46 A STUDY IN HEREDITY 



merce which then sprang up, in the very path of 

 infection. The natives of tropical America seem 

 destined to survive. Defended Hke West Africans 

 by virulent malaria, they are not brought into such 

 close contact with Europeans, who cannot, as 

 colonists, spread over the country in millions, as 

 in North America and Australasia. Consequently, 

 though their races have suffered gready from 

 measles, small-pox, and other air-borne diseases, 

 yet from consumption, the most death-dealing of 

 all diseases, they have suffered comparatively little 

 — so little that the disease selects, and, therefore, 

 does not exterminate. They owe their salvation, 

 besides, to the smallness of their communities, 

 and to the fact that the warmth of the climate 

 renders pleasant the admission of plenteous air 

 to their dwellings. 



See then how the matter stands. Were acquire- 

 ments heritable, races that had longest been afflicted 

 by malaria or consumption would be the weakest 

 against them. In that case malaria, the microbes 

 of which are mainly saprophytic, would destroy 

 all human life within the areas infected by them. 

 Consumption, the microbes of which are entirely 

 parasitic, mainly on man, would render all dense 

 populations, and therefore all civilisation, impossible. 

 But to rise to the full height of this great argument 

 consider, in this relation, the position of the Anglo- 



