SEXUAL SELECTION 689 



been applied to these characters, they must be due to simple 

 variability, together with sexually limited inheritance. 



Hence it appears reasonable to extend this same view- 

 to all analogous cases with animals in a state of nature. 

 Nevertheless I cannot persuade myself that it generally 

 holds good, as in the case of the extraordinary develop- 

 ment of hair on the throat and forelegs of the male Am- 

 motragus, or in that of the immense beard of the male 

 Pithecia. Such study as I have ' been able to give to 

 nature makes me believe that parts or organs which are 

 highly developed were acquired at some period for a 

 special purpose. With those antelopes in which the adult 

 male is more strongly colored than the female, and with 

 those monkeys in which the hair on the face is elegantly 

 arranged and colored in a diversified manner, it seems 

 probable that the crests and tufts of hair were gained as 

 ornaments; and this I know is the opinion of some natural- 

 ists. If this be correct, there can be little doubt that they 

 were gained or at least modified through sexual selection; 

 but how far the same view may be extended to other mam- 

 mals is doubtful. 



Color of the Hair and of the Naked Skin. — I will first give 

 briefly all the cases known to me of male quadrupeds differ- 

 ing in color from the females. With Marsupials, as I am 

 informed by Mr. Gould, the sexes rarely differ in this re- 

 spect; but the great red kangaroo offers a striking excep- 

 tion, "delicate blue being the prevailing tint in those parts 

 of the female which in the male are red." '" In the Didel- 

 phis opossum of Cayenne the female is said to be a little 

 more red than the male. Of the Eodents Dr. Gray re- 

 marks: "African squirrels, especially those found in the 

 tropical regions, have the fur much brighter and more vivid 

 at some seasons of the year than at others, and the fur of 



" Osphranter rufus, Gould, "Mammals of Australia," 1863, vol. li. On 

 tbe Didelphis, Desmarest, "Mammalogie, " p. 256. 



