DISEASE IN RELATION TO HUMAN EVOLUTION 491 



are a menace to Europeans, to whom it is carried by 

 mosquitoes. In New York State the expectation of 

 life for a negro is very much less than that for a member 

 of the white race. This is doubtless due in part to 

 differences in susceptibility to cold and other climatic 

 factors, as well as to differences in power to resist par- 

 ticular diseases. 



4. It is a singular fact that in the struggle between Bacterial 

 allied species or races, the existence of a bacterial th 

 disease brought by one of the participants may mean of races 

 the destruction of the other. This appears to be equally 

 true among plants, animals, and man. Thus the 

 chestnut-blight disease, tolerated by the chestnut of 

 Japan, threatens the extinction of the American tree. 

 Civilized man has destroyed the native tribes of the 

 West Indies, Tasmania, and parts of Polynesia mainly 

 by communicating his diseases. His measles may be 

 more dangerous than his firearms. The adaptive 

 process described above may not take place if the 

 attack is too sudden, or if there is no resistant strain 

 within the population. The groups which now exist 

 have so far been able to leave sufficient survivors in the 

 presence of epidemic disease, but many others have 

 doubtless become extinct. 



(For additional details, see the next chapter.) 



