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.