550 The Descent of Man. Part II. 



and it is inconceivable that they can be of use in any ordinary way 

 to these animals. If so, they have probably been gained through 

 sexual selection, though transmitted equally, or almost equally^ 

 to both sexes. With many of the Quadrumana, we have addi- 

 tional evidence of the action of sexual selection in the greater 

 size and strength of the males, and in the greater development of 

 their canine teeth, in comparison with the females. 



A few instances will suffice of the strange manner in which 

 both sexes of some species are coloured, and of the beauty of others. 

 The face of the Cercopithecus petaurista (fig. 77) is black, the 

 whiskers and beard being white, with a defined, round, white 

 spot on the nose, covered with short white hair, which gives to 

 the animal an almost ludicrous aspect. The Semnopithecus 

 frontatus likewise has a blackish face with a long black beard, 

 and a large naked spot on the forehead of a bluish-white colour. 

 The face of Macacus lasiotus is dirty flesh-coloured, with a 

 defined red spot on each cheek. The appearance of Ctrcocebus 

 xthiops is grotesque, with its black face, white whiskers and 

 collar, chesnut head, and a large naked white spot over each 

 eyelid. In very many species, the beard, whiskers, and crests of 

 hair round the face are of a different colour from the rest of the 

 head, and when different, are always of a lighter tint,' 15 being 

 often pure white, sometimes bright yellow, or reddish. The 

 whole face of the South American Brachyurus calvus is of a 

 " glowing scarlet hue ; " but this colour does not appear until 

 the animal is nearly mature. 46 The naked skin of the face differs 

 wonderfully in colour in the various species. It is often brown 

 or flesh-colour, with parts perfectly white, and often as black as 

 that of the most sooty negro. In the Brachyurus the scarlet tint 

 is brighter than that of the most blushing Caucasian damsel. It 

 is sometimes more distinctly orange than in any Mongolian, and 

 in several species it is blue, passing into violet or grey. In all 

 the species known to Mr. Bartlett, in which the adults of both 

 sexes have strongly-coloured faces, the colours are dull or absent 

 during early youth. This likewise holds good with the mandrill 

 and Ehesus, in which the face and the posterior parts of the body 

 are brilliantly coloured in one sex alone. In these latter cases 

 we have reason to believe that the colours were acquired through 

 sexual selection ; and we are naturally led to extend the same 

 view to the foregoing species, though both sexes when adult 

 have their faces coloured in the same manner. 



43 I observed this fact in the ' Hist. Nat. des Mammiferes.' torn. 



Zoological Gardens; and many cases i. 1824. 



maybe seen in the coloured plates in 46 Bates, 'The Naturalist on the 



Geoffroj St.-HUai/e and F. Cuvkr. Amazons,' 1863, vol. ii. p. 310. 



