254 THE CAUSATION OF DISEASE. 



has resulted from interference with natural selection must 

 tend to lower the health standard. It therefore behoves us 

 to compare the process as at work in man at present and in 

 the lower animals. 



The weeding-out process is quite as rigorous among savages 

 as among many, at least, of the lower animals. This is at 

 once obvious, for savage races do not increase in number, and, 

 inasmuch as they are highly prolific, a very active weediug-out 

 must occur. No doubt the population is largely kept down by 

 infanticide, but we may be quite sure that there is in the main 

 a " survival of the fittest." The process, I say, is as rigorous 

 among savages as among many of the lower animals ; but, since 

 man does not tend to multiply at the same rate as most of 

 these, fewer human beings need die prematurely than is the 

 case with the animals that very rapidly multiply. 



In those communities whose population is increasing, the 

 process of elimination must necessarily be least rigorous ; and 

 this is the case with most civilized peoples. 



In some few civilized countries, and notably in France, the 

 population is kept at a standstill by a careful regulation of the 

 births on the part of the parents. The tendency of this, as 

 we shall see in the next chapter, is probably to lower the 

 standard of health and to hinder the evolutionary process. 



There is no analogy between a stationary population such as 

 that of France and the population of a savage community, 

 because, in spite of infanticide frequently checking the operation 

 of natural selection in the latter, a larger number of children, 

 in proportion to the population, are permitted to grow up than 

 in a country like France, and an active elimination occurring 

 among the adults by warfare and so forth, natural selection is 

 permitted to operate there. Moreover, among many savages 

 the practice of infanticide is unknown ; in which case the 

 population is kept down by continual warfare, and it is chiefly 

 the inferior who are destroyed. 



The cause of the increase in the population of civilized com- 

 munities lies in the altered E. Whereas savages do little or 

 nothing to increase the natural food supply, civilized peoples 

 exert themselves to the utmost to make the yield as large as 

 possible by tilling the soil, rearing live stock, &c. ; and, taking 



