458 EVOLUTION, GENETICS, AND EUGENICS 



peculiarities of the environment which influence the development of 

 somatic characters so affect the germ cells that they will produce these 

 somatic characters in the absence of the peculiar environment ? Can 

 the characteristics of a developed organism enter into its germ cells 

 and be born again in the next generation ? Considering the fact that 

 germ cells are cells and contain no adult characteristics, it seems very 

 unprobable that any peculiarity of environment whether of nutri- 

 tion, use, disuse or injury, which brings about certain peculiarities of 

 developed characters in the adult, could so change the structure of the 

 germ cells as to cause them to produce this same character in subse- 

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

 example, 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 nourished ? 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 lead 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 inheritance 

 of acquired characters, there are many special difficulties. 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. 



There still remains the question of the inheritance of certain 

 characters due to enviroiunent, though here also the most clear-cut 



