536 THE DESCENT OF MAN. 



again, as I hear from Prof. Newton, the males of two 

 species of Oxynotus (shrikes), which represent each other in 

 the Islands of Mauritius and Bourbon,* differ but little in 

 color, while the females differ much. In the Bourbon 

 species the female appears to have partially retained an 

 immature condition of plumage, for at first sight she 

 *' might be taken for the young of the Mauritian species.'" 

 These differences may be compared with those inexplicable 

 ones which occur independently of man's selection in 

 certain sub-breeds of the game-fowl, in which the females 

 are very different, while the males can hardly be distin- 

 guished, f 



As I account so largely by sexual selection for the differ- 

 ences between the males of allied species, how can the 

 differences between the females be accounted for in all 

 ordinary cases? We need not here consider the species 

 which belong to distinct genera; for with these, adaptation 

 to different habits of life, and other agencies, will have 

 come into play. In regard to the differences between the 

 females within the same genus it appears to me almost cer- 

 tain, after looking through various large groups, that the 

 chief agent has been the greater or less transference to the 

 female of the characters acquired by the males through 

 sexual selection. In the several British finches the two 

 sexes dift'er either very slightly or considerably; and if we 

 compare the females of the greenfinch, chaffinch, goldfinch, 

 bullfinch, crossbill, sparrow, etc., we shall see that they 

 differ from one another chiefly in the points in which they 

 partially resemble their respective males; and the colors of 

 the males may safely be attributed to sexual selection. 

 With many gallinaceous species the sexes differ to an 

 extreme degree, as with the peacock, pheasant and fowl, 

 while with other species there has been a partial or even 

 complete transference of character from the male to the 

 female. The females of the several species of Polyplectron 

 exhibit in a dim condition, and chiefly on the tail, the 

 splendid ocelli of their males. The female partridge diff'ers 

 from the male only in the red mark on her breast being 

 smaller; and the female wild turkey only in her colors being 



* These species are described with colored figures, by M. F. Pollen, 

 in " Ibis," 1866, p. 275. 

 f " Variation of Animals, etc., under Domestication," vol. i, p. 251. 



