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—e.g., 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 
