ON SEXUAL SELECTION IN BIRDS. 415 



the Stonechat, affirm that I have seen the finest old males first 

 paired. Under such conditions, where the older and more 

 beautiful males prove more attractive to the females, any theory 

 which is primarily based on supposed advantages gained by a 

 male, which, having through some slight variation proved more 

 attractive, is first paired, and which includes the transmission of 

 such a variation to the offspring, making them in their turn more 

 attractive to the females, inasmuch as such offspring in com- 

 petition with more mature males would not be first selected, 

 becomes untenable. I have already given my reasons for con- 

 cluding that all the males which are competing for a female are 

 in an equally healthy and vigorous condition ; natural selection, 

 therefore, at this point, as far as the future of the species is con- 

 cerned, has done its work, and beyond this point sexual selection 

 comes into play for the development for beauty only. In pro- 

 portion as each successive season a male develops and sees the 

 advantages that accrue from such development, so will the desire 

 for further development increase ; when the limit of such de- 

 velopment is reached, variations will tend to occur — I use the 

 word variation for want of a better ; exceeding development 

 expresses my meaning more clearly — such variations will be 

 transmitted to the offspring, and will appear and be developed 

 as the young matures. , 



Very little appears to be known concerning the age at which 

 a bird commences to fyreed ; this much, however, we do know — 

 that there are yearly great numbers of individuals that do not 

 breed, and the evidence seems to show that such individuals are 

 immature. We have then a gradual process of development, 

 amongst the healthy individuals of a species, due to the action 

 of inherent aesthetic sense in combination with a tendency for 

 the plumage to develop with age, on exactly similar lines — and 

 that this development should be as perfect as possible, a careful 

 display of the male is essential. 



One of the arguments used against Mr. Darwin's theory of 

 sexual selection was that it was improbable that females in 

 different places should have chosen the same variation.; but 

 here such an argument could not be used, inasmuch as variations 

 are due to continuous laws of growth, and only developed by 

 inherent aesthetic sense. The plumage of the female develops 



