218 EVOLUTION, GENETICS, AND EUGENICS 



Exactly what, then, is inherited? A certain complex of genes and 

 a certain cytoplasmic organization are all that can be said to be in- 

 herited. These heritages are to be conceived of as potentialities cap- 

 able of working with the environment to produce individuals with 

 certain particular characters. Individuals will differ from one another 

 partly because the materials constituting the zygote are different and 

 partly because their environments are different. To what extent 

 heredity and environment determine individual differences we must 

 not attempt to decide at present. We shall be in a much better posi- 

 tion to deal with this problem after we have discussed the other factors 

 of the evolution mechanism. 



