Title: The Scientific Evidences of Organic Evolution
Author: Romanes, George John, 1848-1894
Language: English
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                  _NATURE SERIES._

              THE SCIENTIFIC EVIDENCES

                         OF


                        BY
      GEORGE J. ROMANES, M.A., LL.D., F.R.S.,
    ZOOLOGICAL SECRETARY OF THE LINNEAN SOCIETY.

                       London:
                  MACMILLAN AND CO.
                        1882.

_The Right of Translation and Reproduction is Reserved._

                       LONDON:
         R. CLAY, SONS, AND TAYLOR, PRINTERS,
                  BREAD STREET HILL.



PREFACE.


Several months ago I published in the _Fortnightly Review_ a lecture,
which I had previously delivered at the Philosophical Institutions of
Edinburgh and Birmingham, and which bore the above title. The late Mr.
Darwin thought well of the epitome of his doctrine which the lecture
presented, and urged me so strongly to republish it in a form which
might admit of its being "spread broadcast over the land," that I
promised him to do so. In fulfilment of this promise, therefore--which I
now regard as more binding than ever--I reproduce the essay in the
"Nature Series" with such additions and alterations as appear to me, on
second thoughts, to be desirable. The only object of the essay is that
which is expressed in the opening paragraph.

  LONDON,

   _June 1, 1882._

Since this little Essay was published, it has been suggested to me that,
in its mode of presenting the arguments in favour of Evolution, there is
a similarity to that which has been adopted by Mr. Herbert Spencer in
the third part of his _Principles of Biology_. I should therefore like
to state, that while such similarity is no doubt in part due to the
similarity of subject-matter, I think, upon reading again, after an
interval of ten years, his admirable presentation of the evidence it may
also in part be due to unconscious memory. This applies particularly to
the headings of the chapters, which I find to be almost identical with
those previously used by Mr. Spencer.

  G. J. R.



CONTENTS.


            PAGE

INTRODUCTION                                          1


I.
THE ARGUMENT FROM CLASSIFICATION                     17

II.
THE ARGUMENT FROM MORPHOLOGY OR STRUCTURE            26

III.
THE ARGUMENT FROM GEOLOGY                            46

IV.
THE ARGUMENT FROM GEOGRAPHICAL DISTRIBUTION          48

V.
THE ARGUMENT FROM EMBRYOLOGY                         63

VI.
ARGUMENTS DRAWN FROM CERTAIN GENERAL CONSIDERATIONS  70



THE SCIENTIFIC EVIDENCES

OF

ORGANIC EVOLUTION.


Although it is generally recognised that the _Origin of Species_ has
produced an effect both on the science and the philosophy of our age
which is without a parallel in the history of thought, admirers of Mr.
Darwin's genius are frequently surprised at the ignorance of his work
which is displayed by many persons who can scarcely be said to belong to
the uncultured classes. The reason of this ignorance is no doubt partly
due to the busy life which many of our bread-winners are constrained to
live; but it is also, I think, partly due to mere indolence. There are
thousands of educated persons who, on coming home from their daily work,
prefer reading literature of a less scientific character than that which
is supplied by Mr. Darwin's works; and therefore it is that such persons
feel these works to belong to a category of books which is to them a
very large one--the books, namely, which never are, but always to be,
read. Under these circumstances I have thought it desirable to supply a
short digest of the _Origin of Species_, which any man, of however busy
a life, or of however indolent a disposition, may find both time and
energy to follow.

With the general aim of the present abstract being thus understood, I
shall start at the beginning of my subject by very briefly describing
the theory of natural selection. It is a matter of observable fact that
all plants and animals are perpetually engaged in what Mr. Darwin calls
a "struggle for existence." That is to say, in every generation of every
species a great many more individuals 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: the
weakest and the least fitted to live will succumb and die, while the
strongest and the best fitted to live will be triumphant and survive.
Now it is this "survival of the fittest" that Mr. Darwin calls "natural
selection." 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 the fixed laws of heredity, it follows that the
individuals composing each successive generation have a general tendency
to be better suited to their surroundings than were their forefathers.
And this follows, not merely because in every generation it is only the
flower of the race that is allowed to breed, but also because if in any
generation some new and beneficial qualities happen to appear as slight
variations from the ancestral type, these will be seized upon by natural
selection and added, by transmission in subsequent generations, to the
previously existing type. Thus the best idea of the whole process will
be gained by comparing it with the closely analogous process whereby
gardeners and cattlebreeders 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 external
conditions of their life.

Now, if this process of continuously adapting organisms 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 attain to this condition of
perfect adjustment to their environment, and there remain fixed. And so
undoubtedly they would, if the environment were itself unchanging. But
forasmuch as the environment--or the sum total of the external
conditions of life--of almost every organic type alters more or less
from century to century (whether from astronomical, geological, and
geographical changes, or from the immigrations and emigrations of other
species living on contiguous geographical areas), 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 denote the specific type by some
different name, it follows that natural selection has transmuted one
specific type into another. And so the process is supposed to go on over
all the countless species of plants and animals simultaneously--the
world of organic types being thus regarded as in a state of perpetual,
though gradual, flux.

Such, then, is the theory of natural selection, or survival of the
fittest; and the first thing we have to notice with regard to it is,
that it offers to our acceptance a scientific explanation of the
numberless cases of apparent design which we everywhere meet with in
organic nature. For all such cases of apparent design consist only in
the _adaptation_ which is shown by organisms to their environment, and
it is obvious that the facts are covered by the theory of natural
selection no less completely than they are covered by the theory of
intelligent design. Perhaps it may be answered,--"The fact that these
innumerable cases of adaptation may be accounted for by natural
selection is no proof that they are not really due to intelligent
design." And, in truth, this is an objection which is often urged by
minds--even highly cultured minds--which have not been accustomed to
scientific modes of thought. I have heard an eminent professor tell his
class that the many instances of adaptation which Mr. Darwin discovered
and described as occurring in orchids, seemed to him to tell more in
favour of contrivance than in favour of natural causes; and another
eminent professor once wrote to 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 be 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, the exception
_in limine_ to the evidence which we are about to consider, does not
question that natural selection _may_ not be able to do all that Mr.
Darwin ascribes to it: it merely objects to his interpretation of the
facts, because it maintains that these facts might _equally well_ be
ascribed to intelligent design. And so undoubtedly they might, if we
were all childish enough to rush into a supernatural explanation
whenever a natural explanation is found sufficient to account for the
facts. Once admit the glaringly illogical 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 logical barrier between science and superstition. For it is
manifest that it is always possible to give a hypothetical explanation
of any phenomenon whatever, 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 I 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, for instance, 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 explanation, all persons with a scientific habit of mind at
once abandoned the metaphysical explanation. 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 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
influence of gravitation.

So much, then, for the absurdly illogical position that, granting the
evidence in favour of natural selection and supernatural design to be
equal and parallel, we should hesitate for one moment in our choice.
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 relation
is not so competent a theory to explain the facts of adaptation as is
that of intelligent design--then the objection is no longer the one that
we are considering. It is quite another objection, and one which is not
_primâ facie_ absurd; it requires to be met by examining how far the
theory of natural selection _is_ able to explain the facts. Let us state
the problem clearly.

Innumerable cases of adaptation of organisms to their environment 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 manifested in creation; and
the other is, natural selection manifested during the countless ages of
the past. Now it would be proof positive of intelligent design if it
could be shown that all species of plants and animals were
_created_--that is _suddenly_ introduced into the complex conditions of
their life; for it is quite inconceivable that any cause other than
intelligence could be competent to adapt an organism to its environment
_suddenly_. On the other hand, it would be proof presumptive of natural
selection if it could be shown that one species becomes slowly
transmuted into another--_i.e._, that one set of adaptations may be
gradually transformed into another set of adaptations according as
changing circumstances require. This would be proof presumptive of
natural selection, because it would then become amply probable that
natural selection might have brought about many, or most, of the cases
of adaptations which we see; and if so, the law of parsimony excludes
the rival hypothesis of intelligent design. Thus the whole question as
between natural selection and supernatural design resolves itself into
this--Were all the species of plants and animals separately created, or
were they slowly evolved? For if they were specially created, the
evidence of supernatural design remains unrefuted and irrefutable;
whereas if they were slowly evolved, that evidence has been utterly and
for ever destroyed. The doctrine of natural selection therefore depends
for its validity on the doctrine of organic evolution; for if once the
fact of organic evolution were established, no one would dispute that
much of the adaptation was probably effected by natural selection. _How_
much we cannot say--probably never shall be able to say; for even Mr.
Darwin himself does not doubt that other causes besides that of natural
selection have assisted in the modifying of specific types. For the
sake of simplicity, however, I shall not go into this subject; but shall
always speak of natural selection as the only cause of organic
evolution. Let us, then, weigh the evidence in favour of organic
evolution. If we find it wanting, we need have no complaints to make of
natural theologians of to-day; but if we find it to be full measure,
shaken together and running over, we ought to maintain that natural
theologians can no longer adhere to the arguments of such writers as
Paley, Bell, and Chalmers, without deliberately violating the only
logical principle which separates science from fetishism.

To avoid misapprehension, however, I may here add that while Mr.
Darwin's theory is thus in plain and direct contradiction to the theory
of design, or system of teleology, as presented by the school of writers
which I have named, I hold that Mr. Darwin's theory has no point of
logical contact with the theory of design in the larger sense, that
behind all secondary causes of a physical kind, there is a primary cause
of a mental kind. Therefore throughout this essay I refer to design in
the sense understood by the narrower forms of teleology, or as an
_immediate_ cause of the observed phenomena. Whether or not there is an
_ultimate_ cause of a psychical kind pervading all nature, a _causa
causarum_ which is the final _raison d'être_ of the cosmos, this is
another question which, as I have said, I take to present no point of
logical contact with Mr. Darwin's theory, or, I may add, with any of the
methods and results of natural science. The only position, therefore,
which I here desire to render plain is that, if the doctrine of
evolution is seen to be established by sufficient evidence, and
therefore the causes which it sets forth are recognised as adequate to
furnish a scientific explanation of the results observed, then the
facts of organic nature necessarily fall into the same logical category,
with reference to any question of design, as that of all or any other
series of facts in the physical universe.

This being understood, I shall now proceed to render an epitome of the
evidence in favour of organic evolution, and I shall do so by
classifying the arguments in a way tending to show their distinct or
independent character, and therefore calculated to display the
additional force which they acquire from their cumulative nature.



I.

THE ARGUMENT FROM CLASSIFICATION.


I shall first take the argument from classification. Naturalists find
that all species of plants and animals present among themselves
structural affinities. According as these structural affinities are more
or less pronounced, the various species are classified under genera,
orders, families, classes, sub-kingdoms, and kingdoms. Now in such a
classification it is found impossible to place all the species in a
linear series, according to the grade of their organization. For
instance, we cannot say that a wolf is more highly organized than a fox
or a jackal; we can only say that the specific points wherein it
differs from these animals are without significance as proving the one
type to be more highly organized than the others. But of course in many
cases, and especially in the cases of the larger divisions, it is often
possible to say--The members in this division are more highly organized
than are the members in that division. Our system of classification
therefore may be likened to a tree, in which a short trunk may be taken
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 represent 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
will understand that while there is a general advance of organization
from below upwards, there are numberless slight variations in this
respect between leaves growing even on the same branch; but in a still
greater number of cases, leaves growing on the same branch are growing
on the same level--that is, although they represent different species,
it cannot be said that one is more highly organized than the other. Now,
this tree-like arrangement of specific organisms in nature is an
arrangement for which Mr. Darwin is not responsible. I mean that the
framing of this natural classification has been the work of naturalists
for centuries past; and although they did not know what they were doing,
it is now evident to evolutionists that they were tracing the lines of
genetic relationship. For, be it observed, a scientific or natural
classification differs very much from a popular or hap-hazard
classification, and the difference consists in this, that while a
popular classification is framed with exclusive reference to the
external appearance of organisms, a scientific classification is made
with reference to the whole structure. A whale, for instance, is often
thought to be a fish, because it resembles a fish in form and habits;
whereas dissection shows that it is beyond all comparison more unlike a
fish than it is like a horse or a man. This is, of course, an extreme
case; but it was cases such as this that first led naturalists to see
that there are resemblances between organisms much more deep and
important than appear upon the surface; and consequently, that if a
natural classification was possible at all, it must be made with
reference to these deeper resemblances. Of course, it took time to
perceive this distinction between fundamental and superficial
resemblances. I remember once reading a very comical disquisition in one
of Buffon's works on the question as to whether or not a crocodile was
to be classified as an insect; and the instructive feature in the
disquisition was this, that although a crocodile differs from an insect
as regards every conceivable particular of its internal anatomy, no
allusion at all is made to this fact, while the whole discussion is made
to turn on the hardness of the external casing of a crocodile resembling
the hardness of the external casing of a beetle; and when at last Buffon
decides that, on the whole, a crocodile had better not be classified as
an insect, the only reason given is, that as a crocodile is so very
large an animal, it would make "altogether too terrible an insect."

But now, when at last it came to be recognised that internal anatomy
rather than external appearance was to be taken as a guide to
classification, the question was, What features in the internal anatomy
are to take precedence over the other features? And this question it was
not hard to answer. A porpoise, 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, and in this feature it
differs from all fish, while it resembles all mammals. Now, looking at
those two features alone, should we say that a porpoise ought to be
classed as a fish or as a mammal? Assuredly as a mammal, and for this
reason: The number of teeth is a very variable feature both in fish and
in mammals, whereas the giving of suck is an invariable feature among
mammals, and occurs nowhere else in the animal kingdom. This, of course,
is purposely chosen as a very simple illustration; but it exemplifies
the general fact that the guiding principle of scientific
classification is the comparing of organism with organism, with the view
of seeing which of the constituent organs are of the most invariable
occurrence, and therefore of the most typical signification.

Now, since the days of Linnæus this principle has been carefully
followed, and it is by its aid that the tree-like system of
classification has been established. No one, even long before Darwin's
days, ever dreamed of doubting that this system is in reality, what it
always has been in name, a _natural_ system. What, then, is the
inference we are to draw from it? An evolutionist answers, that it is
just such a system as his theory of descent would lead him to expect as
a natural system. For this tree-like system is as clear an expression as
anything could be of the fact that all species are bound together by the
ties of genetic relationship. If all species were separately created, it
is almost incredible that we should everywhere observe this progressive
shading off of characters common to larger groups, into more and more
specialized characters distinctive only of smaller and smaller groups.
At any rate, to say the least, the law of parsimony forbids us to
ascribe such effects to a supernatural cause, acting in so whimsical a
manner, when the effects are precisely what we should expect to follow
from the action of a highly probable natural cause. The classification
of animal forms, indeed, as Darwin, Lyell, and Hæckel 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, by way of genetic descent, to a group of living
languages--Italian, Spanish, French, and, to a large extent, English.
Now what should we think of a philologist who should maintain that
English, French, Spanish, and Italian were all specially created
languages--or languages separately constructed by the Deity, and by as
many separate acts of inspiration communicated to these several
nations--and that their resemblance to the fossil form, Latin, is to 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.



II.

THE ARGUMENT FROM MORPHOLOGY OR STRUCTURE.


I now pass to another line of argument. The theory of evolution by
natural selection 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 we have of such adaptive modifications of
structure, in cases where the need of such modification is apparent. For
the sake of clearness, I shall 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 progenitors must have been
terrestrial quadrupeds of some kind, which became aquatic in their
habits. Now the change in the conditions of their life thus brought
about would render desirable great modifications of structure. These
changes would, in the first instance, begin to affect the least
typical--that is, the least strongly inherited structures--such as the
skin, claws, and teeth, &c. But as time went on, the adaptation would
begin to extend to the more typical structures, until the shape of the
body began to be affected by the bones and muscles required for
terrestrial locomotion becoming better adapted for aquatic locomotion,
and 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, but serving to complete the fish-like taper of the body. But in
the whales the modification has gone even further than this, so that the
hind legs have ceased to be apparent externally, and are only
represented internally by remnants so rudimentary that it is impossible
to make out with certainty the homologies of the bones; moreover, the
head and the whole body have become completely fish-like in shape. But
profound as these changes are, they only affect 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 inclosed in a
fin-shaped sack, so as to render them quite useless for any other
purpose than swimming. 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 relation to one another, but
modified in form so as to offer the least possible amount of resistance
to the water. In short it may be said that all the modifications have
been effected with the least possible divergence from the typical
mammalian type, which is compatible with securing so perfect an
adaptation to a purely aquatic mode of life.

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 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 enormously 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 short and all run together,
and the chief expanse of the wing being 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 elongation of the
fifth finger, and a membrane spread over it and the rest of the hand.
Lastly, in serpents the hand and arm have disappeared altogether.

Thus, even if we confine our attention to a single structure, how
wonderful are the modifications which it is seen to undergo, although
never losing its typical character! How are we to explain this? By
design manifested 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. Now the difficulties
in the way of this supposition are prodigious, if not quite
insurmountable. In the first place, why is it that some structures are
selected as typical and not others? Why should the vertebral skeleton,
for instance, be tortured into every conceivable variety of modification
in order to make it serviceable for 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 to subserve the same function? If so, it appears
to me a most unfortunate circumstance, that throughout both the
vegetable and animal kingdoms, all cases which can be pointed to as
showing ingenious adaptation of the same typical structure to the
performance of widely different functions, 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 performing the
same function are to be found in different groups of plants or animals,
and are therefore suggestive of independent variations arising in the
different 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 appearance, looks wonderfully like the eye of a true fish. 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 almost
fatal to the theory of evolution by natural selection, if the apparent
similarity were a real one. Unfortunately for the objection, however,
Mr. Darwin clearly showed, in his reply, that in no one anatomical
feature of typical importance 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 serve as organs of sight. But now, suppose that this had
not been the case, and that the two structures, besides presenting the
necessary superficial resemblance, had also presented an anatomical
resemblance; with what tremendous 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 type." But as this cannot now be urged in any one
case throughout the whole organic world, we may, 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
typical structures modified so as to perform very different functions,
we never find any vestige of these particular types of structure in
other large divisions of that tree. In other words, 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 allow the structures occurring in the
one type to appear in any of the others." I answer, undoubtedly it may
have done so; but if it did, it is a most unfortunate thing for your
theory; for 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 to me a most capricious thing in the Deity to make the eyes
of an innumerable number of fish on exactly the same ideal type, and
then to make 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 take scrupulous care that in no one ideal particular
should this solitary eye resemble all the host of other eyes. However,
adopting for the sake of argument this gigantic assumption, let us
suppose that God laid down these arbitrary rules for His own guidance in
creation, and let us see to what it leads. If, as is assumed, the Deity
formed a certain number of ideal types, and determined that on no
account should He allow any part of one type 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 desperate efforts, so to speak, there have been made to maintain
the uniformity of type in the case of the arm, and should we not expect
that in other and similar cases similar efforts should be made? Yet we
repeatedly find that this is not the case. Even in the whale, as we have
seen, the hind-limbs are not apparent; and it is impossible to see in
what respect the hind-limbs are of any less ideal value than the
fore-limbs, which, as we have also seen, are so carefully preserved in
nearly all vertebrated animals except the snakes, where again we meet in
this particular with a sudden and sublime indifference to the
maintenance of a typical structure. Now I say that if the theory of
ideal types is true, we have in these facts evidence of the most
unreasonable inconsistency; for no explanation can be assigned why so
much care should have been taken to maintain the type in some cases,
while such reckless indifference should have been displayed towards
maintaining it in others. 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 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--such as the absence of limbs--without
some of the other organs in the body being so far modified as of
themselves to indicate, on the supposition of descent with modification,
that the animal or plant must have been subject to the modifying
influences for a 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.[1]

[1] This consideration is, I believe, original. Several exceptions to
its validity might be adduced, but as a general principle it certainly
holds good.

I will now briefly touch on another branch of the argument from
morphology--the argument, namely, from rudimentary structures.

Throughout the animal and vegetable kingdoms we constantly meet with
organs which are the 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 destined to cut the gums; and we all
know that our own rudimentary tail is of no practical service. Now,
rudimentary organs of this kind are of such common occurrence, that
almost every species presents one or more of them. The question,
therefore, is--How are they to be accounted for? Of course the theory of
descent with adaptive modification has a delightfully simple answer to
supply, viz., that when, from changed conditions of life, an organ which
was previously useful becomes useless, natural selection, combined with
disuse and so-called economy of growth, will cause it to dwindle till it
becomes a rudiment. On the other hand, the theory of special creation
can only maintain that these rudiments are formed for the sake of
adhering to an ideal type. Now, here again the former theory is
triumphant over the latter; for, without waiting to dispute the wisdom
of making dwarfed and useless structures merely for the whimsical motive
assigned, surely if so extraordinary a method is 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
realised. 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, if
possible, in a more aggravated form where, within the limits of the same
natural group of organisms, a rudiment is sometimes present and
sometimes absent. For instance, to take again the case of limbs, in
nearly all the numerous species of snakes there are no vestiges of limbs
at all; but in the python we find beneath the skin very tiny rudiments
of the hind limbs. Now, is it a worthy conception of Deity that, while
neglecting to maintain His unity of 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 type very inefficiently, inasmuch as only two limbs instead of
four are represented? Or, again, take the case of the limb in other
animals. Five toes seem to constitute the ideal type, notwithstanding
that in numberless cases this ideal fails in its structural expression.
Now, in the case of the horse, one toe appears to have become developed
at the expense of the others; for the so-called knee of the horse is
really the wrist or ankle, and the so-called shank the middle toe or
finger very much enlarged. But on each side of this enlarged toe there
are, beneath the skin, rudimentary bones of two other toes--the
so-called splint-bones. So far good, but three toes are not five; so
special creationists must suppose that while in this case the Deity has,
so to speak, struggled to maintain the uniformity of His ideal, His
efforts have nevertheless conspicuously failed. How much less strained
is the scientific interpretation; for I may mention that in this
particular case, besides the general inference that rudiments point us
to a remote ancestry, we have direct palæontological evidence that there
have been a whole series of extinct horse-like animals, that began low
down in the geological strata with five toes (on the fore-feet, one
being rudimentary), which afterwards became reduced to four and then to
three; after which the two lateral toes began to become rudimentary, as
we now see them in oxen, and later on still more so. Lastly, as we come
nearer to recent times, we find fossils of the existing horse, with the
lateral toes shortened up to the condition of splint-bones. Thus we have
some half-dozen different genera of horse, all standing in a linear
series in time as in structure, between the earliest representative with
the typical number of five toes, and the existing very aberrant form
with only one toe.

It is sometimes said that a striking corroboration of a scientific
theory is furnished when it enables us correctly to _predict_
discoveries. Such a corroboration is afforded in this instance; for
Professor Huxley, speaking in 1870, said, "If the expectation raised by
the splints of the horses that, in some ancestor of the horses, these
splints would be found to be complete digits, has been verified, we are
furnished with very strong reasons for looking for a no less complete
verification that the three-toed _plagiolophus_-like 'avus' of the horse
must have had a five-toed 'atavus' at some earlier period. No such
five-toed 'atavus,' however, has yet made its appearance." But since
then the "atavus" has made its appearance, if not with five complete
toes, at least with four complete and one rudimentary; and any day we
may hear that Professor Marsh has found in still earlier strata a more
primitive form with all five toes complete.

I have no space to go into the evidence of similar "missing links" which
have been recently supplied by palæontological researches in the case of
several other groups of animals; but their consideration seems to me
quite to justify a more recent utterance of Professor Huxley, who, in
1878, wrote in the _Encyclopædia Britannica:_ "On the evidence of
palæontology, the evolution of many existing forms of animal life from
their predecessors is no longer an hypothesis, but an historical fact;
it is only the nature of the physiological factors to which that
evolution is due which is still open to discussion."



III.

THE ARGUMENT FROM GEOLOGY.


But this allusion to fossils leads me to the next division of my
subject--the argument from geology. It is not, however, necessary to say
much on this head, for the simple reason that the whole body of
geological evidence is for the most part of one kind, which although of
a very massive, is of a very simple character. That is to say, apart
from the increasingly numerous cases, such as the one just mentioned,
which geology supplies of extinct "intermediate links" between
_particular_ species now living, the great weight of the geological
evidence consists in the _general_ fact, that of all the thousands of
specific forms of life which palæontology reveals to us as having lived
on this planet in times past, there is no instance of a highly organised
form occurring low down in the geological series.[1] On the contrary,
there is the best evidence to show that since the first dawn of life in
the occurrence of the simplest organisms, until the meridian splendour
of life as now we see it, gradual advance from the general to the
special--from the low to the high, from the few and simple to the many
and complex--has been the law of organic nature. And of course it is
needless to say that this is precisely the law to which the process of
descent with adaptive modification would of necessity give rise.

[1] Some of the lower vertebrata (Elasmobranch and Ganoid fishes) occur,
indeed, in early strata (upper Silurian); but still far from the
earliest in which some of the invertebrata are found. The general
statement in the text applies chiefly to the more highly organised forms
of the vertebrate series.



IV.

THE ARGUMENT FROM GEOGRAPHICAL DISTRIBUTION.


The argument from geology is the argument from the distribution of
species in time. I will, therefore, next take the argument from the
distribution of species in space--that is, the present geographical
distribution of plants and animals. It is easy to see that this must be
a most important argument, if we reflect that as the theory of descent
with adaptive modification implies slow and gradual change of one
species into another, and a still more slow and gradual change 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 should be found to resemble or to differ from organic
types living elsewhere, according as the area is connected or
disconnected with other geographical areas. And this we find to be the
case, as abundant evidence proves. For, to quote from Mr. Darwin,
"barriers of any kind, or obstacles to free migration, are related in a
close and important manner to the differences between the productions of
various regions. We see this in the great difference in nearly all the
terrestrial productions of the New and Old Worlds, excepting in the
northern parts, where the land almost joins.... We see the same fact in
the great difference between the inhabitants of Australia, Africa, and
South America under the same latitude, for these countries are almost as
much isolated from one another as possible. On each continent, also, we
see the same fact; for on the opposite sides of lofty and continuous
mountain ranges, of great deserts, and even of large rivers, we find
different productions; though as mountain chains, deserts, &c., are not
so impassable, or likely to have endured so long as the ocean-separated
continents, the differences are very inferior in degree to those
characteristic of distinct continents." That is to say, the differences
are usually confined to species and genera, whereas in the case of
continents the differences extend to orders. Similarly in marine
productions the same laws prevail--the species on the different sides of
the American continent, for instance, being very distinct. Now, this law
cannot be explained by any reasonable argument from design.

And still stronger does the present argument become when we look to the
fossil species contained on different continents; for these fossil
species invariably present the same characteristic stamp as the living
species now flourishing on the same continents. Thus, in America we find
fossils all presenting the characteristically American types of animals,
in Australia the characteristically Australian types, and so on. That is
to say, on every continent the dead species resemble the living species,
as we may expect that they should, if they are all bound together by the
ties of hereditary descent; while, if different continents are compared,
the fossil species are as unlike as we have seen the living species to
be.

Turning next to the case of oceanic islands, situated at some distance
from a continent. In these cases the plants and animals found on the
island, though very often differing from all other plants and animals in
the world as regards their specific type, nevertheless in generic type
resemble the plants and animals of the neighbouring continent. The
inference clearly is, that the island has been stocked from the
continent with these types--either by winds, currents, floating trees,
or numerous other modes of transport--and that, after settling in the
island, some of these imported types have retained their specific
characters, while others have varied so as to become specific types
peculiar to that island. The Galapagos Archipelago islands are
particularly instructive in this connection; for while the whole group
of islands lies at a distance of over five hundred miles from the shores
of South America, the constituent islands are separated from one another
by straits varying from twenty to thirty miles. Now, to quote from
Darwin, "Each separate island of the Galapagos Archipelago is tenanted,
and the fact is a marvellous one, by many distinct species; but these
species are related to each other in a very much closer manner than to
the inhabitants of the American continent." That is to say, the
American continent being some fifteen times the distance from these
islands that they are from one another, emigration to them from the
continent is of much more rare occurrence than emigration from one
island to another; and therefore, as more time for variation is thus
allowed, while the differences between the inhabitants of island and
island are only specific, the differences between the inhabitants of the
islands as a group and the inhabitants of the American continent are
very often generic. I may mention, in passing, that it was upon
discovering these relations in the case of the Galapagos Archipelago,
and pondering upon them as "marvellous facts," that Mr. Darwin was first
led to entertain the idea that the doctrine of descent might be the
grand truth for which the science of the nineteenth century was waiting.

The evidence from oceanic islands, however, is not yet exhausted; for
in no part of the world is there an oceanic island more than a certain
distance from a mainland in which any species of the large class of
frogs, toads, and newts is to be found. Why is this? Simply because
these animals, and their spawn, are quickly killed by contact with
sea-water; and therefore frogs, toads, and newts have never been able to
reach oceanic islands in a living state. Similarly in all oceanic
islands situated more than three hundred miles from land, no species of
the whole class of mammals is to be found, excepting species of the only
order of mammals which can fly, viz., bats. And, as if to make the case
still stronger, these forlornly created species of bats sometimes differ
from all other bats in the world. But can we, as reasonable men, suppose
that the Deity has chosen, without any apparent reason, never to create
any frog, toad, newt, or mammal on any oceanic island, save only such
species as are able to fly? Or, if we go so far as to say,--"There may
have been some hidden reason why batrachians and quadrupeds should not
have been created on oceanic islands," I will adduce another very
remarkable fact, viz., that on some of these islands there occur species
of plants, the seeds of which are provided with numerous hooks adapted
to catch the hair of moving quadrupeds, and so to become disseminated.
But, as we have just seen, there are no quadrupeds in these islands to
meet this case of adaptation; so that special creationists must resort
to the almost impious hypothesis, that in these cases the Deity only
carried out half His plan, in that while He made an elaborate provision
for plants which depended for its efficiency on the presence of
quadrupeds, He nevertheless, after all, neglected to place the
quadrupeds in the same islands as the plants! Now, I submit that such
abortive attempts at adaptation bring the thesis of the special
creationists to a _reductio ad absurdum_; so that the only possible
explanation before us is, that while the seeds of these plants were able
to float to the islands, the quadrupeds were not able to swim.

Perhaps in sheer desperation, however, the special creationists will try
to take refuge in the assumption that oceanic islands differ from
continents in not having been the scenes of creative power, and have
therefore depended on immigration for their inhabitants. But here again
there is no standing-room; for we have already seen that oceanic islands
are particularly rich in peculiar species which occur nowhere else in
the world; so that, as a matter of fact, if the special creation theory
is true, we must conclude that oceanic islands have been the theatres of
extraordinary creative activity; although an exception has always been
carefully made to the detriment of frogs, toads, newts, and mammals,
save only such as are able to fly.

If space permitted, I might adduce several other highly instructive
facts in this argument from geographical distribution; but I will
content myself with mentioning only one other. When Mr. Wallace was at
the Malay Archipelago, he observed that the quadrupeds inhabiting the
various islands belonged to the same or to closely allied species. But
he also observed that all the quadrupeds inhabiting the islands lying on
one side of an imaginary sinuous line, differed widely from the
quadrupeds inhabiting the islands lying on the other side of that line.
Now, soundings showed that in exact correspondence with this imaginary
sinuous line the sea was much deeper than in any other part of the
Archipelago. Consequently, how beautiful is the explanation. We have
only to suppose that at some previous time the sea bottom was raised
sufficiently to unite all the islands on each side of the deep water
into two great tracts of land, separated from one another by the deep
strait of water. Each of these great tracts of land would then have had
their own distinctive kinds of quadrupeds--just as the American
quadrupeds are now distinct from the European; for the comparatively
narrow strait between the then Malay continents would have offered as
effectual a barrier to the migration of quadrupeds as does the Atlantic
Ocean at the present day. Hence, when all the land slowly subsided so as
to leave only its mountain chains and table lands standing above the
surface in the form of islands, we now have the state of things which
Mr. Wallace describes--viz., two large groups of islands with the
quadrupeds on the one group differing widely from the quadrupeds on the
other, while within the limits of the same group the quadrupeds
inhabiting different islands all belong to the same or to closely
allied species. On this highly interesting subject Darwin writes, "I
have not as yet had time to follow up this subject in all quarters of
the globe; but as far as I have gone the relation holds good. For
instance, Britain is separated by a shallow channel from Europe, and the
mammals are the same on both sides, and so it is with all the islands
near the shores of America. The West Indian islands, on the other hand,
stand on a deeply submerged bank nearly 1,000 fathoms in depth, and here
we find American forms, but the species, and even the genera, are
distinct. 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
the islands separated by deeper channels, we can understand how it is
that a relation exists between the depth of the sea separating two
mammalian faunas, and the degree of their affinity--a relation which is
quite inexplicable on the theory of independent acts of creation."

So much, then, for the argument from geographical distribution--the many
facts of crucial importance which it affords almost resembling so many
experiments devised by Nature to prove the falsity of the special
creation hypothesis. For now, let it in conclusion be observed, that
there is no _physiological_ reason why animals and plants of the
different characters observed should inhabit different continents,
islands, seas, and so forth. As Darwin observes, "there is hardly a
climate or condition in the Old World which cannot be paralleled in the
New ... and yet how widely different are their living productions." And
that it is not the suitability of organisms to the areas which they
inhabit which has determined their creation upon those areas, is
conclusively proved by the effects of the artificial transportation of
species by man. For in such cases it frequently happens that the
imported species thrives quite as well in its new as in its old home,
and indeed often supplants the native species. As the Maoris say,--"As
the white man's rat has driven away the native rat, so the European fly
has driven away our fly, so the clover kills our fern, and so will the
Maori himself disappear before the white man."

Upon the whole then we are driven to the conclusion, that if the special
creation theory is true, the various plants and animals have not been
placed in the various habitats which they occupy with any reference to
the suitability of these habitats to the organisations of these
particular plants and animals. So that, considering all the evidence
under the head of geographical distribution, I think we are driven to
the yet further conclusion, that if the special creation theory is true,
the only principle which appears to have been consistently followed in
the geographical deposition of species, is the principle of so
depositing them as in all cases to make it appear that the supposition
of their having been thus deposited is not merely a highly dubious one,
but one which, on the face of it, is conspicuously absurd.



V.

THE ARGUMENT FROM EMBRYOLOGY.


There is still another important line of evidence which we cannot afford
to overlook; I mean the argument from embryology. To economise space, I
shall not explain the considerations which obviously lead to the
anticipation that, if the theory of descent by inheritance is true, the
life history of the individual ought to constitute a sort of condensed
epitome of the whole history of its descent. But taking this
anticipation for granted, as it is fully realised by the facts of
embryology, it follows that the science of embryology affords perhaps
the strongest of all the strong arguments in favour of evolution. From
the nature of the case, however, the evidence under this head requires
special training to appreciate; so I will merely observe, in general
terms, that the higher animals almost invariably pass through the same
embryological stages as the lower ones, up to the time when the higher
animal begins to assume its higher characters. Thus, for instance, to
take the case of the highest animal, man, his development begins from a
speck of living matter similar to that from which the development of a
plant begins. And, when his animality becomes established, he exhibits
the fundamental anatomical qualities which characterise such lowly
animals as the jelly-fish. Next he is marked off as a vertebrate, but it
cannot be said whether he is to be a fish, a snake, a bird or a beast.
Later on it is evident that he is to be a mammal; but not till still
later can it be said to which order of mammals he belongs.

Now this progressive inheritance by higher types of embryological
characters common to lower types is a fact which tells greatly in favour
of the theory of descent, whilst it seems almost fatal to the theory of
design. For instance, to take a specific case, Mr. Lewes remarks of a
species of salamander--which differs from most salamanders in being
exclusively terrestrial--that although its young ones can never require
gills, yet on cutting open a pregnant female we find the young ones to
possess gills like aquatic salamanders; and when placed in the water the
young ones swim about like the tadpoles of the water newt. Now, to
suppose that these utterly useless gills were specially designed is to
suppose design without any assignable purpose; for even the far-fetched
assumption that a unity of ideal is the cause of organic affinities,
becomes positively ridiculous when applied to the case of embryonic
structures, which are destined to disappear before the animal is born.
Who, for instance, would have the courage to affirm that the Deity had
any such motive in providing, not only the unborn young of specially
created salamanders, but also the unborn young of specially created man,
with the essential anatomical features of gills?

But this remark leads us to consider a little more attentively the
anatomical features presented by the human embryo. The gill-slits just
mentioned occur on each side of the neck, and to them the arteries run
in branching arches, as in a fish. This, in fact, is the stage through
which the branchiæ of a fish are developed, and therefore in fish the
slits remain open during life, while the so called "visceral arches"
throw out filaments which receive the arterial branches coming from the
aortic arches, and so become the organs of respiration, or branchiæ.
But in all the other vertebrata (_i.e._ except fish and amphibia) the
gill-slits do not develop branchiæ, become closed (with the frequent
exception of the first), and so never subserve the function of
respiration. Or, as Mr. Darwin states it, "At this period the arteries
run in arch-like branches, as if to carry the blood to branchiæ which
are not present in the higher vertebrata, though the slits on the sides
of the neck still remain, marking their former position."

The heart is at first a simple pulsating vessel, like the heart of the
lowest fishes, and the excreta are voided through a common cloacal
passage--an anatomical feature so characteristic of the lower
vertebrata, that it occurs in no fully formed member of the mammalian
group, with the exception of the bird-like order of monotremata, which
takes its name from presenting so striking a peculiarity.

At a later period the human embryo is provided with a very conspicuous
tail, which is considerably longer than the rudimentary legs occurring
at that period of development, and which Professor Turner has found to
be provided with muscles--the extensor, which is so largely developed in
many animals, being especially well marked.

Again, as Mr. Darwin says, "In the embryos of all air-breathing
vertebrates, certain glands, called the corpora Wolffiana, correspond
with and act like the kidneys of mature fishes;" and during the sixth
month the whole body is covered very thickly with wool-like hair--even
the forehead and ears being closely coated; but it is, as Mr. Darwin
observes, "a significant fact that the palms of the hands and the soles
of the feet are quite naked, like the inferior surfaces of all four
extremities in most of the lower animals," including monkeys.

Lastly, Professor Wyman has found that in a human embryo about an inch
in length, "the great toe was shorter than the others; and, instead of
being parallel to them, projected at an angle from the side of the foot,
thus corresponding with the permanent condition of this part in the
quadrumana."[1]

Therefore, on the whole, we may conclude these brief remarks on
embryology with the words of Professor Huxley:--"Without question, the
mode of origin, and the early stages of the development of man, are
identical with those of the animals immediately below him in the scale;
without a doubt, in these respects he is far nearer to apes than the
apes are to the dog."[2]

[1] _Proc. Amer. Acad. Scs._, vol. iv., 1860, p. 17. It should be added,
however, that although the direction taken by the great toe of man at
this early age is doubtless, as Prof. Wyman states, more like that which
obtains in the quadrumana, there is a slight anatomical difference in
the mode of its articulation with the foot, which seems to assist in
securing the forward direction taken by it in later life.

[2] _Man's Place in Nature_, p. 65.



VI.

ARGUMENTS DRAWN FROM CERTAIN GENERAL CONSIDERATIONS.


There are two or three arguments of a somewhat weighty character, which
do not fall under any of the previous headings, but which we must not on
this account neglect.

1. It is justly deemed a substantiation of a scientific theory if it is
found to furnish an explanation of other classes of phenomena than those
for the explanation of which it was first devised. And this is the case
with the theory of natural selection in the region of psychology. The
theory was first devised to explain the facts of biology, and proving
so successful in that region, Mr. Darwin proceeded to test it in the
region of psychology. The result has been to show that large classes of
phenomena in this region which were previously unaccountable become
fully intelligible. This is especially the case with the phenomena of
instinct, and in a lesser degree with those of reason and conscience.
For the theory shows that if structures admit of being moulded to their
special uses by natural selection, the same must be true of instincts;
and it is found an easy matter to understand how, by seizing upon and
fixing, through hereditary beneficial variations of habit (whether
instinctive or intelligent), natural selection is as competent to
fashion the mental structure of an animal as it is to shape its bodily
structure into agreement with the external conditions of life. Thus the
whole philosophy of animal intelligence is greatly elucidated, and this
fact may justly be regarded as lending much additional credence to the
theory.

Again, by observing that sympathy and the social instincts generally are
developed to a large extent in many of the lower animals, and
particularly so in the quadrumana, the theory of natural selection is
provided with a reasonable basis for furnishing a scientific explanation
of the moral sense in man; and by observing that many of the lower
animals are capable of drawing simple inferences, the theory is likewise
able to explain the development of reason. So that in the province of
human psychology no less than in that of animal, the theory of natural
selection, in showing itself competent to explain much which is
otherwise inexplicable, is seen to derive a large additional measure of
argumentative support.

2. Although the majority of structures and instincts met with in the
animal kingdom are in a marvellous degree suited to the performance of
their functions and uses, it is nevertheless far from being an
invariable rule that the suitability is perfect. Thus, for instance,
even in the case of the eye--which is perhaps the most wonderful and
most highly elaborated structure in organic nature--it is demonstrable
that the organ, considered as an optical instrument, is not ideally
perfect; so that, if it were an artificial production, opticians would
know how to improve it. And as for instinct, numberless cases might be
adduced of imperfection, ranging in all degrees from a slight deficiency
to fatal blundering.

Now if all organic structures are supposed to be mechanisms designed by
the Deity, and all instincts are supposed to be mental attributes
implanted by Him, it becomes unintelligible that in the result the human
mind should thus be able to perceive, either an ignorance of natural
principles in the Author of nature, or a singular absence of thought in
applying His knowledge. But, on the other hand, if all the structures
and instincts are supposed to be due to natural selection (whether alone
or in conjunction with other natural causes), we have no need to feel
staggered at flagrant cases of imperfection; we have only to wonder at
the number of cases in which perfection, more or less complete, has been
attained.

3. Lastly, there is still another general consideration, and one which
appeals to my mind as of immense weight. The question, it will be
remembered, lies between beneficent design and natural selection, and I
think that the consideration about to be adduced is in itself alone
sufficient to decide the question.

This consideration is that amid all the millions of mechanisms and
instincts in the animal kingdom, there is no one instance of a
mechanism or instinct occurring in one species for the exclusive benefit
of another species, although there are a few cases in which a mechanism
or instinct that is of benefit to its possessor has come also to be
utilised by other species. Now, on the beneficent design theory it is
impossible to explain why, when all the mechanisms in the same species
are invariably correlated for the benefit of that species, there should
never be any such correlation between mechanisms in different species,
or why the same remark should apply to instincts. 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 minister to
each other's necessities. Organic species might then have been likened
to a countless multitude of voices all singing in one harmonious psalm
of praise. But, as it is, we see 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.

Such, then, is a sketch of the evidence in favour of organic evolution.
Of course in such a meagre outline it has not been possible to do
justice to that evidence, which should be studied in detail rather than
looked at in such a bird's-eye view as I have presented. Nevertheless,
enough, I hope, has been said to convince all reasonable persons, that
any longer to withhold assent from so vast a body of evidence is a
token, not of intellectual prudence, but of intellectual incapacity.
With Professor Huxley, therefore, I exclaim,--"Choose your hypothesis; I
have chosen mine," and "I refuse to run the risk of insulting any sane
man by supposing that he seriously holds such a notion" as that of
special creation. These words, I submit, are not in the least too
strong; for if any man can study the many and important lines of
evidence all converging on the central truth that evolution has been the
law of organic nature, and still fail to perceive the certainty of that
truth, then I say that that man--either on account of his prejudices, or
from his inability to estimate the value of evidence--must properly be
regarded as a weak-minded man. Or, to state the case in another way, if
such a man were to say to me,--Notwithstanding all your lines of
evidence, I still believe in special design manifested in creation; I
should reply,--And in this I fully agree with you; for if,
notwithstanding these numerous and important lines of evidence, the
theory which they substantiate is false, then to my mind we have the
best conceivable evidence of very special design having been manifested
in creation--the special design, namely, to deceive mankind by an
elaborate, detailed, and systematic fraud. For, if the theory of
special creation is true, I hold that as no one fact can be adduced in
its favour, whilst so vast a body of facts can be adduced against it,
the only possible explanation of so extraordinary a circumstance is that
of a mendacious intelligence of superhuman power carefully disposing all
the observable facts of his creation in such a way as to compel his
rational creatures, by the best and most impartial use of their rational
faculties, to conclude that the theory of evolution is as certainly true
as the theory of special creation is conspicuously false.

But having now concluded this brief review of the leading arguments in
favour of organic evolution, and having expressed as forcibly as I am
able my own opinion upon them, I do not wish it to be supposed, either
that I am intolerant of opinions which are held by others, or that I
have been trying to, "make out a case" by suppressing adverse facts. I
am not intolerant, because I believe that dissent from the general
doctrine of evolution can only arise either from ignorance of some
special departments of science, or from a bias of feeling against the
doctrine--to both of which weaknesses evolutionists can afford to be
indulgent. And in order to show that I have not been trying unfairly to
make out a case, I shall conclude by briefly reviewing the arguments
which have been adduced against the doctrine in question.

The only argument of this kind that I know from the side of reason (if
we neglect those special objections which have been fully shown by Mr.
Darwin himself to be based on inadequate information or erroneous
conception, and therefore futile), is that which says:--Evolution, if
true, can only be proved so by an actual observation of the process, and
as no one pretends to have witnessed the transmutation of species, it
follows that evolution has not been proved.

Now, it is perfectly right to draw a clear distinction between a theory
and a demonstration; but it is a great mistake to suppose that a theory
may then only be admitted by science when it has been demonstrated.
Bishop Butler tells us that "Probability is the guide of life," and not
less true is it that probability is likewise the guide of science. The
business of science, as of common life, is to estimate correctly the
relative degrees of probability presented by this and that theory or
hypothesis; when once a theory or hypothesis is demonstrated it ceases
to be a matter of scientific inquiry, and becomes a matter of scientific
fact. Thus received, we have to consider the doctrine of evolution as
certainly standing in the first rank of scientific theories in respect
of probability sustained by evidence, although no less certainly not
demonstrated as a matter of scientific fact. But when a theory has been
raised to such a level of probability as this, it is, for all practical
purposes, as good as a demonstration. Thus, in the particular instance
before us, even if the sceptical demand for evidence, which from the
nature of the case is clearly impossible, were granted, and if we could
actually observe the transmutation of species, the fact would not exert
any further influence on the progress of science than is now exerted by
the large and converging bodies of evidence which leave no other
rational theory open to us than that such transmutation has taken place.
Therefore, it seems to me, the hypercritical objection which we are
considering is really founded on a misconception of scientific method,
and of what it is that justifies a scientific doctrine. Assuredly, in
the case of every theory, as distinguished from a demonstration, there
must always be a proportion between the evidence of and the warrant for
the proposition which the theory states; and if gauged by this simple
rule the warrant for accepting the theory of evolution is now estimated
by the judgment of all scientifically trained minds as so high, that by
no additional evidence could it be placed higher without becoming a full
demonstration. Or, otherwise stated, as a theory the doctrine of descent
is now in the topmost position of probability, so that by no amount of
additional evidence could it be raised higher without ceasing to be a
probability and becoming a certainty. That is to say, we do not need any
more evidence in any of the lines of evidence to add to the strength of
our belief in, as distinguished from our knowledge of, the truth of
evolution. For the strength of our conviction could not be increased by
the discovery of any additional number of connecting links among fossil
species, further facts relating to geographical distribution, to
morphology, classification, embryology, or any of the other lines of
evidence which have been mentioned; no further evidence the same in kind
is now competent to raise in degree the probability which has already
been raised, as far as from its very nature as a probability it can be
raised.

I have no doubt, however, that the principal obstacle which the doctrine
of evolution encounters in the popular mind is not one of reason, but of
sentiment. It is thought that the conception of man being a lineal
descendant of the monkey is a conception which is degrading to the
dignity of the former animal. Now this obstacle being, as I have said, a
matter of feeling or sentiment, as such I am not able to meet it. If you
think that man is shown to be any less human because his origin is now
shown to have been derivative, I cannot change that decision on your
part; I can only express dissent from it on my own. But although I
cannot affect your sentiments in this matter, I may be permitted to
point out that, as they are only sentiments, they are quite worthless as
arguments or guides to truth. I have yet to learn that the "dignity of
man" is a matter of any concern to our Mother Nature, who in all her
dealings appears, to say the least, to treat us in rather a
matter-of-fact sort of way. Indeed, so far is she from respecting our
ideas of "dignity," that whenever these ideas have been applied to any
of her processes, the progress of science has been destined rudely to
dispel them. Thus, for instance, when the sun-spots were first observed
they were indignantly denied by the Aristotelians, on the ground of its
being "impossible that the eye of the universe could suffer from
ophthalmia;" and when Kepler made his great discovery of the accelerated
and retarded motion of the planets in different parts of their orbits,
many persons refused to entertain the conception, on the ground that it
was "undignified" for heavenly bodies to hurry and slacken their pace in
accordance with Kepler's law. This now seems most absurd to us; but to
posterity it will not seem nearly so much so as that, notwithstanding
such precedents, persons should still be found to object to Darwin's
discovery, not because they were anxious to maintain the dignity of the
heavenly bodies, but because they were so ludicrously anxious to
maintain the dignity of their own! Good it is for man, puffed up with
such silly pride, that Nature teaches him humility.

But, before leaving this subject, I should like further to point out
that those who advance this preposterous objection from dignity appear
to forget one all-important point, viz., that whether or not the monkey
is the parent of the man, the man is certainly made in every way to
_look like_ a child of the monkey. For it is a matter of anatomical
demonstration, that in all the features of our bodily structure--even up
to our brains--we more closely resemble the man-like apes than the
man-like apes resemble the lower quadrumana. And I beg it to be
remembered that the tremendous significance of this fact can only be
duly appreciated by those who know the astounding complexity of our
bodily structure. Those who are ignorant of human anatomy cannot form
any adequate--probably not even an approximate--conception of its
intricacy. Yet we find that this terrifically intricate organisation is
repeated down to all the minute bones and muscles, blood-vessels, nerves
and viscera, in the bodies of the higher apes. Here, then, I say, we
have a fact--or rather let me say a hundred thousand facts--which cannot
possibly be attributed to chance. As reasonable beings we must conclude
that there has been some definite cause for this extraordinary imitation
by the most highly organised being in creation of the next most highly
organised. And if we reject the natural explanation of hereditary
descent from a common ancestry, we can only suppose that the Deity, in
creating man, took the most scrupulous pains to make him in the image of
the ape. This, I say, is a matter of undeniable fact--supposing the
creation theory true--and as a matter of fact, therefore, it calls for
explanation. Why should God have thus conditioned man as an elaborate
copy of the ape, when we know from the rest of creation how endless are
His resources in the invention of types?

I present the matter thus to show that even the weight of sentiment is
not all on the side of special creation. Look on this picture and on
this:--

The Creator has exhibited the extraordinary and unaccountable design of
casting the complex structure of man in the same mould that He had just
previously used to cast the complex structure of the ape.

"When I view all beings, not as special creations, but as the lineal
descendants of some few beings which lived long before the first bed of
the Cambrian system was deposited, they seem to me to become
ennobled.... There is grandeur in this view of life, with its several
powers, having been originally breathed by the Creator into a few forms
or into one; and that, whilst this planet has gone cycling on according
to the first law of gravity, from so simple a beginning endless forms
most beautiful and most wonderful have been and are being evolved."

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