SEXUAL SELECTION 157 



tendency to vary. Some special adornments of the male sex, 

 e.g. the horns of some beetles, are variable to an extraordinary 

 extent. In the human race not only is genius more frequent in 

 the male sex but also congenital idiocy. 1 Even in such a thing 

 as hare lip this greater tendency to deviate from the normal 

 shows itself. Zoologically speaking the female is the con- 

 servative element of the race and the male is the progressive. 

 In any theory that attempts to account for the antlers of the stag 

 and the plumes of the peacock, this fact must not be left out 

 of sight. 



We must now look for the first appearance of what are Secondary 

 ordinarily known as secondary sexual characteristics. It is s ^ 

 among the arthropods, among which are included crustaceans, 

 insects, spiders, scorpions, and others, that the first unmistak- 

 able beginnings are found. In lobsters and crabs the chela or 

 pincers are generally larger in the male. Probably these are 

 used for battles with rivals, certainly they are employed to seize 

 the females ; in many crustaceans there is a wonderful elabora- 

 tion of such clasping organs. In point of colour the sexes 

 seldom differ, but, when they do, the male has the advantage, 

 though as a rule the superiority consists only in a slightly greater 

 depth or brightness of tint. In Squilla sty/tfera, however, a 

 crustacean found in Mauritius, the male is a " beautiful blueish 

 green, with some of the appendages cherry red, while the female 

 is clouded with brown and grey, with the red about her much 

 less vivid than in the male." ' 



Passing on to spiders we often find decided colour distinction 

 between the sexes. Moreover, the male is nearly always smaller 

 than the female, and his courting, as described by those who 

 have seen it, is one of the most extraordinary things in Natural 

 History. He goes through the most astonishing performance of 

 antics, intended, there is every reason to believe, to obtain the 

 female's favour. He may make as many as a hundred and eleven 

 wild gyrations round her to say nothing of other acrobatic feats. 3 



1 See the Census Report for 1891, vol. iv. p. 76. 



2 Quoted by Darwin, Descent of Man, vol. i. p. 385. 



3 See George W. and E. Peck ham on Sexual Selection in spiders of the family Atticl<s 

 (Milwaukee). 



