CONTROLLED NATURAL SELECTION 



For these several reasons, it is not necessary 

 for the females of the above birds, although 

 making open nests, to be cryptically coloured. 

 This completes the list of British Birds, with 

 the exception of the Phalaropes and Dotterel, 

 in which the female sex is the more brightly 

 coloured one. In these birds, the male in- 

 cubates the eggs in an open nest, and so only 

 the female retains the conspicuous colouring 

 that is used for the protection of young. 



One other fact is of some interest: many cases have 

 been observed of females assuming male plumage; this 

 change of plumage has been found to be associated with 

 sterility ; whatever the mechanism by which this is 

 brought about, it is clearly, according to the theory, an 

 advantage to the species. Males are more conspicuous 

 than females because they are less valuable, therefore a 

 sterile female, because she is less valuable than a fertile 

 one, becomes conspicuous. 



It will be well to review the facts which 

 the theory correlates regarding the colour of 

 British Birds : it accounts for 



1. The presence of conspicuous colouring 

 in both sexes. 



2. The more conspicuous colouring of the 

 male in these birds. 



3. The presence of conspicuous colouring 

 in the male only. 



