208 THE PRINCIPLES OF HEREDITY 



good, it must follow that the process of evolving powers of 

 resistance against measles must be much less tedious and 

 difficult than that of evolving powers of resistance against 

 malaria. Since it is more easy for the individual to acquire 

 permanent immunity against measles than against malaria, 

 the race starts from a position of comparative advantage. 

 On the other hand, since no immunity can be acquired by 

 the individual against tuberculosis, the race starts here from 

 a position of great disadvantage, and the process of evolving 

 powers of resistance must be very long and tedious. We 

 know indeed, as a fact, that races that have been greatly 

 afflicted by tuberculosis for thousands of years still suffer 

 grievously, and that when endemic it exterminates, in spite 

 of the utmost care, the races of the New World. We know 

 as a fact also, that endemic measles does not exterminate 

 New World peoples. Careful attendance on the sick reduces 

 the death-rate from it below the birth-rate. These two 

 diseases, therefore, confirm our hypothesis. Of malaria it is 

 not possible to speak positively, but the parallel appears to 

 hold good as regards it also. It is impossible, at any rate it 

 is very difficult, for Europeans, who have had little or no 

 experience of the disease, to colonize West Africa, where it 

 is most virulent ; but Spaniards and Portuguese have suc- 

 ceeded to some extent in colonizing tropical America, where 

 it is very virulent. The Creoles already display great powers 

 of resistance, as do also the descendants of the Portuguese in 

 India. 



354. It seems then, both as regards narcotics and diseases, 

 that the ease with which the race evolves resisting power 

 bears a close relation to the ease with which the individual 

 is able to acquire personal immunity. 



