296 Colour and the Struggle for Life 



A full exposition of Sexual Selection appeared in The Descent of 

 Man in 1871, and in the greatly augmented second edition, in 1874. 

 It has been remarked that the two subjects, The Descent of Man and 

 Selection in Relation to Sex, seem to fuse somewhat imperfectly 

 into the single work of which they form the title. The reason for 

 their association is clearly shown in a letter to Wallace, dated May 

 28, 1864: "...I suspect that a sort of sexual selection has been the 

 most powerful means of changing the races of man 1 ." 



Darwin, as we know from his Autobiography' 2 , was always greatly 

 interested in this hypothesis, and it has been shown in the preceding 

 pages that he was inclined to look favourably upon it as an interpre- 

 tation of many appearances usually explained by Natural Selection. 

 Hence Sexual Selection, incidentally discussed in other sections of 

 the present essay, need not be considered at any length, in the section 

 specially allotted to it. 



Although so interested in the subject and notwithstanding his 

 conviction that the hypothesis was sound, Darwin was quite aware 

 that it was probably the most vulnerable part of the Origin. Thus 

 he wrote to H. W. Bates, April 4, 1861 : "If I had to cut up myself in 

 a review I would have [worried ?] and quizzed sexual selection ; there- 

 fore, though I am fully convinced that it is largely true, you may 

 imagine how pleased I am at what you say on your belief 3 ." 



The existence of sound-producing organs in the males of insects 

 Avas, Darwin considered, the strongest evidence in favour of the 

 operation of sexual selection in this group 4 . Such a conclusion has 

 received strong support in recent years by the numerous careful 

 observations of Dr F. A. Dixey 5 and Dr G. B. Longstaff 6 on the 

 scents of male butterflies. The experience of these naturalists 

 abundantly confirms and extends the account given by Fritz Midler 7 

 of the scents of certain Brazilian butterflies. It is a remarkable fact 

 that the apparently epigamic scents of male butterflies should be 

 pleasing to man while the apparently aposematic scents in both sexes 

 of species with warning colours should be displeasing to him. But 

 the former is far more surprising than the latter. It is not perhaps 

 astonishing that a scent which is ex hypothesi unpleasant to an 

 insect-eating Vertebrate should be displeasing to the human sense ; 

 but it is certainly wonderful that an odour which is ex hypothesi 

 agreeable to a female butterfly should also be agreeable to man. 



1 More Letters, ir. p. 33. 2 Life and Letters, i. p. 94. 



: * More Letters, i. p. 183. 4 Life and Letters, in. pp. 94, 138. 



5 Proc. Ent. Soc. Lond. 1904, p. Ivi; 1905, pp. xxxvii, liv; 1906, p. ii. 

 K Proc. Ent. Soc. Lond. 1905, p. xxxv; Trans. Ent. Soc. Lond. 1905, p. 136; 1908, 

 ].. 007. 



7 Jen. Zeit. Vol. xi. 1877, p. 99 ; Trans. Ent. Soc. Lond. 1878, p. 211. 



