Darwin, and After Darwin, Volume 2 of 3 / Post-Darwinian Questions: Heredity and Utility

by George John Romanes

It will be my endeavour in the following discussion to show that Darwin would have had an immeasurable advantage in this imaginary debate.

To begin with, Wallace's deductive argument is a clear case of circular reasoning. We set out by inferring that natural selection is a cause from numberless cases of observed utility as an effect: yet, when "in a large proportional number" of cases we fail to perceive any imaginable utility, it is argued that nevertheless utility must be there, since otherwise natural selection could not have been the cause.

Be it observed, in any given case we may properly anticipate utility as probable, even where it is not perceived; because there are already so enormous a number of cases where it is perceived, that, if the principle of natural selection be accepted at all, we must conclude with Darwin that it is "the main means of modification." Therefore, in particular cases of unperceived utility we may take this antecedent probability as a guide in our biological researches—as has been done with such brilliant success both by Darwin and Wallace, as well as by many of their followers. But this is a very different thing from laying down the universal maxim, that in all cases utility must be present, whether or not we shall ever be able to detect it[93]. For this universal maxim amounts to an assumption that natural selection has been the "exclusive means of modification." That it has been "the main means of modification" is proved by the generality of the observed facts of adaptation. That it has been "the exclusive means of modification," with the result that these facts are universal, cannot be thus proved by observation. Why, then, is it alleged? Confessedly it is alleged by way of deduction from the theory of natural selection itself. Or, as above stated, after having deduced the theory from the facts, it is sought to deduce the facts from the theory.

Thus far I have been endeavouring to show that the universality of adaptation cannot be inferred from its generality, or from the theory of natural selection itself. But, of course, the case would be quite different if there were any independent evidence—or rather, let us say, any logical argument—to show that natural selection is "the exclusive means of modification." For in this event it would no longer involve circular reasoning to maintain that all specific characters are likewise adaptive characters. It might indeed appear antecedently improbable that no other principle than natural selection can possibly have been concerned in the differentiation of those relatively permanent varieties which we call species—that in all the realm of organic nature, and in all the complexities of living processes, there is no room for any other influence in the production of change, even of the most trivial and apparently unmeaning kind. But if there were any good evidence or logical argument to the contrary, this antecedent presumption would have to give way; and the certainty that all specific characters are likewise adaptive characters would be determined by the cogency of such evidence or argument as could be adduced. In short, we are not entitled to conclude—and still less does it follow "as a necessary deduction from the theory of natural selection"—that all the details of specific differentiation must in every case be either useful, vestigial, or correlated, unless it has been previously shown, by independent evidence, or accurate reasoning, that there is no room for any other principle of specific change.

This, apparently, is the central core of the question. Therefore I will now proceed to consider such arguments as have been adduced to prove that, other than natural selection, there can have been no "means of modification." And, after having exhibited the worthlessness of these arguments, I will devote the next chapter to showing that, as a matter of observable fact, there are a considerable number of other principles, which can be proved to be capable of producing such minute differences of form and colour as "in a large proportional number" of cases constitute diagnostic distinctions between species and species.

First, then, for the reasons a priori—and they are confessedly a priori—which have been adduced to prove that natural selection has been what in Darwin's opinion it has not been,—"the exclusive means of modification." Disregarding the Lamarckian factors—which, even if valid, have but little relation to the present question, seeing that they are concerned, almost exclusively, with the evolution of adaptive characters—it is alleged that natural selection must occupy the whole field, because no other principle of change can be allowed to operate in the presence of natural selection. Now, I fully agree that this statement may hold as regards any principle of change which is deleterious; but clearly it does not hold as regards any principle which is merely neutral. If any one were to allege that specific characters are frequently detrimental to the species presenting them, he would no doubt lay himself open to the retort that natural selection could not allow such characters to persist; or, which amounts to the same thing, that it does "necessarily follow from the theory of natural selection" that specific characters can never be in any large number, or in any large measure, harmful to the species presenting them. But where the statement is that specific characters are frequently indifferent—again to use Professor Huxley's term—the retort loses all its relevancy. No reason has ever been shown why natural selection should interfere with merely indifferent characters, supposing such to have been produced by any of the agencies which we shall presently have to consider. Therefore this argument—or rather assertion—goes for nothing.

The only other argument I have met with on this side of the question is one that has recently been adduced by Mr. Wallace. He says:—

"One very weighty objection to the theory that specific characters can ever be wholly useless appears to have been overlooked by those who have maintained the frequency of such characters, and that is, their almost necessary instability[94]."

This argument he proceeds to elaborate at considerable length, but fails to perceive what appears to me the obvious answer. Provided that the cause of the useless character is constant, there is no difficulty in understanding why the character is stable. Utility is not the only principle that can lead to stability: any other principle must do the same, provided that it acts for a sufficient length of time, and with a sufficient degree of uniformity, on all the individuals of a species. This is a consideration the cogency of which was clearly recognized by Darwin, as the following quotations will show. Speaking of unadaptive characters, he says they may arise as merely

"fluctuating variations, which sooner or later become constant through the nature of the organism and of surrounding conditions, but not through natural selection[95]."