HEREDITY AND VARIATION 



259 



isolate certain characters and by proper selection to breed varieties 

 which have these desired characters, instead of waiting for a chance 

 union of the desired characters by nature. 



Animal Breeding. — It has been pointed out that the domesti- 

 cation of wild animals, the horse, cattle, sheep, goats, and the dog, 

 marked a great advance in civilization in the history of the earth's 

 peoples. As the young of 

 these animals came to be 

 bred in captivity the peo- 

 ples owning them would 

 undoubtedly pick out the 

 strongest and best of 

 the offspring, killing off 

 the others for food. Thus 

 they came unconsciously 

 to select and aid nature 

 in producing a stronger 

 and better stock. Later 

 man began to recognize 

 certain characters that he 

 wished to have in horses, 

 dogs, or cattle, and so by 

 slow processes of breeding 

 and " crossing " or hy- 

 bridizing one nearly allied 

 form with another the 

 numerous groups of do- 

 mesticated animals began 

 to appear. 



In Darwin's time ani- 

 mal breeding was so far 

 advanced that he got his 

 ideas of selection by na- 

 ture in evolution from the artificial selection practiced by animal 

 breeders. A glance at the pictures will give some idea of the 

 changes that have taken place in the form of some animals 

 since man began to breed them a few thousand years ago. 



What has resulted from artificial selection 

 among dogs. (After Romanes.) 



