42 BIRDS OF THE PLAINS 



one another, hence no change in character takes place. 

 The effects of variation are swamped by intercrossing. 

 It is only when intercrossing is checked, as when 

 natural selection weeds out certain varieties, that 

 evolution occurs. 



This theory, of course, explains, or helps to explain, 

 why species are so stable ; but it involves the assump- 

 tion that there is no such thing as sexual selection 

 among animals in a state of nature. The theory 

 assumes that individuals mate in a haphazard manner, 

 that a long-winged hen is as likely to select a short- 

 winged husband as a long-winged one. Are we justified 

 in assuming this? At present there is little evidence 

 on the subject. Evidence can only be procured by 

 measuring a number of pairs of birds that have mated, 

 and seeing whether large hens mate chiefly with large 

 cocks or with small cocks, or indifferently with large or 

 small cock-birds. 



That sexual selection is a reality and not a mere 

 hypothesis there can, I think, be but little doubt. It 

 is with the theory that supposes that the females alone 

 exercise selection that I feel compelled to quarrel. The 

 male selects his partner just as much as the female 

 selects hers. The choice is mutual. 



In the Zoological Gardens at Lahore there are a 

 number of ordinary coloured peacocks and a number of 

 albinos. No coloured hen will mate with a coloured 

 cock if she is allowed to exercise a choice between him 

 and an albino. Here, then, is a clear example of sexual 

 selection. 



Professor Karl Pearson has spent much time in trying 



