278 THE PRINCIPLES OF Part II. 



the acquirement through sexual selection of conspicuous 

 colours, may have been checked from the danger thus 

 incurred. But in other cases the males have probably 

 struggled together during long ages, through brute 

 force, or by the display of their charms, or by both 

 means combined, and yet no effect will have been pro- 

 duced unless a larger number of offspring were left by 

 the more successful males to inherit their superiority, 

 than by the less successful males ; and this, as previously 

 ihewn, depends on various 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 success- 

 ful male merelv fails to obtain a female, or obtains a 

 retarded and less vigorous female later in the season, 

 or, if polygamous, obtains fewer females ; so that they 

 leave fewer, or less vigorous, or no offspring. In re- 

 gard to structures acquired through ordinary or natural 

 selection, there is in most cases, as long as the condi- 

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

 advantageous modification in relation to certain special 

 ends ; 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 frequent and extraordinary amount of variability 

 presented by secondary sexual characters. Nevertheless, 

 natural selection will determine that characters of this 

 kind shall not be acquired by the victorious males, 

 which would be injurious to them in any high degree, 

 either by expending too much of their vital powers, or 



