172 THE PRINCIPLES OF HEREDITY 



the general evolution against disease was not so advanced.i 

 Thus, while many adult Englishmen are able to resist 



1 Of course what is true of disease in general is even more true of 

 disease in particular. Young individuals are much less resistant to a 

 disease against which their race has undergone evolution than older 

 people. This is notoriously true of phthisis in England. Many West 

 African children perish of malaria, but, speaking comparatively, very few 

 adults. The high proportionate death-rate from malaria of native 

 children, and the fact that West Indian Negro soldiers suffer more at the 

 beginning of their residence in Africa than later, has led Koch and 

 other writers to suppose that no race is more resistant to malaria than 

 any other race ; that resisting power to malaria is purely an acquire- 

 ment ; and, therefore, that malarious countries are as suitable for 

 residence to properly "seasoned" Europeans as to the natives. The 

 real truth is, however, that individuals of races that have been long and 

 severely afflicted by malaria are able to acquire immunity much more 

 easily thanjindividuals of races that have been less, or not at all, afflicted. 

 Malaria occupies a position midway between such diseases as tuber- 

 culosis and such diseases as measles. Because permanent immunity 

 against malaria is only slowly and partially acquired, races afflicted by 

 the disease have undergone an evolution of inborn resisting power ; but 

 because it is possible to acquire a considerable degree of immunity there 

 has been an evolution of the power of acquiring immunity as well. It 

 is an undoubted fact that white people find it difficult, even under the 

 best conditions obtainable, to rear families on the West Coast. The 

 writer has in his possession a letter from Captain Henry Eckersley, who 

 died from malaria after three seasons on the West Coast. In it that 

 very brilliant soldier, whose death was so great a loss to his profession, 

 states that when his regiment of West Indian Negroes first arrived on 

 the Coast, both the white officers and the men suffered greatly ; but that, 

 after a single season, the men acquired immunity, whereas the officers 

 continued to suffer as much as ever. The following from Miss Mary 

 Kingsley is very much to the point : 



"Yet remember, before you elect to cast your lot with the West 

 Coasters, that 85 per cent, of them die of fever, or return home with their 

 health permanently wrecked. Also remember that there is no getting 

 acclimatized to the Coast. There are, it is true, a few men out there 

 who, although they have been resident in West Africa for years, have 

 never had fever, but you can count them upon the fingers of one hand. 

 There is another class who have been out twelve months at a time and 

 have not had a touch of fever ; these you want the fingers of your two 

 hands to count, but no more. By far the largest class is the third, 

 which is made up of those who have had a slight dose of fever once a 

 fortnight, and some day, apparently for no extra reason, get a heavy 

 dose and die of it. A very considerable class is the fourth those who 

 die within a month or a fortnight of going ashore. 



"The fate of a man depends solely on his power of resisting the 

 so-called malaria, not in his system becoming immuned to it. The first 

 class of men I have cited have some unknown element in their constitu- 

 tions that renders them immune. With the second class the power of 

 resistance is great, and can be renewed from time to time by a spell 

 home in a European climate. In the third class the state is that of 

 cumulative poisoning ; in the fourth of acute poisoning." (Travels in 

 West Africa, pp. 526-7. Macmillan and Co.) Natives in countries in 



