Influence of Environment 237 



at an early stage in their development may rarely cause changes 

 in their hereditary constitution, but changes produced in somatic 

 cells do not cause corresponding changes in the hereditary con- 

 stitution of the germ cells. (3) Germ cells like somatic cells may 

 undergo modifications which are not hereditary; if starved they 

 may produce stunted individuals and this effect may last for two 

 or three generations; they may he stained with fat stains and 

 the generation to which they give rise he similarly stained; they 

 may be poisoned with alcohol or modified by temperature and 

 such influence be carried over to the next generation without 

 becoming hereditary. All such cases are known as "induction" 

 and many instances of the supposed inheritance of acquired char- 

 acters come under this category. (4) Environment may pro- 

 foundly modify individual development but it does not generally 

 modify heredity. 



E. APPLICATIONS TO HUMAN DEVELOPMENT: EUTHENICS 



Man's Larger Environment. — Man's environment is more ex- 

 tensive than that of any other animal, and its influence on his de- 

 velopment is correspondingly greater. In addition to chemical 

 and physical stimuli which are potent factors of development in 

 the case of all organisms, man lives in a world of psychical, so- 

 cial and moral stimuli which exert a profound influence on him. 

 He is stimulated not merely by present environment but also by 

 memories of past experiences and anticipations of future ones. 

 Through intelligence and social cooperation he is able to control 

 environment for particular ends, in a manner quite impossible 

 to other organisms. On the other hand heredity is no more pow- 

 erful as a factor of development in the case of man than in any 

 other organism. Consequently the relative importance of hered- 

 ity and environment is not the same in the development of an 

 intelligent and social being, like man of the present age, as it is 

 in lower organisms. For man and for every other living crea- 

 ture heredity fixes the possibilities of development, it "sets bounds 

 about us which we cannot pass" ; but the more complex those 



