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DARWIN, AND AFTER DARWIN
AN EXPOSITION OF THE DARWINIAN THEORY
AND A DISCUSSION OF
POST-DARWINIAN QUESTIONS
BY
GEORGE JOHN ROMANES, M.A., LL.D., F.R.S
Honorary Fellow of Gonville and Caius College, Cambridge
I
THE DARWINIAN THEORY
FOURTH EDITION
THE OPEN COURT PUBLISHING COMPANY
1910
The Illustrations of this book (with the exception of the Frontispiece and the
colored plate facing page 332} are copyrighted under the title " Darwinism Illus-
trated."
THE OPEN COURT PUBLISHING Co.
10 I
PRESS OF THE
BLAKELY-OSWALD PRINTING CO.
CHICAGO
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I
PREFACE
SEVERAL years ago Lord Rosebery founded, in
the University of Edinburgh, a lectureship on " The
Philosophy of Natural History," and I was invited by
the Senatus to deliver the lectures. This invitation
I accepted, and subsequently constituted the material
of my lectures the foundation of another course, which
was given in the Royal Institution, under the title
" Before and after Darwin." Here the course extended
over three years— namely from 1888 to 1890. The
lectures for 1888 were devoted to the history of biology
from the earliest recorded times till the publication of
the " Origin of Species " in 1 859 ; the lectures for
1889 dealt with the theory of organic evolution up to
the date of Mr. Darwin's death, in 1882 ; while
those of the third year discussed the further develop-
ments of this theory from that date till the close of
the course in 1890.
It is from these two courses — which resembled each
other in comprising between thirty and forty lectures,
but differed largely in other respects — that the pre-
sent treatise has grown. Seeing, however, that it has
vi Preface.
grown much beyond the bulk of the original lectures,
I have thought it desirable to publish the whole in
the form of three separate works. Of these the first
— or that which deals with the purely historical side
of biological science — may be allowed to stand over
for an indefinite time. The second is the one which
is now brought out. and which, as its sub-title signifies,
is devoted to the general theory of organic evolution
as this was left by the stupendous labours of Darwin.
As soon as the translations shall have been completed,
the third portion will follow (probably in the Autumn
season), under the sub-title, " Post-Darwinian Ques-
tions."
As the present volume is thus intended to be merely
a systematic exposition of what may be termed the
Darwinism of Darwin, and as on this account it is
likely to prove of more service to general readers than
to professed naturalists, I have been everywhere care-
ful to avoid assuming even the most elementary know-
ledge of natural science on the part of those to whom
the exposition is addressed. The case, however, will
be different as regards the next volume, where I shall
have to deal with the important questions touching
Heredity, Utility, Isolation, &c., which have been
raised since the death of Mr. Darwin, and which are
now being debated with such salutary vehemence by
the best naturalists of our time.
My obligations to the Senatus of the University
of Edinburgh, and to the Board of Management of
the Royal Institution, have already been virtually
Preface. vii
expressed ; but I should like to take this opportunity
of also expressing my obligations to the students who
attended the lectures in the University of Edinburgh.
For alike in respect of their large numbers, their
keen intelligence, and their generous sympathy, the
members of that voluntary class yielded a degree of
stimulating encouragement, without which the labour
of preparing the original lectures could not have been
attended with the interest and the satisfaction that I
found in it. My thanks are also due to Mr. R. E.
Holding for the painstaking manner in which he has
assisted me in executing most of the original drawings
with which this volume is illustrated ; and likewise to
Messrs. Macmillan and Co. for kindly allowing me
to reprint — without special acknowledgment in every
case — certain passages from an essay which they
published for me many years ago, under the title
"Scientific Evidences of Organic Evolution. Lastly,
I must mention that I am indebted to the same firm
for permission to reproduce an excellent portrait of
Mr. Darwin, which constitutes the frontispiece.
G. J. R.
CHRIST CHURCH, OXFORD,
April \()th, 1892.
CONTENTS
CHAPTER I.
MOB
INTRODUCTORY . i
CHAPTER II.
CLASSIFICATION 33
CHAPTER III.
MORPHOLOGY 50
CHAPTER IV.
EMBRYOLOGY 98
CHAPTER V.
PALAEONTOLOGY 156
CHAPTER VI.
GEOGRAPHICAL DISTRIBUTION 304
CHAPTER VII.
THE THEORY OF NATURAL SELECTION 251
CHAPTER VIII.
EVIDENCES OF THE THEORY OF NATURAL SELECTION . . 285
x Contents.
CHAPTER IX.
PAGE
CRITICISMS OF THE THEORY OF NATURAL SELECTION . . 333
CHAPTER X.
THE THEORY OF SEXUAL SELECTION, AND CONCLUDING
REMARKS 379
APPENDIX TO CHAPTER V. 431
NOTE A TO PAGE 257 443
NOTE B TO PAGE 295 ....... 445
NOTE C TO PAGE 394 44*
INDEX .. r ........ 451
LIST OF ILLUSTRATIONS
FIG. T. Successive forms of Paludina, from the Tertiary deposits
ofSlavonia ........ 19
2. Skeleton of Seal 52
3. Skeleton of Greenland Whale . . . • • 53
4. Paddle of Whale compared with Hand of Man . . 54
5. Wing of Reptile, Mammal, and Bird . ... 56
6. Skeleton of Dinornis gravit 61
7. Hermit-crabs compared with the cocoa-nut crab . . 64
8. Rudimentary or vestigial hind-limbs of Python . . 67
9. Afleryx Aitstratit 69
10. Illustrations t>f the nictitating membiane in various
animals named . -75
11. Rudimentary, or vestigial and useless, muscles of the
human ear 76
12. Portrait of a young male gorilla ..... 78
13. Portrait of a young male child 79
14. An infant, three weeks old, suppoiting its own weight . 81
15. Sacrum of Gorilla compared with that of Man, showing
the rudimentary tail-bones of each .... 82
16. Diagrammatic outline of the human embryo when about
seven weeks old 83
17. Front and back view of adult human sacrum ... 84
1 8. Appendix vermiformis in Orang and in Man ... 85
19. The same, showing variation in the Orang ... 85
20. Human ear 86
21. T cetus of an Orang 87
32. Vestigial characters of human ears .... 88
23. Hair-tracts on the arms and hands of Man, as compared
with those on the arms and hands of Chimpanzee . 90
34. Molar teeth of lower jaw in Gorilla, Orang, and Man . 93
xii List of I Illustrations.
•Ml
FIG. 15. Perforation of the humerus (supra-condyloid foramen) in
three species of Qnadrumana where it normally occurs,
and in Man, where it does not normally occur . . 95
26. Antlers of stag, showing successive addition of branches
in successive years . . • . . . . . 100
37. Fission of a Protozoon ....... 107
28. Hydra viridis, partly in section 1 1 1
29. Successive stages in the division of the ovum, or egg-cell,
of a worm 113
30. Ovarian ovum of a Mammal 121
31. Amoeboid movements of young egg-cells . . .122
32. Human ovum, mature and greatly magnified . .123
33. Stages in the formation of the polar bodies in the ovum of
a star-fish 12:
34. Fertilization of the ovum of an echinoderm . . .126
35. Fertilization of the ovum of a star- fish . . . .127
36. Karyokinesis of a typical tissue-cell (epithelium of Sala-
mander) 129
37. Study of successive changes taking place in the nucleus
of an epithelium-cell, preparatory to division of the cell 131
38. Formation and conjugation of the pronuclei in Ascaris
megalocephala 132, 133
39. Segmentation of ovum 135
40. The contents of an ovum in an advanced stage of segmen-
tation, drawn in perspective 135
41. Formation of the gastrula of Amphioxm » . . 137
42. Gastrnlation 138
43. Gastrula of a Chalk Sponge 139
44. Prophysema primordiale, an extant gastiaea-form . . 140
45. Ideal prim'tive vertebrate, seen from the left side . . 143
46. The same in transverse section through the ovaries . 144
47. Amphioxus lanceolatitt 145
48. Balatioglossus .148
49. A large Sea-lamprey {Petromyzon marinus) ... 148
50. Adult Shark (Carcharias melanopterus} . . .149
51. Diagram of heart and gill-arches of a fish . . .150
52. One gill-arch, with branchial fringe attached . . 150
53. Diagram of heart and gill-arches in a lizard . . .150
54. Ideal diagram of primitive gill- or aortic- arches . .151
55. The same, modified for a bird ..... 151
56. The same, modified for a mammal . . . .I'll
List of Illustrations. xiii
PAGE
Fic. 57. A scries of embryos at three comparable and progressive
stages of development, representing each of the classes
of vertebrated animals below the Mammalia . . 153
58. Another series of embryos, also at three comparable and
progressive stages of development, representing four dif-
ferent divisions of the class Mammalia . . . J5J
59. Diagram of geological succession of the classes of the
Animal Kingdom . 165
60. Skull of Oreodon Culbertsoni 167
61. 62. Horns of Cervus dicrocerus ..... 168
63. „ C. matheronis 168
64. „ C. pardinensis 168
65. „ C. issiodoremis . . . . . . 168
66. „ C.Sedgwickii 168
67. Successive stages in the development of an existing Deer's
Antlers 169
68. Homocercal tail 169
69. Heterocercal tail 170
70. Vertebrated but symmetrical fill (diphycercal) . .170
71. Tail of Archaopteryx 171
73. Tail of modern Bird 171
73. Archaopteryx macura, restored 17 J
74. Skeleton of Polar Bear . . ... . . . 174
75. Skeleton of Lion . . ." 175
76. Anterior limb of Man, Dog, Hog, Sheep, and Horse . 176
77. Posterior limb of Man, Monk y, Dog, Sheep, and Horse 177
78. Posterior limb of Baptanodon discus, and anterior limb of
Chelydra strpentina . 179
79. Paddle of a Whale 180
80. Fossil skeleton of Phenacodus primcevus . . .184
81. Bones of the foot of four different forms of the perisso-
dactyl type 186
83 Bonet of the foot of four different forms of the artiodactyl
type 187
83. Feet and teeth in fossil pedigree of the Horse . .189
84. Palaeotherhtm. (Lower Tertiary of Paris Basin) . .190
85. Hipparion. (New World Pliocene) .... 192
86. Comparative series of Brains 194
87. Ideal section through all the above stages . . -195
88. Skulls of Canadian Stag, Cervalces Americanus, and Elk 198
89. Transmutations of Planorbis 200
xiv List of Illustrations.
PAGE
FIG. 90. Transformation of Strombus 202
.91. Pigeons. Drawn from life 298
92. Pigeons (continued). Drawn from life . . . . 299
93. Fowls. Drawn from life 300
94. Fowls (continued). Drawn from life .... 301
95. Pair of Japanese Fowls, long-tailed breed ... 302
96. Canaries. Drawn from life . . . ' . . . 303
97. Sebastopol, or Frizzled Goose ..... 304
98. The Dingo, or wild dog of Australia .... 304
99. Dogs. Drawn from life ...... 305
100. Dogs (continued). Drawn from life .... 306
101. The Hairless Dog of Japan 307
102. The skull of a Bull-dog compared with that of a Deer-
hound ......... 307
103. Rabbits. Drawn from life 308
104. Horses. Drawn from life 309
105. Sheep. Drawn from life ...... 310
106. Cattle. Drawn from i if e 311
107. Wild Boar contrasted with a modern Domesticated Pig . 312
108. Seasonal changes of colour in Ptarmigan {Lagopus mutus) 31 7
109. CEdicntmus crepitans, showing the instinntive attitude of
concealment 320
no. Imitative forms and colours in insects .... 322
111. The larva of Puss Moth ( Centra vinuld) . . . 325
112. The larva of Puss Moth in disturbed attitude . . 326
113. Three cases of mimicry . 328
114. Two further cases of mimicry ; flies resembling a wasp in
the one and a bee in the other 329
1 1 5. A case of mimicry where a non-venomous spedes of snake
resembles a venomous one 330
1 1 6. A case of mimicry where a homopterous resembles a leaf-
cutting ant 332
117. Feather-footed pigeon ....... 359
1 1 8. Raia radiata 368
1 1 9. Electric organ of the Skate 369
1 20. Electric cells of Raia radiata 370
121. The Garden Bower-bird (Amblyornis inornatd) . . 382
122. Courtship of Spiders 388
123. Courtship of Spiders (continued} 389
124. The Bell- bird (Chasmorhynchus niveus) . . . 396
125. C. tricar unculatus 397
SECTION 1
EVOLUTION
DARWIN, AND AFTER DARWIN,
CHAPTER I.
INTRODUCTORY.
AMONG the many and unprecedented changes that
have been wrought by Mr. Darwin's work on the Origin
of Species, there is one which, although second in im-
portance to no other, has not received the attention
which it deserves. I allude to the profound modifi-
cation which that work has produced on the ideas of
naturalists with regard to method.
Having had occasion of late years somewhat closely
to follow the history of biological science, I have every-
where observed that progress is not so much marked
by the march of discovery per se, as by the altered
views of method which the march has involved. If
we except what Aristotle called " the first start " in
himself, I think one may fairly say that from the re-
juvenescence of biology in the sixteenth century to
the stage of growth which it has now reached in the
nineteenth, there is a direct proportion to be found
between the value of work done and the degree in
which the worker has thereby advanced the true
conception of scientific working. Of course, up to a
* B
2 Darwin, and after Darwin.
certain point, it is notorious that the revolt against
the purely "subjective methods " in the sixteenth
century revived the spirit of inductive research as this
had been left by the Greeks ; but even with regard
to this revolt there are two things which I should
like to observe.
In the first place, it seems to me, an altogether
disproportionate value has been assigned to Bacon's
share in the movement. At most, I think, he deserves
to be regarded but as a literary exponent of the Zeit-
geist of his century. Himself a philosopher, as dis-
tinguished from a man of science, whatever influence
his preaching may have had upon the general public, it
seems little short of absurd to suppose that it could
have produced any considerable effect upon men who
were engaged in the practical work of research. And
those who read the Novum Organon with a first-hand
knowledge of what is required for such research can
scarcely fail to agree with his great contemporary
Harvey, that he wrote upon science like a Lord
Chancellor.
The second thing I should like to observe is, that
as the revolt against the purely subjective methods
grew in extent and influence it passed to the opposite
extreme, which eventually became only less deleterious
to the interests of science than was the bondage of
authority, and addiction to a priori methods, from
which the revolt had set her free. For, without here
waiting to trace the history of this matter in detail,
I think it ought now to be manifest to everyone who
studies it, that up to the commencement of the present
century the progress of science in general, and of
natural history in particular, was seriously retarded by
Introductory. 3
what may be termed the Bugbear of Speculation. Fully
awakened to the dangers of web-spinning from the
ever- fertile resources of their own inner consciousness,
naturalists became more and more abandoned to the
idea that their science ought to consist in a mere
observation of facts, or tabulation of phenomena,
without attempt at theorizing upon their philosophical
import. If the facts and phenomena presented any
such import, that was an affair for men of letters to
deal with ; but, as men of science, it was their duty to
avoid the seductive temptations of the world, the flesh,
and the devil, in the form of speculation, deduction,
and generalization.
I do not allege that this ideal of natural history was
either absolute or universal ; but there can be no
question that it was both orthodox and general.
Even Linnaeus was express in his limitations of true
scientific work in natural history to the collecting and
arranging of species of plants and animals. In ac-
cordance with this view, the status of a botanist or a
zoologist was estimated by the number of specific
names, natural habitats, &c., which he could retain in
his memory, rather than by any evidences which he
might give of intellectual powers in the way of con-
structive thought. At the most these powers might
legitimately exercise themselves only in the direction
of taxonomic work ; and if a Hales, a Haller, or a
Hunter obtained any brilliant results in the way of
observation and experiment, their merit was taken to
consist in the discovery of facts per se : not in any
endeavours they might make in the way of combining
their facts under general principles. Even as late in
the day as Cuvier this ideal was upheld as the strictly
B 2
4 Darwin, and after Darwin.
legitimate one for a naturalist to follow ; and although
Cuvier himself was far from being always loyal to it,
he leaves no doubt regarding the estimate in which he
held the still greater deviations of his colleagues, St.
Hilaire and Lamarck.
Now, these traditional notions touching the severance
between the facts of natural history and the philosophy
of it, continued more or less to dominate the minds of
naturalists until the publication of the Origin of
Species, in 1859. Then it was that an epoch was
marked in this respect, as in so many other respects
where natural history is concerned. For, looking to
the enormous results which followed from a deliberate
disregard of such traditional canons by Darwin, it has
long since become impossible for naturalists, even of
the strictest sect, not to perceive that their previous
bondage to the law of a mere ritual has been for ever
superseded by what verily deserves to be regarded as
a new dispensation. Yet it cannot be said, or even so
much as suspected, that Darwin's method in any way
resembled that of pre-scientific days, the revolt against
which led to the straight-laced — and for a long time
most salutary — conceptions of method that we have
just been noticing. Where, then, is the difference?
To me it seems that the difference is as follows ; and,
if so, that not the least of our many obligations to
Darwin as the great organizer of biological science
arises from his having clearly displayed the true
principle which ought to govern biological research.
To begin with, he nowhere loses sight of the
primary distinction between fact and theory ; so that,
thus far, he loyally follows the spirit of revolt against
subjective methods. But, while always holding this
Introductory. 5
distinction clearly in view, his idea of the scientific use
of facts is plainly that of furnishing legitimate material
for the construction of theories. Natural history is
not to him an affair of the herbarium or the cabinet.
The collectors and the species-framers are, as it were,
his diggers of clay and makers of bricks: even the
skilled observers and the trained experimentalists are
his mechanics. Valuable as the work of all these men
is in itself, its principal value, as he has finally de-
monstrated, is that which it acquires in rendering
possible the work of the architect. Therefore, although
he has toiled in all the trades with his own hands, and
in each has accomplished some of the best work that
has ever been done, the great difference between him
and most of his predecessors consists in this, — that
while to them the discovery or accumulation of facts
was an end, to him it is the means. In their eyes it
was enough that the facts should be discovered and
recorded. In his eyes the value of facts is due to
their power of guiding the mind to a further discovery
of principles. And the extraordinary success which
attended his work in this respect of generalization
immediately brought natural history into line with the
other inductive sciences, behind which, in this most
important of all respects, she has so seriously fallen.
For it was the Origin of Species which first clearly
revealed to naturalists as a class, that it was the duty
of their science to take as its motto, what is really the
motto of natural science in general,
Felix qui potuit rerum cognoscere causa*.
Not facts, then, or phenomena, but causes or prin-
ciples, are the ultimate objects of scientific quest. It
remains to ask, How ought this quest to be prosecuted ?
6 Darwin, and after Darwin.
Well, in the second place, Darwin has shown that
next only to the importance of clearly distinguishing
between facts and theories on the one hand, and of
clearly recognising the relation between them on the
other, is the importance of not being scared by the
Bugbear of Speculation. The spirit of speculation is
the same as the spirit of science, namely, as we have
just seen, a desire to know the causes of things. The
hypotheses non fingo of Newton, if taken to mean what
it is often understood as meaning, would express
precisely the opposite spirit from that in which all
scientific research must necessarily take its origin.
For if it be causes or principles, as distinguished from
facts or phenomena, that constitute the final aim of
scientific research, obviously the advancement of such
research can be attained only by the framing of
hypotheses. And to frame hypotheses is to specu-
late.
Therefore, the difference between science and specu-
lation is not a difference of spirit ; nor, thus far, is it
a difference of method. The only difference between
them is in the subsequent process of verifying hypo-
theses. For while speculation, in its purest form, is
satisfied to test her explanations only by the degree
in which they accord with our subjective ideas of prob-
ability— or with the " Illative Sense" of Cardinal New-
man,— science is not satisfied to rest in any explanation
as final until it shall have been fully verified by an
appeal to objective proof. This distinction is now so
well and so generally appreciated that I need not
dwell upon it. Nor need I wait to go into any details
with regard to the so-called canons of verification.
My only object is to make perfectly clear, first, that
Introductory. 7
In order to have any question to put to the test of
objective verification, science must already have so far
employed the method of speculation as to have framed
a question to be tested ; and, secondly, that the point
where science parts company with speculation is the
point where this testing process begins.
Now, if these things are so, there can be no doubt
that Darwin was following the truest method of induc-
tive research in allowing any amount of latitude to his
speculative thought in the direction of scientific theo-
rizing. For it follows from the above distinctions that
the danger of speculation does not reside in the width
of its range, or even in the impetuosity of its vehe-
mence. Indeed, the wider its reach, and the greater its
energy, the better will it be for the interests of science.
The only danger of speculation consists in its momen-
tum being apt to carry away the mind from the more
laborious work of adequate verification; and therefore
a true scientific judgment consists in giving a free
rein to speculation on the one hand, while holding
ready the break of verification with the other. Now,
it is just because Darwin did both these things with
so admirable a judgment, that he gave the world of
natural history so good a lesson as to the most effec-
tual way of driving the chariot of science.
This lesson we have now all more or less learnt to
profit by. Yet no other naturalist has proved himself
so proficient in holding the balance true. For the
most part, indeed, they have now all ceased to con-
found the process of speculation per se with the danger
of inadequate verification ; and therefore the old ideal
of natural history as concerned merely with collecting
species, classifying affinities, and, in general, tabulating
8 Darwin, and after Darwin.
facts, has been well-nigh universally superseded. But
this great gain has been attended by some measure of
loss. For while not a few naturalists have since erred
on the side of insufficiently distinguishing between fully
verified principles of evolution and merely specula-
tive deductions therefrom, a still larger number have
formed for themselves a Darwinian creed, and regard
any further theorizing on the subject of evolution as
ipso facto unorthodox.
Having occupied the best years of my life in
closely studying the literature of Darwinism, I shall
endeavour throughout the following pages to avoid
both these extremes. No one in this generation is
able to imitate Darwin, either as an observer or a
generalizer. But this does not hinder that we should
all so far endeavour to follow his method, as always to
draw a clear distinction, not merely between observa-
tion and deduction, but also between degrees of
verification. At all events, my own aim will every-
where be to avoid dogmatism on the one hand, and
undue timidity as regards general reasoning on the
other. For everything that is said justification will
be given ; and, as far as prolonged deliberation has
enabled me to do so, the exact value of such justifica-
tion will be rendered by a statement of at least the
main grounds on which it rests. The somewhat
extensive range of the present treatise, however, will
not admit of my rendering more than a small percen-
tage of the facts which in each case go to corroborate
the conclusion. But although a great deal must thus
be necessarily lost on the one side, I am disposed to
think that more will be gained on the other, by
presenting, in a terser form than would otherwise be
Introductory. 9
possible, the whole theory of organic evolution as I
believe that it will eventually stand. My endeavour,
therefore, will be to exhibit the general structure of
this theory in what I take to be its strictly logical
form, rather than to encumber any of its parts by a
lengthy citation of facts. Following this method, I
shall in each case give only what I consider the main
facts for and against the positions which have to be
argued ; and in most cases I shall arrange the facts
in two divisions, namely, first those of largest gener-
ality, and next a few of the most special character
that can be found.
As explained in the Preface, the present instalment
of the treatise is concerned with the theory of evolu-
tion, from the appearance of the Origin of Species in
1859, to the death of its author in 1882; while the
second part will be devoted to the sundry post-
Darwinian questions which have arisen in the sub-
sequent decade. To the possible criticism that a
disproportionate amount of space will thus be allotted
to a consideration of these post-Darwinian questions,
I may furnish in advance the following reply.
In the first place, besides the works of Darwin
himself, there are a number of others which have
already and very admirably expounded the evidences,
both of organic evolution as a fact, and of natural
selection as a cause. Therefore, in the present
treatise it seemed needless to go beyond the ground
which was covered by my original lectures, namely, a
condensed and connected, while at the same time
a critical statement of the main evidences, and the
main objections, which have thus far been published
with reference to the distinctively Darwinian theory.
io Darwin, and after Darwin.
Indeed while re-casting this portion of my lectures
for the present publication, I have felt that criticism
might be more justly urged from the side of im-
patience at a reiteration of facts and arguments
already so well known. But while endeavouring, as
much as possible, to avoid overlapping the previous
expositions, I have not carried this attempt to the
extent of damaging my own, by omitting any of the
more important heads of evidence ; and I have sought
to invest the latter with some measure of novelty by
making good what appears to me a deficiency which
has hitherto obtained in the matter of pictorial illus-
tration. In particular, there will be found a tolerably
extensive series of woodcuts, serving to represent the
more important products of artificial selection. These,
like all the other original illustrations, have been
drawn either direct from nature or from a comparative
study of the best authorities. Nevertheless, I desire
it to be understood that the first part of this treatise
is intended to retain its original character, as a merely
educational exposition of Darwinian teaching — an
exposition, therefore, which, in its present form,
may be regarded as a compendium, or hand-book,
adapted to the requirements of a general reader, or
biological student as distinguished from those of a
professed naturalist.
The case, however, is different with the second
instalment, which will be published at no very distant
date. Here I have not followed with nearly so much
closeness the material of my original lectures. On
the contrary, I have, had in view a special class of
readers ; and, although I have tried not altogether to
sacrifice the more general class, I shall desire it to be
Introductory. 1 1
understood that I am there appealing to naturalists
who are specialists in Darwinism. One must say
advisedly, naturalists who are specialists in Dar-
winism, because, while the literature of Darwinism
has become a department of science in itself, there
are nowadays many naturalists who, without having
paid any close attention to the subject, deem them-
selves entitled to hold authoritative opinions with
regard to it. These men may have done admirable
work in other departments of natural history, and yet
their opinions on such matters as we shall hereafter
have to consider may be destitute of value. As there
is no necessary relation between erudition in one
department of science and soundness of judgment
in another, the mere fact that a man is distinguished
as a botanist or zoologist does not in itself qualify him
as a critic where specially Darwinian questions are
concerned. Thus it happens now, as it happened
thirty years ago, that highly distinguished botanists
and zoologists prove themselves incapable as judges
of general reasoning. It was Darwin's complaint that
for many years nearly all his scientific critics either
could not, or would not, understand what he had
written — and this even as regarded the fundamental
principles of his theory, which with the utmost clear-
ness he had over and over again repeated. Now the
only difference between such naturalists and their
successors of the present day is, that the latter have
grown up in a Darwinian environment, and so, as
already remarked, have more or less thoughtlessly
adopted some form of Darwinian creed. But this
scientific creed is not a whit less dogmatic and
intolerant than was the more theological one which it
12 Darwin, and after Darwin.
has supplanted ; and while it usually incorporates the
main elements of Darwin's teaching, it still more
usually comprises gross perversions of their conse-
quences. All this I shall have occasion more fully
to show in subsequent parts of the present work ; and
allusion is made to the matter here merely for the
sake of observing that in future I shall not pay
attention to unsupported expressions of opinion from
any quarter : I shall consider only such as are accom-
panied with some statement of the grounds upon
which the opinion is held. And, even as thus limited,
I do not think it will be found that the following
exposition devotes any disproportional amount of
attention to the contemporary movements of Dar-
winian thought, seeing, as we shall see, how active
scientific speculation has been in the field of Dar-
winism since the death of Mr. Darwin.
Leaving, then, these post-Darwinian questions to
be dealt with subsequently, I shall now begin a
systematic rtsumt of the evidences in favour of the
Darwinian theory, as this was left to the world by
Darwin himself.
There is a great distinction to be drawn between
the fact of evolution and the manner of it, or between
the evidence of evolution as having taken place some-
how, and the evidence of the causes which have been
concerned in the process. This most important
distinction is frequently disregarded by popular
writers on Darwinism ; and, therefore, in order to
mark it as strongly as possible, I will effect a com-
plete separation between the evidence which we have
of evolution as a fact, and the evidence which we have
Introductory. 1 3
as to its method. In other words, not until I shall
have fully considered the evidence of organic evolu-
tion as a process which somehow or another has
taken place, will I proceed to consider how it has
taken place, or the causes which Darwin and others
have suggested as having probably been concerned in
this process.
Confining, then, our attention in the first instance
to a proof of evolution considered as a fact, without
any reference at all to its method, let us begin by
considering the antecedent standing of the matter.
First of all we must clearly recognise that there are
only two hypotheses in the field whereby it is possible
so much as to suggest an explanation of the origin of
species. Either all the species of plants and animals
must have been supernaturally created, or else they
must have been naturally evolved. There is no third
hypothesis possible ; for no one can rationally suggest
that species have been eternal.
Next, be it observed, that the theory of a continuous
transmutation of species is not logically bound to
furnish a full explanation of all the natural causes
which it may suppose to have been at work. The
radical distinction between the two theories consists
in the one assuming an immediate action of some
supernatural or inscrutable cause, while the other
assumes the immediate action of natural — and there-
fore of possibly discoverable— causes. But in order
to sustain this latter assumption, the theory of descent
is under no logical necessity to furnish a full proof of
all the natural causes which may have been concerned
in working out the observed results. We do not
14 Darwin, and afUr Darwin.
know the natural causes of many diseases ; but yet
no one nowadays thinks of reverting to any hypo-
thesis of a supernatural cause, in order to explain the
occurrence of any disease the natural causation of
which is obscure. The science of medicine being in
so many cases able to explain the occurrence of
disease by its hypothesis of natural causes, medical
men now feel that they are entitled to assume, on the
basis of a wide analogy, and therefore on the basis of
a strong antecedent presumption, that all diseases are
due to natural causes, whether or not in particular
cases such causes happen to have been discovered.
And from this position it follows that medical men
are not logically bound to entertain any supernatural
theory of an obscure disease, merely because as yet
they have failed to find a natural theory. And so it
is with biologists and their theory of descent. Even
if it be fully proved to them that the causes which
they have hitherto discovered, or suggested, are in-
adequate to account for all the facts of organic nature,
this would in no wise logically compel them to vacate
their theory of evolution, in favour of the theory of
creation. All that it would so compel them to do
would be to search with yet greater diligence for the
natural causes still undiscovered, but in the existence
of which they are, by their independent evidence in
favour of the theory, bound to believe.
In short, the issue is not between the theory of a
supernatural cause and the theory of any one parti-
cular natural cause, or set of causes — such as natural
selection, use, disuse, and so forth. The issue thus
far — or where only the/<3£/ of evolution is concerned —
is between the theory of a supernatural cause as
Introductory. 15
operating immediately in numberless acts of special
creation, and the theory of natural causes as a whole,
whether these happen, or do not happen, to have been
hitherto discovered.
This much by way of preliminaries being under-
stood, we have next to notice that whichever of the
two rival theories we choose to entertain, we are not
here concerned with any question touching the origin
of life. We are concerned only with the origin of
particular forms of life — that is to say, with the origin
of species. The theory of descent starts from life as
a datum already granted. How life itself came to be,
the theory of descent, as such, is not concerned to
show. Therefore, in the present discussion, I will take
the existence of life as a fact which does not fall
within the range of our present discussion. No doubt
the question as to the origin of life is in itself a deeply
interesting question, and although in the opinion of
most biologists it is a question which we may well
hope will some day fall within the range of science to
answer, at present, it must be confessed, science is not
in a position to furnish so much as any suggestion upon
the subject ; and therefore our wisdom as men of
science is frankly to acknowledge that such is the case.
We are now in a position to observe that the theory
of organic evolution is strongly recommended to our
acceptance on merely antecedent grounds, by the fact
that it is in full accordance with what is known as the
principle of continuity. By the principle of continuity
is meant the uniformity of nature, in virtue of which
the many and varied processes going on in nature are
due to the same kind of method, i. e. the method of
1 6 Darwin, and after Darwin.
natural causation. This conception of the uniformity
of nature is one that has only been arrived at step by
step through a long and arduous course of human
experience in the explanation of natural phenomena.
The explanations of such phenomena which are first
given are always of the supernatural kind ; it is not
until investigation has revealed the natural causes
which are concerned that the hypotheses of super-
stition give way to those of science. Thus it follows
that the hypotheses of superstition which are the latest
in yielding to the explanations of science, are those
which refer to the more recondite cases of natural
causation ; for here it is that methodical investigation
is longest in discovering the natural causes. Thus it
is only by degrees that fetishism is superseded by
what now appears a common-sense interpretation of
physical phenomena; that exorcism gives place to
medicine ; alchemy to chemistry ; astrology to astro-
nomy ; and so forth. Everywhere the miraculous is
progressively banished from the field of explanation
by the advance of scientific discovery ; and the places
where it is left longest in occupation are those where
the natural causes are most intricate or obscure, and
thus present the greatest difficulty to the advancing
explanations of science. Now, in our own day there
are but very few of these strongholds of the mira-
culous left. Nearly the whole field of explanation is
occupied by naturalism, so that no one ever thinks of
resorting to supernaturalism except in the compara-
tively few cases where science has not yet been able to
explore the most obscure regions of causation. One
of these cases is the origin of life ; and, until quite
recently, another of these cases was the origin of
Introductory. \ 7
species. But now that a very reasonable explanation
of the origin of species has been offered by science, it
is but in accordance with all previous historical
analogies that many minds should prove themselves
unable all at once to adjust themselves to the new
ideas, and thus still linger about the more venerable
ideas of supernaturalism. But we are now in pos-
session of so many of these historical analogies, that
all minds with any instincts of science in their
composition have grown to distrust, on merely ante-
cedent grounds, any explanation which embodies a
miraculous element. Such minds have grown to
regard all these explanations as mere expressions of
our own ignorance of natural causation; or, in other
words, they have come to regard it as an a priori
truth that nature is everywhere uniform in respect of
method or causation ; that the reign of law universal ;
the principle of continuity ubiquitous.
Now, it must be obvious to any mind which has
adopted this attitude of thought, that the scientific
theory of natural descent is recommended by an
overwhelming weight of antecedent presumption, as
against the dogmatic theory of supernatural design.
To begin with, we must remember that the fact of
evolution — or, which is the same thing, the fact of
continu: y in natural causation — has now been un-
questionably proved in so many other and analogous
departments of nature, that to suppose any interruption
of this method as between species and species becomes,
on grounds of such analogy alone, well-nigh incredible.
For example, it is now a matter of demonstrated fact
that throughout the range of inorganic nature the
principles of evolution have obtained. It is no longer
* c
i8 Darwin, and after Darwin.
possible for any one to believe with our forefathers
that the earth's surface has always existed as it now
exists. For the science of geology has proved to
demonstration that seas and lands are perpetually
undergoing gradual changes of relative positions —
continents and oceans supplanting each other in the
course of ages, mountain-chains being slowly uplifted,
again as slowly denuded, and so forth. Moreover,
and as a closer analogy, within the limits of animate
nature we know it is the universal law that every
individual life undergoes a process of gradual develop-
ment ; and that breeds, races, or strains, may be
brought into existence by the intentional use of
natural processes— the results bearing an unmistake-
able resemblance to what we know as natural species.
Again, even in the case of natural species themselves,
there are two considerations which present enormous
force from an antecedent point of view. The first
is that organic forms are only then recognised as
species when intermediate forms are absent. If the
intermediate forms are actually living, or admit of
being found in the fossil state, naturalists forthwith
regard the whole series as varieties, and name all
the members of it as belonging to the same species.
Consequently it becomes obvious that naturalists, in
their work of naming species, may only have been
marking out the cases where intermediate or con-
necting forms have been lost to observation. For
example, here we have a diagram representing a very
unusually complete series of fossil shells, which
within the last few years has been unearthed from
the Tertiary lake basins of Slavonia. Before the
series was completed, some six or eight of the then
Introductory. 19
disconnected forms were described as distinct species :
but as soon as the connecting forms were found —
showing a progressive modification from the older to
the newer beds. — the whole were included as varieties
of one species.
FIG. i. — Successive forms of Paludina, from the Tertiary deposits
of Slavonia (after Neumayr).
Of course, other cases of the same kind might be
adduced, and therefore, as just remarked, in their
work of naming species naturalists may only have
been marking out the cases where intermediate forms
o 2
2O Darwin, and after Darwin.
have been lost to observation. And this possibility
becomes little less than a certainty when we note the
next consideration which I have to adduce, namely,
that in all their systematic divisions of plants and
animals in groups higher than species — such as genera,
families, orders, and the rest — naturalists have at all
times recognised the fact that the one shades off into
the other by such imperceptible gradations, that it
is impossible to regard such divisions as other than
conventional. It is important to remember that this
fact was fully recognised before the days of Darwin.
In those days the scientifically orthodox doctrine
was, that although species were to be regarded as
fixed units, bearing the stamp of a special creation,
all the higher taxonomic divisions were to be con-
sidered as what may be termed the artificial creation
of naturalists themselves. In other words, it was
believed, and in many cases known, that if we could
go far enough back in the history of the earth, we
should everywhere find a tendency to mutual ap-
proximation between allied groups of species ; so that,
for instance, birds and reptiles would be found to be
drawing nearer and nearer together, until eventually
they would seem to become fused in a single type;
that the existing distinctions between herbivorous
and carnivorous mammals would be found to do like-
wise ; and so on with all the larger group-distinctions,
at any rate within the limits of the same sub-kingdoms.
But although naturalists recognised this even in the
pre-Darwinian days, they stoutly believed that a
great exception was to be made in the case of species.
These, the lowest or initial members of their taxo-
nomic series, they supposed to be permanent — the
Introductory. 2 1
miraculously created units of organic nature. Now,
all that I have at present to remark is, that this
pre-Darwinian exception which was made in favour
of species to the otherwise recognised principle of
gradual change, was an exception which can at no
time have been recommended by any antecedent
considerations. At all times it stood out of analogy
with the principle of continuity ; and, as we shall fully
find in subsequent chapters, it is now directly con-
tradicted by all the facts of biological science.
There remains one other fact of high generality to
which prominent attention should be drawn from the
present, or merely antecedent, point of view. On
the theory of special creation no reason can be
assigned why distinct specific types should present
any correlation, either in time or in space, with their
nearest allies ; for there is evidently no conceivable
reason why any given species, A, should have been
specially created on the same area and at about the
same time as its nearest representative, B, — still less,
of course, that such should be a general rule through-
out all the thousands and millions of species which
have ever inhabited the earth. But, equally of course,
on the theory of a natural evolution this is so necessary
a consequence, that if no correlation of such a two-fold
kind were observable, the theory would be negatived.
Thus the question whether there be any indication
of such a two-fold correlation may be regarded as
a test-question as between the two theories ; for
although the vast majority of extinct species have
been lost to science, there are a countless number
of existing species which furnish ample material for
answering the question. And the answer is so un-
22 Darwin, and after Darwin.
equivocal that Mr. Wallace, who is one of our greatest
^authorities on geographical distribution, has laid it
down as a general law, applicable to all the depart-
ments of organic nature, that, so far as observation
can extend, " every species has come into existence
coincident both in space and time with a pre-existing
and closely allied species." As it appears to me that
the significance of these words cannot be increased by
any comment upon them, I will here bring this intro-
ductory chapter to a close.
CHAPTER II.
CLASSIFICATION.
THE first line of direct evidence in favour of organic
evolution which I shall open is that which may be
termed the argument from Classification.
It is a matter of observable fact that different forms
of plants and animals present among themselves more
or less pronounced resemblances. From the earliest
times, therefore, it has been the aim of philosophical
naturalists to classify plants and animals in accord-
ance with these resemblances. Of course the earliest
attempts at such classification were extremely crude.
The oldest of these attempts with which we are ac-
quainted-—namely, that which is presented in the books
of Genesis and Leviticus — arranges the whole vegetable
kingdom in three simple divisions of Grass, Herbs, and
Trees ; while the animal kingdom is arranged with
almost equal simplicity with reference, first to habitats
in water, earth, or air, and next as to modes of pro-
gression. These, of course, were what may be termed
common-sense classifications, having reference merely
to external appearances and habits of life. But when
Aristotle laboriously investigated the comparative
anatomy of animals, he could not fail to perceive that
their entire structures had to be taken into account in
24 Darwin, and after Darwin.
order to classify them scientifically ; and, also, that
for this purpose the internal parts were of quite as
much importance as the external. Indeed, he per-
ceived that they were of greatly more importance in
this respect, inasmuch as they presented so many
more points for comparison ; and, in the result, he
furnished an astonishingly comprehensive, as well as
an astonishingly accurate classification of the larger
groups of the animal kingdom. On the other hand,
classification of the vegetable kingdom continued
pretty much as it had been left by the book of Genesis
— all plants being divided into three groups, Herbs.
Shrubs, and Trees. Nor was this primitive state of
matters improved upon till the sixteenth century, when
Gesner (1516-1565), and still more Caesalpino (1519-
1603), laid the foundations of systematic botany.
But the more that naturalists prosecuted their
studies on the anatomy of plants and animals, the
more enormously complex did they find the problem
of classification become. Therefore they began by
forming what are called artificial systems, in contra-
distinction to natural systems. An artificial system
of classification is a system based on the more or less
arbitrary selection of some one part, or set of parts ;
while a natural classification is one that is based upon
a complete knowledge of all the structures of all the
organisms which are classified.
Thus, the object of classification has been that of
arranging organisms in accordance with their natural
affinities, by comparing organism with organism, for
the purpose of ascertaining which of the constituent
organs are of the most invariable occurrence, and
therefore of the most typical signification. A porpoise,
Classification. 2 5
for instance, has a large number of teeth, and in this
feature resembles most fish, while it differs from all
mammals. But it also gives suck to its young. Now,
looking to these two features alone, should we say
that a porpoise ought to be classed as a fish or as a
mammal? Assuredly as a mammal ; because the
number of teeth is a very variable feature both in fish
and mammals, whereas the giving of suck is an in-
variable feature among mammals, and occurs nowhere
else in the animal kingdom. This, of course, is chosen
as a very simple illustration. Were all cases, as
obvious, there would be but little distinction between
natural and artificial systems of classification. But it
is because the lines of natural affinity are, as it were,
so interwoven throughout the organic world, and
because there is, in consequence, so much difficulty in
following them, that artificial systems have to be made
in the first instance as feelers towards eventual dis-
covery of the natural system. In other words, while
forming their artificial systems of classification, it has
always been the aim of naturalists — whether con-
sciously or unconsciously — to admit as the bases of
their systems those characters which, in the then state
of their knowledge, seemed most calculated to play an
important part in the eventual construction of the
natural system. If we were dealing with the history
of classification, it would here be interesting to note
how the course of it has been marked by gradual
change in the principles which naturalists adopted as
guides to the selection of characters on which to found
their attempts at a natural classification. Some of
these changes, indeed, I shall have to mention later
on ; but at present what has to be specially noted is,
26 Darwin, and after Darwin.
that through all these changes of theory or principle,
and through all the ever-advancing construction of
their taxonomic science, naturalists themselves were
unable to give any intelligible reason for the faith that
was in them — or the faith that over and above the
artificial classifications which were made for the mere
purpose of cataloguing the living library of organic
nature, there was deeply hidden in nature itself a truly
natural classification, for the eventual discovery of
which artificial systems might prove to be of more or
less assistance.
Linnaeus, for example, expressly says — "You ask
me for the characters of the natural orders ; I confess
that I cannot give them." Yet he maintains that,
although he cannot define the characters, he knows,
by a sort of naturalist's instinct, what in a general way
will subsequently be found to be the organs of most
importance in the eventual grouping of plants under
a natural system. " I will not give my reasons for the
distribution of the natural orders which I have pub-
lished," he said : " you, or some other person, after
twenty or after fifty years, will discover them, and see
that I was right."
Thus we perceive that in forming their provisional
or artificial classifications, naturalists have been guided
by an instinctive belief in some general principle of
natural affinity, the character of which they have not
been able to define ; and that the structures which
they selected as the bases of their classifications when
these were consciously artificial, were selected because
it seemed that they were the structures most likely to
prove of use in subsequent attempts at working out the
natural system.
Classification. 27
This general principle of natural affinity, of which
all naturalists have seen more or less well-marked
evidence in organic nature, and after which they have
all been feeling, has sometimes been regarded as
natural, but more often as supernatural. Those who
regarded it as supernatural took it to consist in a
divine ideal of creation according to types,, so that the
structural affinities of organisms were to them expres-
sions of an archetypal plan, which might be revealed
in its entirety when all organisms on the face of the
earth should have been examined. Those, on the
other hand, who regarded the general principle of
affinity as depending on some natural causes, for the
most part concluded that these must have been utili-
tarian causes ; or, in other words, that the fundamental
affinities of structure must have depended upon funda-
mental requirements of function. According to this
view, the natural classification would eventually be
found to stand upon a basis of physiology. Therefore
all the systems of classification up to the earlier part
of the present century went upon the apparent axiom,
that characters which are of most importance to the
organisms presenting them must be characters most
indicative of natural affinities. But the truth of the
matter was eventually found to be otherwise. For it
was eventually found that there is absolutely no cor-
relation between these two things ; that, therefore, it
is a mere chance whether or not organs which are of
importance to organisms are likewise of importance as
guides to classification ; and, in point of fact, that the
general tendency in this matter is towards an inverse
instead of a direct proportion. More often than not,
the greater the value of a structure for the purpose of
28 Darwin, and after Darwin.
indicating natural affinities, the less is its value to the
creatures presenting it.
Enough has now been said to show three things.
First, that long before the theory of descent was enter-
tained by naturalists, naturalists perceived the fact of
natural affinities, and did their best to construct a
natural system of classification for the purpose of ex-
pressing such affinities. Second, that naturalists had
a kind of instinctive belief in some one principle run-
ning through the whole organic world, which thus
served to bind together organisms in groups subor-
dinate to groups — that is, into species, genera, orders,
families, classes, sub-kingdoms, and kingdoms. Third,
that they were not able to give any very intelligible
reason for this faith that was in them ; sometimes
supposing the principle in question to be that of a
supernatural plan of organization, sometimes regarding
it as dependent on conditions of physiology, and some-
times not attempting to account for it at all.
Of course it is obvious that the theory of descent
furnishes the explanation which is required. For it is
now evident to evolutionists, that although these older
naturalists did not know what they were doing when
they were tracing these lines of natural affinity, and
thus helping to construct a natural classification — I say
it is now evident to evolutionists that these naturalists
were simply tracing the lines of genetic relationship.
The great principle pervading organic nature, which
was seen so mysteriously to bind the whole creation
together as in a nexus of organic affinity, is now easily
understood as nothing more or less than the prin-
ciple of Heredity. Let us, therefore, look a little
more closely at the character of this network, in
Classification. 29
•
order to see how far it lends itself to this new inter-
pretation.
The first thing that we have to observe about the
nexus is, that it is a nexus — not a single line, or even
a series of parallel lines. In other words, some time
before the theory of descent was seriously entertained,
naturalists for the most part had fully recognised that
it was impossible to arrange either plants or animals,
with respect to their mutual affinities, in a ladder-like
series (as was supposed to be the type of classification
by the earlier systematists), or even in map-like groups
(as was supposed to be the type by Linnaeus). And
similarly, also, with respect to grades of organization.
In the case of the larger groups, indeed, it is usually
possible to say that the members of this group as a
whole are more highly organized than the members of
that group as a whole j so that, for instance, we have
no hesitation in regarding the Vertebrata as more
highly organized than the Invertebrata, Birds than
Reptiles, and so on. But when we proceed to smaller
subdivisions, such as genera and species, it is usually
impossible to say that the one type is more highly
organized than another type. A horse, for instance,
cannot be said to be more highly organized than a
zebra or an ass ; although the entire horse-genus is
clearly a more highly organized type than any genus
of animal which is not a mammal.
In view of these facts, therefore, the system of
classification which was eventually arrived at before
the days of Darwin, was the system which naturalists
likened to a tree ; and this is the system which all
naturalists now agreed upon as the true one. Ac-
cording to this system, a short trunk may be taken
30 Darwin, and after Darwin.
to represent the lowest organisms which cannot
properly be termed either plants or animals. This
short trunk soon separates into two large trunks, one
of which represents the vegetable and the other the
animal kingdom. Each of these trunks then gives off
large branches signifying classes and these give off
smaller, but more numerous branches, signifying
families, which ramify again into orders, genera, and
finally into the leaves, which may be taken to repre-
sent species. Now, in such a representative tree of
life, the height of any branch from the ground may be
taken to indicate the grade of organization which the
leaves, or species, present ; so that, if we picture to
ourselves such a tree, we may understand that while
there is a general advance of organization from below
upwards, there are many deviations in this respect.
Sometimes leaves growing on the same branch are
growing at a different level — especially, of course, if
the branch be a large one, corresponding to a class or
sub-kingdom. And sometimes leaves growing on
different branches are growing at the same level :
that is to say, although they represent species be-
longing to widely divergent families, orders, or even
classes, it cannot be said that the one species is more
highly organized than the other.
Now, this tree-like arrangement of species in nature
is an arrangement for which Darwin is not responsible.
For, as we have seen, the detecting of it has been
due to the progressive work of naturalists for centuries
past ; and even when it was detected, at about the
commencement of the present century, naturalists
were confessedly unable to explain the reason of it,
or what was the underlying principle that they were
Classification. 3 1
engaged in tracing when they proceeded ever more
and more accurately to define these ramifications of
natural affinity. But now, as just remarked, we can
clearly perceive that this underlying principle was none
other than Heredity as expressed in family likeness,
— likeness, therefore, growing progressively more
unlike with remoteness of ancestral relationship. For
thus only can we obtain any explanation of the sundry
puzzles and apparent paradoxes, which a working out
of their natural classifications revealed to botanists and
zoologists during the first half of the present century.
It will now be my endeavour to show how these
puzzles and paradoxes are all explained by the theory
that natural affinities are merely the expression of
genetic affinities.
First of all, and from the most general point of
view, it is obvious that the tree- like system of classifi-
cation, which Darwin found already and empirically
worked out by the labours of his predecessors, is as
suggestive as anything could well be of the fact of
genetic relationship. For this is the form that every
tabulation of family pedigree must assume ; and there-
fore the mere fact that a scientific tabulation of natural
affinities was eventually found to take the form of a
tree, is in itself highly suggestive of the inference that
such a tabulation represents a family tree. If all
species were separately created, there can be no assign-
able reason why the ideas of earlier naturalists touch-
ing the form which a natural classification would
eventually assume should not have represented the
truth — why, for example, it should not have assumed
the form of a ladder (as was anticipated in the
seventeenth century), or of a map (as was anticipated in
32 Darwin, and after Darwin.
the eighteenth), or, again, of a number of wholly unre-
lated lines, circles, &c. (as certain speculative writers of
the present century have imagined). But, on the other
hand, if all species were separately and independently
created, it becomes virtually incredible that we should
everywhere observe this progressive arborescence of
characters common to larger groups into more and
more numerous, and more and more delicate, ramifi-
cations of characters distinctive only of smaller and
smaller groups. A man would be deemed insane if he
were to attribute the origin of every branch and every
twig of a real tree to a separate act of special creation ;
and although we have not been able to witness the
growth of what we may term in a new sense the Tree
of Life, the structural relations which are now apparent
between its innumerable ramifications bear quite as
strong a testimony to the fact of their having been
due to an organic growth, as is the testimony furnished
by the branches of an actual tree.
Or, to take another illustration. Classification of
organic forms, as Darwin, Lyell, and Hackel have
pointed out, strongly resembles the classification of
languages. In the case of languages, as in the case
of species, we have genetic affinities strongly marked ;
so that it is possible to some extent to construct a
Language-tree, the branches of which shall indicate,
in a diagrammatic form, the progressive divergence of a
large group of languages from a common stock. For
instance, Latin may be regarded as a fossil language,
which has given rise to a group of living languages —
Italian, Spanish, French, and, to a large extent,
English. Now what would be thought of a philologist
who should maintain that English; French, Spanish.
Classification. 33
and Italian were all specially created languages — or
languages separately constructed by the Deity, and
by as many separate acts of inspiration communicated
to the nations which now speak them— and that their
resemblance to the fossil form, Latin, must be
attributed to special design ? Yet the evidence of the
natural transmutation of species is in one respect
much stronger than that of the natural transmutation
of languages — in respect, namely, of there being a
vastly greater number of cases all bearing testimony
to the fact of genetic relationship.
But, quitting now this most general point of view —
or the suggestive fact that what we have before us is
a tree- let us next approach this tree for the purpose
of examining its structure more in detail. When we
do this, the fact of next greatest generality which we
find is as follows.
In cases where a very old form of life has continued
to exist unmodified, so that by investigation of its
anatomy we are brought back to a more primitive
type of structure than that of the newer forms grow-
ing higher up upon the same branch, two things are
observable. In the first place, the old form is less
differentiated than the newer ones ; and, in the next
place, it is seen much more closely to resemble types
of structure belonging to some of the other and larger
branches of the tree. The organization of the older
form is not only simpler ; but it is, as naturalists say,
more generalized. It comprises within itself char-
acters belonging to its own branch, and also characters
belonging to neighbouring branches, or to the trunk
from which allied branches spring. Hence it becomes
a general rule of classification, that it is by the lowest,
* D
34 Darwin, and after Darwin.
or by the oldest, forms of any two natural groups that
the affinities between the two groups admit of being
best detected. And it is obvious that this is just
what ought to be the case on the theory of descent
with divergent modification ; while, upon the alter-
native theory of special creation, no reason can be
assigned why the lowest or the oldest types should
thus combine the characters which afterwards become
severally distinctive of higher or newer types.
Again, I have already alluded to the remarkable
fact that there is no correlation between the value of
structures to the organisms which present them, and
their value to the naturalist for the purpose of tracing
natural affinity ; and I have remarked that up to the
close of the last century it was regarded as an axiom
of taxonomic science, that structures which are of
most importance to the animals or plants possessing
them must likewise prove of most importance in any
natural system of classification. On this account, all
attempts to discover the natural classification went
upon the supposition that such a direct proportion
must obtain — with the result that organs of most
physiological importance were chosen as the bases of
systematic work. And when, in the earlier part of
the present century, De Candolle found that instead
of a direct there was usually an inverse proportion
between the functional and the taxonomic value of a
structure, he was unable to suggest any reason for
this apparently paradoxical fact. For, upon the
theory of special creation, no reason can be assigned
why organs of least importance to organisms should
prove of most importance as marks of natural affinity.
But on the theory of descent with progressive modi-
Classification. 35
fication the apparent paradox is at once explained.
For it is evident that organs of functional importance
are, other things equal, the organs which are most
likely to undergo different modifications in different
lines of family descent, and therefore in time to have
their genetic relationships in these different lines
obscured. On the other hand, organs or structures
which are of no functional importance are never called
upon to change in response to any change of habit, or
to any change in the conditions of life. They may,
therefore, continue to be inherited through many
different lines of family descent, and thus afford
evidence of genetic relationship where such evidence
fails to be given by any of the structures of vital
importance, which in the course of many generations
have been required to change in many ways according
to the varied experiences of different branches of the
same family. Here, then, we have an empirically
discovered rule in the science of classification, the
raison cfltre of which we are at once able to appre-
ciate upon the theory of evolution, whereas no
possible explanation of why it should ever have
become a rule could be furnished upon the theory of
special creation.
Here, again, is another empirically determined rule.
The larger the number, as distinguished from the
importance, of structures which are found common
to different groups, the greater becomes their value
as guides to the determination of natural affinity.
Or, as Darwin puts it, " the. value of an aggre-
gate of characters, even when none are important,
alone explains the aphorism enunciated by Linnaeus,
namely, that the characters do not give the genus,
D 2
36 Darwin, and after Darwin.
but the genus gives the characters; for this seems
founded on the appreciation of many trifling points
of resemblance, too slight to be defined1."
Now it is evident, without comment, of how much
value aggregates of characters ought to be in classifica-
tion, if the ultimate meaning of classification be that
of tracing lines of pedigree ; whereas, if this ultimate
meaning were that of tracing divine ideals manifested
in special creation, we can see no reason why single
characters are not such sure tokens of a natural
arrangement as are aggregates of characters, even
though the latter be in every other respect unim-
portant. For, on the special creation theory, we
cannot explain why an assemblage, say of four or
five trifling characters, should have been chosen to
mark some unity of plan, rather than some one
character of functional importance, which would have
served at least equally well any such hypothetical
purpose. On the other hand, as Darwin remarks, " 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 with 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 different habits, only by inheritance from a
common parent. We may err in this respect in regard
to single points of structure, but when several char-
acters, 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.
* Origin of Species, p. 367.
Classification. 37
that these characters have been inherited from a
common ancestor ; and we know that such aggregated
characters have especial value in classification V
It is true that even a single character, if found
common to a large number of forms, while uniformly
absent from others, is also regarded by naturalists as
of importance for purposes of classification, although
they recognise it as of a value subordinate to that of
aggregates of characters. But this also is what we
should expect on the theory of descent. If even any
one structure be found to run through a number of
animals presenting different habits of life, the readiest
explanation of the fact is to be found in the theory of
descent ; but this does not hinder that if several such
characters always occur together, the inference of
genetic relationship is correspondingly confirmed.
And the fact that before this inference was ever drawn,
naturalists recognised the value of single characters in
proportion to their constancy, and the yet higher
value of aggregates of characters in proportion to
their number — this fact shows that in their work of
classification naturalists empirically observed the
effects of a cause which we have now discovered, to
wit, hereditary transmission of characters through
ever- widening groups of changing species.
There is another argument which appears to tell
strongly in favour of the theory of descent. We have
just seen that non-adaptive structures, not being
required to change in response to change of habits or
conditions of life, are allowed to persist unchanged
through many generations, and thus furnish excep-
tionally good guides in the science of classification —
1 Origin of Species, p. 3 7 a.
38 Darwin, and after Darwin.
or, according to our theory, in the work of tracing
lines of pedigree. But now, the converse of this
statement holds equally true. For it often happens
that adaptive structures are required to change in
different lines of descent in analogous ways, in order
to meet analogous needs ; and, when such is the case,
the structures concerned have to assume more or
less close resemblances to one another, even though
they have severally descended from quite different
ancestors. The paddles of a whale, for instance, most
strikingly resemble the fins of a fish as to their out-
ward form and movements ; yet, on the theory of
descent, they must be held to have had a widely
different parentage. Now, in all such cases where
there is thus what is called an analogous (or adaptive)
resemblance, as distinguished from what is called an
homologous (or anatomical) resemblance — in all such
cases it is observable that the similarities do not
extend further into the structure of the parts than it
is necessary that they should extend, in order that the
structures should both perform the same functions.
The whole anatomy of the paddles of a whale is quite
unlike that of the fins of a fish — being, in fact, that of
the fore-limb of a mammal. The change, therefore,
which the fore-limb has here undergone to suit it to
the aquatic habits of this mammal, is no greater than
was required for that purpose : the change has not
extended to any one feature of anatomical significance.
This, of course, is what we should expect on the
theory of descent with modification of ancestral char-
acters ; but on the theory of special creation it is not
intelligible why there should always be so marked a
distinction between resemblances as analogical or
Classification. 39
adaptive, and resemblances as homological or of
meaning in reference to a natural classification. To
take another and more detailed instance, the Tas-
manian wolf is an animal separated from true wolves
in a natural system of classification. Yet its jaws and
teeth bear a strong general resemblance to those of
all the dog tribe, although there are differences of
anatomical detail. In particular, while the dogs all
have on each side of the upper jaw four pre-molars
and two molars, the Tasmanian wolf has three pre-
molars and four molars. Now there is no reason, so
far as their common function of dealing with flesh is
concerned, why the teeth of the Tasmanian wolf
should not have resembled homologically as well as
analogically the teeth of a true wolf; and therefore
we cannot assign any intelligible reason why, if all the
species of the dog genus were separately created with
one pattern of teeth, the unallied Tasmanian wolf
should have been furnished with what is practically
the same pattern from a functional point of view,
while differing from a structural point of view. But,
of course, on the theory of descent with modifica-
tion, we can well understand why similarities of
habit should have led to similarities of structural
appearance of an adaptive kind in different lines of
descent, without there being any trace of such real or
anatomical similarities as could possibly point to
genetic relationship.
Lastly, to adduce the only remaining argument
from classification which I regard as of any consider-
able weight, naturalists have found it necessary, while
constructing their natural classifications, to set great
store on what Mr. Darwin calls " chains of affinities."
4O Darwin, and after Darwin.
Thus, for instance, " nothing can be easier than to
define a number of characters common to all birds;
but with crustaceans any such definition has hitherto
been found impossible. There are crustaceans at the
opposite ends of the series, which have hardly a
character in common ; yet the species at both ends,
from being plainly allied to others, and these to others,
and so onwards, can be recognised as unequivocally
belonging to this, and to no other class of the arti-
culata V Now it is evident that this progressive
modification of specific types — where it cannot be
said that the continuity of resemblance is anywhere
broken, and yet terminates in modification so great
that but for the connecting links no one could divine
a natural relationship between the extreme members
of the series, — it is evident that such chains of af-
finity speak most strongly in favour of a transmutation
of the species concerned, while it is impossible to
suggest any explanation of the fact in terms of the
rival theory. For if all the links of such a chain
were separately forged by as many acts of special
creation, we can see no reason why B should re-
semble A, C resemble B, and so on, but with ever
slight though accumulating differences, until there is
no resemblance at all between A and Z.
I hope enough has now been said to show that all
the general principles and particular facts appertaining
to the natural classification of plants and animals, are
precisely what they ought to be according to the
theory of genetic descent ; while no one of them is
such as might be — and, indeed, used to be — expected
1 Origin of Species, pp. 368-9.
Classification. 41
upon the theory of special creation. Therefore, the
only possible way in which all this uniform body of
direct evidence can be met by a supporter of the
latter theory, is by falling back upon the argument
from ignorance. We do not know, it may be said,
what hidden reasons there may have been for fol-
lowing all these general principles in the separate
creation of specific types. Now, it is evident that
this is a form of argument which admits of being
brought against all the actual — and even all the
possible — lines of evidence in favour of evolution.
Therefore I deem it desirable thus early in our pro-
ceedings to place this argument from ignorance on its
proper logical footing.
If there were any independent evidence in favour of
special creation as a fact, then indeed the argument
from ignorance might be fairly used against any sceptical
cavils regarding the method. In this way, for example,
Bishop Butler made a legitimate use of the argument
from ignorance when he urged that it is no reasonable
objection against a revelation, otherwise accredited, to
show that it has been rendered in a form, or after a
method, which we should not have antecedently ex-
pected. But he could not have legitimately employed
this argument, except on the supposition that he had
some independent evidence in favour of the revela-
tion; for, in the absence of any such independent
evidence, appeal to the argument from ignorance
would have become a mere begging of the question,
by simply assuming that a revelation had been made.
And thus it is in the present case. A man, of course,
may quite legitimately say, Assuming that the theory of
special creation is true, it is not for us to anticipate the
42 Darwin, and after Darwin.
form or method of the process. But where the question
is as to whether or not the theory is true, it becomes
a mere begging of this question to take refuge in the
argument from ignorance, or to represent in effect
that there is no question to be discussed. And if,
when the form or method is investigated, it be found
everywhere charged with evidence in favour of the
theory of descent, the case becomes the same as that
of a supposed revelation, which has been discredited
by finding that all available evidence points to a
natural growth. In short, the argument from ignor-
ance is in any case available only as a negative foil
against destructive criticism : in no case has it any
positive value, or value of a constructive kind. There-
fore, if a theory on any subject is destitute of positive
evidence, while some alternative theory is in possession
of such evidence, the argument from ignorance can be
of no logical use to the former, even though it may be
of such use to the latter. For it is only the possession
of positive evidence which can furnish a logical justifi-
cation of the argument from ignorance : in the absence
of such evidence, even the negative value of the argu-
ment disappears, and it then implies nothing more
than the gratuitous assumption of a theory.
I will now sum up the various considerations which
have occupied us during the present chapter.
First of all we must take note that the classification
of plants and animals in groups subordinate to groups
is not merely arbitrary, or undertaken only for a
matter of convenience and nomenclature — such, for
instance, as the classification of stars in constellations.
On the contrary, the classification of a naturalist
Classification. 43
differs from that of an astronomer, in that the
objects which he has to classify present structural
resemblances and structural differences in numberless
degrees ; and it is the object of his classification to
present a tabular statement of these facts. Now,
long before the theory of evolution was entertained,
naturalists became fully aware that these facts of
structural resemblances running through groups sub-
ordinate to groups were really facts of nature, and
not merely poetic imaginations of the mind. No one
could dissect a number of fishes without perceiving
that they were all constructed on one anatomical
pattern, which differed considerably from the equally
uniform pattern on which all mammals were con-
structed, even although some mammals bore an
extraordinary resemblance to fish in external form
and habits of life. And similarly with all the smaller
divisions of the animal and vegetable kingdoms.
Everywhere investigation revealed the bonds of close
structural resemblances between species of the same
genus, resemblance less close between genera of the
same family, resemblance still less close between
families of the same order, resemblance yet more
remote between orders of the same class, and resem-
blance only in fundamental features between classes
of the same sub-kingdom, beyond which limit all
anatomical resemblance was found to disappear —
the different sub-kingdoms being formed on wholly
different patterns. Furthermore, in tracing all these
grades of structural relationship, naturalists were
slowly led to recognise that the form which a natural
classification must eventually assume would be that
of a tree, wherein the constituent branches would
44 Darwin, and after Darwin.
display a progressive advance of organization from
below upwards.
Now we have seen that although this tree-like
arrangement of natural groups was as suggestive as
anything could well be of all the forms of life being
bound together by the ties of genetic relationship,
such was not the inference which was drawn from it.
Dominated by the theory of special creation, natu-
ralists either regarded the resemblance of type subor-
dinate to type as expressive of divine ideals mani-
fested in such creation, or else contented themselves
with investigating the facts without venturing to
speculate upon their philosophical import. But even
those naturalists who abstained from committing
themselves to any theory of archetypal plans, did
not doubt that facts so innumerable and so uni-
versal must have been due to some one co-ordi-
nating principle — that, even though they were not
able to suggest what it was, there must have been
some hidden bond of connexion running through the
whole of organic nature. Now, as we have seen, it is
manifest to evolutionists that this hidden bond can be
nothing else than heredity ; and, therefore, that these
earlier naturalists, although they did not know what
they were doing, were really tracing the lines of
genetic descent as revealed by degrees of structural
resemblance, — that the arboresent grouping of organic
forms which their labours led them to begin, and in
large measure to execute, was in fact a family tree of
life.
Here, then, is the substance of the argument from
classification. The mere fact that all organic nature
thus incontestably lends itself to a natural arrange-
Classification. 45
ment of group subordinate to group, when due
regard is paid to degrees of anatomical resemblance
— this mere fact of itself tells so weightily in favour
of descent with progressive modification in different
lines, that even if it stood alone it would be entitled
to rank as one of our strongest pieces of evidence.
But, as we have seen, it does not stand alone. When
we look beyond this large and general fact of all the
innumerable forms of life being thus united in a
tree-like system by an unquestionable relationship of
some kind, to those smaller details in the science of
classification which have been found most useful as
guides for this kind of research, then we find that all
these details, or empirically discovered rules, are
exactly what we should have expected them to be,
supposing the real meaning of classification to have
been that of tracing lines of pedigree.
In particular, we have seen that the most archaic
types are both simpler in their organization and more
generalized in their characters than are the more
recent types — a fact of which no explanation can be
given on the theory of special creation. But, upon the
theory of natural evolution, we can without difficulty
understand why the earlier forms should have been
the simpler forms, and also why they should have
been the most generalized. For it is out of the older
forms that the newer must have grown ; and, as they
multiplied, they must have become more and more
differentiated.
Again, we have seen that there is no correlation
between the importance of any structure from a
classificatory point of view, and the importance of that
structure to the organism which presents it. On the
46 Darwin> and after Darwin.
contrary, it is a general rule that " the less any part of
the organization is concerned with special habits, the
more important it becomes for classification." Now,
from the point of view of special creation it is unin-
telligible why unity of ideal should be most manifested
by least important structures, whereas from the point of
view of evolution it is to be expected that these life-
serving structures should have been most liable to diver-
gent modification in divergent lines of descent, or in
adaptation to different conditions of life, while the trivial
or less important characters should have been allowed
to remain unmodified. Thus we can now understand
why all primitive classifications were wrong in princi-
ple when they went upon the assumption that divine
ideals were best exhibited by resemblances between
life-serving (and therefore adaptive) structures, with
the result that whales were classed with fishes, birds
with bats, and so on. Nevertheless, these primitive
naturalists were quite logical ; for, from the premises
furnished by the theory of special creation, it is much
more reasonable to expect that unity of ideal should
be shown in plainly adaptive characters than in trivial
and more or less hidden anatomical characters. More-
over, long after biological science had ceased con-
sciously to follow any theological theory, the apparent
axiom continued to be entertained, that structures of
most importance to organisms must also be structures
of most importance to systematists. And when at
last, in the present century, this was found not to be
the case, no reason could be suggested why it was not
the case. But now we are able fully to explain this
apparent anomaly.
Once more, we have seen that aggregates of
Classification. 47
characters presenting resemblances to one another
have always been found to be of special importance
as guides to classification. This, of course, is what we
should have expected, if the real meaning of classifica-
tion be that of tracing lines of pedigree ; but on the
theory of special creation no reason can be assigned
why single characters are not such sure tokens of
a natural arrangement as are aggregates of characters,
however trivial the latter may be. For it is obvious
that unity of ideal might have been even better
displayed by everywhere maintaining the pattern of
some one important structure, than by doing so in the
case of several unimportant structures. Take an
analogous instance from human contrivances. Unity
of ideal in the case of gun-making would be shown by
the same principles of mechanism running through all
the different sizes and shapes of gun-locks, rather than
by the ornamental patterns engraved upon the outside
Yet it must be supposed that in the mechanisniS
assumed to have been constructed by special creation,
it was the trivial details rather than the fundamental
principles of these mechanisms which were chosen by
the Divinity to display his ideals.
And this leads us to the next consideration —
namely, that when in two different lines of descent
animals happen to adopt similar habits of life, the
modifications which they undergo in order to fit them
for these habits often induces striking resemblances of
structure between the two animals, as in the case of
whales and fish. But in all such instances it is
invariably found that the resemblance is only super-
ficial and apparent : not anatomical or real. In other
words, the resemblance does not extend further than
48 Darwin, and after Darwin.
it is necessary that it should, if both sets of organs are
to be adapted to perform the same functions. Now
this, again, is just what one would expect to find as
the universal rule on the theory of descent, with modi-
fication of ancestral characters. But, on the opposite
theory of special creation, I know not how it is to be
explained that among so many instances of close
superficial resemblance between creatures belonging
to different branches of the tree of life, there are
no instances of any real or anatomical resemblance.
So far as their structures are adapted to perform a
common function, there is in all such cases what may
be termed a deceptive appearance of some unity of
ideal ; but, when carefully examined, it is always
found that two apparently identical structures occurring
on different branches of the classificatory tree are in
fact fundamentally different in respect of their struc-
tural plan.
Lastly, we have seen that one of the guiding prin-
ciples of classification has been empirically found to
consist in setting a high value on " chains of affinities."
That is to say, naturalists not unfrequently meet
with a long series of progressive modifications of type,
which, although it cannot be said that the continuity
is anywhere broken, at last leads to so much divergence
of character that, but for the intermediate links, the
members at each end of the chain could not be sus-
pected of being in any way related. Well, such cases
of chains of affinity obviously tell most strongly in
favour of descent with continuous modification ; while
it is impossible to suggest why, if all the links were
separately forged by as many acts of special creation,
there should have been this gradual transmutation of
Classification. 49
characters carried to the point where the original
creative ideal has been so completely transformed
that, but for the accident of the chain being still
complete, no one of nature's interpreters could possibly
have discovered the connexion. For, as we have seen,
this is not a case in which any appeal can be logically
made to the argument from ignorance of divine method,
unless some independent evidence could be adduced
in favour of special creation. And that no such inde-
pendent evidence exists, it will be the object of future
chapters to show.
CHAPTER III,
MORPHOLOGY.
THE theory of evolution supposes that hereditary
characters admit of being slowly modified wherever
their modification will render an organism better
suited to a change in its conditions of life. Let
us, then, observe the evidence which we have of such
adaptive modifications of structure, in cases where
the need of such modification is apparent. We may
begin by again taking the case of the whales and
porpoises. The theory of evolution infers, from the
whole structure of these animals, that their pro-
genitors must have been terrestrial quadrupeds of
some kind, which gradually became more and more
aquatic in their habits. Now the change in the
conditions of their life thus brought about would
have rendered desirable great modifications of struc-
ture. These changes would have begun by affecting
the least typical — that is, the least strongly inherited
— structures, such as the skin, claws, and teeth. But,
as time went on, the adaptation would have ex-
tended to more typical structures, until the shape of
the body would have become affected by the bones
and muscles required for terrestrial locomotion be-
coming better adapted for aquatic locomotion, and
Morphology. 5 1
the whole outline of the animal more fish-like in
shape. This is the stage which we actually observe
in the seals, where the hind legs, although retaining
all their typical bones, have become shortened up
almost to rudiments, and directed backwards, so as
to be of no use for walking, while serving to complete
the fish-like taper of the body. (Fig. 2.) But in the
whales the modification has gone further than this
so that the hind legs have ceased to be apparent
externally, and are only represented internally — and
even this only in some species — by remnants so
rudimentary that it is difficult to make out with
certainty the homologies of the bones ; moreover,
the head and the whole body have become com-
pletely fish-like in shape. (Fig. 3.) But profound
as are these alterations, they affect only those parts
of the organism which it was for the benefit of the
organism to have altered, so that it might be adapted
to an aquatic mode of existence. Thus the arm,
which is used as a fin, still retains the bones of the
shoulder, fore-arm, wrist, and fingers, although they
are all enclosed in a fin-shaped sack, so as to render
them useless for any purpose other than swimming
(Fig. 4.) Similarly, the head, although it so closely
resembles the head of a fish in shape, still retains
the bones of the mammalian skull in their proper
anatomical relations to one another; 'but modified
in form so as to offer the least possible resistance
to the water. In short, it may be said that all the
modifications have been effected with the least pos-
sible divergence from the typical mammalian type,
which is compatible with securing so perfect an
adaptation to a purely aquatic mode of life.
E 2
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54
Darwin, and after Darwin.
Now I have chosen the case of the whale and
porpoise group, because they offer so extreme an
example of profound modification of structure in
adaptation to changed conditions of life. But the
same thing may be seen in hundreds and hundreds
of other cases. For instance, to confine our attention
FIG. 4. — Paddle of Whale compared with Hand \.( Man. Drawn
from nature (X. Coll. Surf. Mus.).
to the arm, not only is the limb modified in the whale
for swimming, but in another mammal — the bat— ^it
is modified for flying, by having the fingers enor-
mously elongated and overspread with a membranous
web.
In birds, again, the arm is modified for flight in
a wholly different way — the fingers here being very
Morphology. 5 5
short and all run together, while the chief expanse
of the wing is composed of the shoulder and fore-
arm. In frogs and lizards, again, we find hands
more like our own ; but in an extinct species of
flying reptile the modification was extreme, the
wing having been formed by a prodigious elonga-
tion of the fifth finger, and a membrane spread
over it and the rest of the hand. (Fig. 5.) Lastly,
in serpents the hand and arm have disappeared alto-
gether.
Thus, even if we confine our attention to a single
organ, how wonderful are the modifications which
it is seen to undergo, although never losing its typical
character. Everywhere we find the distinction be-
tween homology and analogy which was explained
in the last chapter — the distinction, that is, between
correspondence of structure and correspondence of
function. On the one hand, we meet with structures
which are perfectly homologous and yet in no way
analogous : the structural elements remain, but are
profoundly modified so as to perform wholly different
functions. On the other hand, we meet with struc-
tures which are perfectly analogous, and yet in no
way homologous : totally different structures are
modified to perform the same functions. How, then,
are we to explain these things? By design mani-
fested in special creation, or by descent with adaptive
modification ? If it is said by design manifested in
special creation, we must suppose that the Deity
formed an archetypal plan of certain structures, and
that he determined to adhere to this plan through
all the modifications which those structures exhibit.
But, if so, why is it that some structures are selected
FIG. 5. — Wing of Reptile, Mammal, and Bird. Drawn from nature
(Brit. Mus.).
Morphology. 57
as typical and not others ? Why should the vertebral
skeleton, for instance, be tortured into every conceiv-
able variety of modification in order to subserve as
great a variety of functions ; while another structure,
such as the eye, is made in different sub-kingdoms
on fundamentally different plans, notwithstanding
that it has throughout to perform the same function ?
Will any one have the hardihood to assert that in
the case of the skeleton the Deity has endeavoured
to show his ingenuity, by the manifold functions to
which he has made the same structure subservient ;
while in the case of the eye he has endeavoured to
show his resources, by the manifold structures which
he has adapted to serve the same function ? If so,
it becomes a most unfortunate circumstance that,
throughout both the vegetable and animal kingdoms,
all cases which can be pointed to as showing inge-
nious adaptation of the same typical structure to the
performance of widely different functions — or cases
of homology without analogy, — are cases which come
within the limits of the same natural group of plants
and animals, and therefore admit of being equally
well explained by descent from a common ancestry ;
while all cases of widely different structures per-
forming the same function — or cases of analogy
without homology, — are to be found in different
groups of plants or animals, and are therefore sug-
gestive of independent variations arising in the dif-
ferent lines of hereditary descent.
To take a specific illustration. The octopus, or
devil-fish, belongs to a widely different class of animals
from a true fish ; and yet its eye, in general appear-
ance, looks wonderfully like the eye of a true fish.
58 Darwin, and after Darwin.
Now, Mr. Mivart pointed to this fact as a great
difficulty in the way of the theory of evolution by
natural selection, because it must clearly be a most
improbable thing that so complicated a structure as
the eye of a fish should happen to be arrived at
through each of two totally different lines of descent.
And this difficulty would, indeed, be a formidable one
to the theory of evolution, if the similarity were not
only analogical but homological. Unfortunately for
the objection, however, Darwin clearly showed in his
reply that in no one anatomical or homologous
feature do the two structures resemble one another ;
so that, in point of fact, the two organs do not
resemble one another in any particular further than it
is necessary that they should, if both are to be
analogous, or to serve the same function as organs of
sight. But now, suppose that this had not been the
case, and that the two structures, besides presenting
the necessary superficial or analogical resemblance,
had also presented an anatomical or homologous
resemblance, with what force might it have then been
urged, — Your hypothesis of hereditary descent with
progressive modification being here excluded by the
fact that the animals compared belong to two widely
different branches of the tree of life, how are we to
explain the identity of type manifested by these two
complicated organs of vision ? the only hypothesis
open to us is intelligent adherence to an ideal plan or
mechanism. But as this cannot now be urged in any
comparable case throughout the whole organic world,
wemay on the other hand present it as a most significant
fact, that while within the limits of the same large
branch of the tree of life we constantly find the same
Morphology. 59
typical structures modified so as to perform very
different functions, we never find any of these
particular types of structure in other large branches
of the tree. That is to say, we never find typical
structures appearing except in cases where their
presence may be explained by the hypothesis of
hereditary descent ; while in thousands of such cases
we find these structures undergoing every conceivable
variety of adaptive modification.
Consequently, special creationists must fall back
upon another position and say,— Well, but it may have
pleased the Deity to form a certain number of ideal
types, and never to have allowed the structures
occurring in one type to appear in any of the others.
We answer, — Undoubtedly such may have been the
case ; but, if so, it is a most unfortunate thing for your
theory, because the fact implies that the Deity has
planned his types in such a way as to suggest the
counter-theory of descent. For instance, it would
seem most capricious on the part of the Deity to have
made the eyes of an innumerable number of fish on
exactly the same ideal type, and then to have made
the eye of the octopus so exactly like these other eyes
in superficial appearance as to deceive so accomplished
a naturalist as Mr. Mivart, and yet to have taken
scrupulous care that in no one ideal particular should
the one type resemble the other. However, adopting
for the sake of argument this great assumption, let us
suppose that God did lay down these arbitrary rules
for his own guidance in creation, and then let us see to
what the assumption leads. If the Deity formed a
certain number of ideal types, and determined that
on no account should he allow any part of one type
60 Darwin, and after Darwin.
to appear in any part of another, surely we should
expect that within the limits of the same type the
same typical structures should always be present.
Thus, remember what efforts, so to speak, have been
made to maintain the uniformity of type in the case of
the fore-limb as previously explained, and should we
not expect that in other and similar cases a similar
method should have been followed ? Yet we repeatedly
find that this is not the case. Even in the whale, as we
have seen, the hind-limbs are either altogether absent or
dwindled almost to nothing ; and it is impossible to
see in what respect the hind-limbs are of any less ideal
value than the fore-limbs — which are carefully pre-
served in all vertebrated animals except the snakes,
and the extinct Dinornis> where again we meet in
this particular with a sudden and sublime indiffer-
ence to the maintenance of a typical structure. (Fig. 6.)1
Now I say that if the theory of ideal types is true, we
have in these facts evidence of a most unreasonable in-
consistency. But the theory of descent with continued
adaptive modification fully explains all the known
cases ; for in every case the degree of divergence from
the typical structure which an organism presents
corresponds, in a general way, with the length of time
during which the divergence has been going on.
Thus we scarcely ever meet with any great departure
from the typical form with respect to one of the
organs, without some of the other organs being so far
modified as of themselves to indicate, on the sup-
1 It is, however, probable that all species of the genus retained a tiny
rudiment of wings in greatly dwindled scapulo-coracoid bones. And
Mr. H. O. Forbes has detected, in a recently exhumed specimen of the
latter, an indication of the glenoid cavity, for the articulation of an
extremely aborted humerus. (See Nature, Jan. '4th, 1893.)
FlG. 6. — Skeleton of Dinornis gravis, -fa nat. size. Drawn from nature
(Brit. Mus.}. As separate cuts on a larger scale are shown, 1st, the sternum,
as this appears in mounted skeletons, and, and, the same in profile, with its
(hypothetical) scapulo-coracoid attached.
62 Darwin, and after Darwin.
position of descent with modification, that the animal
or plant must have been subject to the modifying
influences for an enormously long series of generations.
And this combined testimony of a number of organs
in the same organism is what the theory of descent
would lead us to expect, while the rival theory of
design can offer no explanation of the fact, that when
one organ shows a conspicuous departure from the
supposed ideal type, some of the other organs in the
same organism should tend to keep it company by
doing likewise.
As an illustration both of this and of other points
which have been mentioned, I may draw attention to
what seems to me a particularly suggestive case. So-
called soldier- or hermit-crabs, are crabs which have
adopted the habit of appropriating the empty shells
of mollusks. In association with this peculiar habit,
the structure of these animals differs very greatly from
that of all other crabs. In particular, the hinder part
of the body, which occupies the mollusk-shell, and
which therefore has ceased to require any hard cover-
ing of its own, has been suffered to lose its calcareous
integument, and presents a soft fleshy character, quite
unlike that of the more exposed parts of the animal.
Moreover, this soft fleshy part of the creature is
specially adapted to the particular requirements of
the creature by having its lateral appendages — i.e.
appendages which in other Crustacea perform the
function of legs — modified so as to act as claspers to
the inside of the mollusk-shell ; while the tail-end of
the part in question is twisted into the form of a spiral,
which fits into the spiral of the mollusk-shell. Now,
in Keeling Island there is a large kind of crab called
Morphology. 63
Birgus latro, which lives upon land and there feeds
upon cocoa-nuts. The whole structure of this crab, it
seems to me, unmistakeably resembles the structure
of a hermit-crab (see drawings on the next page,
Fig. 7). Yet this crab neither lives in the shell ol
a mollusk, nor is the hinder part of its body in the soft
and fleshy condition just described : on the contrary, it
is covered with a hard integument like all the other
parts of the animal. Consequently,! think we may infer
that the ancestors of Birgus were hermit-crabs living
in mollusk-shells ; but that their descendants grad-
ually relinquished this habit as they gradually became
more and more terrestrial, while, concurrently with
these changes in habit, the originally soft posterior
parts acquired a hard protective covering to take the
place of that which was formerly supplied by the
mollusk-shell. So that, if so, we now have, within the
limits of a single organism, evidence of a whole series
of morphological changes in the past history of its
species. First, there must have been the great change
from an ordinary crab to a hermit-crab in all the
respects previously pointed out. Next, there must
have been the change back again from a hermit-crab
to an ordinary crab, so far as living without the ne-
cessity of a mollusk-shell is concerned. From an
evolutionary point of view, therefore, we appear to have
in the existing structure of Birgus a morphological
record of all these changes, and one which gives us a
reasonable explanation of why the animal presents the
extraordinary appearance which it does. But, on the
theory of special creation, it is inexplicable why this
land-crab should have been formed on the pattern of
a hermit-crab, when it never has need to enter the shell
Morphology. 65
of a mollusk. In other words, its peculiar structure
is not specially in keeping with its present habits,
although so curiously allied to the similar structure
of certain other crabs of totally different habits, in
relation to which the peculiarities are of plain and
obvious significance.
I will devote the remainder of this chapter to
considering another branch of the argument from
morphology, to which the case of Birgus serves as
a suitable introduction : I mean the argument from
rudimentary structures.
Throughout both the animal and vegetable king-
doms we constantly meet with dwarfed and useless
representatives of organs, which in other and allied
kinds of animals and plants are of large size and
functional utility. Thus, for instance, the unborn
whale has rudimentary teeth, which are never des-
tined to cut the gums ; and throughout its life this
animal retains, in a similarly rudimentary condition,
a number of organs which never could have been of use
to any kind of creature save a terrestrial quadruped.
The whole anatomy of its internal ear, for example,
has reference to hearing in air — or, as Hunter long ago
remarked, " is constructed upon the same principle as
in the quadruped " ; yet, as Owen says, " the outer
opening and passage leading therefrom to the tym-
panum can rarely be affected by sonorous vibrations
of the atmosphere, and indeed they are reduced, or
have degenerated, to a degree which makes it difficult
to conceive how such vibrations can be propagated to
the ear-drum during the brief moments in which the
opening may be raised above the water."
* F
66 Darwin, and after Darwin.
Now, rudimentary organs of this kind are of such
frequent occurrence, that almost every species presents
one or more of them — usually, indeed, a considerable
number. How, then, are they to be accounted for ?
Of course the theory of descent with adaptive modifi-
cation has a simple answer to supply — namely, that
when, from changed conditions of life, an organ which
was previously useful becomes useless, it will be suf-
fered to dwindle away in successive generations, under
the influence of certain natural causes which we shall
have to consider in future chapters. On the other
hand, the theory of special creation can only maintain
that these rudiments are formed for the sake of ad-
hering to an ideal type. Now, here again the former
theory appears to be triumphant over the latter ; for,
without waiting to dispute the wisdom of making
dwarfed and useless structures merely for the whim-
sical motive assigned, surely if such a method were
adopted in so many cases, we should expect that in
consistency it would be adopted in all cases. This
reasonable expectation, however, is far from being
realized. We have already seen that in numberless
cases, such as that of the fore-limbs of serpents, no
vestige of a rudiment is present. But the vacillating
policy in the matter of rudiments does not end here ;
for it is shown in a still more aggravated form where
within the limits of the same natural group of or-
ganisms a rudiment is sometimes present and some-
times absent. For instance, although in nearly all the
numerous species of snakes there are no vestiges of
limbs, in the Python we find very tiny rudiments of the
hind-limbs. (Fig. 8.) Now, is it a worthy conception of
Deity that, while neglecting to maintain his unity of
Morphology.
67
ideal in the case of nearly all the numerous species
of snakes, he should have added a tiny rudiment in
the case of the Python — and even in that case should
have maintained his ideal very inefficiently, inas-
much as only two limbs, instead of four, are repre-
sented ? How much more reasonable is the natura-
"P y TH o N! .
FIG. 8. — Rudimentary or vestigial hind-limbs of Python, as exhibited
in the skeleton and on the external surface of the animal. Drawn from
nature, J nat. size (Zoological Gardens).
listic interpretation ; for here the very irregularity of
their appearance in different species, which constitutes
rudimentary structures one of the crowning difficulties
to the theory of special design, furnishes the best
possible evidence in favour of hereditary descent ;
seeing that this irregularity then becomes what may
be termed the anticipated expression of progressive
F 2
68 Darwin, and after Darwin.
dwindling due to inutility. Thus, for example, to
return to the case of wings, we have already seen
that in an extinct genus of bird, Dinornis, these
organs were reduced to such an extent as to leave
it still doubtful whether so much as the tiny rudiment
hypothetically supplied to Fig. 6 (p. 61) was present
in all the species. And here is another well-known
case of another genus of still existing bird, which, as
was the case with Dinornis, occurs only in New
Zealand. (Fig. 9.) Upon this island there are no four-
footed enemies — either existing or extinct — to escape
from which the wings of birds would be of any service.
Consequently we can understand why on this island
we should meet with such a remarkable dwindling
away of wings.
Similarly, the logger-headed duck of South America
can only flap along the surface of the water, having
its wings considerably reduced though less so than
the Apteryx of New Zealand. But here the interesting
fact is that the young birds are able to fly perfectly
well. Now, in accordance with a general law to be
considered in a future chapter, the life-history of an
individual organism is a kind of condensed recapitu-
lation of the life-history of its species. Consequently,
we can understand why the little chickens of the
logger-headed duck are able to fly like all other ducks,
while their parents are only able to flap along the
surface of the water.
Facts analogous to this reduction of wings in birds
which have no further use for them, are to be met
with also in insects under similar circumstances.
Thus, there are on the island of Madeira somewhere
between 500 and 600 species of beetles, which are in
Morphology.
69
large part peculiar to that island, though related to
other — and therefore presumably parent — species on
the neighbouring continent. Now, no less than 200
species — or nearly half the whole number — are so far
deficient in wings that they cannot fly. And, if we
FIG. 9. — Apteryx Australis. Drawn from life in the Zoological
Gardens, \ nat. size. The external wing is drawn to a scale in the upper
part of the cut. The surroundings are supplied from the most recent
descriptions.
disregard the species which are not peculiar to the
island — that is to say, all the species which likewise
occur on the neighbouring continent, and therefore,
as evolutionists conclude, have but recently migrated
to the island, — we find this very remarkable proportion.
There are altogether 39 peculiar genera, and out ol
7O Darwin, and after Darwin.
these no less than 23 have all their species in this
condition.
Similar facts have been recently observed by the
Rev. A. E. Eaton with respect to insects inhabiting
Kerguelen Island. All the species which he found
on the island — viz. a moth, several flies, and numerous
beetles — he found to be incapable of flight ; and
therefore, as Wallace observes, " as these insects could
hardly have reached the islands in a wingless state,
even if there were any other known land inhabited by
them, which there is not, we must assume that, like
the Madeiran insects, they were originally winged,
and lost their power of flight because its possession
was injurious to them " — Kerguelen Island being " one
of the stormiest places on the globe," and therefore a
place where insects could rarely afford to fly without
incurring the danger of being blown out to sea.
Here is another and perhaps an even more suggestive
class of facts.
It is now many years ago since the editors of
Sillimaris Journal requested the late Professor Agassiz
to give them his opinion on the following question.
In a certain dark subterranean cave, called the
Mammoth cave, there are found some peculiar species
of blind fishes. Now the editors of Sillimaris Journal
wished to know whether Prof. Agassiz would hold
that these fish had been specially created in these
caves, and purposely devoided of eyes which could
never be of any use to them ; or whether he would
allow that these fish had probably descended from
other species, but, having got into the dark cave,
gradually lost their eyes through disuse. Prof.
Agassiz, who was a believer in special creation,
Morphology. 7 1
allowed that this ought to constitute a crucial test as
between the two theories of special design and here-
ditary descent. " If physical circumstances," he said,
"ever modified organized beings, it should be easily
ascertained here." And eventually he gave it as his
opinion, that these fish " were created under the cir-
cumstances in which they now live, within the limits
over which they now range, and with the structural
peculiarities which now characterise them."
Since then a great deal of attention has been paid
to the fauna of this Mammoth cave, and also to the
faunas of other dark caverns, not only in the New,
but also in the Old World. In the result, the fol-
lowing general facts have been fully established.
(1) Not only fish, but many representatives of other
classes, have been found in dark caves.
(2) Wherever the caves are totally dark, all the
animals are blind.
(3) If the animals live near enough to the entrance
to receive some degree of light, they may have large
and lustrous eyes.
(4) In all cases the species of blind animals are
closely allied to species inhabiting the district where
the caves occur; so that the blind species inhabit-
ing American caves are closely allied to American
species, while those inhabiting European caves are
closely allied to European species.
(5) In nearly all cases structural remnants of eyes
admit of being detected, in various degrees of obsoles-
cence. In the case of some of the crustaceans of the
Mammoth cave the foot-stalks of the eyes are present,
although the eyes themselves are entirely absent.
Now, it is evident that all these general facts are in
72 Darwin, and after Darwin.
full agreement with the theory of evolution, while
they offer serious difficulties to the theory of special
creation. As Darwin remarks, it is hard to imagine
conditions of life more similar than those furnished by
deep limestone caverns under nearly the same climate
in the two continents of America and Europe ; so
that, in accordance with the theory of special creation,
very close similarity in the organizations of the two
sets of faunas might have been expected. But,
instead of this, the affinities of these two sets of
faunas are with those of their respective continents —
as of course they ought to be on the theory of
evolution. Again, what would have been the sense
of creating useless foot-stalks for the imaginary sup-
port of absent eyes, not to mention all the other
various grades of degeneration in other cases ? So
that, upon the whole, if we agree with the late Prof.
Agassiz in regarding these cave animals as furnishing
a crucial test between the rival theories of creation
and evolution, we must further conclude that the
whole body of evidence which they now furnish is
weighing on the side of evolution.
So much, then, for a few special instances of what
Darwin called rudimentary structures, but what may
be more descriptively designated — in accordance with
the theory of descent — obsolescent or vestigial struc-
tures. It is, however, of great importance to add that
these structures are of such general occurrence through-
out both the vegetable and animal kingdoms, that, as
Darwin has observed, it is almost impossible to point
to a single species which does not present one or
more of them. In other words, it is almost impos-
sible to find a single species which does not in this
Morphology. 73
way bear some record of its own descent from other
species ; and the more closely the structure of any
species is examined anatomically, the more numerous
are such records found to be. Thus, for example, of
all organisms that of man has been most minutely
investigated by anatomists ; and therefore I think it
will be instructive to conclude this chapter by giving
a list of the more noteworthy vestigial structures
which are known to occur in the human body. I will
take only those which are found in adult man, reserving
for the next chapter those which occur in a transitory
manner during earlier periods of his life. But, even as
thus restricted, the number of obsolescent structures
which we all present in our own persons is so remark-
able, that their combined testimony to our descent from
a quadrumanous ancestry appears to me in itself con-
clusive. I mean, that even if these structures stood
alone, or apart from any more general evidences of
our family relationships, they would be sufficient to
prove our parentage. Nevertheless, it is desirable to
remark that of course these special evidences which I
am about to detail do not stand alone. Not only is
there the general analogy furnished by the general
proof of evolution elsewhere, but there is likewise
the more special correspondence between the whole
of our anatomy and that of our nearest zoological
allies. Now the force of this latter consideration is so
enormous, that no one who has not studied human
anatomy can be in a position to appreciate it. For
without special study it is impossible to form any ad-
equate idea of the intricacy of structure which is pre-
sented by the human form. Yet it is found that this
enormously intricate organization is repeated in all its
74 Darwin, and after Darwin.
details in the bodies of the higher apes. There is no
bone, muscle, nerve, or vessel of any importance in the
one which is not answered to by the other. Hence
there are hundreds of thousands of instances of the
most detailed correspondence, without there being
any instances to the contrary, if we pay due regard
to vestigial characters. The entire corporeal structure
of man is an exact anatomical copy of that which we
find in the ape.
My object, then, here is to limit attention to those
features of our corporeal structure which, having
become useless on account of our change in attitude
and habits, are in process of becoming obsolete, and
therefore occur as mere vestigial records of a former
state of things. For example, throughout the verte-
brated series, from fish to mammals, there occurs in
the inner corner of the eye a semi-transparent eye-lid,
which is called the nictitating membrane. The object
of this structure is to sweep rapidly, every now and
then, over the external surface of the eye. apparently
in order to keep the surface clean. But although the
membrane occurs in all classes of the sub-kingdom,
it is more prevalent in some than in others — e.g.
in birds than in mammals. Even, however, where it
does not occur of a size and mobility to be of any use,
it is usually represented, in animals above fishes, by a
functionless rudiment, as here depicted in the case of
man. (Fig. 10.)
Now the organization of man presents so many
vestigial structures thus referring to various stages of
his long ancestral history, that it would be tedious so
much as to enumerate them. Therefore I will yet
further limit the list of vestigial structures to be given
Jtftff
FIG. 10. — Illustrations of the nictitating membrane in the various animals named
drawn from nature. The letter N indicates the membrane in each case. In man
it is called the plica semilunarzs, and is represented in the two lower drawing!
under this name. In the case of the shark (Gaieus) the muscular mechaniun u
shown as dissected.
76 Darwin, and after Darwin.
as examples, by not only restricting these to cases
which occur in our own organization ; but of them I
shall mention only such as refer us to the very last
stage of our ancestral history — viz, structures which
FlG. II. — Rudimentary, or vestigial and useless, muscles of the
human ear. (From Gray's Anatomy?)
have become obsolescent since the time when our dis-
tinctively human branch of the family tree diverged from
that of our immediate forefathers, the Quadrumana.
(i) Musctes of the external ear. — These, which are
of large size and functional use in quadrupeds, we
Morphology. 77
retain in a dwindled and useless condition (Fig. u).
This is likewise the case in anthropoid apes ; but in
not a few other Quadrumana (e.g. baboons, macacus,
magots, &c.) degeneration has not proceeded so far,
and the ears are voluntarily moveable.
(2) Panniculus carnosis. — A large number of the
mammalia are able to move their skin by means of
sub-cutaneous muscle — as we see, for instance, in a
horse, when thus protecting himself against the
sucking of flies. We, in common with the Quad-
rumana, possess an active remnant of such a muscle in
the skin of the forehead, whereby we draw up the
eyebrows; but we are no longer able to use other
considerable remnants of it, in the scalp and elsewhere,
— or, more correctly, it is rarely that we meet with
persons who can. But most of the Quadrumana
(including the anthropoids) are still able to do so.
There are also many other vestigial muscles, which
occur only in a small percentage of human beings,
but which, when they do occur, present unmistakeable
homologies with normal muscles in some of the Quad-
rumana and still lower animals T.
(3) Feet. — It is observable that in the infant the
feet have a strong deflection inwards, so that the soles
in considerable measure face one another. This
peculiarity, which is even more marked in the embryo
than in the infant (see p. 153), and which becomes
gradually less and less conspicuous even before the
child begins to walk, appears to me a highly sugges-
tive peculiarity. For it plainly refers to the condition
1 See especially Mr. John Wood's papers, Proc. R. S., xiii to xvi, and
xviii ; also Journ. Anat.',\ and iii. In this connexion Darwin refers
to M. Richard, Annls. d. Sc. Nat. Zoolg., torn, xviii, p. 13, 1853.
78 Darwin, and after Darwin.
of things in the Quadrumana, seeing that in all these
animals the feet are similarly curved inwards, to
facilitate the grasping of branches. And even when
walking on the ground apes and monkeys employ to
a great extent the outside edges of their feet, as does
FIG. 12. — Portrait of a young male gorilla vafter Uartmann).
also a child when learning to walk. The feet of a
young child are also extraordinarily mobile in all
directions, as are those of apes. In order to show
these points, I here introduce comparative drawings
of a young ape and the portrait of a young male
child. These drawings, moreover, serve at the
Morphology.
79
same time to illustrate two other vestigial characters,
which have often been previously noticed with regard
to the infant's foot. I allude to the incurved form of
the legs, and the lateral extension of the great toe,
whereby it approaches the thumb-like character of
FIG. 13. — Portrait of a young male child. Photographed from life,
when the mobile feet were for a short time at rest in a position of
extreme inflection. ,
this organ in the Quadrumana. As in the case of
the incurved position of the legs and feet, so in this
case of the lateral extensibility of the great toe, the
peculiarity is even more marked in embryonic than in
infant life. For, as Prof. Wyman has remarked with
regard to the foetus when about an inch in length.
8o Darwin, and after Darwin.
" The great toe is shorter than the others ; and, instead
of being parallel to them, is projected at an angle from
the side of the foot, thus corresponding with the per-
manent condition of this part in the Quadrumana1."
So that this organ, which, according to Owen, " is
perhaps the most characteristic peculiarity in the
human structure," when traced back to the early
stages of its development, is found to present a
notably less degree of peculiarity.
(4) Hands. — Dr. Louis Robinson has recently
observed that the grasping power of the whole human
hand is so surprisingly great at birth, and during the
first few weeks of infancy, as to be far in excess of
present requirements on the part of a young child.
Hence he concludes that it refers us to our quadru-
manous ancestry — the young of anthropoid apes being
endowed with similar powers of grasping, in order to
hold on to the hair of the mother when she is using
her arms for the purposes of locomotion. This in-
ference appears to me justifiable, inasmuch as no
other explanation can be given of the comparatively
inordinate muscular force of an infant's grip. For
experiments showed that very young babies are able
to support their own weight, by holding on to a
horizontal bar, for a period varying from one half to
more than two minutes2. With his kind permission
I here reproduce one of Dr. Robinson's instantaneous,
and hitherto unpublished, photographs of a very young
infant. This photograph was taken after the above
paragraph (3) was written, and I introduce it here
because it serves to show incidentally — and perhaps
1 Proc. Nat. Hist. Soc., Boston, 1863.
• Nineteenth Century, November, 1891.
Morphology.
81
even better than the preceding figure — the points
there mentioned with regard to the feet and great
toes. Again, as Dr. Robinson observes, the attitude,
and the disproportionately large development of the
arms as compared with the legs, give all the photo-
graphs a striking resemblance to a picture of the
Fig. 14. — An infant, three weeks old, supporting its own weight foi
over two minutes. The attitude of the lower limbs, feet, and tots,
is strikingly simian. Reproduced from an instantaneous photograph,
kindly given for the purpose by Dr. L. Robinson.
chimpanzee " Sally " at the Zoological Gardens. For
" invariably the thighs are bent nearly at right angles
to the body, and in no case did the lower limbs hang
down and take the attitude of the erect position." He
adds, " In many cases no sign of distress is evinced,
* G
82
Darwin, and after Darwin.
and no cry uttered, until the grasp begins to give
way."
(5) Tail. — The absence of a tail in man is popularly
supposed to constitute a difficulty against the doctrine
of his quadrumanous descent. As a matter of fact,
however, the absence of an external tail in man is
MAN
GORILLA
FIG. 15. — Sacrum of Gorilla compared with that of Man, showing the
rudimentary tail- bones of each. Drawn from nature (A1. Coll. Surg.
Mus).
precisely what this doctrine would expect, seeing that
the nearest allies of man in the quadrumanous series
are likewise destitute of an external tail. Far> then,
from this deficiency in man constituting any difficulty
to be accounted for, if the case were not so — i.e. if man
did possess an external tail, — the difficulty would be
Morphology. 83
to understand how he had managed to retain an
organ which had been renounced by his most recent
ancestors. Nevertheless, as the anthropoid apes con-
tinue to present the rudimentary vestiges of a tail
in a few caudal vertebrae below the integuments, we
might well expect to find a similar state of matters in
the case of man. And this is just what we do find, as
a glance at these two comparative illustrations will
show. (Fig. 15.) Moreover, during embryonic life,
both of the anthropoid apes and of man, the tail much
FIG. 16. — Diagrammatic outline of the human embryo when about
seven weeks old, showing the relations of the limbs and tail to the
trunk (after Allen Thomson), r, the radial, and u, the ulnar, border of
the hand and fore-arm ; t, the tibial, and f, the fibular, border of the
foot and lower leg ; au, ear ; s, spinal cord ; v, umbilical cord ; bt branchial
gill-slits ; c , tail.
more closely resembles that of the lower kinds of
quadrumanous animals from which these higher re-
presentatives of the group have descended. For at
a certain stage of embryonic life the tail, both of apes
and of human beings, is actually longer than the legs
(see Fig. 16). And at this stage of development,
also, the tail admits of being moved by muscles
which later on dwindle away. Occasionally, however,
G 2
84
Darwin, and after Darwin.
these muscles persist, and are then described by
anatomists as abnormalities. The following illustra-
tions serve to show the muscles in question, when thus
found in adult man.
FIG. 17. — Front and back view of adult human sacrum, showing
abnormal persistence of vestigial tail-muscles. (The first drawing is
copied from Prof. Watson's paper in Journl. Anal, and Phyriol., vol.
79 : the second is compiled from different specimens.)
(6) Vermiform Appendix of the Ccecum. — This is of
large size and functional use in the process of digestion
among many herbivorous animals ; while in man it is
not only too small to serve any such purpose, but is
even a source of danger to life — many persons dying
every year from inflammation set up by the lodge-
ment in this blind tube of fruit-stones, &c.
In the orang it is longer than in man (Fig. 18), as
Morphology.
FlG. 1 8. — Appendix vermiformis in Orang and in Man. Drawn from
dried inflated specimens in the Cambridge Museum by Mr. J. J. Lis-
ter. //, ilium; Co, colon; C, ccecum; W, a window cut in the wall
of the ccecum ; x x x, the appendix.
MAN
MAM
FfETAL
FlG. 19. — The same, showing variation in the Orang. Drawn from
a specimen in the Museum of the Royal College of Surgeons.
86
Darwin, and after Darwin.
it is also in the human foetus proportionally compared
with the adult. (Fig. 19.) In some of the lower herbi-
vorous animals it is longer than the entire body.
Like vestigial structures in general, however, this one
is highly variable. Thus the above cut (Fig. 19) serves
to show that it may sometimes be almost as short in
the orang as it normally is in man — both the human
subjects of this illustration having been normal.
(7) Ear. — Mr. Darwin writes : —
The celebrated sculptor, Mr. Woolner, informs me of one
little peculiarity in the external ear, which he has often observed
both in men and women .... The
peculiarity consists in a little blunt
point, projecting from the inwardly
folded margin, or helix. When
present, it is developed at birth, and,
according to Prof. Ludwig Meyer,
^f jjlB)'1 j| '-iSI m more frequently in man than in
woman. Mr. Woolner made an exact
model of one such case, and sent me
the accompanying drawing .... The
helix obviously consists of the extreme
margin of the ear folded inwards ;
and the folding appears to be in some
ear> manner connected with the whole ex-
modelled and drawn by . , , . ,
Mr wnnin«- - thl teTnal ear being permanently pressed
backwards. In many monkeys, which
do not stand high in the order, as
baboons and some species of macacus, the upper portion of
the ear is slightly pointed, and the margin is not at all folded
inwards ; but if the margin were to be thus folded, a slight
point would necessarily project towards the centre .... The
following wood-cut is an accurate copy of a photograph of the
foetus of an orang (kindly sent me by Dr. Nitsche), in which it
may be seen how different the pointed outline of the ear is at
this period from its adult condition, when it bears a close
FIG. 20. — Human
Mr. Woolner.
projecting point.
Morphology. 87
general resemblance to that of man [including even the occa-
sional appearance of the projecting point shown in the preceding
woodcut]. It is evident that the folding over of the tip of such
an ear, unless it changed greatly during its further development,
would give rise to a point projecting inwards '.
FIG. ai. — Foetus of an Orang. Exact copy of a photograph,
showing the form of the ear at this early stage.
The following woodcut serves still further to show
vestigial resemblances between the human ear and
that of apes. The last two figures illustrate the
general resemblance between the normal ear of foetal
man and" the ear of an adult orang-outang. The
other two figures on the lower line are intended to
exhibit occasional modifications of the adult human
ear, which approximate simian characters somewhat
more closely than does the normal type. It will be
observed that in their comparatively small lobes these
ears resemble those of all the apes ; and that while the
outer margin of one is not unlike that of the Barbary
1 Descent of Man, and ed., pp. 15-16.
Morphology. 89
ape, the outer margin of the other follows those of the
chimpanzee and orang. Of course it would be easy
to select individual human ears which present either
of these characters in a more pronounced degree ;
but these ears have been chosen as models because
they present both characters in conjunction. The
upper row of figures likewise shows the close similarity
of hair-tracts, and the direction of growth on the part
of the hair itself, in cases where the human ear happens
to be of an abnormally hirsute character. But this
particular instance (which I do not think has been
previously noticed) introduces us to the subject of hair,
and hair-growth, in general.
(8) Hair. — Adult man presents rudimentary hair
over most parts of the body. Wallace has sought to
draw a refined distinction between this vestigial coating
and the useful coating of quadrumanous animals, in
the absence of the former from the human back. But
even this refined distinction does not hold. On the
one hand, the comparatively hairless chimpanzee
which died last year in the Zoological Gardens (T.
calvus) was remarkably denuded over the back ; and,
on the other hand, men who present a considerable
development of hair over the rest of their bodies
present it also on their backs and shoulders. Again,
in all men the rudimentary hair on the upper and
lower arm is directed towards the elbow — a peculiarity
which occurs nowhere else in the animal kingdom,
with the exception of the anthropoid apes and a few
American monkeys, where it presumably has to do
with arboreal habits. For, when sitting in trees, the
orang, as observed by Mr. Wallace, places its hands
above its head with its elbows pointing downwards :
FlG. 23. — Hair-tracts on the arms and hands of Man, as compared
with those on the arms and hands of Chimpanzee. Drawn from life.
Morphology. 91
the disposition of hair on the arms and fore-arms then
has the effect of thatch in turning the rain. Again,
I find that in all species of apes, monkeys, and
baboons which I have examined (and they have been
numerous), the hair on the backs of the hands and
feet is continued as far as the first row of phalanges ;
but becomes scanty, or disappears altogether, on the
second row ; while it is invariably absent on the
terminal row. I also find that the same peculiarity
occurs in man. We all have rudimentary hair on the
first row of phalanges, both of hands and feet : when
present at all, it is more scanty on the second row ;
and in no case have I been able to find any on
the terminal row. In all cases these peculiarities are
congenital, and the total absence or partial presence
of hair on the second phalanges is constant in different
species of Quadrumana. For instance, it is entirely
absent in all the chimpanzees, which I have examined,
while scantily present in all the orangs. As in man,
it occurs in a patch midway between the joints.
Besides showing these two features with regard to
the disposition of hair on the human arm and hand,
the above woodcut illustrates a third. By looking
closely at the arm of the very hniry man from whom
the drawing was taken, it could be seen that there was
a strong tendency towards a whorled arrangement
of the hairs on the backs of the wrists. This is
likewise, as a general rule, a marked feature in the
arrangement of hair on the same places in the gorilla,
orang, and chimpanzee. In the specimen of the
latter, however, from which the drawing was taken,
this characteristic was not well marked. The down-
ward direction of the hair on the backs of the hands
92 Darwin, and after Darwin.
is exactly the same in man as it is in all the anthropoid
apes. Again, with regard to hair, Darwin notices that
occasionally there appears in man a few hairs in the
eyebrows much longer than the others ; and that they
seem to be representative of similarly long and scattered
hairs which occur in the chimpanzee, macacus, and
baboons.
Lastly, it may be here more conveniently observed
than in the next chapter on Embryology, that at
about the sixth month the human foetus is often
thickly coated with somewhat long dark hair over
the entire body, except the soles of the feet and
palms of the hands, which are likewise bare in all
quadrumanous animals. This covering, which is called
the lanugo, and sometimes extends even to the whole
forehead, ears, and face, is shed before birth. So that
it appears to be useless for any purpose other than
that of emphatically declaring man a child of the
monkey.
(9) Teeth. — Darwin writes : —
It appears as if the posterior molar or wisdom-teeth were
tending to become rudimentary in the more civilized races of
man. These teeth are rather smaller than the other molars, as
is likewise the case with the corresponding teeth in the chim-
panzee and orang ; and they have only two separate fangs ....
They are also much more liable to vary, both in structure and in
the period of their development, than the other teeth. In the
Melanian races, on the other hand, the wisdom-teeth are usually
furnished with three separate fangs, and are usually sound [i.e.
not specially liable to decay] ; they also differ from the other
molars in size, less than in the Caucasian races.
Now, in addition to these there are other respects
in which the dwindling condition of wisdom-teeth is
manifested — particularly with regard to the pattern of
Morphology.
93
their crowns. Indeed, in this respect it would seem
that even in the anthropoid apes there is the be-
ginning of a tendency to degeneration of the molai
teeth from behind forwards. For if we compare the
three molars in the lower jaw of the gorilla, orang,
and chimpanzee, we find that the gorilla has five well-
FlG. 24. — Molar teeth of lower jaw in Gorilla, Orang, and Man.
Drawn from nature, nat size (/?. Mus. Coll. Surg.\
marked cusps on all three of them ; but that in the
orang the cusps are not so pronounced, while in the
chimpanzee there are only four of them on the third
molar. Now in man it is only the first of these three
teeth which normally presents five cusps, both the
others presenting only four. So that, comparing all
94 Darwin, and after Darwin.
these genera together, it appears that the numbei
of cusps is being reduced from behind forwards;
the chimpanzee having lost one of them from the
third molar, while man has not only lost this, but
also one from the second molar, — and, it may be added,
likewise partially (or even totally) from the first molar,
as a frequent variation among civilized races. But, on
the other hand, variations are often met with in the
opposite direction, where the second or the third
molar of man presents five cusps — in the one case
following the chimpanzee, in the other the gorilla.
These latter variations, therefore, may fairly be re-
garded as reversionary. For these facts I am indebted
to the kindness of Mr. C. S. Tomes.
(10) Perforations of the humertis. — The peculiarities
which we have to notice under this heading are two in
number. First, the supra condyloid foramen is a nor-
mal feature in some of the lower Quadrumana (Fig. 25),
where it gives passage to the great nerve of the fore-
arm, and often also to the great artery. In man, how-
ever, it is not a normal feature. Yet it occurs in a
small percentage of cases — viz., according to Sir W.
Turner, in about one per cent., and therefore is regarded
by Darwin as a vestigial character. Secondly, there is
inter-condyloid foramen, which is also situated near
the lower end of the humerus, but more in the middle
of the bone. This occurs, but not constantly, in apes,
and also in the human species. From the fact that it
does so much more frequently in the bones of ancient —
and also of some savage — races of mankind (viz. in 20
to 30 per cent, of cases), Darwin is disposed to regard
it also as a vestigial feature. On the other hand, Prof.
Flower tells me that in his opinion it is but an ex-
Morphology.
95
pression of impoverished nutrition during the growth
of the bone.
JAVAI7 LOR.IS.
GAPVCHIJ/.
FIG. 25. — Perforation of the humerus (supra-condyloid foramen) in
three species of Quadrnmana where it normally occurs, and in Man, where
it does not normally occur. Drawn from nature (A'. Coll. Surg. Mus.).
(n) Flattening of tibia. — In some very ancient
human skeletons, there has also been found a lateral
flattening of the tibia, which rarely occurs in any ex-
isting human beings, but which appears to have been
usual among the earliest races of mankind hitherto dis-
covered. According to Broca, the measurements of
these fossil human tibiae resemble those of apes. More-
over, the bone is bent and strongly convex forwards,
while its angles are so rounded as to present the
nearly oval section seen in apes. It is in association
with these ape-like human tibiae that perforated humeri
of man are found in greatest abundance.
96 Darwin, and after Darwin.
On the other hand, however, there is reason to doubt
whether this form of tibia in man is really a survival
from his quadrumanous ancestry. For, as Boyd-
Dawkins and Hartmann have pointed out, the degree
of flattening presented by some of these ancient
human bones is greater than that which occurs in any
existing species of anthropoid ape. Of course the
possibility remains that the unknown species of ape
from which man descended may have had its tibia
more flattened than is now observable in any of the
existing species. Nevertheless, as some doubt attaches
to this particular case. I do not press it — and, indeed,
only mention it at all in order that the doubt may be
expressed.
Similarly, I will conclude by remarking that several
other instances of the survival of vestigial structures
in man have been alleged, which are of a still more
doubtful character. Of such, for example, are the
supposed absence of the genial tubercle in the case
of a very ancient jaw-bone of man, and the disposition
of valves in human veins. From the former it was
argued that the possessor of this very ancient jaw-bone
was probably speechless, inasmuch as the tubercle in
existing man gives attachment to muscles of the
tongue. From the latter it has been argued that all
the valves in the veins of the human body have
reference, in their disposition, to the incidence of blood-
pressure when the attitude of the body is horizontal,
or quadrupedal. Now, the former case has already
broken down, and I find that the latter does not hold.
But we can well afford to lose such doubtful and
spurious cases, in view of all the foregoing unquestion-
able and genuine cases of vestigial structures which are
Morphology. 97
%
to be met with even within the limits of our own
organization — and even when these limits are still
further limited by selecting only those instances which
refer to the very latest chapter of our long ancestral
history.
CHAPTER IV.
EMBRYOLOGY.
WE will next consider what of late years has
become the most important of the lines of evidence,
not only in favour of the general fact of evolution,
but also of its history : I mean the evidence which has
been yielded by the newest of the sciences, the science
of Embryology. But here, as in the analogous case
of adult morphology, in order to do justice to the
mass of evidence which has now been accumulated,
a whole volume would be necessary. As in that
previous case, therefore, I must restrict myself to
giving an outline sketch of the main facts.
First I will display what in the language of Paley
we may call " the state of the argument."
It is an observable fact that there is often a close
correspondence between developmental changes as
revealed by any chronological series of fossils which
may happen to have been preserved, and develop-
mental changes which may be observed during the
life-history of now existing individuals belonging to
the same group of animals. For instance, the
successive development of prongs in the horns of
deer-like animals, which is so clearly shown in the
geological history of this tribe, is closely reprodu* ed
Embryology. 99
in the life-history of existing deer. Or, in other
words, the antlers of an existing deer furnish in their
development a kind of re'sume', or recapitulation, of the
successive phases whereby the primitive horn was grad-
ually superseded by horns presenting a greater and
greater number of prongs in successive species of extinct
deer (Fig. 26). Now it must be obvious that such a re-
capitulation in the life-history of an existing animal of
developmental changes successively distinctive of sundry
allied, though now extinct species, speaks strongly in
favour of evolution. For as it is of the essence of this
theory that new forms arise from older forms by way
of hereditary descent, we should antecedently expect,
if the theory is true, that the phases of development
presented by the individual organism would follow, in
their main outlines, those phases of development
through which their long line of ancestors had passed.
The only alternative view is that as species of deer,
for instance, were separately created, additional prongs
were successively added to their antlers ; and yet
that, in order to be so added to successive species
every individual deer belonging to later species was
required to repeat in his own lifetime the process of
successive additions which had previously taken
place in a remote series of extinct species. Now I
do not deny that this view is a possible view ; but I
do deny that it is a probable One. According to
the evolutionary interpretation of such facts, we can
see a very good reason why the life-history of the
individual is thus a condensed re'sumt of the life-
history of its ancestral species. But according to the
opposite view no reason can be assigned why such
snould be the case. In a previous chapter — the
H 2
FIG. »6. — Antlers of Stag, showing successive addition o/ branches in successive years
Drawn from nature (Brit. Af us.).
Embryology. 101
chapter on Classification — we have seen that if each
species were created separately, no reason can be
assigned why they should all have been turned out
upon structural patterns so strongly suggestive of
hereditary descent with gradual modifications, or slow
divergence — the result being group subordinated to
group, with the most generalized (or least developed)
forms at the bottom, and the highest products of
organization at the top. And now we see — or shall
immediately see — that this consideration admits of
being greatly fortified by a study of the develop-
mental history of every individual organism. If it
would be an unaccountable fact that every separately
created species should have been created with close
structural resemblances to a certain limited number
of other species, less close resemblances to certain
further species, and so backwards ; assuredly it would
be a still more unaccountable fact that every indi-
vidual of every species should exhibit in its own
person a history of developmental change, every term
of which corresponds with the structural peculiarities
of its now extinct predecessors — and this in the exact
historical order of their succession in geological time.
The more that we think about this antithesis between
the naturalistic and the non-naturalistic interpreta-
tions, the greater must we feel the contrast in respect
of rationality to become ; and, therefore, I need not
spend time by saying anything further upon the
antecedent standing of the two theories in this
respect. The evidence, then, which I am about to
adduce from the study of development in the life-
histories of individual organisms, will be regarded by
me as so much unquestionable evidence in favour of
IO2 Darwin, and after Darwin.
similar processes of development in the life-histories
of their respective species — in so far, I mean, as the
two sets of changes admit of being proved parallel.
In the only illustration hitherto adduced — viz. that
of deers' horns — the series of changes from a one-
pronged horn to a fully developed arborescent antler,
is a series which takes place during the adult life of
the animal ; for it is only when the breeding age
has been attained that horns are required to appear.
But seeing that every animal passes through most of
the phases of its development, not only before the
breeding age has been attained, but even before the
time of its own birth, clearly the largest field for
the study of individual development is furnished by
embryology. For instance, there is a salamander
which differs from most other salamanders in being
exclusively terrestrial in its habits. Now, the young
of this salamander before their birth are found to
be furnished with gills, which, however, they are never
destined to use. Yet these gills are so perfectly
formed, that if the young salamanders be removed
from the body of their mother shortly before birth,
and be then immediately placed in water, the
little animals show themselves quite capable of
aquatic respiration, and will merrily swim about in
a medium which would quickly drown their own
parent. Here, then, we have both morphological and
physiological evidence pointing to the possession of
gills by the ancestors of the land salamander.
It would be easy to devote the whole of the present
chapter to an enumeration of special instances of the
kinds thus chosen for purposes of illustration ; but
as it is desirable to take a deeper, and therefore
Embryology. 103
a more general view of the whole subject, I will begin
at the foundation, and gradually work up from the
earliest stages of development to the latest. Before
starting, however, I ask the reader to bear in mind
one consideration, which must reasonably prevent
our anticipating that in every case the life-history of
an individual organism should present a full recapitu-
lation of the life-history of its ancestral line of species.
Supposing the theory of evolution to be true, it must
follow that in many cases it would have been more or
less disadvantageous to a developing type that it
should have been obliged to reproduce in its individual
representatives all the phases of development pre-
viously undergone by its ancestry — even within the
limits of the same family. We can easily understand,
for example, that the waste of material required for
building up the useless gills of the embryonic sala-
manders is a waste which, sooner or later, is likely to
be done away with ; so that the fact of its occurring
at all is in itself enough to show that the change from
aquatic to terrestrial habits on the part of this species
must have been one of comparatively recent occurrence.
Now, in as far as it is detrimental to a developing
type that it should pass through any particular ances-
tral phases of development, we may be sure that natural
selection — or whatever other adjustive causes we may
suppose to have been at work in the adaptation of
organisms to their surroundings — will constantly seek
to get rid of this necessity, with the result, when
successful, of dropping out the detrimental phases.
Thus the foreshortening of developmental history
which takes place in the individual lifetime may be
expected often to take place, not only in the way of
io4 Darwin, and after Darwin.
condensation, but also in the way of excision. Many
pages of ancestral history may be recapitulated in
the paragraphs of embryonic development, while
others may not be so much as mentioned. And that
this is the true explanation of what embryologists
term " direct " development — or of a more or less
sudden leap from one phase to another, without any
appearance of intermediate phases — is proved by the
fact that in some cases both direct and indirect develop-
ment occur within the same group of organisms, some
genera or families having dropped out the intermediate
phases which other genera or families retain.
The argument from embryology must be taken to
begin with the first beginning of individual life in the
ovum. And, in order to understand the bearings of
the argument in this its first stage, we must consider
the phenomena of reproduction in the simplest form
which these phenomena are known to present.
The whole of the animal kingdom is divided into
two great groups, which are called the Protozoa and
the Metazoa. Similarly, the whole of the vegetable
kingdom is divided into the Protophyta and the Meta-
phyta. The characteristic feature of all the Protozoa
and Protophyta is that the organism consists of a
single physiological cell, while the characteristic of all
the Metazoa and Metaphyta is that the organism
consists of a plurality of physiological cells, variously
modified to subserve different functions in the
economy of the animal or plant, as the case may be.
For the sake of brevity, I shall hereafter deal only
with the case of animals (Protozoa and Metazoa); but
it may throughout be understood that everything
Embryology. 105
which is said applies also to the case of plants
(Protophyta and Metaphyta).
A Protozoon (like a Protophyton) is a solitary cell,
or a " unicellular organism," while a Metazoon (like a
Metaphyton) is a society of cells, or a " multicellular
organism." Now, it is only in the multicellular
organisms that there is any observable distinction of
sex. In all the unicellular organisms the phenomena
of reproduction appear to be more or less identical
with those of growth. Nevertheless, as these phe-
nomena are here in some cases suggestively peculiar,
I will consider them more in detail.
A Protozoon is a single corpuscle of protoplasm
which in different species of Protozoa. varies in size
from more than one inch to less than J^TT °f an iflcri
in diameter. In some species there is an enveloping
cortical substance ; in other species no such substance
can be detected. Again, in most species there is a
nucleus, while in other species no such differentiation
of structure has hitherto been observed. Nevertheless,
from the fact that the nucleus occurs in the majority
of Protozoa, coupled with the fact that the demon-
stration of this body is often a matter of extreme
difficulty, not only in some of the Protozoa where it
has been but recently detected, but also in the case of
certain physiological cells elsewhere, — fror these facts
it is not unreasonable to suppose that all the Protozoa
possess a nucleus, whether or not it admits of being
rendered visible by histological methods thus far at
our disposal. If this is the case, we should be justi-
fied in saying, as I have said, that a Protozoon is an
isolated physiological cell, and, like cells in general,
multiplies by means of what Spencer and Hackel
io6 Darwin, and after Darwin.
have aptly called a process of discontinuous growth.
That is to say, when a cell reaches maturity, further
growth takes place in the direction of a severance of
its substance— the separated portion thus starting
anew as a distinct physiological unit. But, notwith-
standing the complex changes which have been more
recently observed to take place in the nucleus of some
Protozoa prior to their division, the process of
multiplication by division may still be regarded as a
process of growth, which differs from the previous
growth of the individual cell in being attended by a
severance of continuity. If we take a suspended drop
of gum, and gradually add to its size by allowing
more and more gum to flow into it, a point will
eventually be reached at which the force of gravity
will overcome that of cohesion, and a portion of the
drop will fall away from the remainder. Here we
have a rough physical simile, although of course no
true analogy. In virtue of a continuous assimilation
of nutriment, the protoplasm of a cell increases in
mass, until it reaches the size at which the forces of
disruption overcome those of cohesion — or, in other
words, the point at which increase of size is no longer
compatible with continuity of substance. Neverthe-
less, it must not be supposed that the process is thus
merely a physical one. The phenomena which occur
even in the simplest — or so-called "direct" — cell-
division, are of themselves enough to prove that the
process is vital, or physiological ; and this in a high
degree of specialization. But so, likewise, are all
processes of growth in organic structures ; and there-
fore the simile of the drop of gum is not to be
regarded as a true analogy : it serves only to
Embryology.
107
indicate the fact that when cell-growth proceeds
beyond a certain point cell-division ensues. The
size to which cells may grow before they thus divide
is very variable in different kinds of cells ; for while
some may normally attain a length of ten or twelve
inches, others divide before they measure Tin>i7 °f an
inch. This, however, is a matter of detail, and does
not affect the general physiological principles on
which we are at present engaged.
FIG. 27. — Fission of a Protozoon. In the left-hand drawing the process
is represented as having advanced sufficiently far to have caused a
division and segregation both of the nucleus and the vesicle. In the
right-hand drawing the process is represented as complete. «, N,
severed nucleus ; vc, severed vesicle ; fs, pseudopodia ;f, ingested food.
Now, as we have seen, a Protozoon is a single cell ;
for even although in some of the higher forms of
protozoal life a colony of cells may be bound together
in organic connexion, each of these cells is in itself an
" individual," capable of self-nourishment, reproduction,
and, generally, of independent existence. Conse-
quently, when the growth of a Protozoon ends in a
division of its substance, the two parts wander away
from each other as separate organisms. (Fig. 27.)
io8 Darwin, and after Darwin.
The next point we have to observe is, that in all
cases where a cell or a Protozoon multiplies by
way of fissiparous division, the process begins in the
nucleus. If the nucleus divides into two parts, the
whole cell will eventually divide into two parts, each
of which retains a portion of the original nucleus, as
represented in the above figure. If the nucleus divides
into three, four, or even, as happens in the develop-
ment of some embryonic tissues, into as many as six
parts, the cell will subdivide into a corresponding
number, each retaining a portion of the nucleus.
Therefore, in all cases of fissiparous division, the
seat or origin of the process is the nucleus.
Thus far, then, the phenomena of multiplication are
identical in all the lowest or unicellular organisms,
and in the constituent cells of all the higher or multi-
cellular. And this is the first point which I desire to
make apparent. For where the object is to prove a
continuity between the phenomena of growth and
reproduction, it is of primary importance to show —
ist, that there is such a continuity in the case of all
the unicellular organisms, and, 2nd, that there are all
the above points of resemblance between the multi-
plication of cells in the unicellular and in the multi-
cellular organisms.
It remains to consider the points of difference, and,
if possible, to show that these do not go to disprove
the doctrine of continuity which the points of resem-
blance so forcibly indicate.
The first point of difference obviously is, that in the
case of all the multicellular organisms the two or
more " daughter-cells," which are produced by division
of the " mother-cell," do not wander away from one
Embryology. 109
another ; but. as a rule, they continue to be held in more
or less close apposition by means of other cells and
binding membranes, — with the result of giving rise to
those various " tissues," which in turn go to constitute
the material of " organs." I cannot suppose, however,
that any advocate of discontinuity will care to take
his stand at this point. But, if any one were so
foolish as to do so, it would be easy to dislodge him
by describing the state of matters in some of the
Protozoa where a number of unicellular " individuals "
are organically united so as to form a " colony."
These cases serve to bridge this distinction between
Protozoa and Metazoa, of which therefore we may
now take leave.
In the second place, there is the no less obvious
distinction that the result of cell-division in the
Metazoa is not merely to multiply cells all of the
same kind: on the contrary, the process here gives
rise to as many different kinds of cells as there are
different kinds of tissue composing the adult organism.
But no one, I should think, is likely to oppose the
doctrine of continuity on the ground of this distinc-
tion. For the distinction is clearly one which must
necessarily arise, if the doctrine of continuity between
unicellular and multicellular organisms be true. In
other words, it is a distinction which the theory of
evolution itself must necessarily pre-suppose, and
therefore it is no objection to the theory that its
pre-supposition is realized. Moreover, as we shall
see better presently, there is no difficulty in under-
standing why this distinction should have arisen, so
soon as it became necessary (or desirable) that indi-
vidual cells, when composing a " colony," should
no Darwin, and after Darwin.
conform to the economic principle of the division of
labour — a principle, indeed, which is already fore-
shadowed in the constituent parts of a single cell,
since the nucleus has one set of functions and its
surrounding protoplasm another.
But now, in the third place, we arrive at a more
important distinction, and one which lies at the root
of the others still remaining to be considered. I refer
to sexual propagation. For it is a peculiarity of the
multicellular organisms that, although many of them
may likewise propagate themselves by other means
(Fig. 28), they all propagate themselves by means
of sexual congress. Now, in its essence, sexual con-
gress consists in the fusion of two specialized cells
(or, as now seems almost certain, of the nuclei thereof),
so that it is out of such a combination that the new
individual arises by means of successive cell-divisions,
which, beginning in the fertilized ovum, eventually
build up all the tissues and organs of the body.
This process clearly indicates very high specializa-
tion on the part of germ -cells. For we see by it that
although these cells when young resemble all other
cells in being capable of self-multiplication by binary
division (thus reproducing cells exactly like them-
selves), when older they lose this power ; but, at
the same time, they acquire an entirely new and very
remarkable power of giving rise to a vast succession
of many different kinds of cells, all of which are
mutually correlated as to their several functions, so
as to constitute a hierarchy of cells — or, to speak
literally, a multicellular co-organization. Here it is
that we touch the really important distinction between
the Protozoa and the Metazoa ; for although I have
Embryology.
in
said that some of the higher Protozoa foreshadow this
state of matters in forming cell-colonies, it must now
be noted that the cells composing such colonies are
all of the same kind ; and, therefore, that the principle
FlG. 28. — Hydra mridit, partly in section. M, mouth ; O, ovary, or
bud containing female reproductive cells ; T, testis, or bud containing
male reproductive cells. In addition to these buds containing ger-
minal elements alone, there is another which illustrates the process of
" gemmation " — i. e. the direct out-growth of a fully formed offspring.
of producing different kinds of cells which, by mutual
co-adaptation of functions, shall be capable of con-
structing a multicellular Metazoon, — this great principle
of co- organization is but dimly nascent in the cell-
1 1 2 Darwin, and after Darwin.
colonies of Protozoa. And its marvellous development
in the Metazoa appears ultimately to depend upon the
highly specialized character of germ-cells. Even in
cases where multicellular organisms are capable of re-
producing their kind without the need of any preceding
process of fertilization (parthenogenesis), and even in
the still more numerous cases where complete or-
ganisms are budded forth from any part of their parent
organism (gemmation, Fig. 28), there is now very good
reason to conclude that these powers of a-sexual
reproduction on the part of multicellular organisms
are all ultimately due to the specialized character of
their germ-cells. For in all these cases the tissues of
the parent, from which the budding takes place, were
ultimately derived from germ-cells — no matter how
many generations of budded organisms may have
intervened. And that propagation by budding, &c.,
in multicellular organisms is thus ultimately due to
their propagation by sexual methods, seems to be
further shown by certain facts which will have to be
discussed at some length in my next volume. Here,
therefore, I will mention only one of them — and this
because it furnishes what appears to be another
important distinction between the Protozoa and the
Metazoa.
In nearly all cases where a Protozoon multiplies
itself by fission, the process begins by a simple
division of the nucleus. But when a Metazoon is de-
veloped from a germ-cell, although the process likewise
begins by a division of the nucleus, this division is not
a simple or direct one ; on the contrary, it is inaugurated
by a series of processes going on within the nucleus,
which are so enormously complex, and withal so
Embryology. 113
beautifully ordered, that to my mind they constitute
the most wonderful — if not also the most suggestive
—which have ever been revealed by microscopical re-
search. It is needless to say that I refer to the
phenomena of karyokinesis. A few pages further on
they will be described more fully. For our present
purposes it is sufficient to give merely a pictorial
FIG. 29. — Successive stages in the division of the ovum, or egg-cell, of
a worm. (After Strasburger. ) a tod show the changes taking place in
the nucleus and surrounding cell-contents, which result in the first
segmentation of the ovum at e : f and g show a repetition of these
changes in each of the two resulting cells, leading to the second seg-
mentation stage at h.
illustration of their successive phases ; for a glance at
such a representation serves to reveal the only point to
which attention has now to be drawn — namely, the
immense complexity of the processes in question, and
therefore the contrast which they furnish to the simple
(or "direct") division of the nucleus preparatory to
cell- division in the unicellular organisms. Here, then
* I
H4 Darwin, and after Darwin.
(Fig. 29), we see the complex processes of karyokinesis
in the first two stages of egg-cell division. But
similar processes continue to repeat themselves in
subsequent stages ; and this, there is now good reason
to believe, throughout all the stages of cell-division,
whereby the original egg-cell eventually constructs an
entire organism In other words, all the cells com-
posing all the tissues of a multicellular organism, at
all stages of its development, are probably originated
by these complex processes, which differ so much
from the simple process of direct division in the
unicellular organisms1. In this important respect,
therefore, it does at first sight appear that we have a
distinction between the Protozoa and the Metazoa of
so pronounced a character, as fairly to raise the
question whether cell-division is fundamentally identical
in unicellular and in multicellular organisms.
Lastly, the only other distinction of a physiologically
significant kind between a single cell when it occurs
as a Protozoon and when it does so as the unfertilized
ovum of a Metazoon is, that in the latter case the
nucleus discharges from its own substance two minute
protoplasmic masses (" polar bodies "), which are then
eliminated from the cell altogether. This process,
which will be more fully described later on, appears
to be of invariable occurrence in the caseof all egg-cells,
1 I say "probably," because analogy points in this direction. As a
matter of fact, in many cases of tissue-formation karyokinesis has not
hitherto been detected. But even if in such cases it does not occur —
i. e. if failure to detect its occurrence be not due merely to still remain-
ing imperfections of our histological methods, — the large number of
cases in which it has been seen to occur in the formation of sundry
tissues are of themselves sufficient to indicate some important difference
between cells derived from ova (metazoal), and cells which have not
been so derived (protozoal). Which is the point now under discussion.
Embryology. 115
while nothing resembling it has ever been observed in
any of the Protozoa.
We must now consider these several points of
difference seriatim.
First, with regard to sexual propagation, we have
already seen that this is by no means the only method
of propagation among the multicellular organisms ;
and it now remains to add that, on the other hand,
there is, to say the least, a suggestive foreshadowing
of sexual propagation among the unicellular organisms.
For although simple binary fission is here the more
usual mode of multiplication, very frequently two
(rarely three or more) Protozoa of the same species
come together, fuse into a single mass, and thus
become very literally "one flesh." This process of
" conjugation" is usually (though by no means invari-
ably) followed by a period of quiescent "encystation";
after which the contents of the cyst escape in the form
of a number of minute particles, or "spores," and these
severally develope into the parent type. Obviously
this process of conjugation, when it is thus a pre-
liminary to multiplication, appears to be in its essence
the same as fertilization. And if it be objected that
encystation and spore-formation in the Protozoa are
not always preceded by conjugation, the answer would
be that neither is oviparous propagation in the Metazoa
invariably preceded by fertilization.
Nevertheless, that there are great distinctions
between true sexual propagation and this fore-
shadowing of it in conjugation I do not deny. The
question, however, is whether they be so great as to
justify any argument against an historical continuity
between them. What, then, are these remaining
I 2
n6 Darwin, and after Darwin.
distinctions? Briefly, as we have seen, they are the
extrusion from egg-cells of polar bodies, and the
occurrence, both in egg-cells and their products
(tissue-cells), of the process of karyokinesis. But. as
regards the polar bodies, it is surely not difficult to
suppose that, whatever their significance may be, it is
probably in some way or another connected with the
high specialization of the functions which an egg- cell
has to discharge. Nor is there any difficulty in further
supposing that, whatever purpose is served by getting
rid of polar bodies, the process whereby they are got rid
of was originally one of utilitarian development — i. e.
a process which at its commencement did not betoken
any difference of kind, or breach of continuity, between
egg-cells and cells of simpler constitution.
Lastly, with respect to karyokinesis, although it
is true that the microscope has in comparatively
recent years displayed this apparently important
distinction between unicellular and multicellular or-
ganisms, two considerations have here to be supplied.
The first is, that in some of the Protozoa processes
very much resembling those of karyokinesis have
already been observed taking place in the nucleus
preparatory to its division. And although such pro-
cesses do not present quite the same appearances as
are to be met with in egg-cells, neither do the karyo-
kinetic processes in tissue-cells, which in their sundry
kinds exhibit great variations in this respect. More-
over, even if such were not the case, the bare fact
that nuclear division is not invariably of the simple
or direct character in the case of all Protozoa, is
sufficient to show that the distinction now before
us — like the one last dealt with — is by no means
Embryology. 1 1 7
absolute. As in the case of sexual propagation, so
in that of karyokinesis, processes which are common
to all the Metazoa are not wholly without their fore-
shadowings in the Protozoa. And seeing how greatly
exalted is the office of egg-cells— and even of tissue-
cells — as compared with that of their supposed ancestry
in protozoal cells, it seems to me scarcely to be
wondered at if their specializations of function should
be associated with corresponding peculiarities of
structure — a general fact which would in no way
militate against the doctrine of evolution. Could
we know the whole truth, we should probably find
that in order to endow the most primitive of egg-cells
with its powers of marshalling its products into a
living army of cell-battalions, such an egg-cell must
have been passed through a course of developmental
specialization of so elaborate a kind, that even the
complex processes of karyokinesis are but a very
inadequate expression thereof.
Probably I have now said enough to show that,
remarkable and altogether exceptional as the pro-
perties of germ-cells of the multicellular organisms
unquestionably show themselves to be, yet when these
properties are traced back to their simplest beginnings
in the unicellular organisms, they may fairly be re-
garded as fundamentally identical with the properties
of living cells in general. Thus viewed, no line of real
demarcation can be drawn between growth and repro-
duction, even of the sexual kind. The one process is,
so to speak, physiologically continuous with the other ;
and hence, so far as the pre-embryonic stage of life-
history is concerned, the facts cannot fairly be regarded
as out of keeping with the theory of evolution.
n8 Darwin, and after Darwin.
I will now pass on to consider the embryogeny of
the Metazoa, beginning at its earliest stage in the
fertilization of the ovum. And here it is that the
constructive argument in favour of evolution which
is derived from embryology may be said properly to
commence. For it is surely in itself a most suggestive
fact that all the Metazoa begin their life in the same
way, or under the same form and conditions. Omne
vivum ex ovo. This is a formula which has now been
found to apply throughout the whole range of the
multicellular organisms. And seeing, as we have just
seen, that the ovum is everywhere a single cell, the
formula amounts to saying that, physiologically
speaking, every Metazoon begins its life as a Pro-
tozoon, and every Metaphyton as a Protophyton !.
Now, if the theory of evolution is true, what should
we expect to happen when these germ- cells are fer-
tilized, and so enter upon their severally distinct
processes of development? Assuredly we should
expect to find that the higher organisms pass through
the same phases of development' as the lower or-
ganisms, up to the time when their higher characters
begin to become apparent. If in the life-history of
species these higher characters were gained by gradual
improvement upon lower characters, and if the de-
velopment of the higher individual is now a general
recapitulation of that of its ancestral species, in studying
this recapitulation we should expect to find the higher
organism successively unfolding its higher characters
from the lower ones through which its ancestral species
had previously passed. And this is just what we do
1 Even when propagated by budding, a multicellular organism has
been ultimately derived from a germ-cell.
Embryology. 119
find. Take, for example, the case of the highest
organism, Man. Like that of all other organisms,
unicellular or multicellular, his development starts
from the nucleus of a single cell. Again, like that
of all the Metazoa and Metaphyta, his development
starts from the specially elaborated nucleus of an
egg-cell, or a nucleus which has been formed by
the fusion of a male with a female element x. When
his animality becomes established, he exhibits the
fundamental anatomical qualities which characterize
such lowly animals as polyps and jelly-fish. And
even when he is marked off as a Vertebrate, it cannot
be said whether he is to be a fish, a reptile, a bird,
or a beast. Later on it becomes evident that he is
to be a Mammal ; but not till later still can it be said
to which order of mammals he belongs.
Here, however, we must guard against an error which
is frequently met with in popular expositions of this
subject. It is not true that the embryonic phases
in the development of a higher form always resemble
so many adult stages of lower forms. This may or
may not be the case ; but what always is the case
1 It has already been stated that both parthenogenesis and gemmation
are ultimately derived from sexual reproduction. It may now be added,
on the other hand, that the earlier stages of parthenogenesis have been
observed to occur sporadically in all sub-kingdoms of the Metazoa,
including the Vertebrata, and even the highest class, Mammalia. These
earlier stages consist in spontaneous segmentations of the ovum ; so
that even if a virgin has ever conceived and borne a son, and even if
such a fact in the human species has been unique, still it would not be-
token any breach of physiological continuity. Indeed, according to
Weismann's not improbable hypothesis touching the physiological
meaning of polar bodies, such a fact need betoken nothing more than
a slight disturbance of the complex machinery of ovulation, on account
of which the ovum failed to eliminate from its substance an almost
inconceivably minute portion of its nucleus.
i2O Darwin, and after Darwin.
is, that the embryonic phases of the higher form
resemble the corresponding phases of the lower forms,
Thus, for example, it would be wrong to suppose
that at any stage of his development a man resembles
a jelly-fish. What he does resemble at an early
stage of his development is the essential or ground-
plan of the jelly-fish, which that animal presents in
its embryonic condition, or before it begins to assume
its more specialized characters fitting it for its own
particular sphere of life. The similarities, therefore,
which it is the function of comparative embryology
to reveal are the similarities of type or morphological
plan : not similarities of specific detail. Specific details
may have been added to this, that, and the other species
for their own special requirements, after they had seve-
rally branched off from the common ancestral stern ;
and so could not be expected to recur in the life-history
of an independent specific branch. The comparison
therefore must be a comparison of embryo with
embryo ; not of embryos with adult forms.
In order to give a general idea of the results thus
far yielded by a study of comparative embryology in
the present connexion, I will devote the rest of this
chapter to giving an outline sketch of the most im-
portant and best established of these results.
Histologically the ovum, or egg-cell, is nearly
identical in all animals, whether vertebrate or- in-
vertebrate. Considered as a cell it is of large size,
but actually it is not more than T^, and may be less
than I\TS of an inch in diameter. In man, as in most
mammals, it is about ^\^. It is a more or less spherical
body, presenting a thin transparent envelope, called
Embryology.
121
the sona pellucida, which contains — first, the proto-
plasmic cell-substance or "yolk," within which lies,
second, the nucleus or germinal vesicle, within which
again lies, third, the nucleolus or germinal spot. This
description is true of the egg-cells of all animals,
if we add that in the case of the lowest animals — such
as sponges, &c. — there is no enveloping membrane:
the egg-cell is here a naked cell, and its constituent
protoplasm, being thus unconfined, is free to perform
protoplasmic movements, which it does after the
FIG. 30. — Ovarian orum of a Mammal, (a) magnified and viewed undei
pressure, (b) burst by increased pressure, with yolk and nucleus
escaping : (c) the nucleus more freed from yolk-substance. (From
Quoin's Anatomy, after Allen Thomson.)
manner, and with all the activity, of an amoeba.
But even with respect to this matter of an enveloping
membrane, there is no essential difference between
an ovum of the lowest and an ovum of the highest
animals. For in their early stages of development
within the ovary the ova of the highest animals
are likewise in the condition of naked cells, exhibiting
amcebiform movements ; the enveloping membrane
of an ovum being the product of a later development.
FlG. 31. — Amoeboid movements of young egg-cells, a, Amoeboid ovum of Hydra
(from Balfour, after Kleinenberg) ; 6 early ovum of Toxopneustes variegatus, with
pseudopodia-like processes (from Balfour. after Selenka) ; <j ovum of Toxopneustes
lividus, more nearly ripe (from Balfour, Hertwig). A I to A 4, the primitive egg-cell
of a Chalk-Sponge (Leuculmis echinus), in four successive conditions of motion'
B i to B 8, ditto of a Hermit-Crab (Chondraaatithus comutus), in eight successive
stages (after E. von Beneden). C I to Cs, ditto of a Cat, in five successive stages
(after Pfluger). D, ditto of Trout ; E, of a Hen ; P, of Man. The first series is take*
from the Encyd. Brit. ; the second from Hackel's Evolution of Man.
Embryology. 123
Moreover this membrane, when present, is usually
provided with one or more minute apertures, through
which the spermatozoon passes when fertilizing the
ovum. It is remarkable that the spermatozoa know,
so to speak, of the existence of these gate-ways, —
their snake-like movements being directed towards
FlG. 33. — Human ovum, mature and greatly magnified. (After Hackel.)
them, presumably by a stimulus due to some emana-
tion therefrom1. In the mammalian ovum, however,
these apertures are exceedingly minute, and distributed
1 The spermatozooids of certain plants can be strongly attracted
towards a pipette which is filled with malic acid— crowding around and
into it with avidity.
124 Darwin, and after Darwin.
all round the circumference of the pellucid envelope,
as represented in this illustration (Fig. 32).
In thus saying that the ova of all animals are, so
far as microscopes can reveal, substantially similar, I
am of course speaking of the egg-cell proper, and
not of what is popularly known as the egg. The egg
of a bird, for example, is the egg-cell, phis an enor-
mous aggregation of nutritive material, an egg-shell,
and sundry other structures suited to the subsequent
development of the egg-cell when separated from the
parent's body. But all these accessories are, from
our present point of view, accidental or adventitious.
What we have now to understand by the ovum, the
egg, or the egg-cell, is the microscopical germ which I
have just described. So far then as this germ is
concerned, we find that all multicellular organisms
begin their existence in the same kind of structure,
and that this structure is anatomically indistinguishable
from that of the permanent form presented by the
lowest, or unicellular organisms. But although anato-
mically indistinguishable, physiologically they present
the sundry peculiarities already mentioned.
Now I have endeavoured to show that none of
these peculiarities are such as to exclude — or even so
much as to invalidate— the supposition of develop-
mental continuity between the lowest egg- cells and
the highest protozoal cells. It remains to show in this
place, and on the other hand, that there is no breach
of continuity between the lowest and the highest egg-
cells ; but, on the contrary, that the remarkable
uniformity of the complex processes whereby their
peculiar characters are exhibited to the histologist, is
such as of itself to sustain the doctrine of continuity
Embryology.
125
in a singularly forcible manner. On this account,
therefore, and also because the facts will again have
to be considered in another connexion when we come
to deal with Weismann's theory of heredity, I will
here briefly describe the processes in question.
We have already seen that the young egg-cell mul-
tiplies itself by simple binary division, after the
manner of unicellular organisms in general— thereby
fPn-
FIG. 33. — Stages in the formation of the polar bodies in the ovum of a
star-fish. (After Hertwig.) g.v., germinal vesicle transformed into a
spindle-shaped system of fibres ; /.', the first polar body becoming ex-
truded ; /., /., both polar bodies fully extruded ; fpn., female pro-
nucleus, or residue of the germinal vesicle.
indicating, as also by its amcebiform movements, its
fundamental identity with such organisms in kind.
But, as we have likewise seen, when the ovum ceases
to resemble these organisms, by taking on its higher
degree of functional capacity, it is no longer able to
multiply itself in this manner. On the contrary, its
cell-divisions are now of an endogenous character,
126 Darwin, and after Darwin.
and result in the formation of many different kinds of
cells, in the order required for constructing the multi-
cellular organism to which the whole series of processes
eventually give rise. We have now to consider these
processes seriatim.
First of all the nucleus discharges its polar bodies,
as previously mentioned, and in the manner here
depicted on the previous page. (Fig. 33.) It will be
observed that the nucleus of the ovum, or the germinal
2. 3.
FIG. 34. — Fertilization of the ovum of an echinoderm. (From Quain's
Anatomy, after Selenka.) S, spermatozoon ; m.pr., male pronucleus;
f.pr., female pronucleus. I to 4 correspond to D to G in the next
figure.
vesicle as it is called, gets rid first of one and after-
wards of the other polar body by an " indirect," or
karyokinetic, process of division. ( Fig. 33.) Extrusion
of these bodies from the ovum (or it may be only from
the nucleus) having been accomplished, what remains
of the nucleus retires from the circumference of the ovum,
and is called the female pronucleus. (Fig. 33. fpn.}
The ovum is now ready for fertilization. A similar
emission of nuclear substance is said by some good
Embryology.
127
observers to take place also from the male germ-cell,
or spermatozoon, at or about the close of its develop-
ment. The theories to which these facts have given
rise will be considered in future chapters on Heredity.
Turning now to the mechanism of fertilization, the
diagrams (Figs. 34, 35) represent what happens in
the case of star-fish.
The sperm-cell, or spermatozoon, is seen in the act
of penetrating the ovum. In the first figure it has
already pierced the mucilaginous coat of the ovum,
FIG. 35. — Fertilization of the ovnm of a star-fish. (From the Encycl.
Brit, after Fol.) A, spermatozoa in the mucilaginous coat of the
ovum ; a prominence is rising from the surface of the ovum towards
a spermatozoon ; B, they have almost met ; C, they have met ; D,
the spermatozoon enters the ovum through a distinct opening ; H,
the entire ovum, showing extruded polar bodies on its upper surface,
and the moving together of the male and female pronuclei ; E, F, G,
meeting and coalescence of the pronuclei.
the limit of which is represented by a line through
which the tail of the spermatozoon is passing : the
head of the spermatozoon is just entering the ovum
proper. It maybe noted that, in the case of many
animals, the general protoplasm of the ovum becomes
aware, so to speak, of the approach of a spermatozoon,
and sends up a process to meet it. (Fig. 35, A, B, C.)
Several — or even many — spermatozoa may thus enter
the coat of the ovum ; but normally only one proceeds
further, or right into the substance of the ovum, for the
128 Darwin, and after Darwin.
purpose of effecting fertilization. This spermatozoon,
as soon as it enters the periphery of the yolk, or cell-
substance proper, sets up a series of remarkable
phenomena. First, its own head rapidly increases in
size, and takes on the appearance of a cell-nucleus : this
is called the male pronucleus. At the same time its
tail begins to disappear, and the enlarged head proceeds
to make its way directly towards the nucleus of the
ovum which, as before stated, is now called the female
pronucleus. The htter in its turn moves towards the
former, and when the two meet they fuse into one
mass, forming a new nucleus. Before the two actually
meet, the spermatozoon has lost its tail altogether ;
and it is noteworthy that during its passage through
the protoplasmic cell-contents of the ovum, it appears
to exercise upon this protoplasm an attractive in-
fluence ; for the granules of the latter in its vicinity
dispose themselves around it in radiating lines. All
these various phenomena are depicted in the above
wood-cuts. (Figs. 34, 35.)
Fertilization having been thus effected by fusion of
the male and female pronuclei into a single (or new)
nucleus, this latter body proceeds to exhibit compli-
cated processes of karyokinesis. which, as before
shown, are preliminary to nuclear division in the case
of egg-cells. Indeed the karyokinetic process may
begin in both the pronuclei before their junction is
effected ; and, even when their junction is effected,
it does not appear that complete fusion of the so-
called chromatin elements of the two pronuclei takes
place. For the purpose of explaining what this
means, and still more for the purpose of giving a
general idea of the karyokinetic processes as a whole.
Embryology. 129
I will quote the following description of them, because,
for terseness combined with lucidity, it is unsur-
passable.
Researches, chiefly due to Flemming, have shown that the
nucleus in very many tissues of higher plants and animals con-
sists of a capsule containing a plasma of" achromatin," not deeply
FIG. 36. — Karyokinesis of a typical tissue-cell (epifhelium of Sala-
mander). (After Flemming and Klein.) The series from A to I
represents the successive stages in the movement of the chromatin
fibres during division, excepting G, which represents the " nucleus-
spindle " of an egg-cell. A, resting nucleus ; D, wreath-form ; E,
single star, the loops of the wreath being broken ; F, separation of
the star into two groups of U-shaped fibres; H, diaster or double
star ; I, completion of the cell-division and formation of two resting
nuclei. In G the chromatin fibres are marked a, and correspond to
the " equatorial plate " ; b, achromatin fibres forming the nucleus-
spindle ; t, granules of the cell-protoplasm forming a " polar star."
Such a polar star is seen at each end of the nucleus-spindle, and is
not to be confused with the diaster H, the two ends of which are
composed of chromatin.
stained by re-agents, ramifying in which is areticulum of "chro-
matin " consisting of fibres which readily take a deep stain.
( Fig. 36, A). Further it is demonstrated that, when the cell is
about to divide into two, definite and very remarkable move-
ments take place in the nucleus, resulting in the disappearance
of the capsule and in the arrangement of its fibres first in the
* K
130 Darwin, and after Darwin.
form of a wreath (D), and subsequently (by the breaking of
the loops formed by the fibres) in the form of a star (E). A
further movement within the nucleus leads to an arrangement of
the broken loops in two groups (F), the position of the open ends
of the broken loops being reversed as compared with what pre-
viously obtained. Now the two groups diverge, and in many
cases a striated appearance of the achromatin substance between
the two groups of chromatin loops is observable (H). In some
cases (especially egg-cells) this striated arrangement of the
achromatin is then termed a " nucleus-spindle," and the group of
chromatin loops (G, a) is known as "the equatorial plate." At each
end of the nucleus-spindle in these cases there is often seen a
star consisting of granules belonging to the general protoplasm
of the cell (G, c). These are known as " polar stars." After the
separation of the two sets of loops (H) the protoplasm of the
general substance of the cell becomes constricted, and division
occurs, so as to include a group of chromatin loops in each of the
two fission products. Each of these then rearranges itself to-
gether with the associated chromatin into a nucleus such as was
present in the mother cell to commence with (I) *.
Since the above was published, however, further
progress has been made. In particular it has been
found that the chromatin fibres pass from phase D
to phase F by a process of longitudinal splitting (Fig.
37 £"» ^ 5 Fig. 38, VI, VII) — which is a point of great
importance for Weismann's theory of heredity, — and
that the protoplasm outside the nucleus seems to
take as important a part in the karyokinetic process
as does the nuclear substance. For the so-called
"attraction-spheres" (Fig. 38 II a, III, III a, VIII to
XII), which were at first supposed to be of subordinate
importance in the process as a whole, are now known
to take an exceedingly active part in it (see especially
IX to XI). Lastly, it may be added that there is a
1 Ray Lankester, Encydop. Brit.t 9th ed., Vol. XIX, pp. 833-3.
Embryology.
FIG. 37. — Study of successive changes taking place in the nucleus of an epithelium
cell, preparatory to division of the cell. (From Quoin's Anatomy, after Flei*.
ming.) a, resting cell, showing the nuclear network ; b, first stage of division.,
the chromatoplasm transformed into a skein of closely contorted filaments ; c toy,
further stages in the growth and looping arrangement of the filaments ; g, stellate
phase, or aster ; h, completion of the splitting of the filaments, already begun in
/and g ; i,j, k, successive stages in separation of the filaments into two groups ;
/, the final result of this (diaster) ; m to q, stages in the division of the whole
cell into two, showing increasing contortion of the filaments, until they reach the
resting stage at q.
K2
132 Larwin, and after Darwin.
FIG. 38. — Formation and conjugation of the pronuclei in Ascaris ntegalocephala.
(From Quoin's Anatomy, after E. von Beneden.) ft female pronucleus ; tn,
male pronucleus ; j>, one of the polar bodies.
I. The second polar body has just been extruded ; both male and female pronuclei
contain two chromatin particles ; those of the male pronucleu* are becoming
transformed into a skein.
II. The chromatin in both pronuclei now forms into a skein.
II a. The skeins are more distinct. Two attraction (or protoplasmic) spheres, each
with a central particle united with a small spindle of achromatic fibres, have made
their appearance in the general substance of the egg close to the mutually
approaching pronuclei. The male pronucleus has the remains of the body of the
spermatozoon adhering to it.
III. Onljr the female pronucleus is shown in this figure. The skein is contracted
and thickened. The attraction-spheres are near one side of the ovum, and are
connected with its periphery by a cone of fibres forming a polar circle, p.c. ; e.c.,
equatorial circle.
III a. The pronuclei have come into contact, and the spindle-system it now
arranged across their common axis.
IV. Contraction of the skein, and formation of two U- or V-shaped chromatin
fibres in each pronucleus.
V. The V-shaped chromatin filaments are now quite distinct : the male and female
pronuclei are in close contact.
Embryology.
TK.
IX.
X.
XL
XII.
VI., VII. The V-shaped filament* are splitting longitudinally ; their structure of fine
VI., and VII.
VIII. Equatorial arrangement of the four chromatin loops in the middle of the
now segmenting ovum : the achromatic substance forming a spindle-shaped
system of granules with fibres radiating from the poles of the spindle (attraction-
spheres) ; the chromatin forms an equatorial plate. (Compare Fig. 36 G.)
IX. Shows diagrammatically the commencing separation of the chromatin fibres
of the conjugated nuclei, and the system of fibres radiating from the attraction-
spheres. (Compare again Fig. 36 G.) p.c ^ polar circle ; t.c., equatorial circle ;
c.e., central particle.
X. Further separation of the chromatin filaments. Each of the central particle*
of the attraction-spheres has divided into two.
XI. The chromatin fibres are becoming developed into the skeins of the two
daughter-nuclei. These are still united by fibres of achromatin. The general
protoplasm of the ovum is becoming divided.
XII. The two daughter-nuclei exhibit a chromatin network. Each of the attraction-
spheres has divided into two, which are joined by fibres of achromatin, and con-
nected with the periphery of the cell in the tame way as in the original or parent
sphere, III.
1 34 Darwin, and after Darwin.
growing consensus of authoritative opinion, that the
chromatin fibres are the seats of the material of
heredity, or, in other words, that they contain those
essential elements of the cell which endow the
daughter-cells with their distinctive characters. There-
fore, where the parent-cell is an ovum, it follows from
this view that all hereditary qualities of the future
organism are potentially present in the ultra-micro-
scopical structure of the chromatin fibres.
As I shall have more to say about these processes
in the next volume, when we shall see the important
part which they bear in Weismann's theory of
heredity, it is with a double purpose that I here
introduce these yet further illustrations of them upon a
somewhat larger scale. The present purpose is merely
that of showing, more clearly than hitherto, the great
complexity of these processes on the one hand, and,
on the other, the general similarity which they display
in egg-cells and in tissue-cells. But as in relation to
this purpose the illustrations speak for themselves, I
may now pass on at once to the history of embryonic
development, which follows fertilization of the ovum.
We have seen that when the new nucleus of the
feitilized ovum (which is formed by a coalescence of the
male pronucleus with the female) has completed its
karyokinetic processes, it is divided into two equal
parts ; that these are disposed at opposite poles of the
ovum ; and that the whole contents of the ovum are
thereupon likewise divided into two equal parts, with
the result that there are now two nucleated cells within
the spherical wall of the ovum where before there had
only been one. Moreover, we have also seen that a
Embryology.
135
precisely similar series of events repeat themselves in
each of these two cells, thus giving rise to four cells
FIG. 39. — Segmentation of ovum. (After ITackel.) Successive stages
are marked by the letters A, B, C. D represents several stages in
advance of C.
(see Fig. 29). It must now be added that such
duplication is continued time after time, as shown in
the accompanying illustrations (Figs. 39, 40). .
All this, it will be noticed, is
a case of cell-multiplication,
which differs from that which
takes place in the unicellular
organisms only in its being in-
variably preceded (as far as we
know) by karyokinesis, and in
the resulting cells being all con-
fined within a common envelope,
and so in not being free to
separate. Nevertheless, from
what has already been said, it
will also be noticed that this feature makes all the
difference between a Metazoon and a Protozoon ; so
that already the ovum presents the distinguishing
character of a Metazoon.
FIG. 40. — The contents of
an ovum in an advanced
stage of segmentation,
drawn in perspective.
(After Hackel.)
136 Darwin, and after Darwin.
I have dealt thus at considerable length upon the
processes whereby the originally unicellular ovum and
spermatozoon become converted into the multicellular
germ, because I do not know of any other exposition
of the argument from Embryology where this, the first
stage of the argument, has been adequately treated.
Yet it is evident that the fact of all the processes
above described being so similar in the case of sexual
(or metazoal) reproduction among the innumerable or-
ganisms where it occurs, constitutes in itself a strong
argument in favour of evolution. For the mechanism
of fertilization, and all the processes which even thus
far we have seen to follow therefrom, are hereby
shown to be not only highly complex, but likewise
highly specialized. Therefore, the remarkable simi-
larity which they present throughout the whole animal
kingdom — not to speak of the vegetable — is expressive
of organic continuity, rather than of absolute dis-
continuity in every case, as the theory of special
creation must necessarily suppose. And it is evident
that this argument is strong in proportion to the
uniformity, the specialization, and the complexity of
the processes in question.
Having occupied so much space with supplying what
appear to me the deficiencies in previous expositions
of the argument from Embryology, I can now afford
to take only a very general view of the more important
features of this argument as they are successively fur-
nished by all the later stages of individual development.
But this is of little consequence, seeing that from the
point at which we have now arrived previous exposi-
tions of the argument are both good and numerous.
The following then is to be regarded as a mere sketch
Embryology. 137
of the evidences of phyletic (or ancestral) evolution,
which are so abundantly furnished by all the subse-
quent phases of ontogenetic (or individual) evolution.
The multicellular body which is formed by the
series of segmentations above described is at first a
sphere of cells (Fig. 40). Soon, however, a watery
fluid gathers in the centre, and progressively pushes
the cells towards the circumference, until they there
FIG. 41. — Formation of the gastrula of Amphioxus. (After Kowalevsky. )
A, wall of the ovnm, composed of a single layer of cells ; B, a stage
in the process of gastrulation ; C, completion of the process ; S,
original or segmentation cavity «f ovum ; al, alimentary cavity of
gastiula ; ect, outer layer of cells ; ent, inner layer of cells ; tt orifice,
constituting the mouth in permanent forms.
constitute a single layer. The ovum, therefore, is now
in the form of a hollow sphere containing fluid, con-
fined within a continuous wall of cells (Fig. 41 A). The
next thing that happens is a pitting in of one portion of
the sphere (B). The pit becomes deeper and deeper,
until there is a complete imagination of this part of the
sphere — the cells which constitute it being progressively
138 Darwin, and after Darwin.
pushed inwards until they come into contact with
those at the opposite pole of the ovum. Consequently,
instead of a hollow sphere of cells, the ovum now
becomes an open sac, the walls of which are composed
FlG. 42. — Gastrulalion. A, Gastrula of a Zoophyte (Gastrophysemd).
( After HackeL) B, Gastrula of a Worm (Sagittd). (After Kow.ilevsky.)
C, Gastrnla of an Echinoderm (Uraster}. (After A. Agassiz.) D,
Gastrula of an Arthropod (Nauplius}. (After Hackel.) E, Gastrula
of a Mollusk (Limnaus). (After Rabl.) F, Gastrala of a Vertebrate
(Amphioxus). (After Kowalevsky.) In all, d, indicates the intestinal
cavity ; o. the primitive mouth ; t, the cleavage- cavity ; »', the endo-
derm, or intestinal layer ; t, the ectoderm or skin-layer.
of a double layer of cells (C). The ovum is now what
has been called a gastrula ; and it is of importance to
observe that probably all the Metazoa pass through
Embryology.
139
this stage. At any rate it has been found to occur in all
the main divisions of the animal kingdom, as a glance at
the accompanying figures will serve to show (Fig. 4 2) *.
Moreover many of the lower kinds of Metazoa never
pass beyond it ; but are all their lives nothing else than
FIG. 43. — Gastrula of a Chalk Sponge. (After Hackel.) A, External
view. B, Longitudinal section, g, digestive cavities; o, mouth ;
i, endoderm ; e, ectoderm.
gastrulae, wherein the orifice becomes the mouth of
the animal, the internal or invaginated layer of cells
the stomach, and the outer layer the skia So that
if we take a child's india-rubber ball, of the hollow
1 In most vertebrated animals this process of gastrulation has been
more or less superseded by another, which is called delamination ; but
it scarcely seems necessary for our present purposes to describe the
latter. For not only does it eventually lead to the same result as-
gastrulation — i.e. the converting of the ovum into a double-walled sac, —
but there is good evidence among the lower Vertebrata of its being pre-
ceded by gastrulation ; so that, even as to the higher Vertebrata,
embryologists are pretty well agreed that delamination has been but a
later development of, or possibly improvement upon, gastrulation.
140 Darwin^ and after Darwin.
kind with a hole in it, and push in one side with our
fingers till internal contact is established all round, by
then holding the indented side downwards we should
get a very fair anatomical model of a gastraea form,
A B
FlG. 44. — Prophysema primordiale, an extant gastrsea-form.
(After
Hackel.) (A). External view of the whole animal, attached by its foot
to seaweed. (B). Longitudinal section of the same. The digestive
cavity (d) opens at its upper end in the mouth (m). Among the cells
of the endoderm (g) lie amceboid egg-cells of large size {e}. The ec-
toderm (A) is encrusted with grains of sand, above the sponge spicules.
such as is presented by the adult condition of many
of the most primitive Metazoa — especially the lower
Calenterata. The preceding figures represent two
Embryology. \ 4 1
other such forms in nature, the first locomotive and
transitory, the second fixed and permanent (Figs.
43> 44)-
Here, then, we leave the lower forms of Metazoa in
their condition of permanent gastrulae. They differ
from the transitory stage of other Metazoa only in
being enormously larger (owing to greatly further
growth, without any further development as to matters
of fundamental importance), and in having sundry
tentacles and other organs added later on to meet
their special requirements. The point to remember
is, that in all cases a gastrula is an open sac composed
of two layers of cells — the outer layer being called the
ectoderm, and the inner the endoderm. They have
also been called the animal layer and the vegetative
layer, because it is the outer layer (ectoderm) that
gives rise to all the organs of sensation and move-
ment— viz. the skin, the nervous system, and the
muscular system ; while it is the inner layer (endoderm)
that gives rise to all the organs of nutrition and
reproduction. It is desirable only further to explain
that gastrulation does not take place in all the Metazoa
after exactly the same plan. In different lines of
descent various and often considerable modifications
of the original and most simple plan have been intro-
duced ; but I will not burden the present exposition
by describing these modifications *. It is enough for us
that they always end in the formation of the two
primary layers of ectoderm and endoderm.
The next stage of differentiation is common to all
the Metazoa, except those lowest forms which, as we
1 The most extreme of them is that which is mentioned in the last
foot-note.
142 Darwin, and after Darwin.
have just seen, remain permanently as large gastrulae,
with sundry specialized additions in the way of
tentacles, &c. This stage of differentiation consists in
the formation of either a pouch or an additional
layer between the ectoderm and the endoderm, which
is called the mesoderm. It is probably in most cases
derived from the endoderm, but the exact mode of its
derivation is still somewhat obscure. Sometimes it
has the appearance of itself constituting two layers ;
but it is needless to go into these details ; for in any
case the ultimate result is the same — viz. that of con-
verting the Metazoon into the form of a tube, the walls
of which are composed of concentric layers of cells.
The outermost layer afterwards gives rise to the
epidermis with its various appendages, and also to the
central nervous system with its organs of special sense.
The median layer gives rise to the voluntary muscles,
bones, cartilages, &c., the nutritive systems of the
blood, the chyle, the lymph, and the muscular tube
of the intestine. Lastly, the innermost layer deve-
lopes into the epithelium lining of the intestine,
with its various appendages of liver, lungs, intestinal
glands, &c.
I have just said that this three or four layered stage
is shared by all the Metazoa, except those very lowest
forms — such as sponges and jelly-fish — which do not
pass on to it. But from this point the developmental
histories of all the main branches of the Metazoa
diverge — the Vcrmes, the Echinodermata, the Mol-
lusca, the Articulata, and the Vertebrata, each taking
a different road in their subsequent evolution. I will
therefore confine attention to only one of these
several roads or methods, namely, that which is
Embryology,
143
followed by the Vertebrata — observing merely that, if
space permitted, the same principles of progressive
though diverging histories of evolution would equally
well admit of being traced in all the other sub-king-
doms which have just been named.
In order to trace these principles in the case of the
Vertebrata, it is desirable first of all to obtain an idea
of the anatomical features which most essentially dis-
tinguish the sub-kingdom as a whole. The following,
FIG. 45. — Ideal primitive vertebrate, seen from the left side. (After
Hackel.) na, nose; au, eye; g, ear; md, mouth ; *J, gill-openings;
x, notochord ; mr, spinal tube ; kg, gill-vessels ; k, gill-intestine ; Az,
heart ; ms, muscles; ma, stomach ; v, intestinal vein ; c, body-cavity ;
a, aorta ; /, liver ; d, small intestine ; e, ovary ; A, testes ; n, kidney
canal ; of, anus ; Ih, true or leather-skin ; oh, outer-skin (epidermis) ;
f, skin-fold, acting as a fin.
then, is what may be termed the ideal plan of verte-
brate organization, as given by Prof. Hackel. First,
occupying the major axis of body we perceive the
primitive vertebral column. The parts lying above
this axis are those which have been developed from
the ectoderm and mesoderm — viz. voluntary muscles,
central nervous system, and organs of special sense.
The parts lying below this axis are for the most part
those which have been developed from the endoderm
144 Darwin, and after Darwin.
— namely, the digestive tract with its glandular ap-
pendages, the circulating system and the respiratory
system. In transverse section;
therefore, the ideal vertebrate
consists of a solid axis, with a
small tube occupied by the
nervous system above, and a
large tube, or body - cavity,
below. This body-cavity con-
tains the viscera, breathing
FIG. 46. — The same
in transverse section organs, and heart, with its
through the ovaries; prolongations into the main
blood-vessels of the organism.
Lastly, on either side of the
central axis are to be found large masses of muscle —
two on the dorsal and two on the ventral. As yet,
however, there are no limbs, nor even any bony
skeleton, for the primitive vertebral column is hitherto
unossified cartilage. This ideal animal, therefore, is to
all appearance as much like a worm as a fish, and swims
by means of a lateral undulation of its whole body,
assisted, perhaps, by a dorsal fin formed out of skin.
Now I should not have presented this ideal repre-
sentation of a primitive vertebrate — for I have very
little faith in the "scientific use of the imagination "
where it aspires to discharge the functions of a Creator
in the manufacture of archetypal forms — I say I should
not have presented this ideal representative of a
primitive vertebrate, were it not that the ideal is
actually realized in a still existing animal. For there
still survives what must be an immensely archaic
form of vertebrate, whose anatomy is almost identical
with that of the imaginary type which has just been
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146 Darwin, and after Darwin.
described. I allude, of course, to Amphioxus, which
is by far the most primitive or generalized type of
vertebrated animal hitherto discovered. Indeed, we
may say that this remarkable creature is almost as
nearly allied to a worm as it is to a fish. For it has
no specialized head, and therefore no skull, brain,
or jaws : it is destitute alike of limbs, of a centralized
heart, of developed liver, kidneys, and, in short, of
most of the organs which belong to the other
Vertebrata. It presents, however, a rudimentary back-
bone, in the form of what is called a notochord. Now
a primitive dorsal axis of this kind occurs at a very
early period of embryonic life in all vertebrated
animals ; but, with the exception of Amphioxus, in
all other existing Vertebrata this structure is not
itself destined to become the permanent or bony
vertebral column. On the contrary, it gives way to,
or is replaced by, this permanent bony structure at
a later stage of development. Consequently, it is very
suggestive that so distinctively embryonic a structure
as this temporary cartilaginous axis of all the other
known Vertebrata should be found actually persisting
to the present day as the permanent axis of Amphioxus.
In many other respects, likewise, the early embryonic
history of other Vertebrata refers us to the permanent
condition of Amphioxus. In particular, we must
notice that the wall of the neck is always perforated
by what in Amphioxus are the gill-openings, and that
the blood-vessels as they proceed from the heart are
always distributed in the form of what are called
gill-arches, adapted to convey the blood round or
through the gills for the purpose of aeration. In all
existing fish and other gill -breathing Vertebrata. this
Embryology. 147
arrangement is permanent. It is likewise met with in a
peculiar kind of worm, called Balanoglossus — a creature
so peculiar, indeed, that it has been constituted by
Gegenbaur a class all by itself. We can see by the
wood-cuts that it presents a series of gill-slits, like the
homologous parts of the fishes with which it is compared
— i.e. fishes of a comparatively low type of organization,
which dates from a time before the development of
external gills. (Figs. 48, 49, 50.) Now, as I have
already said, these gill-slits are supported internally by
the g\\\-arches, or the blood-vessels which convey the
blood to be oxygenized in the branchial apparatus
(see below, Figs. 51, 52, 53) ; and the whole arrange-
ment is developed from the anterior part of the in-
testine— as is likewise the respiratory mechanism
of all the gill-breathing Vertebrata. That so close
a parallel to this peculiar mechanism should be met
with in a worm, is a strong additional piece of evidence
pointing to the derivation of the Vertebrata from the
Vermes.
Well, I have just said that in all the gill-breathing
Vertebrata, this mechanism of gill-slits and vascular
gill-arches in the front part of the intestinal tract is
permanent. But in the air-breathing Vertebrata such
an arrangement would obviously be of no use. Con-
sequently, the gill-slits in the sides of the neck (see
Figs. 1 6 and 57, 58), and the gill-arches of the large
blood-vessels (Figs. 54, 55, 56), are here exhibited
only as transitory phases of development. But as
such they occur in all air-breathing Vertebrata. And,
as if to make the homologies as striking as possible,
at the time when the gill-slits and the gill -arches are
developed in the embryonic young of air-breathing
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- tit
i,
FlG. 57. — A series of embryos at three comparable and progressive stages of
development (marked I, II, III), representing each of the classes of vertebrate^
animals below the Mammalia. (After Haokol.)
FIG. 58.— Another series of embryos, also at three comparable and progressive
stages of development (marked I, II, III), representing four different divisions
of the class Mamma a. (After HackeL)
154 Darwin, and after Darwin.
Vertebrata, the heart is constructed upon the fish-like
type. That is to say, it is placed far forwards, and,
from having been a simple tube as in Worms, is now
divided into two chambers, as in Fish. Later on it
becomes progressively pushed further back between
the developing lungs, while it progressively acquires
the three cavities distinctive of Amphibia, and finally
the four cavities belonging only to the complete
double circulation of Birds and Mammals. Moreover,
it has now been satisfactorily shown that the lungs
of air-breathing Vertebrata, which are thus destined
to supersede the function of gills, are themselves the
modified swim-bladder or float, which belongs to Fish.
Consequently, all these progressive modifications in
the important organs of circulation and respiration in
the air-breathing Vertebrata, together make up as
complete a history of their aquatic pedigree as it
would be possible for the most exacting critic to
require.
If space permitted, it would be easy to present
abundance of additional evidence to the same effect
from the development of the skeleton, the skull, the
brain, the sense-organs, and, in short, of every con-
stituent part of the vertebrate organization. Even
without any anatomical dissection, the similarity of
all vertebrated embryos at comparable stages of de-
velopment admits of being strikingly shown, if we
merely place the embryos one beside the other.
Here, for instance, are the embryos of a fish, a sala-
mander, a tortoise, a bird, and four different mammals.
In each case three comparable stages of development
are represented. Now, if we read the series horizontally,
we can see that there is very little difference between
Embryology. 155
the eight animals at the earliest of the three stages
represented — all having fish-like tails, gill-slits, and
so on. In the next stage further differentiation has
taken place, but it will be observed that the limbs
are still so rudimentary that even in the case of Man
they are considerably shorter than the tail. But in
the third stage the distinctive characters are well
marked.
So much then for an outline sketch of the main
features in the embryonic history of the Vertebrata.
But it must be remembered that the science of com-
parative embryology extends to each of the other three
great branches of the tree of life, where these take
their origin, through the worms, from the still lower,
or gastraea, forms. And in each of these three great
branches — namely, the Echinodermata, tjae Mollusca,
and the Arthropoda — we have a repetition of just the
same kind of evidence in favour of continuous descent,
with adaptive modification in sundry lines, as that
which I have thus briefly sketched in the case of the
Vertebrata. The roads are different, but the method
of travelling is the same. Moreover, when the em-
bryology of the Worms is closely studied, the origin
of these different roads admits of being clearly traced.
So that when all this mass of evidence is taken to-
gether, we cannot wonder that evolutionists should
now regard the science of comparative embryology as
the principal witness to their theory.
CHAPTER V.
PALAEONTOLOGY.
THE present Chapter will be devoted to a con-
sideration of the evidence of organic evolution
which has been furnished by the researches of geo-
logists. On account of its direct or historical nature,
this branch of evidence is popularly regarded as the
most important — so much so, indeed, that in the
opinion of most educated persons the whole doctrine
of organic evolution must stand or fall according to
the so-called " testimony of the rocks." Now, without
at all denying the peculiar importance of this line of
evidence, I must begin by remarking that it does not
present the denominating importance which populai
judgment assigns to it. For although popular judg-
ment is right in regarding the testimony of the rocks
as of the nature of a history, this judgment, as a rule,
is very inadequately acquainted with the great imper-
fections of that history. Knowing in a general way
what magnificent advances the science of geology has
made during the present century, the public mind is
more or less imbued with the notion, that because
we now possess a tolerably complete record of the
chronological succession of geological formations, we
must therefore possess a correspondingly complete
Paleontology. 1 5 7
record of the chronological succession of the forms of
life which from time to time have peopled the globe.
Now in one sense this notion is partly true, but in
another sense it is profoundly false. It is partly true
if we have regard only to those larger divisions of
the vegetable or animal kingdoms which naturalists
designate by the terms classes and orders. But the
notion becomes progressively more untrue when it is
applied to families and genera, while it is most of all
untrue when applied to species. That this must be so
may be rendered apparent by two considerations.
In the first place, it does not follow that because
we have a tolerably complete record of the succession
of geological formations, we have therefore any
correspondingly complete record of their fossiliferous
contents. The work of determining the relative ages
of the rocks does not require that every cubic mile of
the earth's surface should be separately examined, in
order to find all the different fossils which it may
contain. Were this the case, we should hitherto have
made but very small progress in our reading of the
testimony of the rocks. The relative ages of the
rocks are determined by broad comparative surveys
over extensive areas ; and although the identification
of widely separated deposits is often greatly assisted
by a study of tAiJr fossiliferous contents, the mere
pricking of a continent here and there is all that is
required for this purpose. Hence, the accuracy of
our information touching the relative ages of geo-
logical strata does not depend upon — and, therefore,
does not betoken — any equivalent accuracy of know-
ledge touching the fossiliferous material which these
strata may at the present time actually contain. And,
158 Darwin, and after Darwin.
as we well know, the opportunities which the geo-
logist has of discovering fossils are extremely limited,
if we consider these opportunities in relation to the
area of geological formations. The larger portion of
the earth's surface is buried beneath the sea ; and
much the larger portion of the fossiliferous deposits
on shore are no less hopelessly buried beneath the
land. Therefore it is only upon the fractional portion
of the earth's surface which at the present time
happens to be actually exposed to his view that the
geologist is able to prosecute his search for fossils.
But even here how miserably inadequate this search
has hitherto been ! With the exception of a scratch
or two in the continents of Asia and America,
together with a somewhat larger number of similar
scratches over the continent of Europe, even that
comparatively small portion of the earth's surface
which is available for the purpose has been hitherto
quite unexplored by the palaeontologist. How enor-
mously rich a store of material remains to be
unearthed by the future scratchings of this surface,
we may dimly surmise from the astonishing world of
bygone life which is now being revealed in the newly
discovered fossiliferous deposits on the continent of
America.
But, besides all this, we must remember, in the
second place, that all the fossiliferous deposits in the
world, even if they could be thoroughly explored,
would still prove highly imperfect, considered as a
history of extinct forms of life. In order that many
of these forms should have been preserved as fossils,
it is necessary that they should have died upon a
surface neither too hard nor too soft to admit of their
Paleontology. 159
leaving an impression ; that this surface should
afterwards have hardened sufficiently to retain the
impression ; that it should then have been protected
from the erosion of water, as well as from the dis-
integrating influence of the air ; and yet that it should
not have sunk far enough beneath the surface to have
come within the no less disintegrating influence of
subterranean heat Remembering thus, as a general
rule, how many conditions require to have met before
a fossil can have been both formed and preserved,
we must conclude that the geological record is pro-
bably as imperfect in itself as are our opportunities of
reading even the little that has been recorded. If we
speak of it as a history of the succession of life upon
the planet, we must allow, on the one hand, that it is
a history which merits the name of a " chapter of
accidents"; and, on the other hand, that during the
whole course of its compilation pages were being
destroyed as fast as others were being formed, while
even of those that remain it is only a word, a line, or
at most a short paragraph hen and there, that we are
permitted to see. With so fragmentary a record as
this to study, I do not think it is too much to say
that no conclusions can be fairly based upon it,
merely from the absence of testimony. Only if the
testimony were positively opposed to the theory of
descent, could any argument be fairly raised against
that theory on the grounds of this testimony. In
other words, if any of the fossils hitherto discovered
prove the order of succession to have been incom-
patible with the theory of genetic descent, then the
record may fairly be adduced in argument, because
we should then be in possession of definite information
160 Darwin, and after Darwin.
of a positive kind, instead of a mere absence of infor-
mation of any kind. But if the adverse argument
reaches only to the extent of maintaining that the
geological record does not furnish us with so com-
plete a series of " connecting links " as we might have
expected, then, I think, the argument is futile. Even
in the case of human histories, written with the inten-
tional purpose of conveying information, it is an
unsafe thing to infer the non-occurrence of an event
from a mere silence of the historian — and this espe-
cially in matters of comparatively small detail, such
as would correspond (in the present analogy) to the
occurrence of species and genera as connecting links.
And, of course, if the history had only come down to
us in fragments, no one would attach any importance
at all to what might have been only the apparent
silence of the historian.
In view, then, of the unfortunate imperfection of
the geological record per se, as well as of the no less
unfortunate limitation of our means of reading even
so much of the record as has come down to us, I
conclude that this record can only be fairly used
in two ways. It may fairly be examined for
positive testimony against the theory of descent, or
for proof of the presence of organic remains of a
high order of development in a low level of strata.
And it may be fairly examined for negative
testimony, or for the absence of connecting links,
if the search be confined to the larger taxonomic
divisions of the fauna and flora of the world. The
more minute these divisions, the more restricted must
have been the areas of their origin, and hence the
less likelihood of their having been preserved in the
Paleontology. 1 6 1
fossil state, or of our finding them even if they
have been. Therefore, if the theory of evolution is
true, we ought not to expect from the geological
record a full history of specific changes in any but
at most a comparatively small number of instances,
where local circumstances happen to have been
favourable for the writing and preservation of such a
history. But we might reasonably expect to find a
general concurrence of geological testimony to the
larger fact — namely, of there having been throughout
all geological time a uniform progression as regards
the larger taxonomic divisions. And, as I will next
proceed to show, this is, in a general way, what we do
find, although not altogether without some important
exceptions, with which I shall deal in an Appendix.
There is no positive proof against the theory of
descent to be drawn from a study of palaeontology, or
proof of the presence of any kind of fossils in strata
where the fact of their presence is incompatible with
the theory of evolution. On the other hand, there is
an enormous body of uniform evidence to prove two
general facts of the highest importance in the present
connexion. The first of these general facts is, that an
increase in the diversity of types both of plants and
animals has been constant and progressive from the
earliest to the latest times, as we should anticipate that
it must have been on the theory of descent in ever-
ramifying lines of pedigree. And the second general
fact is, that through all these branching lines of ever-
multiplying types, from the first appearance of each
of them to their latest known conditions, there is
overwhelming evidence of one great law of organic
nature — the law of gradual advance from the general
* M
1 62 Darwin, and after Darwin.
to the special, from the low to the high, from the
simple to the complex.
Now, the importance of these large and general
facts in the present connexion must be at once
apparent ; but it may perhaps be rendered more so if
we try to imagine how the case would have stood
supposing geological investigation to have yielded in
this matter an opposite result, or even so much as an
equivocal result. If it had yielded an opposite result,
if the lower geological formations were found to
contain as many, as diverse, and as highly organized
' types as the later geological formations, clearly there
would have been no room at all for any theory of pro-
gressive evolution. And, by parity of reasoning, in
whatever degree such a state of matters were found to
prevail, in that degree would the theory in question
have been discredited. But seeing that these opposite
principles do not prevail in any (relatively speaking)
considerable degree *, we have so far positive testimony
of the largest and most massive character in favour of
this theory. For while all these large and general
facts are very much what they ought to be according
to this theory, they cannot be held to lend any
support at all to the rival theory. In other words, it
is clearly no essential part of the theory of special
creation that species should everywhere exhibit this
gradual multiplication as to number, coupled with a
gradual diversification and general elevation of types,
in all the growing branches of the tree of life. No
one could adopt seriously the jocular lines of Burns,
to the effect that the Creator required to practise his
1 For objections which may be brought against this and similar
statements, see the Appendix.
Paleontology.
163
y
Epochs and Formations.
Fauna! Characters.
^
POST-PLIOCENE.
. Glacial Period.
Man. Mammalia principally of living
species. Mollusca exclusively recent.
TERTIAE
PLIOCBNE, 3,000 feet
Mammalia principally of recent genera
— living species rare. Mollusca very
modern.
INOZOIC or
MIOCENE, 4,000 ft
OLIGOCENE, 8,000 ft.
Mammalia principally of living families ;
extinct genera numerous ; species all
extinct. Mollusca largely of recent
species.
U
i
EOCENE, 10,000 ft.
Mammalia with numerous extinct fam-
ilies and orders; all the species and
most of the genera extinct Modern
type Shell-Fish.
LARAMIE, 4,000 ft.
Passage Beds.
DART.
CRETACEOUS, 12,000 ft.
Chalk.
Dinosaurian (bird-like) Reptiles ; Ptero-
dactyls (flying Reptiles); toothed
Birds ; earliest Snake ; bony Fishes ;
Crocodiles; Turtles; Ammonites.
8
W
*H
u
0
JURASSIC, 6,000 ft.
Oolite.
Lias.
Earliest Birds ; giant Reptiles (Ichthyo-
saurs, Dinosaurs, Pterodactyls) ; Am-
monites ; Clam-and Snail-Shells very
abundant ; decline of Brachiopods ;
Butterfly.
o
H
9
TRIAS, 5,000 ft.
New Red Sandstone.
First Mammalian (Marsupial); a-gilled
Cephalopods (Cuttle-Fishes, Belem-
nites); reptilian Foot-Prints.
PERMIAN, 5,000 ft.
Earliest true Reptiles.
•
r
CARBONIFEROUS,
26,000 ft.
CoaL
Earliest Amphibian (Labyrintho'lont) ;
extinction of Trilobites ; first Cray-
fish ; Beetles; Cockroaches; Centi-
pedes; Spiders.
3
1
M
u
DEVONIAN, 18,000 ft
Old Red Sandstone.
Cartilaginous and Ganoid Fishes; ear-
liest land (snail) and freshwater
Shells; Shell-Fish abundant; decline
of Trilobites ; May-flies; Crab.
PALEOZO
SILURIAN, 33,000 ft
Earliest Fish ; the first Air-Brea thers
(Insect, Scorpion) ; Brachiopods and
4-gilled Cephalopods very abundant;
Trilobites ; Corals ; Graptolites.
CAMBRIAN, 24,000 ft.
Trilobites ; Brachiopod Mollusks.
11
ARCH.EAN, 30,000 ft
Huronian.
Laurentian.
Eozodn (probably not a fossil).
PRIMEVAL.
Non -sedimentary.
M 2
164 Darwin, and after Darwin.
prentice hand on lower types before advancing to the
formation of higher. Yet, without some such assump-
tion, it would be impossible to explain, on the theory
of independent creations, why there should have been
this gradual advance from the few to the many, from
the general to the special, from the low to the high.
I submit, then, that so far as the largest and most
general principles in the matter of palaeontology are
concerned, we have about as strong and massive a
body of evidence as we could reasonably expect this
branch of science to yield ; for it is at once enormous
in amount and positive in character. Therefore, if
I do not further enlarge upon the evidence which
we here have, as it were en masse, it is only because
I do not feel that any words could add to its obvious
significance. It may best be allowed to speak for itself
in tlfe millions of facts which are condensed in this
tabular statement of the order of succession of all the
known forms of animal life, as presented by the
eminent palaeontologist, Professor Cope l.
Or, taking a still more general survey, this tabular
statement may be still further condensed, and pre-
sented in a diagrammatic form, as it has been byanother
eminent American palaeontologist, Prof. Le Conte, in
his excellent little treatise on Evolution and its
Relations to Religious Thought. The following is
his diagrammatic representation, with his remarks
thereon.
When each ruling class declined fa importance, it did not
perish, but continued in a subordinate position. Thus, the
whole organic kingdom became not only higher and higher in
its highest forms, but also more and more complex in its struc-
1 For difficulties and objections, see Appendix.
Palaeontology.
165
ture and in the interaction of its correlated parts. The whole
process and its result is roughly represented in the accompanying
diagram, in which A B represents the course of geological time,
and the curve, the rise, culmination, and decline of successive
dominant classes.
FIG. 59. — Diagram of Geological Succession of the Classes of the
Animal Kingdom. (After Le Conte.)
I will here leave the evidence which is thus yielded
by the most general principles that have been esta-
blished by the science of palaeontology ; and I will
devote the rest of this chapter to a detailed con-
sideration of a few highly special lines of evidence.
By thus suddenly passing from one extreme to the
other, I hope to convey the best idea that can be
conveyed within a brief compass of the minuteness, as
well as the extent, of the testimony which is furnished
by the rocks.
When Darwin first published his Origin of Species,
adverse critics fastened upon the " missing-link " argu-
ment as the strongest that they could bring against
the theory of descent. Although Darwin had himself
strongly insisted on the imperfection of the geological
record, and the consequent precariousness of any ne-
gative conclusions raised upon it, these critics main-
tained that he was making too great a demand upon the
argument from ignorance — that, even allowing for the
imperfection of the record, they would certainly have
expected at least a few cases of testimony to specific
transmutation. For, they urged in effect, looking to
1 66 Darwin, and after Darwin.
the enormous profusion of the extinct species on the
one hand, and to the immense number of known
fossils on the other, it was incredible that no satis-
factory instances of specific transmutation should ever
have been brought to light, if such transmutation had
ever occurred in the universal manner which the theory
was bound to suppose. But since Darwin first
published his great work palaeontologists have been
very active in discovering and exploring fossiliferous
beds in sundry parts of the world ; and the result of
their labours has been to supply so many of the
previously missing links that the voice of competent
criticism in this matter has now been well-nigh silenced.
Indeed, the material thus furnished to an advocate of
evolution at the present time is so abundant that his
principal difficulty is to select his samples. I think,
however, that the most satisfactory result will be
gained if I restrict my exposition to a minute account
of some few series of connecting links, rather than if
I were to take a more general survey of a larger
number. I will, therefore, confine the survey to the
animal kingdom, and there mention only some of the
cases which have yielded well-detailed proof of con-
tinuous differentiation.
It is obvious that the parts of animals most likely
to have been preserved in such a continuous series of
fossils as the present line of evidence requires, would
have been the hard parts. These are horns, bones,
teeth, and shells. Therefore I will consider each of
these four classes of structures separately.
Horns wherever they occur, are found to be of high
importance for purposes of classification. They are
Palaeontology. 1 6 7
restricted to the Ruminants, and appear under three
different forms or types - namely, solid, as in antelopes ;
hollow, as in sheep ; and deciduous, as in deer. Now,
in each of these divisions we have a tolerably complete
palaeontological history of the evolution of horns.
The early ruminants were altogether hornless (Fig. 60).
Fig. 60.— Skull of Oreodon Culbertsoni. (After Leidy.)
Then, in the middle Miocene, the first antelopes ap-
peared with tiny horns, which progressively increased in
size among the ever-multiplying species of antelopes
until the present day. But it is in the deer tribe that we
meet with even better evidence touching the pro-
gressive evolution of horns ; because here not only
size, but shape, is concerned. For deer's horns, or
antlers, are arborescent ; and hence in their case we
have an opportunity of reading the history, not only
of a progressive growth in size, but also of an increasing
development of form. Among the older members of
the tribe, in the lower Miocene, there are no horns at
1 68 Darwin, and after Darwin.
all. In the mid-Miocene we meet with two-pronged
horns (Cervus dicrocerus, Figs. 6l, 62, •£ nat. size).
Next, in the upper Mbcene (C. matheronis, Fig.
63, | nat. size), and extending into the Pliocene
(C. pardinensis, Fig. 64, T\ nat. size), we meet with
three-pronged horns. Then, in the Pliocene we find also
four-pronged horns (C. issiodorensis, Fig. 65, T\ nat.
size), leading us to five-pronged (C. tetraceros). Lastly,
in the Forest-bed of Norfolk we meet with arborescent
FIG. 61. FIG. 62. FIG. 63. FIG. 64. FIG. 65. FIG. 66.
The series is reduced from Gaodry's illustrations, after Farge, Croizet,
Jobert and Boyd Dawkins.
horns (C. Sedgwickii, Fig. 66, ,V nat. size). The
life-history of existing stags furnishes a parallel
development (Fig. 67), beginning with a single horn
(which has not yet been found palaeontologically),
going on to two prongs, three prongs, four prongs, and
afterwards branching.
Coming now to bones, we have a singularly complete
record of transition from one type or pattern of
Paleontology. 169
structure to another in the phylogenetic history of
tails. This has been so clearly and so tersely conveyed
FIG. 67. — Successive itages in the development of an existing Deer's
Antlers. (After Gandry, but a better illustration has already been
given on p. 100.)
B
FlO. 68. — Homocercal Tail, showing (A) external form and
(B) internal structure.
by Prof. Le Conte, that I cannot do better than quote
his statement.
170 Darwin, and after Darwin.
It has long been noticed that there are among fishes two styles
of tail-fins. These are the even-lobed, or homocercal (Fig. 68),
and the uneven-lobed, or heterocercal (Fig. 69). The one is
characteristic of ordinary fishes (teleosts), the other of sharks
FlG. 69. — Heterocercal Tail, showing (A) external form and
(B) internal structure.
FlG. 70. — Vertebrated but symmetrical fin (diphycercal), showing
(A) external form and (B) internal structure.
and some other orders. In structure the difference is even more
fundamental than in form. In the former style the backbone
stops abruptly in a series of short, enlarged joints, and thence
sends off rays to form the tail-fin (Fig. 68) ; in the latter the
Paleontology.
171
backbone runs through the fin to its very point, growing slen-
derer by degrees, and giving off rays above and below from each
joint, but the rays on the lower side are much longer (Fig. 69).
This type of fin is, therefore, vertebrated, the other non-
vertebrated. Figs. 68 and 69 show these two types in form and
structure. But there is still another type found only in the low-
est and most generalized forms of fishes. In these the tail-fin is
vertebrated and yet symmetrical. This type is shown in Fig. 70.
FlG. 7 1 . — Tail of Archizopteryx.
A indicates origin of simply-
jointed tail.
FIG. 72. — Tail of modem Bird.
The numerals indicate the fore-
shortened, enlarged, and con-
solidated joints; ft terminal
segment of the vertebral column;
D, shafts of feathers.
Now, in the development of a teleost fish (Fig. 68), as has
been shown by Alexander Agassiz, the tail-fin is first like Fig.
70 ; then becomes heterocercal, like Fig. 69 ; and, finally, be-
comes homocercal like Fig. 68. Why so ? Not because there
is any special advantage in this succession of forms ; for the
changes take place either in the egg or else in very early em-
bryonic states. The answer is found in the fact that this is the
order of change in the phylogenetic series. The earliest fish-tails
were either like Fig. 69 or Fig. 70 ; never like Fig. 68. The
172 Darwin, and after Darwin.
FIG. 73- — Arch&opteryx macura, restored, -J nat. size. (After
Flower.) The section of the tail is copied from Owen, nat. size.
Palaeontology. 173
earliest of all were almost certainly like Fig. 70 ; then they be-
came like Fig. 69 ; and, finally, only much later in geological
history (Jurassic or Cretaceous), they became like Fig. 68. This
order of change is still retained in the embryonic development
of the last introduced and most specialized order of existing
fishes. The family history is repeated in the individual history.
Similar changes have taken place in the form and structure of
birds' tails. The earliest bird known — the Jurassic Archceo-
pteryx— had a long reptilian tail of twenty-one joints, each joint
bearing a feather on each side, right and left (Fig. 71) : [see also
Fig- 73]. In the typical modern bird, on the contrary, the tail-
joints are diminished in number, shortened up, and enlarged,
and give out long feathers, fan-like, to form the so-called tail
(Fig. 72). The Archaopteryx1 tail is -vertebrated, the typical
bird's non-vertebrcited. This shortening up of the tail did not
take place at once, but gradually. The Cretaceous birds, inter-
mediate in time, had tails intermediate in structure. The Hes-
perornis of Marsh had twelve joints. At first — in Jurassic strata—
the tail is fully a half of the whole vertebral column. It then grad-
ually shortens up until it becomes the aborted organ of typical
modern birds. Now, in embryonic development, the tail of the
modern typical bird pa sses through all these stages. At first the
tail is nearly one hah0 the whole vertebral column ; then, as de-
velopment goes on, while the rest of the body grows, the growth
of the tail stops, and thus finally becomes the aborted organ we
now find. The ontogeny still passes through the stages of the
phylogeny. The same is true of all tailless animals.
The extinct Archaopteryx above alluded to presents
throughout its whole organization a most interesting
assemblage of " generalized characters." For example,
its teeth, and its still unreduced digits of the wings
(which, like those of the feet, are covered with scales),
refer us, with almost as much force as does the verte-
brated tail, to the Sauropsidian type — or the trunk
from which birds and reptiles have diverged.
We will next consider the palaeontological evidence
174 Darwin, and after Darwin.
Paleontology.
which we now possess of the evolution of mammalian
limbs, with special reference to the hoofed animals,
where this line of evidence happens to be most
complete.
I may best begin by describing the bones as these
176 Darwin, and after Darwin.
occur in the sundry branches of the mammalian type
now living. As we shall presently see, the modi-
fications which the limbs have undergone in these
sundry branches chiefly consist in the suppression of
some parts and the exaggerated development of others.
But, by comparing all mammalian limbs together, it is
easy to obtain a generalized type of mammalian limb,
Paleontology.
177
which in actual life is perhaps most nearly conformed
to in the case of bears. I will therefore choose the
bear for the purpose of briefly expounding the bones
of mammalian limbs in general — merely asking it to be
* N
178 Darwin, and after Darwin.
understood, that although in the case of many other
mammalia some of these bones may be dwindled or
altogether absent, while others may be greatly ex-
aggerated as to relative size, in no case do any
additional bones appear.
On looking, then, at the skeleton of a bear (Fig. 74),
the first thing to observe is that there is a perfect serial
homology between the bones of the hind legs and of
the fore legs. The thigh-bone, or femur, corresponds
to the shoulder-bone, or humerus ; the two shank
bones (tibia and fibula) correspond to the two arm-bones
(radius and ulna) ; the many little ankle-bones (tarsals)
correspond to the many little wrist-bones (carpals) ;
the foot-bones (meta-tarsals) correspond to the hand-
bones (meta-carpals) ; and, lastly, the bones of each
of the toes correspond to those of each of the fingers.
The next thing to observe is, that the disposition of
bones in the case of the bear is such that the animal
walks in the way that has been called plantigrade.
That is to say, all the bones of the fingers, as well as
those of the toes, feet, and ankles, rest upon the ground,
or help to constitute the " soles." Our own feet are
constructed on a closely similar pattern. But in the
majority of living mammalian forms this is not the
case. For the majority of mammals are what has
been called digitigrade. That is to say, the bones of
the limb are so disposed that both the foot and hand
bones, and therefore also the ankle and wrist, are
removed from the ground altogether, so that the
animal walks exclusively upon its toes and fingers — as
in the case of this skeleton (Fig. 75), which is the skele-
ton of a lion. The next figures display a series of
limbs, showing the progressive passage of a completely
Palaeontology.
179
plantigrade into a highly digitigrade type — the
curved lines of connexion serving to indicate the
homologous bones (Figs. 76, 77).
I will now proceed to detail the history of mammalian
limbs, as this has been recorded for us in fossil remains.
The most generalized or primitive types of limb
hitherto discovered in any vertebrated animal above
A B
FlO. 78. — A, posterior limb of Baptanodon discus. (After Marsh.) F,
thigh-bone ; I to VI, undifferentiated bones of the leg and foot. B,
anterior limb of Chelydra serpcntina. (After Gcgenbaur.) U and R,
bones of the fore-arm ; I to V, fully differentiated bones of the baud,
following those of the wrist.
the class of fishes, are those which are met with in
some of the extinct aquatic reptiles. Here, for
instance, is a diagram of the left hind limb of
Baptanodon discus (Fig. 78). It has six rows of little
symmetrical bones springing from a leg-like origin.
N a
180 Darwin, and after Darwin.
But the whole structure resembles the fin of a fish
about as nearly as it does the leg of a mammal. For
not only are there six rows
of bone?, instead of five,
suggestive of the numerous
rays which characterise the
fin of a fish ; but the struc-
ture as a whole, having
been covered over with
blubber and skin, was
throughout flexible and
unjointed — thus in func-
tion, even more than in
structure, resembling a fin.
In this respect, also, it
must have resembled the
paddle of a whale (see
Fig. 79) ; but of course the
great difference will be
noted, that the paddle
of a whale reveals the
dwindled though still clearly typical bones of a true
mammalian limb ; so that although in outward form
and function these two paddles are alike, their inward
structure clearly shows that while the one testifies to
the absence of evolution, the other testifies to the
presence of degeneration. If the paddle of Baptanodon
had occurred in a whale, or the paddle of a whale had
occurred in Baptanodon, either fact would in itself have
been well-nigh destructive of the whole theory of
evolution.
Such, then, is the most generalized as it is the most
ancient type of vertebrate limb above the class of
Fro. 79. — Paddle of a Whale.
Paleontology. 1 8 1
fishes. Obviously it is a type suited only to aquatic
life. Consequently, when aquatic Vertebrata began to
become terrestrial, the type would have needed modi-
fication in order to serve for terrestrial locomotion. In
particular, it would have needed to gain in consolida-
tion and in firmness, which means that it would have
needed also to become jointed. Accordingly, we find
that this archaic type gave place in land -reptiles to
the exigencies of these requirements. Here for ex-
ample is a diagram, copied from Gegenbaur, of the right
fore-foot of Chelydra serpentina (Fig. 78). As com-
pared with the homologous limb of its purely aquatic
predecessor, there is to be noticed the disappearance
of one of the six rows of small bones, a confluence of
some of the remainder in the other five rows, a dupli-
cation of the arm-bone into a* radius and ulna, in
order to admit of jointed rotation of the hand, and a
general disposition of the small bones below these
arm-bones, which clearly foreshadows the joint of the
wrist Indeed, in this fore-foot of Chelydra, a child
could trace all the principal homologies of the mam-
malian counterpart, growing, like the next stage in a
dissolving view, out of the primitive paddle of Bapta-
nodon — namely, first the radius and ulna, next the
carpals, then the meta-carpals, and, lastly, the three
phalanges in each of the five digits.
Such a type of foot no doubt admirably meets the
requirements of slow reptilian locomotion over swampy
ground. But for anything like rapid locomotion over
hard and uneven ground, greater modifications would
be needed. Such modifications, however, need not
be other in kind : it is enough that they should con-
tinue in the same line of advance, so as to reach a
1 82 Darwin, and after Darwin.
higher degree of firmness, combined with better joints.
Accordingly we find that this took place, not indeed
among reptiles, whose habits of cold-blooded life have
not changed, but among their warm-blooded de-
scendants, the mammals. Moreover, when we examine
the whole mammalian series, we find that the required
modifications must have taken place in slightly differ-
ent ways in three lines of descent simultaneously. We
have first the plantigrade and digitigrade modifications
already mentioned (pp. 178, 179). Of these the
plantigrade walking entailed least change, because
most resembling the ancestral or lizard-like mode of
progression. All that was here needed was a general
improvement as to relative lengths of bones, with
greater consolidation and greater flexibility of joints.
Therefore I need not say anything more about the
plantigrade division. But the digitigrade modification
necessitated a change of structural plan, to the extent
of raising the wrist and ankle joints off the ground, so
as to make the quadruped walk on its fingers and toes.
We meet with an interesting case of this transition
in the existing hare, which while at rest supports
itself on the whole hind foot after the manner of a
plantigrade animal, but when running does so upon
the ends of its toes, after the manner of a digitigrade
animal.
It is of importance for us to note that this transi-
tion from the original plantigrade to the more recent
digitigrade type, has been carried out on two slightly
different plans in two different lines of mamma-
lian descent. The hoofed mammals — which are all
digitigrade — are sub-classified as artiodactyls and
perissodactyls, L e. even-toed and odd-toed. Now,
Paleontology. 183
whether an animal has an even or an odd number
of toes may seem a curiously artificial distinction
on which to found so important a classification
of the mammalian group. But if we look at the
matter from a less empirical and more intelligent
point of view, we shall see that the alternative of
having an even or an odd number of toes carries with
it alternative consequences of a practically important
kind to any animal of the digitigrade type. For
suppose an aboriginal five-toed animal, walking on
the ends of its five toes, to be called upon to resign
some of his toes. If he is left with an even number,
it must be two or four ; and in either case the animal
would gain the firmest support by so disposing his
toes as to admit of the axis of his foot passing be-
tween an equal number of them — whether it be one or
two toes on each side. On the other hand, if our early
mammal were called upon to retain an odd number
of toes, he would gain best support by adjusting
matters so that the axis of his foot should be coinci-
dent with his middle^oe, whether this were his only
toe, or whether he had one on either side of it.
This consideration shows that the classification
into even-toed and odd-toed is not so artificial as
it no doubt at first sight appears. Let us, then,
consider the stages in the evolution of both these types
of feet.
Going back to the reptile Chelydra, it will be
observed that the axis of the foot passes down the
middle toe, which is therefore supported by two toes
on either side (Fig. 78). It may also be noticed that
the wrist or ankle bones do not interlock, either with one
another or with the bones of the hand or foot below
184 Darwin, and after Darwin.
them. This, of course, would give a weak foot, suited
to slow progression over marshy ground — which, as
we have seen, was no doubt the origin of the mam-
malian plantigrade foot. Here, for instance, to all in-
tents and purposes, is a similar type of foot, which
Palaeontology. 185
belonged to a very early mammal, antecedent to the
elephant series, the horse series, the rhinoceros, the
hog, and, in short, all the known hoofed mammalia
(Fig. 80). It was presumably an inhabitant of
swampy ground, slow in its movements, and low in
its intelligence.
But now, as we have seen, for more rapid progression
on hard uneven ground, a stronger and better jointed
foot would be needed. Therefore we find the bones
of the wrist and ankle beginning to interlock, both
among themselves and also with those of the foot and
hand immediately below them. Such a stage of
evolution is still apparent in the now existing elephant.
(See Fig. 81.)
Next, however, a still stronger foot was made by
the still further interlocking of the wrist and ankle
bones, so that both the first and second rows of them
were thus fitted into each other, as well as into the
bones of the hand and foot beneath. This further
modification is clearly traceable in some of the earlier
perissodactyls, and occurs in the majority at the
present time. Compare, for example, the greater in-
terlocking and consolidation of these small bones in the
Rhinoceros as contrasted with the Elephant (Fig. 81).
Moreover, simultaneously with these consolidating im-
provements in the mechanism of the wrist and ankle
joints, or possibly at a somewhat later period, a reduc-
tion in the number of digits began to take place. This
was a continuation of the policy of consolidating the
foot, analogous to the dropping out of the sixth row
of small bones in the paddle of Baptanodon. (Fig.
78.) In the pentadactyl plantigrade foot of the early
mammals, the first digit, being the shortest, was tiu
1 88 Darwin, and after Darwin.
first to leave the ground, to dwindle, and finally to
disappear. More work being thus thrown on the
remaining four, they were strengthened by inter-
locking with the wrist (or ankle) bones above them, as
just mentioned ; and also by being brought closer
together.
The changes which followed I will render in the
words of Professor Marsh.
Two kinds of reduction began. One leading to the existing
perissodactyl foot, and the other, apparently later, resulting in the
artiodactyl type. In the former the axis of the foot remained
in the middle of the third digit, as in the pentadactyl foot- [See
Fig. 8 1.] In the latter, it shifted to the outer side of this digit,
or between the third and fourth toe. [See Fig. 82.]
In the further reduction of the perissodactyl foot, the fifth
digit, being shorter than the remaining three, next left the ground,
and gradually disappeared. [Fig. 81 B.] Of the three remaining
toes, the middle or axial one was the longest, and retaining its
supremacy as greater strength and speed were required, finally
assumed the chief support of the foot [Fig. 81 C], while the
outer digits left the ground, ceased to be of use, and were lost,
except as splint-bones [Fig. 81 D]. The feet of the existing
horse shows the best example of this reduction in the Peris-
sodactyls, as it is the most specialized known in the Ungulates
[Fig. 81 D].
In the artiodactyl foot, the reduction resulted in the gradual
diminution of the two outer of the four remaining toes, the third
and fourth doing all the work, and thus increasing in size and
power. The fifth digit, for the same reasons as in the perisso-
dactyl foot, first left the ground and became smaller. Next, the
second soon followed, and these two gradually ceased to be
functional, [and eventually disappeared altogether, as shown in
the accompanying drawing of the feet of still existing animals,
Fig. 82 B, C, D].
The limb of the modern race-horse is a nearly perfect piece of
machinery, especially adapted to great speed on dry, level
ground. The limb of an antelope, or deer, is likewise well fitted
Paleontology.
6 e d e
189
0
Equus: Qua-
ternary and
Recent.
Mesohippus :
Lower Mio- U^
Orohippus :
Eocene.
FIG. 83. — Feet and teeth in fossil pedigree of the Horse. (After Marsh.)
a, bones of the fore-foot ; b, bones of the hind-foot ; t, radius and ulna ;
d, tibia and fibula ; e, roots of a tooth ; f and g, crowns of upper and
lower molar teeth.
190 Darwin, and after Darwtn.
for rapid motion on a plain, but the foot itself is adapted to rough
mountain work as well, and it is to this advantage, in part, that
the Artiodactyls owe their present supremacy. The plantigrade
pentadactyl foot of the primitive Ungulate— and even the peris-
sodactyl foot that succeeded it— both belong to the past humid
period of the world's history. As the surface of the earth
slowly dried up, in the gradual desiccation still in progress, new
types of feet became a necessity, and the horse, antelope,
and camel were gradually developed, to meet the altered
conditions.
FIG. 84. — Palaotherium. (Lower Tertiary of Pahs Basin.)
The best instance of such progressive modifications
in the case of perissodactyl feet is furnished by the
fossil pedigree of the existing horse, because here,
within the limits of the same continuous family line,
we have presented the entire series of modifications.
There are now known over thirty species of horse-
like creatures, beginning from the size of a fox, then
progressively increasing in bulk, and all standing in
Paleontology. 191
linear series in structure as in time. Confining
attention to the teeth and feet, it will be seen from
the wood-cut on page 189 that the former grow
progressively longer in their sockets, and also more
complex in the patterns of their crowns. On the
other hand, the latter exhibit a gradual diminution
of their lateral toes, together with a gradual strength-
ening of the middle one. (See Fig. 83.) So that in
the particular case of the horse-ancestry we have a
practically complete chain of what only a few years
ago were "missing links." And this now practically
completed chain shows us the entire history of what
happens to be the most peculiar, or highly specialized,
limb in the whole mammalian class — namely, that of
the existing horse. Of the other two wood-cuts, the
former (Fig. 84) shows the skeleton of a very early
and highly generalized ancestor, while the other is
a partial restoration of a much more recent and
specialized one. (Fig. 85.)
On the other hand, progressive modifications of the
artiodactyl feet may be traced geologically up to the
different stages presented by living ruminants, in some
of which it has proceeded further than in others. For
instance, if we compare the pig, the deer, and the
camel (Fig. 82), we immediately perceive that the
dwindling of the two rudimentary digits has pro-
ceeded much further in the case of the deer than in
that of the pig, and yet not so far as in that
of the camel, seeing that here they have wholly
disappeared. Moreover, complementary differences
are to be observed in the degree of consolidation
presented by the two useful digits. For while in the
pig the two foot-bones are still clearly distinguish-
1 92 Darwin , and after Darwin.
able throughout their entire length, in the deer, and
still more in the camel, their union is more complete,
so that they go to constitute a single bone, whose
double or compound character is indicated externally
only by a slight bifurcation at the base. Nevertheless.
if we examine the state of matters in the unborn
young of these animals, we find that the two bones
in question are still separated throughout their length,
FIG. 85. — Hipparion, (New World Pliocene.)
and thus precisely resemble what used to be their
permanent condition in some of the now fossil species
of hoofed mammalia.
Turning next from bones of the limb to other parts
of the mammalian skeleton, let us briefly consider the
evidence of evolution that is here likewise presented by
the vertebral column, the skull, and the teeth.
As regards the vertebral column, if we examine this
Paleontology. 193
structure in any of the existing hoofed animals, we
find that the bony processes called zygapophyses,
which belong to each of the constituent vertebrae,
are so arranged that the anterior pair belonging to
each vertebra interlocks with the posterior pair be-
longing to the next vertebra. In this way the whole
series of vertebrae are connected together in the form
of a chain, which, while admitting of considerable
movement laterally, is everywhere guarded against
dislocation. But if we examine the skeletons of any
ungulates from the lower Eocene deposits, we find
that in no case is there any such arrangement to
secure interlocking. In all the hoofed mammals of
this period the zygapophyses are flat. Now, from
this flat condition to the present condition of full
interlocking we obtain a complete series of connecting
links. In the middle Miocene period we find a group
of hoofed animals in which the articulation begins
by a slight rounding of the previously flat surfaces:
later on this rounding progressively increases, until
eventually we get the complete interlocking of the
present time.
As regards teeth, and still confining attention to
the hoofed mammals, we find that low down in the
geological series the teeth present on their grinding
surfaces only three simple tubercles. Later on a
fourth tubercle is added, and later still there is de-
veloped that complicated system of ridges and furrows
which is characteristic of these teeth at the present
time, and which was produced by manifold and
various involutions of the three or four simple tuber-
cles of Eocene and lower Miocene times. In other
words, the principle of gradual improvement in the
* o
194 Darwin, and after Darwin.
A B
FIG. 86.— Comparative series of Brains. (After Le Conte.) The series reads from
above downwards, and represents diagrammatically the brain of a Fish, a Reptile,
a Bird, a Mammal, and a Man. In each case the letter A marks a side view, and
the letter B a top view. The small italics throughout signify the following homo-
logous parts: m, medulla; c6, cerebellum; 'op, optic lobes; cf, cerebrum and
thalamus ; ol, olfactory lobes. The series shows a progressive consolidation and
enlargement of the brain in general, and of the cerebrum and cerebellum in
particular, which likewise exhibit continually advancing structure in respect of
convolution. In the case of Man, these two parts of the brain have grown to so
great a size that they conceal all the other parts from the superficial points of view
represented in the diagram.
Paleontology.
construction of teeth, which has already been depicted
as regards the particular case of the Horse-family (Fig.
83), is no less apparent in the pedigree of all the
other mammalia, wherever the palaeontological history
is sufficiently intact to serve as a record at all.
FIG. 87. — Ideal section through all the above stages. (After Le Conte.)
Lastly, as regards the skull, casts of the interior
show that all the earlier mammals had small brains
with comparatively smooth or unconvoluted surfaces ;
and that as time went on the mammalian brain
gradually advanced in size and complexity. Indeed
so small were the cerebral hemispheres of the primitive
mammals that they did not overlap the cerebellum,
while their smoothness must have been such as in this
respect- to have resembled the brain of a bird or reptile.
This, of course, is just as it ought to be, if the brain,
which the skull has to accommodate, has been gradually
O 2
196 Darwin, and after Darwin.
evolved into larger and larger proportions in respect of
its cerebral hemispheres, or the upper masses of it
which constitute the seat of intelligence. Thus, if we
look at the above series of wood-cuts, which re-
presents the comparative structure of the brain in the
existing classes of the Vertebrata, we can immediately
understand why the fossil skulls of Mammalia should
present a gradual increase in size and furrowing, so
as to accommodate the general increase of the brain
in both these respects between the level marked
" maml " and that marked " man," in the last of the
diagrams. (Fig. 87.)
The tabular statement on the following diagram,
which I borrow from Prof. Cope, will serve at a glance
to reveal the combined significance of so many lines
of evidence, united within the limits of the same group
of animals.
To give only one special illustration of the principle
of evolution as regards the skull, here is one of the
most recent instances that has occurred of the dis-
covery of a missing link, or connecting form (see
Fig. 88). The fossil (B), which was found in New
Jersey, stands in an intermediate position between the
stag and the elk. In the stag (A) the skull is high,
showing but little of that anterior attenuation which
is such a distinctive feature of the skull of the elk (C).
The nasal bones (N) of the former, again, are re-
markably long when compared with the similar bones
of the latter, and the premaxillaries (PMX), instead
of being projected forward along the horizontal plane
of the base of the skull, are deflected sharply down-
ward. In all these points, it will be seen, the newly
discovered form (Cervalces) holds an intermediate
Paleontology.
197
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position (B). " The skull exhibits a partial attenua-
tion anteriorly, the premaxillaries are directed about
FlG. 88. — Skulls of — A, Canadian Stag ; B, Cervakes Americanus;
and C, Elk. (After Heilprin.)
equally downward and forward, and the nasal bones
are measurably contracted in size. The horns like-
Paleontology. 199
wise furnish characters which further serve to establish
this dual relationship V
The evidence, then, which is furnished by all parts
of the vertebral skeleton — whether we have regard to
Fishes, Reptiles, Birds, or Mammals — is cumulative
and consistent. Nowhere do we meet with any de-
viation or ambiguity, while everywhere we encounter
similar proofs of continuous transformation — proofs
which vary only with the varying amount of material
which happens to be at our disposal, being most
numerous and detailed in those cases where the
greatest number of fossil forms has been preserved
by the geological record. Here, therefore, we may
leave the vertebral skeleton ; and, having presented
a sample of the evidence as yielded by horns and
bones, I will conclude by glancing with similar brevity
at the case of shells — which, as before remarked, con-
stitute the only other sufficiently hard or permanent
material to yield unbroken evidence touching the
fossil ancestry of animals.
Of course it will be understood that I am everywhere
giving merely samples of the now superabundant
evidence which is yielded by palaeontology ; and, as
this chapter is already a long one, I must content
myself with citing only the case of mollusk-shells,
although shells of other classes might be made to
yield highly important additions to the testimony.
Moreover, even as regards the one division of mollusk-
shells, I can afford to quote only a very few cases.
These, however, are in my opinion the strongest
single pieces of evidence in favour of transmutation
which have thus far been brought to light.
1 Heilprin, Geological Evidences of Evolution, pp. 73-4 (1888).
2OO Darwin, and after Darwin.
Near the village of Steinheim, in Wiirtemberg,
there is an ancient lake-basin, dating from Tertiary
FIG. 89.— Transmutations of Planorbis. (After Hyatt)
times. The lake has long ago dried up ; but its
aqueous deposits are extraordinarily rich in fossil
shells, especially of different species of the genus
Paleontology. 201
Planorbis, The following is an authoritative rtsumt
of the facts.
As the deposits seem to have been continuous for ages, and
the fossil shells very abundant, this seemed to be an excellent
opportunity to test the theory of derivation. With this end in
view, they have been mad' the subject of exhaustive study by
Hilgendorf in 1866, and by Hyatt in 1880. In passing from the
lowest to the highest strata the species change greatly and many
times, the extreme forms being so different that, were it not for
the intermediate forms, they would be called not only different
species, but different genera. And yet the gradations are so in-
sensible that the whole series is nothing less than a demon-
stration, in this case at least, of origin of species by derivation
with modifications. The accompanying plate of successive forms
(Fig. 89), which we take from Prof. Hyatt's admirable memoir,
will show this better than any mere verbal explanation. It will
be observed that, commencing with four slight varieties— pro-
bably sexually isolated varieties— of one species, each series
shows a gradual transformation as we go upward in the strata —
i. e. onward in time. Series I branches into three sub-series, in
two of which the change of form is extreme. Series IV is re-
markable for great increase in size as well as change in form.
In the plate we give only selected stages, but in the fuller plates
of the memoir, and still more in the shells themselves, the sub-
tilest gradations are found1.
Here is another and more recently observed case of
transmutation in the case of mollusks.
The recent species, Strombus accipitrinus, still in-
habits the coasts of Florida. Its extinct prototype,
.S. Leidy, was discovered a few years ago by Prof.
Heilprin in the Pliocene formations of the interior
of Florida. The peculiar shape of the wing, and
tuberculation of the whorl, are thus proved to have
grown out of a previously more conical form of
shell.
1 Le Conte, loc. cit., pp. 236-7.
Paleontology. 203
Lastly, attention may here again be directed to the
very instructive series of shells which has already
been shown in a previous chapter, and which serves
to illustrate the successive geological forms tfPaludina
from the Tertiary beds of Slavonia, as depicted by
Prof. Neumayr of Vienna. (Fig. i, p. 19.)
CHAPTER VI.
GEOGRAPHICAL DISTRIBUTION.
THE argument from geology is the argument from
the distribution of species in time. I will next take
the argument from the distribution of species in space —
that is, the present geographical distribution of plants
and animals.
Seeing that the theory of descent with adaptive
modification implies slow and gradual change of one
species into another, and progressively still more slow
and gradual changes of one genus, family, or order
into another genus, family, or order, we should expect
on this theory that the organic types living on any
given geographical area would be found to resemble
or to differ from organic types living elsewhere, ac-
cording as the area is connected with or disconnected
from other geographical areas. For instance, the
large continental islands of Australia and New Zealand
are widely disconnected from all other lands of the
world, and deep sea soundings show that they have
probably been thus disconnected, either since the time
of their origin, or, at the least, through immense
geological epochs. The theory of evolution, there-
fore, would expect to find two general facts with
regard to the inhabitants of these islands. First, that
Geographical Distribution. 205
the inhabitants should form, as it were, little worlds of
their own, more or less unlike the inhabitants of any
other parts of the globe. And next, that some of
these inhabitants should present us with independent
information touching archaic forms of life. For it is
manifestly most improbable that the course of evo-
lutionary history should have run exactly parallel in
the case of these isolated oceanic continents and in
continents elsewhere. Australia and New Zealand,
therefore, ought to present a very large number, not
only of peculiar species and genera, but even of
families, and possibly of orders. Now this is just
what Australia and New Zealand do present. The
case of the dog being doubtful, there is an absence of
all mammalian life, except that of one of the oldest
and least highly developed orders, the Marsupials.
There even occurs a unique order, still lower in the
scale of organization — so low, in fact, that it deserves
to be regarded as but nascent mammalian : I mean,
of course, the Monotremata. As regards Birds, we
have the peculiar wingless forms alluded to in a
previous chapter (viz. that on Morphology) ; and, with-
out waiting to go into details, it is notorious that the
faunas of Australia and New Zealand are not only
highly peculiar, but also suggestively archaic. Therefore,
in both the respects above mentioned, the anticipations
of our theory are fully borne out. But as it would
take too long to consider, even cursorily, the faunas
and floras of these immense islands, I here allude to
them only for the sake of illustration. In order to
present the argument from geographical distribution
within reasonable limits, I think it is best to restrict
our examination to smaller areas ; for these will better
206 Darwin, and after Darwin.
admit of brief and yet adequate consideration. But
of course it will be understood that the less isolated
the region, and the shorter the time that it has been
isolated, the smaller amount of peculiarity should we
expect to meet with on the part of its present in-
habitants. Or, conversely stated, the longer and the
greater the isolation, the more peculiarity of species
would our theory expect to find. The object of the
present chapter will be to show that these, and other
cognate expectations, are fully realized by facts ; but,
before proceeding to do this, I must say a few words
on the antecedent standing of the argument.
Where the question is, as at present, between the
rival theories of special creation and gradual trans-
mutation, it may at first si^ht well appear that no test
can be at once so crucial and so easily applied as this
of comparing the species of one geographical area
with those of another, in order to see whether
there is any constant correlation between differences
of type and degrees of separation. But a little further
thought is enough to show that the test is not quite so
simple or so absolute — that it is a test to be applied
in a large and general way over the surface of the
whole earth, rather than one to be relied upon as
exclusively rigid in every special case.
In the first place, there is the obvious consideration
that lands or seas which are discontinuous now may
not always have been so, or not for long enough to
admit of the effects of separation having been exerted
to any considerable extent upon their inhabitants.
Next, there is the scarcely less important consideration,
that although land areas may long have been sepa-
rated from one another by extensive tracts of ocean,
Geographical Distribution. 207
birds and insects may more or less easily have been
able to fly from one to the other; while even non-
flying animals and plants may often have been
transported by floating ice or timber, wind or water
currents, and sundry other means of dispersal. Again,
there is the important influence of climate to be taken
into account. We know from geological evidence that
in the course of geological time the self-same con-
tinents have been submitted to enprmous changes of
temperature — varying in fact from polar cold to almost
tropical heat ; and as it is manifestly impossible that
forms of life suited to one of these climates could
have survived during the other, we can here perceive a
further and most potent cause interfering with the test
of geographical distribution as indiscriminately applied
in all cases. When the elephant and hippopotamus
were flourishing in England amid the luxuriant vege-
tation which these large animals require, it is evident
that scarcely any one species of either the fauna or
the flora of this country can have been the same as it
was when its African climate gave place to that of
Greenland. Therefore, as Mr. Wallace observes, " If
glacial epochs in temperate lands and mild climates
near the poles have, as now believed by men of
eminence, occurred several times over in the past
history of the earth, the effects of such great and
repeated changes both on migration, modification, and
extinction of species, must have been of overwhelming
importance — of more importance perhaps than even
the geological changes of sea and land/'
But although for these, and certain other less
important reasons which I need not wait to detail, we
must conclude that the evidence from geographical
208 Darwin, and after Darwin.
distribution is not to be regarded as a crucial test
between the rival theories of creation and evolution
in all cases indiscriminately, I must next remark that
it is undoubtedly one of the strongest lines of evidence
which we possess. When we once remember that,
according to the general theory of evolution itself, the
present geographical distribution of plants and animals
is "the visible outcome or residual product of the
whole past history of the earth," and, therefore, that of
the conditions determining the characters of life in-
habiting this and that particular area continuity or
discontinuity with other areas is but one, — when we
remember this, we find that no further reservation has
to be made : all the facts of geographical distribution
speak with one consent in favour of the naturalistic
theory.
The first of these facts which I shall adduce is, that
although the geographical range of any given species
is, as a rule, continuous, such is far from being
always the case. Very many species have more or
less discontinuous ranges — the mountain-hare, for
instance, extending from the Arctic regions over the
greater portion of Europe to the Ural Mountains and
the Caucasus, and yet over all this enormous tract
appearing only in isolated or discontinuous patches,
where there happen to be either mountain ranges or
climates cold enough to suit its nature. Now, in all
such cases of discontinuity in the range of a species
the theory of evolution has a simple explanation to
offer— namely, either that some representatives of the
species have at some former period been able to
migrate from one region to the other, or else that at
Geographical Distribution. 209
one time the species occupied the whole of the range
in question, but afterwards became broken up as
geographical, climatic, or other changes rendered
parts of the area unfit for the species to inhabit.
Thus, for instance, it is easy to understand that
during the last cold epoch the mountain-hare would
have had a continuous range ; but that as the Arctic
climate gradually receded to polar regions, the species
would be able to survive in southern latitudes only
on mountain ranges, and thus would become broken
up into many discontinuous patches, corresponding
with these ranges. In the same way we can explain
the occurrence of Arctic vegetation on the Alps and
Pyrenees — namely, as left behind by the retreat of
the Arctic climate it the close of the glacial period.
But now, on the other hand, the theory of special
creation cannot so well afford to render this obvious
explanation of discontinuity. In the case of the
Arctic flora of the Alps, for instance, although it is
true that much of this vegetation is of an Arctic type,
it is not true that the species are all identical with
those which occur in the Arctic regions. Therefore
the theory of special creation would here have to
assume that, although the now common species were
left behind on the Alps by the retreat of glaciation
northwards, the peculiar Alpine species were after-
wards created separately upon the Alps, and yet
created with such close affinities to the pre-existing
species as to be included with them under the same
genera. Looking to the absurdity of this supposition,
as well as of others which I need not wait to mention,
certain advocates of special creation have sought to
take refuge in another hypothesis — namely, that
2io Darwin, and after Darwin.
species which present a markedly discontinuous range
may have had a corresponding number of different
centres of creation, the same specific type having
been turned down, so to speak, on widely separated
areas. But to me it seems that this explanation pre-
sents even greater difficulty than the other. If it is
difficult to say why the Divinity should have chosen
to create new species of plants on the Alps on so
precisely the same pattern as the old, much more
would it be difficult to say why, in addition to these
new species, he should also have created again the
old species which he had already placed in the Arctic
regions.
So much, then, for discontinuity of distribution.
The next general fact to be adduced is, that there
is no constant correlation between habitats and ani-
mals or plants suited to live upon them. Of course
all the animals and plants living upon any given area
are well suited to live upon that area ; for otherwise
they could not be there. But the point now is, that
besides the area on which they do live, there are
usually many other areas in different parts of the
globe where they might have lived equally well — as
is proved by the fact that when transported by man
they thrive as well, or even better, than in their
native country. Therefore, upon the supposition that
all species were separately created in the countries
where they are respectively found, we must conclude
that they were created in only some of the places
where they might equally well have lived. Probably
there is at most but a small percentage either of
plants or animals which would not thrive in some
Geographical Distribution. 2 1 1
place, or places, on the earth's surface other than
that in which they occur ; and hence we must say
that one of the objects of special creation — if this
be the true theory — was that of depositing species
in only some among the several parts of the earth's
surface equally well suited to support them.
Now, I do not contend that this fact in itself raises
any difficulty against the theory of special creation.
But I do think that a very serious difficulty is raised
when to this fact we add another — namely, that on
every biological region we encounter species related
to other species in genera, and usually also genera
related to other genera in families. For if each of
all the constituent species of a genus, and even of a
family, were separately created, we must hence con-
clude that in depositing them there was an unaccount-
able design manifested to make areas of distribution
correspond to the natural affinities of their inhabi-
tants. For example, the humming-birds are geogra-
phically restricted to America, and number 120
genera, comprising over 400 species. Hence, if this
betokens 400 separate acts of creation, it cannot
possibly have been due to chance that they were
all performed on the same continent : it must have
been design which led to every species of this large
family of birds having been deposited in one geogra-
phical area. Or, to take a case where only the
species of a single genus are concerned. The rats
and mice proper constitute a genus which comprises
altogether more than 100 species, and they a*re all
exclusively restricted to the Old World. In the
New World they are represented by another genus
comprising about 70 species, which resemble their
p a
212 Darwin, and after Darwin.
Old World cousins in form and habits ; but differ
from them in dentition and other such minor points.
Now, the question is, — Why should all the 100
species have been separately created on one side
of the Atlantic with one pattern of dentition, and
all the 70 species on the other side with another
pattern ? What has the Atlantic Ocean got to do
with any " archetypal plan " of rats' teeth ?
Or again, to recur to Australia, why should all
the mammalian forms of life be restricted to the
one group of Marsupials, when we know that not
only the Rodents, such as the rabbit, but all other
orders of mammals, would thrive there equally well.
And similarly, of course, in countless other instances.
Everywhere we meet with this same correlation
between areas of distribution and affinities of classifi-
cation.
Now, it is at once manifest how completely this
general fact harmonizes with the theory of evolution.
If the 400 species of humming-birds, for instance, are all
modified descendants of common ancestors, and if none
of their constituent individuals have ever been large
enough to make their way across the oceans which
practically isolate their territory from all other tropi-
cal and sub-tropical regions of the globe, then we can
understand why it is that all the 400 species occupy
the same continent. But on the special-creation
theory we can see no reason why the 400 species
should all have been deposited in America. And, as
already observed; we must remember that this corre-
lation between a geographically restricted habitat
and the zoological or botanical affinities of its inhabi-
tants, is repeated over and over and over again in the
Geographical Distribution. 213
faunas and floras of the world, so that merely to
enumerate the instances would require a separate
chapter.
Furthermore, the general argument thus presented
in favour of descent with continuous modification
admits of being enormously strengthened by three
different classes of additional facts.
The first is, that the correlation in question —
namely, that between a geographically restricted
habitat and the zoological or botanical affinities of
its inhabitants — is not limited to the now existing
species, but extends also to the extinct. That is to
say, the dead species are allied to the living species,
as we should expect that they must be. if the latter
are modified descendants of the former. On the
alternative theory, however, we have to suppose that
the policy of maintaining a correlation between geo-
graphical restriction and natural affinity extends very
much further back than even the existing species
of plants and animals ; indeed we must suppose that
a practically infinite number of additional acts of
separate creation were governed by the same policy,
in the case of long lines of species long since extinct.
Thus far, then, the only answer which an advocate
of special creation can adduce is, that for some reason
unknown to us such a policy may have been more wise
than it appears : it may have served some inscrutable
purpose that allied products of distinct acts of crea-
tion should all be kept together on the same areas.
Well, in answer to this unjustifiable appeal to the
argument from ignorance, I will adduce the second
of the three considerations. This is, that in cases
where the geographical areas are not restricted the
214 Darwin, and after Darwin.
policy in question fails. In other words, where the
inhabitants of an area are free to migrate to other
areas, the policy of correlating affinity with distribu-
tion is most significantly forgotten. In this case
species wander away from their native homes; and
the course of their wanderings is marked by the
origination of new species springing up en route.
Now, is it reasonable to suppose that the mere cir-
cumstance of some members of a species being able
to leave their native home should furnish any occasion
for creating new and allied species upon the tracts over
which they travel, or the territories to which they go?
When the 400 existing species of humming-birds
have all been created on the same continent for some
reason supposed to be unknown, why should this
reason give way before the accident of any means
of migration being furnished to humming-birds, so
that they should be able to visit, say the continents
of Africa and Asia, there gain a footing beside the
sun-birds, and henceforth determine a new centre for
the separate creation of additional species of hum-
ming-birds peculiar to the Old World — as has hap-
pened in the case of the majority of species which,
unlike the humming-birds, have been at any time
free to migrate from their original homes ?
Lastly, my third consideration is, that the supposed
policy in question does not extend to affinities which
are wider than those between species and genera —
more rarely to families, scarcely ever to orders, and
never to classes. In other words, nature shows a
double correlation in her geographical distribution
of organic types : — first, that which we have already
considered between geographical restriction and
Geographical Distribution. 215
natural affinity among inhabitants of the same areas ;
second, another of a more detailed character between
degrees of geographical restriction and degrees of
natural affinity. The more distant the affinity, the
more general is the extension. This, of course, is
what we should expect on the theory of descent
with modification, because the more distant the
affinity, and therefore, ex hypothesi, the larger and
the older the original group of organisms, the greater
must be the chance of dispersal. The 400 species
of humming-birds may. well be unable to migrate
from their native continent ; but it would indeed
have been an unaccountable fact if no other species
of all the class of birds had ever been able to have
crossed the Atlantic Ocean. Thus, on the theory of
evolution, we can well understand the second corre-
lation now before us — namely, between remoteness
of affinity and generality of dispersal, — so that
there is no considerable portion of the habitable
globe without representatives of all the classes of
animals, few portions without representatives of all
the orders, but many portions without many of the
families, innumerable portions without innumerable
genera, and, of course, all portions without the great
majority of species. Now, while this general correla-
tion thus obviously supports the theory of natural
descent with progressive modification, it makes di-
rectly against the opposite theory of special creation.
For we have recently seen that when we restrict our
view to the case of species and genera, the theory of
special creation is obliged to suppose that for some
inscrutable reason the Deily had regard to systematic
affinity while determining on what large areas to
216 Darwin, and after Darwin.
create his species1. But now we see that he must
be held to have neglected this inscrutable reason
(whatever it was) when he passed beyond the range
of genera — and this always in proportion to the re-
moteness of systematic affinity on the part of the
species concerned.
I cannot well conceive a reductio ad dbsurdum
more complete than this. But, having now presented
these most general facts of geographical distribution
in their relation to the issue before us, we may next
proceed to consider a few illustrations of them in
detail, for in this way I think that their overwhelming
weight may become yet more abundantly apparent.
It will assist us in dealing with these detailed illus-
trations if we begin by considering the means of
dispersal of organisms from one place to another.
Of course the most ordinary means is that of con-
tinuous wandering, or emigration ; but where geo-
graphical barriers of any kind have to be surmounted,
organisms may only be able to pass them by more
exceptional and accidental means. The principal
barriers of a geographical kind are oceans, rivers,
mountain-chains, and desert-tracts, in the case of
1 I say "large areas" for the sake of argument; but the same cor-
relation between distribution and affinity extends likewise to small
areas where only small differences of affinity are concerned. Thus,
for instance, speaking of smaller areas, Moritz Wagner says : — " The
broader and more rapid the river, the higher and more regular the
mountain-chain, the calmer and more extensive the sea, the more
considerable, as a general rule, will be the taxonomic separation be-
tween the populations " ; and he shows that, in correlation with such
differences in the degrees of separation, are the degrees of diversification —
i. e., the numbers of species, and even of varieties, which these topo-
graphical barriers determine.
Geographical Distribution. 217
terrestrial organisms ; and, in the case of aquatic
organisms, the presence of land. But it is to be
observed that, as regards marine organisms, any con-
siderable difference in the temperature of the water
may constitute a barrier as effectual as the presence
of land ; and also that, in the case of all shallow-
water faunas, a tract of deep ocean constitutes almost
as complete a barrier as it does to terrestrial faunas.
Now, the means whereby barriers admit of being
accidentally or occasionally surmounted are, of course,
various ; and they differ in the case of different
organisms. Birds, bats, and insects, on account of
their powers of flight, are particularly apt to be blown
out great distances to sea, and hence of all animals
are most likely to become the involuntary colonists of
distant shores. Floating timber serves to convey
seeds and eggs of small animals over great distances ;
and Darwin has shown that many kinds of seeds are
able of themselves to float for more than a month in
sea-water without losing their powers of germination.
For instance, out of 87 kinds, 64 germinated after an
immersion of 28 days, and a few survived an immersion
of 137 days. As a result of all his experiments he
concludes, that the seeds of at least ten per cent, of the
species of plants of any country might be floated by
sea-currents during 38 days, without losing their
powers of germination ; and this, at the average rate
of flow of several Atlantic currents, would serve to
transport the seeds to a distance of at least 900 miles.
Again, he proved that even seeds which are quickly
destroyed by contact with sea-water admit of being
successfully transported during 30 days, if they be
contained within the crop of a dead bird. He also
218 Darwin, and after Darwin.
proved that living birds are most active agents in the
work of dissemination, and this not only by taking
seeds into their crops (where, so long as they remain,
the seeds are uninjured), but likewise by carrying seeds
(and even young mollusks) attached to their feet and
feathers. In the course of these experiments he found
that a small cup-full of mud, which he gathered from
the edges of three ponds in February, was so charged
with seeds that when sown in the ground these few
ounces of mud yielded no less than 537 plants, belong-
ing to many different species. It is therefore evident
what opportunities are thus afforded for the trans-
portation of seeds on the feet and bills of wading-birds.
Lastly, floating ice is well known to act as a carrier
of any kind of life which may prove able to survive
this mode of transit.
Such being the nature of geographical barriers, and
the means that organisms of various kinds may
occasionally have of overcoming them, I will now give
a few detailed illustrations of the argument from
geographical distribution, as previously presented in
its general form.
To begin with aquatic animals. As Darwin remarks,
'• the marine inhabitants of the Eastern and Western
shores of South America are very distinct ; with
extremely few shells, Crustacea, or echinodermata in
common." Again, westward of the shores of America,
a wide space of open ocean extends, which, as we
have seen, furnishes as effectual a barrier as does the
land to any emigration of shallow-water animals.
Now, as soon as this reach of deep water is passed, we
meet in the eastern islands of the Pacific with another
and totally distinct fauna. " So that three marine
Geographical Distribution. 219
faunas range northward and southward in parallel
lines not far from each other, under corresponding
climates " : they are, however, " separated from each
other by impassable barriers, either of land or open
sea " : and it is in exact coincidence with the course of
these barriers that we find so remarkable a differen-
tiation of the faunas1. Obviously, therefore, it is
impossible to suggest that this correlation is accidental.
Altogether many thousands of species are involved,
and within this comparatively limited area they are
sharply marked off into three groups as to their
natural affinities, and into three groups as to their
several basins. Hence, if all these species were
separately created, there is no escape from the con-
clusion that for some reason or another the act of
creation was governed by the presence of these
barriers, so that species deposited on the Eastern
shores of South America were formed with one set of
natural affinities, while species deposited on the
Western shore were formed with another set ; and
similarly with regard to the third set of species in the
third basin, which, extending over a whole hemisphere
to the coast of Africa without any further barrier,
nowhere presents, over this vast area, any other case
of a distinct marine fauna. But what conceivable
reason can there have been thus to consult these
geographical barriers in the original creation of specific
The only exception is in the case of the fish on each side of the
Isthmus of Panama, where about 30 per cent, of the species are identi-
cal. But it is possible enough that at some previous time this narrow
isthmus may have been even narrower than at present, if not actually
open. At all events, the fact that this partial exception occurs just
where the land-barrier is so narrow, is more suggestive of migration
than of independent creation.
22O Darwin, and after Darwin.
types ? Even if such a case stood alone, it would be
strongly suggestive of error on the part of the special
creation theory. But let us take another case, this
time from fresh-water faunas.
Although the geographical distribution of fresh-
water fish and fresh-water shells is often surprisingly
extensive and apparently capricious, this may be
explained by the means of dispersal being here so
varied — not only aquatic birds, floods, and whirl-
winds, but also geographical changes of water-shed
having all assisted in the process. Moreover, in
some cases it is possible that the habits of more
widely distributed fresh-water fish may have origin-
ally been wholly or partly marine — which, of course,
would explain the existing discontinuity of their ex-
isting fresh-water distribution. But, be this as it
may (and it is not a question that affects the issue
between special creation and gradual evolution, since
it is only a question as to how a given species has
been dispersed from its original home, whether or
not in that home it was specially created), the
point I desire to bring forward is, that where we
find a barrier to the emigration of fresh-water
forms which is more formidable than a thousand
miles of ocean — a barrier over which neither
water-fowl nor whirlwinds are likely to pass, and
which is above the reach of any geological changes
of water-shed, — where we find such a barrier, we
always find a marked difference in the fresh-water
faunas on either side of it. The kind of barrier
to which I allude is a high mountain-chain. It
may be only a few miles wide ; yet it exercises a
greater influence on, the diversification of specific
Geographical Distribution. 221
types, where fresh-water faunas are concerned, than
almost any other. But why should this be the case
on any intelligible theory of special creation ? Why,
in the depositing of species of newly created fresh-
water fish, should the presence of an impassable
mountain-chain have determined so uniformly a dif-
ference of specific affinity on either side of it ? The
question, so far as I can see, does not admit of an
answer from any reasonable opponent.
Turning now from aquatic organisms to terrestrial,
the body of facts from which to draw is so large,
that I think the space at my disposal may be best
utilized by confining attention to a single division
of them — that, namely, which is furnished by the
zoological study of oceanic islands.
In the comparatively limited — but in itself extensive
— class of facts thus presented, we have a particularly
fair and cogent test as between the alternative theories
of evolution and creation. For where we meet with a
volcanic island, hundreds of miles from any other land,
and rising abruptly from an ocean of enormous depth,
we may be quite sure that such an island can never
have formed part of a now submerged continent. In
other words, we may be quite sure that it always has
been what it now is — an oceanic peak, separated
from all other land by hundreds of miles of sea,
and therefore an area supplied by nature for the
purpose, as it were, of testing the rival theories of
creation and evolution. For, let us ask, upon these
tiny insular specks of land what kind of life should
we expect to find? To this question the theories
of special creation and of gradual evolution would
222 Darwin, and after Darwin.
agree in giving the same answer up to a certain
point. For both theories would agree in supposing
that these islands would, at all events in large part,
derive their inhabitants from accidental or occasional
arrivals of wind-blown or water-floated organisms
from other countries — especially, of course, from the
countries least remote. But, after agreeing upon
this point, the two theories must part company in
their anticipations. The special-creation theory can
have no reason to suppose that a small volcanic
island in the midst of a great ocean should be chosen
as the theatre of any extraordinary creative activity,
or for any particularly rich manufacture of peculiar
species to be found nowhere else in the world. On
the other hand, the evolution theory would expect
to find that such habitats are stocked with more or
less peculiar species. For it would expect that when
any organisms chanced to reach a wholly isolated
refuge of this kind, their descendants should forth-
with have started upon an independent course of
evolutionary history. Protected from intercrossing
with any members of their parent species elsewhere,
and exposed to considerable changes in their con-
ditions of life, it would indeed be fatal to the
general theory of evolution if these descendants,
during the course of many generations, were not to
undergo appreciable change. It has happened on
two or three occasions that European rats have been
accidentally imported by ships upon some of these
islands, and even already it is observed that their
descendants have undergone a slight change of ap-
pearance, so as to constitute them what naturalists
call local varieties. The change, of course, is but
Geographical Distribution. 223
slight, because the time allowed for it has been so
short. But the longer the time that a colony of a
species is thus completely isolated under changed
conditions of life the greater, according to the evolu-
tion theory, should we expect the change to become.
Therefore, in all cases where we happen to know,
from independent evidence of a geological kind, that
an oceanic island is of very ancient formation, the
evolution theory would expect to encounter a
great wealth of peculiar species. On the other
hand, as I have just observed, the special-creation
theory can have no reason to suppose that there
should be any correlation between the age of an
oceanic island and the number of peculiar species
which it may be found to contain.
Therefore, having considered the principles of geo-
graphical distribution from the widest or most general
point of view, we shall pass to the opposite extreme,
and consider exhaustively, or in the utmost possible
detail, the facts of such distribution where the con-
ditions are best suited to this purpose — that is, as I
have already said, upon oceanic islands, which may be
metaphorically regarded as having been formed by
nature for the particular purpose of supplying natura-
lists with a crucial test between the theories of
creation and evolution. The material upon which my
analysis is to be based will be derived from the most
recent works upon geographical distribution — espe-
cially from the magnificent contributions to this depart-
ment of science which we owe to the labours of Mr.
Wallace. Indeed, all that follows may be regarded as
a condensed filtrate of the facts which he has collected.
Even as thus restricted, however, our subject-matter
224 Darwin, and after Darwin.
would be too extensive to be dealt with on the pre-
sent occasion, were we to attempt an exhaustive ana-
lysis of the floras and faunas of all oceanic islands
upon-, the face of the globe. Therefore, what I pro-
pose to do is to select for such exhaustive analysis a
few of what may be termed the most oceanic of
oceanic islands — that is to say, those oceanic islands
which are most widely separated from mainlands,
and which, therefore, furnish the most unquestionable
of test cases as between the theories of special crea-
tion and genetic descent.
Azores. — A group of volcanic islands, nine in num-
ber, about 900 miles from the coast of Portugal,
and surrounded by ocean depths of 1,800 to 2,500
fathoms. There is geological evidence that the origin
of the group dates back at least as far as Miocene
times. There is a total absence of all terrestrial Ver-
tebrata, other than those which are known to have been
introduced by man. Flying animals, on the other hand,
are abundant ; namely, 53 species of birds, one species
of bat, a few species of butterflies, moths, and hymenop-
tera, with 74 species of indigenous beetles. All these
animals are unmodified European species, with the
exception of one bird and many of the beetles. Of
the 74 indigenous species of the latter, 36 are not
found in Europe ; but 19 are natives of Madeira or
the Canaries, and 3 are American, doubtless trans-
planted by drift-wood. The remaining 14 species
occur nowhere else in the world, though for the most
part they are allied to other European species. There
are 69 known species of land-shells, of which 37 are
European, and 32 peculiar, though all allied to Euro-
Geographical Distribution. 225
pean forms. Lastly, there are 480 known species of
plants, of which 40 are peculiar, though allied to
European species.
Bermudas. — A small volcanic group of islands, 700
miles from North Carolina. Although there are
about 100 islands in the group, their total area does
not exceed 50 square miles. The group is surrounded
by water varying in depth from 2,500 to 3,800 fathoms.
The only terrestrial Vertebrate (unless the rats and
mice are indigenous) is a lizard allied to an American
form, but specifically distinct from it, and therefore a
solitary species which does not occur anywhere else in
the world. None of the birds or bats are peculiar,
any more than in the case of the Azores ; but, as in
that case, a large percentage of the land-shells are so
— namely, at least one quarter of the whole. Neither
the botany nor the entomology of this group has been
worked out ; but I have said enough to show how re-
markably parallel are the cases of these two volcanic
groups of islands situated in different hemispheres, but
at about the same distance from large continents. In
both there is an extraordinary paucity of terrestrial
vertebrata, and of any peculiar species of bird or beast.
On the other hand, there is in both a marvellous
wealth of peculiar species of insects and land-shells.
Now these correlations are all abundantly intelligible.
It is a difficult matter for any terrestrial animal to
cross 900, or even 700. miles of ocean : therefore only
one lizard has succeeded in doing so in one of the two
parallel cases ; and. living cut off from intercrossing
with its parent form, the descendants of that lizard
have become modified so as to constitute a peculiar
species. But it is more easy for large flying animals
* o
226 Darwin, and after Darwin.
to cross those distances of ocean : consequently, there
is only one instance of a peculiar species of bird or
bat — namely, a bull-finch in the Azores, which, being a
small land-bird, is not likely ever to have had any
other visitors from its original parent species coming
over from Europe to keep up the original breed.
Lastly, it is very much more easy for insects and
land-mollusca to be conveyed to such islands by wind
and floating timber than it is for terrestrial mammals,
or even than it is for small birds and bats ; but yet
such means of transit are not sufficiently sure to admit
of much recruiting from the mainland for the purpose
of keeping up the specific types. Consequently, the
insects and the land-shells present a much greater
proportion of peculiar species — namely, one half and
one fourth of the land-shells in the one case, and
one eighth of the beetles in the other. All these
correlations, I say, are abundantly intelligible on the
theory of evolution ; but who shall explain, on the
opposite theory, why orders of beetles and land-mol-
lusca should have been chosen from among all other
animals for such superabundant creation on oceanic
islands, so that in the Azores alone we find no less
than 32 of the one and 14 of the other ? And, in this
connexion, I may again allude to the peculiar species
of beetles in the island of Madeira. Here there are
an enormous number of peculiar species, though they
are nearly all related to, or included under the same
genera as, beetles on the neighbouring continent.
Now, as we have previously seen, no less than
200 of these species have lost the use of their
wings. Evolutionists explain this remarkable fact
by their general laws of degeneration under disuse,
Geographical Distribution. 227
and the operation of natural selection, as will be
shown later on ; but it is not so easy for special
creationists to explain why this enormous number
of peculiar species of beetles should have been
deposited on Madeira, all allied to beetles on the
nearest continent, and nearly all deprived of the
use of their wings. And similarly, of course, with
all the peculiar species of the Bermudas and the
Azores. For who will explain, on the theory
of independent creation, why all the peculiar species,
both of animals and plants, which occur on the Ber-
mudas should so unmistakably present American
affinities, while those which occur on the Azores
no less unmistakably present European affinities?
But to proceed to other, and still more remarkable,
cases.
The Galapagos Islands. — This archipelago is of
volcanic origin, situated under the equator between
500 and 600 miles from the West Coast of South
America. The depth of the ocean around them
varies from 2,000 to 3,000 fathoms or more. This
group is of particular interest, from the fact that
it was the study of its fauna which first sug-
gested to Darwin's mind the theory of evolution.
I will, therefore, begin by quoting a short passage
from his writings upon the zoological relations of
this particular fauna.
Here almost every product of the land and of the water bears
the unmistakeable stamp of the American continent. There
are twenty-six land birds ; of these, twenty-one, or perhaps
twenty-three, are ranked as distinct species, and would com-
monly be assumed to have been here created ; yet the close
affinity of most of these birds to American species is manifest in
every character, in their habits, gestures, and tones of voice.
Q3
228 Darwin, and after Darwin.
So it is with the other animals, and with a large proportion of
the plants, as shown by Dr. Hooker in his admirable Flora of
this archipelago. The naturalist, looking at the inhabitants
of these volcanic islands in the Pacific, distant several hundred
miles from the continent, 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 Archi-
pelago, and nowhere else, bear so plainly the stamp of affinity
to those created in America? There is nothing in the con-
ditions 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 de Verde Archi-
pelagoes ; but what an entire and absolute difference in their
inhabitants ! The inhabitants of the Cape de 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, and the Cape
de Verde Islands from Africa ; such colonists would be liable to
modification— the principle of inheritance still betraying their
original birthplace1.
The following is a synopsis of the fauna and flora
of this archipelago, so far as at present known. The
only terrestrial vertebrates are two peculiar species
of land-tortoise, and one extinct species ; five species
of lizards, all peculiar — two of them so much so
as to constitute a peculiar genus ; — and two species
of snakes, both closely allied to South American
forms. Of birds there are 57 species, of which no
1 Origin of Species, pp. 353-+
Geographical Distribution. 229
less than 38 are peculiar ; and all the non-peculiar
species, except one, belong to aquatic tribes. The
true land birds are represented by 31 species, of
which all, except one, are peculiar ; while more than
half of them go to constitute peculiar genera. More-
over, while they are all unquestionably allied to
South American forms, they present a beautiful
series of gradations, " from perfect identity with the
continental species, to genera so distinct that it is
difficult to determine with what forms they are most
nearly allied ; and it is interesting to note that this
diversity bears a distinct relation to the probabilities
of, and facilities for, migration to the islands. The
excessively abundant rice-bird, which breeds in
Canada, and swarms over the whole United States,
migrating to the West Indies and South America,
visiting the distant Bermudas almost every year,
and extending its range as far as Paraquay, is the
only species of land-bird which remains completely
unchanged in the Galapagos ; and we may therefore
conclude that some stragglers of the migrating host
reach the islands sufficiently often to keep up the
purity of the breed V Again, of the thirty peculiar
land-birds, it is observable that the more they differ
from any other species or genefa on the South
American continent, the more certainly are they found
to have their nearest relations among those South
American forms which have the more restricted
range, and are therefore the least likely to have found
their way to the islands with any frequency.
The insect fauna of the Galapagos islands is scanty,
and chiefly composed of beetles. These number 35
1 Wallace, Island Life, pp. 371-3.
230 Darwin, and after Darwin.
species, which are nearly all peculiar, and in some
cases go to constitute peculiar genera. The same
remarks apply to the twenty species of land-shells.
Lastly, of the total number of flowering plants (332
species) more than one half (174 species) are pecu-
liar. It is observable in the case of these peculiar
species of plants — as also of the peculiar species of
birds — that many of them are restricted to single
islands. It is also observable that, with regard both
to the fauna and flora, the Galapagos Islands as a
whole are very much richer in peculiar species than
either the Azores or Bermudas, notwithstanding
that both the latter are considerably more remote
from their nearest continents. This difference, which
at first sight appears to make against the evolu-
tionary interpretation, really tends to confirm it.
For the Galapagos Islands are situated in a calm
region of the globe, unvisited by those periodic
storms and hurricanes which sweep over the North
Atlantic, and which every year convey some strag-
gling birds, insects, seeds, &c., to the Azores and
Bermudas. Notwithstanding their somewhat greater
isolation geographically, therefore, the Azores and
Bermudas are really less isolated biologically 'than
are the Galapagos Islands ; and hence the less degree
of peculiarity on the part of their endemic species.
But, on the theory of special creation, it is impos-
sible to understand why there should be any such
correlation between the prevalence of gales and a
comparative inertness of creative activity. And, as
we have seen, it is equally impossible on this theory
to understand why there should be a further corre-
lation between the degree of peculiarity on the part
Geographical Distribution. 231
of the isolated species, and the degree in which theii
nearest allies on the mainland are there confined
to narrow ranges, and therefore less likely to keep
up any biological communication with the islands.
St. Helena. — A small volcanic island, ten miles long
by eight wide, situated in mid-ocean, noo miles from
Africa, and 1800 from South America. It is very
mountainous and rugged, bounded for the most part
by precipices, rising from ocean depths of 17,000 feet,
to a height above the sea-level of nearly 3,000.
When first discovered it was richly clothed with
forests ; but these were all destroyed by human
agency during the i6th, i7th and i8th centuries.
The records of civilization present no more lament-
able instance of this kind of destruction. From a
merely pecuniary point of view the abolition of
these primeval forests has proved an irreparable
loss ; but from a scientific point of view the loss
is incalculable. These forests served to harbour
countless forms of life, which extended at least from
the Miocene age, and which, having found there an
ocean refuge, survived as the last remnants of a remote
geological epoch. In those days, as Mr. Wallace
observes, St. Helena must have formed a kind of
natural museum or vivarium of archaic species of all
classes, the interest of which we can now only surmise
from the few remnants of those remnants, which are
still left among the more inaccessible portions of the
mountain peaks and crater edges. These remnants
of remnants are as follows.
There is a total absence of all indigenous mam-
mals, reptiles, fresh-water fish, and true land-birds.
There is, however, a species of plover, allied to one
232 ' Darwin, and after Darwin.
in South Africa ; but it is specifically distinct, and
therefore peculiar to the island. The insect life, on
the other hand, is abundant. Of beetles no less than
129 species are believed to be aboriginal, and, with
one single exception, the whole number are peculiar
to the island. " But in addition to this large amount
of specific peculiarity (perhaps unequalled anywhere
else in the world), the beetles of this island are
remarkable for their generic isolation, and for the
altogether exceptional proportion in which the great
divisions of the order are represented. The species
belong to 39 genera, of which no less than 25 are
peculiar to the island ; and many of these are such
isolated forms that it is impossible to find their
allies in any particular country V More than two-
thirds of all the species belong to the group of
weevils — a circumstance which serves to explain the
great wealth of beetle-population, the weevils being
beetles which live in wood, and St. Helena having
been originally a densely wooded island. This cir-
cumstance is also in accordance with the view that
the peculiar insect fauna has been in large part
evolved from ancestors which reached the island by
means of floating timber ; for, of course, no explana-
tion can be suggested why special creation of this
highly peculiar insect fauna should have run so dis-
proportionately into the production of weevils. About
two-thirds of the whole number of beetles, or. over
80 species, show no close affinity with any existing
insects, while the remaining third have some rela-
tions, though often very remote, with European and
African forms. That this high degree of peculiarity
1 Wallace, Island Life, p. 287.
Geographical Distribution. 233
is due to high antiquity is further indicated, accord-
ing to our theory, by the large number of species which
some of the types comprise. Thus, the 54 species of
Cossonidx may be referred to three types ; the 1 1
species of Bembidium form a group by themselves ;
and the Heteromera form two groups. {; Now, each
of these types may well be descended from a single
species, which originally reached the island from
some other land ; and the great variety of generic
and specific forms into which some of them have
diverged is an indication, and to some extent a
measure, of the remoteness of their origin 1." But,
on the counter-supposition that all these 128 pecu-
liar species were separately created to occupy this
particular island, it is surely unaccountable that they
should thus present such an arborescence of natural
affinities amongst themselves.
Passing over the rest of the insect fauna, which has
not yet been sufficiently worked out, we next find that
there are only 20 species of indigenous land-shells —
which is not surprising when we remember by what
enormous reaches of ocean the island is surrounded.
Of these 20 species no less than 13 have become
extinct, three are allied to European species, while
the rest are so highly peculiar as to have no
near allies in any other part of the globe. So that
the land-shells tell exactly the same story as the
insects.
Lastly, the plants likewise tell the same story.
The truly indigenous flowering plants are about 50
in number, besides 26 ferns. Forty of the former
and ten of the latter are peculiar to the island,
1 Wallace, Island Life, p. 287.
234 Darwin, and after Darwin.
and, as Sir Joseph Hooker tells us, " cannot be re-
garded as very close specific allies of any other plants
at all " Seventeen of them belong to peculiar genera,
and the others all differ so markedly as species from
their congeners, that not one comes under the cate-
gory of being an insular form of a continental species.
So that with respect to its plants no less than with
respect to its animals, we find that the island of
St. Helena constitutes a little world of unique species,
allied among themselves, but diverging so much from
all other known forms that in many cases they con-
stitute unique genera.
Sandwich Islands. — These are an extensive group
of islands, larger than any we have hitherto con-
sidered— the largest of the group being about the size
of Devonshire. The entire archipelago is volcanic,
with mountains rising to a height of nearly 14,000
feet. The group is situated in the middle of the North
Pacific, at a distance of considerably over 2,000 miles
from any other land, and surrounded by enormous
ocean depths. The only terrestrial vertebrata are
two lizards, one of which constitutes a peculiar
genus. There are 24 aquatic birds, five of which are
peculiar ; four birds of prey, two of which are pecu-
liar; and 16 land-birds, all of which are peculiar.
Moreover, these 16 land-birds constitute no less
than 10 peculiar genera, and even one peculiar
family of five genera. This is an amount of
peculiarity far exceeding that of any other islands,
and, of course, corresponds with the great isolation of
this archipelago. The only other animals which have
here been carefully studied are the land-shells, and
these tell the same story as the birds. For there are
Geographical Distribution. 235
nc less than 400 species which are all, without any
exception, peculiar ; while about three-quarters of
them go to constitute peculiar genera. Again, of the
plants, 620 species are believed to be endemic ; and
of these 377 are peculiar, yielding no less than 39
peculiar genera.
Prejudice apart, I think we must all now agree that
it is needless to continue further this line of proof. I
have chosen the smallest and most isolated islands
for the purposes of our present argument, first
because these furnish the most crucial kind of
test, and next because they best admit of being dealt
with in a short space. But, if necessary, a vast
amount of additional material could be furnished,
not only from other small oceanic islands, but still
more from the largest islands of the world, such as
Australia and New Zealand. However, after the
detailed inventories which have now been given
in the case of some of the smaller islands most
remote from mainlands, we may well be prepared to
accept it as a general law, that ivherever there is
evidence of land-areas having been for a long time
separated from other land-areas, there we meet with
a more or less extraordinary profusion of unique
species, often running up into unique genera. And,
in point of fact, so far as naturalists have hitherto
been able to ascertain, there is no exception to this
general law in any region of the globe. Moreover,
there is everywhere a constant correlation between
the degree of this peculiarity on the part of the fauna
and flora, and the time during which they have been
isolated. Thus, for instance, among the islands which
236" Darwin, and after Darwin.
I have called into evidence, those that are at once
the most isolated and give independent proofs of the
highest antiquity, are the Galapagos Islands, the Sand-
wich Islands, and St. Helena. Now, if we apply the
method of tabular analysis to these three cases, we
obtain the following most astonishing results. For
the sake of simplicity I will omit the enumeration of
peculiar genera, and confine attention to peculiar
species. Moreover, I will consider only terrestrial
animals ; for, as we have already seen, aquatic animals
are so much more likely to reach oceanic islands that
they do not furnish nearly so fair a test of the evolu-
tionary hypothesis.
PECULIAR SPECIES.
Shells.
Insects.
Reptiles.
Birds.
Mammals.
Sandwich .
400
\
2
16
o
Galapagos
15
35
10
30
o
St. Helena
20
128
0
i
o
Totals .
435
163
I,
47
o
NON-PECULIAR SPECIES.
Shells.
Insects.
Reptiles.
Birds.
Mammals.
Sandwich .
0
I
0
o
0
Galapagos
f
T
o
i
o
St. Helena
o
T
o
o
o
Totals .
0
!
0
i
o
From this synopsis we perceive that out of a total
of 658 species of terrestrial animals known to inhabit
Geographical Distribution. 237
these three oceanic territories, all are peculiar, with
the exception of a single land-bird which is found in
the Galapagos Islands. This is the rice-bird, so very
abundant on the American continent that its repre-
sentatives must not unfrequently become the invo-
luntary colonists of the Archipelago. There are,
however, a few species of non-peculiar insects in-
habiting the Sandwich and Galapagos Islands, the
exact number of which is doubtful, and on this
account are not here quoted. But at most they
would be represented by units, and therefore do not
affect the general result. Lastly, the remarkable
fact will be noted, that there is no single represen-
tative of the mammalian class in any of these islands.
If we turn next to consider the case of plants, we
obtain the following result : —
Peculiar Non-peculiar
Species. Species.
Sandwich 377 343
Galapagos 174 158
St Helena 50 26
Totals 601 437
So that by adding together peculiar species both
of land-animals and plants, we find that on these
three limited areas alone there are 1258 forms of life
which occur nowhere else upon the globe — not to
speak of the peculiar aquatic species, nor of the
presumably large number of peculiar species of all
kinds not hitherto discovered in these imperfectly
explored regions.
Now let us compare these facts with those which
are presented by the faunas and floras of islands less
238 Darwin, and after Darwin.
remote from continents, and known from independent
geological evidence to be of comparatively recent
origin — that is, to have been separated from their
adjacent mainlands in comparatively recent times,
and therefore as islands to be comparatively young.
The British Isles furnish as good an instance as could
be chosen, for they together comprise over 1000
islands of various sizes, which are nowhere separated
from one another by deep seas, and in the opinion of
geologists were all continuous with the European
continent since the glacial period.
BRITISH ISLES.
NON-PECULIAR SPECIES.
Plants.
Land
Shells.
Insects.
Reptiles
and
Amphibia.
Land
Birds.
Land
Mammalt.
1462
83
",55i
«3
130
4°
PECULIAR SPECIES.
Plants.
Shells.
Insects.
Reptiles
and
Amphibia.
Land
Birds.
Land
Mammals.
46
4
149
0
i
0
Total Peculiar Plants ........ 46
Total Peculiar Animals 154
Grand Total . . , , 3OO
I have drawn up this table in the most liberal
manner possible, including as peculiar species forms
Geographical Distribution. 239
which many naturalists regard as merely local varie-
ties. But, even as thus interpreted, how wonderful is
the contrast between the 1000 islands of Great Britain
and the single volcanic rock of St. Helena, where
almost all the animals and about half the plants are
peculiar, instead of about ^V of the animals, and -^ of
the plants. Of course, if no peculiar species of any
kind had occurred in the British Isles, advocates of
special creation might have argued that it was, so to
speak, needless for the Divinity to have added any
new species to those European forms which fully
populated the islands at the time when they were
separated from the continent. But. as the matter
stands, advocates of special creation must face the
fact that a certain small number of new and peculiar
species have been formed on the British Isles ; and,
therefore, that creative activity has not been wholly
suspended in their case. Why, then, has it been so
meagre in this case of a thousand islands, when it has
proved so profuse in the case of all single islands
more remote from mainlands, and presenting a higher
antiquity? Or why should the Divinity have thus
appeared so uniformly to consult these merely acci-
dental circumstances of space and time in the de-
positing of his unique specific types ? Do not such
facts rather speak with irresistible force in favour of the
view, that while all ancient and solitary islands have
had time enough, and separation enough, to admit of
distinct histories of evolution having been written in
their living inhabitants, no one of the thousand islands
of Great Britain has had either time enough, or separa-
tion enough, to have admitted of more than some of the
first pages of such a history having been commenced ?
240 Darwin, and after Darwin.
But this allusion to Great Britain introduces us to
another point. It will have been observed that,
unlike oceanic islands remote from mainlands, Great
Britain is well furnished both with reptiles (including
amphibia) and mammals. For there is no instance of
any oceanic island situated at more than 300 miles
from a continent where any single species of the
whole class of mammals is to be found, excepting
species of the only order which is able to fly — namely,
the bats. And the same has to be said of frogs, toads,
and newts, whose spawn is quickly killed by contact
with sea-water, and therefore could never have reached
remote islands in a living state. Hence, on evolu-
tionary principles., it is quite intelligible why oceanic
islands should not present any species of mammals or
batrachians — peculiar or otherwise,- save such species
of mammals as are able to fly. But on the theory
of special creation we can assign no reason why,
notwithstanding the extraordinary profusion of unique
types of other kinds which we have seen to occur on
oceanic islands, the Deity should have made this
curious exception to the detriment of all frogs, toads,
newts, and mammals, save only such as are able to fly.
Or, if any one should go so far to save a desperate
hypothesis as to maintain that there must have been
some hidden reason why batrachians and quadrupeds
were not specially created on oceanic islands, I may
mention another small — but in this relation a most
significant — fact. This is that on some of these
islands there occur certain peculiar species of plants,
the seeds of which are provided with numerous tiny
hooks, obviously and beautifully adapted — like those
on the seeds of allied plants elsewhere — to catch the
(geographical Distribution. 241
wool or hair of moving quadrupeds, and so to further
their own dissemination. But, as we have just seen,
there are no quadrupeds in the islands to meet
these beautiful adaptations on the part of the plants ;
so that special creationists must resort to the almost
impious supposition that in these cases the Deity has
only carried out half his plan, in that while he made
an elaborate provision for these uniquely created
species of plants, which depended for its efficiency on
the presence of quadrupeds, he nevertheless neglected
to place any quadrupeds on the islands where he had
placed the plants. Such one-sided attempts at adap-
tation surely resolve the thesis of special creation to a
reductio ad absurdum ; and hence the only reasonable
interpretation of them is, that while the seeds of allied
or ancestral plants were able to float to the islands, no
quadrupeds were ever able over so great a distance to
swim.
Although much more evidence might still be given
under the head of geographical distribution, I must
now close with a brief summary of the main points
that have been adduced.
After certain preliminary considerations, I began
by noticing that the theory of evolution has a much
more intelligible account to give than has its rival of
the facts of discontinuous distribution — the Alpine
flora, for instance, being allied to the Arctic, not
because the same species were separately created in
both places, but because during the glacial period
these species extended all over Europe, and were
left behind on the Alps as the Arctic flora receded
northwards — which was sufficiently long ago to ex-
* R
242 Darwin, and after Darwin.
plain why some of the Alpine species are unique,
though closely allied to Arctic forms.
Next we saw that, although living things are always
adapted to the climates under which they live (since
otherwise they could not live there at all), it is equally
true that, as a rule, besides the area on which they do
live, there are many other areas in different parts of
the globe where they might have lived equally well.
Consequently we must conclude that, if all species
were separately created, many species were severally
created on only one among a number of areas where
they might equally well have thrived. Now, although
this conclusion in itself may not seem opposed to the
theory of special creation, a most serious difficulty is
raised when it is taken in connexion with another fact
of an equally general kind. This is, that on every
biological region we encounter chains of allied species
constituting allied genera, families, and so on ; while
we scarcely ever meet with allied species in different
biological regions, notwithstanding that their climates
may be similar, and, consequently, just as well suited
to maintain some of the allied species. Hence we
must further conclude, if all species were separately
created, that in the work of creation some unac-
countable regard was paid to making areas of dis-
tribution correspond to degrees of structural affinity.
A great many species of the rat genus were created
in the Old World, and a great many species of
another, though allied, genus were created in the
New World : yet no reason can be assigned why no
one species of the Old World series should not just
as well have been deposited in the New World, and
•vice versa. On the other hand, the theory of evolution
Geographical Distribution. 243
may claim as direct evidence in its support all the
innumerable cases such as these — cases, indeed, so
innumerable that, as Mr. Wallace remarks, it may
be taken as a law of nature that " every species has
come into existence coincident both in space and
time with a pre-existing and closely allied species."
A general law which, while in itself most strongly
suggestive of evolution, is surely impossible to
reconcile with any reasonable theory of special
creation. Furthermore, this law extends backwards
through all geological time, with the result that the
extinct species, which now occur only as fossils on
any given geological area, resemble the species still
living upon that area, as we should expect that they
must, if the former were the natural progenitors of
the latter. On the other hand, if they were not the
natural progenitors, but all the species, both living
and extinct, were the supernatural and therefore in-
dependent creations which the rival theory would
suppose, then no reason can be given why the extinct
species should thus resemble the living — any more
than why the living species should resemble one
another. For, as we have seen, there are almost
always many other habitats on other parts of the
globe, where any members of any given group of
species might equally well have been deposited ;
and this, of course, applies to geological no less than
to historical time. Yet throughout all time we meet
with this most suggestive correlation between con-
tinuity of a geographical area and structural affinity
between the forms of life which have lived, or are still
living, upon that area.
Similarly, we find the further, and no less suggestive,
R 2
244 Darwin, and after Darwin.
correlation between the birth of new species and the
immediate pre-existence of closely allied species on
the same area — or, at most, on closely contiguous areas.
Where a continuous area has long been circum-
scribed by barriers of any kind, which prevent the
animals from wandering beyond it, then we find that
all the species, both extinct and living, constitute
more or less a world of their own ; while, on the
other hand, where the animals are free to migrate
from one area to another, the course of their migra-
tions is marked by the origination of new species
springing up en route, and serving to connect the
older, or metropolitan, forms with the younger, or
colonising, forms in the way of a graduated series.
This principle, however, admits of being traced only
in certain cases of species belonging to the same
genus, of genera belonging to the same family, or,
at most, of families belonging to the same order.
In other words, the more general the structural
affinity, the more general is the geographical ex-
tension— as we should expect to be the case on the
theory of descent with branching modifications, seeing
that the larger, the older, and the more diverse the
group of organisms compared, the greater must be
their chances of dispersal.
These general considerations led us to contemplate
more in detail the correlation between structural
affinity and barriers to free migration. Such barriers,
of course, differ in the cases of different organisms.
Marine organisms are stopped by land, unsuitable
temperature, or unsuitable depths ; fresh-water or-
ganisms by sea and by mountain-chains ; terrestrial
organisms chiefly by water. Now it is a matter of
Geographical Distribution. 245
fact which admits of no dispute, that in each of these
cases we meet with a direct correlation between the
kind of barrier and the kind of organisms whose
structural affinities are affected thereby. Where we
have to do with marine organisms, barriers such as
the Isthmus of Panama and the varying depth of the
Western Pacific determine three very distinct faunas,
ranging north and south in closely parallel lines, and
under corresponding climates. Where we have to do
with fresh-water organisms, we find that a mountain-
chain only a few miles wide has more influence in
determining differences of organic type on either side
of it than is exercised by even thousands of miles of
a continuous land-area, if this be uninterrupted by
any mountains high enough to prevent water-fowl,
whirlwinds, &c., from dispersing the ova. Again,
where we have to do with terrestrial organisms, the
most effectual barriers are wide reaches of ocean ;
and, accordingly, we find that these exercise an
enormous influence on the modification of terrestrial
types. Moreover, we find that the more terrestrial
an organism, or the greater the difficulty it has in
traversing a wide reach of ocean, the greater is the
modifying influence of such a barrier upon that type.
In oceanic islands, for example, many of the plants
and aquatic birds usually belong to the same species
as those which occur on the nearest mainlands, and
where there are any specific differences, these but
rarely run up to generic differences. But the land-
birds, insects, and reptiles which are found on such
islands are nearly always specifically, and very often
generically, distinct from those on the nearest main-
land— although invariably allied with sufficient close-
246 Darwin, and after Darwin.
ness to leave no manner of doubt as to their affinities
with the fauna of that mainland. Lastly, no am-
phibians and no mammals (except bats) are ever
found on any oceanic islands. Yet, as we have seen,
on the theory of special creation, these islands must
all be taken to have been the theatres of the most
extraordinary creative activity, so that on only three
of them we found no less than 1258 unique species,
whereof 657 were unique species of land animals, to
be set against one single species known to occur else-
where. Nevertheless, notwithstanding this prodigious
expenditure of creative energy in the case of land-
birds, land-shells, insects, and reptiles, no single new
amphibian, or no single new mammal, has been
created on any single oceanic island, if we except
the only kind of mammal that is able to fly, and
the ancestors of which, like those of the land-birds
and insects, might therefore have reached the islands
ages ago. Moreover, with regard to mammals,
even in cases where allied forms occur on either
side of a sea-channel, it is found to be a general rule
that if the channel is shallow, the species on either
side of it are much more closely related than if it be
deep — and this irrespective of its width. Therefore
we can only conclude, in the words of Darwin — " As
the amount of modification which animals of all kinds
undergo partly depends on 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 islands separated by deeper channels, we can
understand how it is that a relation exists between
the depth of the sea separating two mammalian
Geographical Distribution. 247
faunas, and the degree of their affinity— a relation
which is quite inexplicable on the theory of inde-
pendent acts of creation."
Looking to all these general principles of geo-
graphical distribution, and remembering the sundry
points of smaller detail relating to oceanic islands
which I will not wait to recapitulate, to my mind it
seems that there is no escape from the following
conclusion, with which I will bring my brief epitome
of the evidence to a close. The conclusion to which,
I submit, all the evidence leads is, that if the doctrine
of special creation is taken to be true, then it must
be further taken that the one and only principle
which has been consistently followed in the geo-
graphical deposition of species, is that of so de-
positing them as to make it everywhere appear- that
they were not thus deposited at all, but came into
existence where they now occur by way of genetic
descent with perpetual migration and correlative
modification. On no other principle, so far as 1
can see, would it be possible to account for the fact
that " every species has come into existence coincident
both in space and time with a pre-existing and closely
allied species," together with the carefully graduated
regard to physical barriers which the Creator must
have displayed while depositing his newly formed
species on either sides of them — everywhere making
degrees of structural affinity correspond to degrees of
geographical continuity, and degrees of structural differ-
ence correspond to degrees of geographical separation,
whether by mountain-chains in the case of fresh-water
faunas, by land and by deep sea in the case of marine
248 Darwin, and after Darwin.
faunas, or by reaches of ocean in the case of terrestrial
faunas — stocking oceanic islands with an enormous
profusion of peculiar species all allied to those on the
nearest mainlands,yet everywhere avoiding the creation
upon them of any amphibian or mammal, except an
occasional bat. We are familiar with the doctrine
that God is a God who hideth himself; here, however,
it seems to me, we should have but a thinly-veiled
insinuation, not merely that in his works he is
hidden, but that in these works he is untrue. Than
which I cannot conceive a stronger condemnation of
the theory which it has been my object fairly to
represent and dispassionately to criticise.
SECTION II
SELECTION
CHAPTER VII.
THE THEORY OF NATURAL SELECTION.
THUS far we have been considering the main
evidences of organic evolution considered as a fact.
We now enter a new field, namely, the evidences
which thus far have been brought to light touching
the causes of organic evolution v'O'isWf fed as a pro-
cess.
As was pointed out in the opening chapter, this is
obviously the methodical couise t > follow : we must
have some reasonable assurance that a fact is a fact
before we endeavour to explain it. Nevertheless, it
is not necessary that we should actually demonstrate
a fact to be a fact before we endeavour to explain it.
Even if we have but a reasonable presumption as to
its probability, we may find it well worth while to con-
sider its explanation; for by so doing we may obtain
additional evidence of the fact itself. And this because,
if it really is a fact, and if we hit upon the right
explanation of it, by proving the explanation probable,
we may thereby greatly increase our evidence of the fact.
In the very case before us; for example, the evidence
of evolution as a fact has from the first been largely
derived from testing Darwin's theory concerning its
method. It was this theoretical explanation of its
252 Darwin, and after Darwin.
method which first set him seriously to enquire into
the evidences of evolution as a fact ; and ever since he
published his results, the evidences which he adduced
in favour of natural selection as a method have con-
stituted some of the strongest reasons which scientific
men have felt for accepting evolution as a fact. Of
course the evidence in favour of this fact has gone on
steadily growing, quite independently of the assistance
which was thus so largely lent to it by the distinct-
ively Darwinian theory of its method ; and, indeed, so
much has this been the case, that in the present treatise
we have been able to consider such direct evidence of
the fact itself, without any reference at all to the indirect
or accessory evidence which is derived from that of
natural selection as a method. From which it follows
that in most of what I am about to say in subsequent
chapters on the evidences of natural selection as a
method, there will be furnished a large addition to the
evidences which have already been detailed of evolution
as a fact But, as a matter of systematic treatment, I
have thought it desirable to keep these two branches of
our subject separate. Which means that I have made
the evidences of evolution as a fact to stand indepen-
dently on their own feet — feet which in my opinion are
amply strong enough to bear any weight of adverse
criticism that can be placed upon them.
Our position, then, is this. On the foundation of
the previous chapters, I will henceforth assume that
we all accept organic evolution as a fact, without
requiring any of the accessory evidence which is gained
by independent proof of natural selection as a method.
But in making this assumption— namely, that we are
all now firmly persuaded of the fact of evolution — I do
The Theory of Natural Selection. 253
not imagine that such is really the case. I make the
assumption for the purposes of systematic exposition,
and in order that different parts of the subject may be
kept distinct. I confess it does appear to me remark-
able that there should still be a doubt in any educated
mind touching the general fact of evolution ; while it
becomes to me unaccountable that such should be
the case with a few still living men of science, who
cannot be accused of being ignorant of the evidences
which have now been accumulated. But in whatever
measure we may severally have been convinced — or re-
mained unconvinced — on this matter, for the purposes
of exposition I must hereafter assume that we are all
agreed to the extent of regarding the process of
evolution as, at least, sufficiently probable to justify
enquiry touching its causes on supposition of its
truth.
Now, the causes of evolution have been set forth in
a variety of different hypotheses, only the chief of
which need be mentioned here. Historically speaking
the first of these was that which was put forward by
Erasmus Darwin, Lamarck, and Herbert Spencer.
It consists in putting together the following facts
and inferences.
We know that, in the lifetime of the individual,
increased use of structures leads to an increase
of their functional efficiency ; while, on the other
hand, disuse leads to atrophy. The arms of a black-
smith, and the legs of a mountaineer, are familiar
illustrations of the first principle : our hospital wards
are full of illustrations of the second. Again, we know
that the characters of parents are transmitted to their
progeny by means of heredity. Now the hypothesis
254. Darwin, and after Darwin.
in question consists in supposing that if any particular
organs in a species are habitually used for performing
any particular action, they must undergo a structural
improvement which would more and more adapt them
to the performance of that action ; for in each gene-
ration constant use would better and better adapt the
structures to the discharge of their functions, and they
would then be bequeathed to the next generation in
this their improved form by heredity. So that, for in-
stance, if there had been a thousand generations of
blacksmiths, we might expect the sons of the last of
them to inherit unusually strong arms, even if these
young men had themselves taken to some other trade
not requiring any special use of their arms. Similarly,
if there had been a thousand generations of men
who used their arms but slightly, we should expect
their descendants to show but a puny development of
the upper extremities. Now let us apply all this to the
animal kingdom in general. The giraffe, for instance,
is a ruminant whose entire frame has been adapted to
support an enormously long neck, which is of use to
the animal in reaching the foliage of trees. The an-
cestors of the giraffe, having had ordinary necks, were
supposed by Lamarck to have gradually increased the
length of them, through many successive generations,
by constantly stretching to reach high foliage ; and he
further supposed that, when the neck became so long
as to require for its support special changes in the
general form of the animal as a whole, these special
changes would have brought about the dwindling of
other parts from which so much activity was no longer
required — the general result being that the whole or-
ganization of the animal became more and more
The Theory of Natural Selection. 255
adapted to browsing on high foliage. And so in the
cases of other animals, Lamarck believed that the
adaptation of their forms to their habits could be ex-
plained by this simple hypothesis that the habits
created the forms, through the effects of use and dis-
use, coupled with heredity.
Such is what is ordinarily known as Lamarck's
theory of evolution. We may as well remember,
however, that it really constitutes only one part of his
theory ; for besides this hypothesis of the cumulative
inheritance of functionally-produced modifications — to
which we may add the inherited effects of any direct
action exercised by surrounding conditions of life, —
Lamarck believed in some transcendental principle
tending to produce gradual improvement in pre-de-
termined lines of advance. Therefore it would really
be more correct to designate the former hypothesis by
the name either of Erasmus Darwin, or, still better, of
Herbert Spencer. Nevertheless, in order to avoid con-
fusion, I will follow established custom, and subse-
quently speak of this hypothesis as the Lamarckian
hypothesis — understanding, however, that in employ-
ing this designation I am not referring to any part
or factor of Lamarck's general theory of evolution
other than the one which has just been described —
namely, the hypothesis of the cumulative transmission
of functionally-produced, or otherwise "acquired,"
modifications.
This, then, was the earliest hypothesis touching the
causes of organic evolution. But we may at once
perceive that it is insufficient to explain all that stands
to be explained. In the first place, it refers in chief
part only to the higher animals, which are actuated to
256 Darwin, and after Darwin.
effort by intelligence. Its explanatory power in the
case of most invertebrata — as well as in that of all plants
— is extremely limited, inasmuch as these organisms
can never be moved to a greater or less use of their
several parts by any discriminating volition, such as
that which leads to the continued straining of a
giraffe's neck for the purpose of reaching foliage. In
the second place, even among the higher animals there
are numberless tissues and organs which unques-
tionably present a high degree of adaptive evolution,
but which nevertheless cannot be supposed to have
fallen within the influence of Lamarckian principles.
Of such are the shells of Crustacea, tortoises, &c.,
which although undoubtedly of great use to the
animals presenting them, cannot ever have been used
in the sense required by Lamarck's hypothesis, i.e.
actively exercised, so as to increase a flow of nutrition
to the part. Lastly, in the third place, the Validity of
Lamarck's hypothesis in any case whatsoever has of
late years become a matter of serious question, as will
be fully shown and discussed in the next volume.
Meanwhile it is enough to observe that, on account of
all these reasons, the theory of Lamarck, even if it be
supposed to present any truth at all, is clearly in-
sufficient as a full or complete theory of organic
evolution.
In historical order the next theory that was arrived
at was the theory of natural selection, simultaneously
published by Darwin and Wallace on July ist, 1858.
If we may estimate the importance of an idea by
the change of thought which it effects, this idea of
natural selection is unquestionably the most important
The Theory of Natural Selection. 257
idea that has ever been conceived by the mind of man.
Yet the wonder is that it should not have been
hit upon long before. Or rather, I should say, the
wonder is that its immense and immeasurable impor-
tance should not have been previously recognised.
For, since the publication of this idea by Darwin and
Wallace, it has been found that its main features had
already occurred to at least two other minds — namely,
Dr. Wells in 1813, and Mr. Patrick Matthew in 1831.
But neither of these writers perceived that in the few
scattered sentences which they had written upon the
subject they had struck the key-note of organic nature,
and resolved one of the principal chords of the universe.
Still more remarkable is the fact that Mr. Herbert
Spencer — notwithstanding his great powers of abstract
thought and his great devotion of those powers to the
theory of evolution, when as yet this theory was scorned
by science — still more remarkable, I say, is the fact that
Mr. Herbert Spencer should have missed what now
appears so obvious an idea. But most remarkable of
all is the fact that Dr. Whewell, with all his stores of
information on the history of the inductive sciences,
and with all his acumen on the matter of scientific
method, should not only have conceived the idea of
natural selection, but expressly stated it as a logically
possible explanation of the origin of species, and yet
have so stated it merely for the purpose of dismissing
it with contempt *. This, I think, is most remarkable,
because it serves to prove how very far men's minds at
that time must have been from entertaining, as in any
way antecedently probable, the doctrine of trans-
mutation. In order to show this I will here quote one
1 For quotations, see Note A.
* S
258 Darwin, and after Darwin.
passage from the writings of Whewell, and another
from a distinguished French naturalist referred to by
him.
In 1 846 Whewell wrote : —
Not only is the doctrine of the transmutation of species in
itself disproved by the best physiological reasonings, but the
additional assumptions which are requisite to enable its ad-
vocates to apply it to the explanation of the geological and
other phenomena of the earth, are altogether gratuitous and
fantastical *.
Then he quotes with approval the following
opinion : —
Against this hypothesis, which, up to the present time, I regard
as purely gratuitous, and likely to turn geologists out of the
sound and excellent road in which they now are, I willingly raise
my voice, with the most absolute conviction of being in the
right2.
And, after displaying the proof rendered by Lyell
of uniformitarianism in geology, and cordially sub-
scribing thereto, Whewell adds : —
, We are led by our reasonings to this view, that the present
order of things was commenced by an act of creative power
entirely different to any agency which has been exerted since.
None of the influences which have modified the present races of
animals and plants since they were placed in their habitations on
the earth's surface can have had any efficacy in producing them
at first. We are necessarily driven to assume, as the beginning
of the present cycle of organic nature, an event not included in
the course of nature 3.
So much, then, for the state of the most enlightened
and representative opinions on the question of evolution
1 Whewell, Indications of the Creator, 2nd ed., 1846,
• De Blainville, Comfte Rtndu, 1837.
* Whewell, ibid., p. i6a.
The Theory of Natural Selection. 259
before the publication of Darwin's work ; and so much,
likewise, for the only reasonable suggestions as to
the causes of evolution which up to that time had
been put forward, even by those few individuals who
entertained any belief in evolution as a fact. It
was the theory of natural selection that changed all
this, and created a revolution in the thought of our
' time, the magnitude of which in many of its far-reaching
consequences we are not even yet in a position to
appreciate ; but the action of which has already
wrought a transformation in general philosophy, as
well as in the more special science of biology, that
is without a parallel in the history of mankind.
Although every one is now more or less well
acquainted with the theory of natural selection, it is
necessary, for the sake of completeness, that I should
state the theory ; and I will do so in full detail.
It is a matter of observable fact that all plants and
animals are perpetually engaged in what Darwin calls
a " struggle for existence." That is to say, in every
generation of every species a great many more in-
dividuals are born than can possibly survive ; so that
there is in consequence a perpetual battle for life going
on among all the constituent individuals of any given
generation. Now, in this struggle for existence, which
individuals will be victorious and live? Assuredly
those which are best fitted to live, in whatever respect,
or respects, their superiority of fitness may consist.
Hence it follows that Nature, so to speak, selects the
best individuals out of each generation to live. And not
only so ; but as these favoured individuals transmit
their favourable qualities to their offspring, according to
S 2
260 Darwin, and after Darwin.
the fixed laws of heredity, it further follows that the
individuals composing each successive generation have
a general tendency to be better suited to their sur-
roundings than were their forefathers. And this
follows, not merely because in every generation it is
only the " flower of the flock " that is allowed to breed,
but also because, if in any generation some new and
beneficial qualities happen to arise as slight variations
from the ancestral type, they will (other things per-
mitting) be seized upon by natural selection, and, being
transmitted by heredity to subsequent generations, will
be added to the previously existing type. Thus the
best idea of the whole process will be gained by com-
paring it with the closely analogous process whereby
gardeners, fanciers, and cattle-breeders create their
wonderful productions ; for just as these men, by
always "selecting" their best individuals to breed
from, slowly but continuously improve their stock, so
Nature, by a similar process of "selection" slowly but
continuously makes the various species of plants and
animals better and better suited to the conditions of
their life.
Now, if this process of continuously adapting or-
ganisms to their environment takes place in nature
at all, there is no reason why we should set any limits
on the extent to which it is able to go, up to the
point at which a complete and perfect adaptation is
achieved. Therefore we might suppose that all species
would eventually reach this condition of perfect
harmony with their environment, and then remain
fixed. And so, according to the theory, they would,
if the environment were itself unchanging. But for-
asmuch as the environment (i. e. the sum total of the
The Theory of Natural Selection. 261
external conditions of life) of almost every organic
type alters more or less from century to century —
whether from astronomical, geological, and geographi-
cal changes, or from the immigrations and emigrations
of other species living on contiguous areas, and so
on — it follows that the process of natural selection
need never reach a terminal phase. And forasmuch
as natural selection may thus continue, ad infinitum,
slowly to alter a specific type in adaptation to a
gradually changing environment, if in any case the
alteration thus effected is sufficient in amount to lead
naturalists to name the result as a distinct species,
it follows that natural selection has transmuted one
specific type into another. Similarly, by a continuation
of the process, specific types would become transmuted
into generic, generic into family types, and so on. Thus
the process is supposed to go on throughout all the
countless forms of life continuously and simultaneously
— the world of organic types being thus regarded as
in a state of perpetual, though gradual, flux.
Now, the first thing we have to notice about this
theory is, that in all its main elements it is merely
a statement of observable facts. It is an observable
fact that in all species of plants and animals a very
much larger number of individuals are born than can
possibly survive. Thus, for example, it has been
calculated that if the progeny of a single pair of
elephants — which are the slowest breeding of animals
— were all allowed to reach maturity and propagate,
in 750 years there would be living 1 9,000,000 de-
scendants. Again, in the case of vegetables, if a
species of annual plant produces only two seeds a
262 Darwin, and after J^anvin.
year, if these in successive years were all allowed
to reproduce their kind, in twenty years there would
be 11,000,000 plants from a single ancestor. Yet we
know that nearly all animals and plants produce
many more young at a time than in either of these
two supposed cases. Indeed, as individuals of many
kinds of plants, and not a few kinds of animals, pro-
duce every year several thousand young, we may make
a rough estimate and say, that over organic nature as a
whole probably not one in a thousand young are al-
lowed to survive to the age of reproduction. How
tremendous, therefore, must be the struggle for exis-
tence I It is thought a terrible thing in battle when
one half the whole number of combatants perish. But
what are we to think of a baltle for life where only
one in a thousand survives ?
This, then, is the first fact. The second is the fact
so long ago recognised, that the battle is to the strong,
the race to the swift. The thousandth individual
which does survive in the battle for existence — which
does win the race for life — is, without question, one
of the individuals best fitted to do so ; that is to say,
best fitted to the conditions of its existence considered
as a whole. Nature is, therefore, always picking out,
or selecting, such individuals to live and to breed.
The third fact is, that the individuals so selected
transmit their favourable qualities to their offspring
by heredity. There is no doubt about this fact, so
far as we are concerned with it. For although, as I
have already hinted, considerable doubt has of late
years been cast upon Lamarck's doctrine of the
hereditary transmission of acquired characters, it
remains as impossible as ever it was to question the
The Theory of Natural Selection. 263
hereditary transmission of what are called congenital
characters. And this is all that Darwin's theory
necessarily requires.
The fourth fact is, that although heredity as a whole
produces a wonderfully exact copy of the parent in
the child, there is never a precise reduplication. Of
all the millions of human beings upon the face of the
earth, no one is so like another that we cannot
see some difference ; the resemblance is everywhere
specific, nowhere individual. Now this same remark
applies to all specific types. The only reason why
we notice individual differences in the case of the
human type more than we do in the case of any other
types, is because our attention is here more incessantly
focussed upon these differences. We are compelled
to notice them in the case of our own species, however
small they may appear to a naturalist, because, unless
we do so, we should not recognise the members of our
own family, or be able to distinguish between a man
whom we know is ready to do us an important service,
and another man whom we know is ready to cut our
throats. But our common mother Nature is able
thus to distinguish between all her children. Her
eyes are much more ready to detect small individual
peculiarities than are the eyes of any naturalist. No
slight variations in the cast of feature or disposition
of parts, no minute difference in the arrangement of
microscopical cells, can escape her ever vigilant
attention. And, consequently, when among all the
innumerable multitudes of individual variations any
one arises which — no matter in how slight a degree —
gives to that individual a better chance of success in
the struggle for life, Nature chooses that individual
264 Darwin, and after Darwin.
to survive, and so to perpetuate the improvement in
his or her progeny.
Now I say that all these several component parts
of Darwinian doctrine are not matters of theory, but
matters of fact. The only element of theory in his
doctrine of evolution by natural selection has reference
to the degree in which these observable facts, when
thus brought together, are adequate to account for the
process of evolution.
So much, then, as a statement of the theory of
natural selection. But from this statement — i. e. from
the theory of natural selection itself — there follow
certain matters of general principle which it is im-
portant to bear in mind. These, therefore, I shall
here proceed to mention.
First of all, it is evident that the theory is applicable
as an explanation of organic changes in specific types
only in so far as these changes are of use, or so far
as such changes endow the species with better chances
of success in the general struggle for existence. This
is the only sense in which I shall always employ the
terms use, utility, service, benefit, and so forth — that
is to say, in the sense of life-preserving.
Next, it must be clearly understood that the life
which it is the object, so to speak, of natural selection
to preserve, is primarily the life of the species ; not
that of the individual. Natural selection preserves
the life of the individual only in so far as this is
conducive to that of the species. Wherever the life-
interests of the individual clash with those of the
species, that individual is sacrificed in favour of others
The Theory of Natural Selection. 265
who happen better to subserve the interests of the
species. For example, in all organisms a greater or
less amount of vigour is wasted, so far as individual
interests are concerned, in the formation and the
nourishment of progeny. In the great majority of
plants and animals an enormous amount of physio-
logical energy is thus expended. Look at the roe or
the milt of a herring, for instance, and see what a
huge drain has been made upon the individual for the
sake of its species. Again, all unselfish instincts have
been developed for the sake of the species, and usually
against the interests of the individual. An ant which
will allow her head to be slowly drawn from her body
rather than relinquish her hold upon a pupa, is clearly
acting in response to an instinct which has been de-
veloped for the benefit of the hive, though fatal to the
individual. And, in a lesser degree, the parental
instincts, wherever they occur, are more or less de-
trimental to the interests of the individual, though
correspondingly essential to those of the race.
These illustrations will serve to show that natural
selection always works primarily for the life-interests
of the species — and, indeed, only works for those of
the individual at all in so far as the latter happen to
coincide with the former. Or, otherwise stated, the
object of natural selection is always that of producing
and maintaining specific types in the highest degree
of efficiency, no matter what may become of the con-
stituent individuals. Which is a striking republication
by Science of a general truth previously stated by
Poetry : —
So careful of the type she seems,
So careless of the single life.
266 Darwin, and after Darwin.
Tennyson thus noted the fact, and a few years later
Darwin supplied the explanation.
But of course in many, if not in the majority of
cases, anything that adds to the life-sustaining power
of the single life thereby ministers also to the life-
sustaining power of the type ; and thus we can under-
stand why all mechanisms and instincts which minister
to the single life have been developed — namely,
because the life of the species is made up of the lives
of all its constituent individuals. It is only where
the interests of the one clash with those of the other
that natural selection works against the individual.
So long as the interests are coincident, it works in
favour of both.
Natural selection, then, is a theory which seeks to
explain by natural causes the occurrence of every kind
of adaptation which is to be met with in organic
nature, on the assumption that adaptations of every
kind have primary reference to the preservation of
species, and therefore also, as a general rule, to the
preservation of their constituent individuals. And
from this it follows that where it is for the benefit of a
species to change its type, natural selection will effect
that change, thus leading to a specific transmutation,
or the evolution of a new species. In such cases
the old species may or may not become extinct. If
the transmutation affects the species as a whole, or
throughout its entire range, of course that particular
type becomes extinct, although it does so by becoming
changed into a still more suitable type in the course
of successive generations. If, on the other hand,
the transmutation affects only a part of the original
species, or not throughout its entire range, then the
The Theory of Natural Selection. 267
other parts of that species may survive for any number
of ages as they originally were. In the one case there
is a ladder-like transmutation of species in time ; in
the other case a possibly tree-like multiplication of
species in space. But whether the evolution of spe-
cies be thus serial in time or divergent in space, the
object of natural selection, so to speak, is in either
case the same — namely, that of preserving all types
which prove best suited to the conditions of their
existence.
Once more, the term "struggle for existence " must
be understood to comprehend, not only a competition
for life among contemporary individuals of the same
species, but likewise a struggle by all such individuals
taken collectively for the continuance of their own
specific type. Thus, on the one hand, while there is
a perpetual civil war being waged between members
of the same species, on the other hand there is a
foreign war being waged by the species as a whole
against its world as a whole. Hence it follows that
natural selection does not secure survival of the fittest
as regards individuals only, but also survival of the
fittest as regards types. This is a most important
point to remember, because, as a general rule, these
two different causes produce exactly opposite effects.
Success in the civil war, where each is fighting against
all, is determined by indimdiial fitness and self-reliance,
But success in the foreign war is determined by what
may be termed tribal fitness and mutual dependence.
For example, among social insects the struggle for
existence is quite as great between different tribes or
communities, as it is between different individuals of
268 Darwin, and after Darwin.
the same community ; and thus we can understand
the extraordinary degree in which not only co-
operative instincts, but also largely intelligent social
habits, have here been developed \ Similarly, in the
case of mankind, we can understand the still more ex-
traordinary development of these things — culminating
in the moral sense. I have heard a sermon, preached
at one of the meetings of the British Association,
entirely devoted to arguing that the moral sense could
not have been evolved by natural selection, seeing
that the altruism which this sense involves is the
very opposite of selfishness, which alone ought to have
been the product of survival of the fittest in a struggle
for life. And, of course, this argument would have
been perfectly sound had Darwin limited the struggle
for existence to individuals, without extending it to
communities. But if the preacher had ever read
Darwin's works he would have found that, when thus
extended, the principle of natural selection is bound
to work in favour of the co-operative instincts in the
case of so highly social an animal as man ; and that
of these instincts conscience is the highest imaginable
exhibition.
What I have called tribal fitness — in contra-
distinction to individual fitness — begins with the
family, developes in the community (herd, hive, clan,
&c.), and usually ends with the limits of the species.
On the one hand, however, it is but seldom that it
extends so far as to embrace the entire species ; while,
on the other hand, it may in some cases, and as it were
1 For cases, see Animal Intelligence, in the chapters on Ants and
Bees ; and, for discussion of principles, Mental Evolution in Animals.
in the chapters on Instinct.
The Theory of Natural Selection. 269
sporadically, extend beyond the species. In these
latter cases members of different species mutually
assist one another, whether in the way of what is
called symbiosis, or in a variety of other ways which
I need not wait to mention. For the only point
which I now desire to make clear is, that all cases of
mutual aid or co-operation, whether within or beyond
the limits of species, are cases which fall under the
explanatory sweep of the Darwinian theory J.
Another important point to notice is, that it con-
stitutes no part of the theory of natural selection to
suppose that survival of the fittest must invariably
lead to improvement of type, in the sense of superior
organization. On the contrary, if from change of
habits or conditions of life an organic type ceases to
have any use for previously useful organs, natural
selection will not only allow these organs in succes-
sive generations to deteriorate — by no longer placing
any selective premium upon their maintenance — but
may even proceed to assist the agencies engaged in
their destruction. For, being now useless, they may
become even deleterious, by absorbing nutriment,
causing weight, occupying space, &c., without con-
ferring any compensating benefit. Thus we can under-
stand why it is that parasites, for example, present the
phenomena of what is called degeneration, \. e. showing
by their whole structure that they have descended from
a possibly very much higher type of organization than
that which they now exhibit. Having for innumerable
1 Prince Kropotkin in the Nineteenth Century (Feb. 1888, Apr. 1891)
has adduced a large and interesting body of facts, showing the great
prevalence of the principle of co-operation in organic nature.
270 Darwin, and after Darwin.
generations ceased to require their legs, their eyes,
and so forth, all such organs of high elaboration have
either disappeared or become vestigial, leaving the
parasite as a more or less effete representative of its
ancestry.
These facts of degeneration, as we have previously
seen, are of very general occurrence, and it is evident
that their importance in the field of organic evolution
as a whole has been very great. Moreover, it ought to
be particularly observed that, as just indicated, the facts
may be due either to a passive cessation of selection, or
to an active reversal of it. Or, more correctly, these
facts are probably always due to the cessation of
selection, although in most cases where species in a
state of nature are concerned, the process of degener-
ation has been both hastened and intensified by the
super-added influence of the reversal of selection. In
the next volume I shall have occasion to recur to
this distinction, when it will be seen that it is one of
no small importance to the general theory of descent.
We may now proceed to consider certain mis-
conceptions of the Darwinian theory which are largely,
not to say generally, prevalent among supporters of
the theory. These misconceptions, therefore, differ
from those which fall to be considered in the next
chapter, i. e. misconceptions which constitute grounds
of objection to the theory.
Of all the errors connected with the theory of
natural selection, perhaps the one most frequently met
with — especially among supporters of the theory — is
that of employing the theory to explain all cases of
The Theory of Natural Selection. 27 1
phyletic modification (or inherited change of type)
indiscriminately, without waiting to consider whether
in particular cases its application is so much as
logically possible. The term " natural selection " thus
becomes a magic word, or Sesame, at the utterance of
which every closed door is supposed to be immediately
opened. Be it observed, I am not here alluding to
that merely blind faith in natural selection, which of
late years has begun dogmatically to force this
principle as the sole cause of organic evolution in
every case where it is logically possible that the prin-
ciple can have come into play. Such a blind faith,
indeed, I hold to be highly inimical, not only to the
progress of biological science, but even to the true
interests of the natural selection theory itself. As to
this I shall have a good deal to say in the next
volume. Here, however, the point is, that the theory
in question is often invoked in cases where it is not
even logically possible that it can apply, and therefore
in cases where its application betokens, not merely an
error of judgment or extravagance of dogmatism, but a
fallacy of reasoning in the nature of a logical contra-
diction. Almost any number of examples might be
given ; but one will suffice to illustrate what is meant.
And I choose it from the writings of one of the
authors of the selection theory itself, in order to show
how easy it is to be cheated by this mere juggling
with a phrase — for of course I do not doubt that a
moment's thought would have shown the writer the
untenability of his statement.
In his most recent work Mr. Wallace advances an
interesting hypothesis to the effect that differences of
colour between allied species, which are apparently
272 Darwin, and after Darwin.
too slight to serve any other purpose, may act as
" recognition marks," whereby the opposite sexes are
enabled at once to distinguish between members of
their own and of closely resembling species. Of
course this hypothesis can only apply to the higher
animals; but the point here is that, supposing it to
hold for them, Mr. Wallace proceeds to argue thus : —
Recognition marks "have in all probability been
acquired in the process of differentiation for the
purpose of checking the intercrossing of allied forms,"
because " one of the first needs of a new species would
be to keep separate from its nearest allies, and this
could be more readily done by some easily seen
external mark1." Now, it is clearly not so much
as logically possible that these recognition-marks
(supposing them to be such) can have been acquired
by natural selection, "for the purpose of checking
intercrossing of allied forms." For the theory of
natural selection, from its own essential nature as a
theory, is logically exclusive of the supposition that
survival of the fittest ever provides changes in antici-
pation of future uses. Or, otherwise stated, it involves
a contradiction of the theory itself to say that the
colour-changes in question were originated by natural
selection, in order to meet*' one of \hzfirst needs of a
new species," or for the purpose of subsequently
preventing intercrossing with allied forms. If it had
been said that these colour-differentiations were
originated by some cause other than natural selection
(or, if by natural selection, still with regard to some
previous , instead of prophetic, " purpose "), and, when so
" acquired," then began to serve the " purpose" assigned.
1 Darwinism, pp. 218 and 227.
The Theory of Natural Selection. 273
the argument would not have involved the fallacy
which we are now considering. But, as it stands, the
argument reverts to the teleology of pre-Darwinian
days — or the hypothesis of a " purpose " in the literal
sense which sees the end from the beginning, instead
of a " purpose " in the metaphorical sense of an adap-
tation that is evolved by the very modifications which
subserve it \
Another very prevalent, and more deliberate, fallacy
connected with the theory of natural selection is, that
it follows deductively from the theory itself that the
principle of natural selection must be the sole means
of modification in all cases where modification is of
an adaptive kind, — with the consequence that no
other principle can ever have been concerned in the
production of structures or instincts which are of any
use to their possessors. Whether or not natural
selection actually has been the sole means of adaptive
modification in the race, as distinguished from the
individual, is a question of biological fact 2 ; but it
1 Since the above was written Prof. Lloyd Morgan has published a
closely similar notice of the passage in question. " This language," he
says, "seems to savour of teleology (that pitfall of the evolutionist).
The cart is put before the horse. The recognition-marks were, I
believe, not produced to prevent intercrossing, but intercrossing has
been prevented because of preferential mating between individuals
possessing special recognition-marks. To miss this point is to miss
an important segregation-factor." — {Animal Life and Intelligence, p.
103.) Again, on pp. 184-9, ne furnishes an excellent discussion on the
whole subject of the fallacy alluded to in the text, and gives illustrative
quotations from other prominent Darwinians. I should like to add
that Darwin himself has nowhere fallen into this, or any of the other
fallacies, which are mentioned in the text.
3 Of course adaptive modifications produced in the individual life-
time, and not inherited, do not concern the question at all. In this and
* T
274 Darwin, and after Darwin.
involves a grave error of reasoning to suppose that
this question can be answered deductively from the
theory of natural selection itself, as I shall show at
some length in the next volume.
A still more extravagant, and a still more un-
accountable fallacy is the one which represents it as
following deductively from the theory of natural
selection itself, that all hereditary characters are
" necessarily " due to natural selection. In other
words, not only all adaptive, but likewise all non-
adaptive hereditary characters, it is said, must be due
to natural selection. For non-adaptive characters arc
taken to be due to "correlation of growth," in con-
nexion with some of the adaptive ones — natural
selection being thus the indirect means of producing
the former wherever they may occur, on account of its
being the direct and the only means of producing the
latter. Thus it is deduced from the theory of natural
selection itself, — ist, that the principle of natural
selection is the only possible cause of adaptive modifi-
cation : 2nd, that non-adaptive modifications can only
occur in the race as correlated appendages to the
adaptive : 3rd, that, consequently, natural selection is
the only possible cause of modification, whether
adaptive or non-adaptive. Here again, therefore, we
must observe that none of these sweeping general-
izations can possibly be justified by deductive reasoning
from the theory of natural selection itself. Any attempt
at such deductive reasoning must necessarily end in
circular reasoning, as I shall likewise show in the
the following paragraphs, therefore, " adaptations," " adaptive modifica-
tions," &c., refer exclusively to such as are hereditary, i. e. phyletit
The Theory of Natural Selection. 275
second volume, where this whole "question of utility"
will be thoroughly dealt with.
Once more, there is an important oversight very
generally committed by the followers of Darwin. For
even those who avoid the fallacies above mentioned
often fail to perceive, that natural selection can only
begin to operate if the degree of adaptation is already
given as sufficiently high to count for something in the
struggle for existence. Any adaptations which fall
below this level of importance cannot possibly have
been produced by survival of the fittest. Yet the
followers of Darwin habitually speak of adaptative
characters, which in their oivn opinion are subservient
merely to comfort or convenience, as having been
produced by such means. Clearly this is illogical ;
for it belongs to the essence of Darwin's theory to
suppose, that natural selection can have no jurisdiction
beyond the line where structures or instincts already
present a sufficient degree of adaptational value to
increase, in some measure, the expectation of life on
the part of their possessors. We cannot speak of
adaptations as due to natural selection, without
thereby affirming that they present what I have else-
where termed a " selection value."
Lastly, as a mere matter of logical definition, it is
well-nigh self-evident that the theory of natural
selection is a theory of the origin, and cumulative
development, of adaptations, whether these be distinc-
tive of species, or of genera, orders, families, classes,
and sub-kingdoms. It is only when the adaptations
happen to be distinctive of the first (or lowest) of these
Darwin, and after Darwin.
taxonomic divisions, that the theory which accounts
for these adaptations accounts also for the forms which
present them, — i. e. becomes also a theory of the origin
of species. This, however, is clearly but an accident of
particular cases ; and, therefore, even in them the
theory is primarily a theory of adaptations, while it is
but secondarily a theory of the species which present
them. Or, otherwise stated, the theory is no more a
theory of the origin of species than it is of the origin
of genera, families, and the rest ; while, on the other
hand, it is everywhere a theory of the adaptive modifi-
cations whereby each of these taxonomic divisions has
been differentiated as such. Yet, sufficiently obvious
as the accuracy of this definition must appear to any
one who dispassionately considers it, several naturalists
of high standing have denounced it in violent terms.
I shall therefore have to recur to the subject at some-
what greater length hereafter. At present it is enough
merely to mention the matter, as furnishing another
and a curious illustration of the not infrequent
weakness of logical perception on the part of minds
well gifted with the faculty of observation. It may be
added, however, that the definition in question is in
no way hostile to the one which is virtually given by
Darwin in the title of his great work. The Origin of
Species by means of Natural Selection is beyond
doubt the best title that could have been given,
because at the time when the work was published the
fact, no less than the method, of organic evolution had
to be established ; and hence the most important
thing to be done at that time was to prove the
transmutation of species. But now that this has been
done to the satisfaction of naturalists in general, it is.
The Theory of Natural Selection. 277
as I have said, curious to find some of them denouncing
a wider definition of the principle of natural selection,
merely because the narrower (or included) definition is
invested with the charm of verbal associations *.
So much for fallacies and misconceptions touch-
ing Darwin's theory, which are but too frequently
met with in the writings of its supporters. We must
now pass on to mention some of the still greater
fallacies and misconceptions which are prevalent in
the writings of its opponents. And, in order to do
this thoroughly, I shall begin by devoting the re-
mainder of the present chapter to a consideration of
the antecedent standing of the two theories of natural
selection and supernatural design. This having been
done, in the succeeding chapters I shall deal with the
evidences for, and the objections against, the former
theory.
Beginning, then, with the antecedent standing oi
these alternative theories, the first thing to be noticed
is, that they are both concerned with the same subject-
matter, which it is their common object to explain.
Moreover, this subject-matter is clearly and sharply
divisible into two great classes of facts in organic
nature — namely, those of Adaptation and those of
Beauty. Darwin's theory of descent explains the for-
mer by his doctrine oi natural selection, and the latter
by his doctrine of sexual selection. In the first instance,
therefore, I shall have to deal only with the facts of
1 The question as to whether natural selection has been the only pri»
ciple concerned in the origination oi species, is quite distinct from that
as to the accuracy of the above definition.
278 Darwin, and after Darwin.
adaptation, leaving for subsequent consideration the
facts of beauty.
Innumerable cases of the adaptation of organisms
to their surroundings being the facts which now stand
before us to be explained either by natural selection
or by supernatural intention, we may first consider a
statement which is frequently met with — namely, that
even if all such cases of adaptation were proved to
be fully explicable by the theory of descent, this
would constitute no disproof of the theory of design:
all the cases of adaptation, it is argued, might still
be due to design, even though they admit of being
hypothetically accounted for by the theory of descent.
I have heard an eminent Professor tell his class that
the many instances of mechanical adaptation discovered
and described by Darwin as occurring in orchids,
seemed to him to furnish better proof of supernatural
contrivance than of natural causes ; and another emi-
nent Professor has informed me that, although he had
read the Origin of Species with care, he could see in
it no evidence of natural selection • which might not
equally well have been adduced in favour of intelligent
design. But here we meet with a radical misconception
of the whole logical attitude of science. For, be it
observed, this exception in limine to the evidence
which we are about to consider does not question that
natural selection may be able to do all that Darwin
ascribes to it. The objection is urged against his
interpretation of the facts merely on the ground that
these facts might equally well be ascribed to intelligent
design. And so undoubtedly they might, if we were
all simple enough to adopt a supernatural explana-
tion whenever a natural one is found sufficient to
The Theory of Natural Selection. 279
account for the facts. Once admit the irrational
principle that we may assume the operation of higher
causes where the operation of lower ones is sufficient
to explain the observed phenomena, and all our science
and all our philosophy are scattered to the winds.
For the law of logic which Sir William Hamilton
called the law of parsimony — or the law which forbids
us to assume the operation of higher causes when lower
ones are found sufficient to explain the observed
effects — this law constitutes the only barrier between
science and superstition. It is always possible to give
a hypothetical explanation of any phenomenon what-
soever, by referring it immediately to the intelligence
of some supernatural agent ; so that the only difference
between the logic of science and the logic of superstition
consists in science recognising a validity in the law of
parsimony which superstition disregards. Therefore
one can have no hesitation in saying that this way
of looking at the evidence in favour of natural selection
is not a scientific or a reasonable way of looking at it,
but a purely superstitious way. Let us take, as an
illustration, a perfectly parallel case. When Kepler
was unable to explain by any known causes the paths
described by the planets, he resorted to a supernatural
explanation, and supposed that every planet was guided
in its movements by some presiding angel. But when
Newton supplied a beautifully simple physical ex-
planation, all persons with a scientific habit of mind
at once abandoned the metaphysical one. Now, to
be consistent, the above-mentioned Professors, and all
who think with them, ought still to adhere to Kepler's
hypothesis in preference to Newton's explanation ;
for, excepting the law of parsimony, there is certainly
280 Darwin, and after Darwin.
no other logical objection to the statement, that the
movements of the planets afford as good evidence of
the influence of guiding angels as they do of the in-
fluence of gravitation.
So much, then, for the illogical position that, granting
the evidence in favour of natural descent and super-
natural design to be equal and parallel, we should
hesitate in our choice between the two theories. But,
of course, if the evidence is supposed not to be equal
and parallel — i. e. if it is supposed that the theory of
natural selection is not so good a theory whereby to
explain the facts of adaptation as is that of super-
natural design, — then the objection is no longer the one
which we are considering. It is quite another objection,
and one which is not prima facie absurd. Therefore
let us state clearly the distinct question which thus
arises.
Innumerable cases of adaptation of organisms to
their environments are the observed facts for which an
explanation is required. To supply this explanation,
two, and only two, hypotheses are in the field. Of
these two hypotheses one is intelligent design mani-
fested directly in special creation ; the other is natural
causation operating through countless ages of the past.
Now, the adaptations in question involve an innumer-
able multitude of special mechanisms, in most cases
even within the limits of any one given species ; but
when we consider the sum of all these mechanisms
presented by organic nature as a whole, the mind
must indeed be dull which does not feel astounded.
For, be it further observed, these mechanical con-
trivances1 are, for the most part, no merely simple
1 It is often objected to Darwin's terminology, that it embraces such
The Theory of Natural Selection. 281
arrangements, which might reasonably be supposed
due, like the phenomena of crystallization; to com-
paratively simple physical causes. On the contrary,
they everywhere and habitually exhibit so deep-laid,
so intricate, and often so remote an adaptation of
means to ends, that no machinery of human contrivance
can properly be said to equal their perfection from a
mechanical point of view. Therefore, without question,
the hypothesis which first of all they suggest — or
suggest most readily — is the hypothesis of design.
And this hypothesis becomes virtually the only hypo-
thesis possible, if it be assumed — as it generally was
assumed by natural theologians of the past, — that all
species of plants and animals were introduced into
the world suddenly. For it is quite inconceivable that
any known cause, other than intelligent design, could
be competent to turn out instantaneously any one of
these intricate pieces of machinery, already adapted
to the performance of its special function. But, on the
other hand, if there is any evidence to show that one
species becomes slowly transformed into another —
or that one set of adaptations becomes slowly changed
into another set as changing circumstances require, —
then it becomes quite possible to imagine that a
strictly natural causation may have had something
to do with the matter. And this suggestion becomes
greatly more probable when we discover, from geo-
logical evidence and embryological research, that in
the history both of races and of individuals the
words as "contrivance," "purpose," &c., which are strictly applicable
only to the processes or the products of thought. But when it is under-
stood that they are used in a neutral or metaphorical sense, I cannot see
that any harm arises from their use.
,282 Darwin, and after Darwin.
various mechanisms in question have themselves had
a history — beginning in the forms of most uniformity
and simplicity, gradually advancing to forms more
varied and complex, nowhere exhibiting any inter-
ruptions in their upward progress, until the world of
organic machinery as we now have it is seen to have
been but the last phase of a long and gradual growth,
the ultimate roots of which are to be found in the soil
of undifferentiated protoplasm.
Lastly, when there is supplied to us the suggestion
of natural selection as a cause presumably adequate to
account for this continuous growth in the number, the
intricacy, and the perfection of such mechanisms, it is
only the most unphilosophical mind that can refuse to
pause as between the older hypothesis of design and
the newer hypothesis of descent.
Thus it is clear that the a priori standing of the
rival hypotheses of naturalism and supernaturalism in
the case of all these pieces of organic machinery, is
profoundly affected by the question whether they came
into existence suddenly, or whether they did so grad-
ually. For, if they all came into existence suddenly,
the fact would constitute well-nigh positive proof
in favour of supernaturalism, or creation by design ;
whereas, if they all came into existence gradually, this
fact would in itself constitute presumptive evidence in
favour of naturalism, or of development by natural
causes. And, as shown in the previous chapters,
the proof that all species of plants and animals came
into existence gradually — or the proof of evolution as
a fact — is simply overwhelming.
From a still more general point of view I may state
the case in another way, by borrowing and somewhat
The Theory of Natural Selection. 283
expanding an illustration which, I believe, was first
used by Professor Huxley. If, when the tide is out, we
see lying upon the shore a long line of detached sea-
weed, marking the level which is reached by full tide,
we should be free to conclude that the separation of
the sea-weed from the sand and the stones was due
to the intelligent work of some one who intended to
collect the sea-weed for manure, or for any other pur-
pose. But, on the other hand, we might explain the
fact by a purely physical cause — namely, the separa-
tion by the sea-waves of the sea-weed from the sand
and stones, in virtue of its lower specific gravity. Now,
thus far the fact would be explained equally well by
either hypothesis ; and this fact would be the fact of
selection. But whether we yielded our assent to the
one explanation or to the other would depend upon a
due consideration of all collateral circumstances. The
sea-weed might not be of a kind that is of any use to
man ; there might be too great a quantity of it to
admit of our supposing that it had been collected by
man ; the fact that it was all deposited on the high-
water-mark would in itself be highly suggestive of the
agency of the sea ; and so forth. Thus, in such a case
any reasonable observer would decide in favour of the
physical explanation, or against the teleological one.
Now the question whether organic evolution has
been caused by physical agencies or by intelligent
design is in precisely the same predicament. There
can be no logical doubt that, theoretically at all events,
the physical agencies which the present chapter is con-
cerned with, and which are conveniently summed up in
the term natural selection, are as competent to pioduce
these so-called mechanical contrivances, and the other
284 Darwin, and after Darwin.
cases of adaptation which are to be met with in organic
nature, as intelligent design could be. Hence, our
choice as between these two hypotheses must be go-
verned by a study of all collateral circumstances ; that
is to say, by a study of the evidences in favour of the
physical explanation. To this study, therefore, we
shall now address ourselves, in the course of the follow-
ing chapters.
CHAPTER VIII.
EVIDENCES OF THE THEORY OF NATURAL
SELECTION.
I WILL now proceed to state the main arguments in
favour of the theory of natural selection, and then, in
the following chapter, the main objections which have
been urged against it.
In my opinion, the main arguments in favour of the
theory are three in number.
First, it is a matter of observation that the struggle
for existence in nature does lead to the extermination
of forms less fitted for the struggle, and thus makes
room for forms more fitted. This general fact may be
best observed in cases where an exotic species proves
itself better fitted to inhabit a new country than is some
endemic species which it exterminates. In Great
Britain, for example, the so-called common rat is a
comparatively recent importation from Norway, and
it has so completely supplanted the original British rat,
that it is now extremely difficult to procure a single
specimen of the latter : the native black rat has been
all but exterminated by the foreign brown rat. The
same thing is constantly found in the case of imported
species of plants. I have seen the river at Cambridge
so choked with the inordinate propagation of a species
286 Darwin, and after Darwin.
of water-weed which had been introduced from
America, that considerable expense had to be incurred
in order to clear the river for traffic. In New Zealand
the same thing has happened with the European
water-cress, and in Australia with the common rabbit.
So it is doubtless true, as one of the natives is said to
have philosophically remarked, " the white man's rat
has driven away our rat, the European fly drives away
our fly, his clover kills our grass, and so will the Maoris
disappear before the white man himself." Innumer-
able other cases to the same effect might be quoted ;
and they all go to establish the fact that forms less
fitted to survive succumb in their competition with
forms better fitted.
Secondly, there is a general consideration of the
largest possible significance in the present connexion —
namely, that among all the millions of structures and
instincts wh:ch are so invariably, and for the most part
so wonderfully, adapted to the needs of the species
presenting them, we cannot find a single instance,
either in the vegetable or animal kingdom, of a
structure or an instinct which is developed for the
exclusive benefit of another species. Now this great
and general fact is to my mind a fact of the most
enormous, not to say overwhelming, significance. The
theory of natural selection has now been before the
world for more than thirty years, and during that time
it had stood a fire of criticism such as was never en-
countered by any scientific theory before. From the
first Darwin invited this criticism to adduce any single
instance, either in the vegetable or animal kingdom, of
a structure or an instinct which should unquestionably
Evidences of Theory of Natural Selection. 287
be proved to be of exclusive use to any species other
than the one presenting- it. He even went so far as to
say that if any one such instance could be shown he
would surrender his whole theory on the strength of
it — so assured had he become, by his own prolonged
researches, that natural selection was the true agent
in the production of adaptive structures, and, as such,
could never have permitted such a structure to occur
in one species for the benefit of another. Now, as this
invitation has been before the world for so many years,
and has not yet been answered by any naturalist, we
may by this time be pretty confident that it never will
be answered. How tremendous, then, is the significance
of this fact in its testimony to Darwin's theory ! The
number of animal and vegetable species, both living
and extinct, is to be reckoned by millions, and every
one of these species presents on an average hundreds of
adaptive structures, — at least one of- which in many,
possibly in most, if not actually in all cases, is peculiar
to the species that presents it. In other words, there
are millions of adaptive structures (not to speak of in-
stincts) which are peculiar to the species presenting
them, and also many more which are the common
property of allied species : yet, notwithstanding this
inconceivable profusion of adaptive structures in
organic nature, there is no single instance that has
been pointed out of the occurrence of such a structure
save for the benefit of the species that presents it.
Therefore, I say that this immensely large and general
fact speaks with literally immeasurable force in favour
of natural selection, as at all events one of the main
causes of organic evolution. For the fact is precisely
what we should expect if this theory is true, while
288 Darwin, and after Darwin.
upon no other theory can its universality and invari-
ability be rendered intelligible. On the beneficent
design theory, for instance, it is inexplicable that no
species should ever be found to present a structure or
an instinct having primary reference to the welfare of
another species, when, ex hypothesi, such an endless
amount of thought has been displayed in the creation
of structures and instincts having primary reference to
the species which present them. For how magnificent
a display of divine beneficence would organic nature
have afforded, if all — or even some — species had been
so inter-related as to have ministered to each others
wants. Organic species might then have been likened
to a countless multitude of voices, all singing in one
great harmonious psalm. -But, as it is, we see abso-
lutely no vestige of such co-ordination : every species
is for itself, and for itself alone — an outcome of the
always and everywhere fiercely raging struggle for
life.
In order that the force of this argument may not be
misapprehended, it is necessary to bear in mind that
it is in no way affected by cases where a structure or
an instinct is of primary benefit to its possessor, and
then becomes of secondary benefit to some other species
on account of the latter being able in some way or
another to utilise its action. Of course organic nature
is full of cases of this kind ; but they only go to show
the readiness which all species display to utilise for
themselves everything that can be turned to good ac-
count in their own environments, and so, among other
things, the structures and instincts of other animals. For
instance, it would be no answer to Darwin's challenge if
any one were to point to a hermit-crab inhabiting the
Evidences of Theory of Natural Selection. 289
cast-off shell of a mollusk; because the shell was
primarily of use to the mollusk itself, and, so far as the
mollusk is concerned, the fact of its shell being after-
wards of a secondary use to the crab is quite immaterial.
What Darwin's challenge requires is, that some structure
or instinct should be shown which is not merely of such
secondary or accidental benefit to another species, but
clearly adapted to the needs of that other species in the
first instance — such, for example, as would be the case
if the tail of a rattle-snake were of no use to its
possessor, while serving to warn other animals of the
proximity of a dangerous creature ; or, in the case of
instincts, if it were true that a pilot-fish accompanies a
shark for the purpose of helping the shark to discover
food. Both these instances have been alleged ; but
both have been shown untenable. And so it has
proved of all the other cases which thus far have been
put forward.
Perhaps the most remarkable of all the allegations
which ever have been put forward in this connexion
are those that were current with regard to instincts
before the publication of Darwin's work. These
allegations are the most remarkable, because they
serve to show, in a degree which I do not believe
could be shown anywhere else, the warping power
of preconceived ideas. A short time ago I happened
to come across the 8th edition of the Encyclopaedia
Britannicci) and turned up the article on " Instinct "
there, in order to see what amount of change had been
wrought with regard to our views on this subject by
the work of Darwin — the hth edition of the Encyclo-
paedia Britannica having been published shortly before
The Origin of Species by means of Natural Selection.
* U
290 Darwin, and after Darwin.
I cannot wait to give any lengthy quotations from
this representative exponent of scientific opinion upon
the subject at that time ; but its general drift may be
appreciated if I transcribe merely the short concluding
paragraph, wherein he sums up his general results.
Here he says : —
It thus only remains for us to regard instinct as a mental
faculty, sui generis, the gift of God to the lower animals, that
man in his own person, and by them, might be relieved from the
meanest drudgery of nature.
Now, here we have the most extraordinary illus-
tration that is imaginable of the obscuring influence
of a preconceived idea. Because he started with the
belief that instincts must have been implanted in
animals for the benefit of man, this writer, even when
writing a purely scientific essay, was completely
blinded to the largest, the most obvious, and the most
important of the facts which the phenomena of instinct
display. For, as a matter of fact, among all the many
thousands of instincts which are known to occur in
animals, there is no single one that can be pointed to
as having any special reference to man ; while, on the
other hand, it is equally impossible to point to one
which does not refer to the welfare of the animal
presenting it. Indeed, when the point is suggested,
it seems to me surprising how few in number are the
instincts of animals which have proved to be so much
as of secondary or accidental benefit to man, in the
same way as skins, furs, and a whole host of other
animal products are thus of secondary use to Him.
Therefore, this writer not only failed to perceive the
most obvious truth that every instinct, without any
single exception, has reference to the animal which
Evidences of Theory of Natural Selection. 291
presents it ; but he also conceived a purely fictitious
inversion of this truth, and wrote an essay to prove a
statement which all the instincts in the animal kingdom
unite in contradicting.
This example will serve to show, in a striking
manner, not only the distance that we have travelled
in our interpretation of organic nature between two
successive editions of the Encyclopaedia BritannicaJovA.
also the amount of verification which this fact furnishes
to the theory of natural selection. For, inasmuch
as it belongs to the very essence of this theory that all
adaptive characters (whether instinctive or structural)
must have reference to their own possessors, we find
overpowering verification furnished to the theory by
the fact now before us — namely, that immediately prior
to the enunciation of this theory, the truth that all
adaptive characters have reference only to the species
which present them was not perceived. In other
words, it was the testing of this theory by the facts
of nature that revealed to naturalists the general law
which the theory, as it were, predicted — the general
law that all adaptive characters have primary reference
to the species which present them. And when we
remember that this is a kind of verification which is
furnished by millions of separate cases, the whole
mass of it taken together is, as I have before said,
overwhelming.
It is somewhat remarkable that the enormous im-
portance of this argument in favour of natural
selection as a prime factor of organic evolution has
not received the attention which it deserves. Even
Darwin himself, with his characteristic reserve, has
not presented its incalculable significance ; nor do I
U 2
29 2 Darwin, and after Darwin.
know any of his followers who have made any ap-
proach to an adequate use of it in their advocacy
of his views. In preparing the present chapter,
therefore, I have been particularly careful not to pitch
too high my own estimate of its evidential value.
That is to say, I have considered, both in the domain
of structures and of instincts, what instances admit of
being possibly adduced per contra^ or as standing out-
side the general law that adaptive structures and
instincts are of primary use only to their possessors.
In the result I can only think of two such instances.
These, therefore, I will now dispose of.
The first was pointed out, and has been fully dis-
cussed, by Darwin himself. Certain species of ants
are fond of a sweet fluid that is secreted by aphides,
and they even keep the aphides as we keep cows for
the purpose of profiting by their "milk." Now the
point is, that the use of this sweet secretion to the
aphis itself has not yet been made out. Of course, if
it is of no use to the aphis, it would furnish a case
which completely meets Darwin's own challenge. But,
even if this supposition did not stand out of analogy
with all the other facts of organic nature, most of us
would probably deem it prudent to hold that the
secretion must primarily be of some use to the aphis
itself, although the matter has not been sufficiently
investigated to inform us of what this use is. For, in
any case, the secretion is not of any vital importance
to the ants which feed upon it : and I think but few
impartial minds would go so far to save an hypothesis
as to maintain, that the Divinity had imposed this drain
upon the internal resources of one species of insect
for the sole purpose of supplying a luxury to another.
Evidences of Theory of Natural Selection. 293
On the whole, it seems most probable that the fluid
is of the nature of an excretion, serving to carry off
waste products. Such, at all events, was the opinion,
at which Darwin himself arrived, as a result of ob-
serving the facts anew, and in relation to his theory.
The other instance to which I have alluded as
seeming at first sight likely to answer Darwin's
challenge is the formation of vegetable galls. The
great number and variety of galls agree in presenting
a more or less elaborate structure, which is not only
foreign to any of the uses of plant-life, but singularly
and specially adapted to those of the insect-life which
they shelter. Yet they are produced by a growth of
the plant itself, when suitably stimulated by the
insects' inoculation — or, according to recent observa-
tions, by emanations from the bodies of the larvae
which develop from the eggs deposited in the plant
by the insect. Now, without question, this is a most
remarkable fact ; and if there were many more of the
like kind to be met with in organic nature, we might
seriously consider whether the formation of galls should
not be held to make against the ubiquitous agency of
natural selection. But inasmuch as the formation of
galls stands out as an exception to the otherwise
universal rule of every species for itself, and for itself
alone, we are justified in regarding this one apparent
exception with extreme suspicion. Indeed, I think
we are justified in regarding the peculiar pathological
effect produced in the plant by the secretions of the
insect as having been in the first instance accidentally
beneficial to the insects. Thus, if any other effect
than that of a growing tumour had been produced in
294 Darwin, and after Darwin.
the first instance, or if the needs of the insect progeny
had not been such as to have derived profit from
being enclosed in such a tumour, then, of course, the
inoculating instinct of these animals could not have
been developed by natural selection. But. given these
two conditions, and it appears to me there is nothing
very much more remarkable about an accidental
correlation between the effects of a parasitic larva on
a plant and the needs of that parasite, than there is
between the similarly accidental correlation between
a hydated parasite and the nutrition furnished to it by
the tissues of a warm-blooded animal. Doubtless the
case of galls is somewhat more remarkable, inasmuch
as the morbid growth of the plant has more concern
in the correlation — being, in many instances, a more
specialized structure on the part of a host than occurs
anywhere else, either in the animal or vegetable world.
But here I may suggest that although natural selection
cannot have acted upon the plant directly, so as to have
produced galls ever better and better adapted to the
needs of the insect, it may have so acted upon the
plants indirectly through the insects. For it may very
well have been that natural selection would ever
tend to preserve those individual insects, the quality
of whose emanations tended to produce the form of galls
best suited to nourish the insect progeny ; and thus
the character of these pathological growths may have
become ever better and better adapted to the needs
of the insects. Lastly, looking to the enormous
number of relations and inter-relations between all
organic species, it is scarcely to be wondered at that
even so extraordinary an instance of correlation as
this should have arisen thus by accident, and then
Evidences of Theory of Natural Selection. 295
have been perfected by such an indirect agency of
natural selection as is here suggested *.
The third general class of facts which tell so im-
mensely in favour of natural selection as an important
cause of organic evolution, are those of domestication.
The art of the horticulturist, the fancier, the cattle-
breeder, &c., consists in producing greater and greater
deviations from a given wild type of plant or animal,
in any particular direction that may be desired for
purposes either of use or of beauty. Cultivated
cereals, fruits, and flowers are known to have been
all derived from wild species ; and, of course, the same
applies to all our domesticated varieties of animals.
Yet if we compare a cabbage rose with a wild rose, a
golden pippin apple with a crab, a toy terrier with any
species of wild dog, not to mention any number of other
instances, there can be no question that, if such differ-
ences had appeared in nature, the organisms presenting
them would have been entitled to rank as distinct
species — or even, in many cases, as distinct genera.
Yet we know, as a matter of fact, that all these
differences have been produced by a process of arti-
ficial selection, or pairing, which has been continuously
practised by horticulturists and breeders through a
number of generations. It is the business of these men
to note the individual organisms which show most
variation in the directions required, and then to
propagate from these individuals, in order that the
progeny shall inherit the qualities desired. The
results thus become cumulative from generation to
generation, until we now have an astonishing mani-
1 Note B.
296 Darwin, and after Darwin.
festation of useful qualities on the one hand, and of
beautiful qualities on the other, according as the
organisms have bedn thus bred for purposes of use or
for those of beauty.
Now it is immediately obvious that in these cases
the process of artificial selection is precisely analogous
to that of natural selection (and of sexual selection
which will be considered later on), in all respects save
one : the utility or the beauty which it is the aim of
artificial selection continually to enhance, is utility or
beauty in relation to the requirements or to the tastes
of man ; whereas the utility or the beauty which is
produced by natural selection and sexual selection has
reference only to the requirements or the tastes of
the organisms themselves. But, with the exception
of this one point of difference, the processes and the
products are identical in kind. Persevering selection
by man is thus proved to be capable of creating what
are virtually new specific types, and this in any
required direction. Hence, when we remember how
severe is the struggle for existence in nature, it
becomes impossible to doubt that selection by nature
is able to do at least as much as artificial selection in
the way of thus creating new types out of old ones.
Artificial selection, indeed, notwithstanding the many
and marvellous results which it has accomplished, can
only be regarded as but a feeble imitation of natural
selection, which must act with so much greater
vigilance and through such immensely greater periods
of time. In a word, the proved capabilities of arti-
ficial selection furnish, in its best conceivable form,
what is called an argument a fortiori in favour of
natural selection.
Evidences of Theory of Natural Selection. 297
Or, to put it in another way, it may be said that
for thousands of years mankind has been engaged in
making a gigantic experiment to test, as it were by
anticipation, the theory of natural selection. For,
although this prolonged experiment has been carried
on without any such intention on the part of the ex-
perimenters, it is none the less an experiment in the
sense that its results now furnish an overwhelming
verification of Mr. Darwin's theory. That is to say,
they furnish overwhelming proof of the efficacy of the
selective principle in the modification of organic types,
when once this principle is brought steadily and con-
tinuously to bear upon a sufficiently long series of
generations.
In order to furnish ocular evidence of the value of
this line of verification, I have had the following series
of drawings prepared. Another and equally striking
series might be made of the products of artificial
selection in the case of plants ; but it seems to me
that the case of animals is more than sufficient for the
purpose just stated. Perhaps it is desirable to add
that considerable care has been bestowed upon the
execution of these portraits ; and that in every case
the latter have been taken from the most typical
specimens of the artificial variety depicted. Those of
them which have not been drawn directly from life
are taken from the most authoritative sources ; and,
before being submitted to the engraver, they were all
examined by the best judges in each department In
none of the groups, however, have I aimed at an
exhaustive representation of all the varieties : I
have merely introduced representatives of as many
as the page would in each case accommodate.
FIG. 91.— Pigeon*. Drawn from life (priie specimen).
FlG. 92.— Pigeons, continued. Drawn from life (prize specimens).
FlG. y3- — Fowls. Drawn from life (prize specimens).
FIG. 94. — Fowls, continued. Drawn from life (prize specimens).
FlG. 95. — Pair of Japanese Fowls, long-tailed breed. Drawn from stuffed specimen*
in the British Museum.
FlG 96.— Canaries. Drawn from life (prize specimens).
FlG. 97. — Sebastopol, or Frizzled Goose. Drawn troin a photograph.
FlG. 98. — The Dingo, or wild dog of Australia, ^ nat. size. Drawn from life
(Zoological Gardens).
FlG. 99. — Dogs. Drawn from life (prize specimen*).
X
FlG. IQO.— Dogs, continued. Drawn from life (prize specimens).
f'lG 101. — The Hairless Dog of Japan, ,'„ nat. size. Drawn from a photogiapb
kindly lent for the purpose by the proprietor.
DEER t^OUND
FlG. lua. — The skull of a Bull-dog compared with that of a Deerhound. Drawn
Troi.i nature.
X 3.
FIG. 103. Rabbits. Drawn from life (prize specimens).
FlG. 104.— Horses. Drawn from life (prize specimens).
hMhm!
s?Fns«^wiW.f4flr ^rv^^^L:
FIG. 105. Sheep. The illustrations are confined to British breeds. Drawn from
lite (.prize specimens).
FIG. 106 — Cattle. The illustrations are confined to British breeds. Urawa trom
life (prize specimens).
312 Darwin, and after Darwin.
FIG. 107. — Wild Boar contrasted with a modern Domesticated Pig.
Drawn from life {Zoological Gardens, and prize specimen).
The exigencies of space have prevented, in some of
the groups, strict adherence to a uniform scale — with
the result that contrasts between different breeds in
respect of size are not adequately rendered. This
remark applies especially to the dogs ; for although
the artist has endeavoured to draw them in perspective,
unless the distance between those in the foreground
and those in the background is understood to be
more considerable than it appears, an inadequate idea
is given of the relative differences of size. The most
instructive of the groups, I think, is that of the
Canaries ; because the many and great changes in
Evidences of Theory of Natural Selection. 313
different directions must in this case have been
produced by artificial selection in so comparatively
short a time — the first mention of this bird that I can
find being by Gesner, in the sixteenth century.
Now, it is surely unquestionable that in these
typical proofs of the efficacy of artificial selection in
the modification of specific types, we have the strongest
conceivable testimony to the power of natural selection
in the same direction. For it thus appears that
wherever mankind has had occasion to operate by
selection for a sufficiently long time — that is to say, on
whatever species of plant or animal he chooses thus to
operate for the purpose of modifying the type in any
required direction. — the results are always more or less
the same : he finds that all specific types lend them-
selves to continuous deflection in any particulars of
structure, colour, &c., that he may desire to modify.
Nevertheless, to this parallel between the known
effects of artificial selection, and the inferred effects of
natural selection, two objections have been urged.
The first is, that in the case of artificial selection the
selecting agent is a voluntary intelligence, while in the
case of natural selection the selecting agent is Nature
herself; and whether or not there is any counterpart
of man's voluntary intelligence in nature is a question
with which Darwinism has nothing to do. Therefore,
it is alleged, the analogy between natural selection
and artificial selection fails ab initio, or at the fountain-
head of the causes which are taken by the analogy to
be respectively involved.
The second objection to the analogy is, that the
products of artificial selection, closely as they may
314 Darwin, and after Darwin.
resemble natural species in all other respects, never-
theless present one conspicuous and highly important
point of difference : they rarely, if ever, present the
physiological character of mutual infertility, which is
a character of extremely general occurrence in the
case of natural species, even when these are most
nearly allied.
I will deal with these two objections in the next
chapter, where I shall be concerned with the meeting
of all the objections which have ever been urged
against the theory of natural selection. Meanwhile I
am engaged only in presenting the general arguments
which support the theory, and therefore mention these
objections to one of them merely en passant. And I
do so in order to pledge myself effectually to dispose
of them later on, so that for the purposes of my present
argument both these objections may be provisionally
regarded as non-existent ; which means, in other
words, that we may provisionally regard the analogy
between artificial selection and natural selection as
everywhere logically intact
To sum up, then, the results of the foregoing
exposition thus far, what I hold to be the three
principal, or most general, arguments in favour of the
theory of natural selection, are as follows.
First, there is the a priori consideration that, if on
independent grounds we believe in the theory of
evolution at all, it becomes obvious that natural
selection must have had some part in the process.
For no one can deny the potent facts of heredity,
variability, the struggle for existence, and survival of
the fittest But to admit these facts is to admit
Evidences of Theory of Natural Selection. 315
natural selection as a principle which must be, at any
rate, one of the factors of organic evolution, supposing
such evolution to have taken place. Next, when we
turn from these a priori considerations, which thus
show that natural selection must have been concerned
to some extent in the process of evolution, we find in
organic nature evidence a posteriori of the extent to
which this principle has been thus concerned. For we
find that among all the countless millions of adaptive
structures which are to be met with in organic nature,
it is an invariable rule that they exist in relation to the
needs of the particular species which present them :
they never have any primary reference to the needs of
other species. And as this extraordinarily large and
general fact is exactly what the theory of natural
selection would expect, the theory is verified by the
fact in an extraordinarily cogent manner. In other
words, the fact goes to prove that in all cases where
adaptive structures or instincts are concerned, natural
selection must have been either the sole cause at work,
or, at the least, an influence controlling the operation
of all other causes.
Lastly, an actually experimental verification of the
theory has been furnished on a gigantic scale by the
operations of breeders, fanciers, and horticulturists.
For these men, by their process of selective accumula-
tion, have empirically proved what immense changes
of type may thus be brought about; and so have
verified by anticipation, and in a most striking man-
ner, the theory of natural selection — which, as now
so fully explained, is nothing more than a theory
of cumulative modifications by means of selective
breeding.
316 Darwin, and after Darwin.
So much, then, by way of generalities. But perhaps
the proof of natural selection as an agency of the first
importance in the transmutation of species may be best
brought home to us by considering a few of its
applications in detail. I will therefore devote the rest
of the present chapter to considering a few cases of this
kind.
There are so many large fields from which such
special illustrations may be supplied, that it is difficult
to decide which of them to draw upon. For instance,
the innumerable, always interesting, and often aston-
ishing adaptations on the part of flowers to the
fertilising agency of insects, has alone given rise to an
extensive literature since the time when Darwin him-
self was led to investigate the subject by the guidance
of his own theory. The same may be said of the
structures and movements of climbing plants, and, in
short, of all the other departments of natural history
where the theory of natural selection has led to the
study of the phenomena of adaptation. For in all these
cases the theory of natural selection, which first led to
their discovery, still remains the only scientific theory
by which they can be explained. But among all the
possible fields from which evidences of this kind may
be drawn, I think the best is that which may be
generically termed defensive colouring. To this field,
therefore, I will restrict myself. But, even so, the
cases to be mentioned are but mere samples taken
from different divisions of this field ; and therefore it
must be understood at the outset that they could
easily be multiplied a hundred-iold.
Evidences of Theory of Natural Selection. 317
Protective Colouring.
A vast number of animals are rendered more or less
inconspicuous by resembling the colours of the surfaces
on which they habitually rest. Such, for example,
are grouse, partridges, rabbits, &c. Moreover, there
FIG. 108. — Seasonal changes of colour in Ptarmigan (Lagopus mutus).
Drawn from stuffed specimens in the British Museum, \ nat. size,
with appropriate surroundings supplied.
are many cases in which, if the needs of the creature
be such that it must habitually frequent surfaces of
different colours, it has acquired the power of changing
its colour accordingly — e. g. cuttle-fish, flat-fish,
frogs, chameleons, &c. The physiological mechanism
whereby these adaptive changes of colour are pro-
318 Darwin, and after Darwin.
duced differs in different animals; but it is needless
for our purposes to go into this part of the subject.
Again, there are yet other cases where protective
colouring which is admirably suited to conceal an
animal through one part of the year, would become
highly conspicuous during another part of it— namely,
when the ground is covered with snow. Accordingly,
in these cases the animals change their colour in the
winter months to a snowy white : witness stoats,
mountain hares, ptarmigan, &c. (Fig. 108.)
Now, it is sufficiently obvious that in all these
classes of cases the concealment from enemies or
prey which is thus secured is of advantage to the
animals concerned ; and, therefore, that in the theory
of natural selection we have a satisfactory theory
whereby to explain it. And this cannot be said of
any other theory of adaptive mechanisms in nature
that has ever been propounded. The so-called La-
marckian theory, for instance, cannot be brought to
bear upon the facts at all ; and on the theory of
special creation it is unintelligible why the phenomena
of protective colouring should be of such general
occurrence. For, in as far as protective colouring
is of advantage to the species which present it, it is
of corresponding disadvantage to tho^e other species
against the predatory nature of which it acts as a
defence And, of course, the same applies to yet
other species, if they serve as prey. Moreover, the
more minutely this subject is investigated in all its
details, the more exactly is it found to harmonise
with the naturalistic interpretation l.
1 Were it not that some of Darwin's critics have overlooked the very
point wherein the great value of protective colouring as evidence of
Evidences of Theory of Natural Selection. 319
In the first place, we always find a complete cor-
respondence between imitative colouring and instinctive
endowment. If a caterpillar exactly resembles the
colour of a twig, it also presents the instinct of
habitually reposing in the attitude which makes it
most resemble a twig — standing out from the branch
on which it rests at the same angle as is presented
by the real twigs of the tree on which it lives.
Here, again, is a bird protectively coloured so as to
resemble stones upon the rough ground where it
habitually lives ; and the drawing shows the attitude
in which the bird instinctively reposes, so as still further
to increase its resemblance to a stone. (Fig. 109.)
To take only one other instance, hares and rabbits,
like grouse and partridges — or like the plover just
alluded to, — instinctively crouch upon those surfaces
the colours of which they resemble ; and I have often
remarked that if, on account of any individual
peculiarity of coloration, the animal is not able thus
natural selection consists, it would be needless to observe that it does so
in the minuteness of the protective resemblance which in so many
cases is presented. Of course where the resemblance is only very general,
the phenomena might be ascribed to mere coincidence, of which the
instincts of the animal have taken advantage. But in the measure
that the resemblance becomes minutely detailed, the supposition
of mere coincidence is excluded, and the agency of some specially
adaptive cause demonstrated. Again, it is almost needless to say, no real
difficulty is presented (as has been alleged) by the cases above quoted of
seasonal imitations, on the ground that natural selection could not act
alternately on the same individual. Natural selection is not supposed to
act alternately on the same individual. It is supposed to act always in
the same manner, and if, as in the case of a regularly recurring change
in the colours of the environment, correspondingly recurrent changes are
lequired to appear in the colours of the animals, natural selection sets
its premium upon those individuals the constitutions of which best lend
themselves to seasonal changes of the needful kind — probably under the
influence of stimuli supplied by the changes of external conditions
(temperature, moisture, &c.).
320 Darwin, and after Darwin.
to secure concealment, it nevertheless exhibits the
instinct of crouching which is of benefit to all its
kind, although, from the accident of its own abnormal
colouring, this instinct is then actually detrimental
to the animal itself. For example, every sportsman
FIG. 109. — CEdicnemus crepitans, showing the instinctive attitude of
concealment. Drawn from a stuffed specimen in the British Museum,
\ nat. size, with appropriate surroundings supplied.
must have noticed that the somewhat rare melanic
variety of the common rabbit will crouch as steadily
as the normal brownish-gray type, notwithstanding
that, owing to its abnormal colour, a " nigger-rabbit "
thus renders itself the most conspicuous object in the
Evidences of Theory of Natural Selection. 321
landscape. In all such cases, of course, there has
been a deviation from the normal type in respect
of colour, with the result that the inherited instinct
is no longer in tune with the other endowments of
the animal. Such a variation of colour, therefore,
will tend to be suppressed by natural selection ; while
any variations which may bring the animal still more
closely to resemble its habitual surroundings will be
preserved. Thus we can understand the truly
wonderful extent to which this principle of protective
colouring has been carried in many cases where the
need of it has been most urgent.
Not only colour, but structure, may be profoundly
modified for the purposes of protective concealment.
Thus, caterpillars which resemble twigs do so not
only in respect of colour, but also of shape ; and this
even down to the most minute details in cases where
the adaptation is most complete : certain butterflies
and leaf-insects so precisely resemble the leaves upon
which, or among which, they live, that it is almost
impossible to detect them in the foliage — not only
the colour, the shape, and the venation being all
exactly imitated, but in some cases even the defects
to which the leaves are liable, in the way of fungoid
growths, &c. There are other insects which with
similar exactness resemble moss, lichens, and so forth.
A species of fish secures a complete resemblance to
bunches of sea-weed by a frond-like modification
of all its appendages, and so on through many other
instances. Now, in all such cases where there is so
precise an imitation, both in colour and structure,
it seems impossible to suggest any other explana-
tion of the facts than the one which is supplied by
* Y
FIG. i lo.— Imitative forms and colours in insects. Drawn from nature (R. Coll.
Surf. Afus.).
Evidences of Theory of Natural Selection. 323
Mr. Darwin's theory — namely, that the more perfect
the resemblance is caused to become through the
continuous influence of natural selection always picking
out the best imitations, the more highly discriminative
becomes the perception of those enemies against the
depredations of which this peculiar kind of protection
is developed ; so that, in virtue of this action and
re-action, eventually we have a degree of imitation
which renders it almost impossible for a naturalist
to detect the animal when living in its natural en-
vironment.
Warning Colotirs.
'In strange and glaring contrast to all these cases
of protective colouring, stand other cases of conspic-
uous colouring. Thus, for example, although there
are numberless species of caterpillars which present
in an astonishing degree the phenomena of pro-
tective colouring, there are numberless other species
which not only fail to present these phenomena in
any degree, but actually go to the opposite extreme
of presenting colours which appear to have been
developed for the sake of their conspicuousness. At
all events, these caterpillars are usually the most con-
spicuous objects in their surroundings, and therefore
in the early days of Darwinism they were regarded by
Darwin himself as presenting a formidable difficulty
in the way of his theory. To Mr. Wallace belongs
the merit of having cleared up this difficulty in
an extraordinarily successful manner. He virtually
reasoned thus. If the raison d'etre of protective
colouring be that of concealing agreeably flavoured
caterpillars from the eye- sight of birds, may not
Y 2
324 Darwin, and after Darwin.
the raison cfttre of conspicuous colouring be that
of protecting disagreeably flavoured caterpillars
from any possibility of being mistaken by birds?
Should this be the case, of course the more con-
spicuous the colouring the better would it be for
the caterpillars presenting it. Now as soon as this
suggestion was acted upon experimentally, it was
found to be borne out by facts. Birds could not be
induced to eat caterpillars of the kinds in question ;
and there is now no longer any doubt that their con-
spicuous colouring is correlated with their distasteful-
ness to birds, in the same way as the inconspicuous or
imitative colouring of other caterpillars is correlated
with their tastefulness to birds. Here then is yet
another instance, added to those already given, of
the verification yielded to the theory of natural
selection by its proved competency as a guide to facts
in nature ; for assuredly this particular class of facts
would never have been suspected but for its suggestive
agency.
As in the case of protective imitation, so in this
case of warning conspicuousness, not only colour, but
structure may be greatly modified for the purpose
of securing immunity from attack. Here, of course,
the object is to assume, as far as possible, a touch-
me-not appearance ; so that, although destitute of
any real means of offence, the creatures in question
present a fictitiously dangerous aspect. As the
Devil's-coach-horse turns up his stingless tail when
threatened by an enemy, so in numberless ways do
many harmless animals of all classes pretend to be
formidable. But the point now is that these instincts
of self-defence are often helped out by structural
Evidences of Theory of Natural Selection. 325
modifications, expressly and exclusively adapted to
this end. For example, what a remarkable series of
protective adjustments occurs in the life-history of the
Puss Moth — culminating with so comical an instance
of the particular device now under consideration as
the following. I quote the facts from Mr. E. B.
Poulton's admirable book on The Colours of Animals
(pp. 269-271).
The larva of the Puss Moth (Centra vinula) is very common
upon poplar and willow. The circular dome-like eggs are laid,
either singly or in little groups of two or three, upon the upper
side of the leaf, and being of a reddish colour strongly suggest
the appearance of little galls, or the results of some other injury
FIG. in. — The larva of Puss Moth (C. vinula) when undisturbed;
full-fed ; natural size.
to the leaf. The youngest larvae are black, and also rest upon
the upper surface of the leaf, resembling the dark patches which
are commonly seen in this position. As the larva grows, the
apparent black patch would cover too large a space, and would
lead to detection if it still occupied the whole surface of the body.
The latter gains a green ground-colour which harmonises with
the leaf, while the dark marking is chiefly confined to the back.
As growth proceeds the relative amount of green increases, and
the dark mark is thus prevented from attaining a size which
would render it too conspicuous. In the last stage of growth
the green larva becomes very large, and usually rests on the
twigs of its food-plant (Fig. 1 1 1). The dark colour is still present
on the back but is softened to a purplish tint, which tends to be
replaced by a combination of white and green in many of the
largest larvae. Such a larva is well concealed by General Pro-
326 Darwin, and after Darwin.
tective Resemblance, and one may search a long time before
finding it, although assured of its presence from the stripped
branches of the food-plant and the fasces on the ground beneath.
As soon as a large larva is discovered and disturbed it with-
draws its head into the first body-ring, inflating the margin,
which is of a bright red colour. There are two intensely black
spots on this margin in the
appropriate position for eyes,
and the whole appearance is
that of a large flat face ex-
tending to the outer edge of
the red margin (see Fig. 112).
The effect is an intensely ex-
aggerated caricature of a ver-
tebrate face, which is probably
""^ alarming to the vertebrate
FIG. 1 1 2.— The larva of Puss Moth enemies of the caterpillar. The
in its terrifying attitude after be- ., . a- ., r
j- * u j i 11 i j i terrifying effect is therefore
ing disturbed; full-fed j natural 3 °
sjze mimetic. The movements en-
tirely depend on tactile im-
pressions : when touched ever so lightly a healthy larva im-
mediately assumes the terrifying attitude, and turns so as to
present its full face towards the enemy ; if touched on the
other side or on the back it instantly turns its face in the ap-
propriate direction. The effect is also greatly strengthened by
two p.'nk whips which are swiftly protruded from the prongs
of the fork in which the body terminates. The prongs represent
the last pair of larval legs which have been greatly modified
from their ordinary shape and use. The end of the body is at
the same time curved forward over the back (generally much
further than in Fig. 1 12), so that the pink filaments are brandished
above the head.
Mimicry.
Lastly, these facts as to imitative and conspicuous
colouring lead on to the yet more remarkable facts of
what is called mimicry. By mimicry is meant the
imitation in form and colour of one species by another,
Evidences of Theory of Natural Selection. 327
in order that the imitating species may be mistaken
for the imitated, and thus participate in some ad-
vantage which the latter enjoys. For instance, if, as
in the case of the conspicuously-coloui^d caterpillars,
it is of advantage to an ill-savoured species that it
should hold out a warning to enemies, clearly it may
be of no less advantage to a well-savoured species
that it should borrow this flag, and thus be mistaken
for its ill-savoured neighbour. Now, the extent to
which this device of mimicry is carried is highly re-
markable, not only in respect of the number of its
cases, but also in respect of the astonishing accuracy
which in most of these cases is exhibited by the
imitation. There need be little or virtually no,
zoological affinity between the imitating and the
imitated forms ; that is to say, in some cases the
zoological affinity is not closer than ordinal, and
therefore cannot possibly be ascribed to kinship.
Like all the other branches of the general subject of
protective resemblance in form or colouring, this
branch has already been so largely illustrated by
previous writers, that, as in the previous cases, I need
only give one or two examples. Those which I
choose are chosen on account of the colours concerned
not being highly varied or brilliant, and therefore
lending themselves to less ineffectual treatment by
wood- engraving than is the case where attempts are
made to render by this means even more remarkable
instances. (Figs. 113, 114, 115.)
It is surely apparent, without further comment, that
it is impossible to imagine stronger evidence in favour
of natural selection as a true cause in nature, than is
furnished by this culminating fact in the matter of
FlG. 113. — Three cases of mimicry. Drawn from nature • first two pairs nat. size,
last pair s (/?. Coll. Surg. Mus.).
Evidences of Theory of Natural Selection. 329
protective resemblance, whereby it is shown that a
species of one genus, family, or even order, will
accurately mimic the appearance of a species be-
longing to another genus, family, or order, so as to
deceive its natural enemies into mistaking it for a
creature of so totally different a kind. And it must
be added that while this fact of mimicry is of ex-
VnLuceLLA INANS.
VULGARIS.
BOMB ~/LArJs.
BOMBL/S LAPIDAR/JS.
FlG. 114 — Two further cases of mimicry; flies resembling a wasp in
the one and a bee in the other. Drawn from nature : nat. size (Jf.
Coll. Surf. Mus.}.
traordinarily frequent occurrence, there can be no
possibility of our mistaking its purpose. For the fact
is never observable except in the case of species which
occupy the same area or district.
Such being what appears to me the only reasonable
view of the matter, I will now conclude this chapter
on the evidences of natural selection as at all events the
FlG. 115. — A case of mimicry where a non-venomous species of snake resembles a
venomous one Drawn from nature : 4 nat. size (R. Coll. Surg. Mus.).
Evidences of Theory of Natural Selection. 331
main factor of organic evolution, by simply adding
illustrations of two further cases of mimicry, which are
perhaps even more remarkable than any of the fore-
going examples. The first of the two (Fig. 1 15) speaks
for itself. The second will be rendered intelligible by
the following few words of explanation.
There are certain ants of the Amazons which
present the curious instinct of cutting off leaves from
trees, and carrying them like banners over their
heads to the hive, as represented in Fig. 116, B, where
one ant is shown without a leaf, and the others each
with a leaf. Their object in thus collecting leaves is
probably that of growing a fungus upon the "soil"
which is furnished by the leaves when decomposing.
But, be this as it may *, the only point we are now con-
cerned with is the appearance which these ants present
when engaged in their habitual operation of carrying
leaves. For it has been recently observed by Mr. W.
L. Sclater, that in the localities where these hymenop-
terous insects occur, there occurs also a homopterous
insect which mimics the ant, leaf and all, in a wonder-
fully deceptive manner. The leaf is imitated by the
thin flattened body of the insect, " which in its dorsal
aspect is so compressed laterally that it is no thicker
than a leaf, and terminates in a sharp jagged edge."
The colour is exactly the same as that of a leaf,
and the brown legs show themselves beneath the
green body in just the same way as those of the ant
show themselves beneath the leaf. So that both the
form and the colouring of the homopterous insect has
been brought to resemble, with singular exactness,
1 For a full account of this instinct and its probable purpose, see
Animal Intelligence, pp. 93-6.
332 Darwin, and after Darwin.
those belonging to a different order of insect, when
the latter is engaged in its peculiar .avocation. A
glance at the figure is enough to show the means
employed and the result attained In A, an ant and
its mimic are represented as a\jout 1\ times their
natural size, and both proceeding in the same direction.
It ought to be mentioned, however, that in reality
the margin of the leaf is seldom allowed to retain its
natural serrations as here depicted : the ants usually
gnaw the edge of the real leaf, so that the margin of
the false one bears an even closer resemblance to it
than the illustration represents. B is a drawing from
life of a group of five ants carrying leaves, and their
mimic walking beside them1.
1 Both drawings are reproduced from Mr. Poulton's paper upon the
subject (Proe. Zool. Soc., June 16, 1891).
F/G. 116
PROTECTIVE MIMICRY
CHAPTER IX.
CRITICISMS OF THE THEORY OF NATURAL
SELECTION.
I WILL now proceed to consider the various objec-
tions and difficulties which have hitherto been advanced
against the theory of natural selection.
Very early in the day Owen hurled the weight of
his authority against the new theory, and this with a
strength of onslaught which was only equalled by its
want of judgment. Indeed, it is painfully apparent
that he failed to apprehend the fundamental principles
of the Darwinian theory. For he says : —
Natural Selection is an explanation of the process [of trans-
mutation] of the same kind and value as that which has been
proffered of the mystery of " secretion." For example, a par-
ticular mass of matter in a living animal takes certain elements
out of the blood, and rejects them as " bile." Attributes were
given to the liver which can only be predicated of the whole
animal ; the " appetency " of the liver, it was said, was for the
elements of bile, and "biliosity," or the "hepatic sensation,"
guided the gland to their secretion. Such figurative language,
I need not say, explains absolutely nothing of the nature of
bilification l.
Assuredly, it was needless for Owen to say that
figurative language of this kind explains nothing ; but
1 Anatomy of Vertebrates, vol. iii. p. 794.
334 Darwin, and after Darwin.
it was little less than puerile in him to see no more
in the theory of natural selection than such a mere
figure of speech. To say that the liver selects the
elements of bile, or that nature selects specific types,
may both be equally unmeaning re-statements of facts ;
but when it is explained that the term natural selec-
tion, unlike that of " hepatic sensation," is used as
a shorthand expression for a whole group of well-
known natural causes — struggle, variation, survival,
heredity, — then it becomes evidence of an almost
childish want of thought to affirm that the expression
is figurative and nothing more. The doctrine of
natural selection may be a huge mistake ; but, if so,
this is not because it consists of any unmeaning
metaphor : it can only be because the combination of
natural causes which it suggests is not of the same
adequacy in fact as it is taken to be in theory.
Owen further objected that the struggle for existence
could only act as a cause of the extinction of species,
not of their origination — a view of the case which again
shows on his part a complete failure to grasp the
conception of Darwinism. Acting alone, the struggle
for existence could only cause extermination ; but
acting together with variation, survival, and heredity,
it may very well — for anything that Owen, or others
who followed in this line of criticism, show to the
contrary — have produced every species of plant and
animal that has ever appeared upon the face of the
earth.
Another and closely allied objection is, that the
theory of natural selection " personifies an abstrac-
tion." Or, as the Duke of Argyll states it, the theory
is " essentially the image of mechanical necessity
Criticisms of Theory of Natural Selection. 335
concealed under the clothes, and parading in the mask,
of mental purpose. The word ' natural ' suggests
Matter, and the physical forces. The word ' selection'
suggests Mind, and the powers of choice." This, how-
ever, is a mere quarrelling about words. Darwin
called the principle which he had discovered by the
name natural selection in order to mark the analogy
between it and artificial selection. No doubt in this
analogy there is not necessarily supposed to be in
nature any counterpart to the mind of the breeder, nor,
therefore, to his powers of intelligent choice. But
there is no need to limit the term selection (se and lego,
Gr. Aeyco) to powers of intelligent choice. As previously
remarked, a bank of sea-weed on the sea-shore may be
said to have been selected by the waves from all the
surrounding sand and stones. Similarly, we may say
that grain is selected from chaff by the wind in the
process of winnowing corn. Or, if it be thought that
there is any ambiguity involved in such a use of the
term in the case of " Natural Selection/' there is no
objection to employing the phrase which has been
coined by Mr. Spencer as its equivalent — namely,
" Survival of the Fittest." The point of the theory is,
that those organisms which are best suited to their
surroundings are allowed to live and to propagate,
while those which are less suited are eliminated ; and
whether we call this process a process of selection, or
call it by any other name, is clearly immaterial.
A material question is raised only when it is asked
whether the process is one that can be ascribed to
causation strictly natural. It is often denied that
such is the case, on the ground that natural selection
does not originate the variations which it favours,
336 Darwin, and' after Darwin.
but depends upon the variations being supplied by
some other means. For, it is said, all that natural
selection does is to preserve the suitable variations
after they have arisen. Natural selection does not
cause these suitable variations ; and therefore, it is
argued, Darwin and his followers are profoundly
mistaken in representing the principle as one which
produces adaptations. Now, although this objection
has been put forward by some of the most intelligent
minds in our generation, it appears to me to betoken
some extraordinary failure to appreciate the very
essence of Darwinian doctrine. No doubt it is per-
fectly true that natural selection does not produce
variations of any kind, whether beneficial or other-
wise. But if it be granted that variations of many
kinds are occurring in every generation, and that
natural selection is competent to preserve the more
favourable among them, then it appears to me
unquestionable that this principle of selection deserves
to be regarded as, in the full sense of the word, a
natural cause. The variations being expressly re-
garded by the theory as more or less promiscuous1,
1 The degree in which variability is indefinite, or, on the contrary,
determinate, is a question which is not yet ripe for decision — nor even,
in my opinion, for dicussion. But I may here state the following general
principles with regard to it
(1) It is evident that up to some point or another variations must be
pre-determined in definite lines. Men do not gather grapes from thorns,
figs from thistles, nor even moss-roses from sweet-briars. In other words,
" the nature of the organism " in all cases necessitates the limiting of
variations within certain bounds.
(2) But when the question is as to what these bounds may be, we can
only answer in a general way that, according to the general theory of
evolution, they must be such as are imposed by heredity, coupled with
the degree to which external conditions of life (and possibly also use-
inheritance) are capable, in given cases, of modifying congenital
Criticisms of Theory of Natiiral Selection. 337
survival of the fittest becomes the winnowing fan,
whose function it is to eliminate all the less fit in
each generation, in order to preserve the good grain,
out of which to constitute the next generation. And
as this process is supposed to be continuous through
successive generations, its action is supposed to be
cumulative, till from the eye of a worm there is
gradually developed the eye of an eagle. Therefore
it follows from these suppositions (which are not
disputed by the present objection), that if it had not
been for the process of selection, such development
would never have been begun ; and that in the exact
measure of its efficiency will the development pro-
ceed. But any agency without the operation of
which a result cannot take place may properly be
designated the cause of that result : it is the agency
which, in co-operation with all the other agencies
in the cosmos, produces that result.
characters. These are the only causes which the theory of descent can
consistently recognise as producing variations in determinate directions.
(3) Inasmuch as variation presupposes the existence of parts that
vary, and inasmuch as the variation of parts can only be in the alterna-
tive directions of increase or decrease around an average, it follows that,
in the first instance at all events, every variation, if determinate, must
be so only in one or other of these two opposite directions.
(4) In as far as variations are summated in successive generations, so
as eventually to give rise to new structures, organs, mechanisms, &c.,
natural selection is theoretically competent to explain the facts, without
our having to postulate the operation of unknown causes producing
variations in determinate lines, — or not fuither than is stated in para-
graphs i and 2.
(5) Nevertheless, it does not follow that there are not such other
unknown causes ; and, if there are, of course the importance of natural
selection as a cause of adaptive modification would be limited in pro-
portion to their number and the extent of their operation. But it is for
those who, like the late Professors Asa Gray and Nageli, maintain the
existence of such causes, to substantiate their belief by indicating them.
* 7.
338 Darwin, and after Darwin.
Take any analogous case. The selective agency
of specific gravity which is utilised in gold-washing
does not create the original differences between gold-
dust and dust of all other kinds. But these differ-
ences being presented by as many different bodies
in nature, the gold-washer takes advantage oi the
selective agency in question, and, by using it as a
cause of segregation, is enabled to separate the gold
from all the earths with which it may happen to be
mixed. So far as the objects of the gold-washer are
concerned, it is immaterial with what other earths
the gold-dust may happen to be mixed. For
although gold-dust may occur in intimate association
with earths of various kinds in various proportions,
and although in each case the particular admixture
which occurs must have been due to definite causes,
these things, in relation to the selective process of
the washer, are what is called accidental : that is
to say, they have nothing to do with the causative
action of the selective process. Now, in precisely
the same sense Darwin calls the multitudinous varia-
tions of plants and animals accidental. By so calling
them he expressly says he does not suppose them
to be accidental in the sense of not all being due
to definite causes. But they are accidental in rela-
tion to the sifting process of natural selection : all
that they have to do is to furnish the promiscuous
material on which this sifting process acts.
Or let us take an even closer analogy. The power
of selective breeding by man is so wonderful, that in
the course of successive generations all kinds of
peculiarities as to size, shape, colour, special appen-
dages or abortions, &c., can be produced at pleasure,
Criticisms of Theory of Natural Selection. 339
as we saw in the last chapter. Now all the promis-
cuous-variations which are supplied to the breeder,
and out of which, by selecting only those that are
suited to his purpose, he is able to produce the
required result — all those promiscuous variations, in
relation to that purpose, are accidental. Therefore
the selective agency of the breeder deserves to be
regarded as the cause of that which it produces, or
of that which could not have been produced but for
the operation of such agency. But where is thf
difference between artificial and natural selection in
this respect ? And, if there is no difference, is not
natural selection as much entitled to be regarded as a
true cause of the origin of natural species, as artificial
selection is to be regarded as a true cause of our
domesticated races? Here, as in the case of the
previous illustration, if there be any ambiguity in
speaking of variations as accidental, it arises from
the incorrect or undefined manner in which the term
"accidental" is used by Darwin's critics. In its
original and philosophically-correct usage, the term
"accident" signifies a property or quality not essential
to our conception of a substance : hence, it has come
to mean anything that happens as a result of unfore-
seen causes — or, lastly, that which is causeless. But,
as we know that nothing can happen without causes
of some kind, the term " accident " is divested of real
meaning when it is used in the last of these senses.
Yet this is the sense that is sought to be placed upon
it by the objection which we are considering. If the
objectors will but understand the term in its correct
philosophical sense — or in the only sense in which
it presents any meaning at all, — they will see that
Z 2
34-O Darwin, and after Darwin.
Darwinians are both logically and historically justified
in employing the word " accidental " as the word
which serves most properly to convey the meaning
that they intend — namely, variations due to causes
accidental to the struggle for existence. Similarly,
when it is said that variations are " spontaneous,"
or even " fortuitous," nothing further is meant than
that we do not know the causes which lead to them, and
that, so far as the principle of selection is concerned,
it is immaterial what these causes may be. Or, to
revert to our former illustration, the various weights
of different kinds of earths are no doubt all due to
definite causes ; but, in relation to the selective
action of the gold-washer, all the different weights
of whatever kinds of earth he may happen to in-
clude in his washing-apparatus are, strictly speaking^
accidental. And as at different washings he meets
with different proportions of heavy earths with light
ones, and as these "variations "are immaterial to him,
he may colloquially speak of them as " fortuitous," or
due to ': chance," even though he knows that at each
washing they must have been determined by definite
causes.
More adequately to deal with this merely formal
objection, however, would involve more logic-chop-
ping than is desirable on the present occasion. But
I have already dealt with it fully elsewhere, — viz. in
The Contemporary Review for June, 1888, to which
therefore I may refer any one who is interested in
dialectics of this kind l.
* Within the last few months this objection has been presented anew
6y Mr. D. Syme, whose book On the Modification of Organisms exhibits
a curious combination of shrewd criticisms with almost ludicrous mis-
Criticisms of Theory of Natural Selection. 341
I will now pass on to consider another miscon-
ception of the Darwinian theory, which is very
prevalent in the public mind. It is virtually asked,
If some species are supposed to have been improved
by natural selection, why have not all species been
similarly improved? Why should not all inverte-
understandings. One of the latter it is necessary to state, because it
pervades the quotation which I am about to supply. He everywhere
compares "natural selection" with "the struggle for existence," uses
them as convertible terms, and while absurdly stating that " Darwin
defines natural selection as the struggle for existence,'' complains of
" the liability of error, both on his own part and on the part of his
readers," which arises from his not having everywhere adheted to this
definition ! (p. 8).
" Darwin has put forth two distinct and contradictory theories of the
functions of natural selection. According to the one theory natural
selection is selective or preservative, and nothing more. According to
the other theory natural selection creates the variations (!) ... It cer-
tainly seems absurd to speak of natural selection, or the struggle for
existence, as selective or preservative, for the struggle for existence
does not preserve at all, not even the fit variations, as both the fit
and the unfit struggle for existence, the unfit naturally more than the
fit, and the fit are preserved, not in consequence of the struggle, but in
consequence of their fitness. Suppose two varieties of the same species
are driven, by an increase of their numbers, to seek for subsistence in a
colder region than they have been accustomed to, and that one of these
varieties had a hardier constitution than the other ; and let us suppose
that the former withstood the severe climate better than the latter, and
consequently survived, while the other perished. In this case the hardier
survived, not because of the struggle, but because it had a constitution
better adapted to the climate. I wish to ascertain if a certain metal in
my possession is gold or some baser metal, and I apply the usual test ;
but the mere fact of my testing this metal would not make it gold or any
other kind of metal."
1 have thought it worth while to quote this passage for the sake of
showing the extraordinary confusion of mind which still prevails on the
part of Darwin's critics, even with reference to the very fundamental
parts of his theory. For, as I have said, the writer of this passage shows
himself a shrewd critic in some other parts of his essay, where he is not
engaged especially on the theory of natural selection.
342 Darwin, and after Darwin.
brated animals have risen into vertebrated ? Or why
should not all monkeys have become men ?
The answers are manifold. In the first place, it
by no means follows that because an advance in
organization has proved itself of benefit in the case
of one form of life, therefore any or every other
form would have been similarly benefited by a
similar advance. The business of natural selection
is to bring this and that form of life into the closest
harmony with its environment that all the conditions
of the case permit. Sometimes it will happen that
the harmony will admit of being improved by an
improvement of organization. But just as often it
will happen that it will be best secured by leaving
matters as they are. If, therefore, an organism has
already been brought into a tolerably full degree of
harmony with its environment, natural selection will
not try to change it so long as the environment
remains unchanged ; and this, no doubt, is the reason
why some species have survived through enormous
periods of geological time without having undergone
any change. Again, as we saw in a previous chapter,
there are yet other cases where, on account of some
change in the environment or even in the habits of the
organisms themselves, adaption will be best secured
by an active reversal of natural selection, with the
result of causing degeneration.
But, it is sometimes further urged, there are cases
where we cannot doubt that improvement of organi-
zation would have been, of benefit to species ; and
yet such improvement has not taken place — as, for in-
stance, in the case all monkeys not turning into men.
Here, however, we must remember that the operation
Criticisms of Theory of Natural Selection. 343
of natural selection in any case depends upon a variety
of highly complex conditions; and, therefore, that the
fact of all those conditions having been satisfied in
one instance is no reason for concluding that they
must also have been satisfied in other instances. Take,
for example, the case of monkeys passing into men.
The wonder to me appears to be that this improve-
ment should have taken place in even one line of
descent ; not that, having taken place in one line,
it should not also have taken place in other lines.
For how enormously complex must have been the
conditions — physical, anatomical, physiological, psy-
chological, sociological — which by their happy con-
junction first began to raise the inarticulate cries of
an ape into the rational speech of a man. Therefore,
the more that we appreciate the superiority of a man
to an ape, the less ought we to countenance this
supposed objection to Darwin's theory — namely, that
natural selection has not effected the change in more
than one line of descent.
Even in the case of two races of mankind where
one has risen higher in the scale of civilization
than another, it is now generally impossible to assign
the particular causes of the difference ; much more,
then, must this be impossible in the case of still more
remote conditions which have led to the divergence
of species. The requisite variations may not have
arisen in the one line of descent which did arise in
the other ; or if they did arise in both, some
counterbalancing disadvantages may have attended
their initial development in the one case which
did not obtain in the other. In shoit, where
so exceedingly complex a play of conditions are
344 Darwin, and after Darwin.
concerned, the only wonder would be if two different
lines of descent had happened to present two in-
dependent and yet perfectly parallel lines of history.
These general considerations would apply equally
to the great majority of other cases where some types
have made great advances upon others, notwithstand-
ing that we can see no reason why the latter should
not in this respect have imitated the former. But
there is yet a further consideration which must be
taken into account. The struggle for existence is
always most keen between closely allied species, be-
cause, from the similarity of their forms, habits, needs,
&c., they are in closest competition. Therefore it often
happens that the mere fact of one species having made
an advance upon others of itself precludes the others
from making any similar advance: the field, so to
speak, has already been occupied as regards that
particular improvement, and where the struggle for
existence is concerned possession is emphatically nine
points of the law. For example, to return to the
case of apes becoming men, the fact of one rational
species having been already evolved (even if the
rational faculty were at first but dimly nascent) must
make an enormous change in the conditions as
regards the possibility of any other such species being
subsequently evolved — unless, of course, it be by
way of descent from the rational one. Or, as Sir
Charles Lyell has well put it, two rational species can
never coexist on the globe, although the descendants
of one rational species may in time become trans-
formed into another single rational species l.
In view of such considerations, another and exactly
1 Principles of Geology, vol. ii. p. 487 (nth ed.).
Criticisms of Theory of Natural Selection. 345
opposite objection has sometimes been urged — viz.
that we ought never to find inferior forms of or-
ganization in company with superior, because in the
struggle for existence the latter ought to have exter-
minated the former. Or, to quote the most recent
expression of this view, "in every locality there
would only be one species, and that the most highly
organized ; and thus a few superior races would par-
tition the earth amongst them to the entire exclusion
of the innumerable varieties, species, genera, and orders
which now inhabit it V Of course to this statement
it would be sufficient to enquire, On what would these
few supremely organized species subsist? Unless
manna fell from heaven for their especial benefit, it
would appear that such forms could under no circum-
stances be the most improved forms ; in exterminating
others on such a scale as this, they would themselves
be quickly, and very literally, improved off the face
of the earth. But even when the statement is not
made in so extravagant a form as this, it must neces-
sarily be futile as an objection unless it has first been
shown that we know exactly all the conditions of the
complex struggle for existence between the higher
and lower forms in question. And this it is impos-
sible that we ever can know. The mere fact that
one form has been changed in virtue of this struggle
must in many cases of itself determine a change in
the conditions of the struggle. Again, the other
and closely allied forms (and these furnish the best
grounds for the objection) may also have under-
gone defensive changes, although these may be
less conspicuous to our observation, or perhaps less
1 Syme, on the Modification of Organisms, p. 46.
346 Darwin, and after Darwin.
suggestive of "improvement" to our imperfect
means of judging. Lastly, not to continue citing
an endless number of such considerations, there is
the broad fact that it is only to those cases where,
for some reason or another, the lower forms have
not been exposed to a struggle of fatal intensity, that
the objection applies. But we know that in millions
of other cases the lower (i.e. less fitted) forms have
succumbed, and therefore I do not see that the ob-
jection has any ground to stand upon. That there is
a general tendency for lower forms to yield their
places to higher is shown by the gradual advance of
organization throughout geological time ; for if all the
inferior forms had survived, the earth could not have
contained them, unless she had been continually
growing into something like the size of Jupiter.
And if it be asked why any of the inferior forms
have survived, the answer has already been given,
as above.
There is only one other remark to be made in this
connexion. Mr. Syme chooses two cases as illus-
trations of the supposed difficulty. These are suf-
ficiently diverse — viz. Foraminifera and Man. Touch-
ing the former, there is notLing that need be added
to the general answer just given. But with regard to
the latter it must be observed that the dominion of
natural selection as between different races of man-
kind is greatly restricted by the presence of rationality.
Competition in the human species is more concerned
with wits and ideas than with nails and teeth ; and
therefore the "struggle" between man and man is
not so much for actual being, as for well-being. Con-
sequently, in regard to the present objection, the
Criticisms of Theory of Natural Selection. 347
human species furnishes the worst example that could
have been chosen.
Hitherto I have been considering objections which
arise from misapprehensions of Darwin's theory. I
will now go on to consider a logically sound ob-
jection, which nevertheless is equally futile, because,
although it does not depend on any misapprehension
of the theory, it is not itself supported by fact
The objection is the same as that which we have
already considered in relation to the general theory of
descent — namely, that similar organs or structures
are to be met with in widely different branches of the
tree of life. Now this would be an objection fatal to
the theory of natural selection, supposing these organs
or structures in the cases compared are not merely
analogous, but also homologous. For it would be
incredible that in two totally different lines of descent
one and the same structure should have been built up
independently by two parallel series of variations, and
that in these two lines of descent it should always and
independently have ministered to the same function.
On the other hand, there would be nothing against
the theory of natural selection in the fact that two
structures, not homologous, should come by inde-
pendent variation in two different lines of descent to
be adapted to perform the same function. For it
belongs to the very essence of the theory of natural
selection that a useful function should be secured by
favourable variations of whatever structural material
may happen to be presented by different organic
types. Flying, for instance, is a very useful function,
and it has been developed independently in at least
348 Darwin, and after Darwin.
four different lines of descent — namely, the insects,
reptiles, birds, and mammals. Now if in all, or in-
deed in any, of these four cases the wings had been
developed on the same anatomical pattern, so as not
only to present the analogical resemblance which it is
necessary that they should present in order to dis-
charge their common function of flying, but likewise
an homologous or structural resemblance, showing
that they had been formed on the same anatomical
" plan/' — if such has been the case, I say, the theory
of natural selection would certainly be destroyed.
Now it has been alleged by competent naturalists
that there are several such cases in organic nature.
We have already noticed in a previous chapter
(pp. 58, 59), that Mr. Mivart has instanced the eye
of the cuttle-fish as not only analogous to, but also
homologous with, the eye of a true fish — that is to
say, the eye of a mollusk with the eye of a vertebrate.
And he has also instanced the remarkable resemblance
of a shrew to a mouse — that is, of an insectivorous
mammal to a rodent — not to mention other cases.
In the chapter alluded to these instances of homo-
logy, alleged to occur in different branches of the tree
of life, were considered with reference to the process
of organic evolution as a fact : they are now being
considered with reference to the agency of natural
selection as a method. And just as in the former
case it was shown, that if any such alleged instances
could be proved, the proof would be fatal to the
general theory of organic evolution by physical
causes, so in the present case, if this could be
proved, it would be equally fatal to the more spe-
cial theory of natural selection. But, as we have
Criticisms of Theory of Natural Selection. 349
before seen, no single case of this kind has ever been
made out; and, therefore, not only does this sup-
posed objection fall to the ground, but in so doing it
furnishes an additional argument in favour of natural
selection. For in the earlier chapter just alluded to
I showed that this great and general fact of our no-
where being able to find two homologous structures
in different branches of the tree of life, was the
strongest possible testimony in favour of the theory
of evolution. And, by parity of reasoning, I now
adduce it as equally strong evidence of natural selec-
tion having been the cause of adaptive structures,
independently developed in all the different lines of
descent. For the alternative is between adaptations
having been caused by natural selection or by super-
natural design. Now, if adaptations were caused by
natural selection, we can very well understand why
they should never be homologous in different lines of
descent, even in cases where they have been brought
to be so closely analogous as to have deceived so
good a naturalist as Mr. Mivart. Indeed, as I have
already observed, so well can we understand this,
that any single instance to the contrary would be
sufficient to destroy the theory of natural selection in
toto, unless the structure be one of a very simple type.
But on the other hand, it is impossible to suggest
any rational explanation why, if all adaptations are
due to supernatural design, such scrupulous care
should have been taken never to allow homologous
adaptations to occur in different divisions of the animal
or vegetable kingdoms. Why, for instance, should
the eye of a cuttle-fish not have been constructed on
the same ideal pattern as that of vertebrate ? Or why,
350 Darwin, and after Darwin.
among the thousands of vertebrated species, should no
one of their eyes be constructed on the ideal pattern
that was devised for the cuttle-fish ? Of course it may
be answered that perhaps there was some hidden reason
why the design should never have allowed an adapta-
tion which it had devised for one division of organic
nature to appear in another — even in cases where the
new design necessitated the closest possible resem-
blance in everything else, save in the matter of anatomi-
cal homology. Undoubtedly such may have been the
case — or rather such must have been the case — if the
theory of special design is true. But where the ques-
tion is as to the truth of this theory, I think there can
be no doubt that its rival gains an enormous advan-
tage by being able to explain why the facts are such
as they are instead of being obliged to take refuge
in hypothetical possibilities of a confessedly unsub-
stantiated and apparently unsubstantial kind.
Therefore, as far as this objection to the theory of
natural selection is concerned — or the allegation that
homologous structures occur in different divisions of
organic nature — not only does it fall to the ground,
but positively becomes itself converted into one of the
strongest arguments in favour of the theory. As
soon as the allegation is found to be baseless, the
very fact that it cannot be brought to bear upon any
one of all the millions of adaptive structures in
organic nature becomes a tact of vast significance on
the opposite side.
The next difficulty to which I shall allude is that
of explaining by the theory of natural selection the
preservation of the first beginnings of structures which
Criticisms of Theory oj Natural Selection. 3 5 1
are then useless, though afterwards, when more fully
developed, they become useful. For it belongs to
the very essence of the theory of natural selection,
that a structure must be supposed already useful
before it can come under the influence of natural
selection : therefore the theory seems incapable of
explaining the origin and conservation of incipient
organs, or organs which are not yet sufficiently
developed to be of any service to the organisms
presenting them.
This objection is one that has been advanced by
all the critics of Darwinism ; but has been presented
with most ability and force by the Duke of Argyll. I
will therefore state it in his words.
If the doctrine of evolution be true — that is to say, if all
organic creatures have been developed by ordinary generation
from parents— then it follows of necessity that the primaeval
germs must have contained potentially the whole succeeding
series. Moreover, if that series has been developed gradually
and very slowly, it follows, also as a matter of necessity, that
every mpdification of structure must have been functionless at
first, when it began to appear. . . . Things cannot be selected
until they have first been produced. Nor can any structure
be selected by utility in the struggle for existence until it has
not only been produced, but has been so far perfected as to
actually be used.
The Duke proceeds to argue that all adaptive
structures must therefore originally have been due
to special design : in the earlier stages of their develop-
ment they must all have been what he calls "pro-
phetic germs." Not yet themselves of any use,
and therefore not yet capable of being improved by
natural selection, both in their origin and in the first
stages (at all events) of their development, they must
352 Darwin, and after Darwin,
be regarded as intentionally preparatory to the
various uses which they subsequently acquire.
Now this argument, forcible as it appears at first
sight, is really at fault both in its premiss and in its
conclusion. By which I mean that, in the first place
the premiss is not true, and, in the next place, that
even if it were, the conclusion would not necessarily
follow. The premiss is, "that every modification of
structure must have been functionless at first, when it
began to appear ; " and the conclusion is, that, qua
functionless, such a modification cannot have been
caused by natural selection. I will consider these two
points separately.
First as to the premiss, it is not true that every
modification of structure must necessarily be function-
less when it first begins to appear. There are two
very good reasons why such should not be the case in
all instances, even if it should be the case in some.
For, as a matter of observable fact, a very large
proportional number of incipient organs are useful
from the very moment of their inception. Take, for
example, what is perhaps the most wonderful instance
of refined mechanism in nature — the eye of a verte-
brated animal. Comparative anatomy and embryology
combine to testify that this organ had its origin in
modifications of the endings of the ordinary nerves
of the skin. Now it is evident that from the very
first any modification of a cutaneous nerve whereby it
was rendered able, in however small a degree, to be
differently affected by light and by darkness would be
of benefit to the creature presenting it ; for the
creature would thus be able to seek the one and shun
the other according to the requirements of its life.
Criticisms of Theory of Natural Selection. 353
And being thus useful from the very moment of its
inception, it would afterwards be gradually improved
as variations of more and more utility presented them-
selves, until not only would finer and finer degrees of
difference between light and shade become perceptible,
but even the outlines of solid bodies would begin to
be appreciated. And so on, stage by stage, till from
an ordinary nerve-ending in the skin is evolved the
eye of an eagle.
Moreover, in this particular instance there is very
good reason to suppose that the modification of the
cutaneous nerves in question began by a progressive
increase in their sensitiveness to temperature. Wher-
ever dark pigment happened to be deposited in the
skin — and we know that in all animals it is apt to be
deposited in points and patches, as it were by accident,
or without any "prophecy" as to future uses, — the
cutaneous nerves in its vicinity would be better able
to appreciate the difference between sun and shade in
respect of temperature, even though as yet there were
no change at all in these cutaneous nerves tending to
make them responsive to light. Now it is easy to see
how, from such a purely accidental beginning, natural
selection would have had from the first sufficient
material to act upon. It being of advantage to a
lowly creature that it should distinguish with more
and more delicacy, or with more and more rapidity,
between light and darkness by means of its thermal
sensations, the pigment spots in the skin would be
rendered permanent by natural selection, while the
nerves in that region would by the same agency
be rendered more and more specialized as organs
adapted to perceive changes of temperature, until
* A a
354 Darwin, and after Darwin.
from the stage of responding to the thermal rays
of the non-luminous spectrum alone, they become
capable of responding also to luminous.
So much, then, for the first consideration which
serves to invalidate the Duke's premiss. The second
consideration is, that very often an organ which began
by being useful for the performance of one function,
after having been fully developed for the performance
of that function, finds itself, so to speak, accidentally
fitted to the performance of some other and even more
important function, which it thereupon begins to
discharge, and so to undergo a new course of adaptive
development. In such cases, and so far as the new
function is concerned, the difficulty touching the first
inception of an organ does not apply; for here the
organ has already been built up by natural selection
for one purpose, before it begins to discharge the
other. As an example of such a case we may take
the lung of an air-breathing animal. Originally the
lung was a swim-bladder, or float, and as such it was
of use to the aquatic ancestors of terrestrial animals.
But as these ancestors gradually became more and more
amphibious in their habits, the swim-bladder began
more and more to discharge the function of a lung,
and so to take a wholly new point of departure as
regards its developmental history. But clearly there
is here no difficulty with regard to the inception of its
new function, because the organ was already well
developed for one purpose before it began to serve
another. Or, to take only one additional example,
there are few structures in the animal kingdom so
remarkable in respect of adaptation as is the wing of
a bird or a bat ; and at first sight it might well appear
Criticisms of Theory of Natural Selection. 3 .5 5
that a wing could be of no conceivable use until it had
already acquired enormous proportional dimensions,
as well as an immense amount of special elaboration
as to its general form, size of muscle, amount of blood-
supply, and so on. For, obviously, not until it had
attained all these things could it even begin to raise
the animal in the air. But observe how fallacious is
this argument. Although it is perfectly true that a
wing could be of no use as a wing until sufficiently
developed to serve the purpose of flight, this is merely
to say that until it has become a wing it is no use as
a wing. It does not, however, follow that on this
account it was of no prior use for any other purpose.
The first modifications of the fore-limb which ended
in its becoming an organ of flight may very well have
been due to adapting it as an organ for increased
rapidity of locomotion of other kinds — whether on
land as in the case of its now degenerated form in the
ostrich, or in water as in the case of the expanded fins
of fish. Indeed, we may see the actual process of
transition from the one function to the other in the
case of " flying-fish." Here the progressive expansion
of the pectoral fins must certainly have been always
of use for continuously promoting rapidity of loco-
motion through water ; and thus natural selection
may have continuously increased their development
until they now begin to serve also as wings for carry-
ing the animal a short distance through air. Again,
in the case of the so-called flying squirrels we find the
limbs united to the body by means of large extensions
of the skin, so that when jumping from one tree to
another the animal is able to sustain itself through a
long distance in the air by merely spreading out its
A a 2
356 Darwin, and after Darwin.
limbs, and thus allowing the skin-extensions to act
after the manner of a parachute. Here, of course, we
have not yet got a wing, any more than we have in
the case of the flying-fish ; but we have the founda-
tions laid for the possible development of a future wing,
upon a somewhat similar plan as that which has been
so wonderfully perfected in the case of bats. And
through all the stages of progressive expansion which
the skin of the squirrel has undergone, the expansion
has been of use, even though it has not yet so much
as begun to acquire the distinctive functions of a wing.
Here, then, there is obviously nothing " prophetic " in
the matter, any more than there was in the case of the
swim-bladder and the lung, or in that of the nerve-
ending and the eye. In short, it is the business .of
natural selection to secure the highest available degree
of adaptation for the time being ; and, in doing this,
it not unfrequently happens that an extreme develop-
ment of a structure in one direction (produced by
natural selection for the sake of better and better
adapting the structure to perform some particular
function) ends by beginning to adapt it to the perform-
ance of some other function. And, whenever this
happens to be the case, natural selection forthwith
begins to act upon the structure, so to speak, from a
new point of departure.
So much, then, for the Duke's premiss — namely,
that " every modification of structure must have been
functionless at first, when it began to appear." This
premiss is clearly opposed to observable fact But
now, the second position is that, even if this were not
so, the Duke's conclusion would not follow. This
conclusion, it will be remembered, is, that if incipient
Criticisms of Theory of Natural Selection. 357
structures are useless, it necessarily follows that natural
selection can have had no part whatever in their
inception. Now, this is a conclusion which does not
" necessarily " follow. Even if it be granted that there
are structures which in their first beginnings are not
of any use at all for any purpose, it is still possible
that they may owe their origin to natural selection —
not indeed directly, but indirectly. This possibility
arises from the occurrence in nature of a principle
which has been called the Correlation of Growth.
Mr. Darwin, who has paid more attention to this
matter than any other writer, has shown, in consider-
able detail, that all the parts of any given organism
are so intimately bound together, or so mutually
dependent upon each other, that when one part is
caused to change by means of natural selection, some
other parts are very likely to undergo modification as
a consequence. For example, there are several kinds
of domesticated pigeons and fowls, which grow peculiar
wing-like feathers on the feet. These are quite unlike
all the other feathers in the animal, except those of
the wing, to which they bear a very remarkable re-
semblance. Mr. Darwin records the case of a bantam
where these wing-like feathers were nine inches in
length, and I have myself seen a pigeon where they
reproduced upon the feet a close imitation of the
different kinds of feathers which occupy homologous
positions in the wing — primaries, secondaries, and
tertiaries all being distinctly repeated in their proper
anatomical relations. Furthermore, in this case,
as in most cases where such wing-feathers occur
upon the feet, the third and fourth toes were partly
united by skin; and, as is well known, in the wing
358 Darwin, and after Darwin.
of a bird the third and fourth digits are completely
united by skin ; " so that in feather-footed pigeons,
not only does the exterior surface support a row of
long feathers, like wing-feathers [which, as just stated,
may in some cases be obviously differentiated into
primaries, secondaries and tertiaries], but the very
same digits which in the wing are completely united
by skin become partially united by skin in the feet ;
and thus by the law of correlated variation of homo-
logous parts, we can understand the curious connexion
of feathered legs and membrane between the two outer
toes V The illustration is drawn from the specimen
to which I have referred.
Many similar instances of the same law are to be
met with throughout organic nature ; and it is evident
that in this principle we find a conceivable explanation
of the origin of such adaptive structures as could not
have been originated by natural selection acting directly
upon themselves : they may have been originated by
natural selection developing other adaptive structures
elsewhere in the organism, the gradual evolution of
which has entailed the production of these by correla-
tion of growth. And, if so, when once started in this
way, these structures, because thus accidentally useful,
will now themselves come under the direct action of
natural selection, and so have their further evolution
determined with or without the correlated association
which first led to their inception.
Of course it must be understood that in thus apply-
ing the principle of correlated growth, to explain the
origin of adaptive structures where it is impossible to
explain such origin by natural selection having from
1 Variation of Plants and Animals, vol. ii. p. 315.
Criticisms of Theory of Natural Selection. 359
the first acted directly upon these structures them-
selves, Darwinists do not suppose that in all — or even
in most — cases of correlated growth the correlated
structures are of use. On the contrary, it is well
known that structures due to correlated growth are,
FIG. 117.— Feather-footed pigeon. Drawn from nature.
as a rule, useless. Being only the by-products of
adaptive changes going on elsewhere, in any given
case the chances are against these correlated effects
being themselves of any utilitarian significance ; and,
therefore, as a matter of fact, correlated growths
appear to be usually meaningless from the point of
360 Darwin, and after Darwin.
view of adaptation. Still, on the doctrine of chances,
it is to be expected that sometimes a change of
structure which has thus been indirectly produced by
correlation of growth might happen to prove useful
for some purpose or another ; and in as many cases
as such indirectly produced structures do prove useful,
they will straightway begin to be improved by the
direct action of natural selection. In all such cases,
therefore, we should have an explanation of the origin
of such a structure, which is the only point that we
are now considering.
I think, then, that all this effectually disposes of
the doctrine of " prophetic germs." But, before
leaving the subject, I should like to make one
further statement of greater generality than any which
I have hitherto advanced. This statement is, that we
must remember how large a stock of meaningless
structures are always being produced in the course of
specific transmutations, not only by correlation of
growth, which we have just been considering, but also
by the direct action of external conditions, together
with the constant play of all the many and complex
forces internal to organisms themselves. In other
words, important as the principle of correlation
undoubtedly is, we must remember that even this is
very far from being the only principle which is con-
cerned in the origination of structures that may or may
not chance to be useful. Therefore, it is not only
natural selection when operating indirectly through
the correlation of growth that is competent to produce
new structures without reference to utility. In all
the complex action and reaction of internal and ex-
ternal forces, new variations are perpetually arising
Criticisms of Theory of Natural Selection. 361
without any reference to utility, either present or
future. Among all this multitude of promiscuous
variations, the chances must be that some percentage
will prove of some service, either from the first moment
of their appearance, or else after they have undergone
some amount of development. Such development
prior to utility may be due, either to correlation of
growth, to the structure having previously performed
some other function, as already explained, or else to
a continued operation of the causes which were con-
cerned in the first appearance of originally useless
characters. In a series of chapters which will be
devoted to the whole question of utility in the next
volume, I shall hope to give very good reasons for
concluding that useless characters are not only of
highly frequent occurrence, but are due to a variety of
other causes besides correlation of growth. And, if so,
the possibility of originally useless characters happen-
ing in some cases to become, by increased develop-
ment, useful characters, is correspondingly increased.
Among a hundred varietal or specific characters which
are directly produced in as many different species by
a change of climate, for example, some five or six may
be potentially useful : that is to say, characters thus
adventitiously produced in an incipient form may
only require to be further developed by a continuance
of the same causes as first originated them, in order
that some percentage of the whole number shall become
of some degree of use. Those professed followers of
Darwin, therefore, who without any reason — or, as it
appears to me, against all reason — deny the pos-
sibility of useless specific characters in any case or
in any degree (unless correlated with useful characters),
362 Darwin, and after Darwin.
are playing into the hands of Darwin's critics by
indirectly countenancing the difficulty which we are
now considering. For, if correlation of growth is
unreasonably supposed to be the only possible cause
of the origin of incipient structures which are not use-
ful from the first moment of their inception, clearly
the field is greatly narrowed as regards the occurrence
of incipient characters sufficient in amount — and, still
more, in constancy of appearance and persistency of
transmission — to admit of furnishing material for the
working of natural selection. But in the measure that
incipient characters — whether varietal or specific —
are recognised as not always or "necessarily" useful
from the moment of their inception, and yet capable of
being developed to a certain extent by the causes
which first led to their occurrence, in that measure is
this line of criticism closed. For of all the variations
which thus occur, it is only those which afterwards
prove of any use that are laid hold upon and wrought
up by natural selection into adaptive structures, or
working organs. And, therefore, what we see in
organic nature is the net outcome of the development
of all the happy chances. So it comes that the
appearance presented by organic nature as a whole is
that of a continual fulfilment of structural prophecies,
when, in point of fact, if we had a similar record of all
the other variations it would be seen that possibly
not one such prophecy in a thousand is ever destined
to be fulfilled.
Here, then, I feel justified in finally taking leave of
the difficulty from the uselessness of incipient organs,
as this difficulty has been presented, in varying degrees
Criticisms of Theory of Natural Selection. 363
of emphasis, by the Duke of Argyll, Mr. Mivart, Pro-
fessors Nageli, Bronn, Broca, Eimer, and, indeed, by all
other writers who have hitherto advanced it. For, as
thus presented, I think I have shown that it admits of
being adequately met. But now, I must confess, to me
individually it does appear that behind this erroneous
presentation of the difficulty there lies another question,
which is deserving of much more serious attention.
For although it admits of being easily shown — as I have
just shown — that the difficulty as ordinarily presented
fails on account of its extravagance, the question
remains whether, if stated with more moderation, a
real difficulty might not be found to remain.
My quarrel with the conclusion, like my quarrel
with the premiss,, is due to its universality. By say-
ing in the premiss that all incipient organs are neces-
sarily useless at the time of their inception, these
writers admit of being controverted by fact ; and by
saying in the conclusion that, if all incipient organs
are useless, it necessarily follows that in no case can
natural selection have been the cause of building up
an organ until it becomes useful, they admit of being
controverted by logic. For, even if the premiss were
true in fact — namely, that all incipient organs are use-
less at the time of their inception, — it would not
necessarily follow that in no case could natural selec-
tion build up a useless structure into a useful one ;
because, although it is true that in no case can natural
selection do this by acting on a useless structure
directly, it may do so by acting on the useless struc-
ture indirectly, through its direct action on some other
part of the organism with which the useless structure
happens to be correlated. Moreover, as I believe, and
364 Darwin, and after Darwin.
will subsequently endeavour to prove, there is abun-
dant evidence to show that incipient characters are
often developed to a large extent by causes other
than natural selection (or apart from any reference to
utility), with the result that some of them thus happen
to become of use, when, of course, the supposed diffi-
culty is at an end.
But although it is thus easy to dispose of both the
propositions in question, on account of their univer-
sality, stated more carefully they would require, as
I have said, more careful consideration. Thus, if it
had been said that some incipient organs are presum-
ably useless at the time of their inception, and that in
some of these cases it is difficult, or impossible, to con-
ceive how the principle of correlation, or any other
principle hitherto suggested, can apply — then the
question would have been raised from the sphere of
logical discussion to that of biological fact. And
the new question thus raised would have to be de-
bated, no longer on the ground of general or abstract
principles, but on that of special or concrete cases.
Now until within the last year or two it has not been
easy to find such a special or concrete case — that is to
say, a case which can be pointed to as apparently
excluding the possibility of natural selection having
had anything to do with the genesis of an unquestion-
ably adaptive structure. But eventually such a case
has arisen, and the Duke of Argyll has not been slow
in perceiving its importance. This case is the electric
organ in the tail of the skate. No sooner had Pro-
fessor Cossar Ewart published an abstract of his first
paper on this subject, than the Duke seized upon it as
a case for which, as he said, he had long been waiting
Criticisms of Theory of Natural Selection. 365
— namely, the case of an adaptive organ the genesis of
which could not possibly be attributed to natural selec-
tion, and must therefore be attributed to supernatural
design. Now, I do not deny that he is here in pos-
session of an admirable case — a case, indeed, so ad-
mirable that it almost seems to have been specially
designed for the discomfiture of Darwinians. There-
fore, in order to do it full justice, I will show that it is
even more formidable than the Duke of Argyll has
represented.
Electric organs are known to occur in several widely
different kinds of fish — such as the Gymnotus and
Torpedo. Wherever these organs do occur, they
perform the function of electric batteries in storing
and discharging electricity in the form of more or less
powerful shocks. Here, then, we have a function
which is of obvious use to the fish for purposes both
of offence and defence. These organs are everywhere
composed of a transformation of muscular, together
with an enormous development of nervous tissue ;
but inasmuch as they occupy different positions, and
are also in other respects dissimilar in the different
zoological groups of fishes where they occur, no diffi-
culty can be alleged as to these analogous organs
being likewise homologous in different divisions of the
aquatic vertebrata.
Now, in the particular case of the skate, the organ
is situated in the tail, where it is of a spindle-like
form, measuring, in a large fish, about two feet in
length by about an inch in diameter at the middle of
the spindle. Although its structure is throughout
as complex and perfect as that of the electric organ in
Gymnotus or Torpedo, its smaller size does not admit
366 Darwin, and after Darwin.
of its generating a sufficient amount of electricity
to yield a discharge that can be felt by the hand
Nevertheless, that it does discharge under suitable
stimulation has been proved by Professor Burdon
Sanderson by means of a telephone ; for he found
that every time he stimulated the animal its electrical
discharge was rendered audible by the telephone.
Here, then, the difficulty arises. For of what conceiv-
able use is such an organ to its possessor ? We can
scarcely suppose that any aquatic animal is more
sensitive to electric shocks than is the human hand ;
and even if such were the case, a discharge of so feeble
a kind taking place in water would be short-cir-
cuited in the immediate vicinity of the skate itself.
So there can be no doubt that such weak discharges
as the skate is able to deliver must be wholly imper-
ceptible alike to prey and to enemies. Yet for the
delivery of such discharges there is provided an organ
of such high peculiarity and huge complexity, that,
regarded as a piece of living mechanism, it deserves to
rank as at once the most extremely specialized and
the most highly elaborated structure in the whole
animal kingdom. Thousands of separately formed
elements are ranged in row after row, all electrically
insulated one from another, and packed away into the
smallest possible space, with the obvious end, or
purpose, of conspiring together for the simultaneous
delivery of an electric shock. Nevertheless, the shock
when delivered is, as we have just seen, too slight to
be of any conceivable use to the skate. Therefore it
appears impossible to suggest how this astonishing
structure — much more astonishing, in my opinion,
than the human eye or the human hand — can ever
Criticisms of Theory of Natural Selection. 367
have been begun, or afterwards developed, by means
of natural selection. For if it be not even yet of any
conceivable use to its possessor, clearly thus far sur-
vival of the fittest can have had nothing to do with its
formation. On the other hand, seeing that electric
organs when of larger size, as in the Gymnotus and
Torpedo, are of obvious use to their possessors, the
facts of the case, so far as the skate is concerned,
assuredly do appear to sanction the doctrine of " pro-
phetic germs/1 The organ in the skate seems to be on
its way towards becoming such an organ as we meet
with in these other animals ; and, therefore, unless we
can show that it is now, and in all previous stages of
its evolution has throughout been, of use to the skate,
the facts do present a serious difficulty to the theory
of natural selection, while they readily lend themselves
to the interpretation of a disposing or fore-ordaining
mind, which knows how to construct an electric bat-
tery by thus transforming muscular tissue into electric
tissue, and is now actually in process of constructing
such an apparatus for the prospective benefit of future
creatures.
Should it be suggested that possibly the electric
organ of the skate may be in process of degeneration,
and therefore that it is now the practically function-
less remnant of an organ which in the ancestors of
the skate was of larger size and functional use — against
so obvious a suggestion there lie the whole results of
Professor Ewart's investigations, which go to indicate
that the organ is here not in a stage of degeneration,
but of evolution. For instance, in Raia radiata, it does
not begin to be formed out of the muscular tissue until
some time after the animal has left the egg-capsule,
368 Darwin, and after Darwin.
and assumed all the normal proportions (though
not yet the size) of the adult creature. The organ,
therefore, is one of the very latest to appear in the
ontogeny of R. radiata ; and, moreover, it does not
attain its full development (i. e. not merely growth, but
FIG. 1 1 8. — Raia radiata, representing the life size of the youngest in-
dividual in which muscle fibres hare been found developing into electric
cells.
transforming of muscular fibres into electrical ele-
ments) till the fish attains maturity. Read in the
light of embryology, these facts prove, (i) that the
electric organ of R. radiata must be one of the very
IV,
FIG. 1 19. — Electric organ of the Skate. The left-hand drawing (I) represents the
entire organ (natural size) of a full-grown /?. radiata. This is a small sKate, which
rarely exceeds 50 centrns. in length ; but in the large R. dad's, the organ may
exceed two feet in length. The other drawings represent single muscle-fibres in suc-
cessive stages of transition. In the first of the series (II) the motor plate, and the nerves
connected with it, have already been considerably enlarged. In the other three specimens,
the fibre becomes more and more club-like, and eventually cup-like. These changes
of shape are expressive of great changes of structure, as may be seen in the last
of the series (V), where the shallow cup is seen in partial section. The electric
plate lines the concavity of the cup, and is richly supplied with nerves (only a few of
which are represented in the last drawing) : the thick walls of the cup are composed of
muscular fibres, the striation of which is distinctly visible.
* B b
370 Darwin, and after Darwin.
latest products of the animal's phylogeny ; and, (2)
that as yet, at all events, it has not begun to degenerate.
But, if not, it must either be at a stand-still, or it must
be in course of further evolution ; and, whichever of
FIG. 1 20. — Electric cells of Aata radiata. The drawing on the left,
represents one of the clubs magnified, as in the preceding wood-cut.
The drawing on the right represents a number of these clubs, less highly
magnified, in situ.
these alternatives we adopt, the difficulty of account-
ing for its present condition remains. In this con-
nexion also it is worth while to remark that the electric
Criticisms of Theory of Natural Selection. 371
organ, even after it has attained its full development,
continues \tsgrowtk with the growth of the fish, and
this in a much higher ratio, either than the tail alone,
or the whole animal. Lastly, Prof. Burdon Sanderson
finds that section for section the organ in the skate is
as efficient as it is in Torpedo. It is evident that
these facts also point to the skate's organ being in
course of phylogenetic evolution.
Again, it cannot be answered that the principle
of correlation may be drawn upon in mitigation of
the difficulty. The structure of the electric organ
is far too elaborate, far too specialized, and far too
obviously directed to a particular end, to admit of our
conceivably supposing it due to any accidental corre-
lation with structural changes going on elsewhere.
Even as regards the initial changes of muscle-elements
into electrical-elements, I do not think the principle
of correlation can be reasonably adduced by way
of explanation ; for, as shown in the illustrations,
even this initial change is most extraordinarily
peculiar, elaborate, and specialized. But, be this as
it may, I am perfectly certain that the principle of
correlation cannot possibly be adduced to explain the
subsequent association of these electrical elements into
an electric battery, actuated by a special nervous me-
chanism of enormous size and elaboration — unless of
course, the progress of such a structure were assumed
to have been throughout of some utility. Under this
supposition, however, the principle of correlation would
be forsaken in favour of that of natural selection ; and
we should again be in the presence of the same diffi-
culty as that with which we staited.
But now, and further, if we do thus abandon corre-
B b 2
372 Darwin, and after Darwin.
lation in favour of natural selection, and therefore if
for the sake of saving an hypothesis we assume that
the organ as it now stands must be of some use to the
existing skate, we should still have to face the question
— Of what conceivable use can those initial stages of its
formation have been, when first the muscle-elements
began to be changed into the very different electrical-
elements, and when therefore they became useless as
muscles while not yet capable of performing even so
much of the electrical function as they now perform ?
Lastly, we must remember that not only have we
here the most highly specialized, the most complex,
and altogether the most elaboratively adaptive organ
in the animal kingdom ; but also that in the formation
of this structure there has been needed an altogether
unparalleled expenditure of the most physiologically
expensive of all materials- namely, nervous tissue.
Whether estimated by volume or by weight, the
quantity of nervous tissue which is consumed in the
electric organ of the skate is in excess of all the rest
of the nervous system put together. It is need-
less to say that nowhere else in the animal king-
dom— except, of course, in other electric fishes — is
there any approach to so enormous a development of
nervous tissue for the discharge of a special function.
Therefore, as nervous tissue is, physiologically speak-
ing, the most valuable of all materials, we are forced
to conclude that natural selection ought strongly to
have opposed the evolution of such organs, unless from
the first moment of their inception, and throughout the
whole course of their development, they were of some
such paramount importance as biologically to justify so
unexampled an expenditure. Yet this paramount im-
Criticisms of Theory of Natural Selection. 373
portance does not admit of being so much as surmised,
even where the organ has already attained the size and
degree of elaboration which it presents in the skate.
In view of all these considerations taken together,
I freely confess that the difficulty presented by this
case appears to me of a magnitude and importance
altogether unequalled by that of any other single case
— or any series of cases — which has hitherto been en-
countered by the theory of natural selection. So that,
if there were many other cases of the like kind to be
met with in nature, I should myself at once allow that
the theory of natural selection would have to be dis-
carded. But inasmuch as this particular case stands
so far entirely by itself, and therefore out of analogy
with thousands, or even millions, of other cases
throughout the whole range of organic nature, I am
constrained to feel it more probable that the electric
organ of the skate will some day admit of being mar-
shalled under the general law of natural selection — in
just the same way as proved to be the case with the
conspicuous colouring of those caterpillars, which, as
explained in the last chapter, at one time seemed to
constitute a serious difficulty to the theory, and yet,
through a better knowledge of all the relations in-
volved, has now come to constitute one of the strongest
witnesses in its favour.
I have now stated all the objections of any import-
ance which have hitherto been brought against the
theory of natural selection, excepting three, which I
left to be dealt with together because they form a
logically connected group. With a brief consideration
of these, therefore. I will bring this chapter to a close.
374 Darwin, and after Darwin.
The three objections to which I allude are, (i) that
a large proportional number of specific, as well as
of higher taxonomic characters, are seemingly useless
characters, and therefore do not lend themselves to
explanation by the Darwinian theory ; (2) that the
most general of all specific characters — viz. cross-
infertility between allied species — cannot possibly
be due to natural selection, as is demonstrated by
Darwin himself; (3) that the swamping effects of
free intei crossing must always render impossible by
natural selection alone any evolution of species in
divergent (as distinguished from serial) lines of
change.
These three objections have been urged from time
to time by not a few of the most eminent botanists
and zoologists of our century ; and from one point
of view I cannot myself have the smallest doubt that
the objections thus advanced are not only valid in
themselves, but also by far the most formidable
objections which the theory of natural selection has
encountered. From another point of view, however,
I am equally convinced that they all admit of ab-
solute annihilation. This strong antithesis arises, as
I have said, from differences of standpoint, or from
differences in the view which we take of the theory of
natural selection itself. If we understand this theory
to set forth natural selection as the sole cause of
organic evolution, then all the above objections to the
theory are not merely, as already stated, valid and
formidable, but as I will now add, logically insur-
mountable. On the other hand, if we take theory
to consist merely in setting forth natural selection as
a factor of organic evolution, even although we be-
Criticisms of Theory of Natural Selection. 375
lieve it to have been the chief factor or principal cause,
ah the three objections in question necessarily vanish.
For in this case, even if it be satisfactorily proved that
the theory of natural selection is unable to explain the
three classes of facts above mentioned, the theory is
not thereby affected : facts of each and all of these
classes may be consistently left by the theory to be
explained by causes other than natural selection —
whether these be so far capable or incapable of
hypothetical formulation. Thus it is evident that
whether the three objections above named are to
be regarded as logically insurmountable by the
theory, or as logically non-existent in respect to it,
depends simply upon the manner in which the theory
itself is stated.
In the next volume a great deal more will have to
be said upon these matters — especially with regard to
the causes other than natural selection which in my
opinion are capable of explaining these so-called
" difficulties." In the present connexion, however,
all I have attempted to show is, that, whatever may
be thought touching the supplementary theories
whereby I shall endeavour to explain the facts of
inutility, cross-sterility, and non-occurrence of free
intercrossing, no one of these facts is entitled to rank
as an objection against the theory of natural selection,
unless we understand this theory to claim an ex-
clusive prerogative in the field of organic evolution.
This, as we have previously seen, is what Mr. Wallace
does claim for it ; while on the other hand, Mr.
Darwin expressly — and even vehemently— repudiates
the claim : from which it follows that all the three
main objections against the theory of natural selection
376 Darwin, and after Darwin.
are objections which vitally affect the theory only as
it has been stated and upheld by Wallace. As the
theory has been stated and upheld by Darwin, all
these objections are irrelevant. This is a fact which
I had not myself perceived at the time when I men-
tioned these objections in a paper entitled Physio-
logical Selection, which was published in 1886. The
discussions to which that paper gave rise, however, led
me to consider these matters more closely ; and
further study of Darwin's writings, with these matters
specially in view, has led me to see that none of the
objections in question are relevant to his theory, as
distinguished from that of Mr. Wallace. This, I
acknowledge, I ought to have perceived before I
published the paper just alluded to ; but in those
days I had had no occasion to follow out the dif-
ferences between Darwin and Wallace to all their
consequences, and therefore adopted the prevalent
view that their theories of evolution were virtually
identical. Now, however, I have endeavoured to
make it clear that the points wherein they differ
involve the important consequences above set forth.
All these the most formidable objections against the
theory of natural selection arise simply and solely
from what I conceive to be the erroneous manner in
which the theory has been presented by Darwin's
distinguished colleague.
I have now considered, as impartially as I can, all
the main criticisms and objections which have been
brought against the theory of natural selection ; and
the result is to show that, neither singly nor col-
lectively, are they entitled to much weight. On the
Criticisms of Theory of Natural Selection. 377
other hand, as we have seen in the preceding chapter,
there is a vast accumulation of evidence in favour of
the theory. Hence, it is no wonder that the theory
has now been accepted by all naturalists, with scarcely
any one notable exception, as at any rate the best
working hypothesis which has ever been propounded
whereby to explain the facts of organic evolution.
Moreover, in the opinion of those most competent to
judge, the theory is entitled to be regarded as some-
thing very much more than a working hypothesis :
it is held to be virtually a completed induction, or,
in other words, the proved exhibition of a general
law, whereby the causation of organic evolution ad-
mits of being in large part — if not altogether —
explained.
Now, whether or not we subscribe to this latter
conclusion ought, I think, to depend upon what we
mean by an explanation in the case which is before
us. If we mean only that, given the large class of
known facts and unknown causes which are conveni-
ently summarized under the terms Heredity and
Variability, then the further facts of Struggle and
Survival serve, in some considerable degree or
another, to account for the phenomena of adaptive
evolution, I cannot see any room to question that
the evidence is sufficient to prove the statement.
But it is clear that by taking for granted these great
facts of Heredity and Variability, we have assumed
the larger part of the problem as a whole. Or, more
correctly, by thus generalizing, in a merely verbal
form, all the unknown causes which are concerned in
these two great factors of the process in question, we
are not so much as attempting to explain the pre-
378 Darwin, and after Darwin.
cedent causation which serves as a condition to the
process. Much more than half the battle would
already have been won, had Darwin's predecessors
been able to explain the causes of Heredity and
Variation ; hence it is but a very partial victory
which we have hitherto gained in our recent discovery
of the effects of Struggle and Survival.
Yet partial though it be in relation to the whole
battle, in itself, or considered absolutely, there can be
no reasonable doubt that it constitutes the greatest
single victory which has ever been gained by the
science of Biology. For this very reason, however,
it behoves us to consider all the more carefully the
extent to which it goes. But my discussion of this
matter must be relegated to the next volume, where
I hope to give abundant proof of the soundness of
Darwin's judgment as conveyed in the words : — " I
am convinced that natural selection has been the main,
but not the exclusive, means of modification."
CHAPTER X.
THE THEORY OF SEXUAL SELECTION, AND
CONCLUDING REMARKS.
ALTHOUGH the explanatory value of the Darwinian
theory of natural selection is, as we have now seen,
incalculably great, it nevertheless does not meet those
phenomena of organic nature which perhaps more
than any other attract the general attention, as well
as the general admiration, of mankind : I mean all
that class of phenomena which go to constitute the
Beautiful. Whatever value beauty as such may have,
it clearly has not a life-preserving value. The gorgeous
plumage of a peacock, for instance, is of no advantage
to the peacock in his struggle for life, and therefore
cannot be attributed to the agency of natural selection.
Now this fact of beauty in organic structures is a fact
of wide generality — almost as wide, indeed, as is the
fact of their utility. Mr. Darwin, therefore, suggested
another hypothesis whereby to render a scientific
explanation of this fact. Just as by his theory of
natural selection he sought to explain the major fact
of utility, so did he endeavour to explain the minor
fact of beauty by a theory of what he termed Sexual
Selection.
380 Darwin, and after Darwin.
It is a matter of observation that the higher
animals do not pair indiscriminately ; but that the
members of either sex prefer those individuals of the
opposite sex which are to them most attractive. It
is important to understand in limine that nobody has
ever attempted to challenge this statement. In other
words, it is an unquestionable fact that among many of
the higher animals there literally and habitually occurs
a sexual selection ; and this fact is not a matter of
inference, but, as I have said, a matter of observation.
The inference only begins where, from this observable
fact, it is argued, — ist, that the sexual selection has
reference to an aesthetic taste on the part of the
animals themselves ; and and, that, supposing the
selection to be determined by such a taste, the cause
thus given is adequate to explain the phenomena of
beauty which are presented by these animals. I will
consider these two points separately.
From the evidence which Darwin has collected, it
appears to me impossible to doubt that an aesthetic
sense is displayed by many birds, and not a few
mammals. This of course does not necessarily imply
that the standards of such a sense are the same as
our own ; nor does it necessarily imply that there is
any constant relation between such a sense and high
levels of intelligence in other respects. In point of
fact, such is certainly not the case, because the best
evidence that we have of an aesthetic sense in animals
is derived from birds, and not from mammals. The
most cogent cases to quote in this connexion are
those of the numerous species of birds which habi-
tually adorn their nests with gaily coloured feathers,
wool, cotton, or any other gaudy materials which they
The Theory of Sexual Selection. 381
may find lying about the woods and fields. In many
cases a marked preference is shown for particular
objects — as, for instance, in the case of the Syrian
nut-hatch, which chooses the iridescent wings of
insects, or that of the great crested fly- catcher, which
similarly chooses the cast-off skins of snakes. But
no doubt the most remarkable of these cases is that
of the baya-bird of Asia, which after having com-
pleted its bottle- shaped and chambered nest1, studs it
over with small lumps of clay, both inside and out,
upon which the cock-bird sticks fire-flies, apparently
for the sole purpose of securing a brilliantly decorative
effect. Other birds, such as the hammer-head of
Africa, adorn the surroundings of their nests (which
are built upon the ground) with shells, bones, pieces
of broken glass and earthenware, or any objects of a
bright and conspicuous character which they may
happen to find. The most consummate artists in this
respect are, however, the bower-birds ; for the species
of this family construct elaborate play-houses in the
form of arched tunnels, built of twigs upon the ground.
Through and around such a tunnel they chase one
another ; and it is always observable that not only is
the floor paved with a great collection of shells, bones,
coloured stones, and any other brilliant objects which
they are able to carry in their beaks, but also that the
walls are decorated with the most gaudy articles
which the birds can find. There is one genus, in
Papua, which even goes so far as to provide the
theatre with a surrounding garden. A level piece of
1 The chambers are three in number. The two upper ones are
occupied respectively by the male and the sitting female. The lower
one serves as a general living room when the young are hatched.
382 Darwin, and after Darwin.
ground is selected as a site for the building. The
latter is about two feet high, and constructed round
the growing stalk of a shrub, which therefore serves
as a central pillar to which the frame-work of the
roof is attached. Twigs are woven into this frame-
work until the whole is rendered rain-proof. The tent
FlG. iai. — The Garden Bower-bird (Amblyortiis inornata . Reduced
from Gould's Birds of New Guinea to £ nat. size.
thus erected is about nine feet in circumference at its
base, and presents a large arch as an entrance. The
central pillar is banked up with moss at its base, and
a gallery is built round the interior of the edifice.
This gallery is decorated with flowers fruits, fungi, &c.
These are also spread over the garden, which covers
The Theory of Sexual Selection. 383
about the same area as the play-house. The flowers
are said to be removed when they fade, while fresh
ones are gathered to supply their places. Thus the
garden is always kept bright with flowers, as well as
with the brilliant green of mosses, which are col-
lected and distributed in patches, resembling tiny
lawns.
Now these sundry cases alone seem to prove a high
degree of the aesthetic sense as occurring among
birds ; for, it is needless to say, none of the facts just
mentioned can be due to natural selection, seeing that
they have no reference to utility, or the preservation
of life. But if an aesthetic sense occurs in birds, we
should expect, on a priori grounds, that it would
probably be exercised with reference to the personal
appearance of the sexes. And this expectation is
fully realized. For it is an observable fact that in
most species of birds where the males are remarkable
for the brilliancy of their plumage, not only is this
brilliancy most remarkable during the pairing season,
but at this season also the male birds take elaborate
pains to display their charms before the females.
Then it is that the peacock erects his tail to strut
round and round the hens, taking care always to
present to them a front view, where the coloration is
most gorgeous. And the same is true of all other
gaily coloured male birds. During the pairing
season they actively compete with one another in
exhibiting their attractiveness to the females ; and in
many cases there are added all sorts of extraordinary
antics in the way of dancings and Growings. Again,
in the case of all song-birds, the object of the singing
is to please the females ; and for this purpose the
384 Darwin, and after Darwin.
males rival one another to the best of their musical
ability.
Thus there can be no question that the courtship
of birds is a highly elaborate business, in which the
males do their best to surpass one another in charming
the females. Obviously the inference is that the males
do not take all this trouble for nothing ; but that the
females give their consent to pair with the males
whose personal appearance, or whose voice, proves to
be the most attractive. But, if so, the young of the
male bird who is thus selected will inherit his superior
beauty ; and thus, in successive generations, a con-
tinuous advance will be made in the beauty of
plumage or of song, as the case may be, — both the
origin and development of beauty in the animal world
being thus supposed due to the aesthetic taste of
animals themselves.
Such is the theory of sexual selection in its main
outlines ; and with regard to it we must begin by
noting two things which are of most importance. In
the first, place, it is a theory wholly and completely
distinct from the theory of natural selection ; so that
any truth or error in the one does not in the least
affect the other. The second point is, that there is
not so great a wealth of evidence in favour of sexual
selection as there is in favour of natural selection ;
and, therefore, that while all naturalists nowadays
accept natural selection as a (whether or not the] cause
of adaptive, useful, or life-preserving structures, there
is no such universal — but only a very general — agree-
ment with reference to sexual selection as a cause
of decorative, beautiful, or life-embellishing struc-
tures. Nevertheless, the evidence in favour of sexual
Tke Theory of Sexual Selection. 385
selection is both large in amount and massive in
weight.
Our consideration of this evidence will bring us to
the second division of our subject, as previously marked
out for discussion — namely, granting that an aesthetic
sense occurs in certain large divisions of the animal
kingdom, what is the proof that such a sense is a
cause of the beauty which is presented by the animals
in question?
Before proceeding to state this proof, however, it
is desirable to observe that under the theory of sexual
selection Darwin has included two essentially different
classes of facts. For besides the large class of facts
to which I have thus far been alluding, — i. e. the cases
where two sexes of the same species differ from one
another in respect of ornamentation, — there is another
class of facts equally important, namely, the cases
where the two sexes of the same species differ from
one another in respect of size," strength, and the
possession of natural weapons, such as spurs, horns,
&c. In most of these cases it is the males which
are thus superiorly endowed ; and it is a matter of
observation that in all cases where they are so en-
dowed they use their superior strength and natural
weapons for fighting together, in order to secure
possession of the females. Hence results what Mr.
Darwin has called the Law of Battle between males
of the same species ; and this law of battle he includes
under his theory of sexual selection. But it is evident
that the principle which is operative in the law of
battle differs from the principle which is concerned in
the form of sexual selection that has to do with
embellishment, and consequent charm. The law of
* c c
386 Darwin, and after Darwin.
battle, in fact, more nearly approaches the law of
natural selection ; seeing that it expresses the natural
advantages of brute force in the struggling of rival
animals, and so frequently results in death of the less
fitted, as distinguished from a mere failure to propa-
gate. Now against this doctrine of the law of battle,
and the consequences to which it leads in the superior
fighting powers of male animals, no objection has
been raised in any quarter. It is only with regard to
the other aspect of the theory of sexual selection —
or that which is concerned with the superior em-
bellishment of male animals — that any difference of
opinion obtains. I will now proceed to give the
main arguments on both sides of this question,
beginning with a rhumt of the evidences in favour of
sexual selection.
In the first place, the fact that secondary sexual
characters of the embellishing kind are so generally
restricted to the male sex in itself seems to constitute
very cogent proof that, in some way or another, such
characters are connected with the part which is played
by the male in the act of propagation. Moreover,
secondary sexual characters of this kind are of quite
as general occurrence as are those of the other kind
which have to do with rivalry in battle ; and the former
are usually of the more elaborate description. There-
fore, as there is no doubt that secondary sexual char-
acters of the one order have an immediate purpose to
serve in the act of propagation, we are by this close
analogy confirmed in our surmise that secondary sexual
characters of the other, and still more elaborate, order
are likewise so concerned. Moreover, this view of their
meaning becomes still further strengthened when we
The Theory of Sexual Selection. 387
take into consideration the following facts. Namely,
(a) secondary sexual characters of the embellishing
kind are, as a rule, developed only at maturity ; and
most frequently during only a part of the year, which
is invariably the breeding season : (b) they are always
more or less seriously affected by emasculation: (c)
they are always, and only, displayed in perfection
during the act of courtship : (d] then, however, they are
displayed with the most elaborate pains ; yet always,
and only, before the females : (e) they appear, at all
events in many cases, to have the effect of charming
the females into a performance of the sexual act ;
while it is certain that in many cases, both among
quadrupeds and birds, individuals of the. one sex are
capable of feeling a strong antipathy against, or a strong
preference for, certain individuals of the opposite sex.
Such are the main lines of evidence in favour of the
theory of sexual selection. And although it is enough
that some of them should be merely stated as above
in order that their immense significance should be-
come apparent, in the case of others a bare statement
is not sufficient for this purpose. More especially is
this the case as regards the enormous profusion, variety,
and elaboration of sexually- embellishing characters
which occur in birds and mammals — not to mention
several divisions of Arthropoda ; together with the
extraordinary amount of trouble which, in a no less
extraordinary number of different ways, is taken by
the male animals to display their embellishments
before the females. And even in many cases where
to our eyes there is no particular embellishment to
display, the process of courtship consists in such an
elaborate performance of dancings, struttings, and
C C 2
88 Darwin, and after Darwin,
ttitudinizings that it is scarcely possible to doubt their
bject is to incite the opposite sex. Here, for instance,
FIG. iaa. — Courtship of Spiders. A few examples of some of the
attitudes adopted by different species of males when approaching their
females. (After Peckham.)
is a series of drawings illustrating the courtship of
spiders. I choose this case as an example, partly
The Theory of Sexual Selection. 380
FIG. 123. — Courtship of Spiders. Continued from Fig. 122, similarly
showing some of the attitudes of approach adopted by males of yet
other different species. (After Feckham.)
390 Darwin, and after Darwin.
because it is the one which has been published most
recently, and partly because it is of particular interest
as occurring so low down in the zoological scale. I
am indebted to the kindness of Mr. and Mrs. Peckham
for permission to reproduce these few selected drawings
from their very admirable work, which is published by
the Natural History Society of Wisconsin, U.S. It is
evident at a glance that all these elaborate, and to our
eyes ludicrous, performances are more suggestive of
incitation than of any other imaginable purpose. And
this view of the matter is strongly corroborated by
the fact that it is the most brightly coloured parts of
the male spiders which are most obtruded upon the
notice of the female by these peculiar attitudes — in
just the same way as is invariably the case in the
analogous phenomena of courtship among birds,
insects, &c.
But so great is the mass of material which Darwin
has collected in proof of all the points mentioned in
the foregoing paragraph, that to attempt anything
in the way of an epitome would really be to damage
its evidential force. Therefore I deem it best simply
to refer to it as it stands in his Descent of Man,
concluding, as he concludes, — " This surprising uni-
formity in the laws regulating the differences between
the sexes in so many and such widely separated
classes is intelligible if we admit the action throughout
all the higher divisions of the animal kingdom of one
common cause, namely, sexual selection " ; while, as
he might well have added, it is difficult to imagine
that all the large classes of facts which an admission of
this common cause serves to explain, can ever admit
of being rendered intelligible by any other theory.
The Theory of Sexual Selection. 391
We may next proceed to consider the objections
which have been brought against the theory of sexual
selection. And this is virtually the same thing as
saying that we may now consider Mr. Wallace's views
upon the subject
Reserving for subsequent consideration the most
general of these objections — namely, that at best the
theory can only apply to the more intelligent animals,
and so must necessarily fail to explain the phenomena
of beauty in the less intelligent, or in the non-
intelligent, as well as in all species of plants — we may
take seriatim the other objections which, in the opinion
of Mr. Wallace, are sufficient to dispose of the theory
even as regards the higher animals.
In the first place, he argues that the principal
cause of the greater brilliancy of male animals in
general, and of male birds in particular, is that they
do not so much stand in need of protection arising
from concealment as is the case with their respective
females. Consequently natural selection is not so
active in repressing brilliancy of colour in the males,
or, which amounts to the same thing, is more active
in " repressing in the female those bright colours
which are normally produced in both sexes by general
laws."
Next, he argues that not only does natural selection
thus exercise a negative influence in passively per-
mitting more heightened colour to appear in the
males, but even exercises a positive influence in
actively promoting its development in the males,
while, at the same time, actively repressing its ap-
pearance in the females. For heightened colour, he
says, is correlated with health and vigour ; and as there
392 Darwin , and after Darwin.
can be no doubt that healthy and vigorous birds best
provide for their young, natural selection, by always
placing its premium on health and vigour in the males,
thus also incidentally promotes, through correlated
growth, their superior coloration.
Again, with regard to the display which is practised
by male birds, and which constitutes the strongest
of all Mr. Darwin's arguments in favour of sexual
selection, Mr. Wallace points out that there is no
evidence of the females being in any way affected
thereby. On the other hand, he argues that this
display may be due merely to general excitement ;
and he lays stress upon the more special fact that
moveable feathers are habitually erected under the
influence of anger and rivalry, in order to make the
bird look more formidable in the eyes of antago-
nists.
Furthermore, he adduces the consideration that,
even if the females are in any way affected by colour
and its display on the part of the males, and if, there-
fore, sexual selection be conceded a true principle in
theory, still we must remember that, as a matter of
fact, it can only operate in so far as it is allowed to
operate by natural selection. Now, according to Mr.
Wallace, natural selection must wholly neutralize any
such supposed influence of sexual selection. For,
unless the survivors in the general struggle for exis-
tence happen to be those which are also the most
highly ornamented, natural selection must neutralize
and destroy any influence that may be exerted by
female selection. But obviously the chances against
the otherwise best fitted males happening to be like-
wise the most highly ornamented must be many to
The Theory of Sexual Selection. 393
one, unless, as Wallace supposes, there is some cor-
relation between embellishment and general perfection,
in which case, as he points out, the theory of sexual
selection lapses altogether, and becomes but a special
case of natural selection.
Once more, Mr. Wallace argues that the evidence
collected by Mr. Darwin himself proves that each bird
finds a mate under any circumstances — a general fact
which in itself must quite neutralize any effect of
sexual selection of colour or ornament, since the less
highly coloured birds would be at no disadvantage as
regards the leaving of healthy progeny.
Lastly, he urges the high improbability that through
thousands of generations all the females of any par-
ticular species — possibly spread over an enormous
area — should uniformly and always have displayed
exactly the same taste with respect to every detail of
colour to be presented by the males.
Now, without any question, we have here a most
powerful array of objections against the theory of
sexual selection. Each of them is ably developed by
Mr. Wallace himself in his work on Tropical Nature \
and although I have here space only to state them in
the most abbreviated of possible forms, I think it will
be apparent how formidable these objections appear.
Unfortunately the work in which they are mainly pre-
sented was published several years after the second
edition of the Descent of Man, so that Mr. Darwin
never had a suitable opportunity of replying. But, if
he had had such an opportunity, as far as I can judge
it seems that his reply would have been more or less
as follows.
In the first place, Mr. Wallace fails to distinguish
394 Darwin, and after Darwin.
between brilliancy and .ornamentation — or between
colour as merely " heightened," and as distinctively
decorative. Yet there is obviously the greatest pos-
sible difference between these two things. We may
readily enough admit that a mere heightening of al-
ready existing coloration is likely enough — at all
events in many cases — to accompany a general increase
of vigour, and therefore that natural selection, by pro-
moting the latter, may also incidentally promote the
former, in cases where brilliancy is not a source of
danger. But clearly this is a widely different thingfrom
showing that not only a general brilliancy of colour ;
but also the particular disposition of colour s> in the
form of ornamental patterns, can thus be accounted
for by natural selection. Indeed, it is expressly in
order to account for the occurrence of such ornamental
patterns that Mr. Darwin constructed his theory of
sexual selection ; and therefore, by thus virtually
ignoring the only facts which that theory endeavours
to explain, Mr. Wallace is not really criticizing the
theory at all. By representing that the theory has to
do only with brilliancy of colour, as distinguished
from disposition of colours, he is going off upon a
false issue which has never really been raised *. Look,
for example, at a peacock's tail. No doubt it is suf-
ficiently brilliant ; but far more remarkable than its
brilliancy is its elaborate pattern on the one hand, and
its enormous size on the other. There is no conceiv-
able reason why mere brilliancy of colour^ as an ac-
cidental concomitant of general vigour, should have
run into so extraordinary, so elaborate, and so beau-
1 Note C.
The Theory of Sexual Selection. 395
tiful a design of colours. Moreover, this design is only
unfolded when the tail is erected, and the tail is not
erected in battle (as Mr. Wallace's theory of the
erectile function in feathers would require), but in
courtship ; obviously, therefore, the purpose of the
pattern, so to speak, is correlated with the act of
courtship — it being only then, in fact, that the general
purpose of the whole structure, as well as the more
special purpose of the pattern, becomes revealed.
Lastly, the fact of this whole structure being so large,
entailing not only a great amount of physiological
material in its production, but also of physiological
energy in carrying about such a weight, as well as of
increased danger from impeding locomotion and in-
viting capture — all this is obviously incompatible with
the supposition of the peacock's tail having been pro-
duced by natural selection. And such a case does
not stand alone. There are multitudes of other in-
stances of ornamental structures imposing a drain
upon the vital energies of their possessors, without
conferring any compensating benefit from a utilitarian
point of view. Now, in all these cases, without any
exception, such structures are ornamental structures
which present a plain and obvious reference to the
relationship of the sexes. Therefore it becomes almost
impossible to doubt — first, that they exist for the sake
of ornament ; and next, that the ornament exists on
account of that relationship. If such structures were
due merely to a superabundance of energy, as Mr.
Wallace supposes, not only ought they to have been
kept down by the economizing influence of natural
selection ; but we can see no reason, either why they
should be so highly ornamental on the one hand, or
396 Darwin, and after Darwin.
so exclusively related to the sexual relationship on the
other.
Finally, we must take notice of the fact that where
peculiar structtires are concerned for purposes of dis-
play in courtship, the elaboration of these structures is
often no less remarkable than that of patterns where
FlG. 124 — The Bell-bird (Chasmorhynchus niveus, \ natural size).
Drawn from nature (/?. Coll. Stirg. Mus.\ In the drawing of the
adult male the ornamental appendage is represented in its inflated
condition, during courtship ; in the drawing of the young male it is
shown in its flaccid condition.
colours are thus concerned. Take, for example, the case
of the Bell-bird, which I select from an innumerable
number of instances that might be mentioned because,
while giving a verbal description of this animal,
Darwin does not supply a pictorial representation
The Theory of Sexual Selection. 397
thereof. The bird, which lives in South America, has
a very loud and peculiar call, that can be heard at a
distance of two or three miles. The female is dusky-
green ; but the adult male is a beautiful white, ex
cepting the extraordinary structure with which we
are at present concerned. This is a tube about three
FIG. 125. — C. tricarunculatus, j natural size. Copied from the Ibis.
The ornamental appendages of the male are represented in a partly
inflated condition.
inches long, which rises from the base of the beak.
It is jet black, and dotted over with small downy
feathers. The tube is closed at the top, but its cavity
communicates with the palate, and thus the whole
admits of being inflated from within, when, of course,
it stands erect as represented in one of the two draw-
398 Darwin, and after Darwin.
ings. When not thus inflated, it hangs down, as
shown in the second figure, which represents the
plumage of a young male. (Fig. 124.)
In another species of the genus there are three of these
appendages — the two additional ones being mounted
on the corners of the mouth. (Fig. 12,5.) In all species
of the genus (four in number) the tubes are inflated
during courtship, and therefore perform the function
of sexual embellishments. Now the point to which I
wish to draw attention is, that so specialized and mor-
phologically elaborate a structure cannot be regarded
as merely adventitious. It must have been developed
by some definite cause, acting through a long series of
generations. And as no other function can be as-
signed to it than that of charming the female when it
is erected in courtship, the peculiarity of form and
mechanism which it presents — like the elaboration of
patterns in cases where colour only is concerned —
virtually compels us to recognise in sexual selection
the only conceivable cause of its production.
For these reasons I think that Mr. Wallace's main
objection falls to the ground. Passing on to his sub-
sidiary objections, I do not see much weight in his
merely negative difficulty as to there being an absence
of evidence upon hen birds being charmed by the
plumage, or the voice, of their consorts. For, on the
one hand, it is not very safe to infer what sentiments
may be in the mind of a hen ; and, on the other hand,
it is impossible to conceive what motive can be in the
mind of a cock, other than that of making himself
attractive, when he performs his various antics, displays
his ornamental plumes, or sings his melodious songs.
Considerations somewhat analogous apply to the
The Theory of Sexual Selection. 399
difficulty of supposing so much similarity and con-
stancy of taste on the part of female animals as Mr.
Darwin's theory undoubtedly requires. Although we
know very little about the psychology of the lower
animals, we do observe in many cases that small
details of mental organization are often wonderfully
constant and uniform throughout all members of a
species, even where it is impossible to suggest any
utility as a cause.
Again, as regards the objection that each bird finds
a mate under any circumstances, we have here an
obvious begging of the whole question. That every
feathered Jack should find a feathered Jill is perhaps
what we might have antecedently expected ; but when
we meet with innumerable instances of ornamental
plumes, melodious songs, and the rest, as so many
witnesses to a process of sexual selection having
always been in operation, it becomes irrational to ex-
clude such evidence on account of our antecedent
prepossessions.
There remains the objection that the principles of
natural selection must necessarily swallow up those of
sexual selection. And this consideration, I doubt
not, lies at the root of all Mr. Wallace's opposition to
the supplementary theory of sexual selection. He is
self-consistent in refusing to entertain the evidence of
sexual selection, on the ground of his antecedent per-
suasion that in the great drama of evolution there is
no possible standing-ground for any other actor than
that which appears in the person of natural selection.
But here, again, we must refuse to allow any merely
antecedent presumption to blind our eyes to the
actual evidence of other agencies having co-operated
4OO Darwin, and after Darwin.
with natural selection in producing the observed results.
And, as regards the particular case now before us, I
think I have shown, as far as space will permit, that
in the phenomena of decorative colouring (as distin-
guished from merely brilliant colouring), of melodious
song (as distinguished from merely tuneless cries), of
enormous arborescent antlers (as distinguished from
merely offensive weapons), and so forth — I say that in
all these phenomena we have phenomena which can-
not possibly be explained by the theory of natural
selection ; and, further, that if they are to be explained
at all, this can only be done, so far as we can at
present see, by Mr. Darwin's supplementary theory of
sexual selection.
I have now briefly answered all Mr. Wallace's
objections to this supplementary theory, and, as pre-
viously remarked, I feel pretty confident that, at all
events in the main, the answer is such as Mr. Darwin
would himself have supplied, had there been a third
edition of his work upon the subject. At all events,
be this as it may, we are happily in possession of un-
questionable evidence that he believed all Mr. Wallace's
objections to admit of fully satisfactory answers. For
his very last words to science — read only a few hours
before his death at a meeting of the Zoological
Society — were :
I may perhaps be here permitted to say that, after having
carefully weighed, to the best of my ability, the various argu-
ments which have been advanced against the principle of sexual
selection, I remain firmly convinced of its truth '.
1 Since the above exposition of the theory of sexual selection was
written, Mr. Poulton has published his work on the Colours of Animals.
He there reproduces some of the illustrations which occur in Mr. and
The Theory of Sexual Selection. 401
Concluding Remarks.
I will now conclude this chapter, and with it the
present volume, by offering a few general remarks on
what may be termed the philosophical relations of
Darwinian doctrine to the facts of adaptation on the
one hand, and to those of beauty on the other. Of
course we are all aware that before the days of this
doctrine the facts of adaptation in organic nature were
taken to constitute the clearest possible evidence of
special design, on account of the wonderful mechanisms
which they everywhere displayed ; while the facts of
beauty were taken as constituting no less conclusive
evidence of the quality of such special design as
beneficent, not to say artistic. But now that the
Darwinian doctrine appears to have explained
scientifically the former class of facts by its theory of
natural selection, and the latter class of facts by its
theory of sexual selection, we may fitly conclude this
brief exposition of the doctrine as a whole by consi-
dering what influence such naturalistic explanations
may fairly be taken to exercise upon the older, or
super-naturalistic, interpretations.
To begin with the facts of a'daptation, we must
first of all observe that the Darwinian doctrine is
immediately concerned with these facts only in so far
Mrs. Peckham's work on Sexual Selection in Spiders, and furnishes
appropriate descriptions. Therefore, while retaining the illustrations,
I have withdrawn my own descriptions.
Mr. Poulton has also in his book supplied a rlsumi of the arguments
for and against the theory of sexual selection in general. Of course in
nearly all respects this corresponds with the rfaumt which is given in
the foregoing pages; but I have left the latter as it was originally
written, because all the critical part is reproduced verbatim from a
review of Mr. Wallace's Darwinism, of a date still earlier than that of
Mr. Poulton'g book — viz. Contemporary Review, August, 1889.
* D d
402 Darwin, and after Darwin.
as they occur in organic nature. With the adapta-
tions— if they can properly be so called — which occur
in all the rest of nature, and which go to constitute the
Cosmos as a whole so wondrous a spectacle of
universal law and perfect order, this doctrine is but
indirectly concerned. Nevertheless, it is of course
fundamentally concerned with them to the extent that
it seeks to bring the phenomena of organic nature into
line with those of inorganic ; and therefore to show
that whatever view we may severally take as to the
kind of causation which is energizing in the latter we
must now extend to the former. This is usually
expressed by saying that the theory of evolution by
natural selection is a mechanical theory. It endea-
vours to comprise all the facts of adaptation in organic
nature under the same category of explanation as
those which occur in inorganic nature — that is to
say, under the category of physical, or ascertainable,
causation. Indeed, unless the theory has succeeded
in doing this, it has not succeeded in doing anything —
beyond making a great noise in the world. If Mr.
Darwin has not discovered a new mechanical cause in
the selection principle, his labour has been worse than
in vain.
Now, without unduly repeating what has already
been said in Chapter VIII, I may remark that, what-
ever we may each think of the measure of success
which has thus far attended the theory of natural
selection in explaining the facts of adaptation, we ought
all to agree that, considered as a matter of general
reasoning, the theory does certainly refer to a vera
causa of a strictly physical kind ; and, therefore, that
no exception can be taken to the theory in this respect
The Theory of Sexual Selection. 403
on grounds of logic. If the theory in this respect is to
be attacked at all, it can only be on grounds of fact —
namely, by arguing that the cause does not occur in
nature, or that, if it does, its importance has been exag-
gerated by the theory. Even, however, if the latter
proposition should ever be proved, we may now be
virtually certain that the only result would be the rele-
gation of all the residual phenomena of adaptation to
other causes of the physical order — whether known or
unknown. Hence, as far as the matter of principle is
concerned, we may definitely conclude that the great
naturalistic movement of our century has already
brought all the phenomena of adaptation in organic
nature under precisely the same category of mecha-
nical causation, as similar movements in previous
centuries have brought all the known phenomena of
inorganic nature : the only question that remains for
solution is the strictly scientific question touching the
particular causes of the mechanical order which have
been at work.
So much, then, for the phenomena of adaptation.
Turning next to those of beauty, we have already seen
that the theory of sexual selection stands to these in
precisely the same relation as the theory of natural
selection does to those of adaptation. In other words,
it supplies a physical explanation of them ; because,
as far as our present purposes are concerned, it may
be taken for granted, or for the sake of argument, that
inasmuch as psychological elements enter into the
question the cerebral basis which they demand involves
a physical side.
There is, moreover, this further point of resemblance
between the two theories : neither of them has any
D d 2
404 Darwin, and after Darwin.
reference to inorganic nature. Therefore, with the
charm or the loveliness of landscapes, of earth and sea
and sky, of pebbles, crystals, and so forth, we have at
present nothing to do. How it is that so many inani-
mate objects are invested with beauty— why it is that
beauty attaches to architecture, music, poetry, and
many other things- these are questions which do not
specially concern the biologist. If they are ever to
receive any satisfactory explanation in terms of
natural causation, this must be furnished at the hands
of the psychologist. It may be possible for him to
show, more satisfactorily than hitherto, that all beauty,
whenever and wherever it occurs, is literally " in the
eyes of the beholder"; or that objectively considered,
there is no such thing as beauty. It may be — and in
my opinion it probably is— purely an affair of the
percipient mind itself, depending on the association of
ideas with pleasure-giving objects. This association
may well lead to a liking for such objects, and so to the
formation of what is known as aesthetic feeling with
regard to them. Moreover, beauty of inanimate nature
must be an affair of the percipient mind itself, unless
there be a creating intelligence with organs of sense
and ideals of beauty similar to our own. And, apart
from any deeper considerations, this latter possibility is
scarcely entitled to be regarded as a probability, looking
to the immense diversities in those ideals among dif-
ferent races of mankind. But, be this as it may, the
scientific problem which is presented by the fact of
aesthetic feeling, even if it is ever to be satisfactorily
solved, is a problem which, as already remarked, must
be dealt with by psychologists. As biologists we have
simply to accept this feeling as a fact, and to consider
The Theory of Sexual Selection. 405
how, out of such a feeling as a cause, the beauty of
organic nature may have followed as an effect.
Now we have already seen how the theory of sexual
selection supposes this to have happened. But
against this theory a formidable objection arises, and
one which I have thought it best to reserve for treat-
ment in this place, because it serves to show the
principal difference between Mr. Darwin's two great
generalizations, considered as generalizations in the
way of mechanical theory. For while the theory of
natural selection extends equally throughout the whole
range of organic nature, the theory of sexual selection
has but a comparatively restricted scope, which, more-
over, is but vaguely defined. For it is obvious that
the theory can only apply to living organisms which
are sufficiently intelligent to admit of our reasonably
accrediting them with aesthetic taste — namely, in
effect, the higher animals. And just as this con-
sideration greatly restricts the possible scope of the
theory, as compared with that of natural selection, so
does it render undefined the zoological limits within
which it can be reasonably employed. Lastly, this
necessarily undefined, and yet most important limita-
tion exposes the theory to the objection just alluded
to, and which I shall now mention.
The theory, as we have just seen, is necessarily
restricted in its application to the higher animals.
Yet the facts which it is designed to explain are not
thus restricted. For beauty is by no means restricted
to the higher animals. The whole of the vegetable
world, and the whole of the animal world at least as
high up in the scale as the insects, must be taken as
incapable of aesthetic feeling. Therefore, the extreme
406 Darwin, and after Darwin.
beauty of flowers, sea-anemones, coral.;, and so forth,
cannot possibly be ascribed to sexual selection.
Now, with regard to this difficulty, we must begin
by excluding the case of the vegetable kingdom as
irrelevant. For it has been rendered highly probable—
if not actually proved — by Darwin and others, that the
beauty of flowers and of fruits is in large part due to
natural selection. It is to the advantage of flowering
plants that their organs of fructification should be
rendered conspicuous — and in many cases also
odoriferous, — in order to attract the insects on which
the process of fertilization depends. Similarly, it is
to the advantage of all plants which have brightly
coloured fruits that these should be conspicuous for
the purpose of attracting birds, which eat the fruits and
so disseminate the seed. Hence all the gay colours
and varied forms, both of flowers and fruits, have been
thus adequately explained as due to natural causes,
working for the welfare, as distinguished from the
beauty, of the plants. For even the distribution of
colours on flowers, or the beautiful patterns which so
many of them present, are found to be useful in guiding
insects to the organs of fructification.
Again, the green colouring of leaves, which lends
so much beauty to the vegetable world, has likewise
been shown to be of vital importance to the physiology
of plant-life ; and, therefore, may also be ascribed to
natural selection. Thus, there remains only the forms
of plants other than the flowers. But the forms of
leaves have also in many cases been shown to be
governed by principles of utility ; and the same is to
be said of the branching structure which is so
characteristic of trees and shrubs, since this is the
The Theory of Sexual Selection. 407
form most effectual for spreading out the leaves to the
light and air. Here, then, we likewise find that the
cause determining plant beauty is natural selection;
and so we may conclude that the only reason why
the forms of trees which are thus determined by
utility appeal to us as beautiful, is because we are
accustomed to these the most ordinary forms. Our
ideas having been always, as it were, moulded upon
these forms, aesthetic feeling becomes attached to
them by the principle of association. At any rate, it
is certain that when we contemplate almost any forms
of plant-structure which, for special reasons of utility,
differ widely from these (to us) more habitual forms,
the result is not suggestive of beauty. Many of the
tropical and un-tree-like plants — such as the cactus
tribe — strike us as odd and quaint, not as beautiful.
Be this however as it may, I trust I have said enough
to prove that in the vegetable world, at all events, the
attainment of beauty cannot be held to have been an
object aimed at, so to speak, for its own sake. Even
if, for the purposes of argument, we were to suppose
that all the forms and colours in the vegetable world
are due to special design, there could be no doubt
that the purpose of this design has been in chief part
a utilitarian purpose ; it has not aimed at beauty ex-
clusively for its own sake. For most of such beauty as
we here perceive is plainly due to the means adopted
for the attainment of life-preserving ends, which, of
course, is a metaphorical way of saying that it is
probably due to natural selection *.
1 The beauty of autumnal tints in fading leaves may possibly be
adduced per contra. But here we have to remember that it is only
some kinds of leaves which thus become beautiful when fading, while,
408 Darwin, and after Darwin.
Turning, then, to the animal kingdom below the
level of insects, here we are bound to confess that
the beauty which so often meets us cannot reasonably
be ascribed either to natural or to sexual selection.
Not to sexual selection for the reasons already given ;
the animals in question are neither sufficiently in-
telligent to possess any aesthetic taste, nor, as a matter
of fact, do we observe that they exercise any choice
in pairing. Not to natural selection, because we cannot
here, as in the case of vegetables, point to any benefit
as generally arising from bright colours and beautiful
forms. On the principles of naturalism, therefore, we
are driven to conclude that the beauty here is purely
adventitious, or accidental. Nor need we be afraid to
make this admission, if only we take a sufficiently wide
view of the facts. For, when we do take such a view,
we find that beauty here is by no means of invariable,
or even of general, occurrence. There is no loveliness
about an oyster or a lob-worm ; parasites, as a rule,
are positively ugly, and they constitute a good half of
all animal species. The truth seems to be, when we
look attentively at the matter, that in all cases where
beauty does occur in these lower forms of animal life,
its presence is owing to one of two things — either
to the radiate form, or to the bright tints. Now,
seeing that the radiate form is of such general
occurrence among these lower animals — appearing
over and over again, with the utmost insistence, even
among groups widely separated from one another by
even as regards those that do, it is not remarkable that their chlorophyll
should, as it were, accidentally assume brilliant tints while breaking
down into lower grades of chemical constitution. The case, in fact, is
exactly parallel to those in the animal kingdom which are considered in
the ensuing paragraphs.
The Theory of Sexual Selection. 409
the latest results of scientific classification— seeing this,
it becomes impossible to doubt that the radiate form
is due to some morphological reasons of wide gener-
ality. Whether these reasons be connected with the
internal laws of growth, or to the external conditions
of environment, I do not pretend to suggest But I
feel safe in saying that it cannot possibly be due to
any design to secure beauty for its own sake. The
very generality of the radiate form is in itself enough
to suggest that it must have some physical, as dis-
tinguished from an aesthetic, explanation ; for, if the
attainment of beauty had here been the object, surely
it might have been even more effectually accomplished
by adopting a greater variety of typical forms — as, for
instance, in the case of flowers.
Coming then, lastly, to the case of brilliant tints in
the lower animals, Mr. Darwin has soundly argued
that there is nothing forced or improbable in the
supposition that organic compounds, presenting as
they do such highly complex and such varied chemical
constitutions, should often present brilliant colouring
incidentally. Considered merely as colouring, there
is nothing in the world more magnificent than arterial
blood ; yet here the colouring is of purely utilitarian
significance. It is of the first importance in the
chemistry of respiration ; but is surely without any
meaning from an aesthetic point of view. For the
colour of the cheeks, and of the flesh generally, in
the white races of mankind, could have been produced
quite as effectually by the use of pigment — as in the
case of certain monkeys. Now the fact that in the
case of blood, as in that of many other highly
coloured fluids and solids throughout the animal
4io Darwin, and after Darwin*
kingdom, the colour is concealed, is surely sufficient
proof that the colour, if regarded from an aesthetic
point of view, is accidental. Therefore, when, as in
other cases, such colouring occurs upon the surface,
and thus becomes apparent, are we not irresistibly
led to conclude that its exhibition in such cases is
likewise accidental, so far as any question of aesthetic
design is concerned ?
I have now briefly glanced at all the main facts of
organic nature with reference to beauty ; and, as a
result, I think it is impossible to resist the general
conclusion, that in organic nature beauty does not
exist as an end per se. All cases where beauty can
be pointed to in organic nature are seemingly due —
either to natural selection, acting without reference
to beauty, but to utility; to sexual selection, act-
ing with reference to the taste of animals ; or else
to sheer accident. And if this general conclusion
should be held to need any special verification, is it
not to be found in the numberless cases where or-
ganic nature not only fails to be beautiful, but reveals
itself as the reverse. Not again to refer to the case
of parasites, what can be more unshapely than a
hippopotamus, or more generally repulsive than a
crocodile ? If it be said that these are exceptions,
and that the forms of animals as a rule are graceful,
the answer — even apart from parasites — is obvious.
In all cases where the habits of life are such as to
render rapid locomotion a matter of utilitarian
necessity, the outlines of an animal must be
graceful — else, whether the locomotion be terrestrial,
aerial, or aquatic, it must fail to be swift. Hence it
is only in such cases as that of the hippopotamus,
The Theory of Sexual Selection. 411
rhinoceros, elephant, crocodile, and so forth, where
natural selection has had no concern in developing
speed, that the accompanying accident of gracefulness
can be allowed to disappear. But if beauty in or-
ganic nature had been in itself what may be termed
an artistic object on the part of a divine Creator, it
is absurd to suggest that his design in this matter
should only have been allowed to appear where we
are able to detect other and very good reasons for its
appearance.
Thus, whether we look to the facts of adaptation
or to those of beauty, everywhere throughout organic
nature we meet with abundant evidence of natural
causation, while nowhere do we meet with any in-
dependent evidence of supernatural design. But,
having led up to this conclusion, and having thus
stated it as honestly as I can, I should like to finish
by further stating what, in my opinion is its logical
bearing upon the more fundamental tenets of religious
thought.
As I have already observed at the commencement
of this brief exposition, prior to the Darwinian theory
of organic evolution, the theologian was prone to point
to the realm of organic nature as furnishing a peculiarly
rich and virtually endless store of facts, all combining
in their testimony to the wisdom and the beneficence
of the Deity. Innumerable adaptations of structures
to functions appeared to yield convincing evidence
in favour of design ; the beauty so profusely shed
by living forms appeared to yield evidence, no less
convincing, of that design as beneficent. But both
these sources of evidence have now, as it were, been
412 Darwin, and after Darwin.
tapped at their fountain-head : the adaptation and
the beauty are alike receiving their explanation at
the hands of a purely mechanical philosophy. Nay,
even the personality of man himself is assailed ; and
this not only in the features which he shares with
the lower animals, but also in his god-like attributes
of reason, thought, and conscience. All nature has
thus been transformed before the view of the present
generation in a manner and to an extent that has
never before been possible : and inasmuch as the
change which has taken place has taken place in
the direction of naturalism, and this to the extent of
rendering the mechanical interpretation of nature uni-
versal,it is no wonder if the religious mind has suddenly
awakened to a new and a terrible force in the words of
its traditional enemy — Where is now thy God ?
This is not the place to discuss the bearings of
science on religion l ; but I think it is a place where
one may properly point out the limits within which no
such bearings obtain. Now, from what has just been
said, it will be apparent that I am not going to
minimise the change which has been wrought. On
the contrary, I believe it is only stupidity or affecta-
tion which can deny that the change in question is
more deep and broad than any single previous change
in the whole history of human thought. It is a fun-
damental, a cosmical, a world-transforming change.
Nevertheless, in my opinion, it is a change of a non-
theistic, as distinguished from an a-theistic, kind. It
has rendered impossible the appearance in literature
of any future Paley, Bell, or Chalmers ; but it has
1 The best treatise on this subject is Pro£ Le Conte's Evolution and
its Relation to Religious Thought (Appleton & Co. 1888).
The Theory of Sexual Selection. 4 1 3
done nothing in the way of negativing that belief in a
Supreme Being which it was the object of these
authors to substantiate. If it has demonstrated the
futility of their proof, it has furnished nothing in the
way of disproof. It has shown, indeed, that their line
of argument was misjudged when they thus sought
to separate organic nature from inorganic as a theatre
for the special or peculiar display of supernatural
design ; but further than this it has not shown anything.
The change in question therefore, although greater in
degree, is the same in kind as all its predecessors : like
all previous advances in cosmological theory which
have been wrought by the advance of science, this
latest and greatest advance has been that of revealing
the constitution of nature, or the method of causation,
as everywhere the same. But it is evident that this
change, vast and to all appearance final though it be,
must end within the limits of natural causation itself.
The whole world of life and mind may now have been
annexed to that of matter and energy as together
constituting one magnificent dominion, which is
everywhere subject to the same rule, or method of
government. But the ulterior and ultimate question
touching the nature of this government as mental or
non-mental, personal or impersonal, remains exactly
where it was. Indeed, this is a question which cannot
be affected by any advance of science, further than
science has proved herself able to dispose of erroneous
arguments based upon ignorance of nature. For while
the sphere of science is necessarily restricted to that
of natural causation which it is her office to explore,
the question touching the nattire of this natural
causation is one which as necessarily lies without the
414 Darwin, and ajter Darwin.
whole sphere of such causation itself: therefore it lies
beyond any possible intrusion by science. And not
only so. But if the nature of natural causation be
that of the highest order of known existence, then,
although we must evidently be incapable of conceiving
what such a Mind is, at least we seem capable of
judging what in many respects it is not. It cannot
be more than one ; it cannot be limited either in
space or time ; it cannot be other than at least as
self-consistent as its manifestations in nature are in-
variable. Now, from the latter deduction there arises
a point of first-rate importance in the present con-
nexion. For if the so-called First Cause be intelligent,
and therefore all secondary causes but the expression
of a supreme Will, in as far as such a Will is self-
consistent, the operation of all natural causes must
be uniform,— with the result that, as seen by us, this
operation must needs appear to be what we call
mechanical. The more unvarying the Will, the more
unvarying must be this expression thereof; so that,
if the former be absolutely self-consistenf, the latter
cannot fail to be as reasonably interpreted by the
theory of mindless necessity, as by that of ubiquitous
intention. Such being, as it appears to me, the pure
logic of the matter, the proof of organic evolution
amounts to nothing more than the proof of a natural
process. What mode of being is ultimately concerned
in this process — or in what it is that this process
ultimately consists — is a question upon which science
is as voiceless as speculation is vociferous.
But, it may still be urged, surely the principle of
natural selection (with its terrible basis in the struggle
for existence) and the principle of sexual selection
The Theory of Sexual Selection. 415
(with its consequence in denying beauty to be an end
in itself) demonstrate that, if there be design in nature,
such design at all events cannot be beneficent. To
this, however, I should again reply that, just as
touching the major question of design itself, so as
touching this minor question of the quality of such
design as beneficent, I do not see how the matter has
been much affected by a discovery of the principles
before us. For we did not need a Darwin to tell us
that the whole creation groaneth and travaileth to-
gether in pain. The most that in this connexion
Darwin can fairly be said to have done is to have
estimated in a more careful and precise manner than
any of his predecessors, the range and the severity of
this travail. And if it be true that the result of what
may be called his scientific analysis of nature in respect
of suffering is to have shown the law of suffering even
more severe, more ubiquitous, and more necessary
than it had ever been shown before, we must remember
at the same time how he has proved, more rigidly
than was ever proved before, that suffering is a
condition to improvement — struggle for life being the
raison dfare of higher life, and this not only in the
physical sphere, but also in the mental and moral.
Lastly, if it be said that \ht choice of such a method,
whereby improvement is only secured at the cost of
suffering, indicates a kind of callousness on the part
of an intelligent Being supposed to be omnipotent, I
confess that such does appear to me a legitimate
conclusion — subject, however, to the reservation that
higher knowledge might displace it. For, as far as
matters are now actually presented to the unbiased
contemplation of a human mind, this provisional
416 Darwin, and after Darwin.
inference appears to me unavoidable — namely, that
if the world of sentient life be due to an Omnipotent
Designer, the aim or motive of the design must have
been that of securing a continuous advance of animal
improvement, without any regard at all to animal suf-
fering. For I own it does not seem to me compatible
with a fair and honest exercise of our reason to set the
sum of animal happiness over against the sum of animal
misery, and then to allege that, in so far as the former
tends to balance — or to over-balance — the latter, thus
far is the moral character of the design as a whole
vindicated. Even if it could be shown that the sum of
happiness in thebrute creation considerably preponder-
ates over that of unhappiness — which is the customary
argument of theistic apologists, — we should still remain
without evidence as to this state of matters having
formed any essential part of the design. On the other
hand, we should still be in possession of seemingly good
evidence to the contrary. For it is clearly a condition
to progress by survival of the fittest, that as soon as
organisms become sentient selection must be ex-
ercised with reference to sentiency ; and this means
that, if further progress is to take place, states of
sentiency must become so organized with reference to
habitual experience of the race, that pleasures and
pains shall answer respectively to states of agreement
and disagreement with the sentient creature's environ-
ment. Those animals which found pleasure in what
was deleterious to life would not survive, while those
which found pleasure in what was beneficial to life
would survive ; and so eventually, in every species of
animal, states of sentiency as agreeable or disagreeable
must approximately correspond with what is good for
The Theory of Sexual Selection. 417
the species or bad for the species. Indeed, we may
legitimately surmise that the reason why sentiency
(and, a fortiori, conscious volition) has ever appeared
upon the scene at all, has been because it furnishes —
through this continuously selected adjustment of states
of sentiency to states of the sentient organism — so
admirable a means of securing rapid, and often refined,
adjustments by the organism to the habitual conditions
of its life *. But, if so, not only is this state of matters
a condition to progress in the future ; it is further,
and equally, a consequence of progress in the past.
However, be this as it may, from all that has gone
before does it not become apparent that pleasure or
happiness on the one hand, and pain or misery on the
other, must be present in sentient nature? And so
long as they are both seen to be equally necessary
under the process of evolution by natural selection,
we have clearly no more reason to regard the pleasure
than the pain as an object of the supposed design.
Rather must we see in both one and the same
condition to progress under the method of natural
causation which is before us ; and therefore I cannot
perceive that it makes much difference — so far as the
argument for beneficence is concerned — whether the
pleasures of animals outweigh their pains, or vice
vcrsd.
Upon the whole, then, it seems to me that such
evidence as we have is against rather than in favour
of the inference, that if design be operative in animate
nature it has reference to animal enjoyment or well-
being, as distinguished from animal improvement or
evolution. And if this result should be found dis-
1 See Mental Evolution in Animals, pp. uo-iii.
* EC
41 8 Darwin, and after Darwin.
tasteful to the religious mind — if it be felt that there
is no desire to save the evidences of design unless
they serve at the same time to testify to the nature of
that design as beneficent, — I must once more observe
that the difficulty thus presented to theism is not a
difficulty of modern Creation. On the contrary, it has
always constituted the fundamental difficulty with
which natural theologians have had to contend. The
external world appears, in this respect, to be at
variance with our moral sense ; and when the an-
tagonism is brought home to the religious mind, it
must ever be with a shock of terrified surprise. It
has been newly brought home to us by the general-
izations of Darwin ; and therefore, as I said at the
beginning, the religious thought of our generation
has been more than ever staggered by the question —
Where is now thy God ? But I have endeavoured to
show that the logical standing of the case has not
been materially changed ; and when this cry of
Reason pierces the heart of Faith, it remains for
Faith to answer now, as she has always answered
before — and answered with that trust which is at
once her beauty and her life — Verily thou art a God
that hidest thyself.
APPENDIX AND NOTES
APPENDIX TO CHAPTER V.
OH OBJECTIONS WHICH HAVE BEEN BROUGHT AGAINST THK
THEORY OF ORGANIC EVOLUTION ON GROUNDS OF
PALAEONTOLOGY.
WHILE stating in the text, and in a necessarily general way,
the evidence which is yielded by palaeontology to the theory
of organic evolution, I have been desirous of not overstating
it. Therefore, in the earlier paragraphs of the chapter,
which deal with the most general heads of such evidence, I
introduced certain qualifying phrases ; and I will now give
the reasons which led me to do so.
Of all the five biological sciences which have been called
into evidence — viz. those of Classification, Morphology,
Embryology, Palaeontology, and Geographical Distribution —
it is in the case of palaeontology alone that any important
or professional opinions still continue to be unsatisfied.
Therefore, in order that justice may be done to this line of
dissent, I have thought it better to deal with the matter in
a separate Appendix, rather than to hurry it over in the
text. And, as all the difficulties or objections which have
been advanced against the theory of evolution on grounds of
palaeontology must vary, as to their strength, with the estimate
which is taken touching the degree of imperfection of the
geological record, I will begin by adding a few paragraphs to
what has already been said in the text upon this subject.
First, then, as to the difficulties in the way of fossils being
422 Darwin, and after Darwin.
formed at all. We have already noticed in the text that it is
only the more or less hard parts of organisms which under
any circumstances can be fossilized; and even the hardest
parts quickly disintegrate if not protected from the weather
on land, or from the water on the sea-bottom. Moreover, as
Darwin says, "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 proportion of the ocean, the bright blue
tint of the water bespeaks its purity. The many cases on
record of a formation conformably covered, after an immense
interval of time, by another and a later formation, without the
underlying bed having suffered in the interval any wear and
tear, seem explicable only on the view of the bottom of the
sea not rarely lying for ages in an unaltered condition."
Next, as regards littoral animals, he shows the difficulty
which they must have in becoming fossils, and gives a
striking example in several of the existing species of a sub-
family of cirripedes (Chthamalince), " which coat the rocks all
over the world in infinite numbers," yet, with the exception of
one species which inhabits deep water, no vestige of any of
them has been found in any tertiary formation, although it is
known that the genus Chthamalus existed through the Chalk
period. Lastly, " with respect to the terrestrial productions
which lived through the secondary and palaeozoic periods, it
is superfluous to state 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 one exception ; while, " in regard to mammiferous
remains, a glance at the historical table in Lyell's Manual
will bring home the truth, how accidental and rare has been
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
Appendix to Chapter V. 423
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 perhaps of even more importance than all these known
causes which prevent the formation of fossils, is the existence
of unknown causes which make for the same result. For
example, the Flysch-formation is a formation of several
thousand feet in thickness (as much as 6000 in some places),
and it extends for at least 300 miles from Vienna to
Switzerland; moreover, it consists of shale and sandstone.
Therefore, alike in respect of time, space, and character, it is
just such a formation as we should expect to find highly rich
in fossils; yet, "although this great mass has been most
carefully searched, no fossils, except a few vegetable remains,
have been found."
So much then for the difficulty, so to speak, which nature
experiences in the manufacture of fossils. Probably not one
per cent, of the species of animals which have inha'nted the
earth has left a single individual as a fossil, whereby to record
its past existence.
But of even more importance than this difficulty of making
fossils in the first instance, is the difficulty of preserving them
when they are made. The vast majority of fos.-ils have been
formed under water, and a large proportional number of
these — whether the animals were marine, terrestrial, or
inhabitants of fresh water — have been formed in sedimentary
deposits either of sand, gravel, or other porous material.
Nosv. where such deposits have been afterwards raised into
the air for any considerable time — and this has been more or
less the case with all deposits which are available for explora-
tion— their fossiliferous contents will have been, as a general
rule, dissolved by the percolation of rain-water charged with
carbonic acid. Similarly, sea-water has recently been found
to be a surprisingly strong solvent of calcareous material:
hence, Saturn-like, the ocean devours her own progeny
424 Darwin, and after Darwin.
as far as shells and bones of all kinds are concerned —
and this to an extent of which we have probably no adequate
conception.
Of still greater destructive influence, however, than these
solvent agencies in earth and sea, are the erosive agencies of
both. Any one who watches the pounding of the waves
upon the shore ; who then observes the effect of it upon the
rocks broken into shingle, and on the shingle reduced to
sand ; who, looking behind him at the cliffs, sees there the
evidence of the gradual advance of this all-pulverising power
— an advance so gradual that no yard of it is accomplished
until within that yard the " white teeth " have eaten well into
the " bowels of the earth " ; who then reflects that this process
is going on simultaneously over hundreds of thousands of miles
of coast-lines throughout the world ; and who finally extends
his mental vision from space to time, by trying dimly to
imagine what this ever-roaring monster must have consumed
during the hundreds of millions of years that slowly rising
and slowly sinking continents have exposed their whole areas
to her jaws ; whoever thus observes and thus reflects must be
a dull man, if he does not begin to feel that in the presence
of such a destroyer as this we have no reason to wonder at a
frequent silence in the testimony of the rocks.
But although the erosive agency of the sea is thus so
inconceivably great, it is positively small if compared with
erosive agencies on land. The constant action of rain, wind,
and running water, in wearing down the surfaces of all lands
into " the dust of continents to be " ; the disintegrating
effects on all but the very hardest rocks of winter frosts
alternating with summer heats ; the grinding power of ice
in periods of glaciation; and last, but not least, the whole-
sale melting up of sedimentary formations whenever these
have sunk for any considerable distance beneath the earth's
surface : — all these agencies taken together constitute so
prodigious a sum of energies combined through immeasure-
Appendix to Chapter V. 425
able ages in their common work of destruction, that when
we try to realise what it must amount. to, we can scarcely
fail to wonder, not that the geological record is highly im-
perfect, but that so much of the record has survived as we
find to have been the case. And, if we add to these erosive
and solvent agencies on land the erosive and solvent agencies
of the sea, we may almost begin to wonder that anything
deserving the name of a geological record is in existence
at all.
That such estimates of the destructive powers of nature
are not mere matters of speculative reasoning may be amply
shown by stating one single fact, which, like so many others
where the present subject is concerned, we owe to the
generalizations of Darwin. Plutonic rocks, being those which
have emerged from subterranean heat of melting intensity,
must clearly at some time or another have lain beneath the
whole thickness of sedimentary deposits, which at that time
occupied any part of the earth's surface where we now find
the Plutonic rocks exposed to view. Or, in other words,
wherever we now find Plutonic rocks at the surface of the earth,
we must conclude that all the sedimentary rocks by which they
were covered when in a molten state have since been entirely
destroyed ; several vertical miles of the only kinds of rocks
in which fossils can possibly occur must in all such cases
have been abolished in Mo. Now, in many parts of the
world metamorphic rocks — which have thus gradually risen
from Plutonic depths, while miles of various other rock-
formations have been removed from their now exposed
surfaces — cover immense areas, and therefore testify by their
present horizontal range, no less than by their previously
vertical depth, to the enormous scale on which a total
destruction has taken place of everything that once lay
above them. For instance, the granitic region of Parime is
at least nineteen times the size of Switzerland; a similar
region south of the Amazon is probably larger than France,
426 Darwin, and after Darwin.
Spain, Italy, and Great Britain all put together; and, more
remarkable still, over the area of the United States and
Canada, granitic rocks exceed in the proportion of 19 to \z\
the whole of the newer Palaeozoic formations. Lastly, after
giving these examples, Darwin adds the important con-
sideration, that "hi 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 rest unconformably on them, and which
could not have formed part of the original mantle under
which they were crystallized."
The above is a brief condensation of the already condensed
statement which Darwin has given of the imperfection of the
geological record ; but I think it is enough to show, in a
general way, how precarious must be the nature of any
objections to the theory of evolution which are founded
merely upon the silence of palaeontology in cases where, if
the record were anything like complete, we should be entitled
to expect from it some positive information. But, as we
have seen in the text, imperfect though the record be, in as
far as it furnishes positive information at all, this is well-nigh
uniformly in favour of the theory; and therefore, even on
grounds of palaeontology alone, it appears to me that Darwin
is much too liberal where he concludes his discussion by
saying, — " Those who believe that the geological record is
in any degree perfect, will undoubtedly at once reject the
theory." If in any measure reasonable, such persons ought
rather to examine their title to such a belief; and even if they
disregard the consensus of testimony which is yielded by all
the biological sciences to the theory of evolution, they ought
at least to hold their judgment in suspense until they shall
have not only set against the apparently negative testimony
which is yielded by geology its unquestionably positive testi-
mony, but also well considered the causes which may — or
rather must — have so gravely impaired the geological record.
Appendix to Chapter V. 427
However, be this as it may, I will now pass on to con-
sider the difficulties and objections which have been brought
against the theory on grounds of palaeontology.
These may be classified under four heads. First, the ab-
sence of varietal links between allied species ; second, the
sudden appearance of whole groups of species — not only as
genera and families, but even sometimes as orders and classes
— without any forms leading up to them ; third, the occurrence
of highly organized types at much lower levels of geological
strata than an evolutionist would antecedently expect ; and,
fourth, the absence of fossils of any kind lower down than
the Cambrian strata.
Now all these objections depend on est'mates of the im-
perfection of the geological record much lower than that
which is formed by Darwin. Therefore I have arranged the
objections in their order of difficulty in this respect, or in the
order that requires successively increasing estimates of the
imperfection of the record, if they are to be successively
answered.
I think that the first of them has been already answered in
the text, by showing that even a very moderate estimate of the
imperfection of the record is enough to explain why interme-
diate varieties, connecting allied species, are but comparatively
seldom met with. Moreover it v\ as shown that in some cases,
where shells are concerned, remarkably well-connected series
of such varieties have been met with. And the same applies
to species and genera in certain other cases, as in the
equine family.
But no doubt a greater difficulty arises where whole groups
of species and genera, or even families and orders, appear to
arise suddenly, without anything leading up to them. Even
this the second difficulty, however, admits of being fully met,
when we remember that in very many cases it has been
proved, quite apart from the theory of descent, that super-
jacent formations have been separated from one another by
428 Darwin, and after Darwin.
wide intervals of time. And even although it often happens
that intermediate deposits which are absent in one part of
the world are present in another, we have no right to assume
that such is always the case. Besides, even if it were, we
should have no right further to assume that the faunas of
widely separated geographical areas were identical during the
time represented by the intermediate formation. Yet, unless
they were identical, we should not expect the fossils of the
intermediate formation, where extant, to yield evidence of
what the fossils would have been in this same formation else-
where, had it not been there destroyed. Now, as a matter of
fact, " geological formations of each region are almost in-
variably intermittent " ; and although in many cases a more
or less continuous record of past forms of life can be
obtained by comparing the fossils of one region and forma-
tion with those of another region and adjacent formations,
it is evident (from what we know of the present geographical
distribution of plants and animals) that not a few cases there
must have been where the interruption of the record in
one region cannot be made good by thus interpolating the
fossils of another region. And we must remember it is
by selecting the cases where this cannot be done that the
objection before us is made to appear formidable. In other
words, unless whole groups of new species which are un-
known in formation A appear suddenly in formation C
of one region (X), where the intermediate formation B is
absent; and unless in some other region (Y), where B is
present, the fossiliferous contents of B fail to suj ply the fossil
ancestry of the new species in A (X) ; unless such a state of
matters is found to obtain, the objection before us has nothing
to say. But at best this is negative evidence ; and, in order
to consider it fairly, we ought to set against it the cases where
an interposition of fossils found in B (Y) does furnish the fossil
ancestry of what would otherwise have been an abrupt appear-
ance ot whole groups of new species in A (X). Now such
Appendix to Chapter V. 429
cases are neither few nor unimportant, and therefore they
deprive the objection of the force it would have had if the
selected cases to the contrary were the general rule.
In addition to these considerations, the following, some of
which are of a more special kind, appear to me so important
that I will quote them almost in extenso.
We continually forget how large the world is, compared with
the area over which our geological formations have been care-
fully-examined : we forget that groups of species may elsewhere
have long existed, and have slowly multiplied, before they in-
vaded the ancient archipelagoes of Europe and the United States.
We do not make due allowance for the intervals of time which
have elapsed between our consecutive formations, — longer per-
haps 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 of 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 form 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 compara-
tively short time would be necessary to produce many divergent
forms, which would spread rapidly and widely throughout the
world. . . .
In geological treatises, 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 commence-
ment 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
430 Darwin, and after Darwin.
back as the miocene stage. Had it not been for the rare accident
of the preservation of footsteps in the new red sandstone of the
United States, who would have ventured to suppose that, no
less than at least thirty kinds of 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
palaeontologists maintained that the whole class of birds came
suddenly into existence during the eocene period ; but now
we know, on the authority of Professor Owen, that a bird
certainly lived during the deposition of the upper green-sand.
And still more recently that strange bird, the Archeopteryx . . .
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 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 recognized ; from all these circumstances, I
inferred that had sessile cirripedes existed during the secondary
periods, they would certainly have been preserved and dis-
covered ; 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 thought one more
instance of the abrupt appearance of a great group of species.
But my work had hardly been published, when a skilful palaeon-
tologist, M. Bosquet, sent me a drawing of a perfect specimen of
an unmistakeable sessile cirripede, which he had himself ex-
tracted from the chalk of Belgium. And, as if to make the case
as striking as possible, this sessile cirripede was a Chthamalus,
a very common, large, and ubiquitous genus, of which not one
specimen has as yet been found even in any tertiary stratum.
Still more recently, a Pyrgoma, a member of a distinct sub-
Appendix to Chapter V. 431
family of sessile cirripedes, has been discovered by Mr. Woodward
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 been thus classed by one high authority. If the
teleosteans had really appeared suddenly in the northern
hemisphere, the fact would have been highly remarkable ; but
it would not have formed an insuperable difficulty, unless
it could likewise have been shown that at the same period
the species were suddenly and simultaneously developed in
other quarters of the world. It is almost superfluous to re-
mark 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 fish might formerly have had
a similarly confined range, and after having been largely
developed in some one sea, might 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 Archipelago 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
southern 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 palasontological 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
43 2 Darwin, and after Darwin.
forms throughout the world, as it would be for a naturalist to
land for five minutes on some one barren point in Australia,
and then to discuss the number and range of its productions l.
In view of all the foregoing facts and considerations, it
appears to me that the second difficulty on our list is com-
pletely answered. Indeed, even on a moderate estimate of
the imperfection of the geological record, the wonder would
have been if many cases had not occurred where groups of
species present the fictitious appearance of having been
suddenly and simultaneously created in the particular forma-
tions where their remains now happen to be observable.
Turning next to the third objection, there cannot be any
question that every here and there in the geological series
animals occur of a much higher grade zoologically than the
theory of evolution would have expected to find in the strata
where they are found. At any rate, speaking for myself, I
should not have antecedently expected to meet with such
highly differentiated insects as butterflies and dragonflies in
the middle of the Secondaries : still less should I have ex-
pected to encounter beetles, cockroaches, spiders, and May-
flies in the upper and middle Primaries — not to mention an
insect and a scorpion even in the lower. And I think
the same remark applies to a whole sub-kingdom in the case
of Vertebrata. For although it is only the lowest class of
the sub-kingdom which, so far as we positively know, was
represented in the Devonian and Silurian formations, we
must remember, on the one hand, that even a cartilaginous
or ganoid fish belongs to the highest sub-kingdom of the
animal series ; and, on the other hand, that such animals are
thus proved to have abounded in the very lowest strata
where there is good evidence of there having been any forms of
life at all. Lastly, the fact that Marsupials occur in the Trias,
1 Origin of Species, 382-5.
Appendix to Chapter V. 433
coupled with the fact that the still existing Monotremata
are what may be termed animated fossils, referring us by their
lowly type of organization to some period enormously more
remote, — these facts render it practically certain that some
members of this very highest class of the highest sub-kingdom
must have existed far back in the Primaries.
These things, I say, I should not have expected to find,
and I think all other evolutionists ought to be prepared to
make the same acknowledgment. But as these things have
been found, the only possible way of accounting for them on
evolutionary principles is by supposing that the geological
record is even more imperfect than we needed to suppose in
order to meet the previous objections. I cannot see, however,
why evolutionists should be afraid to make this acknowledg-
ment. For I do not know any reason which would lead us to
suppose that there is any common measure between the
distances marked on our tables of geological formations, and
the times which those distances severally represent. Let the
reader turn to the table on page 163, and then let him say
why the 30,000 feet of so-called Azoic rocks may not represent
a greater duration of time than does the thickness of all the
Primary rocks above them put together. For my own part I
believe that this is probably the case, looking to the enormous
ages during which these very early formations must have been
exposed to destructive agencies of all kinds, now at one time
and now at another, in different parts of the world. And,
of course, we are without any means of surmising what
ranges of time are represented by the so-called Primeval
rocks, for the simple reason that they are non-sedimentary,
and non-sedimentary rocks cannot be expected to contain
fossils.
But, it will be answered, the 30,000 feet of Azoic rocks,
lying above the Primeval, are sedimentary to some extent :
they are not all completely metamorphic: yet they are
all destitute of fossils. This is the fourth and last difficulty
* F f
434 Darwin, and after Darwin.
which has to be met, and it can only be met by the con-
siderations which have been advanced by Lyell and Darwin.
The former says : —
The total absence of any trace of fossils has inclined many
geologists to attribute the origin of the most ancient strata to
an azoic period, or one antecedent to the existence of organic
beings. Admitting, they say, the obliteration, in some cases, of
fossils by plutonic action, we might still expect that traces of
them would oftener be found in certain ancient systems of slate,
which can scarcely be said to have assumed a crystalline structure.
But in urging this argument it seems to be forgotten that there
are stratified formations of enormous thickness, and of various
ages, some of them even of tertiary date, and which we know
were formed after the earth had become the abode of living
creatures, which are, nevertheless, in some districts, entirely
destitute of all vestiges of organic bodies '.
He then proceeds to mention sundry causes (in addition to
plutonic action) which are adequate to destroy the fossiliferous
contents of stratified rocks, and to show that these may well
have produced enormous destruction of organic remains in
these oldest of known formations.
Darwin's view is that, during the vast ages of time
now under consideration, it is probable that the distribution
of sea and land over the earth's surface has not been uni-
formly the same, even as regards oceans and continents.
Now, if this were the case, "it mjght 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 superincumbent water, might have undergone far
more metamorphic action than strata which have always
remained nearer to the surface. The immense areas in
some parts of the world, for instance in South America,
of naked metamorphic rocks, which must have been heated
under great pressure, have always seemed to me to require
1 Elements of Geology, p. 587.
Appendix to Chapter V. 435
some special explanation ; and we may perhaps believe that we
see, in these large areas, the many formations long anterior tc
the Cambrian epoch in a completely metamorphosed and
denuded condition1." The probability of this view he
sustains by certain general considerations, as well as par-
ticular facts touching the geology of oceanic islands, &c.
On the whole, then, it seems to me but reasonable to
conclude, with regard to all four objections in question, as
Darwin concludes with regard to them : —
For my part, following out Lyell's metaphor, I look at the
geological record as a history of the world imperfectly kept,
written in a changing dialect ; of this history we possess the last
volume alone, relating only to two or three countries. Of this
volume, only here and there a short chapter has been preserved ;
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 us to have been abruptly introduced. On this view,
the difficulties above discussed are greatly diminished, or even
disappear*.
As far as I can see, the only reasonable exception that
can be taken to this general view of the whole matter, is one
which has been taken from the side of astronomical
physics.
Put briefly, it is alleged by one of the highest authorities
in this branch of science, that there cannot have been any
such enormous reaches of unrecorded time as would be
implied by the supposition of there having been a lost history
of organic evolution before the Cambrian period. The
grounds of this allegation I am not qualified to examine ;
but in a general way I agree with Prof. Huxley in feeling
that, from the very nature of the case, they are necessarily
1 Origin of Species, p. 289.
» Ibid.
F f a
436 Darwin, and after Darwin.
precarious, — and this in so high a degree that any conclusions
raised on such premises are not entitled to be deemed for-
midable \
Turning now to plants, the principal and the ablest
opponent of the theory of evolution is here unquestionably
Mr. Carruthers 2. The difficulties which he adduces may be
classified under three heads, as follows : —
i. There is no evidence of change in specific forms of
existing plants. Not only are the numerous species of
plants which have been found in Egyptian mummies in-
distinguishable from their successors of to-day ; but, what
is of far more importance, a large number of our own
indigenous plants grew in Great Britain during the glacial
period (including under this term the warm periods between
those of successive glaciations), and in no one case does it
appear that any modification of specific type has occurred.
This fact is particularly remarkable as regards leaves,
because on the one hand they are the organs of plants which
are most prone to vary, while on the other hand they are
likewise the organs which lend themselves most perfectly
to the process of fossilization, so that all details of their
structure can be minutely observed in the fossil state. Yet
the interval since the glacial period, although not a long one
geologically speaking, is certainly what may be called an
appreciable portion of time in the history of Dicotyledonous
plants since their first appearance in the Cretaceous epoch.
Again, if we extend this kind of enquiry so as to include the
world as a whole, a number of other species of plants dating
from the glacial epoch are found to tell the same story —
notwithstanding that, in the opinion of Mr. Carruthers, they
must all have undergone many changes of environment
1 See Lay Sermons, Lecture on Geological Reform.
2 See especially the following Presidential addresses:— Geol Assoc,
NOT. 1876 ; Section D. Brit. Assoc., 1886 ; Lin. Soc., 1890.
Appendix to Chapter V. 437
while advancing before, and retreating after, successive
glaciations in different parts of the globe. Or, to quote his
own words : — " The various physical conditions which of
necessity affected these [41] species in their diffusion over
such large areas of the earth's surface in the course of, say,
250,000 years, should have led to the production of many
varieties ; but the uniform testimony of the remains of this
considerable pre-glacial flora, as far as the materials admit
of a comparison, is that no appreciable change has taken
place."
2. There is no appearance of generalized forms among
the earliest plants with which we are acquainted. For ex-
ample, in the first dry land flora — the Devonian — we have
representatives of the Filices, Equisetacece, and Lycopodiacece,
all as highly specialized as their living representatives, and
exhibiting the differential characters of these closely related
groups. Moreover, these plants were even more highly
organized than their existing descendants in regard to their
vegetative structure, and in some cases also in regard to
their reproductive organs. So likewise the Gymnosperms
of that time show in their fossil state the same highly organ-
ized woody structure as their living representatives.
3. Similarly, and more generally, the Dicotyledonous plants,
which first appear in the Cretaceous rocks, appear there
suddenly, without any forms leading up to them — notwith-
standing that " we know very well the extensive flora of the
underlying Wealden." Moreover, we have all the three great
divisions of the Dicotyledons appearing together, and so
highly differentiated that all the species are referred to ex-
isting genera, with the exception of a very few imperfectly
preserved, and therefore uncertain fragments.
Such being the facts, we may begin by noticing that, even
at first sight, they present different degrees of difficulty.
Thus, I cannot see that there is much difficulty with
regard to those in class a. Only if we were to take the
438 Darwin, and after Darwin.
popular (and very erroneous) view of organic evolution as
a process which is always and everywhere bound to promote
the specialization of organic types — only then ought we to
see any real difficulty in the absence of generalized types
preceding these existing types. Of course we may wonder
why still lower down in the geological series we do not
meet with more generalized (or ancestral) types; but this
is the difficulty number 3, which we now proceed to
examine.
Concerning the other two difficulties, then, the only possible
way of meeting that as to the absence of any parent forms
lower down in the geological series is by falling back — as in
the analogous case of animals — upon the imperfection of the
geological record. Although it is certainly remarkable that
we should not encounter any forms serving to connect the
Dicotyledonous plants of the Chalk \vuh the lower forms of
the underlying Wealden, we must again remember that diffi-
culties thus depending on the absence of any corroborative
record, are by no means equivalent to what would have
arisen in the presence of an adverse record — such, for in-
stance, as would have been exhibited had the floras of the
Wealden and the Chalk been inverted. But, as the case
actually stands, the mere fact that Dicotyledonous plants,
where they first occur, are found to have been already differ-
entiated into their three main divisions, is in itself sufficient
evidence, on the general theory of evolution, that there must
be a break in the record as hitherto known between the
Wealden and the Chalk. Nor is it easy to see how the op-
ponents of this theory can prove their negative by furnishing
evidence to the contrary. And although such might justly be
deemed an unfair way of putting the matter, were this the only
case where the geological record is in evidence, it is not so
when we remember that there are numberless other cases
where the geological record does testify to connecting links in
a most satisfactory manner. For in view of this consideration
Appendix to Chapter V. 439
the burden of proof is thrown upon those who point to par-
ticular cases where there is thus a conspicuous absence of
transitional forms — the burden, namely, of proving that such
cases are not due merely to a break in the record. Besides,
the break in the record as regards this particular case may
be apparent rather than real. For I suppose there is no
greater authority on the pure geology of the subject than
Sir Charles Lyell, and this is what he says of the particular
case in question. " If the passage seem at present to be
somewhat sudden from the flora of the Lower or Neocomian
to that of the Upper Cretaceous period, the abruptness of
the change will probably disappear when we are better ac-
quainted with the fossil vegetation of the uppermost tracts of
the Neocomian and that of the lowest strata of the Gault, or
true Cretaceous series '."
Lastly, the fact of the flora of the glacial epoch not
having exhibited any modifications during the long residence
of some of its specific types in Great Britain and else-
where, is a fact of some importance to the general theory of
evolution, since it shows a higher degree of stability on the
part of these specific types than might perhaps have been ex-
pected, supposing the theory to be true. But I do not see that
this constitutes a difficulty against the theory, when we have so
many other cases of proved transmutation to set against it.
For instance, not to go further afield than this very glacial
flora itself, it will be remembered that in an earlier chapter
I selected it as furnishing specially cogent proof of the
transmutation of species. What, then, is the explanation of
so extraordinary a difference between Mr. Carruthers' views
and my own upon this point ? I believe the explanation to
be that he does not take a sufficiently wide survey of the
facts.
To begin with, it seems to me that he exaggerates the
vicissitudes to which the species of plants that he calls into "
1 Elements of Geology, p. 280.
440 Darwin, and after Darwin.
evidence have been exposed while advancing before, and
retreating after, the ice. Rather do I agree with Darwin
that " they would 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 indicated in this volume, these forms will not
have been liable to much modification V But, be this
matter of opinion as it may, a much better test is afforded
by those numerous cases all the world over, where arctic
species have been left stranded on alpine areas by the retreat
of glaciation j because here there is no room for differences
of opinion as to a " change of environment " having taken
place. Not to speak of climatic differences between arctje
and alpine stations, consider merely the changes which must
have taken place in the relations of the thus isolated species
to each other, as well as to those of all the foreign plants,
insects, &c., with which they have long been thrown into
close association. If in such cases no variation or transmu-
tation had taken place since the glacial epoch, then indeed
there would have been a difficulty of some magnitude. But,
by parity of reasoning, whatever degree of difficulty would
have been thus presented is not merely discharged, but
converted into at least an equal degree of corroboration,
when it is found that under such circumstances, in whatever
part of the world they have occurred, some considerable
amount of variation and transmutation has always taken
place, — and this in the animals as well as in the plants.
For instance, again to quote Darwin, " If we compare the
present Alpine plants and animals of the several great Euro-
pean mountain-ranges one with another, though many of
the species remain identically the same, some exist as varie-
ties, some as doubtful forms or sub-species, and some as
distinct yet closely allied species representing each other on
1 Origin of Species, p. 338.
Appendix to Chapter V. 441
the several ranges V Lastly, if instead of considering the
case of alpine floras, we take the much larger case of the
Old and New World as a whole, we meet with much larger
proofs of the same general facts. For, " during the slowly
decreasing warmth of the Pliocene period, as soon as the
species in common, which inhabited the New and Old
Worlds, migrated south of the Polar Circle, they will have
been completely cut off from each other. This separation,
as far as the more temperate productions are concerned,
must have taken place long ages ago. As the plants and
animals migrated southward, they will have become mingled
in one great region with the native American productions,
and would have had to compete with them; and, in the
other great region, with those of the Old World. Conse-
quently we have here everything favourable for much modifi-
cation,— for far more modification than with the Alpine
productions left isolated, within a much more recent period,
on the several mountain ranges and on the arctic lands of
Europe and N. America. Hence it has come, that when
we compare the now living productions of the temperate
regions of the New and Old Worlds, we find very few iden-
tical species ; but we find in every 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 specifically
distinct*."
In view then of all the above considerations — and
especially those quoted from Darwin — it appears to me that
far from raising any difficulty against the theory of evolution,
the facts adduced by Mr. Carruthers make in favour of it.
For when once these facts are taken in connection with the
others above mentioned, they serve to complete the cor-
respondence between degrees of modification with degrees
1 Origin of Species, p. 333.
1 Ibid. pp. 333-4.
442 Darwin, and after Darwin.
of time on the one hand, and with degrees of evolution, of
change of environment, &c., on the other. Or, in the
words of Le Conte, when dealing with this very subject, " It
is impossible to conceive a more beautiful illustration of
the principles we have been trying to enforce V
1 Evolution and Us Relation to Religious Thought, p. 194.
NOTE A TO PAGE 257.
The passages in Dr. Whewell's writings, to which allusion is
here made, are somewhat too long to be quoted in the text. But
as I think they deserved to be given, I will here reprint a letter
which I wrote to Nature in March, 1888.
In his essay on the Reception of the Origin of Species, Prof. Huxley
writes : —
" It is interesting to observe that the possibility of a fifth alterna-
tive, in addition to the four he has stated, has not dawned upon Dr.
Whewell's mind " (Lift and Lectures of Charles Darwin, vol. ii, p.
195)-
And again, in the article Science, supplied to The Reign of Queen
Victoria, he says : —
" Whewell had not the slightest suspicion of Darwin's main theorem,
even as a logical possibility " (p 365).
Now, although it is true that no indication of such a logical
possibility is to be met with in the History of the Inductive Sciences,
there are several passages in the Rridgewater Treatise which show a
glimmering idea of such a possibility. Of these the following are,
perhaps, worth quoting Speaking of the adaptation of the period of
flowering to the length of a year, he says : —
'; Now such an adjustment must surely be accepted as a proof of
design, exercised in the formation of the world. Why should the
solar year be so long and no longer? or, this being such a length,
why should the vegetable cycle be exactly of the same length ? Can
this be chance ? . . . . And, if not by chance, how otherwise could
such a coincidence occur than by an intentional adjustment of these
two things to one another ; by a selection of such an organization in
plants as would fit them to the earth on which they were to grow ;
by an adaptation of construction to conditions; of the scale of con-
struction to the scale of conditions? It cannot be accepted as an
explanation of this fact in the economy of plants, that it is necessary
to their existence ; that no plants could possibly have subsisted,
444 Darwin, and after Darwin.
and come down to us, except those which were thus suited to their
place on the earth. This is true ; but it does not at all remove the
necessity of recurring to design as the origin of the construction by
which the existence and continuance of plants is made possible. A
watch could not go unless there were the most exact adjustment in
the forms and positions of its wheels ; yet no one would accept it as
an explanation of the origin of such forms and positions that the watch
would not go if these were other than they were. If the objector were
to suppose that plants were originally fitted to years of various lengths,
and that such only have survived to the present time as had a cycle
of a length equal to our present year, or one which could be accom-
modated to it, we should reply that the assumption is too gratuitous
and extravagant to require much consideration."
Again, with regard to "the diurnal period," he adds: —
" Any supposition that the astronomical cycle has occasioned the
physiological one, that the structure of plants has been brought to be
what it is by the action of external causes, or that such plants as
could not accommodate themselves to the existing day have perished,
would be not only an arbitrary and baseless assumption, but, more-
over, useless for the purposes of explanation which it professes, as
we have noticed of a similar supposition with respect to the annual
cycle."
Of course these passages in no way make against Mr. Huxley's
allusions to Dr. Whewell's writings in proof that, until the publi-
cation of the Origin of Species, the " main theorem " of this work had
not dawned on any other mind, save that of Mr. Wallace. But
these passages show, even more emphatically than total silence with
regard to the principle of survival could have done, the real distance
which at that time separated the minds of thinking men from all that
was wrapped up in this principle. For they show that Dr. Whewell,
even after he had obtained a glimpse of the principle " as a logical
possibility," only saw in it an " arbitrary and baseless assumption."
Moreover, the passages show a remarkable juxtaposition of the very
terms in which the theory of natural selection was afterwards for-
mulated. Indeed, if we strike out the one word "intentional"
(which conveys the preconceived idea of the writer, and thus
prevented him from doing justice to any naturalistic view), all the
following parts of the above quotations might be supposed to have
been written by a Darwinian. " If not by chance, how otherwise
could such a coincidence occur, than by an adjustment of these two
things to one another; by a selection of such an organization in
plants as would fit them to the earth on which they were to grow ;
by an adaptation of construction to conditions ; of the scale of con-
struction to the scale of conditions 1 " Yet he immediately goes on to
Note B to Page 295. 445
say : " If the objector were to suppose that plants were originally
fitted to years of various lengths, and that such only have survived to
the present time . . . as could be accommodated to it (i. e. the
actual cycle), we should reply that the assumption is too gratuitous
and extravagant to require much consideration." Was there ever a
more curious exhibition of failure to perceive the importance of a
" logical possibility " ? And this at the very time when another mind
was bestowing twenty years of labour on its " consideration."
NOTE B TO PAGE 295.
Since these remarks were delivered in my lectures as here
printed, Mr. Mivart has alluded to the subject in the following
and precisely opposite sense : —
Many of the more noteworthy instincts lead us from manifesta-
tions of purpose directed to the maintenance of the individual, to no
less plain manifestations of a purpose directed to the preservation of
the race. But a careful study of the interrelations and interdepen-
dencies which exist between the various orders of creatures inhabiting
this planet shows us yet a more noteworthy teleology— the existence
of whole orders of such creatures being directed to the service of
other orders in various degrees of subordination and augmentation
respectively. This study reveals to us, as a fact, the enchainment of
all the various orders of creatures in a hierarchy of activities, in
harmony with what we might expect to find in a world the outcome
of a First Cause possessed of intelligence and will '.
Having read this much, a Darwinian is naturally led to expect
that Mr. Mivart is about to offer some examples of instincts
or structures exemplifying what in the margin he calls the
" Hierarchy of Ministrations." Yet the only facts he proceeds
to adduce are the sufficiently obvious facts, that the inorganic
world existed before the organic, plants before herbivorous
animals, these before carnivorous, and so on : that is to say,
everywhere the conditions to the occurrence of any given stage
of evolution preceded such occurrence, as it is obvious that they
must, if, as of course it is not denied, the possibility of such
occurrence depended on the precedence of such conditions.
1 On Truth, p. 493.
446 Darwin, and after Darwin.
Now, it is surely obvious that such a " hierarchy of ministrations"
as this, far from telling against the theory of natural selection, is
the very thing which tells most in its favour. The fact that
animals, for instance, only appeared upon the earth after there
were plants for them to feed upon, is clearly a necessity of the
case, whether or not there was any des;gn in the matter. Such
" ministrations," therefore, as plant-organisms yield to animal-
organisms is just the kind of ministration that the theory of
natural selection requires. Thus far, then, both the theories-
natural selection and super-natural design— have an equal right
to appropriate the facts. But now, if in no one instance can
it be shown that the ministration of plant-life to animal-life is
of such a kind as to subserve the interests of animal-life without
at the same time subserving those of the plant-life itself, then
the fact makes wholly in favour of the naturalistic explanation
of such ministration as appears. If any plants had presented
any characters pointing prospectively to needs of animals without
primarily ministering to their own, then, indeed, there would
have been no room for the theory of natural selection. But as
this can nowhere be alleged, the theory of natural selection finds
all the facts to be exactly as it requires them to be : such minis-
tration as plants yield to animals becomes so much evidence
of natural selection having slowly formed the animals to appro-
priate the nutrition which the plants had previously gathered—
and gathered under the previous influence of natural selection
acting on themselves entirely for their own sakes. Therefore
I say it is painfully manifest that " the enchainment of all the
various orders of creatures in a hierarchy of activities," is
not "in harmony with what we might expect to find in a
world the outcome of a First Cause possessed of intelligence
and [beneficent] will." So far as any argument from such "en-
chainment" reaches, it makes entirely against the view which
Mr. Mivart is advocating. In point of fact, there is a total
absence of any such " ministration " by one " order of crea-
tures" to the needs of any other order, as the beneficent design
theory would necessarily expect; while such ministration as
actually does obtain is exactly and universally the kind which
the naturalistic theory requires.
Again, quite independently, and still more recently, Mr. Mivart
Note B to Page 295. 447
alluded in Nature (vol. xli, p. 41) to the difficulty which the
apparently exceptional case of gall-formation presents to the
theory of natural selection. Therefore I supplied (vol. xli, p. 80)
the suggestion given in the text, viz. that although it appears im-
possible that the sometimes remarkably elaborate and adaptive
structures of galls can be due to natural selection acting directly
on the plants themselves— seeing that the adaptation has refer-
ence to the needs of their parasites — it is quite possible that
the phenomena may be due to natural selection acting indirectly
on the plants, by always preserving those individual insects (and
larvae) the character of whose secretions is such as will best in-
duce the particular shapes of galls that are required. Several
other correspondents took part in the discussion, and most of
them accepted the above explanation. Mr. T. D. A. Cockerell,
however, advanced another and very ingenious hypothesis,
showing that there is certainly one conceivable way in which
natural selection might have produced all the phenomena of
gall-formation by acting directly on the plants themselves1.
Subsequently Mr. Cockerell published another paper upon the
subject, stating his views at greater length. The following is the
substance of his theory as there presented : —
Doubtless there were internal plant-feeding larvae before there
were galls : and, indeed, we have geological evidence that boring in-
sects date very far back indeed. The primitive internal feeders, then,
were miners in the roots, stems, twigs, or leaves, such as occur very
commonly at the present day. These miners are excessively harmful
to plant-life, and form a class of the most destructive insect-pests
known to the farmer : they frequently cause the death of the whole
or part of the plant attacked. Now, we may suppose that the secre-
tions of certain of these insects caused a swelling to appear where
the larvae lived, and on this excrescence the larvae fed. It is easy to
see that the greater the excrescence, and the greater the tendency ot
the larvae to feed upon it, instead of destroying the vital tissues, the
smaller is the amount of harm to the plant. Now the continued life
and vitality of the plant is beneficial to the larvae, and the larger or
more perfect the gall, the greater the amount of available food.
Hence natural selection will have preserved and accumulated the
gall-forming tendencies, as not only beneficial to the larvae, but as a
means whereby the larvae can feed with least harm to the plant So
1 Nature, vol. xli, p. 344.
448 Darwin, and after Darwin.
far from being developed for the exclusive benefit of the larvae, it is
easy to see that, allowing a tendency to gall-formation, natural
selection would have developed galls exclusively for the benefit of the
plants, so that they might suffer a minimum of harm from the unavoid-
able attacks of insects.
But here it may be questioned — have we proof that internal feeders
tend to form galls ? In answer to this I would point out that gall-
formation is a peculiar feature, and cannot be expected to arise in
every group of internal feeders. But I think we can afford sufficient
proof that wherever it has arisen it has been preserved ; and further,
that even the highly complex forms of galls are evolved from forms
so simple that we hesitate to call them galls at all \
The paper then proceeds to give a number of individual cases.
No doubt the principal objection to which Mr. Cockerell's
hypothesis is open is one that was pointed out by Herr Wet-
terhan, viz. " the much greater facility afforded to the indirect
action through insects, by the enormously more rapid succession
of generations with the latter than with many of their vegetable
hosts — oaks above all2." This difficulty, however, Mr. Cockerell
believes may be surmounted by the consideration that a growing
plant need not be regarded as a single individual, but rather
as an assemblage of such :'.
NOTE C TO PAGE 394.
The only remarks that Mr. Wallace has to offer on the
pattern of colours, as distinguished from a mere brilliancy of
colour, are added as an afterthought suggested to him by the
late Mr. Alfred Tyler's book on Colouration of Animals and
Plants (1886). But, in the first place, it appears to me that
Mr. Wallace has formed an altogether extravagant estimate of the
value of this work. For the object of the work is to show,
" that diversified colouration follows the chief lines of structure,
and changes at points, such as the joints, where function
changes." Now, in publishing this generalization, Mr. Tylor —
who was aot a naturalist — took only a very limited view of the
1 Entomologist, March, 1890. a Nature, vol. xli, p. 394.
3 Ibid. vol. xli, pp. 559-560.
Note C to Page 394. 449
facts. When applied to the animal kingdom as a whole, the
theory is worthless ; and even within the limits of mammals,
birds, and insects — which are the classes to which Mr. Tylor
mainly applies it — there are vastly more facts to negative than
to support it This may be at once made apparent by the
following brief quotation from Prof. Lloyd Morgan : —
It can hardly be maintained that the theory affords us any adequate
explanation of the specific colour-tints of the humming-birds, or the
pheasants, or the Papilionidae among butterflies. If, as Mr. Wallace
argues, the immense tufts of golden plumage in the bird of paradise
owe their origin to the fact that they are attached just above the
point where the arteries and nerves for the supply of the pectoral
muscles leave the interior of the body — and the physiological rationale
is not altogether obvious, — are there no other birds in which similar
arteries and nerves are found in a similar position T Why have
these no similar tufts ? And why, in the birds of paradise themselves,
does it require four years ere these nervous and arterial influences
take effect upon the plumage ? Finally, one would inquire how the
colour is determined and held constant in each species. The difficulty
of the Tylor- Wallace view, even as a matter of origin, is especially
great in those numerous cases in which the colour is determined by
delicate lines, thin plates, or thin films of air or fluid. Mr. Poulton,
who takes a similar line of argument in his Colours of Animals
(p. 326), lays special stress on the production of white (pp. 201-202).
As regards the latter point, it may be noticed that not in any
part of his writings, so far as I can find, does Mr. Wallace allude
to the highly important fact of colours in animals being so
largely due to these purely physical causes. Everywhere he
argues as if colours were universally due to pigments ; and in
my opinion this unaccountable oversight is the gravest defect
in Mr. Wallace's treatment both of the facts and the philosophy
of colouration in the animal kingdom. For instance, as regards
the particular case of sexual colouration, the oversight has pre-
vented him from perceiving that his theory of " brilliancy " as
due to "a surplus of vital energy," is not so much as logically
possible in what must constitute at least one good half of the
facts to which he applies it — unless he shows that there is some
connection between vital energy and the development of stria-
tions, imprisonment of air-bubbles, &c. But any such connection
* Gg
450 Darwin, and after Darwin.
— so essentially important for his theory — he does not even
attempt to show. Lastly, and quite apart from these remarkable
oversights, even if Mr. Tylor's hypothesis were as reasonable and
well-sustained as it is fanciful and inadequate, still it could not
apply to sexual colouration : it could apply only to colouration
as affected by physiological functions common to both sexes.
Yet it is in order to furnish a " preferable substitute " for Mr.
Darwin's theory of sexual colouration, that Mr. Wallace adduces
the hypothesis in question as one of " great weight " ! In this
matter, therefore, I entirely agree with Poulton and Lloyd
Morgan.
INDEX
Accident, Darwin's use of the
word, 334-340 ; beauty due to,
408, 409.
Achromatin, 126-134.
Acquired characters, see Characters.
Acrcea eurita, 328.
Adaptation, facts of, in relation
to theory of natural selection,
401-403, 411.
Adaptive characters, .^Characters.
Esthetic sense in animals, 380-
385 ; see Beautiful.
Agassiz, Prof. A., on fauna of the
Mammoth cave, 70.
Alpine plants, 209, 210, 440-
442. t
Amauns niavius, 328.
Amblyornis inornata, 381-383.
Amphioxus, 137, 138, 145, 146.
Analogy, 38, 50-65, 176, 177,
347-350.
Anthropoid, see Apes.
Antlers, 98-100, 167-169.
Ants, co-operative instincts of,
268 ; leaf-cutting, 332 ; keeping
aphides, 292.
Ape, eye of, 75 ; appendix vermi-
formis of, 84-86.
Apes, ears of, compared with those
of man, 88 ; muscles of, 77, 82,
83; feet of, 77, 78; tail of,
compared with that of man,
82-84 ; hair of, compared with
that of man, 89-91 ; teeth of,
compared with those of man,
92-94; flattening of tibiae of,
95, 96-
Aphides, 292.
Appendix vermiformis of man
cumpared with that of orang,
84-86.
Apteryx, 68, 69.
Archtzopteryx, 171-173.
Arctic plants, 209, 210, 440-442.
Argyll, Duke of, on natural selec-
tion, 334-362.
Aristotle, his idea of scientific
method, i ; on classification,
33, 24.
Arm, distribution of hair on, in
man and apes, 89-92.
Arthropoda, embryology of, 155.
Artificial selection, analogy of,
to natural selection, 295-314:
pictorial representations of pro-
ducts of, 298-312.
Artiodactyls, 182-191.
Association, principle of, in
aesthetics, 404-407.
Aster, 129-133.
Attraction-spheres, 128, 132, 133.
Australia, fauna of, 204, 205 ;
thriving of exotic species in,
286 ; portrait of wild dog of,
3°4-
Azores, 224, 225.
B.
Bacon , Lord , on scientific method , 2 .
Balanoglossus, 147, 148.
BaptanoJon discus, posterior limb
of, i"79-i8i.
Barriers, in relation to geographical
distribution, 216-224.
Bats, 56, 224, 226, 240.
Battle, law of, 385, 386.
Bay a- bird, 381.
Gg 2
452
Index.
Bear, skeleton of, 174; feet off
178.
Beautiful, the, sense of, in animals,
380-385 ; standards of, 380-
404; Darwin's explanation of,
in organic nature, 379-411;
facts of, in inorganic nature in
relation to Darwin's theory of,
in organic, 404 ; often determined
by natural selection, 406, 407 ;
absent in mnny plants and
animals, 408 ; in nature oftep
accidental, 409-411 ; does not
exist in organic nature as an
end per se, 410, 411.
Bees, co-operative instincts of,
268.
Beetles, wingless, 68-70; on
oceanic islands, 324, 226, 229,
332.
Bell, Dr., on natural theology, 412.
Bell-bird, 396-398.
Bembidium, 233.
Bermudas, 225-227.
Biology, ideas of method in, 1-9.
Birds, ovum of, 1 24 ; embryology
of, 151-155; palaeontology of,
163-165, 172, 173 ; brain of,
194-197 ; as carriers of seed,
eggs, and small organisms, 217,
218; distribution of, 224-240;
aesthetic sense of, 380-385 ;
courtship of, 380-385.
Birgus latro, 62-65.
Blood, colour of arterial, 409.
Boar, see Pig.
Bom bus lapidarius, 331.
Bower-birds, play-houses of, 381-
383-
Boyd-Dawkins, on flattening of
early human tibiae, 96.
Brain, palaeontology of, 194-197.
British Isles, see Islands.
Broca, 363.
Bronn, 363.
Budding, see Germination.
Burdon-Sanderson, Pi of., on electric
organ of skate, 366.
Butler, Bishop, on argument from
ignorance, 41.
Butterflies, defensive colouring of,
381-339.
Csesalpino, on classification, 34.
Calf, embryology of, 153.
Camel, foot of, 187-191.
Canadian stag, 196, 198, 199.
Canaries, portraits of, 303 ; first
mentioned by Gesner, 312, 313.
Cape de Verde Archipelagoes,
fauna of, 228.
Carcharias melanopterus, 149.
Carruthers, on evolution, 436-442.
Caterpillars, colours and forms
of, 519, 322-326.
Cattle, portraits of, 311.
Causation, natural, 402, 413, 414.
Caves, faunas of dark, 70-72.
Cell, physiological, and properties
of the, 104-134.
Centra vinula, 325, 326.
Cervalces Americanus, 196, 198,
199.
Cervus dicroeerus, issiodorensis,
matheronis, pardinensis, Sedg-
wickii, tetraceros, 168.
Chalmers, Dr., on natural theology,
412.
Chameleons, 317.
Characters, as adaptive, 273-276,
286-293, 349 ; as specific, 274-
376, 286-295 ; as congenital
and acquired, 274-276.
Chasmorhynchus niveus, and C.
tricarunculatus, 396-3<;8.
Chelydra serpentina, anterior limb
of, 179-181.
Chick, embryology of, 153.
Chimpanzee, see Apes.
Chlorophyll, 408.
C hondr acanthus comuttts, 123.
Cirripedes, 430.
Classification, 33-49 » °f organic
nature by Genesis and Leviticus,
33 ; artificial and natural, 24-
36 ; empirical rules of, 33-40 ;
Darwin on, 35, 36, 39, 40 ; form
of, a nexus or tree, 29-32 ;
of organic forms like that of
languages, 32 ; single characters
in relation to, 37 ; aggregates of
characters in relation to, 35-37 ;
adaptive and non-adaptive cha-
Index.
453
racters in relation to, 34, 35,
38, 39 ; chains of affinities in
relation to, 39-40 ; biological
differs from astronomical, 43.
Cockerell, on vegetable galls,
447, 448.
Colours, of plants and animals in
relation to the theory of natural
selection, 317-332; in relation
to the theory of sexual selection,
39'. 392, S94-396. 4°8-4IO»
448-450.
Colouring, see Recognition marks,
Protective, Seasonal, Warning,
and Mimicry.
Congenital characters, see Charac-
ters.
Conjugation, of Protozoa, 115-
117.
Continuity, principle of, in nature,
15-21. -
Contrivance, Darwin's use of the
word, 281.
Co-operation, mutual, of species
alleged, 445-448.
Co-operative instincts, due to
natural selection, 267, 269.
Cope, Professor, his table of geo-
logical formations, 163, 164;
his table of palaeontological
development of feet, vertebral
column, and brain, 197.
Correlation of growth, 357-363.
Cossonidtz, 233.
Courtship, see Sexual Selection.
Crabs, 62-65, J39-
Cuttle-fish, 317.
Cuvier, on method in natural
history, 3-4 ; on monkeys, 429.
Cyst, see Encystation.
D.
Darwin, Charles, his influence on
ideas of method, 1-9; on classifi-
cation, 35, 36, 39, 40 ; on ves-
tigial characters in man, 77, 86,
87, 92 ; on imperfection of
geological record, 165, and Ap-
pendix ; on means of dispersal,
a 1 6, 218; on geographical dis-
tribution, 218, 219 ; on fauna of
the Galapagos Archipelago, 227,
228; on natural selection, 252,
353, 255, 256, 286, 375, 376;
his use of such wordsas ' accident,'
'fortuitous,' 'purpose,' 'contri-
vance,' &c., 281, 334-340: on
sexual selection, 379-400.
Darwin, Erasmus, his theory of
evolution, 253.
De Blainville, on the theory of
descent, 258.
De Candolle, on classification, 34.
Deer, 98, 99, 167-169, 187, 191,
196, i«j8, 199.
Degeneration, 269, 270, 342.
Delamination, 139.
Diadema euryta, 330,
Diaster, 129-133.
Dingo, see Dog.
Dinornis, 60, 61.
Diptera mimicking Hymenoptera,
329-
Dog, dentition of, 39 ; Dingo, 304 ;
domesticated varieties of, 305,
307 ; hairless, 307 ; skulls of,
307-
Duck, logger-headed, 68.
Dugong, eye of, 75.
E.
Eagle, eye of, 75.
Ear, of whales, 65 ; vestigial
features of human, 76, 86-89; of
man and apes compared, 88.
Eaton, Rev. A. E., on wingless
insects, 70.
Echinodermata, 125-127, 138,
155-
Ectoderm, 137-142.
Egg, see Ovum.
Eimer, 363.
Elaps fulvius imitated by non-
venomous snakes, 330.
Electric organs, 365-373.
Elephant, foot of, 185, 186 ; rate
of propagation of, 261, 262.
Elk, 196-198, 199.
Embryo, human, see Man.
Embryogeny, see Ontogeny.
Embryology, 98-155.
Embryos, comparative series of,
153. 153-
454
Index.
Encyclopedia Bmlannica, eighth
ed., on instinct, 289-291.
Kncys'ation of Protozoa, 115.
Kndoderm, 137-142.
Kquatoiial plate, 1^.9.
Lquns, see Horse
Erythrolainprus vemistissiinus,
330-
Evolution, organic, fact of, Section
I ; Method of, Section II ; ideas
upon, prior to Darwin, 253-258;
divergent , 266, 267.
I1. wart, Professor Cossar, on electric
organ of skate, 364, 367.
Existence, see Struggle for.
Kye, of octopus, 57, 58, 347-350;
ab cnce of, in dark-cave animals,
70-72; nictitating membrane of,
74> 75 ! development of, from
cutaneous nerve-ending, 352-
354-
F.
Feet, 51-59, 66, 77-80, 174-192,
K)7.
Fertilization of ova, 127, 128 ; oi
flowers by insects, 406.
Fish, embryology of, 143-155 ;
palaeontology of, 163, 165, 169-
171; brain of, 194-197 ; distribu-
tion of, 224-246; flying, 355.
Fission, reproduction by, 106, 107.
Flat fish, 317.
F'loat, see Swim-bladder.
Flowers, fertilization of, by insects,
406.
Fly, imitating a wasp, 329.
Flying-fish, and squirrels, 355.
Foraminifera, 34').
Forbes, H. O., on scapulo-coracoid
bones of Dinornis, 60.,
Fortuitous, Darwin's use of the
word, 340.
Fossils, see Palaeontology.
Frogs, 317.
G.
Galapagos Islands, 227-231, 236,
217.
Calf us, eye of, 75.
Galls, vegetable, 293-295, 446-
448.
Gastraea, 137-140.
Gastrophysevta, 138.
Castrulation, 137, 140.
Gegenbaur, 147, iSi.
Gemmation, reproduction by, 106,
107, no, in.
Generalization, 5.
Generalized types, 33.
Genesis, classification of organic
nature in, 23.
Genial tubercle, 96.
Geographical distribution, 204-
248; see Glacial period, Barriers
Transport of organisms, Oceanic
islands, &C.
Geology, record of imperlect, 156-
160, and Appendix ; see Palae-
ontology.
Germs, prophetic, 272, 351 -362.
Gesncr, on classification, 24 ; on
canaries, 313.
Gill-arches, 146, 147, 150, 151.
Gill-slits, 146, 147,150-153.
Gills, of young salamanders, 102 ;
origin of, in embryo, 144 ; of
fish, 150, 152.
Giiaffe, neck of, in relation to
Lamarck's theory, 254.
Glacial periods, effects of, on dis-
tribution of plnnts and animals,
209, 210, nnd Appendix
Goose, Frizzled, portrait of, 304.
Gorilla, see Apes.
Gray, Professor Asa, 337
Great -toe, in man and apes, 79-81.
Grouse, 317-319
Growth, correlation of, 357, 362.
Gymnotus, 365, 367.
H.
Hackel, on analogy between
species and languages, 32 ; on
reproduction as discontinuous
growth, 105, 106; his ideal
primitive vertebrate, 143, 144.
Hair, vestigial characters of, in
man, 89 92.
Hales, 3.
Haller, 3.
Hamilton, Sir William, 272.
Hands, 51-55, 66,80-82,174-193.
Hare, 318, 319.
Index.
455
Hartmann, on flattening of early
human tibise, 96.
Harvey, on Lord Bacon's writings,
2.
Heart, development of, 154.
Heilprin, on skulls of deer, 198,
199; on fossil shells, 201, 202.
Hen, ovum of, 1 22.
Heredity, in relation to classifica-
tion, 28-31 ; in relation to em-
bryology, 98-102 ; chromatin-
fibres in relation to, 134; in
relation to theories of organic
evolution, 253-255, 260-264,
377-
Hei mit-crabs, 62-65, 288, 289.
Heteromera, 233
Hilgendorf, on shells of Planar bis,
201.
Hipparion, 191, 192.
Hippopotamus, foot of, 187.
Hog, see Pig.
Homology, 38, 50-65, 176, 177,
347-350, 357-359-
Homopterotis insect, imitating
leaf-cutting ants, 331, 332.
Hooker, Sir Joseph, on flora of
St. Helena, 234
Horns, 98-100, 167-169.
Horse, eye of, 75 ; limb-bones of,
176, 177, 186, 188-192; teeth
of, 1 89-191 ; portraits of do-
mesticated breeds of, 309.
Human, see Man.
Humerus, perforations of, in quad-
rumana and man, 94, 95.
Humming-birds, restricted to the
New World, an.
Hunter, 3 ; on ear of whale, 65.
Huxley, Prof., on mechanical se-
lection, 283; on age of the earth,
435. 436 : on Dr. VVhewell, 243.
Hyatt, on shells of Planorbis, 201.
Hydra, in, 122.
ffyrax, foot of, 185, 186.
I.
Ignorance, argument from, 41, 42,
49;
Illative Sense, 6.
Imitative colours, 317-323, 326-
33'-
Infant, feet of, 78, 79 ; grasping
power of, 81.
Infertility, inter-specific, in relation
to natural selection, 374-376.
Insects, wingless, 68-70 ; in pri-
mary formations, 163, Appendix ;
on oceanic islands, 224-238; in
relation to galls, 293-295, 446-
448; defensive colouring of, 321-
332 ; fertilizing flowers, 406.
Instincts, always of primary use to
species presen ting them,286-293.
Intercrossing, in relation to natural
selection, 374-376.
Inutility of specific characters, in
relation to natural selection,
374-376.
Islands, oceanic, 234-237 ; British,
338-241.
J.
Japan, hairless dog of, 101.
Jelly-fish, 119, 120.
K.
Kallima, 323.
Karyokinesis, 113-114, 128-134.
Kepler, 272.
Kerguelen Island, flightless in-
sects of, 70.
Kropotkin, Prince, on co-operative
instincts, 369.
L.
Lagopus mutus, 317, 318.
Lamarck, his method in natural
history, 4 ; his theory of evolu-
tion, 253-256.
Lamprey, 148.
Languages, classification of, re-
sembles that of organic forms,
32-
Lankester, E. Ray, on karyo-
kinesis, 129, 130.
Leaf insect, 322.
Le Conte, on geological succession
of animal classes, 164, 165; on
types of tails, 169-173; on fossil
shells of Planorbis, 201 ; his
work on the relation of the
theory of evolution to religious
thought, 412.
456
Index.
Left alts, 328.
Leuculmis echinus, 123.
Leviticus, classification of organic
nature in, 23.
Life, origin of, 1 5.
Linnaeus, on method in natural
history, 3; on classification, 26,
35-4°-
Lion, skeleton of, 175 ; feet of, 178.
Lizard, heart and gill-arches of,
150.
Lloyd Morgan, 273, 449, 450.
Lungs, development of, 1154, 354.
Lyell, Sir Charles, on classification,
32 ; on uniformitarianism, 258 ;
on rational species, 344 ; on geo-
logical record, 420, 435, 439.
M.
Madeira, wingless beetles of, 68-
70 ; peculiar beetles of, 226, 227.
Mammals, ovum of, 120-124; em-
bryology of, 1 5 1 - 1 55 ; palseonto-
logyof, 163, 165, 167, i8o-.'99;
limbs 0^174-178,182-199; brain
of, 194-199; of Australia and
New Zealand, 204, 205; distri-
bution of, on islands, 2 24-240.
Mammoth cave, fauna of, 70-72.
Man, nictitating membrane of, 75 »
Testigial muscles of, 76, 77,
82, 83 ; tail of, compared with
that of apes, 82-84 ; hair of,
compared with that of apes, 89-
92 ; teeth of, compared with
those of apes, 92-94 ; perforation
of humerus of, 94, 95 ; flattening
•f ancient tibiae of, 95, 96 ;
embryology of, 119, 153; hand
of, 54 ; arm of, 90, 91 ; limb-
bones of, 1 76, 1 77 ; palaeontology
of, 163, 165 ; brain of, 194, 195 ;
Mr. Syme on, 346, 347.
Marsh, on palaeontology of the
horse, 188-190.
Matthew, Patrick, on natural
selection, 257.
Mesoderm, 142.
Mesokippw, 189, 192.
Metaphyta, 104, 105.
Metazoa, 104.
Method, ideas of, in natural history,
1-9 ; of organic evolution, 252-
261.
Meyer, Professor Ludwig, on helix
of the human ear, 86.
Mimicry, 320-322.
Ministration, mutual, of species
alleged, 445, 446.
Miohippus, 189.
Mivart, St. George, on eye of
octopus, 57, 58, 348, 349; on
incipient organs, 362 ; on mutual
ministration of species, 445, 446.
Mollusca, shells of, 19, 199-203;
eye of, 57, 58 ; embryology of,
155 ; palaeontology of, 163, 165.
Monkeys, why all, do not become
men, 342-344.
Monotremata, 205.
Morgan, see Lloyd Morgan.
Morphology, 50-97.
Mule, portrait of, 309.
Multicellular organisms, 104.
Multiplication, see Reproduction.
N.
Nageli, Prof., 337, 367.
Natural History, ideas of method
in, 1-9.
Natural, interpretations as opposed
to super-natural, 13-15 ; causa-
tion, 13-15.
Natural, selection, 252-378, 401-
410; Wells, Matthew, and
Whewell on, 257, 258,443-445 ;
statementof theory of, 256-284,
of evidences of, 285-332, of
criticisms of, 333-378; relation
of theoryof, to religious thought,
401-410; preserves types, 264-
267 ; cessation and reversal of,
270, 342 ; errors touching theory
of, 270-284, 332-364 ; definition
of, 275-376; antecedent standing
of theory of, 277-284; Prof.
Owen on, 333, 334; Duke of
Argyll on, 334-362 ; Mr. Syme
on, 340, 341, 345 ; need not
always make for improvement,
341-347 ; homology and analogy
in relation to, 347-350 ; often
determines beauty, 406, 407; in
Index.
457
relation to the formation of galls,
293-295, 446-448.
Nature, organic, 17 ; inorganic, I,
17, 18.
Nauplius, 138.
Neumayr, 19.
New Zealand, fauna of, 68, 204,
205 ; thriving of exotic species
in, 286.
Newman, on the Illative Sense, 6.
Newton, his idea of scientific
method, 6.
Nictitating membrane, 74, 75.
Notochord, 146.
Novum Organon, the, on scientific
method, 2.
Nucleus, 105, 112-134.
Nucleus-spindle, 129.
Nut-hatch, Syrian, ornamented
nests of, 381.
O.
Objective methods, 6.
Oceanic islands, see Islands.
Octopus, eye of, 57, 58, 348-350.
CEdicnemus crepitans, 320.
Ontogeny, as recapitulation of
phylogeny, 98-104.
Orang Outang, see Apes.
Ore Jon Culbertsoni, 167.
Origin of Species, the, influence
exercised by, on ideas of method,
1-9.
Orohippus, 189.
Otaria, eye of, 75.
Ovum, 113-142; human, 120-123;
amoeboid movements of young,
121-123; segmentation of, 134,
135-
Owen, on ear of whale, 65; on
natural selection, 333, 334.
Owl, eye of, 75.
P.
Paddle, see Whale, and Baptanodon
discus.
Pagurus bemhardus, 64.
Pain, in relation to the theory of
evolution, 417.
Palaeontology, 159-203; general
testimony of, 1 56-165 ; te.-timony
of, in particular cases, 165-203 ;
consideration of objections to
theory of evolution founded on
grounds of, 156-165, and Ap-
pendix.
Palceotherium, 190, 191.
Paley, on natural theology, 98, 41 2.
Paludina, successive forms of, 19.
Panama, Isthmus of, 219.
Panniculus carnosis, 77.
Papilio merope, 330.
Parasites, of animals, devoid of
beauty, 408.
Parsimony, law of, 273.
Parthenogenesis, 119.
Partridges, 319.
Peacock, tail of, 378 ; courtship of,
383.
Peckham, Mr. and Mrs., on court-
ship of spiders, 388-390.
Perissodactyls, 182-192.
Petromyzon marinus, 148.
Phcnacodus primcevus, 184, 185.
Phylogeny, see Ontogeny.
Physiological selection, 376.
Pig, embryology of, 153 ; feet of,
176, 187 ; portraits of wild and
domesticated, 313.
Pigeons, portraits of, 298, 299 ;
leather-footed, 359.
Pilot fish, 289.
Planorbis, transmutations of, 200,
201.
Pleasure and pain, in relation to
the theory of evolution, 417.
Plica semilunaris, 75.
Pliohippus, 189.
Polar bear, skeleton of, 1 74 ; feet
of, 178.
Polar bodies, 125, 126.
Polar star, 129.
Polyps, 114.
Porpoises, 24, 25, 50.
Poulton, E. B., on warning colours,
325, 326; on mimicry, 331, 332 ;
sexual selection, 400, 401, 449,
45°-
Poultry, portraits of, 300-302.
Pronucleus, 126-128.
Prophetic types, 272, 351-362.
Praphysema primordiale, 140.
Protective colouring, 317-323.
Protohippus, 189.
Index.
Protozoa, 104.
Ptarmigan, 317, 318.
Pterodactyl, wing of, 56.
Purpose, Darwin's use of the word,
281, 340.
Puss moth, larva of, 325, 326.
Python, 66, 67.
Q.
Quadrumana, musclesof, 76, 82, 83;
perforations of humeri of, 94,
95 ; hair on phalanges of, 91.
R.
Rabbit, embryology of, 153 ; mul-
tiplication of. in Australia, 286 ;
portraits of wild and domesticated
breeds of, 308 ; protective colour-
ing of, 319,320.
Radiate form, beauty of, 408, 409.
Raia radiata, and batis, 367 -371.
Rats, species of, restricted to Old
and New Worlds, 212; British
and Norwegian, 285, 286.
Rattle-snake, tail of, 289.
Recognition marks, 271-273.
Religion, in relation to Darwinism,
401-418.
Reproduction, different methods of,
106-1 17 ; essence of sexual, no;
foreshadow ing of sexual in uni-
cellular organisms, 115-117.
Reptiles, wing of flying. 56 ; rudi-
mentary limbs of, (17; nictitating
membrane of, 75 ; branchial
arches of, 1 50 ; embryology of,
152 ; palaeontology of, 163, 165,
178-180; brain of, 194-197;
distribution of, 224-240.
Rhinoceros, foot of, 186.
Robinson, Dr L., on grasping
power of an infant'shands,8o-82.
Rudimentary organs, 65-97.
Ruminants, palaeontology of, 167,
168.
a
Sacrum of man, compared with
that of apes, 82-84.
Sagitta, 138.
Salamander, young of terrestrial,
living in water, 102 ; embryo
logy of, 152.
Sandwich Islands, 234-237.
Science, method of, 1-9.
Sclater, W. L., on a case of
mimicry, 33 1, 332.
Scorpion in Silurian formation,
163.
Sea, lamprey, 148; destructive
agency of the, 423, 424.
Seal, 51,52, 75.
Seasonal changes of colour, 317-
3!9-
Selection, value, 275 ; by physical
processes, 282, 283, 335. See
also Natural selection, Artificial
selection, Sexual selection, Phy-
siological selection.
Sentiency, in relation to the
theory of evolution, 417.
Sex, difference of, restricted to
Metazoa and Metaphyta, 105.
Sexual reproduction, see Repro-
duction.
Sexual selection, theory of, 277,
378-410 ; statement and evi-
dences of, 379-.'9' ; criticisms
of, 391-400 ; includes law of
battle with that of charming,.
385.386; in relation to religious
thought,4i 1-418; Tylor's theory
substituted for, by Wallace, 449,
45°-
Shark, eye of, 75 ; man-eating.
149 ; and pilot-fish. 289.
Sheep, limb-bones of, 176, 177;
portraits of, 310.
Shells, of crabs, 62-64 '•> palaeon-
tology of mollusk's, 199-203 ;
land on oceanic islands, 224-
240.
Silliman's Journal, on fauna of the
Mammoth Cave, 70.
Skate, electric organ of, 364-373.
Skull, palaeontology of, 194-199;
of bull-dog compared with that
of deer-hound, 307.
Slavonia, Tertiary deposits of,
18, 19.
Species, not eternal, but either
created or evolved, 13 ; named
as such through absence ol
Index.
459
intermediate forms, 18-20 ;
groups of, in classification, 20,
and appearing suddenly in
geological formations, 427-432,
437-440 ; origin of, coincide
in space and time with pre-
existing and allied species,
32 ; geographical distribution
of, 204-248 ; extinct and living
allied on same areas, 213; life
of, preserved by natural selec-
tion, 264-270 ; not room for
more than one rational, 344 ;
characters of, 274-276, 286-
295> 374-376 5 inter-sterility of
allied, 374-376 ; mutual minis-
tration of alleged, 44 5, 446.
Specific characters, see Characters.
Speculation, method of, 3-9.
Spencer, Herbert, on reproduction
as discontinuous growth, 105,
106; on use-inheritance, 253-
256 ; his failure to conceive the
idea of natural selection, 257.
Spermatozoa, 123, 126-128.
Spiders, in primary formations,
163 ; courtship of, 388, 389.
Sponges, 122, 139, 140.
Spontaneous, Darwin's use of the
term, 340.
Spores, 115.
Squirrels, flying, 355.
Sterility, see Infertility.
St. Helena, 231-234, 236-237.
St. Hilaire, 4.
Stick-insect, 322.
Stoat, 318.
Strombus accipitrinui, 20"
Strombus Leidy 201.
Struggle for existence, 259-270.
Subjective, methods, 6.
Survival of the fittest, 335. See
also Natural selection.
Swim- bladder of fish, 154, 354.
Symbiosis, 269.
Syme, David, on the theory of
natural selection, 340, 341.
T.
Fail, types of, in fish and birds,
169-173.
Tasmanian wolf, dentition of, 39.
Teeth, of Tasmanian wolf, 39 ;
molar, of man, compared with
those of apes, 92-94 ; palaeon-
tology of horses', 189-191.
Temperature, sense of, probable
origin of that of sight, 353, 354.
Tennyson, 266.
Tibiae, flattening of, 95, 96.
Tissue-cells, see Cell.
Toes, 79, 80 ; see also Feet.
Tomes, C. S., on molar teeth of
man and apes, 94.
Torpedo, 365, 367.
Tortoise, embryology of, 152,
!54-
Toxopneustes variegatus, and T.
lividus, 122.
Transport of organisms, means of,
207, 216-218.
Tribal fitness, as distinguished
from individual, 267-269.
Trout, ovum of, 122.
Turtle, eye of, 75.
Tylor, Alfred, on colouration of
animals, 448-450.
Type, preserved by natural selec-
tion, 264-269 ; improvement of,
by natural selection, 269, 270;
prophetic, 272, 351-362.
Types, as simple and generalized,
33-
U.
Unicellular organisms, 104.
Uraster, 138.
Utility, of specific characters, 274,
275 ; of incipient characters,
35J~363; of electric organs,
3<>5 373-
Variation, in relation to natural
selection, 263, 335-340, 377.
Verification, 6-9.
Vertebral column, embryology of
145, 146 ; palaeontology of,
192, 193.
Vertebrated animal, ideal primi-
tive, 143, 144; embryology of,
143 -'55-
Vespa vulgaris, 331.
Vestigial organs, 65-97.
Volucella inans, and V. bomby-
lans, 329.
Index.
w.
Wagner, Moritz, on geographical
distribution, 216.
Wallace, A. R., on origin of
species as coincident in time
and space with pre-existing and
allied species, 22 ; on wingless
insects, 70 ; on absence of hair
from human back, and function
of on arms of orang, 89 ; on
geographical distribution, 207,
231, 232,233, 243; on natural
selection, 256; on recognition
marks, 271-273; on alleged de-
ductive consequences of the na-
tural selection theory, 273-276;
his theory of warning colours,
323> 324 J on sexual selection,
391-400, 450 ; his principal
defect in treating of animal
colouration, 449, 450.
Warning colours, 323-326.
Wasp, imitated by a fly, 339.
Water cress, multiplication of, ik
New Zealand, 286.
Weevils, on St. Helena, 232.
Weismann, his theory of heredity,
'3°, 134-
Wells, Dr., on natural selection,
257-
Wetterhan, Prof., on vegetable
galls, 448.
Whales 38, 50, 53, 54, 65, 180.
Whewell, on natural selection,
257, 258, 443-445.
Wmgs, 54-56, 60, 61, 68-70, 355.
Wolf, Tasmanian, dentition of, 34.
Wood, John, on vestigial muscles
in man, 77.
Woodward,on fossil cirripedes,43 1 .
Woolner, on the human ear, 86.
Worms, embryology of, 155.
Wyman, Prof., on the great toeol
human embryo, 79, 80.
Zona pettudda, lai.
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