320 Relation of Use and Disuse to Evolution 



day makes a distinction between inheriting a disease and 

 inheriting a disposition. This is a vaHd distinction even if 

 the medical profession is not in possession of all the relevant 

 facts. Tuberculosis illustrates the point because it is so 

 widepread and has been so extensively studied. If you take 

 an infant from a family that has been tuberculous for gen- 

 erations there is a chance, in favorable surroundings and 

 away from infected persons, to raise it to maturity without 

 infection. The disposition or susceptibility is there; but the 

 disease cannot manifest itself unless there is also an infection. 

 Whole communities have been decimated by an infection 

 imported from without. The end results show that the 

 people were susceptible, but they were free from the disease 

 for generations because the specific infectious agency had 

 not come into their lives. 



If a family is not exposed to infection for several gen- 

 erations we have no way of knowing its susceptibility. 

 Statistical and epidemiological facts would indicate, how- 

 ever, that resistance to a particular disease, or special sus- 

 ceptibility, is inherited. Certain factors of musical ability 

 seem to be inherited among people who have no musical 

 training, living in communities having no musical traditions. 

 Under favorable conditions — that is, suitable stimuli — 

 some of these will manifest themselves, whether the parents 

 had the opportunity to cultivate them or not. 



V roving a Negative 



One of the diflSculties with the doctrine that the results 

 of use and disuse are inherited is the circumstance that its 

 opponents are trying to prove a negative. From the nature 

 of things, this is an impossibility. It is almost as futile as 

 it would be for a monist to attempt to prove that the earth 

 was not created in six days or sixty. At the same time there 

 has been accumulated a body of facts that militate against 

 the Lamarckian assumption, and render it unnecessary for 

 logical purposes. As we have seen, the transmission of char- 



