EVOLUTION OF ANIMALS AND PLANTS 567 



the hundreds of varieties of animals and plants which are 

 raised under domestication. For example, we have dozens 

 of varieties of chickens at the poultry shows and most of them 

 are known to have descended from certain breeds ; and prob- 

 ably all of them came from one or few wild species, one of 

 which was certainly the East Indian jungle-fowl. Several 

 hundred varieties of pigeons have developed from one (or 

 possibly a few) species of wild pigeon. Numerous varieties 

 of many common plants cultivated for food, ornament, or 

 other use have been selected and improved by horticulturists. 

 In short, any one who looks through books describing the 

 numerous breeds or varieties of common domesticated ani- 

 mals and plants will not doubt the fact that organisms do 

 change. And it must be remembered that most of these 

 changes under domestication have occurred within a few 

 hundred years ; while tens of thousands of years have been 

 available for changes in wild animals and plants. 



It should be noted that man has affected animals and plants 

 under his care chiefly by selecting peculiar individuals. 

 When we speak of making a new variety of corn or a new 

 breed of cattle we simply mean that we have selected for 

 propagation certain individuals that by nature were better 

 than their relatives. For example, breeds of hornless cattle 

 have within recent years been started by selecting individuals 

 born without power of growing horns and able to transmit 

 this characteristic to their progeny. Likewise, horticulturists 

 select every year certain extra-valuable plants and from them 

 obtain seed of new varieties. With new varieties of either 

 animals or plants improvements may be made with each new 

 generation by selecting the best individuals as parents. For 

 example, the hornless cattle are now being improved rapidly 

 by selecting for propagation only those which are entirely 

 hornless and which are also excellent for milk or meat. This 

 is an illustration of the kind of selection which scientific 

 agriculturists are constantly applying to all kinds of animals 



