22 THE EVOLUTION OF SEX. 



combats between males, and the effect produced on the 

 accumulative constitution of the females by the increased 

 maternal sacrifice characteristic of the highest animals. 



§ 4. Other Cha7'acters. — A\'hile it is easy to point to the 

 general physiological import of large size and the reverse, 

 physiology is not yet far enough advanced to afford firm foot- 

 hold in dealing with the details of secondary sexual characters. 

 It is only possible to point out the path which will eventually 

 lead us to their complete rationale. This path will appear less 

 vague if reverted to after some of the succeeding chapters have 

 been grasped. The point of view is simple enough. The 

 agility of males is not a special adaptation to enable that sex 

 to exercise its functions with relation to the other, but is a 

 natural characteristic of the constitutional activity of maleness ; 

 and the small size of many male fishes is not an advantage at all, 

 but simply again the result of the contrast between the more 

 vegetative growth of the female and the costly activity of the 

 male. So, brilliancy of colour, exuberance of hair and feathers, 

 activity of scent-glands, and even the development of weapons, 

 are not, and cannot 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 arc exhibited. Thus the male bird of 

 paradise, eventually so resplendent, is usually in its youth 

 comparatively dull and female- like in its colouring 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 



* That Mr Wallace has adopted the same explanation of the different 

 sexual characters in his new I)ook, has l)een already pointed out (see p. II, 

 note). 



