Influence of Environment 249 



inheritance of acquired characters due to use, disuse, or external 

 environment and the crude mechanisms proposed for such inheri- 

 tance are not confirmed by these experiments. It remains to be 

 seen whether the more subtile" influences of the internal environ- 

 ment, such as hormones, anti-bodies and enzymes may affect the 

 germplasm in a specific manner, and thus modify inheritance. 



In conclusion : ( i ) Developed characters, whether "acquired" 

 or not, are never transmitted by heredity, and the hereditary con- 

 stitution of the germ is not changed by changes in such charac- 

 ters. (2) Possibly environmental stimuli acting upon germ cells 

 at an early stage in their development may rarely cause changes 

 in their hereditary constitution, but changes produced in somatic 

 cells do not usually, if ever, cause corresponding changes in the 

 hereditary constitution 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 be stained with 

 fat stains and the generation to which they give rise be similarly 

 stained ; they may be poisoned with alcohol or modified by unusual 

 temperature and such influence may be carried over to the next 

 generation without becoming hereditary. All such cases are 

 known as "induction" and many instances of the supposed in- 

 heritance of acquired characters come under this category. (4) 

 Environment may profoundly 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 



