Darwin, and After Darwin Volume Ii Part 10

Here, then, we have in brief compa.s.s the whole essence of our opponents'

argument. It is confessedly an argument _a priori_, a deduction from the theory of natural selection, a supposed consequence of that theory which is alleged to be so necessary that to dispute the consequence is tantamount to denying the theory from which it is derived. In short, as before stated, it is a question of theory, not a question of fact: our difference of opinion is logical, not biological: it depends on our interpretation of principles, not on our observation of species. It will therefore be my endeavour to show that the reasoning in question is fallacious: that it is _not_ a necessary deduction from the theory of natural selection that no characteristic form or marking, no peculiarities of instinct or of habit, can exist, but which must now be, or once have been, useful, or correlated with some other peculiarity that is useful.

"The tuft of hair on the breast of a wild turkey-c.o.c.k _cannot be of any use_, and it is doubtful whether it can be ornamental in the eyes of the female bird;--indeed, had the tuft appeared under domestication, it would have been called a monstrosity[90]."

[90] _Origin of Species_, p. 70: italics mine.

As a matter of common sense, unprejudiced by dogma, this appears to be a perfectly sound judgement; but if Wallace had asked Darwin to prove such a negative, Darwin could only have replied that it was for Wallace to prove the affirmative--and thus the issue would have been thrown back upon a discussion of general principles. Then Wallace would have said--"The a.s.sertion of inutility in the case of any organ or peculiarity which is not a rudiment or a correlation _is not, and can never be_, the statement of a fact, but _merely an expression of our ignorance of its purpose or origin_[91]." Darwin, however, would have replied:--"Our ignorance of the laws of variation is profound"; and while, on this account, we ought "to be extremely cautious in _pretending to decide what structures are now, or have formerly been, of use to each species_," in point of fact "there can be little doubt that the tendency to vary in the same manner has _often_ been so strong, that _all_ individuals of the same _species_ have been similarly modified _without the aid of any form of selection_[92]."

[91] _Darwinism_, p. 137: italics mine.

[92] _Origin of Species_, p. 72: Mr. Wallace himself quotes this pa.s.sage (_Darwinism_, p. 141); but says with regard to it "the important word 'all' is probably an oversight." In the Appendix (II), on Darwin's views touching the doctrine of utility I adduce a number of precisely equivalent pa.s.sages, derived from all his different works on evolution, and _every one of them_ presenting "the important word 'all.'"

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 antic.i.p.ate 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 a.s.sumption 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.

[93] See Introductory Chapter, p. 20.

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 ent.i.tled 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 const.i.tute 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 a.s.sertion--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]."

[94] _Darwinism_, p. 138.

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]."

[95] _Origin of Species_, p. 176: italics mine, as also in the following.

Elsewhere we read:--

"Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the _same_ cause were to act _uniformly_ during a long series of generations on _many_ individuals, _all_ probably would be modified in the same manner."

As special ill.u.s.trations of this fact I may quote the following cases from Darwin's works.

"Dr. Bachman states that he has seen turkeys raised from the eggs of wild species, lose their metallic tints, and become spotted in the third generation. Mr. Yarrell many years ago informed me that the wild ducks bred in St James' Park lost their true plumage after a few generations. An excellent observer (Mr. Hewitt) ...

found that he could not breed wild ducks true for more than five or six generations, as they proved so much less beautiful. The white collar round the neck of the mallard became broader and more irregular, and white feathers appeared in the duckling's wings &c.[96]"

[96] _Var._ vol. ii. p. 250.

Now, such cases--to which numberless others might be added--prove that even the subtle and inconspicuous causes incidental to domestication are capable of inducing changes of specific character quite as great, and quite as "stable," as any that in a state of nature are taken to const.i.tute specific distinctions. Yet there can here be no suggestion of utility, inasmuch as the change takes place in the course of a few generations, and therefore without leaving time for natural selection to come into play--even if it ever could come into play among the sundry domesticated birds in question.

But the facts of domestication also make for the same conclusion in another way--namely, by proving that when time enough _has_ been allowed for the production of useless changes of greater magnitude, such changes are not infrequently produced. And the value of this line of evidence is that, great as are the changes, it is impossible that either natural or artificial selection can have been concerned in their production. It will be sufficient to give two examples--both with regard to structure.

The first I will render in the words whereby it has already been stated in my own paper on _Physiological Selection_, because I should like to take this opportunity of answering Mr. Wallace's objection to it.

"Elsewhere (_Origin of Species_, p. 158) Mr. Darwin points out that modifications which appear to present obvious utility are often found on further examination to be really useless. This latter consideration, therefore, may be said to act as a foil to the one against which I am arguing, namely, that modifications which appear to be useless may nevertheless be useful. But here is a still more suggestive consideration, also derived from Mr. Darwin's writings.

Among our domesticated productions changes of structure--or even structures wholly new--not unfrequently arise, which are in every way a.n.a.logous to the apparently useless distinctions between wild species. Take, for example, the following most instructive case:--

[Ill.u.s.tration: Fig. 2.--Old Irish Pig, showing jaw-appendages (after Richardson).]

"'Another curious anomaly is offered by the appendages described by M. Eudes-Deslongchamps as often characterizing the Normandy pigs.

These appendages are always attached to the same spot, to the corners of the jaws; they are cylindrical, about three inches in length, covered with bristles, and with a pencil of bristles rising out of a sinus on one side; they have a cartilaginous centre with two small longitudinal muscles; they occur either symmetrically on both sides of the face, or on one side alone. Richardson figures them on the gaunt old Irish Greyhound pig; and Nathusius states that they occasionally appear in all the long-eared races, but are not strictly inherited, for they occur or fail in the animals of the same litter. As no wild pigs are known to have a.n.a.logous appendages, we have at present no reason to suppose that their appearance is due to reversion; and if this be so, we are forced to admit that a somewhat complex, though apparently useless, structure may be suddenly developed without the aid of selection[97].'"

[97] _Variation_, &c. vol. i. pp. 78-79.

To this case Mr. Wallace objects:--

"But it is expressly stated that they are not constant; they appear 'frequently' or 'occasionally,' they are 'not strictly inherited, for they occur or fail in animals of the same litter'; and they are not always symmetrical, sometimes appearing on one side of the face alone. Now, whatever may be the cause or explanation of these anomalous appendages, they cannot be cla.s.sed with 'specific characters,' the most essential features of which are, that they _are_ symmetrical, that they _are_ inherited, and that they _are_ constant[98]."

[98] _Darwinism_, pp. 139-40.

But, to begin with, I have not cla.s.sed these appendages with "specific characters," nor maintained that Normandy pigs ought to be regarded as specifically distinct on account of them. What I said was:--

"Now, if any such structure as this occurred in a wild species, and if any one were to ask what is the use of it, those who rely on the argument from ignorance would have a much stronger case than they usually have; for they might point to the cartilage supplied with muscles, and supporting a curious arrangement of bristles, as much too specialized a structure to be wholly meaningless. Yet we happen to know that this particular structure is wholly meaningless[99]."

[99] Mr. Wallace deems the concluding words "rather confident." I was not, however, before aware that he extended his _a priori_ views on utility to domesticated varieties which are bred for the slaughter-house. If he now means to indicate that these appendages are possibly due to natural selection, he is surely going very far to save his _a priori_ dogma; and in the case next adduced will have to go further still.

In the next place, is it either fair or reasonable to expect that a varietal character of presumably very recent origin should be as strongly inherited--and therefore as constant both in occurrence and symmetry--as a true specific character, say, of a thousand times its age? Even characters of so-called "constant varieties" in a state of nature are usually less constant than specific characters; while, again, as Darwin says, "it is notorious that specific characters are more variable than generic,"--the reason in both cases being, as he proceeds to show, that the less constant characters are characters of more recent origin, and therefore less firmly fixed by heredity[100]. Hence I do not understand how Mr. Wallace can conclude, as he does, "that, admitting that this peculiar appendage is wholly useless and meaningless, the fact would be rather an argument against specific characters being also meaningless, because the latter never have the characteristics [i.e.

inconstancy of occurrence, form, and transmission] which this particular variation possesses[101]." Mr. Wallace can scarcely suppose that when specific characters first arise, they present the three-fold kind of constancy to which he here alludes. But, if not, can it be denied that these peculiar appendages appear to be pa.s.sing through a phase of development which all "specific characters" must have pa.s.sed through, before they have had time enough to be firmly fixed by heredity[102]?

[100] _Origin of Species_, pp. 122-3.

[101] _Darwinism_, p. 140.

[102] In the next paragraph Mr. Wallace says that the appendages in question "are apparently of the same nature as the 'sports'

that arise in our domesticated productions, but which, as Mr.

Darwin says, without the aid of selection would soon disappear." But I cannot find that Mr. Darwin has made any such statement: what he does say is, that whether or not a useless peculiarity will soon disappear without the aid of selection depends upon the nature of the causes which produce it. If these causes are of a merely transitory nature, the peculiarity will also be transitory; but if the causes be constant, so will be the result. Again, the point to be noticed about this "sport" is, that, unlike what is usually understood by a "sport," it affects a whole race or breed, is transmitted by s.e.xual propagation, and has already attained so definite a size and structure, that it can only be reasonably accounted for by supposing the continued operation of _some constant_ cause. This cause can scarcely be correlation of growth, since closely similar appendages are often seen in so different an animal as a goat. Here, also, they run in breeds or strains, are strongly inherited, and more "constant," as well as more "symmetrical" than they are in pigs. This, at all events, is the account I have received of them from goat-breeders in Switzerland.

If, however, even this should be denied, what will be said of the second case, that of the niata cattle?

"I saw two herds on the northern bank of the Plata.... The forehead is very short and broad, with the nasal end of the skull, together with the whole plane of the upper molar-teeth, curved upwards. The lower jaw projects beyond the upper, and has a corresponding upward curvature.... The skull which I presented to the College of Surgeons has been thus described by Professor Owen. 'It is remarkable from the stunted development of the nasals, premaxillaries, and fore part of the lower jaw, which is unusually curved upwards to come into contact with the premaxillaries. The nasal bones are about one-third the ordinary length, but retain almost their normal breadth. The triangular vacuity is left between them and the frontal and lachrymal, which latter bone articulates with the premaxillary, and thus excludes the maxillary from any junction with the nasal.' So that even the connexion of some of the bones is changed. Other differences might be added: thus the plane of the condyles is somewhat modified, and the terminal edge of the premaxillaries forms an arch. In fact, on comparison with the skull of a common ox, scarcely a single bone presents the same exact shape, and the whole skull has a wonderfully different appearance[103]."

[103] Darwin, _Variation_, &c., vol. i. pp. 92-4.

[Ill.u.s.tration: Fig. 3.--Drawn from nature. R. Coll. Surg. Mus.]

As I cannot find that this remarkable skull has been figured before, I have had the accompanying woodcut made in order to compare it with the skull of a Charsley Forest ox; and a glance is sufficient to show what "a wonderfully different appearance" it presents.