2 80 



GENERAL BIOLOGY 



Plymouth Rock 



Black Minorca 



Brahma 



'Houdan 



short-lived, of nervous 

 temperament and of weak 

 constitution. A belleflower 

 apple is a beautiful, fragrant 

 and luscious fruit, but the 

 tree that bears it is quite 

 incapable of entering into 

 open competition with the 

 worthless wild crab apple. 

 Nothing could be more 

 striking in illustration of 

 this point than the certainty 

 with which wild species 

 crowd out the cultivated 

 ones on abandoned farms. 

 Lop-eared rabbits, and 

 flightless ducks, and udder- 

 encumbered cows, and 

 small-boned, small-brained 

 pigs, and hairless, witless, 

 barkless and tailless dogs 

 are all freaks, and nature 

 will have none of them. 

 Her own creations, while 

 often far more curious and 

 extraordinary than any of 

 these, differ from them all 

 in the one essential quality 

 of fitness. 



This then, in brief, is the 

 doctrine of natural selec- 

 tion, as a partial explana- 

 tion of the process of evo- 

 lution. Heritable varia- 



FIG. 169. Standard varieties of 

 chickens (after Rice). 



