3i6 Relation of Use and Disuse to Evolution 



even if they do not solve the theoretical problem presented 

 by regenerating leaves and earthworms. We do not know 

 how eggs or sperms arise in specialized tissues that seem to be 

 without embryonic or germinal cells. We do know, how- 

 ever, that the germ cells carry within themselves whatever 

 material substance or structure determines the inheritance 

 of the individual. 



What Are Acquired Characters? 



A more direct approach to Lamarckism is to be found 

 by examining actual facts. First of all it becomes necessary 

 to make more precise the distinction between " acquired " 

 characters and others — presumably inherited. A person 

 learns to play the piano; his twin brother does not. In this 

 case ability to play the piano is acquired. Disregarding for 

 the sake of the discussion the possible influence of the other 

 parent, will the children of the first play the piano more 

 easily, or learn to play more easily, than the children of the 

 second? This is the usual form of the issue. 



Is grayness of hair in old age an acquired character? Cer- 

 tainly, one is not " born with " gray hair. Is the milk pro- 

 duction of a prize cow an acquired trait? Is the pigment 

 on the upper surface of a fish, or the whiteness of the belly? 

 Are we to consider the differences between two groups of 

 plants grown from the same pod of seeds, under two sets 

 of conditions, acquired characters? Is defective bone de- 

 velopment in a rachitic child acquired? 



We could go on endlessly only to find increasing diffi- 

 culty in making the distinction between inherited charac- 

 ters and acquired ones. As we have already seen, however, 

 the distinction itself is impossible because it rests upon an 

 unsound assumption (see pages i66 ff ) . This is the assump- 

 tion that a given character in an adult plant or animal is due 

 entirely to heredity or entirely to environment. Depriva- 

 tions in the form of mutilations or injuries, and acquirements 

 in the form of habits or knowledge, may be considered in 



