Chap. VIII.] SEXUAL SELECTION. 240 



finding the female ; but in the vast majority of cases, they 

 serve only to give one male an advantage over another, 

 for the less well-endowed males, if time were allowed them, 

 would succeed in pairing with the females; and they 

 would in all other respects, judging from the structure 

 of the female, be equally well adapted for their ordinary 

 habits of life. In such cases sexual selection must have 

 come into action, for the males have acquired their pres- 

 ent structure, not from being better fitted to survive in 

 the struggle for existence, but from having gained an ad- 

 vantage over other males, and from having transmitted 

 this advantage to their male offspring alone. It was the 

 importance of this distinction which led me to designate 

 this form of selection as sexual selection. So, again, if the 

 chief service rendered to the male by his prehensile organs 

 is to prevent the escape 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 males over their 

 rivals. But in most cases it is scarcely possible to distin- 

 guish between the effects of natural and sexual selection. 

 Whole chapters could easily 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 almost pass them over, giving only 

 a few instances under each class. 



There are many other structures and instincts which 

 must have been developed through sexual selection — such 

 as the weapons of offence and the means of defence pos- 

 sessed by the males for fighting with and driving away 

 their rivals — their courage and pugnacity — their orna- 

 ments of many kinds — their organs for producing vocal 

 or instrumental music — and their glands for emitting 

 odors ; most of these latter structures serving only to al- 



