ON SEXUAL SELECTION IN BIRDS. 411 



is adduced to prove that selection by the female is being carried 

 on during the whole of this period, and that such should be the 

 case is highly improbable, for if, as must be so, both sexes are 

 in a fit condition to breed during the whole of this period, con- 

 siderable and valuable time will have lapsed before any choice on 

 the part of the female takes place ; such loss of time, owing to 

 reasons which must be apparent, could only result in being the 

 reverse of beneficial to the species, and contrary to the laws of 

 natural selection. But apart from such a consideration as the 

 above, I cannot call to mind a single instance in which the 

 selection has taken more than a very short period ; sometimes it 

 is a day or so, frequently only a matter of hours, and with 

 migratory species the duration of this period appears to vary to 

 some extent with the condition of the seasons. For these reasons 

 I am convinced that the selection is usually of short duration, 

 and, this being the case, it will readily be seen what a difficult 

 matter it becomes to understand in what direction the young of 

 those individuals that were first paired could gain any advantage ; 

 food being as plentiful for the late as the early broods. Whether, 

 amongst those species which rear two or more broods, the fact of 

 one pair of individuals commencing to breed a few hours before 

 another could be of any advantage is very doubtful ; on the other 

 hand, a very large number of species do not rear two broods. I 

 fully admit that an advantage, however small, when maintained 

 over such a vast period, must be effective, but in this case I can- 

 not see where the advantage lies ; and, on the contrary, it might 

 frequently happen, owing to adverse climatic conditions at the 

 time when the young are hatched, that the young of those in- 

 dividuals that were the later breeders might thus have an advan- 

 tage. Mr. Wallace, however, has pointed out an objection which 

 makes it almost impossible to believe that sexual selection can 

 act in the way in which Mr. Darwin interpreted it. Briefly it is 

 this : that the extremely rigid action of natural selection must 

 render any attempt to select mere ornament utterly nugatory, 

 unless the most ornamented always coincide with the fittest in 

 other respects ; and if such is the case, then no other kind of 

 selection is necessary. The force of such an objection will at 

 once be seen. 



In the same work Mr. Wallace gives his reasons for regarding 



