226 The Descent of Man. Pabt li. 



Df the habits of animals, this view is hardly p]'obable, for the 

 male is generally eager to pair with any female. It is more 

 probable that the ornaments common to both sexes were acquired 

 liy one sex, generally the male, and then transmitted to the off- 

 spring 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 sex is brilliantly coloured or provided with special orna- 

 ments, and yet the members of both sexes or of one alone have 

 probably acquired simple colours, such as wliite 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 tho 

 acquirement through sexual selection of conspicuous colours, 

 appears to have been sometimes 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 

 shewn, 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 individuals. 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 poly- 

 gamous, obtains fewer females ; so that they leave fewer, less vigor- 

 ous, or no offspring. In regard to structures acquired through 

 ordinary or natural selection, there is inmost cases, as long as tho 

 conditions of life remain the same, a limit to the amount of 

 advantageous modification in relation to certain special purposes ; 

 bat 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 

 eelection will go on. This circumstance may partly account for 

 tile ficquent and extraordinary amount of variability presented 



