INFLUENCE OF ENVIRONMENT 347 



hypertrophy of the heart, so affect the 

 germ cells that they, in turn, would produce 

 hypertrophied hearts in the absence of over- 

 exertion, seeing that germ cells have no hearts ? 

 Or how could the loss or injury of eyes or 

 teeth or legs lead to the absence or weakened 

 development of these organs in future genera- 

 tions, seeing that inheritance must be through 

 germ cells which possess none of these 

 structures ? 



But, apart from these general objections to 

 the doctrine of the inheritance of acquired 

 characters, there are many special difficulties. 

 There is no conclusive and satisfactory evi- 

 dence in favor of such inheritance. Almost all 

 the evidence adduced serves to show only that 

 characters are acquired, not that they are 

 inherited. 



It is a matter of common observation that 

 mutilations are not inherited; wooden legs do 

 not run in families, although wooden heads do. 

 The evidence for the inheritance of peculiari- 

 ties due to use or disuse is wholly inconclu- 

 sive; for example, did the giraffe get his long 

 neck because he browsed on trees, or does he 



