Improvement through Variation 155 



The tendency to vary is transmitted from pa- 

 rents to progeny in the same way that other pecu- 

 liarities are transmitted. This has often been of the 

 greatest importance in the improvement of fowls, 

 mammals and plants. Breeders who are trying 

 to improve their stock are continually endeavoring 

 to bring the law of heredity into force so far as 

 desirable characteristics are concerned, and as 

 continually striving to prevent the operation of 

 the law so far as undesirable characteristics are 

 concerned. 



The fact that animals vary permits of an indi- 

 vidual being an improvement on its parents. If 

 this individual is allowed to transmit its good char- 

 acteristics, improvement may be attained. With- 

 out progressive variation breeders could not secure 

 improvement. Probably all they could do would 

 be to prevent deterioration. 



If a breeder is trying to improve his . flock, he 

 looks closely for those individuals that show the 

 greatest tendency to vary. These individuals he 

 selects for breeding stock. He finds that their 

 young vary considerably. They do not closely 

 resemble each other, nor do they closely resemble 

 their parents. If an abundance of good food and 

 congenial surroundings be provided, he may expect, 

 in the course of a few generations, that some indi- 

 viduals will show a marked tendency to vary in 

 the direction of improvement. By judicious mating, 



