314 ANIMAL BIOLOGY 



environment is one of the most important and perplexing problems 

 of the science of genetics. This is especially true in the case of 

 Man. Development is a form of behavior, and how a child develops 

 physically and mentally is determined not by its heritage alone nor 

 by its environing conditions alone, but by both in intricate com- 

 bination. (Fig. 198.) 



Although apparently we do not inherit the effects on our fore- 

 bears of their surroundings and training, nevertheless we are the 



heirs to their customs — each gen- 

 7 eration builds upon the intellectual 

 / and material foundations of all of 

 its predecessors — and this entails 

 added responsibilities as well as 

 opportunities for each succeeding 

 generation. Already in certain 

 fields the applications of science to 



Fig. 199. — Scheme to illustrate l mman affairs tax the ability of 



the contributions of nature and ^r ., . , r™ 



nurture to the make-up of the in- Man to USe them W1Sel y- ThuS 



dividual. The triangles represent 'social heredity' bids fair to out- 



various types of individuals which str i p our conservative and essen- 



mav be produced by the same germ .. n , . • i •. i 



cells (heritage) if environment and tiall y unchanging inherited nature. 



training are variable. The foun- The EUTHENIST emphasizes nur- 

 dation of the 'triangle of life' is ture> t h e EUG ENIST emphasizes na- 



heritaare. (After Conklin.) K p. .1 i 



ture. As is so olten the case, how- 

 ever, when doctrines are opposed, the truth combines both ; though 

 we cannot doubt, knowing what we know of the genetic constitu- 

 tion of organisms, that from the standpoint of permanent advance 

 — racial rather than individual — the path to progress is chiefly 

 through eugenics, the science of being well born. (Fig. 199.) 



This distinction between heritage and acquirements leaves a 

 fatalistic impression in many minds, which to a slight extent is 

 justified. We cannot get away from inheritance. On the other 

 hand, although the organism changes slowly in its heritable or- 

 ganization, it is very modifiable individually; and this is Man's 

 particular secret — to correct his internal organic inheritance by 

 what we may call his external heritage of material and spiritual 

 influences. It is therefore clear that the problem of human im- 

 provement has two aspects: in the first place, the effects of 

 culture on the individual which, though not inherited, are cum- 

 ulative from generation to generation through training; and 



