Volume Ii Part 15 (1/2)
So that, upon the whole, I do not see how on grounds of general reasoning it is logically possible to maintain Mr. Wallace's distinction between specific and generic characters in respect of necessary utility.
[132] _Origin of Species_, p. 122.
But now, and lastly, we shall reach the same conclusion if, discarding all consideration of general principles and formal reasoning, we fasten attention upon certain particular cases, or concrete facts. Thus, to select only two ill.u.s.trations within the limits of genera, it is a diagnostic feature of the genus _Equus_ that small warty callosities occur on the legs. It is impossible to suggest any useful function that is now discharged by these callosities in any of the existing species of the genus. If it be a.s.sumed that they must have been of some use to the species from which the genus originally sprang, the a.s.sumption, it seems to me, can only be saved by further a.s.suming that in existing species of the genus these callosities are in a vestigial condition--i. e. that in the original or parent species they performed some function which is now obsolete. But against these a.s.sumptions there lies the following fact. The callosities in question are not similarly distributed through all existing species of the genus. The horse has them upon all his four legs, while other species have them only upon two. Therefore, if all specific characters are necessarily due to natural selection, it is manifest that these callosities are _not_ now vestigial: on the contrary, they _must_ still be--or, at best, have recently been--of so much importance to all existing species of the genus, that not only is it a matter of selection-value to all these species that they should possess these callosities; but it is even a matter of selection-value to a horse that he should possess four of them, while it is equally a matter of selection-value to the a.s.s that he should possess only two.
Here, it seems to me, we have once more the doctrine of the necessary utility of specific characters reduced to an absurdity; while at the same time we display the incoherency of the distinction between specific characters and generic characters in respect of this doctrine. For the distinction in such a case amounts to saying that a generic character, if evenly distributed among all the species, need not be an adaptive character; whereas, if any one of the species presents it in a slightly different form, the character must be, on this account, necessarily adaptive. In other words, the uniformity with which a generic character occurs among the species of the genus is taken to remove that character from the necessarily useful cla.s.s, while the absence of such uniformity is taken as proof that the character must be placed within the necessarily useful cla.s.s. Which is surely no less a _reductio ad absurdum_ with regard to the generic character than the one just presented with regard to its variants as specific characters. And, of course, this twofold absurdity is presented in all cases where a generic character is unequally distributed among the const.i.tuent species of a genus.
[Ill.u.s.tration: Fig. 4.--Lower Teeth of Orang (after Tomes).]
But here is an ill.u.s.tration of another cla.s.s of cases. Mr. Tomes has shown that the molar teeth of the Orang present an extraordinary and altogether superfluous amount of attachment in their sockets--the fangs being not only exceedingly long, and therefore deeply buried in the jaw-bone, but also curving round one another, so as still further to strengthen the whole[133]. In the allied genera of anthropoid apes there is no such abnormal amount of attachment. Now, the question is, of what conceivable use can it _ever_ have been, either to the existing genus, or to its parent species, that such an abnormal amount of attachment should obtain? It certainly is not required to prevent dislocation of the teeth, seeing that in all allied genera, and even in man himself, the amount of attachment is already so great that teeth will break before they can be drawn by anything short of a dentist's forceps.
Therefore I conclude that this peculiarity in the dent.i.tion of the genus must have arisen in its parent species by way of what Darwin calls a ”fluctuating variation,” without utilitarian significance. And I adduce it in the present connexion because the peculiarity is one which is equally unamenable to a utilitarian explanation, whether it happens to occur as a generic or a specific character.
[133] _A Manual of Dental Anatomy_, p. 455.
Numberless similar cases might be quoted; but probably enough has now been said to prove the inconsistency of the distinction which our opponents draw between specific and all higher characters in respect of utility. In point of fact, a very little thought is enough to show that no such distinction admits of being drawn; and, therefore, that any one who maintains the doctrine of utility as universal in the case of specific characters, must in consistency hold to the same doctrine in the case of generic and all higher characters. And the fact that our opponents are unable to do this becomes a virtual confession on their part of the futility of the generalization which they have propounded[134].
[134] It may be observed that this distinction was not propounded by Mr. Wallace--nor, so far as I am aware, by anybody else--until he joined issue with me on the subject of specific characters.
Whether he has always held this important distinction between specific and generic characters, I know not; but, as originally enunciated, his doctrine of utility as universal was subject to no such limitation: it was stated unconditionally, as applying to all taxonomic divisions indifferently. The words have already been quoted on page 180; and, if the reader will turn to them, he may further observe that, prior to our discussion, Mr. Wallace made no allowance for the principle of correlation, which, as we have seen, furnishes so convenient a loop-hole of escape in cases where even the argument from our ignorance of possible utility appears absurd. In his latest work, however, he is much less sweeping in his statements. He limits his doctrine to the case of ”specific characters” alone, and even with regard to them makes unlimited drafts upon the principle of correlation.
On what then do Mr. Wallace and his followers rely for their great distinction between specific and all other characters in respect of utility? This is the final and fundamental question which I must leave these naturalists themselves to answer; for my whole contention is, that it is unanswerable. But although I am satisfied that they have nothing on which to base their generalization, it seems worth while to conclude by showing yet one further point. And this is, that these naturalists themselves, as soon as they quit merely abstract a.s.sertions and come to deal with actual facts, contradict their own generalization. It is worth while to show this by means of a few quotations, that we may perceive how impossible it is for them to sustain their generalization in the domain of fact.
As it is desirable to be brief, I will confine myself to quoting from Mr. Wallace.
”Colour may be looked upon as a necessary result of the highly complex chemical const.i.tution of animal tissues and fluids. The blood, the bile, the bones, the fat, and other tissues have characteristic, and often brilliant colours, which we cannot suppose to have been determined for any special purpose as colours, since they are usually concealed. The external organs and integuments, would, by the same general laws, naturally give rise to a greater variety of colour[135].”
[135] _Darwinism_, p. 297.
Surely comment is needless. Have the colour of external organs and integuments nothing to do with the determining of specific distinctions by systematists? Or, may we not rather ask, are there any other ”characters” which have had more to do with their delineation of animal species? Therefore, if ”the external organs and integuments naturally give rise to a greater variety of colours,” for non-utilitarian reasons, than is the case with internal organs and tissues; while even the latter present, for similarly non-utilitarian reasons, such variety and intensity of colours as they do; must it not follow that, on the ground of the ”Laws of Growth” alone, Mr. Wallace has conceded the entire case as regards ”a large proportional number of specific characters” being non-adaptive--”spontaneous” in their occurrence, and ”meaningless” in their persistence?
Once more:--
”The enormously lengthened plumes of the bird of paradise and of the peac.o.c.k, can, however, have no such use [i.e. for purposes of defence], but must be rather injurious than beneficial in the birds' ordinary life. The fact that they have been developed to so great an extent in a few species is an indication of such perfect adaptation to the conditions of existence, such complete success in the battle for life, that there is, in the adult male at all events, a surplus of strength, vitality, and growth-power, which is able to expend itself in this way without injury. That such is the case is shown by the great abundance of most of the species which possess these wonderful superfluities of plumage.... Why, in allied species, the development of accessory plumes has taken different forms, we are unable to say, except that it may be due to that individual variability which has served as a starting-point for so much of what seems to us strange in form, or fantastic in colour, both in the animal and vegetable world[136].”
[136] _Darwinism_, pp. 292-3.
Here, again, one need only ask, How can such statements be reconciled with the great dogma, ”which is indeed a necessary deduction from the theory of Natural Selection, namely, that none of the definite facts of organic nature, no special organ, no characteristic form or marking can exist, but which must now be, or once have been, _useful_”? Can it be said that the plumes of a bird of paradise present ”no characteristic form,” or the tail of a peac.o.c.k ”no characteristic marking”? Can it be held that all the ”fantastic colours,” which Darwin attributes to s.e.xual selection, and all the ”strange forms” in the vegetable world which present no conceivable reference to adaptation, are to be ascribed to ”individual variability” without reference to utility, while at the same time it is held, ”as a necessary deduction from the theory of Natural Selection,” that _all_ specific characters must be ”_useful_”? Or must we not conclude that we have here a contradiction as direct as a contradiction can well be[137]?
[137] Since the above was written both Mr. Gulick and Professor Lloyd Morgan have independently noticed the contradiction.
Nor is it any more possible to reconcile these contradictory statements by an indefinite extension of the term ”correlation,” than we found it to be in the cases previously quoted. It might indeed be logically possible, howsoever biologically absurd, to attribute the tail of a peac.o.c.k--with all its elaboration of structure and pattern of colour, with all the drain that its large size and weight makes upon the vital resources of the bird, with all the increased danger to which it exposes the bird by rendering it more conspicuous, more easy of capture, &c.--to correlation with some useful character peculiar to peac.o.c.ks. But to say that it is due to correlation with general ”vitality,” is merely to discharge the doctrine of correlation of any a.s.signable meaning.
Vitality, or ”perfect adaptation to the conditions of existence,” is obviously a prime condition to the occurrence of a peac.o.c.k's tail, as it is to the occurrence of a peac.o.c.k itself; but this is quite a different thing from saying that the specific characters which are presented by a peac.o.c.k's tail, although useless in themselves, are correlated with some other and useful specific characters of the same bird--as we saw in a previous chapter with reference to secondary s.e.xual characters in general. Therefore, when Mr. Wallace comes to the obvious question why it is that even in ”allied species,” which must be in equally ”perfect adaptation to the conditions of existence,” there are no such ”wonderful superfluities of plumage,” he falls back--as he previously fell back--on whatever unknown _causes_ it may have been which produced the peac.o.c.k's tail, when the primary _condition_ to their operation has been furnished by ”complete success in the battle for life.”
I have quoted the above pa.s.sages, not so much for the sake of exposing fundamental inconsistencies on the part of an adversary, as for the sake of observing that they const.i.tute a much truer exposition of ”Darwinism”
than do the contradictory views expressed in some other parts of the work bearing that t.i.tle. For even if characters of so much size and elaboration as the tail of a peac.o.c.k, the plumes of a bird of paradise &c., are admitted to be due to non-utilitarian causes, much more must innumerable other characters of incomparably less size and elaboration be mere ”superfluities.” Without being actually deleterious, ”a large proportional number of specific characters,” whose utility is not apparent, must _a fortiori_ have been due to ”individual variation,” to ”general laws which determine the production” of such characters--or, in short, to some causes other than natural selection. And this, I say, is a doctrine much more in harmony with ”Darwinism” than is the contradictory doctrine which I am endeavouring to resist.
But once again, and still more generally, after saying of ”the delicate tints of spring foliage, and the intense hues of autumn,” that ”as colours they are unadaptive, and appear to have no more relation to the well-being of plants themselves than do the colours of gems and minerals,” Mr. Wallace proceeds thus:--
”We may also include in the same category those algae and fungi which have bright colours--the red snow of the Arctic regions, the red, green, or purple seaweeds, the brilliant scarlet, yellow, white or black agarics, and other fungi. All these colours are probably the direct results of chemical composition or molecular structure, and being thus normal products of the vegetable organism, need no special explanation from our present point of view; and the same remark will apply to the varied tints of the bark of trunks, branches and twigs, which are often of various shades of brown and green, or even vivid reds and yellows[138].”
[138] _Darwinism_, p. 302.
Here, as Mr. Gulick has already observed, ”Mr. Wallace seems to admit that instead of useless specific characters being unknown, they are so common and so easily explained by 'the chemical const.i.tution of the organism' that they claim no special attention[139].” And whatever answer Mr. Wallace may make to this criticism, I do not see how he is to meet the point at present before us--namely, that, upon his own showing, there are in nature numberless instances of ”characters which are useless without being hurtful,” and which nevertheless present absolute ”constancy.” If, in order to explain the contradiction, he should fall back upon the principle of correlation, the case would not be in any way improved. For, here again, if the term correlation were extended so as to include ”the chemical const.i.tution or the molecular structure of the organism,” it would thereby be extended so as to discharge all Darwinian significance from the term.