate forms.
So again in the mountainous island of Fernando Po, in the Gulf
of Guinea, Mr. Mann found temperate European forms beginning
to appear at the height of about five thousand feet. On the moun-
tains of Panama, at the height of only two thousand feet. Dr.
Seemann found the vegetation like that of Mexico, " with forms
of the torrid zone harmoniously blended with those of the tem-
perate."

Now let us see whether Mr. Croll's conclusion that when the

342 ORIGIN OF SPECIES

northern hemisphere suffered from the extreme cold of the great
Glacial period, tiie southern hemisphere was actually warmer,
throws any clear light on the present apparently inexplicable
distribution of various organisms in the temperate parts of both
hemispheres, and on the mountains of the tropics. The Glacial
period, as measured by years, must have been very long; and when
we remember over what vast spaces some naturalised plants and
animals have spread within a few centuries, this period will have
been ample for any amount of migration. As the cold became
more and more intense, we know that Arctic forms invaded the
temperate regions; and, from the facts just given, there can
hardly be a doubt that some of the more vigorous, dominant, and
widest-spreading temperate forms invaded the equatorial lowlands.
The inhabitants of these hot lowlands would at the same time have
migrated to the tropical and subtropical regions of the south,
for the southern hemisphere was at this period warmer. On the
decline of the Glacial period, as both hemispheres gradually re-
covered their former temperatures, the northern temperate forms
living on the lowlands under the equator, would have been driven
to their former homes or have been destroyed, being replaced by
the equatorial forms returning from the south. Some, however, of
the northern temperate forms would almost certainly have ascend-
ed any adjoining high land, where, if sufficiently lofty, they
would have long survived like the Arctic forms on the mountains
of Europe. They might have survived, even if the climate was not
perfectly fitted for them, for the change of temperature must
have been very slow, and plants undoubtedly possess a certain
capacity for acclimatisation, as shown by their transmitting to
their offspring different constitutional powers of resisting heat
and cold.

In the regular course of events the southern hemisphere would
in its turn be subjected to a severe Glacial period, with the
northern hemisphere rendered warmer; and then the southern
temperate forms would invade the equatorial lowlands. The
northern forms which had before been left on the mountains
would now descend and mingle with the southern forms. These
latter, when the warmth returned, would return to their former
homes, leaving some few species on the mountains, and carrying
southward with them some of the northern temperate forms which
had descended from their mountain fastnesses. Thus, we should
have some few species identically the same in the northern and
southern temperate zones and on the mountains of the intermediate
tropical regions. But the species left during a long time on these
mountains, or in opposite hemispheres, would have to compete with

GEOGRAPHICAL DISTRIBUTION 343

many new forms and would be exposed to somewhat different phys-
ical conditions; hence they would be eminently liable to modifica-
tion, and would generally now exist as varieties or as representa-
tive species; and this is the case. We must, also, bear in mind
the occurrence in both hemispheres of former Glacial periods; for
these will account, in accordance with the same principles, for the
many quite distinct species inhabiting the same widely separated
areas, and belonging to genera not now found in the intermediate
torrid zones.

It is a remarkable fact strongly insisted on by Hooker in regard
to xVmerica, and by Alph. de Candolle in regard to Australia, that
many more identical or slightly modified species have migrated
from the north to the south, then in a reversed direction. We
see, however, a few southern forms on the mountains of Borneo
and Abyssinia. I suspect that this preponderant migration from
the north to the south is due to the greater extent of land in the
north, and to the northern forms having existed in their own
homes in greater numbers, and having consequently been advanced
through natural selection and competition to a higher stage of
perfection, or dominating power, than the southern forms. And
thus, when the two sets became commingled in the equatorial
regions, during the alternations of the Glacial periods, the northern
forms were the more pov/erful and were able to hold their places
on the mountains, and afterwards to migrate southward with the
southern forms; but not so the southern in regard to the northern
forms. In the same manner at the present day, we see that very
many European productions cover the ground in La Plata, New
Zealand, and to a lesser degree in Australia, and have beaten the
natives; whereas extremely few southern forms have become nat-
uralised in any part of the northern hemisphere, though hides,
wool, and other objects likely to carry seeds have been largely
imported into Europe during the last two or three centuries
from La Plata and during the last forty or fifty j^ears from Aus-
tralia. The ISTeilgherrie mountains in India, however, offer a par-
tial exception; for here, as I hear from Dr. Hooker, Australian
forms are rapidly sowing themselves and becoming natu'ralised.
Before the last great Glacial period, no doubt the intertropical
mountains were stocked v/ith endemic Alpine forms ; but these
have almost everywhere yielded to the more dominant forms
generated in the larger areas and more efficient workshops of
the north. In many islands the native productions are nearly
equalled, or even outnumbered, by those which have become nat-
uralised; and this is the first stage towards their extinction.
Mountains are islands on the land, and their inhabitants have

344 ORIGIN OF SPECIES

yielded to those produced within the larger areas of the north,
just in the same way as the inhabitants of real islands have every-
where yielded and are still yielding to continental forms natural-
ised through man's agency.

The same principles apply to the distribution of terrestrial
animals and of marine productions, in the northern and southern
temperate zones, and on the intertropical mountains. When, dur-
ing the height of the Glacial period, the ocean-currents were widely
different to what they now are, some of the inhabitants of the
temperate seas might have reached the equator; of these a few
would perhaps at once be able to migrate southward, by keeping
to the cooler currents, whilst others might remain and survive
in the colder depths until the southern hemisphere was in its turn
subjected to a glacial climate and permitted their further progress;
in nearly the same manner as, according to Forbes, isolated spaces
inhabited by Arctic productions exist to the present day in the
deeper parts of the northern temperate seas.

I am far from supposing that all the difficulties in regard to
the distribution and affinities of the identical and allied species,
which now live so widely separated in the north and south, and
sometimes on the intermediate mountain-ranges, are removed on
the views above given. The exact lines of migration cannot be
indicated. We cannot say why certain species and not others
have migrated; why certain species have been modified and
have given rise to new forms, whilst others have remained unal-
tered. We cannot hope to explain such facts, until we can say
why one species and not another becomes naturalised by man's
agency in a foreign land; why one species ranges twice or thrice
as far, and is twice or thrice as common, as another species within
their own homes.

Various special difficulties also remain to be solved; for in-
stance, the occurrence, as shown by Dr. Hooker, of the same plants
at points so enormously remote as Kerguelen Land, New Zea-
land, and Fuegia; but icebergs, as suggested by Lyell, may have
been concerned in their dispersal. The existence at these and other
distant points of the southern hemisphere, of species, which,
though distinct, belong to genera exclusively confined to the
south, is a more remarkable case. Some of these species are so
distinct, that we cannot suppose that there has been time since
the commencement of the last Glacial period for their migration
and subsequent modification to the necessary degree. The facts
seem to indicate that distinct species belonging to the same genera
have migrated in radiating lines from a common centre ; and I am
inclined to look in the southern, as in the northern hemisphere, to

GEOGRAPHICAL DISTRIBUTIOIS 345

a former and warmer period, before the commencement of the last
Glacial period, when the Antarctic lands, now covered with ice,
supported a highly peculiar and isolated flora. It may be sus-
pected that before this flora was exterminated during the last
Glacial epoch, a few forms had been already widely dispersed
to various points of the southern hemisphere by occasional means
of transport, and by the aid as halting-places, of now sunken
islands. Thus the southern shores of America, Australia, and
New Zealand may have become slightly tinted by the same peculiar
forms of life.

Sir C. Lyell in a striking passage has speculated, in language
almost identical with mine, on the effects of great alterations of
climate throughout the w^orld on geographical distribution. And
we have now seen that Mr. Croll's conclusion that successive
Glacial periods in the one hemisphere coincide with warmer pe-
riods in the opposite hemisphere, together with the admission of the
slow modification of species, explains a multitude of facts in
the distribution of the same and of the allied forms of life in all
I)arts of the globe. The living waters have flowed during one
period from the north and during another from the south, and
in both cases have reached the equator; but the stream of life
has flowed with greater force from the north than in the opposite
direction, and has consequently more freely inundated the south.
As the tide leaves its drift in horizontal lines, rising higher on the
shores where the tide rises highest, so have the living waters left
their living drift on our mountain summits, in a line gently rising
from the Arctic lowlands to a great altitude under the equator.
The various beings thus left stranded may be compared with savage
races of man, driven up and surviving in the mountain fastnesses
of almost every land, which serve as a record, full of interest to
us, of the former inhabitants of the surrounding lowlands.

UQ OitlGIX OF Si'JLJCiES

CHAPTER XIIL

GEOGRAPHICAL DISTRIBUTION continued.

Distribution of fresh-Avater productions — On the inhabitants of oceanic
islands — xVbsence of Batrachians and of terrestrial Mammals — On
the relation of tlie inhabitants of islands to those of the nearest main-
land— On colonisation from the nearest source with subsequent modi-
fication — Summary of the last and present chapter.

Fresli-water Produciions.

AS lakes and river-systems are separated from each other
by barriers of land, it might have been thought that fresh-
water productions would not have ranged widely within
the same country, and as the sea is apparently a still more for-
midable barrier, that they would never have extended to distant
countries. But the case is exactly the reverse. Not only have
many fresh- water species, belonging to different classes, an enor-
mous range, but allied species prevail in a remarkable manner
throughout the world. When first collecting in the fresh waters
of Brazil, I well remember feeling much surprised at the similarity
of the fresh-water insects, shells, &c., and at the dissimilarity of the
surrounding terrestrial beings, compared with those of Britain.

But the wude ranging power of fresh-water productions can,
I think, in most cases be explained by their having become fitted,
in a manner highly useful to them, for short and frequent mi-
grations from, pond to pond, or from stream to stream, within
their own countries; and liability to wide dispersal would follow
from this capacity as an almost necessary consequence. We can
here consider only a few cases; of these, some of the most
difficult to explain are presented by fish. It was formerly believed
that the same fresh- water sTiecies never existed on two continents
distant from each other. But Dr. Giinther has lately shown that
the Galaxias atfenuatus inliabits Tasmania, New Zealand, the
Falkland Islands and the mainland of South America. This
is a wonderful case, and probably indicates dispersal from an
Antarctic centre during a former warm period. This case, how-
ever, is rendered in some degree less surprising by the species
of this genus having the power of crossing by some unknown

GEOGRAPHICAL DISTRIBUTION — CONTINUED 347

means considerable spaces of open ocean : thus there is one species
common to New Zealand and to the Auckland Islands, though
separated by a distance of about 2;j() miles. On the same continent
fresh-\vater fish often range widely, and as if capriciously; for in
two adjoining river-systems some of the species may be the same,
and some wholly difl'erent.

It is probable that they are occasionally transported by what
may be called accidental means. Thus fishes still alive are not
very rarely dropped at distant points by whirlwinds; and it is
known that the ova retain their vitality for a considerable time
after removal from the water. Their dispersal may, however, be
mainly attributed to changes in the level of the land within the re-
cent period, causing rivers to flow into each other. Instances, also,
could be given of this having occurred during floods, without any
change of level. The wide difference of the fish on the opposite
sides of most mountain-ranges, which are continuous, and which
consequently must from an early period have completely pre-
vented the inosculation of the river-systems on the two sides,
leads to the same conclusion. Some fresh-water fish belong to
very ancient forms, and in such cases there will have been ample
time for great geographical changes, and consequently time and
means for much migration. Moreover, Dr. Glinther has recently
been led by several considerations to infer that with fishes the
same forms have a long endurance. Salt-water fish can with
care be slowly accustomed to live in fresh water; and, accord-
ing to Valenciennes, there is hardly a single group of which all
the members are confined to fresh water, so that a marine species
belonging to a fresh-water group might travel far along the
shores of the sea, and could, it is probable, become adapted with-
out much difficulty to the fresh waters of a distant land.

Some species of fresh-w^ater shells have very wide ranges, and
allied species which, on our theory, are descended from a common
parent, and must have proceeded from a single source, prevail
throughout the world. Their distribution at first perplexed me
much, as their ova are not likely to be transported by birds;
and the ova, as well as the adults, are immediately killed
by sea-water. I could not even understand how some naturalised
species have spread rapidly throughout the same country. But
two facts, which I have observed — and many others no doubt
will be discovered — throw some light on this subject. When
ducks suddenly emerge from a pond covered with duck-weed, I
have twice seen these little plants adhering to their backs; and
it has happened to me, in removing a little duck-weed from one
aquarium to another, that I have unintentionally stocked the one

348 ORIGIN OF SPECIES

with fresh-water shells from the other. But another agency is
perhaps more effectual: I suspended the feet of a duck in an
aquarium, where many ova of fresh-water shells were hatching;
and I found that numbers of the extremely minute and just-
hatched shells crawled on the feet, and clung to them so firmly that
when taken out of the water they could not be jarred off, though
at a somewhat more advanced age they would voluntarily drop
off. These just-hatched molluscs, though aquatic in their nature,
survived on the duck's feet, in damp air, from twelve to twenty
hours; and in this length of time a duck or heron might fly at least
six or seven hundred miles, and if blown across the sea to an
oceanic island, or to any other distant point, would be sure to
alight on a pool or rivulet. Sir Charles Lyell informs me that
a Dytiscus has been caught with an Ancylus (a fresh-water shell
like a limpet) firmly adhering to it; and a water-beetle of the
same family, a Colymbetes, once flew on board the ^ Beagle,' when
forty-five miles distant from the nearest land : how much farther
it might have been blown by a favouring gale no one can tell.

With respect to plants, it has long been known what enormous
ranges many fresh-water, and even marsh species, have, both
over continents and to the most remote oceanic islands. This is
strikingly illustrated, according to Alph. de Candolle, in those
large groups of terrestrial plants, which have very few aquatic
members; for the latter seem immediately to acquire, as if in
consequence, a wide range. I think favourable means of dispersal
explain this fact. I have before mentioned that earth occasionally
adheres in some quantity to the feet and beaks of birds. Wading
birds, which frequent the muddy edges of ponds, if suddenly
flushed, would be the most likely to have muddy feet. Birds of this
order wander more than those of any other; and they are occa-
sionally found on the most remote and barren islands of the
open ocean ; they would not be likely to alight on the surface of the
sea, so that any dirt on their feet would not be washed off; and
when gaining the land, they would be sure to fly to their natural
fresh-water haunts. I do not believe that botanists are aware
how charged the mud of ponds is with seeds; I have tried several
little experiments, but will here give only the most striking case :
I took in February three tablespoonfuls of mud from three differ-
ent points, beneath water, on the edge of a little pond : this mud
when dried weighed only 6%^ ounces; T kept it covered up in
my study for six months, pulling up and counting each plant as it
grew; the plants were of many kinds, and were altogether 537 in
number; and yet the viscid mud was all contained in a breakfast
cup ! Considering these facts, I think it would be an inexplicable

GEOGRAPHICAL DISTRIBUTION — CONTINUED 349

circumstance if water-birds did not transport the seeds of fresh-
water plants to unstocked ponds and streams, situated at very
distant points. The same agency may have come into play with
the eggs of some of the smaller fresh-water animals.

Other and unknown agencies probably have also played a
part. I have stated that fresh-water fish eat some kinds of seeds,
though they reject many other kinds after having swallowed
them; even small fish swallow seeds of moderate size, as of the
yellow water-lily and Potamogeton. Herons and other birds, cen-
tury after century, have gone on daily devouring fish; they then
take flight and go to other waters, or are blown across the sea;
and we have seen that seeds retain their power of germination,
when rejected many hours afterwards in pellets or in the excre-
ment. When I saw the great size of the seeds of that fine water-
lily, the Nelumbium, and remembered Alph. de Candolle's remarks
on the distribution of this plant, I thought that the means of
its dispersal must remain inexplicable ; but Audubon states that he
found the seeds of the great southern water-lily (probably, ac-
cording to Dr. Hooker, the Nelumbium luteum) in a heron's stom-
ach. Now this bird must often have flown with its stomach thus
well stocked to distant ponds, and then getting a hearty meal of
fish, analogy makes me believe that it would have rejected the
seeds in a pellet in a fit state for germination.

In considering these several means of distribution, it should be
remembered that when a pond or stream is first formed, for
instance, on a rising islet, it will be unoccupied ; and a single seed
or egg will have a good chance of succeeding. Although there will
always be a struggle for life between the inhabitants of the same
pond, however few in kind, yet as the number even in a well-
stocked pond is small in comparison with the number of species
inhabiting an equal area of land, the competition between them
will probably be less severe than between terrestrial species; con-
sequently an intruder from the waters of a foreign country would
have a better chance of seizing on a new place, than in the case
of terrestrial colonists. We should also remember that many
fresh-water productions are low in the scale of nature, and we
have reason to believe that such beings become modified more
slowly than the high; and this will give time for the migration of
aquatic species. We should not forget the probability of many
fresh-water forms having formerly ranged continuously over im-
mense areas, and then having become extinct at intermediate
points. But the wide distribution of fresh-water plants and of the
lower animals, whether retaining the same identical form or in
some degree modified, apparently depends in main part on the

350 ORIGIN OP SPECIES

wide dispersal of tlieir seeds and eggs by animals, more especir,!!/
by fresh-water birds, which have great powers of flight, and nat-
urally travel from one piece of water to another.

On the Inhahitants of Oceanic Islands.

We now come to the last of the three classes of facts, which I
have selected as presenting the greatest amount of difficulty with
respect to distribution, on the view that not only all the individuals
of the same species have migrated from some one area, but
that allied species, although now inhabiting the most distant
points, have proceeded from a single area, — the birthplace of their
early progenitors. I have already given my reasons for disbeliev-
ing in continental extensions within the period of existing species,
on so enormous a scale that all the many islands of the several
oceans were thus stocked with their present terrestrial inhabitants.
This view removes many difficulties, but it does not accord with all
the facts in regard to the production of islands. In the following
remarks I shall not confine myself to the mere question of dis-
persal, but shall consider some other cases bearing on the truth
of the two theories of independent creation and of descent with
modification.

The species of all kinds which inhabit oceanic islands are few
in number compared with those on equal continental areas : Alph.
de Candolle admits this for plants, and Wollaston for insects.
New Zealand, for instance, with its lofty mountains and diversified
stations, extending over 780 miles of latitude, together with the
outlying islands of Auckland, Campbell and Chatham, contain
altogether only 960 kinds of flowering plants; if we compare this
moderate number with the species which swarm over equal areas in
Southwestern Australia or at the Cape of Good Hope, we must
admit that some cause, independently of different physical condi-
tions, has given rise to so great a difference in number. Even the
uniform county of Cambridge has 847 plants, and the little island
of Anglesea 764, but a few ferns and a few introduced plants
are included in these numbers, and the comparison in some other
respects is not quite fair. We have evidence that the barren
island of Ascension aboriginally possessed less than half-a-dozen
flowering plants ; yet many species have now become naturalised on
it, as they have in New Zealand and on every other oceanic island
which can be named. In St. Helena there is reason to believe that
the naturalised plants and animals have nearly or quite exter-
minated many native productions. He who admits the doctrine of
the creation of each separate species, will have to admit that a

GEOGRAPHICAL DISTRIBUTION — CONTINUED 351

sufficient number of the best adapted plants and animals were
not created for oceanic islands; for man has unintentionally
stocked them far more fully and perfectly than did nature.

Although in oceanic islands the species are few in number, the
proportion of endemic kinds (i. e. those found nowhere else in
the world) is often extremely large. If we compare, for instance,
the number of endemic land-shells in Madeira, or of endemic birds
in the Galapagos Archipelago, with the number found on any
continent, and then compare the area of the island with that of
the continent, we shall see that this is true. This fact might
have been theoretically expected, for, as already explained, species
occasionally arriving after long intervals of time in the new and
isolated district, and having to compete with new associates,
would be eminently liable to modification, and would often pro-
duce groups of modified descendants. But it by no means follows
that, because in an island nearly all the species of one class are
peculiar, those of another class, or of another section of the same
class, are peculiar; and this difference seems to depend partly on
the species which are not modified having immigrated in a body,
so that their mutual relations have not been much disturbed; and
partly on the frequent arrival of unmodified immigrants from the
mother-country, wdth which the insular forms have intercrossed.
It should be borne in mind that the offspring of such crosses
would certainly gain in vigour; so that even an occasional cross
would produce more effect than might have been anticipated. I
will give a few illustrations of the foregoing remarks: in the
Galapagos Islands there are 26 land-birds; of these 21 (or perhaps
23) are peculiar, whereas of the 11 marine birds only 2 are
peculiar; and it is obvious that marine birds could arrive at these
islands much more easily and frequently than land-birds. Ber-
muda, on the other hand, which lies at about the same distance
from North America as the Galapagos Islands do from South
America, and which has a very peculiar soil, does not possess a
single endemic land-bird; and we know from Mr. J. M. Jones's
admirable account of Bermuda, that very many ISTorth American
birds occasionally or even frequently visit this island. Almost
every year, as I am informed by Mr. E. V. Harcourt, many
European and African birds are blown to Madeira; this island
is inhabited by 99 kinds of which one alone is peculiar, though
very closely related to a European form; and three or four other
species are confined to this island and to the Canaries. So that
the islands of Bermuda and Madeira have been stocked from
the neighbouring continents with birds, which for long ages have
there struggled together, and have become mutually co-adapted.

352 ORIGIN OF SPECIES

Hence when settled in their new homes, each kind will have been
kept by the others to its proper place and habits, and will conse-
quently have been but little liable to modification. Any tendency
to modification will also have been checked by intercrossing with
the unmodified immigrants, often arriving from the mother-coun-
try. Madeira again is inhabited by a wonderful number of
peculiar land-shells, whereas not one species of sea-shell is peculiar
to its shores : now, though we do not know how sea-shells are
dispersed, yet we can see that their eggs or larvse, perhaps attached
to seaweed or floating timber, or to the feet of wading-birds, might
be transported across three or four hundred miles of open sea
far more easily than land-shells. The different orders of insects
inhabiting Madeira present nearly parallel cases.

Oceanic islands are sometimes deficient in animals of certain
whole classes, and their places are occupied by other classes ; thus in
the Galapagos Islands reptiles, and in New Zealand gigantic
wingless birds, take, or recently took, the place of mammals.
Although New Zealand is here spoken of as an oceanic island,
it is in some degree doubtful whether it should be so ranked;
it is of large size, and is not separated from Australia by a
profoundly deep sea; from its geological character and the direc-
tion of its mountain-ranges, the E-ev. W. B. Clarke has lately
maintained that this island, as well as New Caledonia, should
be considered as appurtenances of Australia. Turning to plants,
Dr. Hooker has shown that in the Galapagos Islands the pro-
portional numbers of the different orders are very different from
what they are elsewhere. All such differences in number, and
the absence of certain whole groups of animals and plants, are
generally accounted for by supposed differences in the physical
conditions of the islands ; but this explanation is not a little doubt-
ful. Facility of immigration seems to have been fully as im-
portant as the nature of the conditions.

Many remarkable little facts could be given with respect to
the inhabitants of oceanic islands. For instance, in certain islands
not tenanted by a single mammal, some of the endemic plants
have beautifully hooked seeds ; yet few relations are more manifest
than that hooks serve for the transportal of seeds in the wool or
fur of quadrupeds. But a hooked seed might be carried to an
island by other means ; and the plant then becoming modified would
form an endemic species, still retaining its hooks, which would
form a useless appendage like the shrivelled wings under the
soldered wing-covers of many insular beetles. Again, islands
often possess trees or bushes belonging to orders which else-
where include only herbaceous species ; now trees, as Alph. de Can-

GEOGRAPHICAL DISTRIBUTION — CONTINUED 353

dolle has shown, generally have, whatever the cause may be, con-
fined ranges. Hence trees would be little likely to reach distant
oceanic islands; and an herbaceous i^lant, which had no chance
of successfully competing with the many fully developed trees
growing on a continent, might, when established on an island,
gain an advantage over other herbaceous plants by growing taller
and taller and overtopping them. In this case, natural selection
would tend to add to the stature of the plant, to whatever order
it belonged, and thus first convert it into a bush and then into a
tree.

Absence of Batrachians and Terrestrial Mammals on Oceanic

Islands.

With respect to the absence of whole orders of animals on
oceanic islands, Bory St. Vincent long ago remarked that Ba-
trachians (frogs, toads, newts) are never found on any of the
many islands with which the great oceans are studded. I have
taken pains to verify this assertion, and have found it true, with
the exception of New Zealand, New Caledonia, the Andaman
Islands, and perhaps the Salomon Islands and the Seychelles. But
I have already remarked that it is doubtful whether New Zealand
and New Caledonia ought to be classed as oceanic islands; and
this is still more doubtful with respect to the Andaman and
Salomon groups and the Seychelles. This general absence of frogs,
toads, and newts on so many true oceanic islands cannot be ac-
counted for by their physical conditions : indeed it seems that
islands are peculiarly fitted for these animals; for frogs have
been introduced into Madeira, the Azores, and Mauritius, and
have multiplied so as to become a nuisance. But as these animals
and their spawn are immediately killed (with the exception, as
far as known, of one Indian species) by sea-water, there would
be great difficulty in their transportal across the sea, and there-
fore we can see why they do not exist on strictly oceanic islands.
But why, on the theory of creation, they should not have been
created there, it would be very difficult to explain.

Mammals offer another and similar case. I have carefully
searched the oldest voyages, and have not found a single in-
stance, free from doubt, of a terrestrial mammal (excluding
domesticated animals kept by the natives) inhabiting an island
situated above 300 miles from a continent or great continental
island; and many islands situated at a much less distance are
equally barren. The Falkland Islands, which are inhabited by a
wolf -like fox, come nearest to an exception; but this group can-

354 ORIGIN OF SPECIES

not be considered as oceanic, as it lies on a bank in connection
with the mainland at the distance of about 280 miles; moreover,
icebergs formerly brought boulders to its western shores, and they
may have formerly transported foxes, as now frequently happens
in the arctic regions. Yet it cannot be said that small islands will
not support at least small mammals, for they occur in many parts
of the world on very small islands, when lying close to a con-
tinent; and hardly an island can be named on which our smaller
quadrupeds have not become naturalised and greatly multiplied.
It cannot be said, on the ordinary view of creation, that there has
not been time for the creation of mammals; many volcanic is-
lands are sufficiently ancient, as shown by the stupendous degrada-
tion which they have suffered, and by their tertiary strata: there
has also been time for the production of endemic species belonging
to other classes; and on continents it is known that new species
of mammals appear and disappear at a quicker rate than other
and lower animals. Although terrestrial mammals do not occur
on oceanic islands, aerial mammals do occur on almost every
island. New Zealand possesses two bats found nowhere else in
the world: Norfolk Island, the Viti Archipelago, the Bonin Is-
lands, the Caroline and Marianne Archipelagoes, and Mauritius,
all possess their peculiar bats. Why, it may be asked, has the
supposed creative force produced bats and no other mammals
on remote islands? On my view this question can easily be
answered; for no terrestrial mammal can be transported across
a wide space of sea, but bats can fly across. Bats have been seen
wandering by day far over the Atlantic Ocean; and two North
American species either regularly or occasionally visit Bermuda,
at the distance of 600 miles from the mainland. I hear from Mr.
Tomes, who has specially studied this family, that many species
have enormous ranges, and are found on continents and on far dis-
tant islands. Hence we have only to suppose that such wander-
ing species have been modified in their new homes in relation to
their new position, and we can understand the presence of endemic
bats on oceanic islands, with the absence of all other terrestrial
mammals.

Another interesting relation exists, namely between the depth
of the sea separating islands from each other or from the nearest
continent, and the degree of affinity of their mammalian inhabi-
tants. Mr. Windsor Earl has made some striking observations on
this head, since greatly extended by Mr. Wallace's admirable re-
searches, in regard to the great Malay Archipelago, which is
traversed near Celebes by a space of deep ocean, and this separates
two widely distinct mammalian faunas. On either side the islands

GEOGRAPHICAL DISTRIBUTION —"CONTINUED 355

stand on a moderately shallow submarine bank, and these islands
are inhabited by the same or by closely allied quadrupeds. I
have not as yet had time to follow up this subject in all quarters of
the world; but as far as I have gone, the relation holds good.
For instance, Britain is separated by a shallow channel from
Europe, and the mammals are the same on both sides; and so it is
with all the islands near the shores of Australia. The West
Indian Islands, on the other hand, stand on a deeply submerged
bank, nearly 1000 fathoms in depth, and here we find American
forms, but the species and even the genera are quite distinct.
As the amount of modification which animals of all kinds undergo
partly depends on the lapse of time, and as the islands which
are separated from each other or from the mainland by shallow
channels, are more likely to have been continuously united within
a recent period than the islands separated by deeper channels, we
can understand how it is that a relation exists between the depth of
the sea separating two mammalian faunas, and the degree of their
affinity, — a relation which is quite inexplicable on the theory of
independent acts of creation.

The foregoing statements in regard to the inhabitants of oceanic
islands, — namely, the fewness of the species, with a large pro-
portion consisting of endemic forms — the members of certain
groups, but not those of other groups in the same class, having
been modified — the absence of certain whole orders, as of batra-
chians and of terrestrial mammals, notwithstanding the presence
of aerial bats, — the singular proportions of certain orders of
plants, — herbaceous forms having been developed into trees, &c.,
— seem to me to accord better with the belief in the efficiency of
occasional means of transport, carried on during a long course of
time, than with the belief in the former connection of all oceanic
islands with the nearest continent; for on this latter view it
is probable that the various classes would have immigrated more
uniformly, and from the species having entered in a body their
mutual relations would not have been much disturbed, and conse-
quently they would either have not been modified, or all the
species in a more equable manner.

I do not deny that there are many and serious difficulties in
understanding how many of the inhabitants of the. more remote
islands, whether still retaining the same specific form or subse-
quently modified, have reached their present homes. But the
probability of other islands having once existed as halting-places,
of which not a wreck now remains, must not be overlooked. I
will specify one difficult case. Almost all oceanic islands, even
the most isolated and smallest, are inhabited by land-shells,

356 ORIGIN OP SPECIES

generally by endemic species, but sometimes by species found
elsewhere, — striking instances of which, have been given by Dr.
A. A. Gould in relation to the Pacific. Now it is notorious that
land-shells are easily killed by sea-water; their eggs, at least
such as I have tried, sink in it and are killed. Yet there must
be some, unknown, but occasionally efficient means for their trans-
portal. Would the just-hatched young sometimes adhere to the
feet of birds roosting on the ground, and thus get transported? It
occurred to me that land-shells, when hybernating and having
a membranous diaphragm over the mouth of the shell, might
be floated in chinks of drifted timber across moderately wide
arms of the sea. And I find that several species in this state
withstand uninjured an immersion in sea-water during seven days :
one shell, the Helix pomatia, after having been thus treated and
again hybernating was put into sea-water for twenty days, and
perfectly recovered. During this length of time the shell might
have been carried by a marine current of average swiftness, to a
distance of 660 geographical miles. As this Helix has a thick
calcareous operculum, I removed it, and when it had formed a
new membranous one, I again immersed it for fourteen days in
sea-water, and again it recovered and crawled* away. Baron Au-
capitaine has since tried similar experiments : he placed 100 land-
shells, belonging to ten species, in a box pierced with holes, and
immersed it for a fortnight in the sea. Out of th3 hundred shells,
twenty-seven recovered. The presence of an operculum seems
to have been of importance, as out of twelve specimens of Cyclos-
toma elegans, which is thus furnished, eleven revived. It is
remarkable, seeing how well the Helix pomatia resisted with me
the salt-water, that not one of fifty-four specimens belonging to
four other species of Helix tried by Aucapitaine, recovered. It
is, however, not at all probable that land-shells have often been
thus transported ; the feet of birds offer a more probable method.

On the Relations of the Inhabitants of Islands to those of the

nearest Mainland.

The most striking and important fact for us is the affinity
of the species which inhabit islands to those of the nearest
mainland, without being actually the same. Numerous instances
could be given. The Galapagos Archipelago, situated under the
equator, lies at the distance of between 500 and 600 miles from
the shores of South America. Here almost every product of
the land and of the water bears the unmistakable stamp of the
American continent. There are twenty-six land-birds; of these,

I

GEOGRAPHICAL DISTRIBUTION — CONTINUED 357

twenty-one, or perhaps twenty-three arc ranked as distinct species,
and would commonly be assumed to have been here created ; yet the
close affinity of most of these birds to American species is mani-
fest in every character, in their habits, gestures, and tones of
voice. So it is with the other animals, and with a large propor-
tion of the plants, as shown by Dr. Hooker in his admirable Flora
of this archipelago. The naturalist, looking at the inhabitants
of these volcanic islands in the Pacific, distant several hundred
^Tiiles from the continent, feels that he is standing on American
land. Why should this be so? why should the species which are
supposed to have been created in the Galapagos Archipelago, and
nowhere else, bear so plainly the stamp of affinity to those created
m America? There is nothing in the conditions of life, in the
geological nature of the islands, in their height or climate, or in
the proportions in which the several classes are associated together,
which closely resembles the conditions of the South American
coast : in fact, there is a considerable dissimilarity in all these
respects. On the other hand, there is a considerable degree of
resemblance in the volcanic nature of the soil, in the climate,
height, and size of the islands, between the Galapagos and Cape
Verde Archipelagoes : but what an entire and absolute difference
in their inhabitants! The inhabitants of the Cape Verde Islands
are related to those of Africa, like those of the Galapagos to
America. Facts such as these, admit of no sort of explanation
on the ordinary view of independent creation; whereas on the
view here maintained, it is obvious that the Galapagos Islands
would be likely to receive colonists from America, whether by
occasional means of transport or (though I do not believe in
this doctrine) by formerly continuous land, and the Cape Verde
Islands from Africa ; such colonists would be liable to modification,
— the principle of inheritance still betraying their original birth-
place.

Many analogous facts could be given : indeed it is an almost
universal rule that the endemic productions of islands are related
to those of the nearest continents, or of the nearest large island.
The exceptions are few, and most of them can be explained.
Thus although Kerguelen Land stands nearer to Africa than
to America, the plants are related, and that very closely, as we
know from Dr. Hooker's account, to those of America : but on
the view that this island has been mainly stocked by seeds brought
with earth and stones on icebergs, drifted by the prevailing cur-
rents, this anomaly disappears. 'New Zealand in its endemic
plants is much more closely related to Australia, the nearest
mainland, than to any other region : and this is what might have

358 ORIGIN OF SPECIES

been expected; but it is also plainly related to South America,
which, although the next nearest continent, is so enormously
remote, that the fact becomes an anomaly. But this difficulty
partially disappears on the view that New Zealand, South America,
and the other southern lands have been stocked in part from a
nearly intermediate though distant point, namely from the ant-
arctic islands, when they were clothed with vegetation, during a
warmer tertiary period, before the commencement of the last
Glacial period. The affinity, which though feeble, I am assured
by Dr. Hooker is real, between the flora of the south-western corner
of Australia and of the Cape of Good Hope, is a far more remark-
able case; but this affinity is confined to the plants, and will,
no doubt, some day be explained.

The same law which has determined the relationship between
the inhabitants of islands and the nearest mainland, is some-
times displayed on a small scale, but in a most interesting manner,
within the limits of the same archipelago. Thus each separate
island of the Galapagos Archipelago is tenanted, and the fact is
a marvellous one, by many distinct species; but these species
are related to each other in a very much closer manner than to
the inhabitants of the American continent, or of any other quarter
of the world. This is what might have been expected, for islands
situated so near to each other would almost necessarily receive
immigrants from the same original source, and from each other.
But how is it that many of the immigrants have been differently
modified, though only in a small degree, in islands situated within
sight of each other, having the same geological nature, the same
height, climate, &c. ? This long appeared to me a great difficulty :
but it arises in chief part from the deeply-seated error of con-
sidering the physical conditions of a country as the most impor-
tant; whereas it cannot be disputed that the nature of the other
species with which each has to compete, is at least as important,
and generally a far more important element of success. Now
if we look to the species which inhabit the Galapagos Archipelago,
and are likewise found in other parts of the world, we find that
they differ considerably in the several islands. This difference
might indeed have been expected if the islands had been stocked
by occasional means of transport — a seed, for instance, of one
plant having been brought to one island, and that of another
plant to another island, though all proceeding from the same
general source. Hence, when in former times an immigrant
first settled on one of the islands, or when it subsequently spread
from one to another, it would undoubtedly be exposed to different
conditions in the different islands, for it would have to compete

GEOGRAPHICAL DISTRIBUTION — CONTINUED 359

with a different set of organisms; a plant, for instance, would
find the ground best fitted for it occupied by somewhat different
species in the different islands, and would be exposed to the
attacks of somewhat different enemies. If then it varied, natural
selection would probably favour different varieties in the different
islands. Some species, however, might spread and yet retairi
the same character throughout the group, just as we see some
species spreading widely throughout a continent and remaining the
same.

The really surprising fact in this case of the Galapagos Archi-
pelago, and in a lesser degree in some analogous cases, is that
each new species after being formed in any one island, did not
spread quickly to the other islands. But the islands, though in
sight of each other, are separated by deep arms of the sea, in
most cases wider than the British Channel, and there is no reason
to suppose that they have at any former period been continuously
united. The currents of the sea are rapid and sweep between the
islands, and gales of wind are extraordinarily rare; so that the
islands are far more effectually separated from each other than
they appear on a map. Nevertheless some of the species, both of
those found in other parts of the world and of those confined
to the archipelago, are common to the several islands; and we
may infer from their present manner of distribution, that they
have spread from one island to the others. But we often take, I
think, an erroneous view of the probability of closely-allied
species invading each other's territory, when put into free inter-
communication. Undoubtedly, if one species has any advantage
over another, it will in a very brief time wdiolly or in part
supplant it; but if both are equally well fitted for their own
places, both will probably hold their separate places for almost
any length of time. Being familiar with the fact that many
species, naturalised through man's agency, have spread with aston-
ishing rapidity over wide areas, we are apt to infer that most
species would thus spread ; but we should remember that the species
which become naturalised in new countries are not generally
closely allied to the aboriginal inhabitants, but are very distinct
forms, belonging in a large proportion of cases, as shown by
Alph. de Candolle, to distinct genera. In the Galapagos Archi-
pelago, many even of the birds, though so well adapted for flying
from island to island, differ on the different islands; thus there
are three closely-allied species of mocking-thrush, each confined
to its own island. NTow let us suppose the mocking-thrush of
Chatham Island to be blown to Charles Island, which has its own
mocking-thrush; why should it succeed in establishing itself

3G0 ORIGIN OF SPECIES

there? We may safely infer that Charles Island is well stocked
with its own species, for annually more eggs are laid and young
birds hatched, than can possibly be reared; and we may infer
that the mocking-thrush peculiar to Charles's Island is at least
as well fitted for its home as is the species peculiar to Chatham
Island. Sir C. Lyell and Mr. Wollaston have communicated to
me a remarkable fact bearing on this subject; namely, that Ma-
deira and the adjoining islet of Porto Santo possess many dis-
tinct but representative species of land-shells, some of which live
in crevices of stone; and although large quantities of stone are
annually transported from Porto Santo to Maderia, yet this latter
island has not become colonised by the Porto Santo species;
nevertheless both islands have been colonised by European land-
shells, which no doubt had some advantage over the indigenous
species. From these considerations I think we need not greatly
marvel at the endemic species which inhabit the several islands
of the Galapagos Archipelago, not having all spread from island
to island. On the same continent, also, j^reoccupation has prob-
ably played an important part in checking the commingling of the
species which inhabit different districts with nearly the same
physical conditions. Thus, the south-east and south-west corners
of Australia have nearly the same physical conditions, and are
united by continuous land, yet they are inhabited by a vast
number of distinct mammals, birds, and plants; so it is, according
to Mr. Bates, with the butterflies and other animals inhabiting the
great, open, and continuous valley of the Amazons.

The same principle which governs the general character of
the inhabitants of oceanic islands, namely, the relation to the
source whence colonists could have been most easily derived, to-
gether with their subsequent modification, is of the widest applica-
tion throughout nature. We see this on every mountain-summit,
in every lake and marsh. For Alpine species, excepting in as far
as the same species have become widely spread during the Glacial
epoch, are related to those of the surrounding lowlands; thus
we have in South America, Alpine humming-birds, Alpine rodents,
Alpine plants, &c., all strictly belonging to American forms;
and it is obvious that a mountain, as it became slowly upheaved,
would be colonised from the surrounding lowlands. So it is with
the inhabitants of lakes and marshes, excepting in so far as great
facility of transport has allowed the same forms to prevail through-
out large portions of the world. We see this same principle in
the character of most of the blind animals inhabiting the caves
of America and of Europe. Other analogous facts could be given.
It will, I believe, be found universally true, that wherever in

GEOGRAPHICAL DISTRIBUTION — CONTINUED 361

two regions, let them be ever so distant, many closely allied or
representative species occur, there will likewise be found some
identical species; and wherever many closely-allied species occur,
there will be found many forms which some naturalists rank as
distinct species, and others as mere varieties; these doubtful
forms showing- us the steps in the progress of modification.

The relation between the power and extent of migration in
certain species, either at the present or at some former period,
and the existence at remote points of the world of closely-allied
species, is shown in another and more general way. Mr. Gould
remarked to me long ago, that in those genera of birds which range
over the world, many of the species have very wide ranges. I
can hardly doubt that this rule is generally true, though difficult
of proof. Amongst mammals, we see it strikingly displayed
in Bats, and in a lesser degree in the Felidse and Canidse. We
see the same rule in the distribution of butterflies and beetles.
So it is with most of the inhabitants of fresh water, for many
of the genera in the most distinct classes range over the world,
and many of the species have enormous ranges. It is not meant
that all, but that some of the species have very wide ranges in
the genera which range very widely. Nor is it meant that the
species in such genera have on an average a very wide range;
for this will largely depend on how far the process of modification
has gone ; for instance, two varieties of the same species inhabit
America and Europe, and thus the species has an immense
range ; but, if variation were to be carried a little further, the
two varieties would be ranked as distinct species, and their range
would be greatly reduced. Still less is it meant, that species
which have the capacity of crossing barriers and ranging widely,
as in the case of certain powerfully-winged birds, will necessarily
range widely; for we should never forget that to range widely
implies not only the power of crossing barriers, but the more
important power of being victorious in distant lands in the
struggle for life with foreign associates. But according to the
view that all the species of a genus, though distributed to the most
remote points of the world, are descended from a single pro-
genitor, we ought to find, and I believe as a general rule we
do find, that some at least of the species range very widely.

We should bear in mind that many genera in all classes are
of ancient origin, and the species in this case will have had
ample time for dispersal and subsequent modification. There is
also reason to believe from geological evidence, that within each
great class the lower organisms change at a slower rate than the
higher; consequently they will have had a better chance of

362 ORIGIN OF SPECIES

ranging widely and of still retaining the same specific character.
This fact, together with that of the seeds and eggs of most
lowly organised forms being very minute and better fitted for
distant transportal, probably accounts for a law which has long
been observed, and which has lately been discussed by Alph. de
Candolle in regard to plants, namely, that the lower any group
of organisms stands the more widely it ranges.

The relations just discussed, — namely, lower organisms ranging
more widely than the higher, — some of the species of widely-
ranging genera themselves ranging widely, — such facts, as alpine,
lacustrine, and marsh productions being generally related to those
which live on the surrounding low lands and dry lands, — the
striking relationship between the inhabitants of islands and those
of the nearest mainland — the still closer relationship of the
distinct inhabitants of the islands in the same archipelago — are
inexplicable on the ordinary view of the independent creation of
each species, but are explicable if we admit colonisation from
the nearest or readiest source, together with the subsequent adap-
tation of the colonists to their new homes.

Summary of the last and present Chapters.

In these chapters I have endeavoured to show, that if we make
due allowance for our ignorance of the full effects of changes of
climate and of the level of the land, which have certainly occurred
within the recent period, and of other changes which have prob-
ably occurred, — if we remember how ignorant we are with re-
spect to the many curious means of occasional transport, — if
we bear in mind, and this is a very important consideration, how
often a species may have ranged continuously over a wide area,
and then have become extinct in the intermediate tracts, — the
difficulty is not insuperable in believing that all the individuals
of the same species, wherever found, are descended from common
parents. And we are led to this conclusion, which has been
arrived at by many naturalists under the designation of single
centres of creation, by various general considerations, more es-
pecially from the importance of barriers of all kinds, and from
the analogical distribution of sub-genera, genera, and families.

With respect to distinct species belonging to the same genus,
which on our theory have spread from one parent-source; if
we make the same allowances as before for our ignorance, and
remember that some forms of life have changed very slowly,
enormous periods of time having been thus granted for their
migration, the difficulties are far from insuperable; though in

GEOGRAPHICAL DISTRIBUTION — CONTINUED 303

this case, as in that of the individuals of the same species, th«y
are often great.

As exemplifying the effects of climatal changes on distribution,
1 have attempted to show how important a part the last Glacial
period has played, which affected even the equatorial regions^
and which, during the alternations of the cold in the north and
south, allowed the productions of opposite hemispheres to mingle,
and left some of them stranded on the mountain-summits in all
parts of the world. As showing how diversified are the means of
occasional transport, I have discussed at some little length the
means of dispersal of fresh-water productions.

If the difficulties be not insuperable in admitting that in the
long course of time all the individuals of the same species, and
likewise of the several species belonging to the same genus, have
proceeded from some one source; then all the grand leading facts
of geographical distribution are explicable on the theory of mi-
gration, together with subsequent modification and the multiplica-
tion of new forms. We can thus understand the high importance
of barriers, whether of land or water, in not only separating, but
in apparently forming the several zoological and botanical prov-
inces. We can thus understand the concentration of related
species within the same areas; and how it is that under different
latitudes, for instance in South America, the inhabitants of the
plains and mountains, of the forests, marshes, and deserts, are
linked together in so mysterious a manner, and are likewise linked
to the extinct beings which formerly inhabited the same conti-
nent. Bearing in mind that the mutual relation of organism to
organism is of the highest importance, we can see why two
areas having nearly the same physical conditions should often
be inhabited by very different forms of life; for according to
the length of time which has elapsed since the colonists entered
one of the regions, or both; according to the nature of the com-
munication which allowed certain forms and not others to enter,
either in greater or lesser numbers ; according or not, as those which
entered happened to come into more or less direct competition
with each other and with the aborigines; and according as the
immigrants were capable of varying more or less rapidly, there
would ensue in the two or more regions, independently of their
physical conditions, infinitely diversified conditions of life, — there
would be an almost endless amount of organic action and reaction,
— and we should find some groups of beings greatly, and some
only slightly modified, — some developed in great force, some
existing in scanty numbers — and this we do find in the several
great geographical provinces of the world.

3G4 ORIGIN OF SPECIES

On these same principles we can understand, as I liave en-
deavoured to show, why oceanic islands should have few inhab-
itants, but that of these, a large proportion should be endemic
or peculiar; and why, in relation to the means of migration, one
group of beings should have all its species peculiar, and another
group, even within the same class, should have all its species the
same with those in an adjoining quarter of the world. We can
see why whole groups of organisms, as batrachians and terrestrial
mammals, should be absent from oceanic islands, whilst the most
isolated islands should possess their own peculiar species of
aerial mammals or bats. We can see why, in islands, there should
be some relation between the presence of mammals, in a more or
less modified condition, and the depth of the sea between such
islands and the mainland. We can clearly see why all the in-
habitants of an archipelago, though specifically distinct on the
several islets, should be closely related to each other; and should
likewise be related, but less closely, to those of the nearest con-
tinent, or other source whence immigrants might have been
derived. We can see why, if there exist very closely allied or
representative species in two areas, however distant from each
other, some identical species will almost always there be found.

As the late Edward Forbes often insisted, there is a striking
parallelism in the laws of life throughout time and space; the
laws governing the succession of forms in past times being nearly
the same with those governing at the present time the differences
in different areas. We see this in many facts. The endurance
of each species and group of species is continuous in time; for
the apparent exceptions to the rule are so few, that they may
fairly be attributed to our not having as yet discovered in an
intermediate deposit certain forms which are absent in it, but
which occur both above and below: so in space, it certainly is
the general rule that the area inhabited by a single species, or by
a group of species, is continuous, and the exceptions, which are
not rare, may, as I have attempted to show, be accounted for by
former migrations under different circumstances, or through oc-
casional means of transport, or by the species having become
extinct in the intermediate tracts. Both in time and space species
and groups of species have their points of maximum development.
Groups of species, living during the same period of time, or
living within the same area, are often characterised by trifling
features in common, as of sculpture or colour. In looking to
the long succession of past ages, as in looking to distant provinces
throughout the world, we find that species in certain classes differ
little from each other, whilst those in another class, or only in

I

GEOGRAPHICAL DISTRIBUTION — CONTINUED 365

a different section of the same order, differ greatly from each
other. In both time and space the lowly organised members of
each class generally change less than the highly organised; but
there are in both cases marked exceptions to the rule. Accord-
ing to our theory, these several relations throughout time and
space are intelligible; for whether we look to the allied forms
of life which have changed during successive ages, or to those
which have changed after having migrated into distant quarters,
in both cases they are connected by the same bond of ordinary
generation ; in both cases the laws of variation have been the same,
and modifications have been accumulated by the same means of
natural selection.

366 ORIGIN OF SPECIES

CHAPTER XIV.

MUTUAL AFFINITIES OF ORGANIC BEINGS! MORPHOLOGY: EMBRYOLOGY:

RUDIMENTARY ORGANS.

Classification.

FROM the most remote period in the history of the world
organic beings have been found to resemble each other in
descending degrees, so that they can be classed in groups
under groups. This classification is not arbitrary like the group-
ing of the stars in constellations. The existence of groups would
have been of simple significance, if one group had been exclusively
fitted to inhabit the land and another the water; one to feed on
flesh, another on vegetable matter, and so on; but the case is
widely different, for it is notorious how commonly members of
even the same sub-group have different habits. In the second
and fourth chapters, on Variation and on Natural Selection, I
have attempted to show that within each country it is the widely
ranging, the much diffused and common, that is the dominant
species, belonging to the larger genera in each class, which vary
most. The varieties, or incipient species, thus produced, ulti-
mately become converted into new and distinct species; and these,
on the principle of inheritance, tend to produce other new and
dominant species. Consequently the groups which are now large,
and which generally include many dominant species, tend to go
on increasing in size. I further attempted to show that from
the varying descendants of each species trying to occupy as many
and as different places as possible in the economy of nature, they
constantly tend to diverge in chnracter. This latter conclusion
is supported by observing the great diversity of forms which, in
any small area, come into the closest competition, and by certain
facts in naturalisation.

I attempted also to show that there is a steady tendency in the
forms which are increasing in number and diverging in character,
to supplant and exterminate the preceding, less divergent and less
improved forms. I request the reader to turn to the diagram
illustrating the action, as formerly explained, of these several

MUTUAL AFFINITIES OF ORGANIC BEINGS 3G7

principles; and he will see that the inevitable result is, that the
modified descendants proceeding from one progenitor become
broken up into groups subordinate to groups. In the diagram
each letter on the uppermost line may represent a genus including
several species, and the whole of the genei^a along this upper
line form together one class, for all are descended from one
ancient parent, and, consequently, have inherited something in
common. But the three genera on the left hand have, on this
same principle, much in common, and form a sub-family, distinct
from that containing the next two genera on the right hand,
which diverged from a common parent at the fifth stage of descent.
These five genera have also much in common, though less than
when grouped in sub-families; and they form a family distinct
from that containing the three genera still farther to the right
hand, which diverged at an earlier period. And all these genera,
descended from (A), form an order distinct from the genera
descended from (I). So that we here have many species descended
from a single progenitor grouped into genera; and the genera into
sub-families, families, and orders, all under one great class. The
grand fact of the natural subordination of organic beings in
groups under groups, which, from its familiarity, does not always
sufficiently strike us, is in my judgment thus explained. No
doubt organic beings, like all other objects, can be classed in
many ways, either artificially by single characters, or more natu-
rally by a number of characters. We know, for instance, that
minerals and the elemental substances can be thus arranged. In
this case there is of course no relation to genealogical succession,
and no cause can at present be assigned for their falling into
groups. But with organic beings the case is different, and the
view above given accords with their natural arrangement in group
under group ; and no other explanation has ever been attempted.

Naturalists, as we have seen, try to arrange the species, genera,
and families in each class, on what is called the Natural System.
But what is meant by this system? Some authors look at it
merely as a scheme for arranging together those living objects
which are most alike, and for separating those which are most
unlike; or as an artificial method of enunciating, as briefly as
possible, general propositions, — that is, by one sentence to give
the characters common, for instance, to all mammals, by another
those common to all carnivora, by another those common to the
dog-genus, and then, by adding a single sentence, a full description
is given of each kind of dog. The ingenuity and utility of this
system are indisputable. But many naturalists think that some-
thing more is meant by the Naturnl System; they believe that it

3G8 ORIGIN OF SPECIES

reveals the plan of the Creator; but unless it be specified whether
order in time or space, or both, or what else is meant by the plan
of the Creator, it seems to me that nothing is thus added to our
knowledge. Expressions such as that famous one by Linnaeus,
which we often meet with in a more or less concealed form,
namely, that the characters do not make the genus, but that the
genus gives the characters, seem to imply that some deeper bond
is included in our classifications than mere resemblance. I be-
lieve that this is the case, and that community of descent — the
one known cause of close similarity in organic beings — is the
bond, which though observed by various degrees of modification,
is partially revealed to us by our classifications.

Let us now consider the rules followed in classification, and the
difficulties which are encountered on the view that classification
either gives some unknown plan of creation, or is simply a
scheme for enunciating general propositions and of placing to-
gether the forms most like each other. It might have been thought
(and was in ancient times thought) that those parts of the struc-
ture which determined the habits of life, and the general place of
each being in the economy of nature, would be of very high im-
portance in classification. Nothing can be more false. No one
regards the external similarity of a mouse to a shrew, of a dugong
to a whale, of a whale to a fish, as of any importance. These
resemblances, though so intimately connected with the whole life
of the being, are ranked as merely " adaptive or analogical charac-
ters ; '^ but to the consideration of these resemblances we shall
recur. It may even be given as a general rule, that the less any
part of the organisation is concerned with special habits, the
more important it becomes for classification. As an instance :
Owen, in speaking of the dugong, says, " The generative organs,
being those which are most remotely related to the habits and food
of an animal, I have always regarded as affording very clear indi-
cations of its true affinities. We are least likely in the modifications
of these organs to mistake a merely adaptive for an essential
character.'' With plants how remarkable it is that the organs of
vegetation, on which their nutrition and life depend, are of little
signification; whereas the organs of reproduction, with their prod-
uct the seed and embryo, are of paramount importance ! So again
in formerly discussing certain morphological characters which
are not functionally important, we have seen that they are often
of the highest service in classification. This depends on their
constancy throughout many allied groups; and their constancy
chiefly depends on any slight deviations not having been preserved

MUTUAL AFFINITIES OF ORGANIC BEINGS 309

and accumulated by natural selection, which acts only on service-
able characters.

That the mere physiological importance of an organ does not
determine its classificatory value, is almost proved by the fact that
in allied groups, in which the same organ, as we have every reason
to suppose, has nearly the same physiological value, its classificatory
value is widely different. No naturalist can have worked long at
any group without being struck with this fact; and it has been
fully acknowledged in the writings of almost every author. It
will suffice to quote the highest authority, Robert Brown, who,
in speaking of certain organs in the Proteacese, says their generic
importance, " like that of all their parts, not only in this, but, as
I apprehend, in every natural family, is very unequal, and in some
cases seems to be entirely lost." Again, in another work he says,
the genera of the Connaracese " differ in having one or more
ovaria, in the existence or absence of albumen, in the imbricate
or valvular aestivation. Any one of these characters singly is
frequently of more than generic importance, though here even
when all taken together they appear insufficient to separate
Cnestis from Connarus." To give an example amongst insects:
in one great division of the Hymenoptera, the antennae, as West-
wood has remarked, are most constant in structure; in another
division they differ much, and the differences are of quite sub-
ordinate value in classification; yet no one will say that the
antennse in these two divisions of the same order are of unequal
physiological importance. Any number of instances could be
given of the varying importance for classification of the same
important organ within the same group of beings.

Again, no one will say that rudimentary or atrophied organs
are of high physiological or vital importance; yet, undoubtedly,
organs in this condition are* often of much value in classification.
No one will dispute that the rudimentary teeth in the upper jaws
of young ruminants, and certain rudimentary bones of the leg, are
highly serviceable in exhibiting the close affinity between rumi-
nants and pachyderms. Robert Brown has strongly insisted on
the fact that the position of the rudimentary florets is of the
highest importance in the classification of the grasses.

Numerous instances could be given of characters derived from
parts which must be considered of very trifling physiological
importance, but which are universally admitted as highly service-
able in the definition of whole groups-. For instance, whether
or not there is an open passage from the nostrils to the mouth,
the only character, according to Owen, which absolutely dis-
tinguishes fishes and reptiles — the inflection, of the angle of the

.370 ORIGIN OF SPECIES

lower jaw in Marsupials — the manner in which the wings of
insects are folded — mere colour in certain Algae — mere pubes-
cence on parts of the flower in grasses — the nature of the dermal
covering, as hair or feathers, in the 'Vertebrata. If the Ornitho-
rhynchus had been covered with feathers instead of hair, this
external and trifling character would have been considered by
naturalists as an important aid in determining the degree of
affinity of this strange creature to birds.

The importance, for classification, of trifling characters, mainly
depends on their being correlated with many other characters
of more or less importance. The value indeed of an aggregate
of characters is very evident in natural history. Hence, as has
often been remarked, a species may depart from its allies in
several characters, both of high physiological importance, and of
almost, universal prevalence, and yet leave us in no doubt where
it should be ranked. Hence, also, it has been found that a classi-
fication founded on any single character, however important that
may be, has always failed; for no part of the organisation is in-
variably constant. The importance of an aggregate of characters,
even when none are important, alone explains the aphorism enun-
ciated by Linnseus, namely, that the characters do not give the
genus, but the genus gives the characters; for this seems founded
on the appreciation of many trifling points of resemblance, too
slight to be defined. Certain plants, belonging to the Malpighia-
cese, bear perfect and degraded flowers; in the latter, as A. de
Jussieu has remarked, " the greater number of the characters
proper to the species, to the genus, to the family, to the class,
disappear, and thus laugh at our classification." When Aspicarpa
produced in France, during several years, only these degraded
flowers, departing so wonderfully in a number of the most im-
portant points of structure from the proper type of the order,
yet M. Richard sagaciously saw, as Jussieu observes, that this
genu^ should still be retained amongst the Malpighiacese. This
case well illustrates the spirit of our classifications.

Practically, when naturalists are at work, they do not trouble
themselves about the physiological value of the characters which
they use in defining a group or in allocating any particular species.
If they find a character nearly uniform, and. common to a great
number of forms, and not common to others, they use it as one of
high value; if common to some lesser number, they use it as of
subordinate value. This principle has been broadly confessed by
some naturalists to be the true one; and by none more clearly
than by that excellent botanist, Aug. St. Hilaire. If several
trifling characters are always found in combination, though no

I

MUTUAL AFFINITIES OF ORGANIC BEINGS 371

apparent bond of connection can be discovered between them, es-
pecial value is set on them. As in most groups of animals, im-
portant organs, such as those for propelling the blood, or for aerat-
ing it, or those for propagating the race, are found nearly uniform,
they are considered as highly serviceable in classification; but
in some groups all these, the most important vital organs, are
found to offer characters of quite subordinate value. Thus, as
Fritz Miiller has lately remarked, in the same group of crusta-
ceans, Cypridina is furnished with a heart, whilst in two closely
allied genera, namely Cypris and Cytherea, there is no such organ ;
one species of Cypridina has well-developed branchiae, whilst an-
other species is destitute of them.

We can see why characters derived from the embryo should be
of equal importance v/ith those derived from the adult, for a
natural classification of course includes all ages. But it is by
no means obvious, on the ordinary view, why the structure of
the embryo should be more important for this purpose than that
of the adult, which alone plays its full part in the economy of
nature. Yet it has been strongly urged by those great naturalists,
Milne Edwards and Agassiz, that embryological characters are
the most important of all; and this doctrine has very generally
been admitted as true. Nevertheless, their importance has some-
times been exaggerated, owing to the adaptive characters of larvae
not having been excluded; in order to show this, Fritz Miiller
arranged by the aid of such characters alone the great class of
crustaceans, and the arrangement did not prove a natural one.
But there can be no doubt that embryonic, excluding larval char-
acters, are of the highest value for classification, not only with
animals but with plants. Thus the main divisions of flowering
plants are founded on differences in the embryo, — on the number
and position of the cotyledons, and on the mode of development
of the plumule and radicle. We shall immediately see why these
characters possess so high a value in classification, namely, from
4he natural system being genealogical in its arrangement.

Our classifications are often plainly influenced by chains of
afiinities. Nothing can be easier than to define a number of
characters common to all birds; but with crustaceans, any such
definition has hitherto been found impossible. There are crusta-
ceans at the opposite ends of the series, which have hardly a
character in common; yet the species at both ends, from being
plainly allied to others, and these to others, and so onwards,
can be recognised as unequivocally belonging to this, and to no
other class of the Articulata.

GreOgraphical distribution has. often been used, though perhaps

372 OIUGIN OF SPECIES

not quite logically, in classitication. more especially in very large
groups of closely allied forms. Temniinck insists on the utility
or even necessity of this practice in certain groups of birds; and
it has been followed by several entomologists and botanists.

Finally, with respect to the comparative value of the various
groups of species, such as orders, sub-orders, families, sub-fam-
ilies, and genera, they seem to be, at least at present, almost
arbitrary. Several of the best botanists, such as Mr. Bentham and
others, have strongly insisted on their arbitrary value. Instances
could be given amongst plants and insects, of a group tirst ranl^ed
by practised naturalists as only a genus, and then raised to the
rank of a sub-family or family ; and this has been done, not because
further research has detected important structural differences, at
Urst overlooked, but because numerous allied species with slightly
different grades of difference, have been subsequently discovered.

All the foregoing rules and aids and difficulties in classification
may be explained, if I do not gre^itly deceive myself, on the view
that the Xatural System is founded on descent with modification;
— that the characters which naturalists consider as showing true
affinity between any two or more sjiecies. are those which have
been inherited from a common parent, all true classification being
genealogical; — that community of descent is the hidden bond
which naturalists have been unconsciously seeking, and not some
unknown plan of creation, or the enunciation of general proposi-
tions, and the mere putting together and separating objects more
or less alike.

Btit I must exidain my meaning more fully. I believe that the
arrangement of the groups within each class, in due subordina-
tion- and relation to each other, must be strictly genealogical in
order to be natural; but that the amount of difference in the sev-
eral branches or groups, though allied in the same degree in blood
to their common progenitor, may differ greatly, being due to the
different degrees of modification which they have undergone ; and
this is expressed by the forms being ranked under different genera,
families, sections, or orders. The reader will best understand what
is meant, if he will take the trouble to refer to the diagram in
the fourth chapter. VTe will suppose the letters A to L to represent
allied genera existing during the Silurian epoch, and descended
from some still earlier form. In three of these genera (A. F, and
I), a species has transmitted modified descendants to the jn-esent
day, represented by the fifteen genera (a" to z^*) on the uppermost
horizontal line. Xow all these modified descendants from a single
species, are related in blood or descent in the same degree: they
may metaphorically be called cousins to the same millionth degree ;

MUTUAL AFFINITIES OF ORCANIC BEINGS 373

yet they differ widely and in different degrees from each other.
The forms descended from A, now broken up into two or three
families, constitute a distinct order from those descended from I,
also broken up into two families. Nor can the existing species,
descended from A, be ranked in the same genus w^th the parent
A ;. or those from 1, with the parent I. But the existing genus f"
may be supposed to have been but slightly modified; and it will
then rank with the parent-genus F; just as some few still living
organisms belong to Silurian genera. So that the comparative
value of the differences between these organic beings, which are
all related to each other in the same degree in blood, has come to
be widely different. Nevertheless their genealogical arrangement
remains strictly true, not only at the present time, but at each suc-
cessive period of descent. All the modified descendants from A
will have inherited something in common from their common
parent, as will all the descendants from I; so will it be with each
subordinate branch of descendants, at each successive stage. If,
however, we suppose any descendant of A, or of I, to have become
so much modified as to have lost all traces of its parentage, in this
case, its place in the natural system will be lost, as seems to have
occurred with some few existing organisms. All the descendants
of the genus F, along its whole line of descent, are supposed to
have been but little modified, and they form a single genus. But
this genus, though much isolated, will still occupy its proper in-
termediate iDosition. The. representation of the groups, as here
given in the diagram on a flat surface, is much too simple. The
branches ought to have diverged in all directions. If the names
of the groups had been simply written down in a linear series, the
representation would have been still less natural; and it is noto-
riously not possible to represent in a series, on a flat surface, the
affinities which we discover in nature amongst the beings of the
same group. Thus, the natural system is genealogical in its ar-
rangement, like a pedigree: but the amount of modification which
the different groups have undergone has to be expressed by ranking
them under different so-called genera, sub-families, families, sec-
tions, orders, and classes.

It may be worth while to illustrate this view of classification,
by taking the case of languages. If we possessed a perfect pedi-
gree of mankind, a genealogical arrangement of the races of man
would afford the best classification of the various languages now
spoken throughout the world; and if all extinct languages, and
all intermediate and slowly changing dialects, were- to be included,
such an arrangement would be the only possible one. Yet it
might be that some ancient languages had altered very little and

374 ORIGIN OF SPECIES

had given rise to few new languages, whilst others had altered
much owing to the spreading, isolation, and state of civilisation
of the several co-descended races, and had thus given rise to many-
new dialects and languages. The various degrees of difference
between the languages of the same stock, would have to be ex-
pressed by groups subordinate to groups; but the proper or even
the only possible arrangement would still be genealogical; and
this would be strictly natural, as it would connect together all lan-
guages, extinct and recent, by the closest*afEnities, and would give
the filiation and origin of each tongue.

In confirmation of this view, let us glance at the classification
of varieties, which are known or believed to be descended from a
single species. These are grouped under the species, with the
sub-varieties under the varieties; and in some cases, as with the
domestic pigeon, with several other grades of difference. Nearly
the same rules are followed as in classifying species. Authors
have insisted on the necessity of arranging varieties on a natural
instead of an artificial system; we are cautioned, for instance, not
to class two varieties of the pine-apple together, merely because
their fruit, though the most important part, happens to be nearly
identical; no one puts the Swedish and common turnip together,
though the esculent and thickened stems are so similar. What-
ever part is found to be most constant, is used in classing varie-
ties: thus the great agriculturist Marshall says the horns are
very useful for this purpose with cattle, because they are less
variable than the shape or colour of the body, &c. ; whereas with
sheep the horns are much less serviceable, because less constant.
In classing varieties, I apprehend that if we had a real pedigree,
a genealogical classification would be universally preferred; and
it has been attempted in some cases. For we might feel sure,
whether there had been more or less modification, that the prin-
ciple of inheritance would keep the forms together which were
allied in the greatest number of points. In tumbler pigeons,
though some of the sub- varieties differ in the important character
of the length of the beak, yet all are kept together from having
the common habit of tumbling; but the short-faced breed has
nearly or quite lost this habit : nevertheless, without any thought on
the subject, these tumblers are kept in the same group, because
allied in blood and alike in some other respects.

With species in a state of nature, every naturalist has in fact
brought descent into his classification; for he includes in his low-
est grade, that of species, the two sexes ; and how enormously these
sometimes differ in the most important characters, is known to
every naturalist: scarcely a single fact can be predicated in com-

MUTUAL AFFINITIES OF ORGANIC BEINGS 375

mon of the adult males and hermaphrodites of certain cirripedes,
and yet no one dreams of separating them. As soon as the three
Orchidean forms, Monachanthus, Myanthus, and Catasetum, which
had previously been ranked as three distinct genera, were known
to be sometimes produced on the same plant, they were immediately
considered as varieties; and now I have been able to show that
they are the male, female, and hermaphrodite forms of the same
species. The naturalist includes as one species the various larval
stages of the same individual, however much they may differ from
each other and from the adult, as well as the so-called alternate
generations of Steenstrup, which can only in a technical sense be
considered as the same individual. He includes monsters and va-
rieties, not from their partial resemblance to the parent-form, but
because they are descended from it.

As descent has universally been used in classing together the
individuals of the same species, though the males and females
and larvae are sometimes extremely different; and as it has been
used in classing varieties which have undergone a certain, and
sometimes a considerable amount of modification, may not this
same element of descent have been unconsciously used in group-
ing species under genera, and genera under higher groups, all
under the so-called natural system? I believe it has been uncon-
sciously used; and thus only can I understand the several rules
and guides which have been followed by our best systematists. As
we have no written pedigrees, we are forced to trace community of
descent by resemblances of any kind. Therefore we chose those
characters which are the least likely to have been modified, in rela-
tion to the conditions of life to which each species has been re-
cently exposed. Rudimentary structures on this view are as good
as, or even sometimes better than, other parts of the organisation.
We care not how trifling a character may be — let it be the mere
inflection of the angle of the jaw, the manner in which an insect's
wing is folded, whether the skin be covered by hair or feathers —
if it prevail throughout many and different species, especially those
having very different habits of life, it assumes high value; for
we can account for its presence in so many forms with such differ-
ent habits, only by inheritance from a common parent. We may
err in this respect in regard to single points of structure, but when
several characters, let them be ever so trifling, concur throughout
a large group of beings having different habits, we may feel almost
sure, on the theory of descent, that these characters have been in-
herited from a common ancestor; and we know that such aggre-
gated characters have especial value in classification.

We can understand why a species or a group of species may de-

376 ORIGIN OF SPECIES

part from its allies, in several of its most important characteris-
tics, and yet be safely classed with them. This may be safely done,
and is often done, as long as a sufficient number of characters, let
them be ever so unimportant, betrays the hidden bond of com-
munity of descent. Let two forms have not a single character in
common, yet, if these extreme forms are connected together by a
chain of intermediate groups, we may at once infer their com-
munity of descent, and we put them all into the same class. As
we find organs of high physiological importance — those which
serve to preserve life under the most diverse conditions of exist-
ence — are generally the most constant, we attach especial value
to them ; but if these same organs, in another group or section of a
group, are found to differ much, we at once value them less in our
classification. We shall presently see why embryological charac-
ters are of such high classificatory importance. Geographical dis-
tribution may sometimes be brought usefully into play in classing
large genera, because all the species of the same genus, inhabiting
any distinct and isolated region, are in all probability descended
from the same parents.

Analogical Resemblances. — We can understand, on the above
views, the very important distinction between real affinities and
analogical or adaptive resemblances. Lamarck first called atten-
tion to this subject, and he has been ably followed by Macleay and
others. The resemblance in the shape of the body and in the fin-
like anterior limbs between dugongs and whales, and between these
two orders of mammals and fishes, are analogical. So is the re-
semblance between a mouse and a shrew-mouse (Sorex), which
belong to different orders; and the still closer resemblance, in-
sisted on by Mr. Mivart, between the mouse and a small marsupial
animal (Antechinus) of Australia. These latter resemblances
may be accounted for, as it seems to me, by adaptation for sim-
ilarly active movements through thickets and herbage, together
with concealment from enemies.

Amongst insects there are innumerable similar instances; thus
Linnaeus, misled by external appearances, actually classed an
homopterous insect as a moth. We see something of the same
kind even with our domestic varieties, as in the strikingly similar
shape of the body in the improved breeds of the Chinese and com-
mon pig, which are descended from distinct species; and in the
similarly thickened stems of the common and specifically distinct
Swedish turnip. The resemblance between the greyhound and
the racehorse is hardly more fanciful than the analogies which
have been drawn by some authors between widely different ani-
mals.

MUTUAL AFFINITIES OF ORGANIC BEINGS 377

On the view of characters being of real importance for classi-
fication, only in so far as they reveal descent, we can clearly un-
derstand why analogical or adaptive characters, although of the
utmost importance to the welfare of the being, are almost valueless
to the systematist. For animals, belonging to two most distinct
lines of descent, may have become adapted to similar conditions,
and thus have assumed a close external resemblance; but such
resemblances will not reveal — will rather tend to conceal their
blood-relationship. We can thus also understand the apparent
paradox, that the very same characters are analogical when one
group is compared with another, but give true affinities when the
members of the same group are compared together : thus, the shape
of the body and fin-like limbs are only analogical when whales are
compared with fishes, being adaptations in both classes for swim-
ming through the water; but between the several members of the
whale family, the shape of the body and the fin-like limbs offer
characters exhibiting true affinity ; for as these parts are so nearly
similar throughout the whole family, we cannot doubt that they
have been inherited from a common ancestor. So it is with
fishes.

Numerous cases could be given of striking resemblances in
quite distinct beings between single parts or organs, which have
been adapted for the same functions. A good instance is afforded
by the close resemblance of the jaws of the dog and Tasmanian
wolf or Thylacinus, — animals which are widely sundered in the
natural system. But this resemblance is confined to general ap-
pearance, as in the prominence of the canines, and in the cutting
shape of the molar teeth. For the teeth really differ much : thus
the dog has on each side of the upper jaw four pre-molars and
only two molars ; whilst the Thylacinus has three pre-molars and
four molars. The molars also differ much in the two animals in
relative size and structure. The adult dentition is preceded by a
widely different milk dentition. Any one may of course deny that
the teeth in either case have been adapted for tearing flesh, through
the natural selection of successive variations; but if this be ad-
mitted in the one case, it is unintelligible to me that it should be
denied in the other. I am glad to find that so high an authority as
Professor Flower has come to this same conclusion.

The extraordinary cases given in a former chapter, of widely
different fishes possessing electric organs, — of widely different in-
sects possessing luminous organs, — and of orchids and asclepiads
having pollen-masses with viscid discs, come under this same head
of analogical resemblances. But these cases are so wonderful that
they were introduced as difficulties or objections to our theory. In

378 ORIGIN OF SPECIES

all such cases some fundamental difference in the growth or de-
velopment of the parts, and generally in their matured structure,
can be detected. The end gained is the same, but the means,
though appearing superficially to be the same, are essentially dif-
ferent. The principle formerly alluded to under the term of
analogical variation has probably in these cases often come into
play; that is, the members of the same class, although only dis-
tantly allied, have inherited so much in common in their consti-
tution, that they are apt to vary under similar exciting causes
in a similar manner; and this would obviously aid in the acquire-
ment through natural selection of parts or organs, strikingly like
each other, independently of their direct inheritance from a com-
mon progenitor.

As species belonging to distinct classes have often been adapted
by successive slight modifications to live under nearly similar cir-
cumstances,— to inhabit, for instance, the three elements of land,
air, and water, — we can perhaps understand how it is that a
numerical parallelism has sometimes been observed between the
sub-groups of distinct classes. A naturalist, struck with a paral-
lelism of this nature, by arbitrarily raising or sinking the value
of the groups in several classes (and all our experience shows that
their valuation is as yet arbitrary), could easily extend the paral-
lelism over a wide range; and thus the septenary, quinary, quar-
ternary and ternary classifications have probably arisen.

There is another and curious class of cases in which close ex-
ternal resemblance does not depend on adaptation to similar habits
of life, but has been gained for the sake of protection. I allude
to the wonderful manner in which certain butterflies imitate, as
first described by Mr. Bates, other and quite distinct species. This
excellent observer has shown that in some districts of S. America,
whefe, for instance, an Ithomia abounds in gaudy swarms, an-
other butterfly, namely, a Leptalis, is often found mingled in the
same flock ; and the latter so closely resembles the Ithomia in every
shade and stripe of colour and even in the shape of its wings, that
Mr. Bates, with his eyes sharpened by collecting during eleven
years, was, though always on his guard, continually deceived.
When the mockers and the mocked are caught and compared, they
are found to be very different in essential structure, and to belong
not only to distinct genera, but often to distinct families. Had
this mimicry occurred in only one or two instances, it might have
been passed over as a strange coincidence. But, if we proceed
from a district where one Leptalis imitates an Ithomia, another
mocking and mocked species belonging to the same two genera,
equally close in their resemblance, may be found. Altogether no

MUTUAL AFFINITIES OF ORGANIC BEINGS 379

less than ten genera are enumerated, which include species that
imitate other butterflies. The mockers and mocked always in-
habit the same region; we never find an imitator living remote
from the form which it imitates. The mockers are almost in-
variably rare insects; the mocked in almost eveyy case abound in
swarms. In the same district in which a species of Leptalis closely
imitates an Ithomia, there are sometimes other Lepidoptera
mimicking the same Ithomia : so that in the same place, species
of three genera of butterflies and even a moth are found all closely
resembling a butterfly belonging to a fourth genus. It deserves
especial notice that many of the mimicking forms of the Leptalis,
as well as of the mimicked forms, can be shown by a graduated
series to be merely varieties of the same species; whilst others
are undoubtedly distinct species. But why, it may be asked, are
certain forms treated as the mimicked and others as the mimickers ?
Mr. Bates satisfactorily answers this question, by showing that the
form which is imitated keeps the usual dress of the group to which
it belongs, whilst the counterfeiters have changed their dress and
do not resemble their nearest allies.

We are next led to inquire what reason can be assigned for cer-
tain butterflies and moths so often assuming the dress of another
and quite distinct form; why, to the perplexity of naturalists, has
nature condescended to the tricks of the stage? Mr. Bates has,
no doubt, hit on the true explanation. The mocked forms, which
always abound in numbers, must habitually escape destruction to
a large extent, otherwise they could not exist in such swarms; and
a large amount of evidence has now been collected, showing that
they are distasteful to birds and other insect-devouring animals.
The mocking forms, on the other hand, that inhabit the same dis-
trict, are comparatively rare, and belong to rare groups; hence
they must suffer habitually from some danger, for otherwise, from
the number of eggs laid by all butterflies, they would in three or
four generations swarm over the whole country. Now if a mem-
ber of one of these persecuted and rare groups were to assume a
dress so like that of a well-protected species that it continually
deceived the practised eyes of an entomologist, it would often de-
ceive predaceous birds and insects, and thus often escape destruc-
tion. Mr. Bates may almost be said to have actually witnessed
the process by which the mimickers have come so closely to resem-
ble the mimicked ; for he found that some of the forms of Lep-
talis which mimic so many other butterflies, varied in an extreme
degree. In one district several varieties occurred, and of these
one alone resembled to a certain extent, the common Ithomia of
the same district. In another district there were two or three

380 ORIGIN OP SPECIES

varieties, one of which was much commoner than the others, and
this closely mocked another form of Ithomia. From facts of this
nature, Mr. Bates concludes that the Leptalis first varies; and
when a variety happens to resemble in some degree any common
butterfly inhabiting the same district, this variety, from its resem-
blance to a flourishing and little-persecuted kind, has a better
chance of escaping destruction from predaceous birds and insects,
and is consequently oftener preserved ; — " the less perfect degrees
of resemblance being generation after generation eliminated, and
only the others left to propagate their kind." So that here we
have an excellent illustration of natural selection.

Messrs. Wallace and Trimen have likewise described several
equally striking cases of imitation in the Lepidoptera of the Malay
Archipelago and Africa, and with some other insects. Mr. Wal-
lace has also detected one such case with birds, but we have none
with the larger quadrupeds. The much greater frequency of imi-
tation with insects than with other animals, is probably the con-
sequence of their small size; insects cannot defend themselves,
excepting indeed the kinds furnished with a sting, and I have
never heard of an instance of such kinds mocking other insects,
though they are mocked ; insects cannot easily escape by flight from
the larger animals which prey on them; therefore, speaking meta-
phorically, they are reduced, like most weak creatures, to trickery
and dissimulation.

It should be observed that the process of imitation probably
never commenced between forms widely dissimilar in colour. But
starting with species already somewhat like each other, the closest
resemblance, if beneficial, could readily be gained by the above
means ; and if the imitated form was subsequently and gradually
modified through any agency the imitating form would be led
along the same track, and thus be altered to almost any extent,
so that it might ultimately assume an appearance or colouring
wholly unlike that of the other members of the family to which it
belonged. There is, however, some difliculty on this head, for it is
necessary to suppose in some cases that ancient members belonging
to several distinct groups, before they had diverged to their present
extent, accidentally resembled a member of another and protected
group in a sufficient degree to afford some slight protection; this
having given the basis for the subsequent acquisition of the most
perfect resemblance.

On the Nature of the Affinities connecting Organic Beings. —
As the modified descendants of dominant species, belonging to the
larger genera, tend to inherit the advantages which made the
groups to which they belong large and their parents dominant,

MUTUAL AFFINITIES OF ORGANIC BEINGS 381

they are almost sure to spread widely, and to seize on more and
more places in the economy of nature. The larger and more
dominant groups within each class thus tend to go on increasing
in size; and they consequently supplant many smaller and feebler
groups. Thus we can account for the fact that all organisms, re-
cent and extinct, are included under a few great orders, and under
still fewer classes. As showing how few the higher groups are in
number, and how widely they are spread throughout the world, the
fact is striking that the discovery of Australia has not added an
insect belonging to a new class ; and that in the vegetable kingdom,
as I learn from Dr. Hooker, it has added only two or three families
of small size.

In the chapter on Geological Succession I attempted to show,
on the principle of each group having generally diverged much in
character during the long-continued process of modification, how
it is that the more ancient forms of life often present characters
in some degree intermediate between existing groups. As some
few of the old and intermediate forms have transmitted to the
present day descendants but little modified, these constitute our so-
called esculent or aberrant species. The more aberrant any form
is, the greater must be the number of connecting forms which have
been exterminated and utterly lost. And we have some evidence of
aberrant groups having suffered severely from extinction, for they
are almost always represented by extremely few species; and such
species as do occur are generally very distinct from each other, which
again implies extinction. The genera Ornithorhynchus and Lepi-
dosiren, for example, would not have been less aberrant had each
been represented by a dozen species, instead of as at present by a
single one, or by two or three. We can, I think, account for this
fact only by looking at aberrant groups as forms which have been
conquered by more successful competitors, with a few members
still preserved under unusually favourable conditions.

Mr. Waterhouse has remarked that, when a member belonging to
one group of animals exhibits an affinity to a quite distinct group,
this affinity in most cases is general and not special; thus, accord-
ing to Mr. Waterhouse, of all Rodents, the bizcacha is most nearly
related to Marsupials ; but in the points in which it approaches this
order, its relations are general, that is, not to any one marsupial
species more than to another. As these points of affinity are be-
lieved to be real and not merely adaptive, they must be due in
accordance with our view to inheritance from a common progeni-
tor. Therefore we must suppose either that all Rodents, including
the bizcacha, branched off from some ancient Marsupial, which will
naturally -have been more or less intermediate in character with

882 ORIGIN OF SPECIES

respect to all existing Marsupials; or that both Rodents and Mar-
supials branched off from a common progenitor, and that both
groups have since undergone much modification in divergent di-
rections. On either view we must suppose that the bizcacha has
retained, by inheritance, more of the characters of its ancient pro-
genitor than have other Rodents; and therefore it will not be spe-
cially related to any one existing Marsupial, but indirectly to all
or nearly all Marsupials, from having partially retained the char-
acter of their common progenitor, or of some early member of the
group. On the other hand, of all Marsupials, as Mr. Waterhouse
has remarked, the Phascolomys T'esembles most nearly, not any one
species, but the general order of Rodents. In this case, however,
it may be strongly suspected that the resemblance is only analog-
ical, owing to the Phascolomys having become adapted to habits
like those of a Rodent. The elder De Candolle has made nearly
similar observations on the general nature of the affinities of dis-
tinct families of plants.

On the principle of the multiplication and gradual divergence
in character of the species descended from a common progenitor,
together with their retention by inheritance of some characters in
common, we can understand the excessively complex and radiating
affinities by which all the members of the same family or higher
group are connected together. For the common progenitor of a
whole family, now broken up by extinction into distinct groups
and sub-groups, will have transmitted some of its characters, modi'
fled in various ways and degrees, to all the species; and they will
consequently be related to each other by circuitous lines of affinity
of various lengths (as may be seen in the diagram so often re-
ferred to), mounting up through many predecessors. As it is
difficult to show the blood-relationship between the numerous kin-
dred of any ancient and noble family even by the aid of a
genealogical tree, and almost impossible to do so without this aid,
we can understand the extraordinary difficulty which naturalists
have experienced in describing, without the aid of a diagram, the
various affinities which they perceive between the many living and
extinct members of the same great natural class.

Extinction, as we have seen in the fourth chapter, has played an
important part in defining and widening the intervals between the
several groups in each class. We may thus account for the dis-
tinctness of whole classes from each other — for instance, of birds
from all other vertebrate animals — by the belief that many an-
cient forms of life have been utterly lost, through which the early
progenitors of birds were formerly connected with the early pro-
genitors of the other and at that time less differentiated vertebrate

MUTUAL AFFINITIES OF ORGANIC BEINGS 383

classes. There has been much less extinction of the forms of life
which once connected fishes with batrachians. There has been still
less within some whole classes, for instance, the Crustacea, for
here the most wonderfully diverse forms are still linked together
by a long and only partially broken chain of affinities. Extinction
has only defined the groups : it has by no means made them ; for if
every form which has ever lived on this earth were suddenly to
reappear, though it would be quite impossible to give definitions
by which each group could be distinguished, still a natural classi-
fication, or at least a natural arrangement, would be possible. We
shall see this by turning to the diagram; the letters, A to L, may
represent eleven Silurian genera, some of which have produced
large groups of modified descendants, with every link in each
branch and sub-branch still alive; and the links not greater than
those between existing varieties. In this case it would be quite
impossible to give definitions by which the several members of the
several groups could be distinguished from their more immediate
parents and descendants. Yet the arrangement in the diagram
would still hold good, and would be natural; for, on the principle
of inheritance, all the forms descended, for instance, from A, would
have something in common. In a tree we can distinguish this or
that branch, though at the actual fork the two unite and blend
together. We could not, as I have said, define the several groups;
but we could pick out types, or forms, representing most of the
characters of each group, whether large or small, and thus give a
general idea of the value of the differences between them. This
is what we should be driven to, if we were ever to succeed in col-
lecting all the forms in any one class which have lived throughout
all time and space. Assuredly we shall never succeed in making
so perfect a collection : nevertheless, in certain classes, we are
tending towards this end; and Milne Edwards has lately insisted,
in an able paper, on the high importance of looking to types,
whether or not we can separate and define the groups to which sucli
types belong.

Finally, we have seen that natural selection, which follows from
the struggle for existence, and which almost inevitably leads to
extinction and divergence of character in the descendants from
any one parent-species, explains that great and universal feature
in the affinities of all organic beings, namely, their subordination
in group under group. We use the element of descent in classing
the individuals of both sexes and of all ages under one species, al-
though they may have but few characters in common; we use
descent in classing acknowledged varieties, however different they
may be from their parents; and I believe that this element of de-

384 ORIGIN OF SPECIES

scent is the hidden bond of connection which naturalists have
sought under the term of the Natural System. On this idea of
the natural system being, in so far as it has been perfected,
genealogical in its arrangement, with the grades- of difference ex-
pressed by the terms genera, families, orders, &c., we can under-
stand the rules which we are compelled to follow in our classifica-
tion. We can understand why we value certain resemblances far
more than others; why we use rudimentary and useless organs, or
others of trifling physiological importance; why, in finding the re-
lations between one group and another, we summarily reject
analogical or adaptive characters, and yet use the same characters
within the limits of the same group. We can clearly see how it is
that all living and extinct forms can be grouped together within
a few great classes ; and how the several members of each class are
connected together by the most complex and radiating lines of
affinities. We shall never, probably, disentangle the inextricable
web of the affinities between the members of any one class; but
when we have a distinct object in view, and do not look to some
unknown plan of creation, we may hope to make sure but slow
progress.

Professor Hackel in his ' Generelle Morphologic ' and in other
works, has recently brought his great knowledge and abilities to
bear on what he calls phylogeny, or the lines of descent of all
organic beings. In drawing up the several series he trusts chiefly
to embryological characters, but receives aid from homologous
and rudimentary organs, as well as from the successive periods
at which the various forms of life are believed to have first ap-
peared in our geological formations. He has thus boldly made
a great beginning, and shows us how classification will in the
future be treated^

Morph fiy.

We have seen that the members of the same class, independently
of their habits of life, resemble each other in the general plan of
their organisation. This resemblance is often expressed by the
term " unity of type ; " or by saying that the several parts and
organs in the different species of the class are homologous. The
whole subject is included under the general term of Morphology.
This is one of the most interesting departments of natural his-
tory, and may almost be said to be its very soul. What can be
more curious than that the hand of a man, formed for grasping,
that of a mole for digging, the leg of the horse, the paddle of the
porpoise, and the wing of the bat, should all be constructed on the

MUTUAL AFFINITIES OF ORGANIC P>KIN(;S 38.*-)

same pattern, and should include similar bones, in the same rela-
tive positions? How curious it is, to give a subordinate though
striking instance, that the hind-feet of the kangaroo, which are
so well fitted for bounding- over the open plains, — those of
the climbing, leaf-eating koala, equally well fitted for grasping the
branches of trees, — those of the ground-dwelling, insect or root
eating, bandicoots, — and those of some other Australian marsu-
pials,— should all be constructed on the same extraordinary type,
namely with the bones of the second and third digits extremely
slender and enveloped within the same skin, so that they appear
like a single toe furnished with two claws. Notwithstanding this
similarity of pattern, it is obvious that the hind feet of these sev-
eral animals are used for as widely different purposes as it is pos-
sible to conceive. The case is rendered all the more striking by
the American opossums, which follow nearly the same habits of
life as some of their Australian relatives, having feet constructed
on the ordinary plan. Professor Flower, from whom these state-
ments are taken, remarks in conclusion : " We may call this con-
formity to type, without getting much nearer to an explanation of
the phenomenon ; " and he then adds " but is it not powerfully
suggestive of true relationship, of inheritance from a common an-
cestor ? "

Geoffrey St. Hilaire has strongly insisted on the high importance
of relative position or connexion in homologous parts ; they may
differ to almost any extent in form and size, and yet remain con-
nected together in the same invariable order. We never find, for
instance, the bones of the arm and fore-arm, or of the thigh and
leg, transposed. Hence the same names can be given to the homol-
ogous bones in widely different animals. We see the same great
law in the construction of the mouths of insects : what can be
more different than the immensely long spiral proboscis of a
sphinx-moth, the curious folded one of a bee or bug, and the great
jaws of a beetle ? — yet all these organs, serving for such widely
different purposes, are formed by infinitely numerous modifications
of an upper lip, mandibles, and two pairs of maxillae. The same
law governs the construction of the mouths and limbs of crusta-
ceans. So it is with the flowers of plants.

Nothing can be more hopeless than to attempt to explain this
similarity of pattern in members of the same class, by utility or
by the doctrine of final causes. The hopelessness of the attempt
has been expressly admitted by Owen in his most interesting work
on the ^ Nature of Limbs.' On the ordinary view of the independ-
ent creation of each being, we can only say that so it is; — that
it has pleased the Creator to construct all the animals and plants

386 ORIGIN OF SPECIES

in each great class on a uniform plan; but this is not a scientific
explanation.

The explanation is to a large extent simple on the theory of the
selection of successive slight modifications, — each modification
being profitable in some way to the modified form, but often af-
fecting by correlation other parts of the organisation. In changes
of this nature, there will be little or no tendency to alter the
original pattern, or to transpose the parts. The bones of a limb
might be shortened and flattened to any extent, becoming at the
same time enveloped in thick membrane, so as to serve as a fin; or
a webbed hand might have all its bones, or certain bones, length-
ened to any extent, with the membrane connecting them increased,
so as to serve as a wing; yet all these modifications would not tend
to alter the framework of the bones or the relative connection of
the parts. If we suppose that an early progenitor — the archetype
as it may be called — of all mammals, birds, and reptiles, had its
limbs constructed on the existing general pattern, for whatever
purpose they served, we can at once perceive the plain signification
of the homologous construction of the limbs throughout the class.
So with the mouths of insects, we have only to suppose that their
common progenitor had an upper lip, mandibles, and two pairs of
maxillae, these parts being perhaps very simple in form; and then
natural selection will account for the infinite diversity in the
structure and functions of the mouths of insects. Nevertheless, it
is conceivable that the general pattern of an organ might become
so much obscured as to be finally lost, by the reduction and ulti-
mately by the complete abortion of certain parts, by the fusion of
other parts, and by the doubling or multiplication of others, — va-
riations which we know to be within the limits of possibility. In
the paddles of the gigantic extinct sea-lizards, and in the mouths
of certain suctorial crustaceans, the general pattern seems thus to
have become partially obscured.

There is another and equally curious branch of our subject;
namely, serial homologies, or the comparison of the different parts
or organs in the same individual, and not of the same parts or
organs in different members of the same class. Most physiologists
believe that the bones of the skull are homologous — that is, cor-
respond in number and in relative connexion — with the elemental
parts of a certain number of vertebra}. The anterior and posterior
limbs in all the higher vertebrate classes are plainly homologous.
So it is with the wonderfully complex jaws and legs of crustaceans.
It is familiar to almost every one, that in a flower the relative
position of the sepals, petals, stamens, and pistils, as well as their
intimate structure, are intelligible on the view that they consist

MUTUAL AFFINITIES OF ORGANIC BEINGS 387

of metamorijhosed leaves, arranged in a spire. In monstrous
plants, we often get direct evidence of the possibility of one organ
being transformed into another; and we can actually see, during
the early or embryonic stages of development in flowers, as well as
in crustaceans and many other animals, that organs, which when
mature become extremely different are at first exactly alike.

How inexplicable are the cases of serial homologies on the or-
dinary view of creation ! Why should the brain be enclosed in a
box composed of such numerous and such extraordinarily shaped
pieces of bone, apparently representing vertebrae? As Owen has
remarked, the benefit derived from the yielding of the separate
pieces in the act of parturition by mammals, will by no means ex-
plain the same construction in the skulls of birds and reptiles.
Why should similar bones have been created to form the wing and
the leg of a bat, used as they are for such totally different pur-
poses, namely flying and walking? Why should one crustacean,
which has an extremely complex mouth formed of many parts,
consequently always have fewer legs; or conversely, those with
many legs have simpler mouths? Why should the sepals, petals,
stamens, and pistils, in each flower, though fitted for such distinct
purposes, be all constructed on the same pattern ?

On the- theory of natural selection, we can, to a certain extent,
answer these questions. We need not here consider how the bodies
of some animals first became divided into a series of segments, or
how they became divided into right and left sides, with correspond-
ing' organs, for such questions are almost beyond investigation. It
is, however, probable that some serial structures are the result
of cells multiplying by division, entailing the multiplication of the
parts developed from such cells. It must suflice for our purpose
to bear in mind that an indefinite repetition of the same part or or-
gan is the common characteristic, as Owen has remarked, of all low
or little specialised forms ; therefore the unknown progenitor of the
Vertebrata probably possessed many vertebra? ; the unknown progeni-
tor of the Articulata, many segments ; and the unknown progenitor
of flowering plants, many leaves arranged in one or more spires. We
have also formerly seen that parts many times repeated are emi-
nently liable to vary, not only in number, but in form. Conse-
quently such parts, being already present in considerable numbers,
and being highly variable, would naturally afford the materials for
adaptation to the most different purposes; yet they would gener-
ally retain, through the force of inheritance, plain traces of their
original or fundamental resemblance. They would retain this re-
semblance all the more, as the variations, which afforded the basis
for their subsequent modification through natural selection, would

388 OlIIGIN OF SPECIES

tend from the first to be similar; the parts being at an early-
stage of growth alike, and being subjected to nearly the same
conditions. Such parts, whether more or less modified, unless
their common origin became wholly obscured, would be serially
homologous.

In the great class of molluscs, though the parts in distinct spe-
cies can be shown, to be homologous, only a few serial homologies,
such as the valves of Chitons, can be indicated; that is, we are
seldom enabled to say that one part is homologous with another
part in the same individual. And we can understand this fact;
for in molluscs, even in the lowest members of the class, we do not
find nearly so much indefinite repetition of any one part as
we find in the other great classes of the animal and vegetable
kingdoms.

But morphology is a much more complex subject than it at first
appears, as has lately been well shown in a remarkable paper by
Mr. E. Ray Lankester, who has drawn an important distinction
between certain classes of cases which have all been equally ranked
by naturalists as homologous. He proposes to call the structures
which resemble each other in distinct animals, owing to their
descent from a common progenitor with subsequent modification,
homogeneous; and the resemblances which cannot thus be accounted
for, he proposes to call homoplastic. For instance, he believes
that the hearts of birds and mammals are as a whole homogeneous,
— that is, have been derived from a common progenitor; but that
the four cavities of the heart in the two classes are homoplastic, —
that is, have been independently developed. Mr. Lankester also
adduces the close resemblance of the parts on the right and left
sides of the body, and in the successive segments of the same in-
dividual animal; and here we have parts commonly called homo-
logous, which bear no relation to the descent of distinct species
from a common progenitor. Homoplastic structures are the same
with those which I have classed, though in a very imperfect man-
ner, as analogous modifications or resemblances. Their forma-
don may be attributed in part to distinct organisms, or to distinct
parts of the same organism, having varied in an analogous man-
ner; and in part to similar modifications, having been preserved
for the same general purpose or function, — of which many in-
stances have been given.

Naturalists frequently speak of the skull as formed of meta-
morphosed vertebrae ; the jaws of crabs as metamorphosed legs ; the
stamens and pistils in flowers as metamorphosed leaves; but it
would in most cases be more correct, as Professor Huxley has re-
marked, to speak of both skull and vertebrae, jaws and legs, &c., as

MUTUAL AFFINITIES OF ORGANIC BEINGS 389

having been metamorphosed, not one from the other, as they now
exist, but from some common and simpler element. Most natural-
ists, however, use such language only in a metaphorical sense;
they are far from meaning that during a long course of descent,
primordial organs of any kind — vertebra3 in the one case and legs
in the other — have actually been converted into skulls or jaws.
Yet so strong is the appearance of this having occurred, that
naturalists can hardly avoid employing language having this plain
signification. According to the views here maintained, such lan-
guage may be used literally; and the wonderful fact of the jaws,
for instance, of a crab retaining numerous characters which they
probably would have retained through inheritance, if they had
really been metamorphosed from true though extremely simple
legs, is in part explained.

Development and Embryology.

This is one of the most important subjects in the whole round of
history. The metamorphoses of insects, with which every one is
familiar, are generally effected abruptly by a few stages; but the
transformations are in reality numerous and gradual, though con-
cealed. A certain ephemerous insect (Chloeon) during its devel-
opment, moults, as shown by Sir J. Lubbock, above twenty times,
and each time undergoes a certain amount of change; and in this
case we see the act of metamorphosis performed in a primary and
gradual manner. Many insects, and especially certain crustaceans,
show us what wonderful changes of structure can be effected dur-
ing development. Such changes, however, reach their acme in the
so-called alternate generations of some of the lower animals. It
is, for instance, an astonishing fact that a delicate branching
coralline, studded with polypi and attached to a submarine rock,
should produce, first by budding and then by transverse division.
a host of huge floating jelly-fishes; and that these should produce
eggs, from which are hatched swimming animalcules, which attach
themselves to rocks and become developed into branching coral-
lines; and so on in an endless cycle. The belief in the essential
identity of the process of alternate generation and of ordinary
metamorphosis has been greatly strengthened by Wagner's dis-
covery of the larva or maggot of a fly, namely the Cecidorayia,
producing asexually other larvfe, and these others, which finally are
developed into mature males and females, propagating their kind
in the ordinary manner by eggs.

It may be worth notice that when Wagner's remarkable dis-
covery was first announced, I was asked how was it possible to

390 OtliaiN OP SPECIES

account for the larvae of this fly having acquired the power of
asexual reproduction. As long as the case remained unique no
answer could be given. But already Grimm has shown that an-
other fly, a Chironomus, reproduces itself in nearly the same man-
ner, and he believes that this occurs frequently in the Order. It
is the pupa, and not the larva, of the Chironomus which has this
power; and Grimm further shows that this case, to a certain ex-
tent, " unites that of the Cecidomyia with the parthenogenesis of
the Coccidae ; " — the term parthenogenesis implying that the ma-
ture females of the Coccidae are capable of producing fertile eggs
without the concourse of the males. Certain animals belonging to
several classes are now known to have the power of ordinary re-
production at an unusually early age ; and we have only to ac-
celerate parthenogenetic production by gradual steps to an earlier
and earlier age, — Chironomus showing us an almost exactly inter-
mediate stage, viz., that of the pupa — and we can perhaps account
for the marvellous case of the Cecidomyia.

It has already been stated that various parts in the same indi-
vidual which are exactly alike during an early embryonic period,
become widely different and serve for widely different purposes in
the adult state. So again it has been shown that generally the
embryos of the most distinct species belonging to the same class
are closely similar, but become, when fully developed, widely dis-
similar. A better proof of this latter fact cannot be given than the
statement by Von Baer that " the embryos of mammalia, of birds,
lizards, and snakes, probably also of chelonia are in their earliest
states exceedingly like one another, both as a whole and in the
mode of development of their parts; so much so, in fact, that we
can often distinguish the embryos only by their size. In my pos-
session are two little embryos in spirit, whose names I have omitted
to attach, and at present I am quite unable to say to what class
they belong. They may be lizards or small birds, or very young
mammalia, so complete is the similarity in the mode of formation
of the head and trunk in these animals. The extremities, however,
are still absent in these embryos. But even if they had existed
in the earliest stage of their development we should learn nothing,
for the feet of lizards and mammals, the wings and feet of birds,
no less than the hands and feet of man, all arise from the same
fundamental form." The larvae of most crustaceans, at cor-
responding stages of development, closely resemble each other, how-
ever different the adults may become; and so it is with very many
other animals. A trace of the law of embryonic resemblance occa-
sionally lasts till a rather late age : thus birds of the same genus,
and of allied genera, often resemble each other in their immature

MUTUAL AFFINITIES OF ORGANIC BEINGS 391

plumage; as we see in the spotted feathers in the young of the
thrush group. In the cat tribe, most of the species when adult
are striped or spotted in lines; and stripes or spots can be plainly
distinguished in the whelp of the lion and the puma. We occa-
sionally though rarely see something of the same kind in plants;
thus the first leaves of the ulex or furze, and the first leaves of the
phyllodineous acacias, are pinnate or divided like the ordinary
leaves of the leguminosa).

The points of structure, in which the embryos of widely differ-
ent animals within the same class resemble each other, often have
no direct relation to their conditions of existence. We cannot, for
instance, suppose that in the embryos of the vertebrata the pe-
culiar loop-like courses of the arteries near the branchial slits are
related to similar conditions, — in the young mammal which is
nourished in the womb of its mother, in the egg of the bird which
is hatched in a nest, and. in the spawn of a frog under water. We
have no more reason to believe in such a relation, than we have to
believe that the similar bones in the hand of a man, wing of a bat,
and fin of a porpoise, are related to similar conditions of life. No
one supposes that the stripes on the whelp of a lion, or the spots
on the young blackbird, are of any use to these animals.

The case, however, is different when an animal during any part
of its embryonic career is active, and has to provide for itself.
The period of activity may come on earlier or later in life; but
whenever it comes on, the adaptation of the larva to its conditions
of life is just as perfect and as beautiful as in the adult animal.
In how important a manner this has acted, has recently been well
shown by Sir J. Lubbock in his remarks on the close similarity of
the larvae of some insects belonging to very different orders, and
on the dissimilarity of the larva3 of other insects within the same
order, according to their habits of life. Owing to such adapta-
tions, the similarity of the larvse of allied animals is sometimes
greatly obscured; especially when there is a division of labour
during the different stages of development, as when the same larva
has during one stage to search for food, and during another stage
has to search for a place of attachment. Cases can even be given
of the larvae of allied species, or groups of species, differing more
from each other than do the adults. In most cases, however, the
larvae, though active, still obey, more or less closely, the law of
commion embryonic resemblance. Cirripedes afford a good in-
stance of this; even the illustrious Cuvier did not perceive that a
barnacle was a crustacean: but a glance at the larva shows this
in an unmistakable manner. So again the two main divisions
of cirripedes, the pedunculated and sessile, though differing widely

392 ORIGIN OF SPECIES

in external appearance, have larvae in all their stages barely dis
tinguishable.

The embryo in the course of development generally rises in or-
ganisation; I use this expression, though I am aware that it is
hardly possible to define clearly what is meant by the organisation
being higher or lower. But no one probably will dispute that the
butterfly is higher than the caterpillar. In some cases, however,
the mature animal must be considered as lower in the scale than
the larva, as with certain parasitic crustaceans. To refer once
again to cirripedes: the larvae in the first stage have three pairs
of locomotive organs, a simple single eye, and a probosciformed
mouth, with which they feed largely, for they increase much in
size. In the second stage, answering to the chrysalis stage of but-
terflies, they have six pairs of beautifully constructed natatory
legs, a pair of magnificent compound eyes, and extremely complex
antennae; but they have a closed and imperfect mouth, and cannot
fecvl : their function at this stage is, to search out by their- well-
developed organs of sense, and to reach by their active powers of
swinmiing, a jiroper place on which to become attached and to
undergo their final metamorphosis. AVhen this is completed they
are fixed for life: their legs are now converted into prehensile
organs ; they again obtain a well-constructed mouth ; but they have
no antennae, and their two eyes are now reconverted into a minute,
single, simple eye-spot. In this last and complete state, cirripedes
may be considered as either more highly or more lowly organised
than they w^ere in the larval condition. But in some genera the
larvae become developed into hermaphrodites having the ordinary
structure, and into what I have called complemental males; and
in the latter the development has assuredly been retrograde, for
the male is a mere sack, which lives for a short time and is desti-
tute of mouth, stomach, and every other organ of importance, ex-
cepting those for reproduction.

We are so much accustomed to see a difference in structure be-
tween the embryo and the adult, that w^e are tempted to look at
this difference as in some necessary manner contingent on growth.
But there is no reason why, for instance, the wing of a bat, or
the fin of a porpoise, should not have been sketched out with all
their parts in proper proportion, as soon as any part became visible.
In some whole groups of animals and in certain members of other
groups this is the case, and the embryo does not at any period
differ widely from the adult: thus Owen has remarked in regard to
cuttle-fish, "there is no metamorphosis; the cephalopodic character
is manifested long before the parts of the embryo are completed."
Land-shells and fresh-wafer crustaceans are born having their

MUTUAL AFFINITIES OF ORGANIC BEINGS 393

proper forms, whilst the marine members of the same two great
classes pass through considerable and often great changes during
their development. Spiders, again, barely undergo any metamor-
phosis. The larvffi of most insects pass through a worm-like stage,
whether they are active and adapted to diversified habits, or are
inactive from being placed in the midst of proper nutriment or
from being fed by their parents ; but in some few cases, as in that
of Aphis, if we look to the admirable drawings of the development
of this insect, by Professor Huxley, we see hardly any trace of the
vermiform stage.

Sometimes it is only the earlier developmental stages which fail.
Thus Fritz Miiller has made the remarkable discovery that cer-
tain shrimp-like crustaceans (allied to Penoeus) first appear under
the simple nauplius-form, and after passing through two or more
zoea-stages, and then through the mysis-stage, finally acquire their
mature structure : now in the whole great malacostracan order, to
which these crustaceans belong, no other member is as yet known
to be first developed under the nauplius-form, though many appear
as zoeas; nevertheless Miiller assigns reasons for his belief, that
if there had been no suppression of development, all these crusta-
ceans would have apx:)eared as nauplii.

How, then, can we explain these several facts in embryology, —
namely, the very general, though not universal, difference in struc-
ture between the embryo and the adult ; — the various parts in the
same individual embryo, which ultimately become very unlike and
serve for diverse purposes, being at an early period of growth
alike ; — the common, but not invariable, resemblance between the
embryos or larvae of the most distinct species in the same class ; —
the embryo often retaining whilst within the egg or womb, struc-
tures which are of no service to it, either at that or at a later
period of life; on the other hand larvae, which have to provide for
their own wants, being perfectly adapted to the surrounding con-
ditions ; — and lastly the fact of certain larvae standing higher in
the scale of organisation than the mature animal into which they
are developed? I believe that all these facts can be explained, as
follows.

It is commonly assumed, perhaps from monstrosities affecting
the embryo at a very early period, that slight variations or indi-
vidual differences necessarily appear at an equally early period.
We have little evidence on this head, but what we have certainly
points the other way; for it is notorious that breeders of cattle,
horses, and various fancy animals, cannot possibly tell, until
some timje after birth, what will be the merits or demerits of their
young animals. We see this plainly in our own children; we can-

394 ORIGIN OF SPECIES

not tel'l whether a child will be tall or short, or what its precise
features will be. The question is not, at what period of life each
variation may have been caused, but at what period the effects are
displayed. The cause may have acted, and I believe often has
acted, on one or both parents before the act of generation. It de-
serves notice that it is of no importance to a very young animal,
as long as it remains in its mother's womb or in the egg, or as
long as it is nourished and protected by its parent, whether most of
its characters are acquired a little earlier or later in life. It would
not signify, for instance, to a bird which obtained its food by hav-
ing a much-curved beak whether or not whilst young it possessed
a beak of this shape, as long as it was fed by its parents.

I have stated in the first chapter, that at whatever age a varia-
tion first api)ears in the parent, it tends to re-appear at a cor-
responding age in the offspring. Certain variations can only
appear at corresponding ages; for instance, peculiarities in th(i
caterpillar, cocoon, or imago states of the silk-moth: or, again, in
the full-grown horns of cattle. But variations, which, for all that
we can see might have first appeared either earlier or later in life,
likewise tend to re-appear at a corresponding age in the offspring
and parent. I am far from meaning that this is invariably the
case, and I could give several exceptional cases of variations
(taking the word in the largest sense) which have supervened at
an earlier age in the child than in the parent.

These two principles, namely, that slight variations generally
appear at a not very early period of life, and are inherited at a
corresponding not early period, explain, as I believe, all the above
specified leading facts in embryology. But first let us look to a
few analogous cases in our domestic varieties. Some authors who
have written on Dogs, maintain that the greyhound and bulldog,
though so different, are really closely allied varieties, descended
from the same wild stock ; hence I was curious to see how far their
puppies differed from each other: I was told by breeders that they
differed just as much as their parents, and this, judging by the
eye, seemed almost to be the case; but on actually measuring the
old dogs and their six-days-old puppies, I found that the puppies
had not acquired nearly their full amount of proportional differ-
ence. So, again, I was told that the foals of cart and race-horses
— breeds which have been almost wholly formed by selection under
domestication — differed as much as the full-grown animals ; but
having had careful measurements made of the dams and of three-
days-old colts of race and heavy cart-horses, I find that this is by
no means the case.

As we have conclusive evidence that the breeds of the Pigeon

I

MUTUAL AFFINITIES OF ORGANIC BEINGS 805

are descended from a single wild species, I compared tlie young
within twelve hours after being hatched; I carefully measured the
proportions (but will not here give the details) of the beak, width
of mouth, length of nostril and of eyelid, size of feet and length
of leg, in the wild parent-species, in pouters, fantails, runts, barbs,
dragons, carriers, and tumblers. Now some of these birds, when
mature, differ in so extraordinary a maimer in the length and
form of beak, and in other characters, that they would certainly
have been ranked as distinct genera if found in a state of nature.
But when the nestling birds of these several breeds were placed in
a row, though most of them could just be distinguished, the pro-
portional differences in the above specified points were incompar-
ably less than in the full-grown birds. Some characteristic points
of difference — for instance, that of the width of mouth — could
hardly be detected in the young. But there was one remarkable
exception to this rule, for the young of the short-faced tumbler
differed from the young of the wild rock-pigeon and of the other
breeds, in almost exactly the same proportions as in the adult state.

These facts are explained by the above two principles. Fanciers
select their dogs, horses, pigeons, &c., for breeding, when nearly
grown up : they are indifferent whether the desired qualities are
acquired earlier or later in life, if the full-grown animal pos-
sesses them. And the cases just given, more especially that of the
pigeons, show that the characteristic differences which have been
accumulated by man's selection, and which give value to his
breeds, do not generally appear at a very early period of life, and
are inherited at a corresponding not early period. But the case
of the short-faced tumbler, which when twelve hours old pos-
sessed its proper characters, proves that this is not the universal
rule; for here the characteristic differences must either have
appeared at an earlier period than usual, or, if not so, the differ-
ences must have been inherited, not at a corresponding, but at an
earlier age.

Now let us apply these two principles to species in a state of
nature. Let us take a group of birds, descended from some an-
cient form and modified through natural selection for different
habits. Then, from the many slight successive variations having
supervened in the several species at a not early age, and having
been inherited at a corresponding age, the young will have been
but little modified, and they will still resemble each other much
more closely than do the adults, — just as we have seen with the
breeds of the pigeon. We may extend this view to widely distinct
structures and to whole classes. The fore-limbs, for instance,
which once served as legs to a remote progenitor, may have be-

390 ORIGIN OP SPECIES

come, through a long course of modification, adapted in one de-
scendant to act as hands, in another as paddles, in another as
wings ; but on the above two principles the fore-limbs will not have
been much modified in the embryos of these several forms; al-
though in each form the fore-limb will differ greatly in the adult
state. Whatever influence long-continued use or disuse may have
had in modifying the limbs or other parts of any species, this will
chiefly or solely have affected it when nearly mature, when it was
compelled to use its full powers to gain its own living; and the
effects thus produced will have been transmitted to the offspring
at a corresponding nearly mature age. Thus the young will not
be modified, or will be modified only in a slight degree, through the
effects of the increased use or disuse of parts.

With some animals the successive variations may have super-
vened at a very early i)eriod of life, or the steps may have been
inherited at an earlier age than that at which they first occurred.
In either of these cases, the young or embryo will closely resem-
ble the mature parent-form, as we have seen with the short-faced
tumbler. And this is the rule of development in certain whole
groups, or in certain sub-groups alone, as with cuttle-fish, land-
shells, fresh-water crustaceans, spiders, and some members of the
great class of insects. With respect to the final cause of the
young in such groups not passing through any metamorphosis, we
can see that this would follow from the following contingencies;
namely, from the young having to provide at a very early age for
their own wants, and from their following the same habits of life
with their parents; for in this case, it would be indispensable for
their existence that they should be modified in the same manner as
their parents. Again, with respect to the singular fact that many
terrestrial and fresh-water animals do not undergo any metamor-
phosis, whilst marine members of the same groups pass through
various transformations, Fritz Mliller has suggested that the
process of slowly modifying and adapting an animal to live on the
land or in fresh water, instead of in the sea, would be greatly
simplified by its not passing through any larval stage ; for it is not
probable that places well adapted for both the larval and mature
stages, under such new and greatly changed habits of life, would
commonly be found unoccupied or ill-occupied by other organ-
isms. In this case the gradual acquirement at an earlier and
earlier age of the adult structure would be favoured by natural
selection; and all traces of former metamorphoses would finally be
lost.

If, on the other hand, it profited the young of an animal to
follow habits of life slightly different from those of the parent-

MUTUAL AFFINITIES OF ORGANIC BEINGS 397

form, and consequently to be constructed on a slightly different
plan, or if it profited a larva already different from its parent to
change still further, then, on the principle of inheritance at cor-
responding ages, the young or the larva? might be rendered by
natural selection more and more different from their parents to
any conceivable extent. Differences in the larva might, also, be-
come correlated with successive stages of its development; so that
the larva, in the first stage, might come to differ greatly from the
larva in the second stage, as is the case with many animals. The
adult might also bcome fitted for sites or habits, in which organs
of locomotion or of the senses, &c., would be useless; and in this
case the metamorphosis would be retrograde.

From the remarks just made we can see how bj'' changes of
structure in the young, in conformity with changed habits of life,
together with inheritance at corresponding ages, animals might
come to pass through stages of development, perfectly distinct
from the primordial condition of their adult progenitors. Most
of our best authorities are now convinced that the various larval
and pupal stages of insects have thus been acquired through adap-
tation, and not through inheritance from some ancient form. The
curious case of Sitaris — a beetle which passes through certain
unusual stages of development — will illustrate how this might
occur. The first larval form is described by M. Fabre, as an active,
minute insect, furnished with six legs, two long antennas, and four
eyes. These larvae are hatched in the nests of bees; and when the
male-bees emerge from their burrows, in the spring, which they do
before the females, the larvae spring on them, and afterwards crawl
on to the females whilst paired with the males. As soon as the
female bee deposits her eggs on the surface of the honey stored in
the cells, the larvae of the Sitaris leap on the eggs and devour
them. Afterwards they undergo a complete change; their eyes
disappear; their legs and antennae become rudimentary, and they
feed on honey; so that they now more closely resemble the ordi-
nary larvae of insects; ultimately they undergo a further trans-
formation, and finally emerge as the perfect beetle. Now, if an
insect, undergoing transformations like those of the Sitaris, were
to become the progenitor of a whole new class of insects, the course
of development of the new class would be widely different from
that of our existing insects; and the first larval stage certainly
would not represent the former condition of any adult and an-
cient form.

On the other hand it is highly probable that with many animals
the embryonic or larval stages show us, more or less completely,
the condition of the progenitor of the whole group in its adult

398 ORIGIN OF SPECIES

state. In the great class of the Crustacea, forms wonderfully dis-
tinct from each other, namely, suctorial parasites, cirripedes,
entomostraca, and even the malacostraca, appear at first as larvse
under the nauplius-f orm ; and as these larvse live and feed in the
open sea, and are not adapted for any peculiar habits of life, and
from other reasons assig-ned by Fritz Miiller, it is probable that at
some very remote period an independent adult animal, resembling
the Nauplius, existed, and subsequently produced, along several di-
vergent lines of descent, the above-named great Crustacean groups.
So again it is probable, from what we know of the embryos of
mammals, birds, fishes, and reptiles, that these animals are the
modified descendants of some ancient progenitor, which was fur-
nished in its adult state with branchiae, a swim-bladder, four fin-
like limbs, and a long tail, all fitted for an aquatic life.

As all the organic beings, extinct and recent, which have ever
lived, can be arranged within a few great classes ; and as all within
each class have, according to our theory, been connected together
by fine gradations, the best, and, if our collections were nearly per-
fect, the only possible arrangement, would be genealogical ; descent
being the hidden bond of connexion which naturalists have been
seeking under the term of the Natural System. On this view we
can understand how it is that, in the eyes of most naturalists, the
structure of the embryo is even more important for classification
than that of the adult. In two or more groups of animals, however
much they may differ from each other in structure and habits in
their adult condition, if they pass through closely similar em-
bryonic stages, we may feel assured that they all are descended
from one parent-form, and are therefore closely related. Thus,
community in embryonic structure reveals community of descent;
but dissimilarity in embryonic development does not prove discom-
munity of descent, for in one of two groups the developmental
stages may have been suppressed, or may have been so greatly
modified through adaptation to new habits of life, as to be no
longer recognisable. Even in groups, in which the adults have
been modified to an extreme degree, community of origin is often
revealed by the structure of the larvae; we have seen, for instance,
that cirripedes, though externally so like shell-fish, are at once
known by their larvse to belong to the great class of crustaceans.
As the embryo often shows us more or less plainly the structure
of the less modified and ancient progenitor of the group, we can
see why ancient and extinct forms so often resemble in their adult
state the embryos of existing species of the same class. Agassiz
believes this to be a universal law of nature; and we may hope
hereafter to see the law proved true. It can, however, be proved

MUTUAL AFFINITIES OF ORGANIC BEINGS 399

true only in those cases in which the ancient state of the pro-
genitor of the group, has not been wholly obliterated, either by
successive variations having supervened at a very early period of
growth, or by such variations having been inherited at an earlier
age than that at which they first appeared. It should also be
borne in mind, that the law may be true, but yet, owing to the
geological record not extending far enough back in time, may re-
main for a long period, or for ever, incapable of demonstration.
The law will not strictly hold good in those cases in which an an-
cient form became adapted in its larval state to some special line
of life, and transmitted the same larval state to a whole group of
descendants; for such larvsD will not resemble any still more an-
cient form in its adult state.

Thus, as it seems to me, the leading facts in embryology, which
are second to none in importance, are explained on the principle
of vari-ations in the many descendants from some one ancient pro-
genitor, having appeared at a not very early period of life, and
having been inherited at a corresponding period. Embryology
rises greatly in interest, when we look at the embryo as a i)icture,
more or less obscured, of the progenitor, either in its adult or larval
state, of all the members of the same great class.

Rudimentary, Atrophied, and Aborted Organs.

Organs or parts in this strange condition, bearing the plain
stamp of inutility, are extremely common, or even general, through-
out nature. It would be impossible to name one of the higher
animals in which some part or other is not in a rudimentary
condition. In the mammalia, for instance, the males possess rudi-
mentary mammae; in snakes one lobe of the lungs is rudimentary;
in birds the " bastard-wing " may safely be considered as a rudi-
mentary digit, and in some species the whole wing is so far
rudimentary that it cannot be used for flight. What can be more
curious than the presence of teeth in foetal whales, which when
grown up have not a tooth in their heads; or the teeth, which
never cut through the gums, in the upper jaws of unborn calves ?

Rudimentary organs plainly declare their origin and meaning in
various ways. There are beetles belonging to closely allied spe-
cies, or even to the same identical species, which have either full-
sized and perfect wings, or mere rudiments of membrane, which
not rarely lie under wing-covers firmly soldered together; and in
these cases it is impossible to doubt, that the rudiments repre-
sent wings. Rudimentary organs sometimes retain their potential-
ity: this occasionally occurs with the mammae of male mammals,

400 ORIGIN OF SrECIES

which have been known to become well developed and to secrete
milk. So again in the udders in the genus Bos, there are normally
four developed and two rudimentary teats; but the latter in our
domestic cows sometimes become well developed and yield milk.
In regard to plants the petals are sometimes rudimentary, and
sometimes well-developed in the individuals of the same species.
In certain plants having separated sexes Kolreuter found that by
crossing a species, in which the male flowers included a rudiment
of a pistil, with an hermaphrodite species, having of course a well-
developed pistil, the rudiment in the hybrid offspring was much
increased in size; and this clearly shows that the rudimentary and
perfect pistils are essentially alike in nature. An animal may
possess various parts in a perfect state, and yet they may in one
sense be rudimentary, for they are useless : thus the tadpole of the
common Salamander or Water-newt, as Mr. G. IT. Lewes remarks,
"has gills, and passes its existence in the water; but the Sala-
mandra atra, which lives high up among the mountains, brings
forth its young full-formed. This animal never lives in the
water. Yet if Vv^e open a gravid female, we find tadpoles inside her
with exquisitely feathered gills; and when placed in water they
swim about like the tadpoles of the water-newt. Obviously this
aquatic organisation has no reference to the future life of the
animal, nor has it any adaptation to its embryonic condition; it
has solely reference to ancestral adaptations, it repeats a phase
in the development of its progenitors."

An organ, serving for two purposes, may become rudimentary
or utterly aborted for one, even the more important purpose, and
remain i^erfectly efficient for the other. Thus in plants, the office
of the pistil is to allow the pollen- tubes to reach the ovules within
the ovarium. The pistil consists of a stigma supported on a
style; but in some Compositae, the male florets, which of course
oannot be fecundated, have a rudimentary pistil, for it is not
crowned with a stigma; but the style remains well developed
and is clothed in the usual manner with hairs, which serve to
brush the pollen out of the surrounding and conjoined anthers.
Again, an organ may become rudimentary for its proper purpose,
and be used for a distinct one: in certain fishes tjie swim-bladder
seems to be rudimentary for its proper function of giving buoy-
ancy, but has become converted into a nascent breathing organ or
lung. Many similar instances could be given.

Useful organs, however little they may be developed, unless we
have reason to suppose that they were formerly more highly devel-
oped, ought not to be considered as rudimentary. They may be
in a nascent condition, and in progress towards further develop-

MUTUAL AFFINITIES OF ORGANIC BEINGS 401

nient. Rudimentary organs, on the other hand, are either quite
useless, such as teeth which never cut through the gums, or ahnost
useless, such as the wings of an ostrich, which serve merely as
sails. As organs in this condition would formerly, when still
less developed, have been of even less use than at present, they
cannot formerly have been produced through variation and natural
selection, which acts solely by the preservation of useful modi-
fications. They have been partially retained by the power of
inheritance, and relate to a former state of things. It is, how-
ever, often difficult to distinguish between rudimentary and
nascent organs; for we can judge only by analogy whether a part
is capable of further development, in which case alone it deserves
to be called nascent. Organs in this condition will always be
somewhat rare; for beings thus provided will commonly have
been supplanted by their successors with the same organ in a
more perfect state, and consequently will have become long ago
extinct. The wing of the penguin is of high service, acting as a
fin ; it may, therefore, represent the nascent state of the wing : not
that I believe this to be the case; it is more probably a reduced
organ, modified for a new function: the wing of the Apteryx,
on the other hand, is quite useless, and is truly rudimentary.
Owen considers the simple filamentary limbs of the Lepidosiren
as the " beginnings of organs which attain full functional devel-
opment in higher vertebrates ; " but, according to the view lately
advocated by Dr. Giinther, they are probably remnants, consisting
of the persistent axis of a fin, with the lateral rays or branches
aborted. The mammary glands of the Ornithorhynchus may be
considered, in comparison with the udders of a cow, as in a
nascent condition. The ovigerous frena of certain, cirripedes,
which have ceased to give attachment to the ova and are feebly
developed, are nascent branchiss.

Rudimentary organs in the individuals of the same species are
very liable to vary in the degree of their development and in
other respects. In closely allied species, also, the extent to whicli
the same organ has been reduced occasionally differs much. This
latter fact is well exemplified in the state of the wings of female
moths belonging to the same family. Rudimentary organs may
be utterly aborted; and this implies, that in certain animals or
plants, parts are entirely absent which analogy would lead us to
expect to find in them, and which are occasionally found in mon-
strous individuals. Thus in most of the Scrophulariacese the fifth
stamen is utterly aborted; yet we may conclude that a fifth stamen
once existed, for a rudiment of it is found in many species of
the family, and this rudiment occasionally becomes perfectly

J-02 ORIGIN OF SPECIES

developed, as may sometimes be seen in the common snap-dragon.
In tracing the homologies of any part in different members of the
same class, nothing is more common, or, in order fully to under-
stand the relations of the parts, more useful than the discovery of
rudiments. This is well shown in the drawings given by Owen
of the leg-bones of the horse, ox, and rhinoceros.

It is an important fact that rudimentary organs, such as teeth
in the upper jaws of whales and ruminants, can often be detected in
the embryo, but afterwards wholly disappear. It is also, I believe,
a universal rule, that a rudim,entary part is of greater size in
the embryo relatively to the adjoining parts, than in the adult;
so that the organ at this early age is less rudimentary, or even
cannot be said to be in any degree rudimentary. Hence rudimen-
tary organs in the adult are often said to have retained their
embryonic condition.

I have now given the leading facts with respect to rudimentary
organs. In reflecting on them, every one must be struck with
astonishment; for the same reasoning power which tells us that
most parts and organs are exquisitely adapted for certain pur-
poses, tells us with equal plainness that these rudimentary or
atrophied organs are imperfect and useless. In works on natural
history, rudimentary organs are generally said to have been created
" for the sake of symmetry," or in order " to complete the scheme
of nature.'' But this is not an explanation, merely a re-statement
of the fact. Nor is it consistent with itself; thus the boa-con-
strictor has rudiments of hind-limbs and of a pelvis, and if it be
said that these bones have been retained " to complete the scheme
of nature," why, as Professor Weismann asks, have they not
been retained by other snakes, which do not possess even a ves-
tige of these same bones? What would be the thought of an
astronomer who maintained that the satellites revolve in elliptic
courses round their planets " for the sake of symmetry," because
the planets thus revolve round the sun? An eminent physiologist
accounts for the presence of rudimentary organs, by supposing
that they serve to excrete matter in excess, or matter injurious to
the system; but can we suppose that the minute papilla, which
often represents the pistil in male flowers, and which is formed
of mere cellular tissue, can thus act? Can we suppose that rudi-
mentary teeth, which are subsequently absorbed, are beneficial to
the rapidly growing embryonic calf by removing matter so precious
as phosphate of lime? When a man's fingers have been ampu-
tated, imperfect nails have been known to appear on the stumps,
and I could as soon believe that these vestiges of nails are devel-
oped in order to excrete horny matter, as that the rudimentary nails

MUTUAL AFFINITIES OF ORGANIC BEINGS 403

<;n the fin of the manatee have been developed for this same pur-
pose.

On the view of descent with modification, the origin of rudi-
mentary organs is comparatively simple;^ and we can understand
to a large extent the laws governing their imperfect development.
We have plenty of cases of rudimentary organs in our domestic
productions, — as the stump of a tail in tailless breeds, — the ves-
tige of an ear in earless breeds of sheep, — the reappearance of
minute dangling horns in hornless breeds of cattle, more espe-
cially, according to Youatt, in young animals, — and the state of
the whole flower in the cauliflower. We often see rudiments of
various parts in monsters; but I doubt whether any of these cases
throw light on the origin of rudimentary organs in a state of
nature, further than by showing that rudiments can be produced;
for the balance of evidence clearly indicates that species under
nature do not undergo great and abrupt changes. But we learn
from the study of our domestic productions that the disuse of
parts leads to their reduced size ; and that the result is inherited.

It appears probable that disuse has been the main agent in ren-
dering organs rudimentary. It would at first lead by slow steps to
the more and more complete reduction of a part, until at last it
became rudimentary, — as in the case of Ihe eyes of animals inhab-
iting dark caverns, and of the wings of birds inhabiting oceanic
islands, which have seldom been forced by beasts of prey to take
flight, and have ultimately lost the power of flying. Again, an
organ, useful under certain conditions, might become injurious
under others, as with the wings of beetles living on small and
exposed islands ; and in this case natural selection will have aided
in reducing the organ, until it was rendered harmless and rudi-
mentary.

Any change in structure and function, which can be effected
by small stages, is within the power of natural selection; so that
an organ rendered, through changed habits of life, useless or in-
jurious for one purpose, might be modified and used for another
purpose. An organ might, also, be retained for one alone of its
former functions. Organs, originally formed by the aid of nat-
ural selection, when rendered useless may well be variable, for
their variations can lio longer be checked by natural selection.
All this agrees well with what we see under nature. Moreover, at
whatever period of life either disuse or selection reduces an organ,
and this will generally be when the being has come to maturity
and has to exert its full powers of action, the principle of inherit-
ance at corresponding ages will tend to reproduce the organ in its
reduced state at the same rpature age, but will seldom effect it in

404 ORIGIN OF SPECIES

the embryo. Thus we can understand the greater size of rudi-
mentary organs in the embryo relatively to the adjoining parts,
and their lesser relative size in the adult. If, for instance, the
digit of an adult animal was used less and less during many
generations, owing to some change of habits, or if an organ or
gland was less and less functionally exercised, we may infer that it
would become reduced in size in the adult descendants of this
animal, but would retain nearly its original standard of develop-
ment in the embryo.

There remains, however, this difficulty. After an organ has
ceased being used, and has become in consequence much reduced,
how can it be still further reduced in size until the merest vestige
is left; and how can it be finally quite obliterated? It is scarcely
possible that disuse can go on producing any further effect after
the organ has once been rendered functionless. Some additional
explanation is here requisite which I cannot give. If, for instance,
it could be proved that every part of the organisation tends to
vary in a greater degree towards diminution than towards aug-
mentation or size, then we should be able to understand how an
organ which has become useless would be rendered, independently
of the effects of disuse, rudimentary and would at last be wholly
suppressed ; for the variations towards diminished size would no
longer be checked by natural selection. The principle of the
economy of growth, explained in a former chapter, by which the
materials forming any part, if not useful to the possessor, are
saved as far as possible, will perhaps come into play in rendering
a useless part rudimentary. But this principle will almost neces-
sarily be confined to the earlier stages of the process of reduction ;
for we cannot suppose that a minute papilla, for instance, rep-
resenting in a male flower the pistil of the female flower, and
formed merely of cellular tissue, could be further reduced or
absorbed for the sake of economising nutriment.

Finally, as rudimentary organs, by whatever steps they may
have been degraded into their present useless condition, are the
record of a former state of things, and have been retained solely
through the power of inheritance, — we can understand, on the
genealogical view of classification, how it is that systematists,
in placing organisms in their proper place in the natural system,
have often found rudimentary parts as useful as, or even some-
times more useful than, parts of high physiological importance.
Eudimentary organs may be compared with the letters in a word,
still retained in the spelling, but become useless in the pronuncia-
tion, but which serve as a clue for its derivation. On the view of
4escent with modificatipn, we may conclude that the existence

MUTUAL AFFINITIES OF ORGANIC BEINGS 405

of organs in a rudimentary, imperfect, and useless condition, or
quite aborted, far from presenting a strange difficulty, as they as-
suredly do on the old doctrine of creation, might even have been
anticipated in accordance with the views here explained.

Summary,

In this chapter I have attempted to show, that the arrange-
ment of all organic beings throughout all time in groups under
groups — that the nature of the relationships by which all living
and extinct organisms are united by complex, radiating, and
circuitous lines of affinities into a few grand classes, — the rules
followed and the difficulties encountered by naturalists in their
classifications, — the value set upon characters, if constant and
prevalent, whether of high or of the most trifling importance,
or, as with rudimentary organs, of no importance, — the wide
opposition in value between analogical or adaptive characters, and
characters of true affinity ; and other such rules ; — all naturally
follow if we admit the common parentage of allied forms, together
with their modification through variation and natural selection,
with the contingencies of extinction and divergence of character.
In considering this view of classification, it should be borne in
mind that the element of descent has been universally used in
ranking together the sexes, ages, dimorphic forms, and acknowl-
edged varieties of the same species, however much they may
differ from each other in structure. If we extend the use of this
element of descent, — the one certainly known cause of similarity
in organic beings, — we shall understand what is meant by the
Natural System: it is genealogical in its attempted arrangement,
with the grades of acquired difference marked by the terms, va-
rieties, species, genera, families, orders, and classes.

On this same view of descent with modification, most of the great
facts in Morphology become intelligible, — whether we look to the
same pattern displayed by the different species of the same class
in their homologous organs, to whatever purpose apijlied; or to
the serial and lateral homologies in each individual animal and
plant.

On the principle of successive slight variations, not neces-
sarily or generally supervening at a very early period of life,
and being inherited at a corresponding period, we can under-
stand the leading facts in Embryology; namely, the close resem-
blance in the individual embryo of the parts which are homologous,
and which when matured become widely different in struc-
ture and function; and the resemblance of the homologous parts or

40G ORIGIN OF SPECIES

organs in allied though distinct species, though fitted in the
adult state for habits as different as is possible. Larvse are active
embryos, which have been specially modified in a greater or less
degree in relation to their habits of life, with their modifications
inherited at a corresponding early age. On these same principles,
■ — • and bearing in mind that when organs are reduced in size, either
from disuse or through natural selection, it will generally be at
that period of life when the being has to provide for its own
wants, and bearing in mind how strong is the force of inheri-
tance— -the occurrence of rudimentary organs might even have
been anticipated. The importance of embryological characters and
of rudimentary organs in classification is intelligible, on the view
that a natural arrangement must be genealogical.

Finally, the several classes of facts which have been con-
sidered in this chapter, seem to me to proclaim so plainly, that
the innumerable species, genera and families, with which this world
is peopled, are all descended, each within its own class or group,
from common parents, and have all been modified in the course
of descent, that I should without hesitation adopt this view, even
if it were unsupported by other facts or arguments.

RECAPITULATION AND CONCLUSION 407

CHAPTEE XV.

RECAPITULATION AND CONCLUSION.

Recapitulation of the objections to the theory of Natural Selection —
Recapitulation of the general and special circumstances in its favour
— Causes of the general belief in the immutability of species — How-
far the theory of Natural Selection may be extended — Effects of its
adoption on the study of Natural History — Concluding Remarks.

AS this whole volume is one long argument, it may be con-
venient to the reader to have the leading facts and in-
ferences briefly recapitulated.

That many and serious objections may be advanced against the
theory of descent with modification through variation and nat-
ural selection, I do not deny. I have endeavoured to give to them
their full force. ]!!^othing at first can appear more difficult to
believe than that the more complex organs and instincts have been
perfected, not by means superior to, though analogous with,
human reason, but by the accumulation of innumerable slight var-
iations, each good for the individual possessor. Nevertheless, this
difficulty, though appearing to our imagination insuperably great,
cannot be considered real if we admit the following propositions,
namely, that all parts of the organisation and instincts offer,
at least, individual differences — that there is a struggle for exist-
ence leading to the preservation of profitable deviations of struc-
ture or instinct — and, lastly, that gradations in the state of
perfection of each organ may have existed, each good of its kind.
The truth of these propositions cannot, I think, be disputed.

It is, no doubt, extremely difficult even to conjecture by what
gradations many structures have been perfected, more especially
amongst broken and failing groups of organic beings, which have
suffered much extinction, but we see so many strange gradations
in nature, that we ought to be extremely cautious in saying that
any organ or instinct, or any whole structure, could not have
arrived at its present state by many graduated steps. There are,
it must be admitted, cases of special difficulty opposed to the
theory of natural selection; and one of the most curious of these
is the existence in the same community of two or three defined

408 ORIGIN OF SPECIES

castes of workers or sterile female ants; but I have attempted to
show how these difficulties can be mastered.

With respect to the almost universal sterility of species when
first crossed, which forms so remarkable a contrast with the almost
universal fertility of varieties when crossed, I must refer the
reader to the recapitulation of the facts given at the end of
the ninth chapter, which seem to me conclusively to show that this
sterility is no more a special endowment than is the incapacity
of two distinct kinds of trees to be grafted together; but that
it is incidental on differences confined to the reproductive sys-
tems of the intercrossed species. We see the truth of this con-
clusion in the vast difference in the results of crossing the same two
species reciprocally, — that is, when one species is first used as the
father and then as the mother. Analogy from the consideration of
dimorphic and trimorphic plants clearly leads to the same con-
clusion, for when the forms are illegitimately united, they yield
few or no seed, and their offspring are more or less sterile; and
these forms belong to the same undoubted species, and differ
from each other in no respect except in their reproductive organs
and functions.

Although the fertility of varieties when intercrossed and of
their mongrel offspring has been asserted by so many authors to be
universal, this cannot be considered as quite correct after the
facts given on the high authority of Gartner and Ivolreuter.
Most of the varieties which have been experimented on have been
produced under domestication; and as domestication (I do not
mean mere confinement) almost certainly tends to eliminate that
sterility which, judging from analogy, would have affected the
parent-species if intercrossed, we ought not to expect that domes-
tication would likewise induce sterility in their modified descend-
ants when crossed. This elimination of sterility apparently fol-
lows from the same cause which allows our domestic animals to
breed freely under diversified circumstances; and this again ap-
parently follows from their having been gradually accustomed
to frequent changes in their conditions of life.

A double and parallel series of facts seems to throw much light
on the sterility of species, when first crossed, and of their hybrid
offspring. On the one side, there is good reason to believe that
slight changes in the conditions of life give vigour and fertility
to all organic beings. We know also that a cross between the dis-
tinct individuals of the same variety, and between distinct var-
ieties, increases the number of their offspring, and certainly
gives to them increased size and vigour. This is chiefly owing to
the forms which are crossed having been exposed to somewhat

RECAPITULATION AND CONCLUSION 409

different conditions of life; for I have ascertained by a laborious
series of experiments that if all the individuals of the same
variety be subjected during several generations to the same condi-
tions, the good derived from crossing is often much diminished
or wholly disappears. This is one side of the case. On the other
side, we know that species which have long been exposed to nearly
uniform conditions, when they are subjected under confinement to
new and greatly changed conditions, either perish, or if they
survive, are rendered sterile, though retaining perfect health.
This does not occur, or only in a very slight degree, with our
domesticated productions, which have long been exposed to fluc-
tuating conditions. Hence when we find that hybrids produced
by a cross between two distinct species are few in number, owing
to their perishing soon after conception or at a very early age,
or if surviving that they are rendered more or less sterile, it
seems highly probable that this result is due to their having been in
fact subjected to a great change in their conditions of life, from
being compounded of two distinct organisations. He who will
explain in a definite manner why, for instance, an elephant or a
fox will not breed under confinement in its native country, whilst
the domestic pig or dog will breed freely under the most diversified
conditions, will at .the same time be able to give a definite answer
to the question why two distinct species, when crossed, as well
as their hybrid offspring, are generally rendered more or less
sterile, whilst two domesticated varieties when crossed and their
mongrel offspring are perfectly fertile.

Turning to geographical distribution, the difficulties encoun-
tered on the theory of descent with modification are serious
enough. All the individuals of the same species, and all the
species of the same genus, or even higher group, are descended
from common parents ; and therefore, in however distant and iso-
lated parts of the world they may now be found, they must in
the course of successive generations have travelled from some
one point to all the others. We are often wholly unable even
to conjecture how this could have been effected. Yet, as we
have reason to believe that some species have retained the same
specific form for very long periods of time, immensely long as
measured by years, too much stress ought not to be laid on the
occasional wide diffusion of the same species ; for during very long
periods there will always have been a good chance for wide mi-
gration by many means. A broken or interrupted range may
often be accounted for by the extinction of the species in the
intermediate regions. It cannot be denied that we are as yet
very ignorant as to the full extent of the various climatal and

410 ORIGIN OF SPECIES

geographical changes which have affected the earth during modern
periods; and such changes will often have facilitated migration.
As an example, I have attempted to show how potent has been
the influence of the Glacial period on the distribution of the same
and of allied species throughout the world. We are as yet pro-
foundly ignorant of the many occasional means of transport.
With respect to distinct species of the same genus inhabiting
distant and isolated regions, as the process of modification has
necessarily been slow, all the means of migration will have been
possible during a very long period ; and consequently the difficulty
of the wide diffusion of the species of the same genus is in some
degree lessened.

As according to the theory of natural selection an interminable
number of intermediate forms must have existed, linking' together
all the species in each group by gradations as fine as are our
existing varieties, it may be asked. Why do we not see these link-
ing forms all around us? Why are not all organic beings blended
together in an inextricable chaos ? With respect to existing forms,
we should remember that we have no right to expect (excepting in
rare cases) to discover directly connecting links between them,
but only between each and some extinct and supplanted form.
Even on a wide area, which has during a long period remained
continuous, and of which the climatic and other conditions of life
change insensibly in proceeding from a district occupied by one
species into another district occupied by a closely allied species,
we have no just right to expect often to find intermediate varieties
in the intermediate zones. For we have reason to believe that only
a few species of a genus ever undergo change ; the other species
becoming utterly extinct and leaving no modified progeny. Of
the species which do change, only a few within the same country
change at the same time; and all modifications are slowly effected.
I have also shown that the intermediate varieties which probably
at first existed in the intermediate zones, would be liable to be sup-
planted by the allied forms on either hand ; for the latter, from
existing in greater numbers, would generally be modified and
improved at a quicker rate than the intermediate varieties, which
existed in lesser numbers ; so that the intermediate varieties would,
in the long run, be supplanted and exterminated.

On this doctrine of the extermination of an infinitude of
connecting links, between the living and extinct inhabitants of
the world, and at each successive period between the extinct and
still older species, why is not every geological formation charged
with such links? Why does not every collection of fossil remains
aiford plain evidence of the gradation and mutation gf the forms

RECAPITULATION AND CONCLUSION 411

of life? Although geological research has undoubtedly revealed
the former existence of many links, bringing numerous forms of
life much closer together, it does not yield the infinitely many
fine gradations between past and present species required on the
theory; and this is the most obvious of the many objections
which may be urged against it. Why, again, do whole groups of
allied species appear, though this appearance is often false, to
have come in suddenly on the successive geological stages? Al-
though we now know that organic beings appeared on this globe,
at a period incalculably remote, long before the lowest bed of
the Cambrian system was deposited, why do we not find beneath
this system great piles of strata stored with the remains of the
progenitors of the Cambrian fossils? For on the theory, such
strata must somewhere have been deposited at these ancient and
utterly unknown epochs of the world's history.

I can answer these questions and objections only on the sup-
position that the geological record is far more imperfect than
most geologists believe. The number of specimens in all our
museums is absolutely as nothing compared with the countless
generations of countless species which have certainly existed. The
parent-form of any two or more species would not be in all its char-
acters directly intermediate between its modified offspring, any
more than the rock-pigeon is directly intermediate in crop and tail
between its descendants, the pouter and fantail pigeons. We
should not be able to recognise a species as the parent of another
and modified species, if we were to examine the two ever so closely,
unless we possessed most of the intermediate links; and owing
to the imperfection of the geological record, we have no just right
to expect to find so many links. If two or three, or even more
linking forms were discovered, they would simply be ranked by
many naturalists as so many new species, more especially if found
in different geological sub-stages, let their differences be ever so
slight. Numerous existing doubtful forms could be named which
are probably varieties; but who will pretend that in future ages
so many fossil links will be discovered, that naturalists will
be able to decide whether or not these doubtful forms ought to
be called varieties? Only a small portion of the world has been
geologically explored. Only organic beings of certain classes can
be preserved in a fossil condition, at least in any great number.
Many species when once formed never undergo any further change
but become extinct without leaving modified descendants; and the
periods, during which species have undergone modification, though
long as measured by years, have probably been short in com-
parison with the periods during which they retain the same form.

412 ORIGIN OF SrEClES

It is the dominant <and widely ranging species whicli vary most
frequently and vary most, and varieties are often at first local —
both causes rendering the discovery of intermediate links in any
one formation less likely. Local varieties will not spread into
other and distant regions until they are considerably modified and
improved; and when they have spread, and are discovered in a
geological- formation, they appear as if suddenly created there,
and will be simply classed as new species. Most formations have
been intermittent in their accumulation; and their duration has
I)robably been shorter than the average duration of specific forms.
Successive formations are in most cases separated from each other
by blank intervals of time of great length; for fossiliferous for-
mations thick enough to resist future degradation can as a general
rule be accumulated only where much sediment is deposited on the
subsiding bed of the sea. During the alternate periods of eleva-
tion and of stationary level the record will generally be blank.
During these latter periods there will probably be more variability
in the forms of life ; during periods of subsidence, more extinction.

With respect to the absence of strata rich in fossils beneath
the Cambrian formation, I can recur only to the hyiDothesis given in
the tenth chapter; namely, that though our continents and oceans
have endured for an enormous period in nearly their present
relative positions, we have no reason to assume that this has
always been the case; consequently formations much older than
any now known may lie buried beneath the great oceans. With
respect to the lapse of time not having been sufficient since our
planet was consolidated for the assumed amount of organic
change, and this objection, as urged by Sir William Thompson,
is probably one of the gravest as yet advanced, I can only say,
firstly, that we do not know at what rate species change as meas-
ured by years, and secondly, that many philosophers are not as
yet willing to admit that we know enough of the constitution of
the universe and of the interior of our globe to speculate with
safety on its past duration.

That the geological record is imperfect all will admit; but that
it is imperfect to the degree required by our theory, few will be
inclined to admit. If we look to long enough intervals of time,
geology plainly declares that species have all changed; and they
have changed in the manner required by the theory, for they have
changed slowly and in a graduated manner. We clearly see this
in the fossil remains from; consecutive formations invariably
being much more closely related to each other, than are the
fossils from widely separated formations.

Such is the sum of the several chief objections and difficulties

RECAriTULATION AND CONCLUSION 413

which may bo justly urged against the theory; and I have now
briefly recapitulated the answers and explaaations which, as far
as I can see, may be given. I have felt these difficulties far too
heavily during many years to doubt their weight. But it de-
serves especial notice that the more important objections relate
to questions on which we are confessedly ignorant ; nor do we know
how ignorant we are. We do not know all the i^ossible transitional
gradations between the simplest and the most perfect organs; it
cannot be pretended that we know all the varied means of Dis-
tribution during the long lapse of years, or that we know how
imperfect is the Geological Record. Serious as these several objec-
tions are, in my judgment they are by no means sufficient to over-
throw the theory of descent with subsequent modification.

Now let us turn to the other side of the argument. Under
domestication we see much variability, caused, or at least excited,
by changed conditions of life; but often in so obscure a manner,
that we are tempted to consider the variations as spontaneous.
Variability is governed by many complex laws, — by correlated
growth, compensation, the increased use and disuse of parts,
and the definite action of the surrounding conditions. There is
much difficulty in ascertaining how largely our domestic i^roduc-
tions have been modified ; but we may safely infer that the amount
has been large, and that modifications can be inherited for long
periods. As long as the conditions of life remain the same,
we have reason to believe that a modification, which has already
been inherited for many generations, may continue to be inher-
ited for an almost infinite number of generations. On the other
hand, we have evidence that variability when it has once come
into play, does not cease nnder domestication for a very long
period; nor do we know that it ever ceases, for new varieties
are still occasionally produced by our oldest domesticated pro-
ductions.

Variability is not actually caused by man; he only uninten-
tionally exposes organic beings to nev/ conditions of life, and
then nature acts on the organisation and causes it to vary.
But man can and does select the variations given to him by nature,
and thus accumulates them in any desired manner. He thus
adapts animals and plants for his own benefit or pleasure. He
may do this methodically, or he may do it unconsciously by pre-
serving the individuals most useful or pleasing to him without any
intention of altering the breed. It is certain that he can largely
influence the character of a breed by selecting, in each successive
generation, individual differences so slight as to be inappreciable

414 ORIGIN OF SPECIES

except by an educated eye. This unconscious process of selection
has been the great agency in the formation of the most distinct
and useful domestic breeds. That many breeds produced by man
have to a large extent the character of natural species, is shown
by the inextricable doubts whether many of them are varieties or
aboriginally distinct species.

There is no reason why the principles which have acted so
efficiently under domestication should not have acted under na-
ture. In the survival of favoured individuals and races, during
the constantly-recurrent Struggle for Existence, we see a powerful
and ever-acting form of Selection. The struggle for existence
inevitably follows from the high geometrical ratio of increase
which is common to all organic beings. This high rate of in-
crease is proved by calculation, — by the rapid increase of many
animals and plants during a succession of peculiar seasons, and
when naturalised in new countries. More individuals are born
than can possibly survive. A grain in the balance may deter-
mine which individuals shall live and which shall die, — which
variety of species shall increase in number, and which shall
decrease, or finally become extinct. As the individuals of the
same species come in all respects into the closest competition with
each other, the struggle will generally be most severe between
them ; it will be almost equally severe between the varieties of the
same species, and next in severity between the species of the same
genus. On the other hand the struggle will often be severe be-
tween beings remote in the scale of nature. The slightest ad-
vantage in certain individuals, at any age or during any season,
over those wdth which they come into competition, or better
adaptation in however slight a degree to the surrounding physical
conditions, will, in the long run, turn the balance.

With animals having separated sexes, there will be in most
cases a struggle between the males for the possession of the
females. The most vigorous males, or those which have most
successfully struggled with their conditions of life, will generally
leave most progeny. But success will often depend on the males
having special weapons, or means of defence, or charms; and a
slight advantage will lead to victory.

As geology plainly proclaims that each land has undergone
great physical changes, we might have expected to find that or-
ganic beings have varied under nature, in the same way as they
have varied under domestication. And if there has been any
variability under nature, it would be an unaccountable fact if nat-
ural selection had not come into play. It has often been asserted,
but the assertion is incapable of proof, that the amount of varia-

RECAPITULATION AND CONCLUSION 415

tioii under nature is a strictly limited quantity. Man, tliouj^li
acting on external characters alone and often capriciously, can
produce within a short period a great lesult by adding up mere
individual differences in his domestic productions; and every one
admits that species present individual differences. But, besides
such differences, all naturalists admit that natural varieties exist,
which are considered sufficiently distinct to be worthy of record,
in systematic works. No one has drawn any clear distinction
between individual differences and slight varieties; or between
more plainly marked varieties and sub-species, and species. On
separate continents, and on different parts of the same continent
when divided by barriers of any kind, and on outlying islands, what
a multitude of forms exist, which some experienced naturalists
rank as varieties, others as geographical races or sub-species, and
others as distinct, though closely allied species !

If then, animals and plants do vary, let it be ever so slightly
or slowly, why should not variations or individual differences,
which are in any way beneficial, be preserved and accumulated
through natural selection, or the survival of the fittest? If man
can by patience select variations useful to him, why, under chang-
ing and complex conditions of life, should not variations useful to
nature's living products often arise, and be preserved or selected?
What limit can be put to this power, acting during long ages and
rigidly scrutinising the whole constitution, structure, and habits
of each creature, — favouring the good and rejecting the bad ?
I can see no limit to this power, in slowly and beautifully adapt-
ing each form to the most com.plex relations of life. The theory
of natural selection, even if we look no farther than this, seems
to be in the highest degree probable. I have already recapitulated,
as fairly as I could, the opposed difficulties and objections: now
let us turn to the special facts and arguments in favour of the
theory.

On the view that species are only strongly marked and per-
manent varieties, and that each species first existed as a variety,
we can see why it is that no line of demarcation can be drawn
between species, commonly supposed to have been produced by
special acts of creation, and varieties which are acknowledged
to have been produced by secondary laws. On this same view
we can understand how it is that in a region where many species
of a genus have been produced, and where they now flourish, these
same species should present many varieties; for where the man-
ufactory of species has been active, we might expect, as a general
rule, to find it still in action; and this is the case if varieties be

41G OUIGIN OF SPECIES

incipient species. Moreover, the species of the hirger genera, which
afford the greater number of varieties or incipient species, retain
to a certain degree the character of varieties; for they differ from
each other by a less amount of difference than do the species of
smaller genera. The closely allied species also of the larger
genera apparently have restricted ranges, and in their affinities
they are clustered in little groups round other species — in both
respects resembling varieties. These are strange relations on the
view ^ that each species was independently created, but are in-
telligible if each existed first as a variety.

As each species tends by its geometrical rate of reproduction
to increase inordinately in number; and as the modified descendants
of each species will be enabled to increase by as much as they
become more diversified in habits and structure, so as to be able to
seize on many and widely different places in the economy of
nature, there will be a constant tendency in natural selection to
preserve the most divergent offspring of any one species. Hence,
during a long-continued course of modification, the slight differ-
ences characteristic of varieties of the same species, tend to be
augmented into the greater differences characteristic of the species
of the same genus. New and improved varieties will inevitably
supplant and exterminate the older, less improved, and interme-
diate varieties; and thus species are rendered to a large extent
defined and distinct objects. Dominant species belonging to the
larger groups within each class tend to give birth to new and
dominant forms; so that each large group tends to become still
larger, and at the same time more divergent in character. But as
all groups cannot thus go on increasing in size, for the world
would not hold them, the more dominant groups beat the less
dominant. This tendency in the large groups to go on increasing
in size and diverging in character, together with the inevitable
contingency of much extinction, explains the arrangement of all
The forms of life in groups subordinate to groups, all within a few
great classes, which has prevailed throughout all time. This grand
fact of the grouping of all organic beings under what is called the
Natural System, is utterly inexplicable on the theory of creation.

As natural selection acts solely by accumulating slight, suc-
cessive, favourable variations, it can produce no great or sudden
modifications; it can act only by short and slow steps. Hence,
the canon of " Natura non facit saltum," which every fresh ad-
dition to our knowledge tends to confirm, is on this theory intel-
ligible. We can see why throughout nature the same general
end is gained by an almost infinite diversity of means, for
every peculiarity when once acquired is long inherited, and

RECAPITULATION AND CONCLUSION 417

structures already modified in many different ways have to be
adapted for the same general purpose. We can, in short, see
why n'ature is prodigal in variety, though niggard in innovation.
But why this should be a law of nature if each species has been
independently created no man can explain.

Many other facts are, as it seems to me, explicable on this
theory. Plow strange it is that a bird, under the form of a
woodpecker, should prey on insects on the ground; that upland
geese w^iich rarely or never swim, should possess webbed feet; that
a thrush-like bird should dive and feed on sub-aquatic insects ; and
that a petrel should have the habits and structure fitting it for the
life of an auk! and so in endless other cases. But on the view
of each species constantly trying to increase in number, with nat-
ural selection always ready to adapt the slowly varying descendants
of each to any unoccupied or ill-occupied place in nature, these
facts cease to be strange, or might even have been anticipated.

We can to a certain extent understand how it is that there is
so much beauty throughout nature; for this may be largely at-
tributed to the agency of selection. That beauty, according to
our sense of it, is not universal, must be admitted by every one
who will look at some venomous snakes, at some fishes, and at
certain hideous bats with a distorted resemblance to the human
face. Sexual selection has given the most brilliant colours, ele-
gant patterns, and other ornaments to the males, and sometimes
to both sexes of many birds, butterflies, and other animals. With
birds it has often rendered the voice of the male musical to the
female, as well as to our ears. Flowers and fruit have been
rendered conspicuous by brilliant colours in contrast with the green
foliage, in order that the flowers may be readily seen, visited and
fertilised by insects, and the seeds disseminated by birds. How
it comes that certain colours, sounds, and forms should give
pleasure to man and the lower animals, — that is, how the sense of
beauty in its simplest form was first acquired, — we do not know
any more than how certain odours and flavours were first ren-
dered agreeable.

As natural selection acts by competition, it adapts and im^Droves
the inhabitants of each country only in relation to their co-inhabi-
tants; so that we need feel no surprise at the species of any one
country, although on the ordinary view supposed to have been
created and specially adapted for that country, being beaten and
supplanted by the naturalised productions from another land.
Nor ought we to marvel if all the contrivances in nature be not,
as far as we can judge, absolutely perfect, as in the case even
of the human eye; or if some of them be abhorrent to our ideas

418 ORIGIN OP SPECIES

of fitness. We need not marvel at the sting of tlie bee, wlien
used against an enemy, causing tlie bee's own death; at drones
being produced in such great numbers for one single act, and
being then slaughtered by their sterile sisters; at the astonishin,^,-
waste of pollen by our fir-trees; at the instiiactive hatred of the
queen-bee for her own fertile daughters ; at the ichneumonidse feed-
ing within the living bodies of caterpillars; or at other such
cases. The wonder indeed is, on the theory of natural selection,
that more cases of the want of absolute perfection have not been
detected.

The complex and little known laws governing the production
of varieties are the same, as far as we can judge, with the laws
which have governed the production of distinct species. In both
cases physical conditions seem to have produced some direct and
definite effect, but how much we cannot say. Thus, when varie-
ties enter any new station, they occasionally assume some of the
characters proper to the species of that station. With both varie-
ties and species, use and disuse seem to have produced a con-
siderable effect; for it is impossible to resist this conclusion when
we look, for instance, at the logger-headed duck, which has wings
incapable of flight, in nearly the same condition as in the domestic
duck; or when we look at the burrowing tucu-tucu, which is occa-
sionally blind, and then at certain moles, which are habitually blind
and have their eyes covered with skin; or when we look at the
blind animals inhabiting the dark caves of America and Europe.
With varieties and species, correlated variation seems to have
played an important part, so that when one part has been modi-
fied other parts have been necessarily modified. With both varie-
ties and species, reversions to long-lost characters occasionally
occur. How inexplicable on the theory of creation is the occasional
appearance of stripes on the shoulders and legs of the several
species of the horse-genus and of their hybrids! How simply is
this fact explained if we believe that these species are all de-
scended from a striped progenitor, in the same manner as the sev-
eral domestic breeds of the pigeon are descended from the blue
and barred rock-pigeon!

On the ordinary view of each species having been independ-
ently created, why should specific characters, or those by which the
species of the same genus differ from each other, be more variable
than generic characters in which they all agree? Why, for in-
stance, should the colour of a flower be more likely to vary in
any one species of a genus, if the other species possess differently
coloured flowers, than if all possessed the same coloured flowers?
If species are only well-marked varieties, of which the characters

RECAPITULATION AND CONCLUSION 419

have become in a high degree permanent, we can understand this
fact; for they have ah'cady varied since they branched off from a
common progenitor in certain characters, by which they have come
to be specifically distinct from each other; therefore these same
characters would be more likely again to vary than the generic
characters which have been inherited without change for an
immense period. It is inexplicable on the theory of creation why
a part developed in a very unusual manner in one species alone
of a genus, and therefore, as we may naturally infer, of great
importance to that species, should be eminently liable to varia-
tion; but, on our view, this part has undergone, since the several
species branched off from a common progenitor, an unusual
amount of variability and modification, and therefore we might
expect the part generally to be still variable. But a part may be
developed in the most unusual manner, like the wing of a bat,
and yet not be more variable than any other structure, if the part
be common to many subordinate forms, that is, if it has been
inherited for a very long period; for in this case it will have
been rendered constant by long-continued natural selection.

Glancing at instincts, marvellous as some are, they offer no
greater difficulty than do corporeal structures on the theory of the
natural selection of successive, slight, but profitable modifications.
We can thus understand why nature moves by graduated steps in
endowing different animals of the same class with their several
instincts. I have attempted to show how much light the prin-
ciple of gradation throws on the admirable architectural powers
of the hive-bee. Habit no doubt often comes into play in modify-
ing instincts; but it certainly is not indispensable, as we see in
the case of neuter insects, which leave no progeny to inherit the
effects of long-continued habit. On the view of all the species of
the same genus having descended from a common parent, and hav-
ing inherited much in common, we can understand how it is that
allied species, when placed under widely different conditions of
life, yet follow nearly the same instincts; why the thrushes of
tropical and temperate South America, for instance, line their
nests with mud like our British species. On the view of instincta
having been slowly acquired through natural selection, we need
not marvel at some* instincts being not perfect and liable to mis-
takes, and at many instincts causing other animals to suffer.

If species be only well-marked and permanent varieties, we
can at once see why their crossed offspring should follow the same
complex) laws in their degrees and kinds of resemblance to their
parents, — in being absorbed into each other by successive crosses,
find in other such points, — as do the crossed offspring of acknowl-

420 ORIGIN OF SPECIES

edged varieties. This similarity would be a strange fact, if species
had been independently created and varieties had been produced
through secondary laws.

If we admit that the geological record is imperfect to an
extreme degree, then the facts, which the record does give, strongly
support the theory of descent with modification. New species have
come on the stage slowly and at successive intervals; and the
amount of change, after equal intervals of time, is widely differ-
ent in different groups. The extinction of species and of whole
groups of species which has played so conspicuous a part in the
history of the organic world, almost inevitably follows from the
principle of natural selection ; for old forms are supplanted by
new and improved forms. Neither single species nor groups of
species reappear when the chain of ordinary generation is once
broken. The gradual diffusion of dominant forms, with the
slow modification of their descendants, causes the forms of life,
after long intervals of time, to appear as if they had changed simul-
taneously throughout the world. The fact of the fossil remains
of each formation being in some degree intermediate in character
between the fossils in the formations above and below, is simply
explained by their intermediate position in the chain of descent.
The grand fact that all extinct beings can be classed with all
recent beings, naturally follows from the living and the extinct
being the offspring of common parents. As species have generally
diverged in character during their long course of descent and
modification, we can understand why it is that the more ancient
forms, or early progenitors of each group, so often occupy a
position in some degree intermediate between existing groups.
Recent forms are generally looked upon as being, on the whole,
higher in the scale of organisation than ancient forms; and they
must be higher, in so far as the later and more improved forms
have conquered the older and less improved forms in the struggle
for life; they have also generally had their organs more special-
ised for different functions. This fact is perfectly compatible with
numerous beings still retaining simple and but little improved
structures, fitted for simple conditions of life; it is likewise com-
patible with some forms having retrograded in organisation, by
having become at each stage of descent better fitted for new and
degraded habits of life. Lastly, the wonderful law of the long
endurance of allied forms on the same continent, — of marsupials in
Australia, of edentata in America, and other such cases, — is in-
telligible, for within the same country the existing and the extinct
will be closely allied by descent.

Looking to geographical distribution, if we admit that there

RECAPITULATION AND CONCLUSION 4^1

has been during the long course of ages much migration from one
part of the world to another, owing to former climatal and geo-
graphical changes and to the many occasional and unknown
means of dispersal, then we can understand, on the theory of de-
scent with modification, most of the great leading facts in Dis-
tribution. We can see why there should be so striking a parallel-
ism in the distribution of organic beings throughout space, and
in their geological succession throughout time; for in both cases
the beings have been connected by the bond of ordinary genera-
tion, and the means of modification have been the same. We
see the full meaning of the wonderful fact, which has struck
every traveller namely, that on the same continent, under the most
diverse conditions, under heat and cold, on mountain and lowland,
on deserts and marshes, most of the inhabitants within each
great class are plainly related; for they are the descendants of the
same progenitors and early colonists. On this same principle of
former migration, combined in most cases with modification, we
can understand, by the aid of the Glacial period, the identity of
some few plants, and the close alliance of many others, on
the most distant mountains, and in the northern and southern
temperate zones ; and likewise the close alliance of some of the
inhabitants of the sea in the northern and southern temperate
latitudes, though separated by the whole intertropical ocean. Al-
though two countries may present physical conditions as closely
similar as the same species ever require, we need feel no surprise
at their inhabitants being widely different, if they have been for
a long period completely sundered from each other; for as the
relation of organism to organism is the most important of all
relations, and as the two countries will have received colonists
at various periods and in different proportions, from some other
country or from each other, the course of modification in the two
areas will inevitably have been different.

On this view of migration, with subsequent modification, we
see why oceanic islands are inhabited by only few species, but of
these, why many are peculiar or endemic forms. We clearly see
why species belonging to those groups of animals which cannot
cross wide spaces of the ocean, as frogs and terrestrial mammals,
do not inhabit oceanic islands; and why, on the other hand, new
and peculiar species of bats, animals which can traverse the ocean,
are often found on islands far distant from any continent. Such
cases as the presence of peculiar species of bats on oceanic islands
and the absence of all other terrestrial mammals, are facts utterly
inexplicable on the theory of independent acts of creation.

The existence of closely allied or representative species in any

422 ORIGIN OF SPECIES

two areas, implies, on the theory of descent with modification,
that the same parent-forms formerly inhabited both areas; and we
almost invariably find that wherever many closely allied species
inhabit two areas, some identical species are still common to both.
Wherever many closely allied yet distinct species occur, doubtful
forms and varieties belonging to the same groups likewise occur.
It is a rule of high generality that the inhabitants of each area
are related to the inhabitants of the nearest source whence im-
migrants might have been derived. We see this in the striking
relation of nearly all the plants and animals of the Galapagos
archipelago, of Juan Eernandez, and of the other American
islands, to the plants and animals of the neighboring American
mainland ; and of those of the Cape de Verde archipelago, and
of the other African islands to the African mainland. It must
be admitted that these facts receive no explanation on the theory
of creation.

The fact, as we have seen, that all past and present organic
beings can be arranged within a few great classes, in groups
subordinate to groups, and with the extinct groups often falling
in between the recent groups, is intelligible on the theory of
natural selection with its contingencies of extinction and di-
vergence of character. On these same principles we see how it is,
that the mutual afiinities of the forms within each class are so
complex and circuitous. We see why certain characters are far
more serviceable than others for classification; — why adaptive
characters, though of paramount importance tO' the beings, are of
hardly any importance in classification ; why characters derived
from rudimentary parts, though of no service to the beings, arc
often of high classificatory value ; and why embryological char-
acters are often the most valuable of all. The real affinities of all
organic beings, in contradistinction to their adaptive resemblances,
are due to inheritance or community of descent. The Natural
System is a genealogical arrangement, with the acquired grades
of difference, marked by the terms, varieties, species, genera, fam-
ilies, &c. ; and we have to discover the lines of descent by the
most permanent characters whatever they may be and of however
slight vital importance.

The similar framework of bones in the hand of a man, wing of
a bat, fin of the porpoise, and leg of the horse, — the same number
of vertebrgg forming the neck of the giraffe and of the elephant,
— and innumerable other such facts, at once explain themselves
on the theory of descent with slow and slight successive modifica-
tions. The similarity of pattern in the wing and in the leg of
a bat, though used for such different purpose, — in the jaws and

RECAPITULATION AND CONCLUSION 423

legs of a crab, — in the petals, stamens, and pistils of a flower, is
likewise, to a large extent, intelligible on the view of the gradual
modification of parts or organs, which were aboriginally alike in
an early progenitor in each of these classes. On the principle of
successive variations not always supervening at an early age,
and being inherited at a corresponding not early period of life,
we clearly see why the embryos of mammals, birds, reptiles, and
fishes should be so closely similar, and so unlike the adult forms.
We may cease marvelling at the embryo of an air-breathing
mammal or bird having branchial slits and arteries running in
loops, like those of a fish which has to breathe the air dissolved
in water by the aid of well-developed branchiae.

Disuse, aided sometimes by natural selection, will often have
reduced organs when rendered useless under changed habits or
conditions of life; and we can understand on this view the mean-
ing of rudimentary organs. But disuse and selection will generally
act on each creature, when it has come to maturity and has to play
its full part in the struggle for existence, and will thus have little
power on an organ during early life ; hence the organ will not be
reduced or rendered rudimentary at this early age. The calf,
for instance, has inherited teeth, which never cut through the
gums of the upper jaw, from an early progenitor having well-
developed teeth; and we may believe, that the teeth in the mature
animal were formerly reduced by disuse, owing to the tongue and
palate, or lips, having become excellently fitted through natural
selection to browse without their aid; whereas in the calf, the
teeth have been left unaffected, and on the principle of inheritance
at corresponding ages have been inherited from a remote period
lo the present day. On the view of each organism with all its
separate parts having been specially created, how utterly inex-
plicable is it that organs bearing the plain stamp of inutility,
such as the teeth in the embryonic calf or the shrivelled wings
under the soldered wing-covers of many beetles, should so fre-
quently occur. Nature may be said to have taken pains to reveal
her scheme of modification, by means of rudimentary organs, of
embryological and homologous structures, but we are too blind to
understand the meaning.

I have now recapitulated the facts and considerations which
have thoroughly convinced me that species have been modified,
during a long course of descent. This has been effected chiefly
through the natural selection of numerous successive, slight,
favourable variations; aided in an important manner by the
inherited effects of the use and disuse of parts; and in an unim-
portant manner, that is in relation to adaptive structures, whether

424 ORIGIN OF SrECIES

past or present, by the direct action of external conditions, and
by variations which seem to us in our ignorance to arise spon-
taneously. It appears that I formerly underrated the frequency
and value of these latter forms of variation, as leading to per-
manent modifications of structure independently of natural se-
lection. But as my conclusions have lately been much misrepre-
sented, and it has been stated that I attribute the modification of
species exclusively to natural selection, I may be permitted to
remark that in the first edition of this work, and subsequently,
I placed in a most conspicuous position — namely, at the close
of the Introduction — the following words : " I am convinced that
natural selection has been the main but not the exclusive means
of modification." This has been of no avail. Great is the power
of steady misrepresentation; but the history of science shows
that fortunately this power does not long endure.

It can hardly be supposed that a false theory would explain,
in so satisfactory a manner as does the theory of natural selection,
the several large classes of facts above specified. It has recently
been objected that this is an unsafe method of arguing; but it is
ii method used in judging of the common events of life, and has
often been used by the greatest natural philosophers. The un-
dulatory theory of light has thus been arrived at; and the belief
in the revolution of the earth on its own axis was until lately
supported by hardly any direct evidence. It is no valid objection
that science as yet throws no light on the far higher problem
of the essence or origin of life. Who can explain what is the
essence of the attraction of gravity? No one now objects to fol-
lowing out the results consequent on this unknown element of
attraction; notwithstanding that Leibnitz formerly accused New-
ton of introducing " occult qualities and miracles into philosophy.''

I see no good reason why the views given in this volume should
shock the religious feelings of any one. It is satisfactory, as
showing how transient such impressions are, tO' remember that the
greatest discovery ever made by man, namely, the law of the at-
traction of gravity, was also attacked by Leibnitz, " as subversive
of natural, and inferentially of revealed, religion." A celebrated
author and divine has written to me that " he has gradually learnt
to see that it is just as noble a conception of the Deity to believe
that He created a few original forms capable of self-development
into other and needful forms, as to believe that He required a
fresh act of creation to supply the voids caused by the action of
His laws."

Why, it may be asked, until recently did nearly all the most
eminent living naturalists and geologists disbelieve in the muta-

RECAPITULATION AND CONCLUSION 425

bility of species. It cannot be asserted that organic beings in a
state of nature are subject to no variation; it cannot be proved
that the amount of variation in the course of long ages is a lim-
ited quantity; no clear distinction has been, or can be, drawn
between species and well-marked varieties. It cannot be main-
tained that species when intercrossed are invariably sterile, and
varieties invariably fertile; or that sterility is a special endow-
ment and sign of creation. The belief that species were immutable
productions was almost unavoidable as long as the history of
the world was thought to be of short duration; and now that we
have acquired some idea of the lapse of time, we are too apt to
assume, without proof, that# the geological record is so perfect
that it would'have afforded us plain evidence of the mutation of
species, if they had undergone mutation.

But the chief' cause* of our natural unwillingness to admit that
one species has given birth to clear and distinct species, is that
we» are always slow in admitting great changes of which we do
not see the steps. The difficulty is the same as that felt by so
n^any geologists, when Lyell first insisted that long lines of
inland cliffs had been formed, and great valleys excavated, by
the» agencies which we see still at work. The mind cannot possibly
grasp the full meaning of the term of even a million years; it
cannot add up and perceive the full effects of many slight varia-
tions, accumulated during an almost infinite number of genera-
tions.

Although I am! fully convinced of the truth of the views given
in this volume under the form of an abstract, I by no means expect
to convince experienced naturalists whose minds are stocked with
a multitudet of facts all viewed, during a long course of years,
from a point of view directly opposite to mine. It is so easy
to hide our ignorance under such expressions as the " plan of
creation," " unity of design,'' &c., and to think that we give an
explanation when we only re-state a fact. Any one whose dispo-
sition leads him to attach more weight to unexplained difficulties
than to the explanation of a certain number of facts will cer-
tainly reject the theory. A few naturalists, endowed with much
flexibility of mind, and who have already begun to doubt the
immutabili4;y of species, may be influenced by this volume; but
I look with confidence to the future, — to young and rising natu-
ralists, who will be able to view both sides of the question with
impartiality. Whoever is led to believe that species are mutable
will do good service by conscientiously expressing his conviction;
for thus only can the load of prejudice by which this subject i^
overwhelmed be removed,

426 ORIGIN OF SPECIES

Several eminent naturalists have of late published their belief
that a multitude of reputed species in each genus are not real
species; but that other species are real, that is, have been inde-
pendently created. This seems to me a strange conclusion to
arrive at. They admit that a multitude of forms, which till lately
they themselves thought were special creations, and which are
still thus looked at by the majority of naturalists, and which
consequently have all the external characteristic features of true
species, — they admit that these have been produced by variation,
but they refuse to extend the same view to other and slightly
different forms. Nevertheless they do not pretend that they can
define, or even conjecture, which are the created forms of life,
and which are those produced by secondary laws. They admit
variation as a vera causa in one case, they arbitrarily reject it in
another, without assigning any distinction in the two cases. The
day will come when this will be given as a curious illustration
of the blindness of preconceived opinion. These authors seem no
more startled at a miraculous act of creation than at an ordinary
birth. But do they really believe that at innumerable periods in
the earth's history certain elemental atoms have been commanded
suddenly to flash into living tissues? Do they believe that at
each supposed act of creation one individual or many were pro-
duced? Were all the infinitely numerous kinds of animals and
plants created as eggs or seeds, or as full grown? and in the case
of mammals, were they created bearing tlie false marks of nourish-
ment from the mother's womb? Undoubtedly some of these same
questions cannot be answered by those who believe in the appear-
ance or creation of only a few forms of life, or of some one form
alone. It has been maintained by several authors that it is as
easy to believe in the creation of a million beings as of one;
but Maupertuis' })hilosophical axiom " of least action " leads the
mind more willingly to admit the smaller number; and certainly
we ought not to believe that innumerable beings within each great
class have been created with plain, but deceptive, marks of descent
from a single parent.

As a record of a former state of things, I have retained in the
foregoing paragraphs, and elsewhere, several sentences which imply
that naturalists believe in the separate creation of each species;
and I have been much censured for having thus expressed myself.
But undoubtedly this was the general belief when the first edition
of the present work appeared. I formerly spoke to very many
naturalists on the subject of evolution, and never once met with
any sympathetic agreement. It is probable that some did then
believe in evolution, but they were either silent, or expressed

RECAPITULATION AND CONCLUSION 427

themselves so ambiguously that it was not easy to understand
their meaning. Now things are wholly changed, and almost every
naturalist admits the great principle of evolution. There are,
however, some who still think that species have suddenly given
birth, through quite unexplained means, to new and totally differ-
ent forms: but, as I have attempted to show, weighty evidence
can be opposed to the admission of great and abrupt modifications.
Under a scientific point of view, and as leading to further investi-
gation, but little advantage is gained by believing that new forms
are suddenly developed in an inexplicable manner from old and
widely different forms, over the old beliefs in the creation of species
from the dust of the earth.

It may be asked how far I extend the doctrine of the modification
of species. The question is difficult to answer, because the more
distinct the forms are which we consider, by so much the argu-
raents in favour of community of descent become fewer in num-
ber and less in force. But some arguments of the greatest weight
extend very far. All the members of whole classes are connected
together by a chain of afiinities, and all can be classed on the same
principle, in groups subordinate to groups. Tossil remains some-
times tend to fill up very wide intervals between existing orders.

Organs in a rudimentary condition plainly show that an early
progenitor had the organ in a fully developed condition; and this
in some cases implies an enormous amount of modification in the
descendants. Throughout whole classes various structures are
formed on the same pattern, and at a very early age the embryos
closely resemble each other. Therefore I cannot doubt that the
theory of descent with modification embraces all the members
of the same great class or kingdom. I believe that animals are
descended from at most only four or five progenitors, and plants
from an equal or lesser number.

Analogy would lead me one step farther, namely, to the belief
that all animals and plants are descended from some one prototype.
But analogy may be a deceitful guide. Nevertheless all living
things have much in common, in their chemical composition, their
cellular structure, their laws of growth, and their liability to
injurious influences. We see this even in so trifling a fact as that
the same poison often similarly affects plants and animals; or that
the poison secreted by the gall-fly produces monstrous growths
on the wild rose or oak-tree. With all organic beings, excepting
perhaps some of the very lowest, sexual production seems to be
essentially similar. With all, as far as is at present known, the
germinal vesicle is the same; so that all organisms start from a
common origin. If we look even to the two main divisions — •

428 ORIGIN OF SPECIES

namely, to the animal and vegetable kingdoms — certain low
forms are so far intermediate in character that naturalists have
disputed to which kingdom they should be referred. As Professor
Asa Gray has remarked, " the spores and other reproductive bodies
of many of the lower algae may claim to have first a character-
istically animal, and then an unequivocally vegetable existence."
Therefore, on the principle of natural selection with divergence
of character, it does not seem incredible that, from some such low
and intermediate form, but animals and plants may have been
developed; and, if we admit this, we must likewise admit that all
the organic beings which have ever lived on this earth may be
descended from some one primordial form. But this inference
is chiefly grounded on analogy, and it is immaterial whether or
not it be accepted. No doubt it is possible, as Mr. G. H. Lewes
has urged, that at the first commencement of life many different
forms were evolved; but if so, we may conclude that only a very
few have left modified descendants. For, as I have recently re-
marked in regard to the members of each great kingdom, such as
the Vertebrata, Articulata, &c., we have distinct evidence in their
embryological, homologous, and rudimentary structures, that with-
in each kingdom all the members are descended from a single
progenitor.

When the views advanced by me in this volume, and by Mr.
Wallace, or when analogous views on the origin of species are
generally admitted, we can dimly foresee that there will be a
considerable revolution in natural history. Systematists will be
able to pursue their labours as at present; but they will not be
incessantly haunted by the shadowy doubt whether this or that
form be a true species. This, I feel sure and I speak after ex-
perience, will be no slight relief. The endless disputes whether or
not some fifty species of British brambles are good species will
cease. Systematists will have only to decide (not that this will
be easy) whether any form be sufiiciently constant and distinct
from other forms, to be capable of definition; and if definable,
whether the differences be sufficiently important to deserve a specific
name. This latter point will become a far more essential con-
sideration than it is at present; for differences, however slight,
between any two forms, if not blended by intermediate gradations,
are looked at by most naturalists as sufficient to raise both forms
to the rank of species.

Hereafter we shall be compelled to acknowledge that the only
distinction between species and well-marked varieties is, that the
latter are known, or believed, to be connected at the present day
by intermediate gradations, whereas species were formerly thus

RECAPITULATION AND CONCLUSION 429

connected. Hence, without rejecting the consideration of the pres-
ent existence of intermediate gradations between any two lorms,
we shall be led to weigh more carefully and to value higher the
actual amount of difference between them. It is quite possible
that forms now generally acknowledged to be merely varieties may
hereafter be thought worthy of specific names; and m this case
scientific and common language will come into accordance in
short, we shall have to treat species in the same manner as those
naturalists treat genera, who admit that genera are merely artificial
combinations made for convenience. This may not be a cheering
prospect; but we shall at least be free from the vam search for
the undiscovered and undiscoverable essence of the term_ species.

The other and more general departments of natural history wih
rise greatly in interest. The terms used by naturalists, of aamty,
relationship, community of type, paternity, morphology, adaptive
characters, rudimentary and aborted organs, &c., will cease to be
metaphorical, and will have a plain signification. When we no
longer look at an organic being as a savage looks at a ship, as
something wholly beyond his comprehension; when we regard
every production of nature as one which has had a long history,
when we contemplate every complex structure and instinct as the
summing up of many contrivances, each useful to the possessor,^ m
the same way as any great mechanical invention is the summing
up of the labour, the experience, the reason, and even the blunders
of numerous workmen; when we thus view each organic being,
how far more interesting - 1 speak from experience - does the
study of natural history become!

A grand and almost untrodden field of inquiry will be opened,
on the causes and laws of variation, on correlation, on the etiects
of use and disuse, on the direct action of external conditions, and
so forth. The study of domestic productions will rise immensely
in value. A new variety raised by man will be a more important
and interesting subject for study than one more species added
to the infinitude of already recorded species. Our classifications
will come to be, as far as they can be so made, genealogies; and
will then truly give what may be called the plan of creation. Ihe
rules for classifying will no doubt become simpler when we have
a definite object in view. We possess no pedigrees or armorial
bearings; and we have to discover and trace the many diverging
lines of descent in our natural genealogies, by characters ol any
kind which have long been inherited. Rudimentary organs wilJ
speak infallibly with respect to the nature of long-lost structures.
Species and groups of species which are called aberrant, and which
may fancifully be called living fossils, will aid us m forming a

43^ ORIGIN OF SPECIES

picture of the ancient forms of life. Embryology will often re^ ,.
to us the structure, m some degree obscured, of the prototyp.«
ol each great class. ^

When we can feel assured that all the individuals of the same
species, and all the closely allied species of most genera, have
withm a not very remote period descended from one parent, and
have migrated from some one birth-place; and when we better
know the many means of migration, then, by the ligU which
geolop^ now throws and will continue to throw, on former changes
of climate and of the level of the land, we shall surely be enabled
to trace m an admirable manner the former migrations of the
inhabitants of the whole world. Even at present, by comparing
the differences between the inhabitants of the sea on the opposite
sides of a continent and the nature of the various inhabitants on
that continent m relation to their apparent means of immigration
some light can be thrown on ancient geography.

The noble science of Geology loses glory from the extreme im-
perfection of the record. The crust of the earth with its imbedded
remains must not be looked at as a well-filled museum, but as
a poor collection made at hazard and at rare intervals. The
accumulation of each great fossiliferous formation will be recog-
nised as having depended on an unusual concurrence of favourable
circumstances, and the blank intervals between the successive
stages as having been of vast duration. But we shall be able to
gauge with some security the duration of these intervals by a com-
parison of the preceding and succeeding organic forms. We must
be cautious m attempting to correlate as strictly contemporaneous
two formations, which do not include many identical species, by
the general succession of the forms of life. As species are pro-
duced and exterminated by slowly acting and still existing causes
and not by miraculous acts of creation; and as the most important
ol all causes of organic change is one which is almost independent
o± altered and perhaps suddenly altered physical conditions, name-
ly, the mutual relation of organism to organism,— the improve-
ment of one organism entailing the improvement or the exter-
mination of others; it follows, that the amount of organic change
m the fossils of consecutive formations probably serves as a fair
measure of the relative though not actual lapse of time. A num-
ber of species, however, keeping in a body might remain for a long
period unchanged, whilst within the same period several of these
species by migrating into new countries and coming into competi-
tion with foreign associates, might become modified; so that we
must not overrate the accuracy of organic change as a measure
01 time.

RECAPITULATION AND CONCLUSION 431

In tho future I sec open fields for far more important researches.
Psychology will be securely based on the foundation already well
laid by Mr. Herbert Spencer, that of the necessary acquirement
of each mental power and capacity by gradation. Much light will
be thrown on the origin of man and his history.

Authors of the highest eminence seem to be fully satisfied with
the view that each species has been independently created. To
my mind it accords better with what we know of the laws im-
pressed on matter by the Creator, that the production and extinc-
tion of the past and present inhabitants of the world should have
been due to secondary causes, like those determining the birth
and death of the individual. When I view all beings not as special
creations, but as the lineal descendants of some few beings which
lived long before the first bed of the Cambrian system was
deposited, they seem to me to become ennobled. Judging from the
past, we may safely infer that not one living species will transmit
its unaltered likeness to a distant futurity. And of the species
now living very few will transmit progeny of any kind to a far
distant futurity; for the manner in which all organic beings are
grouped, shows that the greater number of species in each genus,
and all the species in many genera, have left no descendants, but
have become utterly extinct. We can so far take a prophetic
glance into futurity as to foretell that it will be the common and
widely-spread species, belonging to the larger and dominant groups
within each class, which will ultimately prevail and procreate new
and dominant species. As all the living forms of life are the
lineal descendants of those which lived long before the Cambrian
epoch, we may feel certain that the ordinary succession by genera-
tion has never once been broken, and that no cataclysm has
desolated the whole world. Plence we may look with some con-
fidence to a secure future of great length. And as natural selec-
tion works solely by and for the good of each being, all cor-
poreal and mental endowments will tend to progress towards
perfection.

It is interesting to contemplate a tangled bank, clothed with
many plants of many kinds, with birds singing on the bushes, with
various insects flitting about, and with worms crawling through
the damp earth, and to reflect that these elaborately constructed
forms, so different from each other, and dependent upon each
other in so complex a manner, have all been produced by laws
acting around us. These laws, taken in the largest sense, being
Growth with Reproduction; Inheritance which is almost implied
by reproduction; Variability from the indirect and direct action
of the conditions of life, and from use and disuse : a Ratio of

432 ORIGIN OF SPECIES

Increase so high as to lead to a Struggle for Life, and as a con-
sequence to Natural Selection, entailing Divergence of Character
and the Extinction of less-improved forms. Thus, from the war of
nature, from famine and death, the most exalted object which
we are capable of conceiving, namely, the production of the higher
animals, directly follows. There is grandeur in this view of life,
with its several powers, having been originally breathed by the
Creator into a few forms or into one ; and that, whilst this planet
has gone cycling on according to the fixed law of gravity, from
so simple a beginning endless forms most beautiful and most
wonderful have been, and are being evolved.

INDEX.

Aborted organs, in classification,

399
Acclimatisation, effort of, 112-114
Affinities connecting organic beings,
nature of, 380
of extinct species to living

forms, 304
of species in some areas of
land and sea, 321
Analogical resemblances in class-
ification, 37G
Animals always changing, 5
Atrophied organs, in classification,
399

Barriers, importance of, in distri-
bution, 320

Batrachians and land mammals not
found on oceanic islands,
353

Bears, do not breed in confinement,
7

Beauty, how acquired, IGl

Black hogs in Virginia, 9

Butterflies, variations in, 35

Candolle, A. de, observations on
oaks, 40

Cannibalism in Tierra del Fuego,
26

Cell-making instinct of bees, 220-
227

Changed conditions, effects of, lOG

Changes in life forms, simultane-
ous throughout the world,
300

Character changed by natural se-
lection, 86-90
convergence of, 100-102

Circumstances, influence of on se-
lection, 29-32

Classification of organic life, 366

Climbing plants, movements of,
195, 196

Color in animals, a protection
against some poisons, 9

Compensation and economy of
growth, 117-118

Conditions of existence, the higher
law in natural selection, 167

Convergence of character under
natural selection, 100-102

Correlated variation, 8, 114-117

483

Creation, single centres of, 323-

326
Crustaceans, pincers of, 193
Cuckoo, instincts of, 212-216

Descent, modified, difficulties of the
theory, 133

Descendants of a common ancestor,
probable effects in due to
natural selection, 90-97

Development of ancient forms, com-
pared with living forms, 310

Development in classification of
organic beings, 389

Difficulties of the theory of natural
selection, 150

Dimorphism and trimorphism,
253-257

Dispersal of species, means of, 326-
333
during Glacial period, 333

Distribution, geographical, not ex-
plained by present condi-
tions, 319

Divergence of character by natural
selection. 86-90

Dogs, descended from distinct spe-
cies, 11, 13

Domestic animals, origin of, 11

Doubtful species, 36

Ducks, origin of, 13

Embryology in classification, 389

Extinction caused by natural se-
lection, 85, 86, 296

Factors in variation, 6

False correlations, 118

Fertility of crossed varieties not
universal, 257

Flat-fish, changes in, during
growth, 186

Flight and vision changes in or-
gans of, 107

Fowls, descended from the wild
Indian fowl, 13

Fresh water productions, distribu-
tion of, 346

Geographical distribution of spe-
cies, 319-365

Geologic record, imperfection of,
266-292
succession of organic beings,
293

434

INDEX

Geological formations, gaps in, 277
Glacial period, dispersal of species
during, 333

Habit, effect of on variation, 8
Habits, different in same species,

141
Horses, descended from one species,

13
Hybridism and natural selection,

23G
Hybrids, compared with mongrels,

260

Imperfection of the geologic rec-
ord, 266-292

Increase, geometrical ratio of, 50
checks, upon, 53

Individual variation, 34-36

Indian cattle, origin of, 13

Individuals and varieties of some
species in the struggle for
life, 59

Inheritance, 8

Inherited instinct in domesticated
animals, 209

Insects, protective mimicry of, 181-
183

Instinct, development of, 205-235
and natural selection, 228-234

Intercrossing of individuals, 76-79

Knight, Andrew, theory of, 5

Lake dwellers, industries and ani-
mals of, 13

Laws of variation, 106-132

Life forms, simultaneous changes
of, throughout the world,
300

Life of oceanic islands, and rela-
tions to life of nearest main-
land, 356

Longevity, as an objection to the-
ory of natural selection, 168

Lubbock, observations on Coccus,
35

Lucas, Dr. Prosper, quoted, 9

Mammary glands, evolution of, 189-
191

Mistletoe, 2

Mivart's objections to theory of
natural selection, 176-204

Modes of transition, 147-150

Modifications not simultaneous, 169
of no apparent service, as an
objection to natural selec-
tion, 170
affecting only part of struc-
ture, 174

Mongrels, compared to hybrids, 260

Monkeys, prehensile tails of, 189

Monstrosities, origin of, 6

not fertile, 34
Morphology, in classification, 384
Multiple, rudimentary and lowly-
organized structures are va-
riable, 118, 119

Natural selection, illustrations of,
70-76
or survival of the fittest, 62-

105
summary of the arguments for,
407-432

Neuter and sterile insects, and nat-
ural selection, 233, 234

New forms, production of, through
natural selection, 80-85

Oceanic islands, animals and plants

of, 350
Organic beings, mutual affinities

of, 366
Organization, how far it advances,

97-100
Organs not always perfect, 158
of extreme perfection and

complication, in theory of

natural selection, 143-147
rudimentary, atrophied and

aborted, in classification, 399

Palseontological collections, form-
ers of, 272

Parts, specially developed, highly
variable, 119-122

Phytophagic varieties and species,
38

Pigeons, their differences and ori-
gin, 15-21

Plants, always changing under cul-
ture, 5

Polymorphic genera, 35

Polyzoa, special organs of, 192,
193

Progressive development, 171

Protean genera, 35

Rabbit, origin of, 13

Relation of animals and plants,
in struggle of existence, 55

Reproductive system, susceptibility
of to changes, 7

Reversion of species, 10

Rudimentary organs, in classifica-
tion, 399

Secondary sexual characters vari-
able, 123-125
Selection, principles of, 21-25
Sexual selection, 69-70
Selection, unconscious, 25-29
Similar types succeed each other
in similar areas, during lat-
er tertiary periods, 313

INDEX

435

Specific characters more variable
than generic, 122, 123

Shoveler-duck, beak of, 183

Slave-making instinct of ants, 216-
220

Spencer, on survival of the fittest,
49

Special instincts, examples of, 212-
228

Species, sudden appearance of
groups of allies, 284-292

Star-fish, tridactyle forceps of, 191,
192

Sterility, laws governing, in hy-
brids, 242-248
origin and causes of, in hy-
brids, 248-253
degrees of, 237-242

Strawberries, how improved, 30

Struggle for existence, 48-61

Survival of the fittest, or natural
^selection, 49, 62-105

Time in geology, lapse of, 268
Transitional forms, absence or rar-
ity of, 134
Transitions in habits of life, 138

Transition, modes of, 147-150

Unimportant organs as affected by
natural selection, 157

Utilitarian doctrine, how far true,
160

Unity of type, law of, 164

Use or disuse, effect of on varia-
tion, 8
combined with natural selec-
tion, 107, 108-112

Variation, laws of, 106-132
under domestication, 5-32
under nature, 33-47
greater among the larger gen-
era, 44
Variability of species, causes of, 5
" Variety," definition of, 33
Varieties and species, distinctions

between, 11, 42
Vision and flight, changes in or-
gans of, 107

Wallace, on limit of variation, 31
Whalebone, how originated, 183-

185
Woodpecker, 2

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