154 



SCIENCE. 



[Vol. XIV. No. 34^ 



that there can be no room for the operation of such a principle in 

 the presence of natural selection : the greater principle must swal- 

 low up the less. This a priori argument he extends to all the 

 other supplementary principles which have ever been suggested, 

 and appears to regard it as " a short and easy method " with the 

 Darwinists. He urges it with special vehemence against the so- 

 called Lamarckian principles, and therefore it is suitable that under 

 this head we should consider more carefully the value of such an 

 argument. 



In the present connection this argument is that, even admitting 

 the abstract possibility of Lamarckian principles, in the presence of 

 natural selection they could never have an opportunity of acting, 

 inasmuch as the needful changes would be effected by a natural 

 selection of fortuitous variations more rapidly than they could be 

 by an inheritance of the effects of use and disuse. Now this argu- 

 ment admits of two rejoinders. First, it is surely conceivable that 

 m many cases where slight (because initial and afterwards finely 

 graduated) improvements are concerned, such improvements need 

 not have been, in every stage of their progress, matters of life and 

 death to the organisms presenting them. Yet, unless at every 

 stage of their progress they were matters of life and death, they 

 could not have been produced by the unaided influence of natural 

 selection. Now it is just in such cases that the supplementary or 

 Lamarckian principles are supposed by Darwinists to come in ; for 

 to the operation of these principles it is not necessary that at each 

 stage of the process every slight improvement should be a matter 

 of life and death to the organisms presenting it. To me it appears 

 that we have here a consideration of the highest importance. 

 Nowadays no one disputes the supremacy of natural selection over 

 all other principles of organic change hitherto suggested, or even, 

 it may be predicted, suggestable. But this acceptance of natural 

 selection as supreme by no means necessitates (as Mr. Wallace 

 appears to imagine) acceptance of natural selection as unique. Nor 

 is there any incompatibility between our acceptance of natural se- 

 lection as supreme and a further acceptance of any other principles 

 as subordinate or co-operative. What we all agree upon is, that 

 no such other principles can act, save in so far as they are allowed 

 to act by natural selection ; but to maintain that there can be no 

 room for the action of any other principle hitherto suggested, or in 

 the future suggestable, appears to me extravagant. At all events, 

 the burden of proof must lie with any one who affirms that no 

 adaptive improvement — or, indeed, change of any kind — can ever 

 take place unless every stage in the gradual process has been a 

 matter of life and death to the organisms presenting it, a burden 

 of proof which it is obviously impossible that any one can ever fe 

 in a position to discharge. 



In view of this consideiation it seems to me that Mr. Wallace's 

 a. priori objection to the abstract possibility of Lamarckian princi- 

 ples falls to the ground, although of course the question remains 

 whether there is any sufficient evidence a posteriori of their opera- 

 tion in actual fact. And a virtual answer to this question appears 

 to me to be involved in the second consideration, which, as above 

 stated, remains to be adduced. 



Long ago Mr. Herbert Spencer pointed to the facts of co-adap- 

 tation within the limits of the same organism as presenting the 

 strongest possible evidence of Lamarckian principles working in 

 association with Darwinian. Thus, taking one of Lamarck's own 

 illustrations, Mr. Spencer showed that there must be thousands 

 and thousands of changes — extending to all the organs and even 

 to all the tissues of the animal — which in the course of numberless 

 generations have conspired to turn an antelope into a giraffe. 

 Now the point is that, throughout the entire history of these 

 changes, their utility must have always been dependent on their 

 association. It would be useless that an incipient giraffe should 

 present a tapering down of the hind-quarters, unless at the same 

 time it presented a tapering up of the fore-quarters ; and as each 

 of these modifications entails innumerable subordinate modifica- 

 tions throughout both halves of the creature concerned, the chances 

 must be infinity to one against the required association of so many 

 changes happening to arise by way of merely fortuitous variation. 

 Yet, if we exclude the Lamarckian interpretation as adopted by 

 Darwin, which gives us an intelligible cause of co-adaptation, we 

 are required to suppose that such a happy concurrence of innu- 



merable co-adaptations must have occurred by mere accident, and 

 this thousands and thousands of times in the bodies of as many 

 successive ancestors of the existing species ; for, at each successive 

 stage of the improvement,, natural selection (if working alone) must 

 have needed all, or at any rate most, of the co-adaptations to occur 

 in the same individual organisms. 



Against this formidable consideration Mr. Wallace adduces the 

 following rejoinder : " The best answer to this objection may, per- 

 haps, be found in the fact that the very thing said to be impossible 

 by variation and natural selection has been again and again ef- 

 fected by variation and artificial selection." This analogy he then 

 enforces by special illustrations, etc., but does not appear to per- 

 ceive that it really misses the whole point of the difficulty against 

 which it is brought. 



The point of the difficulty is, not that the needful variations do 

 not occur, but that they occur associated in the same individual, 

 and that unless they do thus occur associated in the same individual 

 they must be useless ; i.e., cannot fall under the sway of natural 

 selection. Therefore the analogy of artificial selection is here ir- 

 relevant, seeing that it fails in respect of the very point which it is 

 adduced to meet. The difference between natural selection and 

 artificial selection is, that, while the former acts with exclusive 

 reference to the utility (or life preserving character) of variations, 

 the latter acts without such reference. Hence, there is obviously 

 no difficulty in understanding how artificial selection is able to 

 choose this, that, and the other congenital variation as each hap- 

 pens to occur in so many different individuals, and, by suitable 

 pairing, to blend them together in any required proportions. But 

 artificial selection is able to do this simply because the selected 

 individuals do not depend for their lives upon presenting the 

 blended characters which it is the object of such selection to produce. 

 Natural selection, on the other hand, if working alone must wait 

 until the blended characters happen to arise fortuitously in the 

 same individuals ; in all cases, that is, where utility depends on the 

 co-adaptation of characters, which are the only cases now under 

 consideration. Thus the two forms of selection present absolutely 

 no point of analogy in the very respects where it is necessary that 

 they should, if Mr. Wallace's appeal from one to the other is 

 to be logically justified. In the one case the association of char- 

 acters is purposely produced by the selection ; in the other case it 

 must arise by chance before its resulting utility can be offered to 

 the selection. 



Natural Selection as a Cause of Sterility Between Species. 



After matured deliberation Mr. Darwin came to the conclusion 

 that natural selection could not be a cause of sterility between spe- 

 cies. Mr. Wallace now furnishes an argument to show that in this 

 respect also Mr. Darwin " underrated " the powers of natural se- 

 lection. The argument, however, is too abstruse to admit of re- 

 production here. On the present occasion, therefore, I will merely 

 remark that it does not seem so much as to try to meet the con- 

 siderations which determined Mr. Darwin's judgment in the oppo- 

 site direction. Nevertheless the theory is profound as well as in- 

 genious, and, although it fails to convince me, I am glad to note 

 that in the course of its exposition Mr. Wallace appears to sanc- 

 tion the essential principle of my own hypothesis of " physio- 

 logical selection ; " viz., to quote his own words, " it is by no means 

 necessary that all varieties should exhibit incipient infertility, but 

 only some varieties ; for we know that of the innumerable varieties 

 that occur but few become developed into distinct species, and it 

 may be that the absence of infertility, to obviate the effects of in- 

 tercrossing, is one of the usual causes of their failure." The 

 words which I have italicized very tersely convey the whole gist of 

 " physiological selection." 



Later on, however, he criticises adversely what I have written 

 upon this subject, and also represents me as having misunderstood 

 Mr. Darwin's views with respect to the utility and inutility of spe- 

 cific characters. On both these points I shall have an answer to 

 make on some future and more suitable occasion. In this article I 

 have confined attention to points wherein Mr. Wallace differs from 

 Mr. Darwin ; and although in so doing it has been necessary for 

 me to express uniform disagreement with the author of " Darwin- 

 ism," this has been due only to the limitations of my project, and 



