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 
shewn, 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 successful 
male merely fails to obtain a female, or obtains later 
in the season a retarded and less vigorous female, or, 
if polygamous, obtains fewer females ; so that they 
leave fewer, or 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 
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 
