Influence of Environment 229 



generation? Considering the fact that germ cells are cells and 

 contain no adult characteristics, it seems very improbable that any 

 peculiarity of environment whether of nutrition, use, disuse or 

 injury, which brings about certain peculiarities of developed char- 

 acters in the adult, could so change the structure of the germ cells 

 as to cause them to produce this same character in subsequent 

 generations in the absence of its extrinsic cause. How, for ex- 

 ample, could defective nutrition, which leads to the production 

 of rickets, affect the germ cells, which contain no bones, so as to 

 produce rickets in subsequent generations, although well nour- 

 ished ? Or how can over-exertion, leading to 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 lea'd to the absence or weakened development 

 of these organs in future generations, seeing that inheritance must 

 be through germ cells which possess none of these structures? 



Lack of Evidence for Inheritance of Acquired Characters. 

 But, apart from these general objections to the doctrine of the in- 

 heritance of acquired characters, there are many special difficul- 

 ties. There is no conclusive and satisfactory evidence 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 peculiarities due 

 to use or disuse is wholly inconclusive; for example, did the 

 giraffe get his long neck because he browsed on trees, or does he 

 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 struggle 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. 



