THE SEXES, AND CRITICISM OF SEXUAL SELECTION. I9 



exuberance of hair and feathers, activity of scent-glands, and even the 

 development of weapons, are not and can not be (except teleologically) 

 explained by sexual selection, but in origin and continued development 

 are outcrops of a male as opposed to a female constitution. To sum 

 up the position in a paradox, all secondary sexual characters are at 

 bottom primary, and are expressions of the same general habit of body 

 (or to use the medical term, diathesis) as that which results in the 

 production of male elements in the one case, or female elements in 

 the other.* 



Three well-known facts must be recalled to the reader's mind at 

 this point; and firstly, that in a great number of cases the secondary 

 sexual characters make their appearance step by step with sexual 

 maturity itself. When the animal — be it a bird or insect — becomes 

 emphatically masculine, then it is that these minor outcrops are 

 exhibited. Thus the male bird-of-paradise, eventually so resplendent, 

 is usually in its youth comparatively dull and female-like in its coloring 

 and plumage. Very often, too, whether in the wedding-robe of male 

 fishes or in the scent-glands of mammals, the character rises and wanes 

 in the same rhythm as that of the reproductive periods. It is 

 impossible not to regard at least many of the secondary sexual 

 characters as part and parcel of the sexual diathesis, — as expressions 

 for the most part of exuberant maleness. Secondly, when the 

 reproductive organs are removed by castration, the secondary sexual 

 characters tend to remain undeveloped. Thus, as Darwin notes, stags 

 never renew their antlers after castration, though normally of course 

 they renew them each breeding season. The reindeer, where the 

 horns occur on the females as well, is an interesting exception to the 

 rule, for after castration the male still renews the growth. This, how- 

 ever, merely indicates that the originally sexual characters have 

 become organized into the general life of the body. In sheep, 

 antelopes, oxen, &c. , castration modifies or reduces the horns; and the 

 same is true of odoriferous glands. The parasitic crustacean Sacculina 

 has been shown by Delage to effect a partial castration of the crabs to 

 which it fixes itself, and the same has been observed by Giard in other 

 cases. In two such cases an approximation to the female form of 

 appendage has been observed. Lastly, in aged females, which have 

 ceased to be functional in reproduction, the minor peculiarities of their 

 sex often disappear, and they become liker males, both in structure 

 and habits, — witness the familiar case of " crowing hens." 



<- That Mr. Wallace has adopted the same explanation of the different sexual 

 characters in his new book " Darwinism," [No. 115 and No. 116 of The Humboldt 

 Library'] has been already pointed out (see p. 10, note). 



