THE ROOTS OF EMPIRE 41 



Stone Age they can have afflicted mankind but 

 little. But, for thousands of years, certain areas of 

 the Old World, China, India, and the Coasts of the 

 Mediterranean, have been thickly populated. In 

 ancient, as in modern cities, the wholly-parasitic 

 diseases took toll in human lives, and age after age 

 eliminated the unfittest. Our oldest records tell of 

 plague and pestilence, of water- and air-borne dis- 

 eases. With the advance of civilisation, as cities 

 enlarged and multiplied, as the densely populated 

 areas widened, the tendency to Disease Selection 

 increased. The conditions became more and more 

 favourable to the spread of infectious disease. 

 Sanitation has done something in England, yet, 

 even now, measles and consumption, for instance, 

 are so prevalent, that no man escapes the chance 

 of infection. Evolution against purely parasitic 

 diseases has proceeded very far. We speak of the 

 West Coast of Africa as having a deadly climate. 

 It is deadly to us, who have not undergone evolu- 

 tion against malaria. But just as deadly is the 

 climate of our own great cities to races that have 

 undergone no evolution against consumption and 

 measles. Polynesians and Esquimaux, for instance, 

 perish as surely in London as Englishmen in West 

 Africa. To judge by analogy, our ancestors of the 

 Stone Age must have been as susceptible to measles 

 and consumption as Red Indians and Polynesians 



