COURTSHIP OF BIRDS 145 



chance of being established and of being perfected by the 

 success it entails. Sexual Selection is thus only a special 

 case of Natural Selection, with this difference, that the female 

 bird takes the place of the general environment in picking 

 and choosing what is fit, or in leaving out what is relatively 

 unfit. 



Darwin's illustrious collaborateur, Alfred Russel Wallace, 

 has taken a different view of the facts. Attaching little 

 importance to the alleged Sexual Selection, he interprets 

 the sex dimorphism in terms of Natural Selection. Con- 

 spicuousness during incubation is dangerous. The more 

 conspicuous females are picked off the nest by hawks, foxes, 

 and the like, and hence only sober-coloured females remain. 

 According to Darwin, the gayness of male birds is due to 

 Sexual Selection on the part of the females ; according to 

 Wallace, the plainness of the female birds is due to Natural 

 Selection, which has eliminated those that persisted to the 

 death in their gay plumage. Darwin starts from uniform 

 sexes, and accounts for the gorgeous males by Sexual Selec- 

 tion ; Wallace starts from uniform sexes, and accounts for 

 the sober-coloured females by Natural Selection. In 1773, 

 the Hon. Daines Barrington, a naturalist still remembered as 

 the correspondent of Gilbert White, suggested that singing- 

 birds were small and the hen-birds mute for safety's sake. 

 This is in principle the same idea as that which Wallace 

 has elaborated. 



It is quite possible that there is truth on both sides, for 

 Sexual Selection might in some cases act as an accelerant of 

 the evolution of bright plumage, while Natural Selection 

 might in other cases have a retarding influence when 

 conspicuousness was dangerous. The difficulty is to get at 

 the facts. We have not sufficient data to answer the crucial 

 question whether a considerable number of males are left out 

 in the cold unmated, and, if so, whether they are appreciably 



