Now, since the days of Linnæus this principle has been caref

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_NATURE SERIES._

THE SCIENTIFIC EVIDENCES

OF

ORGANIC EVOLUTION.

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.