Part 1 (1/2)

The Scientific Evidences of Organic Evolution.

by George John Romanes.

PREFACE.

Several months ago I published in the _Fortnightly Review_ a lecture, which I had previously delivered at the Philosophical Inst.i.tutions of Edinburgh and Birmingham, and which bore the above t.i.tle. 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.

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 cla.s.ses. 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 circ.u.mstances 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 const.i.tuent individuals of any given generation.

Now, in this struggle for existence, which individuals will be victorious and live? a.s.suredly those which are best fitted to live: the weakest and the least fitted to live will succ.u.mb 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 a.n.a.logous 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 trans.m.u.ted 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 cla.s.s 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 att.i.tude 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 a.s.sume 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 a.s.sume the operation of higher causes when lower ones are found sufficient to explain the observed effects--this law const.i.tutes the only logical barrier between science and superst.i.tion. 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 superst.i.tion consists in science recognising a validity in the law of parsimony which superst.i.tion 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 superst.i.tious way. Let us take, for instance, as an ill.u.s.tration, 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 _prima 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 trans.m.u.ted into another--_i.e._, that one set of adaptations may be gradually transformed into another set of adaptations according as changing circ.u.mstances 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 a.s.sisted 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 fetis.h.i.+sm.

To avoid misapprehension, however, I may here add that while Mr.