Influence of Environment 229 



generation? Considering the fact that germ cells are cells and 

 xmtain no adult characteristics,^ seems very improbable that any 

 peculiarity of environment whether of nutrition, use, disuse or 

 njury, which brings about certain peculiarities of developed char- 

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

 is to cause them to produce this same character in subsequent 

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

 tmple, could defective nutrition, which leads to the production 

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

 )roduce rickets in subsequent generations, although well nour- 

 shed? Or how can over-exertion, leading to hypertrophy of the 

 icart, so affect the germ cells that they, in turn, would produce 

 lypertrophied hearts in the absence of over-exertion, seeing that 

 jerm cells have no hearts? Or how could the loss or injury of 

 yes or teeth or legs lead to the absence or weakened development 

 )f these organs in future generations, seeing that inheritance must 

 >e 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- 

 leritance of acquired characters, there are many special difficul- 

 ies. There is no conclusive and satisfactory evidence in favor 

 if such inheritance. Almost all the evidence adduced serves to 

 how^only that characters are acquired, not that they are inherited. 



It is a matter of common observation that mutilations are not 

 nherited ; wooden legs do not run in families, althaugh wooden 

 leads do. The evidence for the inheritance of peculiarities due 

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

 iraffe get his long neck because he browsed on trees, or dotes he 

 .rowse on trees because he has by inheritance a long neck? Did 

 ttempts to fly lead to the development of wings in birds, or do 

 irds fly because heredity has given them wings? Did life in 

 aves make cave animals blind, or did blind animals resort to 

 aves because the struggle for existence there was less severe 

 or them? The evidence is in favor of the second of each of 

 hese alternatives rather than of the first. 



