268 EVOLUTION OF TO-DAY. 



necessary that the trade of blacksmith should be 

 followed by the same family for many generations, 

 and who could tell at first how much the young 

 smith owed the large size of his arm to inheritence, 

 and how much to direct use ? But our American 

 scientists have collected many instances which show 

 that the effects of use are inherited. One example 

 is the shape of the teeth of ungulates. A careful 

 study has shown that the shape of the tubercles of 

 their teeth is exactly such as would have resulted 

 from the motions of their jaws. Different groups 

 of ungulates have different shaped teeth ; but the 

 motion of their jaws is also different, and the two 

 are found to be correlated. Now since these tubercles 

 appear while the animal is very young, they must 

 be due to inheritance. And since it is hardly pos- 

 sible to conceive them of enough importance to be 

 developed by natural selection, it is claimed that 

 they are instances of the inherited effect of use. A 

 number of cases of similar import have been ad- 

 vanced as proofs of the fact, so necessary for the 

 neo-Lamarckiann theory, that the effects of use and 

 disuse are inherited. 



This brings us to a final question, which really 

 lies at the bottom of the whole matter. What are 

 the laws of heredity ? What sort of characters does 

 an animal inherit from its parents? We can cer- 

 tainly find abundant variations arising either from 

 the indefinite variability of Darwin, the extraordi- 

 nary births of Mivart, or the effects of use and 

 effort. Are these variations all inherited ? The 

 final question is thus the explanation of heredity. 



