348 HEREDITY AND ENVIRONMENT 



browse on trees because he has by inheritance 

 a long neck? Did attempts to fly lead to the 

 development of wings in birds, or do birds fly 

 because heredity has given them wings? Did 

 life in caves make cave animals blind, or did 

 blind animals resort to caves because the strug- 

 gle for existence there was less severe for them? 

 The evidence is in favor of the second of each 

 of these alternatives rather than of the first. 



There still remains the question of the inheri- 

 tance of certain characters due to environ- 

 ment, though here also the most clear-cut 

 evidence is against this proposition. That un- 

 usual conditions of food, temperature, moist- 

 ure, etc., may affect the germ cells so as to 

 produce general and indefinite variations in 

 offspring is probable, but this is a very different 

 thing from the inheritance of acquired char- 

 acters. The germ cells being a part of the 

 parental organism may be modified by such 

 changes in the environment as affect the 

 body as a whole, they may be well nourished 

 or starved, they may be modified by changed 

 conditions of gravity, salinity, pressure, tem- 

 perature, etc., and these modifications of the 



