igS 



NA TURE 



[December 27, 1900 



It has already been stated that the author repeats, and 

 therefore presumably gives weight to, the stock objection 

 against Darwinism that that doctrine does not account 

 for the origin of the variations which selection has 

 to deal with (p. 30). True ; but the writer of this 

 notice is not aware that the selectionists have ever pre- 

 tended that it did, or that it might be expected to. There 

 have been supplementary hypotheses of variation, and 

 there is reason to believe that variability or instability of 

 form, if of advantage to a species subject to rapid changes 

 of environment, might be seized upon and perpetuated 

 by selection like any other character, structural or 

 physiological. But this has nothing to do with the origin 

 of variation as the result of physiological processes. On 

 the other hand, if the theory of natural selection is con- 

 sidered to break down because it fails to account for the 

 origin of variations (which at any rate are facts) what 

 value can be assigned to a theory which asswnes a 

 special plasticity of the organism under particular 

 " physiological conditions " at a certain period of its life 

 without any adequate proof that such plasticity does 

 exist, and which further assumes that external stimuli, 

 acting upon the individual at that period, produce 

 hereditary modifications of structure? 



I hope I am not misrepresenting the author's views 

 in pointing out how much in the way of assumption 

 exists in them. It will, no doubt, be said by Mr. 

 Cunningham that his method is logically sound and 

 scientifically correct. Haying come to the conclusion 

 that selection is inadequate to account for the facts of 

 sexual dimorphism, he has a perfect right to ask 

 naturalists to examine the evidence which he considers 

 to weigh in favour of his alternative explanation. He 

 says (p. 42) : — 



■ "I maintain . . . that theories of selection being 

 found on application to the facts to be insufficient for 

 their explanation, and the theory of the inheritance of 

 acquired characters being found to harmonise with the 

 facts, we are logically bound to believe that such in- 

 heritance does take place, at any rate until some other 

 explanation can be found. I do not concern myself 

 with the question how such inheritance can be pro- 

 duced, ?'/ is a fact that the modifications are hereditary, 

 and my object is to produce inductive evidence that they 

 were determined by special stimulations P (Italics the 

 author's.) 



The author's position towards the question of the 

 inheritance of acquired characters may be paraphrased 

 thus : — Secondary sexual characters appear to be, on 

 critical examination, the result of direct mechanical 

 action upon the individual ; therefore we must believe 

 that these characters have been so produced. The 

 non-transmissibility of acquired characters is not an 

 established truth, but only a belief (p. 15) ; therefore, in 

 view of the foregoing conclusion, we must beheve that 

 acquired characters are transmitted. 



In answer to this we can only repeat the statement 

 so frequently made in reply to Lamarckian arguments : — 

 All the evidence hitherto adduced in favour of the view 

 that acquired characters are hereditary is either negative 

 or ambiguous, and in cases where, on such hypothesis, 

 the evidence might fairly be expected to be positive, it 

 is also negative or ambiguous. The probabilities are 

 therefore antecedently against Mr. Cunningham's ex- 

 NO. 1626, VOL. 63] 



planation of secondary sexual characters, and we are 

 justified in asking that his proofs shall be very cogent 

 and convincing before we abandon a theory so probable 

 a priori as Darwin's sexual selection in favour of a 

 theory which is based on unproved principles. If the 

 non-transmissibility .of acquired characters is not an 

 established truth neither is the opposite view, and the 

 author — outside the domain of sexual dimorphism — ad- 

 duces no new evidence in favour of this view. He says 

 explicitly (p. 37) that he does not propose to prove that 

 acquired characters are inherited, but a few paragraphs 

 further on he lays down a statement of his own opinion 

 which is tantamount to a declaration that such characters 

 are inherited. It may be well, also, before attempting to 

 deal with the detailed statements contained in the seven 

 chapters following the introduction, to point out once 

 again that the obvious adaptation of the parts of an 

 animal to the life habits is no proof that the structural 

 modifications have been produced by the habits. It 

 may appear, prima facie, that the structure is caused 

 by habit, but this is no proof that it is so caused. The 

 same result can be brought about by selection, and 

 it is quite unnecessary to insist here that this is the 

 essence of the Darwinian theory. But Mr. Cunningham 

 is quite consistently Lamarckian in his inversion of the 

 Darwinian position. Throughout this work the reader 

 will meet with statements which remind us of the old 

 Lamarckism — that such and such a structure is produced 

 by such and such habit. In one illustration (p. 171) he 

 even goes so far as to demonstrate that by moving a J 

 pen-holder coated with seahng-wax to and fro in hot 

 water the softened wax forms a lamina above and below 

 in the plane perpendicular to the plane of the motion, 

 from which he apparently wishes us to believe that the 

 crest of the male crested- newt "is due to the active 

 movements of the male in courting the female in the 

 breeding season " ! 



The special evidence which the author brings forward 

 in support of his views is contained in some two hundred 

 and sixty pages, divided into seven chapters, each deal- 

 ing with the secondary sexual characters of some class 

 or classes of the animal kingdom, from mammals down- 

 wards. It is impossible to deal with the various cases in 

 detail, but a few typical examples may be selected in 

 order to illustrate the position of those who, like Mr. 

 Cunningham, regard habit as the cause . of structure. 

 The discussion of the sexual differences in man, in the 

 first chapter, will be found particularly instructive. The 

 hair on the face of the male is supposed to be " due to 

 the stimulation of the growth of the hair by teeth or 

 hands in the combats of mature males" (p. 49). That is 

 to say that man's ancestors, by pulling each other by the 

 hair of the face during their struggles for the female, 

 developed a beard and moustache. But if mechanical 

 irritation or stimulation of the hair follicles is the cause 

 of increased growth of hair, why should the hairless 

 condition of man's body, as compared with that of the 

 apes, be attributed to the wearing of clothes (p. 52) ; the 

 baldness of civilised races to the wearing of hats (p. 53), 

 and the greater length of hair in woman to the wearing 

 of lighter head-gear (p. 54) ? Surely the hair follicles of 

 a clothed animal are subject to more pressures and 

 stimulations than in the naked animal ? In a similar way, 



