480 HEREDITY AND ENVIRONMENT 



tions of germ cells are relatively few and 

 fixed, the possible reactions of a complex ani- 

 mal are relatively many and behavior is more 

 plastic; and thus this very complexity and 

 plasticity allow adaptations to the minutest al- 

 terations of environment. 



3. Birth and Growth of Freedom. — In ani- 

 mals below man and in the stages of human 

 development one may trace the birth and 

 growth of freedom. Even in some of the 

 simplest organisms one can observe inhibitions 

 of responses and modifications of behavior 

 which seem to be due to conflicting stimuli or 

 to changes in the physiological state. In 

 higher organisms such inhibitions or modifica- 

 tions proceed particularly from internal 

 stimuli, which in turn are probably conditioned 

 by hereditary constitution and past experience. 

 The factors which determine behavior are not 

 merely the present stimulus and the heredi- 

 tary constitution, but also the experiences 

 through which the organism has passed and 

 the habits which it has formed. 



A moth cannot avoid the impulse to fly 

 toward the light, and it does not learn by ex- 



