154 THE PRINCIPLES OF HEREDITY 



demies are known to have occurred in the Old World, none 

 were so terrible as those recorded in the New. Perhaps 

 nothing demonstrates the low resisting power of races that 

 have undergone no evolution against small-pox so clearly as 

 the fact that a party of Esquimaux, who were taken to 

 Berlin and vaccinated there, perished of the attenuated form 

 of the disease. 1 Most even of our little children are able to 

 recover from the unmodified form. 



258. Dysentery, Diarrhoea, Enteric Fever, etc. Malaria, 

 tuberculosis, measles, whooping-cough, and small-pox afford 

 ample proof that man's present evolution is mainly against 

 disease ; and moreover, that in different countries the direc- 

 tion of the evolution is different because different diseases 

 differently determine it. Similar evidence is afforded by 

 the study of a host of other diseases, for these like malaria 

 and tuberculosis are invariably more fatal to strangers from 

 beyond their areas of distribution, than to races that have 

 long dwelt within the districts they infest. But, since few 

 diseases are so prevalent within their areas of distribution, 

 or so fatal as malaria or tuberculosis, evolution against few 

 others is so clearly marked as against them. Moreover most 

 other very prevalent and fatal diseases against which con- 

 siderable evolution has occurred are those affecting the 

 alimentary tract that is, are those in which, generally 

 speaking, infection depends on the character of the food and 

 water-supply, especially the latter ; and, therefore, as regards 

 them, since strangers who enter the infected districts are 

 usually Europeans, more careful as to their food and water 

 than the natives of Africa and Asia, where these diseases 

 chiefly prevail, they usually suffer from them less in pro- 

 portion to their susceptibility than the natives. For instance, 

 Europeans actually suffer less from cholera in India than do 

 the natives, though their great susceptibility is proved by 

 the history of the various pandemics during which the 

 disease has overpassed its normal boundaries and ravaged 

 Europe. It is therefore difficult to estimate with any degree 

 of accuracy the extent of the evolution undergone by races 

 that have had extended and disastrous experience of these 

 diseases, for we cannot with accuracy contrast them with 

 races that have had little or no experience of them, and, 

 therefore, have undergone little or no evolution in relation 

 to them. Nevertheless in all publications in which the 

 subject is alluded to official reports, medical works, travels, 

 and so forth we continually meet statements, collectively so 



1 The Scottish Medical and Surgical Journal, April 1900, p. 330. 



