CHAPTER V 



CONTROL OF HEREDITY: EUGENICS 



It is the aim of science to interpret phenomena and as far as 

 possible to control them. To what extent is it possible to control 

 heredity and thus to improve the race, as well as the individual? 



A. DOMESTIC ANIMALS AND CULTIVATED PLANTS 



The history of domesticated animals and cultivated plants 

 shows that it is possible to control or rather guide phenomena of 

 heredity and evolution. Very many species of wild animals have 

 been tamed by man but only about 40 species may be classed 

 as domesticated. DeCandolle recognized 247 species of cultivated 

 food plants, 193 of which still exist in the wild state.* In a num- 

 ber of instances the wild stocks from which these domestic forms 

 came are known and it is possible to compare them with their 

 modified descendants and thus to determine the degree of change 

 which has been brought about under human guidance. In other 

 cases where the original wild species are unknown it is possible 

 to determine the amount of modification which has taken place 

 within recent times. 



The degree of. change which has taken place under human guid- 

 ance is very remarkable. In some cases dozens and even hun- 

 dreds of races have been formed, showing the most remarkable 

 differences in size, structure and proportion of parts, as well as 

 in functions, instincts and behavior. The extent to which hered- 



* Bailey says that more than 20,000 kinds of plants in cultivation are 

 described in the "Standard Cyclopedia of Horticulture," although not 

 nearly all of these species are domesticated. 



