March 27, 1890] 



NATURE 



487 



disuse are transmitted from the affected generation to its off- 

 spring. He refers by chapter and page to the instances which 

 Mr. Darwin considered as examples of the transmission of the 

 effects of habit or of use and disuse. He then says : " Clearly 

 the first thing to be done by those who deny the inheritance of 

 acquired characters is to show that the evidence Mr. Darwin 

 has furnished by these numerous instances is all worthless," I 

 entirely disagree with this way of putting the matter. It is not 

 necessary to show that anything Mr. Darwin wrote was " worth- 

 less," but it is necessary to show that certain facts cited by Mr. 

 Darwin admit of another interpretation or explanation than that 

 which he gave to them. Naturally those who have taken up 

 the anti-Lamarckian position have done long ago what Mr. 

 Herbert Spencer says is the first thing for them to do. Of 

 course the cases cited by Darwin were the first to be dealt with. 

 It is extremely unfortunate that Mr. Spencer has not come 

 across the work in which this is done. Otherwise, instead of a 

 well-meant direction from Mr. Spencer as to what we ought to 

 do, we might have the advantage of reading what he has to say 

 after considering what has been done. It is seven years since 

 Prof. Weismann published his essay on heredity ; last spring 

 this and other essays appeared in English under the auspices of 

 the Clarendon Press. In that particular essay Darwin's cases 

 are dealt with at length. Am I to reproduce Prof. Weismann's 

 essay or a precis of it in this letter? "Will not Mr. Spencer 

 and others who are interested in these matters read Weismann's 

 " Essays " ? I think that those who will take the trouble to do 

 so will see that Mr. Spencer's injunction was superfluous. 



It is, however, apart from other branches of the question, 

 important that a correct appreciation of Mr. Darwin's position 

 in this matter of the " transmission of acquired characters " 

 should be arrived at. Mr. Herbert Spencer's letter is, I think, 

 likely to produce an erroneous conception on this matter. We 

 know from his letters published since his death that Darwin 

 held the " Philosophic Zoologique" to be "veritable rubbish" — 

 "extremely poor ; I got not a fact nor an idea from it." The 

 notion that his own view was a modification of Lamarck's 

 appeared to Darwin absurd. The " obvious view " was pro- 

 pounded by Lamarck, he says, *' that if species were not created 

 separately they must have descended from other species, and I 

 can see nothing else in common between the ' Origin ' and 

 Lamarck." This was Mr. Darwin's attitude of mind to 

 Lamarck's theory, and the cases in which he attributes import- 

 ance to the effects of use and of disuse, and to acquired habit, 

 and consequently to the Lamarckian principle of the trans- 

 mission of acquired characters, are clearly to be regarded as 

 concessions or admissions on his part, given with increasing 

 generosity in the later editions of the " Origin " ; but always 

 treated as of quite subordinate importance. It is not going too 

 far to say that Mr. Darwin never troubled himself very much 

 with the question as to whether acquired characters are trans- 

 mitted or not. It was the object of his works to show that the 

 main effective principle in the origin of species is the natural 

 selection in the struggle for existence of congenital characters. 

 He explicitly states that he believes other causes to be at work ; 

 one of which at least, viz. sexual selection, he himself investi- 

 gated at length. It must be remembered that no evolutionist 

 in Darwin's life-time had prominently challenged the truth of the 

 Lamarckian assumption that acquired characters are transmitted. 

 For Darwin it was sufficient to show that, granting such a 

 process to take place, it would not account for much ; he 

 was content to accept it as a subordinate factor. His view is 

 best stated in his own words in the "Origin of Species": 

 " On the whole we may conclude that habit, or use and disuse, 

 have, in some cases, played a considerable part in the modi- 

 fication of the constitution and structure." 



Whilst it is true that Mr. Darwin in various parts of his 

 works alludes to cases which he interprets as due to the trans- 

 mission of characters acquired by parents through habit, use, or 

 disuse, it is obvious, when we read what he has to say in each 

 case (as in the examples cited by Mr. Herbert Spencer), that 

 he preferred, where it occurred to him another interpretation. 

 Thus, after referring to the wings of the logger-headed duck 

 and the domestic Aylesbury duck as dwindled by the trans- 

 mission in successive generations of the effects of disuse, he 

 interposes his own explanation by natural selection of the wing- 

 less beetles of Madeira, prefaced by the words : " in some cases 

 we might easily put down to disuse modifications of structure 

 which are wholly or mainly due to natural selection." He 

 refuses to regard the defective anterior tarsi of dung-beetles as 



due to inherited mutilation, though he supposes they may have 

 become deficient through disuse. He regards the defective 

 eyes of cave-animals as due to the inheritance of the effects of 

 disuse. I can scarcely doubt that, had it occurred to him, he 

 would have preferred an explanation similar to that given by 

 him of the wingless island beetles, viz. that a natural selection 

 of animals with defective eyes takes place in a cave ; since 

 ultimately only those remain in a cave and breed in it which, 

 in the course of their wanderings, are unable to see the faint 

 light which penetrates to a great distance from the mouth, and 

 must guide all those but the congenitally blind or weak-sighted 

 to the exterior. The defective eyes of moles are ascribed by 

 him not merely to disuse but to the selective action of inflam- 

 mation. The case of the silkworm caterpillars with defective 

 instincts (which is one of those given by Mr. Spencer) does not 

 appear to me to bear on the present question. Of acquired 

 characters, other than those due to disuse, Mr. Darwin accepts 

 very few as being transmitted. He accepts the statements of 

 Brown-Sequard as to the transmission of the effects of mutila- 

 tions of guinea-pigs only so far as to " make us cautious in 

 denying such transmission." He regards the dislocation of 

 the eye of flat-fishes as due to the inheritance in successive 

 generations of an increasing displacement caused by muscular 

 effort. Besides these two instances (noted by Mr. Spencer) 

 there is one other prominent passage in which Darwin asserts his 

 belief in the inheritance of an acquired character which is not 

 merely the result of disuse. I am anxious to separate those cases 

 which Darwin speaks of as "due to the effects of disuse," 

 for a reason which will appear below. The additional passage 

 not noted by Mr. Spencer is this (" Origin of Species," p. 206, 

 sixth edition) : — " If we suppose any habitual action to become 

 inherited — and it can be shown that this does sometimes happen 

 — then the resemblance between what originally was a habit and 

 an instinct becomes so close as not to be distinguished. If 

 Mozart, instead of playing the pianoforte at three years' old with 

 wonderfully little practice, had played a tune with no practice at 

 all, he might be truly said to have done so instinctively. But it 

 would be a serious error to suppose that the greater number of 

 instincts have been acquired by habit in one generation and then 

 transmitted by inheritance to succeeding generations. It can 

 be clearly shown that the most wonderful instincts with which 

 we are acquainted — namely, those of the hive bee and of many 

 ants — could not possibly have been acquired by habit." 



The cases of the epileptic guinea-pigs, the eyes of flat-fishes, 

 and of some acquired habits, have been discussed by Weismann 

 and by Wallace. I will not now allude further to those classes 

 of cases. But I am anxious to draw attention to the special 

 subject of the "effects of disuse" as set forth by Mr. Darwin. 

 This phrase is not only used by him in regard to special in- 

 stances, but, in treating of the large subject of rudimentary 

 organs, he frequently refers to the "effects of disuse." He 

 says, " It appears probable that disuse has been the main agent 

 in rendering organs rudimentary " (" Origin," p. 401). 



Now I am anxious to point out three things in regard to the 

 "effects of disuse." (i) There are other possible effects of 

 disuse of an organ than the dwindling of that organ in one 

 generation, and the inheritance of the organ in a diminished size 

 by the next generation. (2) The anti-Lamarckians attribute a 

 very great effect to disuse, although they do not attribute to it 

 the particular result which Lamarck did. (3) The particular 

 way in which, according to the anti-Lamarckians, disuse acts so 

 as 10 lead to the dwindling or complete loss of the di«used organ 

 has been called by Weismann by a convenient name — "panmixia." 

 The doctrine of panmixia is already indicated by Darwin him- 

 self, and in view of this fact we must suppose that, when he 

 attributed the loss or dwindling of an organ to "disuse" or the 

 "effects of disuse," he did not necessarily (though probably he 

 frequently did) refer to the Lamarckian modus operandi of 

 disuse, but may very well have had in mind the results which 

 are attributed to disuse by the anti-Lamarckian doctrine of 

 panmixia. 



The doctrine of panmixia is this. When there is no longer, 

 owing to changed conditions of life, any use for an organ, it 

 will cease to be the subject of natural selection. Consequently 

 all possible variations of the organ will have (so far as the now 

 lapsed use of the organ is concerned) an equal chance. Amongst 

 the possible variations there will be the variation in the direction 

 of increased size, and its exact complement — the variation in the 

 direction of diminished size. Prof. Weismann has stated briefly 

 that this equal survival of all possible variations must lead to the 



