56 THE DESCENT OF MAN. 



transmitted to the offspring of both sexes. If, indeed, 

 during a lengthened period the males of any species were 

 greatly to exceed the females in number, and then during 

 another lengthened period, but under different conditions, 

 the reverse were to occur, a double, but not simultaneous, 

 process of sexual selection might easily be carried on, by 

 which the two sexes might be rendered widely different. 



We shall hereafter see that many animals exist, of which 

 neither sax is brilliantly colored or provided with special 

 ornaments, and yet the members of both sexes or of one 

 alone have probably acquired simple colors, such as white 

 or black, through sexual selection. The absence of bright 

 tints or other ornaments may be the result of variations of 

 the right kind never having occurred, or of the animals 

 themselves having preferred plain black or white. Obscure 

 tints have often been developed through natural selection for 

 the sake of protection, and the acquirement through sexual 

 selection of conspicuous colors appears to have been some- 

 times checked from the danger thus incurred. But in 

 other cases the males during long ages may have struggled 

 together for the possession of the females, and yet no effect 

 will have been produced, unless a larger number of 

 offspring were left by the more successful males to inherit 

 their superiority than by the less successful; and this, as 

 previously shown, depends on many complex contingencies. 



Sexual selection acts in a less rigorous manner than 

 natural selection. The latter produces its effects by the 

 life or death at all ages of the more or less successful indi- 

 viduals. Death, indeed, not rarely ensues from the 

 conflicts of rival males. But generally the less successful 

 male merely fails to obtain a female, or obtains a retarded 

 and less vigorous female later in the season, or, if polyga- 

 mous, obtains fewer females; so that they leave fewer, less 

 vigorous, or no offspring. In regard to structures acquired 

 through ordinary or natural selection there is in most cases, 

 as long as the conditions of life remain the same, a limit to 

 the amount of advantageous modification in relation to 

 certain special purposes; but in regard to structures adapted 

 to make one male victorious over another, either in fighting 

 or in charming the female, there is no definite limit to the 

 amount of advantageous modification; so that as long as 

 the proper variations arise the work of sexual selection will 

 go on. This circumstance may partly account for the 



