2 



GENETICS 



breeding animals and plants with an insight denied 

 to breeders of preceding centuries. 



The study of the origin of the individual, which 

 has grown out of the more general consideration of 

 the origin of species, forms the subject-matter of 

 heredity, or, to use the more definitive word of Bate- 

 son, of genetics. 



It is not with the individual as a whole that 



HER! T A G E 



Fig. 1. — The triangle of life. 



genetics is chiefly concerned, but rather with char- 

 acteristics of the individual. 



Three factors determine the characteristics of an 

 individual, namely, environment, training, and heri- 

 tage as expressed diagrammatically in Figure 1. It 

 may indeed be said that an individual is the result 

 of the interaction of these three factors since he 

 may be modified by changing any one of them. 

 Although no one factor can possibly be omitted, the 

 student of genetics places the emphasis upon heritage 

 as the factor of greatest importance. Heritage, or 



