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NA TURE 



\_Feb. 24, li 



LETTERS TO THE EDITOR 



[T/te Editor does not hold himself responsible for opinions ex- 

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[ The Editor urgently requests correspondents to keep their letters 

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Mr. Wallace on Physiological Selection 

 Seeing that Mr. Wallace has now changed front with regard 

 to some of tlie points at issue between us, I must once again 

 address you upon this subject. 



(1) He appears to have forgotten that the whole plan of his 

 original idipeachment consisted in representing me as an arrogant 

 heretic. This impeachment was published under the heading 

 "Romanes j/tv-jiM Darwin," and point by point it laboured to 

 .show that I was deserving of excommunication as a rebel 

 against the highest authority. In my reply, therefore, I was 

 obliged to show that the charge was misdirected ; and this I did 

 by simply quoting passages from that higliest authority himself. 

 It is needless to say that I am now as much satisfied as surprised 

 to find this charge, not only abandoned, but reversed. Whereas 

 I was previously accused of presumption for disregarding authority, 

 now the remonstrance is — "he appeals to authority against 

 me," and "I decline to accept authority as an infallible guide." 

 So do I. But I quoted my authority merely for the avowed 

 purpose of defending myself from the specific charge of my 

 opponent. It was he who ajipealed to Ctesar, and cannot 

 therefore now complain if to Ciesar he had to go. Truly, if I 

 may employ his own mode of e.xpression, "further discussion of 

 the matter with such an adversary is out of the question." 



(2) But, as regards one of the points, he says that my quota- 

 tions appear to him to support his own view s rather than mine. 

 The shortest way of testing the value of this judgment will be to 

 print in succession three passages, which I have selected as 

 serving in each case most concisely and most fairly to embody the 

 opinion of its writer. The point in question is as to whether 

 specific characters are " invariably " adaptive, or "frequently" 

 not so, and the italics are mine. 



" When, from the nature of the organism and of the conditions, 

 modifications have been induced which are unimportant for the 

 welfare of the species, they may be, and apparently often have 

 been, transmitted in nearly the same state to numerous, otherwise 

 modified, descendants." (Darwin, "Origin of Species,"p. 175.)' 



" I believe, therefore, that the alleged vaw'C&ly of [many] specific 

 characters claimed by Mr. Romanes as one of the foundations of 

 his new tlieory, has no other foundation than our extreme ignor- 

 ance " (Wallace, Fortiiightly Review.) 



" The matured judgment of Mr. Darwin clearly recognised tlie 

 distinction between the origin o{ species and the origin of adaptations, 

 ■ — a distinction, indeed, which necessarily follows from his repu- 

 diation of the doctrine of utility as universal Tlierefore, 



with him I believe that an incalculable number of specific 

 characters are of an adaptive kind, and that many more which 

 now appear to us (in our ignorance) to be useless, will hereafter 

 be proved to be useful, But with him also I believe that a liirge 

 proportional number of such characters actually are destitute of 

 utility, having been due, as he says, to ' fluctuating variations, 

 which sooner or later became constant through the nature of the 

 organism and of surrounding conditions, as well as through the 

 intercrossing of distinct individuals ; but not through naitiral 

 selection.'" (Myself, Nineteenth Century.) 



(3) "The impossibility of proving a negative is proverbial, 

 but my opponent declares that his negative — the uselessnes-; of 

 specific characters — wants no proving, but must be accepted till 

 in every case the affirmative is proved." Now, I have made no 

 such declaration. My statement was : " It is too large a demand 

 to make upon our faith in natural selection to appeal to the argu- 

 ment from ignorance, when the facts require that this appeal 

 should be made over so large a jsroportional number of instances." 

 It is really Mr. Wallace who declares that his affirmative — the 

 invariable usefulness of specific characters — wants no proving, 

 but must be accepted till in every case the negative is proved, 



I By a curious and undesigned coincidence, the same issueof Nature which 

 contains Mr. W.illace's letter also contains my review of Mr. Spencer's essay 

 on the '■ Factors of Organic Evolution." In that review several other 

 passages are quoted from Mr. Darwin's works to the same effect. 



notwithstanding that, as he allows, "the impossibility of proving 

 a negative is proverbial." Of course, if it has been previously 

 assumed that natural selection is the only factor of organic evolu- 

 tion, we are entitled to conclude that the doctrine of utility as 

 universal requires no further proof, since it follows deductively 

 from the assumption. But where the very question in dispute is 

 as to the validity of this assumption, it becomes an almost 

 comical instance of circular reasoning to construct our biological 

 catechism thus : — Why do you believe that natural selection is 

 the only factor of organic evolution ? Because I know that in 

 organic Nature utility is universal. But how do you know this, 

 seeing that "our extreme ignorance" renders it impossible to 

 suggest, in a vast number of cases, what the utility can be ? Be- 

 cause 1 have already proved that natural selection has been the 

 only factor at work. 



(4) Mr. Wallace imports from the monthly periodicals part of 

 our discussion on the swamping effects of intercrossing. Here 

 therefore, I must follow him. In my Linnean Society paper I 

 had urged that natural selection must be seriously handicapped 

 in its action by the swatnping effects of fortuitous variations 

 intercrossing with their parent forms. This statement Mr. 

 Wallace contradicted on the ground that Mr. J. A. Allen had 

 furnished "a complete demonstration of indi\'idual and simulta- 

 neous variability by a series of minute comparisons and measure- 

 ments," with the result of showing that, whatever modification 

 might be required, "wt always (italics his) find a considerable 

 number, say from 10 to 20 per cent, of the whole, varying 

 simultaneously, and to a considerable amount, on either side of 

 the mean value." Now, in my reply I pointed out that all the 

 variations thus recorded by Mr. Allen were of a kind which had 

 " nothing to do with the difficulty," seeing that they had reference 

 only to such features as " size, strength, ileetness, colour, relative 

 proportions of different parts, and so on, all of which — as we 

 well know without going beyond the limits of our own species — 

 are so highly variable as never all to be precisely the same in any 

 two individuals." Then, by way of illustration, I said : suppose 

 " it were required to produce a breed of race-horses with horns 

 upon the frontal bone, . . . or a fighting spur on a duck, clearly 

 it could not he done by natural selection alone " in the latter case, 

 or by artificial selection in the former ; the principle of selection 

 would here require to be assisted by "some common cause [of 

 variation] acting on a number of individuals simultaneously." 

 But there was nothing in the use of this illustration to provoke 

 the remark that it indicates "the belief, apparently, that these 

 are a class of ch.aracters which are distinctive of closely allied 

 species " — although such does happen to be the case as regards 

 certain allied genera. I merely requested Mr. Wallace to show 

 me his " consider.ible number of specimens diverging from the 

 mean condition," as regards either of these structures, however 

 incipioil — or as regards any other structures, save those the 

 general variability of which as to relative size, &c., no one would 

 dream of disputing. And this I still hold he is obviously bound to 

 do, if he is to sustain his sweeping statement that whatever 

 modification of type may be required, we always find from 10 to 

 20 per cent, varying in the needful way. Thus, as a mere 

 matter of dialectic, I confess it appears to me a somewhat un- 

 azcountable expedient to affirm that my reductio ad absurdum is 

 "preposterous" — such happening to be the very quality which 

 this mode of refutation is ordinarily designed to present. 



(5) Lastly, my critic says; — "The argument to .show that 

 the supposed physiological variations would be perpetuated, 

 seems to me as weak and unsatisfactory as ever." This may 

 well be. Indeed, I never supposed th.at anything would be 

 likely to influence the judgment of Mr. Wallace where natural 

 selection is concerned. But I did not write with any such 

 object. I wrote merely to dispose of a particular criticism which 

 he had advanced, and there can be no two opinions as to the 

 result. For I have shown that whatever may be thought , 

 about the truth or falsehood of my theor)',' at least it is 

 certain that it cannot be affected by the criticism of Mr. 

 Wallace ; and this for the simple reason that he has run a tilt, 

 not against my theory at all, but against a completely difterent 

 theory, which, like a figure of straw, he had himself set up. 

 Now that he can no longer have any doubt as to wdiat my theory 

 is, I willingly conclude that he must still have some reasons for 

 thinking it improbable that the supposed physiological variations 

 (if they occur) should be perpetuated. But I am free to confess 

 that it passes my powers of conception to divine what these 



' I call it my theory, because I now understand that i; difl'ers widely from 

 that of iVlr. Catchpo j1 (see Nature, vol. xxxiv. p. 617). 



