What are Acquired Characters? 317 



a strict sense as exclusive results of environment. Yet even 

 in such acquirements it is obvious that an identical environ- 

 ment cannot produce the same results in different types of 

 individuals. 



Organisms are modified by cutting off tails or limbs, 

 piercing eyes or ears, repressing growth through under- 

 nourishment or drouth, distorting structures through cramp- 

 ing by corsets, shoes, head-boards. Such changes, however, 

 are not strictly speaking modifications in any organic sense. 

 They were not so considered by Lamarck, although uncrit- 

 ically accepted as such by many of his followers as well 

 as by opponents of his theories. Yet the moment we seek 

 for a true example of organic modification — one due, 

 that is, to the dynamic responsiveness of living matter — 

 we have to revise our antithesis between heredity and en- 

 vironment. 



The minnow inherits the capacity to develop into a 

 two-eyed fish. That is true but it can become a two-eyed 

 fish only in a certain kind of ocean. In a different environ- 

 ment it becomes normally, that is, because of its inherited 

 constitution, a one-eyed fish (see page 172). A human 

 infant is born with the capacity to develop a certain 

 grade of intelligence. It can attain to that intelligence 

 only in a special kind of environment — including iodin 

 salts and social stimuli. We discover what is " normal " 

 from the occasional appearance of abnormalities. Un- 

 der routine conditions we take for granted that varia- 

 tions are due to " heredity." Differences which appear after 

 the diffusion of a homogeneous population into a variegated 

 environment are attributed to the latter. The essential fact 

 that stands out is this: The characters actually present repre- 

 sent the reaction of a given heredity to a given environment. 

 The identities observed generation after generation depend, 

 as Weismann argued, upon the common source in a con- 

 tinuous stream of specific germ plasm; but these repeated 

 identities are possible only in a uniform environment (that 

 is, uniform with respect to the essential factors) . 



