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. 



9. 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. 



