Volume I Part 15 (1/2)

Or let us take an even closer a.n.a.logy. The power of selective breeding by man is so wonderful, that in the course of successive generations all kinds of peculiarities as to size, shape, colour, special appendages or abortions, &c., can be produced at pleasure, as we saw in the last chapter. Now all the promiscuous variations which are supplied to the breeder, and out of which, by selecting only those that are suited to his purpose, he is able to produce the required result--all those promiscuous variations, in relation to that purpose, are accidental.

Therefore the selective agency of the breeder deserves to be regarded as the cause of that which it produces, or of that which could not have been produced but for the operation of such agency. But where is the difference between artificial and natural selection in this respect?

And, if there is no difference, is not natural selection as much ent.i.tled to be regarded as a true cause of the origin of natural species, as artificial selection is to be regarded as a true cause of our domesticated races? Here, as in the case of the previous ill.u.s.tration, if there be any ambiguity in speaking of variations as accidental, it arises from the incorrect or undefined manner in which the term ”accidental” is used by Darwin's critics. In its original and philosophically-correct usage, the term ”accident” signifies a property or quality not essential to our conception of a substance: hence, it has come to mean anything that happens as a result of unforeseen causes--or, lastly, that which is causeless. But, as we know that nothing can happen without causes of some kind, the term ”accident” is divested of real meaning when it is used in the last of these senses. Yet this is the sense that is sought to be placed upon it by the objection which we are considering. If the objectors will but understand the term in its correct philosophical sense--or in the only sense in which it presents any meaning at all,--they will see that Darwinians are both logically and historically justified in employing the word ”accidental” as the word which serves most properly to convey the meaning that they intend--namely, variations due to causes accidental to the struggle for existence. Similarly, when it is said that variations are ”spontaneous,”

or even ”fortuitous,” nothing further is meant than that we do not know the causes which lead to them, and that, so far as the principle of selection is concerned, it is immaterial what these causes may be. Or, to revert to our former ill.u.s.tration, the various weights of different kinds of earths are no doubt all due to definite causes; but, in relation to the selective action of the gold-washer, all the different weights of whatever kinds of earth he may happen to include in his was.h.i.+ng-apparatus are, _strictly speaking_, accidental. And as at different was.h.i.+ngs he meets with different proportions of heavy earths with light ones, and as these ”variations” are immaterial to him, he may colloquially speak of them as ”fortuitous,” or due to ”chance,” even though he knows that at each was.h.i.+ng they must have been determined by definite causes.

More adequately to deal with this merely formal objection, however, would involve more logic-chopping than is desirable on the present occasion. But I have already dealt with it fully elsewhere,--viz. in _The Contemporary Review_ for June, 1888, to which therefore I may refer any one who is interested in dialectics of this kind[43].

[43] Within the last few months this objection has been presented anew by Mr. D. Syme, whose book _On the Modification of Organisms_ exhibits a curious combination of shrewd criticisms with almost ludicrous misunderstandings. One of the latter it is necessary to state, because it pervades the quotation which I am about to supply.

He everywhere compares ”natural selection” with ”the struggle for existence,” uses them as convertible terms, and while absurdly stating that ”Darwin defines natural selection as the struggle for existence,” complains of ”the liability of error, both on his own part and on the part of his readers,” which arises from his not having everywhere adhered to this definition! (p. 8).

”Darwin has put forth two distinct and contradictory theories of the functions of natural selection. According to the one theory natural selection is selective or preservative, and nothing more. According to the other theory natural selection creates the variations(!) ...

It certainly seems absurd to speak of natural selection, or the struggle for existence, as selective or preservative, for the struggle for existence does not preserve at all, not even the fit variations, as both the fit and the unfit struggle for existence, the unfit naturally more than the fit, and the fit are preserved, not in consequence of the struggle, but in consequence of their fitness. Suppose two varieties of the same species are driven, by an increase of their numbers, to seek for subsistence in a colder region than they have been accustomed to, and that one of these varieties had a hardier const.i.tution than the other; and let us suppose that the former withstood the severe climate better than the latter, and consequently survived, while the other perished. In this case the hardier survived, not because of the struggle, but because it had a const.i.tution better adapted to the climate. I wish to ascertain if a certain metal in my possession is gold or some baser metal, and I apply the usual test; but the mere fact of my testing this metal would not make it gold or any other kind of metal.”

I have thought it worth while to quote this pa.s.sage for the sake of showing the extraordinary confusion of mind which still prevails on the part of Darwin's critics, even with reference to the very fundamental parts of his theory. For, as I have said, the writer of this pa.s.sage shows himself a shrewd critic in some other parts of his essay, where he is not engaged especially on the theory of natural selection.

I will now pa.s.s on to consider another misconception of the Darwinian theory, which is very prevalent in the public mind. It is virtually asked, If some species are supposed to have been improved by natural selection, why have not all species been similarly improved? Why should not all invertebrated animals have risen into vertebrated? Or why should not all monkeys have become men?

The answers are manifold. In the first place, it by no means follows that because an advance in organization has proved itself of benefit in the case of one form of life, therefore any or every other form would have been similarly benefited by a similar advance. The business of natural selection is to bring this and that form of life into the closest harmony with its environment that all the conditions of the case permit. Sometimes it will happen that the harmony will admit of being improved by an improvement of organization. But just as often it will happen that it will be best secured by leaving matters as they are. If, therefore, an organism has already been brought into a tolerably full degree of harmony with its environment, natural selection will not try to change it so long as the environment remains unchanged; and this, no doubt, is the reason why some species have survived through enormous periods of geological time without having undergone any change. Again, as we saw in a previous chapter, there are yet other cases where, on account of some change in the environment or even in the habits of the organisms themselves, adaption will be best secured by an active _reversal_ of natural selection, with the result of causing _degeneration_.

But, it is sometimes further urged, there are cases where we cannot doubt that improvement of organization would have been of benefit to species; and yet such improvement has not taken place--as, for instance, in the case all monkeys not turning into men. Here, however, we must remember that the operation of natural selection in any case depends upon a variety of highly complex conditions; and, therefore, that the fact of all those conditions having been satisfied in one instance is no reason for concluding that they must also have been satisfied in other instances. Take, for example, the case of monkeys pa.s.sing into men. The wonder to me appears to be that this improvement should have taken place in even one line of descent; not that, having taken place in one line, it should not also have taken place in other lines. For how enormously complex must have been the conditions--physical, anatomical, physiological, psychological, sociological--which by their happy conjunction first began to raise the inarticulate cries of an ape into the rational speech of a man. Therefore, the more that we appreciate the superiority of a man to an ape, the less ought we to countenance this supposed objection to Darwin's theory--namely, that natural selection has not effected the change in more than one line of descent.

Even in the case of two races of mankind where one has risen higher in the scale of civilization than another, it is now generally impossible to a.s.sign the particular causes of the difference; much more, then, must this be impossible in the case of still more remote conditions which have led to the divergence of species. The requisite variations may not have arisen in the one line of descent which did arise in the other; or if they did arise in both, some counterbalancing disadvantages may have attended their initial development in the one case which did not obtain in the other. In short, where so exceedingly complex a play of conditions are concerned, the only wonder would be if two different lines of descent _had_ happened to present two independent and yet perfectly parallel lines of history.

These general considerations would apply equally to the great majority of other cases where some types have made great advances upon others, notwithstanding that we can see no reason why the latter should not in this respect have imitated the former. But there is yet a further consideration which must be taken into account. The struggle for existence is always most keen between closely allied species, because, from the similarity of their forms, habits, needs, &c., they are in closest compet.i.tion. Therefore it often happens that the mere fact of one species having made an advance upon others of itself precludes the others from making any similar advance: the field, so to speak, has already been occupied as regards that particular improvement, and where the struggle for existence is concerned possession is emphatically nine points of the law. For example, to return to the case of apes becoming men, the fact of one rational species having been already evolved (even if the rational faculty were at first but dimly nascent) must make an enormous change in the conditions as regards the possibility of any other such species being subsequently evolved--unless, of course, it be by way of descent from the rational one. Or, as Sir Charles Lyell has well put it, two rational species can never _coexist_ on the globe, although the descendants of one rational species may in time become _transformed_ into another single rational species[44].

[44] _Principles of Geology_, vol. ii. p. 487 (11th ed.).

In view of such considerations, another and exactly opposite objection has sometimes been urged--viz. that we ought never to find inferior forms of organization in company with superior, because in the struggle for existence the latter ought to have exterminated the former. Or, to quote the most recent expression of this view, ”in every locality there would only be one species, and that the most highly organized; and thus a few superior races would part.i.tion the earth amongst them to the entire exclusion of the innumerable varieties, species, genera, and orders which now inhabit it[45].” Of course to this statement it would be sufficient to enquire, On what would these few supremely organized species subsist? Unless manna fell from heaven for their especial benefit, it would appear that such forms could under no circ.u.mstances be the most improved forms; in exterminating others on such a scale as this, they would themselves be quickly, and very literally, improved off the face of the earth. But even when the statement is not made in so extravagant a form as this, it must necessarily be futile as an objection unless it has first been shown that we know exactly all the conditions of the complex struggle for existence between the higher and lower forms in question. And this it is impossible that we ever can know. The mere fact that one form has been changed in virtue of this struggle must in many cases of itself determine a change in the conditions of the struggle. Again, the other and closely allied forms (and these furnish the best grounds for the objection) may also have undergone defensive changes, although these may be less conspicuous to our observation, or perhaps less suggestive of ”improvement” to our imperfect means of judging. Lastly, not to continue citing an endless number of such considerations, there is the broad fact that it is only to those cases where, for some reason or another, the lower forms have not been exposed to a struggle of fatal intensity, that the objection applies. But we know that in millions of other cases the lower (i. e.

less fitted) forms _have_ succ.u.mbed, and therefore I do not see that the objection has any ground to stand upon. That there is a general tendency for lower forms to yield their places to higher is shown by the gradual advance of organization throughout geological time; for if _all_ the inferior forms had survived, the earth could not have contained them, unless she had been continually growing into something like the size of Jupiter. And if it be asked why any of the inferior forms have survived, the answer has already been given, as above.

[45] Syme, on the _Modification of Organisms_, p. 46.

There is only one other remark to be made in this connexion. Mr. Syme chooses two cases as ill.u.s.trations of the supposed difficulty. These are sufficiently diverse--viz. Foraminifera and Man. Touching the former, there is nothing that need be added to the general answer just given.

But with regard to the latter it must be observed that the dominion of natural selection as between different races of mankind is greatly restricted by the presence of rationality. Compet.i.tion in the human species is more concerned with wits and ideas than with nails and teeth; and therefore the ”struggle” between man and man is not so much for actual _being_, as for _well-being_. Consequently, in regard to the present objection, the human species furnishes the worst example that could have been chosen.

Hitherto I have been considering objections which arise from misapprehensions of Darwin's theory. I will now go on to consider a logically sound objection, which nevertheless is equally futile, because, although it does not depend on any misapprehension of the theory, it is not itself supported by fact.

The objection is the same as that which we have already considered in relation to the general theory of descent--namely, that similar organs or structures are to be met with in widely different branches of the tree of life. Now this would be an objection fatal to the theory of natural selection, supposing these organs or structures in the cases compared are not merely a.n.a.logous, but also h.o.m.ologous. For it would be incredible that in two totally different lines of descent one and the same structure should have been built up independently by two parallel series of variations, and that in these two lines of descent it should always and independently have ministered to the same function. On the other hand, there would be nothing against the theory of natural selection in the fact that two structures, _not_ h.o.m.ologous, should come by independent variation in two different lines of descent to be adapted to perform the same function. For it belongs to the very essence of the theory of natural selection that a useful function should be secured by favourable variations of whatever structural material may happen to be presented by different organic types. Flying, for instance, is a very useful function, and it has been developed independently in at least four different lines of descent--namely, the insects, reptiles, birds, and mammals. Now if in all, or indeed in any, of these four cases the wings had been developed on the same anatomical pattern, so as not only to present the a.n.a.logical resemblance which it is necessary that they should present in order to discharge their common function of flying, but likewise an h.o.m.ologous or structural resemblance, showing that they had been formed on the same anatomical ”plan,”--if such has been the case, I say, the theory of natural selection would certainly be destroyed.

Now it has been alleged by competent naturalists that there are several such cases in organic nature. We have already noticed in a previous chapter (pp. 58, 59), that Mr. Mivart has instanced the eye of the cuttle-fish as not only a.n.a.logous to, but also h.o.m.ologous with, the eye of a true fish--that is to say, the eye of a mollusk with the eye of a vertebrate. And he has also instanced the remarkable resemblance of a shrew to a mouse--that is, of an insectivorous mammal to a rodent--not to mention other cases. In the chapter alluded to these instances of h.o.m.ology, alleged to occur in different branches of the tree of life, were considered with reference to the process of organic evolution as a fact: they are now being considered with reference to the agency of natural selection as a method. And just as in the former case it was shown, that if any such alleged instances could be proved, the proof would be fatal to the general theory of organic evolution by physical causes, so in the present case, if this could be proved, it would be equally fatal to the more special theory of natural selection. But, as we have before seen, no single case of this kind has ever been made out; and, therefore, not only does this supposed objection fall to the ground, but in so doing it furnishes an additional argument in favour of natural selection. For in the earlier chapter just alluded to I showed that this great and general fact of our nowhere being able to find two h.o.m.ologous structures in different branches of the tree of life, was the strongest possible testimony in favour of the theory of evolution. And, by parity of reasoning, I now adduce it as equally strong evidence of natural selection having been the cause of _adaptive_ structures, independently developed in all the different lines of descent. For the alternative is between adaptations having been caused by natural selection or by supernatural design. Now, if adaptations were caused by natural selection, we can very well understand why they should never be h.o.m.ologous in different lines of descent, even in cases where they have been brought to be so closely a.n.a.logous as to have deceived so good a naturalist as Mr. Mivart. Indeed, as I have already observed, so well can we understand this, that any single instance to the contrary would be sufficient to destroy the theory of natural selection _in toto_, unless the structure be one of a very simple type. But on the other hand, it is impossible to suggest any rational explanation why, if all adaptations are due to supernatural design, such scrupulous care should have been taken never to allow h.o.m.ologous adaptations to occur in different divisions of the animal or vegetable kingdoms. Why, for instance, should the eye of a cuttle-fish _not_ have been constructed on the same ideal pattern as that of vertebrate? Or why, among the thousands of vertebrated species, should no one of their eyes be constructed on the ideal pattern that was devised for the cuttle-fish?

Of course it may be answered that perhaps there was some hidden reason why the design should never have allowed an adaptation which it had devised for one division of organic nature to appear in another--even in cases where the new design necessitated the closest possible resemblance in everything else, save in the matter of anatomical h.o.m.ology.

Undoubtedly such may have been the case--or rather such _must_ have been the case--if the theory of special design is true. But where the question is as to the truth of this theory, I think there can be no doubt that its rival gains an enormous advantage by being able to _explain_ why the facts are such as they are instead of being obliged to take refuge in hypothetical possibilities of a confessedly unsubstantiated and apparently unsubstantial kind.

Therefore, as far as this objection to the theory of natural selection is concerned--or the allegation that h.o.m.ologous structures occur in different divisions of organic nature--not only does it fall to the ground, but positively becomes itself converted into one of the strongest arguments in favour of the theory. As soon as the allegation is found to be baseless, the very fact that it cannot be brought to bear upon any one of all the millions of adaptive structures in organic nature becomes a fact of vast significance on the opposite side.

The next difficulty to which I shall allude is that of explaining by the theory of natural selection the preservation of the first beginnings of structures which are then useless, though afterwards, when more fully developed, they become useful. For it belongs to the very essence of the theory of natural selection, that a structure must be supposed already useful before it can come under the influence of natural selection: therefore the theory seems incapable of explaining the origin and conservation of _incipient_ organs, or organs which are not yet sufficiently developed to be of any service to the organisms presenting them.

This objection is one that has been advanced by all the critics of Darwinism; but has been presented with most ability and force by the Duke of Argyll. I will therefore state it in his words.