THE EVOLUTION OF SEX. 



tion. The colours too of the males are often more sharply 

 contrasted, and there are minor differences, in voice and the 

 like, which cannot be ignored. Of weapons, the larger canine 

 teeth of many male animals, such as boars ; the special tusks 

 of, for instance, the elephant and narwhal ; the antlers of stags, 



The development of antlers in the successive years of a 

 s'as^s life, or in the general history of stags. — From 

 Cams Sterne. 



all but exclusively restricted to the combative sex ; the horns 

 of antelopes, goats and sheep, oxen and the like, — which at least 

 predominate in the males, — are well-known illustrations. The 

 manes of male lions, bisons, and baboons ; the beards of 

 certain goats ; the crests along the backs of some antelopes ; 

 the dewlaps of bulls, — illustrate another set of secondary 

 characters. The odoriferous glands of many mammals are more 

 developed in the males, and become specially functional during 

 the breeding season. This is well illustrated in the case of 

 goats, deer, shrew-mice, elephants. The differences in colour 

 are slight compared with those seen between the sexes in birds, 

 but in not a few orders the distinction is marked enough, males 

 being, in the great majority of cases, the more strongly and 

 brilliantly coloured. Among monkeys the difference in colour 

 in the bare regions, and the subtler decorations in the arrange- 

 ment of the hair on the face, are often very conspicuous. 



§ 3. Darwin's Explanation — Sexual Selection. — Darwin 

 started from the occurrence of such variations, in structure and 

 habit, as might be useful either for attraction between the sexes 

 or in the direct contests of rival males. The possessors of 

 these variations succeeded l)etter than their neighbours in the 

 art of courtship ; the factors which constituted success were 

 transmitted to the offspring ; and, gradually, the variations were 



