332 READINGS IN 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 
improbable 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 environment, though here also the most clear-cut 
