238 THE DESCENT OF MAN. 



for existence, but from having gained an advantage over 

 other males, and from liaving transmitted this advantage to 

 their male offspring alone, sexual selection must here have 

 come into action. It was the importance of this distinction 

 which led me to designate this form of selection as sexual 

 selection. ^1^0 again, if the chief service rendered to the 

 male by his prehensile organs is to prevent the escajie of the 

 female before the arrival of other males, or when assaulted 

 by them these organs will have been perfected through 

 sexual selection, that is, by the advantage acquired by certain 

 individuals over their rivals. J But in most cases of this 

 kind it is impossible to distinguish between the effects of 

 natural and sexual selection. Whole chapters could be 

 filled with details on the differences between the sexes 

 in their sensory, locomotive and prehensile organs. As, 

 however, these structures are not more interesting than 

 others adapted for the ordinary purposes of life I shall pass 

 them over almost entirely, giving only a few instances under 

 each class. 



CThere are many other structures and instincts which 

 must have been developed through sexual selection, such 

 as the weapons of offense and the means of defense of the 

 males for fighting with and driving away their rivals their 

 courage and pugnacity their various ornaments their 

 contrivances for producing vocal or instrumental music 

 and their glands for omitting odors, most of these latter 

 structures serving only to allure or excite the female. It 

 is clear that these characters are the result of sexual and 

 not of ordinary selection, since unarmed, unornamented, or 

 unattractive males would succeed equally well in the battle 

 for life and in leaving a numerous progeny, but for the 

 presence of better endowed males. We may infer that this 

 would be the case, because the females, which are unarmed 

 and unornamented, are able to survive and procreate their 

 kind. Secondary sexual characters of the kind just 

 referred to, will be fully discussed in the following chap- 

 ters, as being in many respects interesting, but especially 

 as depending on the will, choice, and rivalry of the indi- 

 viduals of either sex. When we behold two males fighting 

 for the possession of the female, or several male birds dis- 

 playing their gorgeous plumage and performing strange 

 antics before an assembled body of females, we cannot doubt 

 that, though led by instinct, they know what they are 



