Darwin's Theory of Sexual Selection 217 
to be destroyed but run away, they live to find mates of their 
own. In fact, the conduct of the males at the breeding 
“season appears to be much more the outcome of their own 
excitement than an attempt to attract the females. 
8. There is another side to the question, the importance 
of which is so great, that it is surprising that Darwin has 
not taken any notice of it. If, in order to bring about, or 
even maintain, the results of sexual selection, such a tre- 
mendous elimination of individuals must take place, it is 
surprising that natural selection would not counteract this 
by destroying those species in which a process, so useless for 
the welfare of the species, is going on. It is curious that this 
has not been realized by those who believe in both of these 
two hypotheses. 
g.. What has just been said applies also with almost equal 
force to the development of such structures as the horns of 
deer, bison, antelopes, and the brilliant colors of many insects 
and birds. If in nature, competition between species takes 
place on the scale that the Darwinian theory of natural selec- 
tion postulates, such forms, if they are much exposed, would 
be needlessly reduced in numbers in the process of acquiring 
these structures. So many individuals would have been at 
such a disadvantage in breeding, that if competition is as se- 
vere as the theory of natural selection postulates, these species 
could hardly be expected to compete successfully with other 
species in which sexual selection was not taking place. 
10. Darwin admits that, in certain cases, external condi- 
tions may have acted directly to produce the colors in certain 
forms, and if these were not injurious he thinks they might 
have become constant. Such cases are left unexplained in 
the sense that they are not supposed to be adaptations to any- 
thing in particular. That colors produced in this way might 
afterward be found useful, irrespective of how they arose, is 
admitted as one of the ways in which sexual differences may 
have arisen. 
