NATURAL SELECTION 33 



to render it immune against those particular diseases. 

 When, by exploration or conquest, two races, hitherto 

 separate, came into close contact, each infected the 

 other with new diseases, against which the infected had 

 none of the protection given by centuries of stringent 

 selection. 



The classical instance is the conquest of the New 

 World by the diseases of those who followed Columbus. 

 The East was full of teeming cities, in which centuries 

 of infection had selected the most resistant stocks. In 

 the West men lived a nomad life where there was no 

 need for selective protection against the microbic diseases 

 of crowded communities. As Dr Archdall Reid says : 

 " On the one side of the Atlantic were peoples who 

 for thousands or tens of thousands of years had been 

 slowly evolving resisting power against a multitude of 

 maladies ... on the other side of the Atlantic were 

 peoples who had undergone no evolution against any 

 zymotic disease except malaria. ... At once . . . 

 diseases began to sweep in great waves of pestilence 

 over the whole vast regions of the West. The entire 

 population was susceptible ; and therefore almost- every 

 individual was stricken down. . . . Whole tribes and 

 nations were exterminated. . . . The white colonization 

 of Australasia is having similar results. In Polynesia, 

 as soon as the trader brings his clothes and the 

 missionary insists on his converts wearing them and 

 attending crowded churches and schools, the work of 

 extermination begins." 



A process, similar to that which is slowly rendering 

 the nations of the world more and more immune to 

 specific diseases, has been going on with regard to 



3 



