306 Heredity and Environment 



It practically denies development altogether. If the germ is a 

 closed system and receives nothing from without, and if adult 

 characteristics are predetermined in the germ, they are as irre- 

 vocably fixed as if they were predelineated. 



At the opposite extreme is the old voluntaristic view of abso- 

 lute freedom and absolute responsibility. This view, like the old 

 epigenesis, virtually postulates a new creation for each individual. 

 As far as the mind and soul are concerned there is no hereditary 

 continuity with past generations and none with future ones. But 

 while such a view may be logically complete and theologically 

 satisfying, it is not scientific, for it also contradicts the evidence. 



The truth then seems to lie somewhere between these two ex- 

 tremes. Our personalities were not absolutely predetermined in 

 the germ cells from which we came, and yet they have arisen 

 from those germ cells and have been conditioned by them. When 

 it is said that any characteristic is predetermined in the germ cell, 

 what does this mean? What but that the development of that 

 characteristic is made possible? Adult characteristics are poten- 

 tial and not actual in the germ, and their actual appearance de- 

 pends upon many complicated reactions of the germinal. units with 

 one another and with the environment. In short, our actual per- 

 sonalities are not predetermined in the germ cells, but our pos- 

 sible personalities are. 



2. The Determinism of Environment. This determinism of 

 heredity is matched by a corresponding determinism of environ- 

 ment. Life is possible only within rather narrow limits of physi- 

 cal and chemical conditions and in the main these limits are 

 'fixed by the constitution of nature. But apart from these ante- 

 cedent conditions of life in general there are many minor condi- 

 tions of environment which exercise a profound influence upon 

 organisms, especially in the course of their development. Very 

 slight changes in food, temperature, moisture and atmospheric 

 conditions may produce great changes in the developing organ- 

 ism, and these conditions are for the most part entirely beyond 

 the control of the individual affected. 



