152 



SCIENCE. 



[Vol. XIV. No. 343 



school, those which arise fortuitously as congenital variations, for 

 the accidental occurrence of which natural selection is always, so 

 to speak, waiting and watching. The human hand, for example, 

 considered as a mechanism, owes nothing to its continued use 

 through numberless generations as an instrument for the perform- 

 ance of functions which it is now so admirably adapted to dis- 

 charge ; on the contrary, its evolution has throughout been ex- 

 clusively dependent on the occurrence of fortuitous variations, 

 which, whenever they happen to occur in a prolitable direction, 

 were preserved by natural selection, and passed on to the next 

 generation. Now, it is evident that, according to this theory, nat- 

 ural selection is constituted the one and only cause of organic 

 evolution ; and for this reason the followers of Weismann are in 

 the habit of calling his doctrine " pure Darwinism," inasmuch as 

 without invoking any aid from the Lamarckian principles above de- 

 scribed, it constitutes the Darwinian principle of natural selection the 

 sole, and not merely as he said the " main, means of modification." 



Obviously, without going further than this quotation, which I 

 have already made from the last edition of the " Origin of Species," 

 it is a misnomer to designate the doctrine in question " pure Dar- 

 winism." That quotation presents the only note of bitterness 

 which is to be met with in the whole range of Mr. Darwin's writ- 

 ings, and it is a note which has express reference to this very point. 

 Notwithstanding the multifarious directions in which his doctrines 

 were abused, the only protest against " steady misrepresentation '' 

 that he has ever allowed himself to lodge, he lodged against those 

 who imputed to him this so-called doctrine of " pure Darwinism." 

 On the other hand, it is no less manifest that this doctrine, although 

 not pure Darwinism, assuredly is, and always has been, pure 

 " Wallaceism." In point of fact, it is with reference to this very 

 doctrine of natural selection as the sole cause of organic evolution 

 that the opinion of these two renovators of biology has been from 

 the first divided. It is upon this point, and upon this point alone, 

 that there has ever been any serious difference between them, — 

 for, as we shall presently find, every other point in which they failed 

 to agree, save with respect to the origin of man, has a direct logical 

 reference to this one, or grows out of this one by way of logical 

 consequence. 



And here we arrive at what seems to me the dramatic interest 

 attaching to Mr. Wallace's latest work. On the present occasion I 

 am not going to consider the pros and the cons of the momentous 

 question which has"always divided his teaching from that of his 

 great compatriot. But, whether he is right or whether he is wrong 

 he has lived to see a most extraordinaiy revolution of biological 

 thought in the direction of opinions which have always been dis- 

 tinctively his own, and which for a large part of a lifetime he has 

 been virtually alone in maintaining. 



Yet, notwithstanding the gratification with which Mr. Wallace 

 must have watched this remarkable change within the last few 

 years, there is in his recently published book no sound of exultation. 

 On the contrary, his aim everywhere appears to be that of conceal- 

 ing his personal interest in this matter ; and so well does he suc- 

 ceed that, after having finished his book, not one in a hundred of 

 his readers will be in a position to surmise that for more than a 

 quarter of a century their author has steadily maintained the opin- 

 ions which are now being adopted by an influential and rapidly 

 increasing body of evolutionists. Therefore, it is partly for the 

 sake of drawing attention to a claim which Mr. Wallace character- 

 istically abstains from making on his own behalf that I ventured to 

 write this review of his latest work. If ever there was an occasion 

 when a man of science might have felt himself justified in express- 

 ing a personal gratification at the turning of a tide of scientific 

 opinion, assuredly such an occasion is the present ; and in which- 

 ever direction the truth may eventually be found to lie, historians 

 of science should not omit to notice that in the very hour when his 

 lifelong belief is gaining so large a measure of support Mr. Wal- 

 lace quietly accepts the fact without one word of triumph. 



To me individually it does not appear that the recent movement, 

 of scientific opinion in the direction of " Wallaceism " is scientific- 

 ally justifiable ; and therefore I remain an adherent of " Darwin- 

 ism," as this was left by the matured judgment of Darwin. For,, 

 on the one hand, I cannot find that the school of Weismann has. 



added anything of importance to the body of facts previously 

 known ; while, on the other hand, I do find that Professor 

 Weismann himself is put to the sorest straits while trying to main- 

 tain his theory in the presence of some of these facts. So that, 

 while fully recognizing the extraordinary ability with which he has 

 marshalled his evidence, — and also, it may be added, the great 

 service which he has rendered to biological science in raising cer- 

 tain questions of the highest possible importance in the acutest 

 possible form, — I must still confess that to my mind there does 

 not seem to have been hitherto shown any adequate reason to pass 

 from the theory of evolution as this was always held by Darwin, to 

 the theory of evolution as it has always been held by Wallace. 

 Therefore I am free to conclude this article by briefly considering 

 the points upon which Wallace, in his matured publication on 

 "Darwinism," expressly differs from the teachings of Darwin. 



As already stated, all these points of difference, with the one ex- 

 ception as to the origin of man, arise by way of logical necessity 

 from the great or radical difference which we have hitherto been 

 considering ; viz., as to whether natural selection is only the 

 " main " or actually " the exclusive means of modification." Never- 

 theless, it is desirable to consider what Mr. Wallace has to say 

 upon these secondary or sequent points of difference, because, by 

 examining them in the light of the diverse facts which they severally 

 involve, we may obtain valuable material for guiding our judgment 

 upon the larger issue. 



Sexual Selection. 



Against Mr. Darwin's theory of sexual selection, — i.e., selection 

 which depends on the superior power which males may be sup- 

 posed to present in the way of charming their females, — Mr. 

 Wallace urges the following objections, which, in his opinion, are 

 sufficient to dispose of the theory in ioio. 



In the first place, he argues that the principal cause of the greater 

 brilliancy of male animals in general, and of male birds in particu- 

 lar, is that they do not so much stand in need of protection arising 

 from concealment as is the case with their respective females. 

 Consequently natural selection is not so active in repressing brill- 

 iancy of color in the males, or, which amounts to the same thing, is 

 more active in " repressing in the female those bright colors which 

 are normally produced in both sexes by general laws." 



Next, he argues that not only does nktural selection thus exer- 

 cise a negative influence in passively permitting more heightened 

 color to appear in the males, but even exercises a positive influence 

 in actively promoting its development in the males, while, at the 

 same time, actively repressing its appearance in the females. For 

 heightened color, he says, is correlated with health and vigor ; and 

 as there can be no doubt that healthy and vigorous birds best pro- 

 vide for their young, natural^ selection, by always placing its pre- 

 mium on health and vigor in the males, thus also incidentally pro- 

 motes, through correlated growth, their superior coloration. 



Again, with regard to the display which is practised by male 

 birds, and which constitutes the strongest of all Mr. Darwin's 

 arguments in favor of sexual selection, Mr. Wallace points out that 

 there is no evidence at all of the females being in any way affected 

 thereby. On the other hand, he argues that this display may be 

 due merely to general excitement ; and he lays stress upon the 

 more special fact that movable feathers are habitually erected un- 

 der the influence of anger and rivalry, in order to make the bird 

 look more formidable in the eyes of his antagonists. 



Furthermore, he adduces the consideration that, even if the 

 temales are in any way affected by color and its display on the part 

 •of the males, and if, therefore, sexual selection be conceded a true 

 principle in theory, still we must remember that, as a matter of 

 fact, it can only operate in so far as it is allowed to operate by nat- 

 ural selection. Now, according to Mr. Wallace, natural selection 

 must wholly neutralize any such supposed influence of sexual selec- 

 tion. For, unless the survivors in the general struggle for existence 

 happen to be those which are also the most highly ornamented, 

 natural selection must neutralize and destroy any influence that 

 may be exerted by female selection. But obviously the chances 

 against the otherwise best fitted males happening to be hkewise 

 the most highly ornamented must be many to one, unless, as Wal- 

 lace supposes, there is some correlation between embellishment 

 and general perfection, in which case, as he points out, the theory 



