xi COLOUR AND SONG 317 



greatest living champion of the theory of Natural 

 Selection through the struggle for existence. Else- 

 where, Dr. Wallace speaks of this struggle as un- 

 ceasing. As with artificial selection, every advan- 

 tageous variation is selected, every disadvantageous 

 one is weeded out. In Domestic Pigeons—^., in 

 the Dragons and the Pouters— peculiarities have been 

 artificially produced which are not well suited to 

 wild birds. If such breeds of Pigeons are not kept up 

 by constant selection on the part of the breeder, they 

 will soon tend to return to the characters of the 

 wild Rock-dove from which they have sprung. If 

 highly-bred horses are allowed to run wild they 

 gradually lose many of the points which were pro- 

 duced by artificial selection. But the Peacock and the 

 Argus Pheasant, whose plumes render them ill-fitted 

 for wild life, are, according to Dr. Wallace's theory, so 

 full of vigour and vitality that Natural, Selection ceases 

 in their case to operate. These birds, it seems, having 

 won their laurels, are not compelled any longer to 

 enter the lists, and are at liberty to expend their 

 vigour on finery which, however beautiful to us, must 

 be pernicious to them. Of the dancing and antics, 

 however, the theory gives a satisfactory explanation, 

 and perhaps even of the elaborate vocal performances 

 of the Thrushes and Nightingales. These do not, as 

 a rule, endanger the birds in question, or draw largely 

 upon their vitality. ' Health and high spirits are the 

 result of the working of Natural Selection. 



Dr. Wallace's view has been developed by Professor 

 Geddes. In nearly all species of animals, the males 

 are the more vigorous ; in them most variations are 



