THE PURPOSIVE IMPROVEMENT OF THE HUMAN RACE 57 1 



Likewise traits that occur repeatedly in the same family 

 and under various environmental conditions are certainly 

 inherited, and this is true not only of physical traits but 

 also of psychical ones. In the case of dogs the type of behavior 

 characteristic of different breeds is as certainly inherited 

 as is their physical form. There is good evidence that the 

 same is true of different breeds of men. Some famiHes are 

 predominantly highly emotional, others stohd; some intel- 

 lectually brilhant, others stupid; some contain many feeble- 

 minded individuals, others many that are insane. Where 

 such traits are repeated in several members of a family 

 and under various environmental conditions there can 

 be no doubt that they are inherited. By the very defini- 

 tion of racial or family traits they are inherited; otherwise 

 they are not racial or family traits. 



It is only when we come to the individual differences 

 that appear in members of the same race or family that 

 questions arise as to whether they are hereditary or environ- 

 mental. Children of the same family may be male or female, 

 tall or short, hght or dark, cheerful or morose, wise or foohsh. 

 and therefore it was formerly held that such individual 

 differences must be the results of differences in early environ- 

 ment, since all children of the same parents were once 

 supposed to have the same heredity. But since the redis- 

 covery of Mendel's law in 1900 we know that each parent 

 transmits only half of his or her inheritance factors to children 

 and ahnost never the same combination of factors. Of 

 course parents can never transmit factors which they 

 do not possess and consequently "the inherited nature 

 of the offspring is determined by that of the parents until 

 men gather grapes of thorns or figs of thistles." (Bateson, 

 192 1). 



Individual differences, therefore, may be caused by 

 new combinations of inheritance factors and very rarely 

 by new mutations of those factors, or by modifications 

 of the environment; sometimes only a study of large numbers 

 of individuals of the same stock and under varying environ- 

 mental conditions will reveal whether these differences are 

 hereditary or environmental. 



