EVOLUTION AS A NATURAL PROCESS 137 



one type of horse. With other objects in view, the 

 heavy draught horse, the spirited hackney, and the 

 agile polo pony have been severally bred by exactly 

 the same method. Among cattle many kinds occur, 

 again the products of an artificial or human selection ; 

 hornless breeds have been originated, as well as others 

 with wide-spreading or sharply curved horns ; the 

 Holstein has been bred for an abundant supply of 

 milk as an object, while Jerseys and Alderneys excel 

 in the rich quality of their milk. .Various kinds of 

 domesticated sheep and rabbits and cats also owe their 

 existence to the employment of the selfsame method, 

 unconsciously copied by man from nature ; for men 

 have found variations arising naturally among their 

 domesticated animals, and they have simply substituted 

 their practical purposes or their fancy for nature's 

 criterion of adaptive fitness, preserving those that they 

 wish to perfect and eliminating those unfitted to their 

 requirements or ideas. 



In the case of many of these and other examples, 

 wild forms still occur which seem to be like the ancestral 

 stock from which the domesticated forms have been 

 produced. All the varied forms of dogs — from mastiff 

 to toy-terrier, and from greyhound to dachshund and 

 bulldog — find their prototypes in wild carnivora like 

 the wolf and jackal. In Asia and Malaysia the jungle 

 fowl still lives, while its domesticated descendants 

 have altered under human direction to become the 

 diverse strains of the barnyard, and even the peculiar 

 Japanese product with tail feathers sometimes as long 

 as twenty feet. That far-reaching changes can be 

 brought about in a relatively short time is proved by 



