042 THU DESCENT OF MAN 



result. The gradations which may be observed between 

 the males of allied species indicate the nature of the steps 

 through which they have passed. They explain alao in 

 the most interesting manner how certain characters have 

 originated, such as the indented ocelli on the tail-feathers 

 of the peacock, and the ball-and-socket ocelli on the wing- 

 feathers of the Argus pheasant. It is evident ,that the bril- 

 liant colors, topknots, fine plumes, etc., of many male birds 

 cannot have been acquired as a protection; indeed, they 

 sometimes lead to danger. That they are not due to the 

 direct and definite action of the conditions of life we may 

 feel assured, because the females have been exposed to the 

 same conditions, and yet often differ from the males to an 

 extreme degree. Although it is probable that changed con- 

 ditions acting during a lengthened' period have in some cases 

 produced a definite effect on both sexes, or sometimes on 

 one sex alone, the more important result will have been 

 an increased tendency to vary or to present more strongly 

 marked individual differences; and such differences will 

 have afforded an excellent groundwork for the action of 

 sexual selection. 



The laws of inheritance, irrespectively of selection, appear 

 to have determined whether the characters acquired by the 

 males for the sake of ornament, for producing various sounds, 

 and for fighting together, have been transmitted, to the males 

 alone or to both sexes, either permanently or periodically, 

 during certain seasons of the year. Why various charac- 

 ters should have been transmitted, sometimes in one way 

 and sometimes in another, is not in most cases known; but 

 the period of variability seems often to have been the deter- 

 mining cause. When the two sexes have inherited all char- 

 acters in common they necessarily resemble each other; but 

 as the successive variations may be differently transmitted, 

 every possible gradation may be found, even within the 

 same genus, from the closest similarity to the widest dis- 

 similarity between the sexes. With many closely allied 

 species, following nearly the same habits of life, the males 



