THE MIGRATIONS OF NEGROES 265 



The statistics unused are those published by Departments of 

 Public Health, which, especially in the conquests and colonies of 

 Europeans, show clearly the real effects which have flowed from 

 racial experience of disease. 



439. It is hardly necessary to quote evidence that races are 

 resistant to diseases in proportion to their past experience of 

 them. 1 The evolution of negroes against tuberculosis, however, is 

 so very illuminating and typical that it is worth while to devote a 

 paragraph to it. There are no accounts of negro conquests outside 

 the limits of Africa, but from very ancient times a constant stream, 

 of slaves has passed to Southern Europe and Asia, where they 

 have been employed mainly in domestic service, and in more 

 recent times to America, where their principal occupation has been 

 agriculture. The invasion of Asia has continued to our own day ; 

 but, notwithstanding the great antiquity and volume of the stream, 

 one may search from Spain to the Malay Peninsula, and, except in 

 recent importations, find no trace of a negro ancestry. Yet slaves 

 like cattle are valuable property, more cheaply bred than imported. 

 In Eastern countries they have often been kindly treated, and 

 many have achieved wealth and power. Yet they all perished in 

 a few generations, the elimination of the unfit being so stringent 

 as to cause extinction, not evolution. A permanent, colony of 

 native Africans in the midst of an ancient tuberculosis-infested 

 civilization is impossible. The fate of negro migration into 

 America has been different. The race had undergone some 

 evolution against tuberculosis in Africa, and therefore was more 

 resistant than the vanishing aborigines. In its new home, 

 employed in agriculture in a hot climate where white men and 

 tubercle bacilli, also recent importations, were yet few in number, it 

 was placed under the best conditions possible. Gradually, as the 

 stringency of selection waxed, it evolved increasing resisting power. 

 To-day the descendants of the migrants have undergone such an 

 extent of protective evolution that they are able to dwell even in 

 North American and European cities, though it is still said of 

 them that "every other adult negro dies of consumption." 



1 The reader who requires evidence will find it in convincing quantities in my 

 work, The Principles of Heredity, chapter xi. 



