April 3, 1890] 



NATURE 



II 



■ciently detailed to make the construction of the table 

 readily understood, assuming a knowledge of the use of 

 logarithms. The book will prove a handy substitute for 

 more bulky volumes in cases where extreme accuracy is 

 not required, such as computations in chemistry and 

 physics. 



LETTERS TO THE EDITOR. 



{TAe Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature, 

 No notice is taken of anonymous communications. '\ 



Panmixia. 



Mv letter of March 6 commenced with the remark that, 

 •without entering into controversy, I proposed to draw attention 

 to the opinions expressed concerning the inheritance of acquired 

 •characters by Mr. Darwin. The reasons for my own beliefs on 

 the questions at issue I have given in "The Principles of 

 'Biology," § 166, and, with other illustrations, in "The Factors 

 of Organic Evolution." Here it must suffice to say that 1 have 

 seen no reason to abandon the conclusions there set forth. 



Respecting the doctrine of " panmixia," either as enunciated 

 by Prof. VVeismann, or as recently presented in modified forms, 

 I will say no more than that I should like to see its adequacy 

 discussed in connection with a specific instance—say the drooping 

 •ears of many domesticated animals. "Cats in China, horses in 

 parts of Russia, sheep in Italy and elsewhere, the guinea-pig in 

 •Gtrmanv, goats and cattle in India, rabbits, pigs, and dogs in all 

 long-civilized countries, have dependent ears." 



Here the influence of natural selection is almost wholly 

 ■excluded ; nor can artificial selection be supposed to have 

 •operated in most of the cases : save, perhaps, in some pet 

 animals, selection has been carried on to develop othej- traits. 

 In the cases of most of these creatures, too, artificially fed and 

 often over-fed, it does not sem that individual fates can have 

 been affected by economy of nutrition, either general or 

 special ; since there has been no struggle for existence to cause 

 the survival of those in which nutriment was most advantageously 

 distributed. Further, the parts in question are not of such sizes 

 that economy in nutrition of them could sensibly affect the fates 

 of individuals, even had the struggle for existence been going on. 

 Again, it seems that in respect of the ears themselves (though 

 not in respect of their motor muscles) there has been extravagance 

 of nutrition rather than economy of nutrition ; since even where 

 selection has been carried on for increasing other traits, the ears 

 have not dwindled but rather increased. Lastly, at the same 

 time that there has been this surperfluity of nutrition in the ears 

 themselves, their motor muscles appear to have dwindled either 

 relatively or absolutely— at least relatively, we must suppose, 

 where the weight of the ears has increased, and absolutely 

 where the weight of the ears has not increased. 



The question presented by these facts is one in the solution of 

 ■which the theory of " panmixia " may, I think, be satisfactorily 

 tested ; and without expressing any opinion upon the matter 

 myself, I should be glad to see it discussed. 



Herhert Spencer, 



I AM not aware how far Prof Ray Lankester is disposed to 

 acknowledge his obligations to Prof. Weismann for what I am 

 glad to see he now calls his "anti-Lamarckian " (as distinguished 

 from " pure Darwinian") proclivities. Therefore I do not know 

 how far he professes to be one of " the followers of Prof. 

 Weismann," to whom my previous letter on this subject was 

 addressed. But it seems desirable that I should take some 

 notice of the altogether distinct question which he has now 

 raised— viz. whether, or how far. Prof. Weismann's anti- 

 Lamarckian views were anticipated by Mr. Darwin. 



His argument is that Darwin must have been a Lankesterian 

 anti-Lamarckian in disguise; and, more particularly, that "the 

 doctrine of panmixia is recognized ani formulated in the last 

 (sixth) edition of the 'Origin of .Species' published in 1872." 



Taking the most general statement first, Prof. Lankester 

 represents it as not improbable that " when Darwin refers, here 

 and there throughout his works, to a reduced or rudimentary 



condition of an organ as 'due to disuse,' or 'explained by the 

 effects of disuse,' he does not ncicssarily mean such effects as 

 the Lamarckian second law asserted and assumed (though often 

 he does appear to mean such) ; but he may mean, and probably 

 had in his mind, the effects of disuse as worked out through 

 panmixia and economy of growth." 



Now, here we have a specimen of Prof. Lankester's dialectic 

 at its worst. Truly, with such an interpreter, Darwin ^' may" 

 be made to "mean" anything. First it is represented as 

 seeming "not at all improbable that when Darwin refers " to one 

 principle, "he does not necessarily mean" what he says ; and 

 then it is concluded that " he may mean, and probably had in his 

 mind a totally different principle." Moreover, what is re- 

 presented as mere references, " here and there throughout his 

 works," are, as all the world knows, one whole and "highly 

 important " (though still subordinate) side of Darwin's system. 

 Yet again, in all passages where the meaning assigned to his term 

 " disuse ' is explained, there can be no shadow of ambiguity 

 attaching to it, and everywhere it is alluded to as a principle 

 wholly distinct from the "economy of growth" ; while pan- 

 mixia, as I shall presently prove, is nowhere mentioned at all. 

 This, indeed, is clearly shown even in the passages quoted by 

 Prof Lankester, and now re-quoted below. For it is there said 

 that, could a certain explanation be found, "then we should be 

 able to understand how an organ which has become useless would 

 be rendered, independently of the effects of disiise, rudimentary." 

 Obviously, in this context, "the effects of disuse" cannot 

 possibly mean "the effects of disuse as worked out through 

 panmixia and economy of growth " : they can only mean the 

 direct effects of disuse itself in causing inherited atrophy. And 

 now, lastly, "the effects of disuse" are habitually pointed to by 

 Mr. Darwin in association with the " effects of increased use" ; 

 and how he can " seein " to have "explained" th se either by 

 the economy of growth (which he fully recognized), or by 

 panmixia (which he never recognized), I must leave Prof. 

 Lankester to indicate. 



It will be observed, from the point last mentioned, that this 

 attempt to read the doctrines of Weismann into the writings of 

 Darwin must equally ollapse, whether or not any other human 

 being can be found to follow Prof. Lankester in his commentary 

 on Darwin's "here and there" references to " the effects of 

 disuse " : the equally constant and as frequently detailed re- 

 ferences to ' ' the effects of the increased use of parts, which I 

 have always maintained to be highly important," are of them- 

 selves sufficient to dispose of the Lankesterian gloss. Never- 

 theless, it remains worth while to see whether there is any shred 

 of evidence in support of the narrower or more particular state- 

 ment, that the principle of panmixia is to be found "already 

 indicated " in the " Origin of Species." The following are the 

 passages upon which this statement is founded — passages, I may 

 remark, which have certainly neither been "missed" nor 

 "neglected " by me. 



(i) "If under changed conditions of life a structure before 

 usefid, becomes less useful, its diminution will be favoured, yi?;- it 

 7Ciill profit the individual not to have ifs nulri?nent wasted in 

 building tip a useless structure. . . . Thus, as 1 believe, natural 

 selection will tend in the long run to reduce any part of the 

 organization as s )on as it becomes, through changed habits, 

 superfluous, without by any means causing some other part to 

 be largely developed in a corresponding degree" ("Origin of 

 Species," sixth edition, p. 118). 



(2) " Organs, originally formed by the aid of natural selection, 

 when rendered useless, may well be variable, for their variations 

 can no longer be checked by natural selection. ... It is 

 scarcely possible that disuse can go on producing any furthe 

 effect after the organ has once been rendered functionless. 

 Some additional explanation is here requisite, which I cannot 

 give. If, for instance, it could be proved that every part of the 

 organization tends to vary in a greater degree towards diminu- 

 tion than towards augmentation of size, then we should be able 

 to understand how an organ which has become useless would 

 be rendered, independently of the effects of disuse, rudimentary, 

 and would at last be wholly suppressed ; for the variations 

 towards diminished size would no longer He checked by natural 

 selection. IVie principle of the economy of growth explained in 

 a former chapter [cited in quotation No. l], by which the 

 materials forming any part, if not useful to the possessor, are 

 saved as far as possible, will perha )S come into play in rendering 

 a useless part rudimentary " (" Origin of Species," sixth edition, 

 pp. 401-402^ 



