396 AGRICULTURE. 



of the characteristics mentioned as unexpected 

 the difference would be called spontaneous or 

 extraordinary variation, and might result from 

 many different causes. 



Animals that have been bred for a long time 

 with a certain type in view are more likely to 

 produce animals of that type than are those 

 animals that have come to this desired type by 

 differing greatly from their parents. Thus, one 

 of the values of pure-bred animals is their 

 ability to reproduce themselves with a greater 

 degree of accuracy than animals which have not 

 been bred pure. 



1. Atavism. It sometimes happens that ani- 

 mals are born with one or more characteristics 

 which were not possessed by their parents or 

 grandparents, but which were possessed by 

 their ancestors many generations prior to their 

 existence. This inborn tendency of animals to 

 revert to their original type is called atavism, or 

 reversion. 



2. Ordinary Variation, for the most part, is 

 caused by some of the many factors of environ- 

 ment. Among these factors are food, climate, 

 soil, exercise and general management. Food 

 is one of the most important among them. 

 Ample food supply is necessary to the maximum 

 growth of animals, yet overfeeding leads to 

 sterility and lack of vitality in offspring. A 

 striking example of the effect of nutrition upon 



