VARIATION AND HEREDITY n 



children of apt scholars will ofttimes emulate the 

 parental achievement of " teaching themselves to read " 

 as the saying goes. It is this inborn part of a man's 

 endowment which tends to appear again in his 

 descendants. 



On the results of large numbers of measurements, 

 we find that the sons of naturally tall fathers are taller 

 than the average, and that the children of able and 

 industrious parents show a higher level of ability and 

 require less attention and expenditure of energy to 

 enable them to attain an average standard of achieve- 

 ment than do the bulk of the population. The 

 children of habitual criminals more often show vicious 

 tendencies even in youth, while the offspring of men- 

 tally defective parents are themselves feeble-minded. 

 Do men gather grapes of thorns or figs of thistles ? 



It is on these inborn variations that selection has 

 to work. Some variations will give a man an advantage 

 in the struggle for life ; some will cause him more 

 easily to succumb. In a primitive community, where 

 the forces of heredity are acting naturally, unconsciously 

 and effectively, men of the first type will tend to live 

 and beget offspring ; men of the second type will more 

 often die in infancy or youth, and either leave no 

 progeny or leave them with but precarious chances of 

 survival. Thus the more favourable variations tend 

 to appear by the process of heredity in the next genera- 

 tion, while the unfavourable variations tend to get 

 stamped out. In this way the race is continually more 

 and more moulded to fit its environment ; it is relieved 

 of the strains of blood of the failures which tend more 

 and more to become encumbrances on the better stocks, 



