CHAPTER XIX 



NATURAL SELECTION AS APPLIED TO BIRDS 



The theory of " Natural Selection " applied to birds. Modes of selection. 

 Inter-specific selection. Pigs and Penguins. Skuas and natural selection. Pro- 

 tective coloration. Winter whitening of Ptarmigan. Mimicry among birds. 

 Protective resemblance and aggressive resemblance. Importance of inter-specific 

 selection on the evolution of species. Intra-selection. 



THAT Darwin's theory of natural selection is the main 

 factor in the evolution of species is now generally 

 conceded ; and some of the most striking of his 

 illustrations thereof were furnished from the life-histories of 

 birds. 



This being so, one would have expected to find that, during 

 the half-century which has now passed since the Origin of 

 Species was given to the world, the number of additional facts 

 bearing on this momentous question would have increased a 

 thousand-fold. But, unhappily, strange though it be, this is 

 not the case. Though Ornithologists profess, as a body, to 

 accept Darwin's work, their contributions thereto are of a 

 miserably meagre character. 



Hence, then, we cannot do more in this chapter than give 

 a brief survey of what is so far known as to the nature of the 

 action of natural selection on birds, and the nature of the facts 

 to be sought by future workers. 



The known facts are chiefly those collected by Darwin. 



We shall deal with the selection theory under three main 

 heads : — 



1. Natural selection — Inter-specific, Intra-specific, Intra- 

 organismal. 



2. Artificial selection. 



3. Sexual selection. 



With regard to inter-specific selection, the struggle, between 

 different species occupying the same area, to maintain existence, 



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