THE COMING OF EVOLUTION 229 



In civilized states, it is probable that the most 

 effective selective agent is disease. Those specially 

 liable to any particular weakness tend to die early 

 and leave no offspring. Thus, the hereditary predis- 

 position to the complaint is bred out of the race. 



But, in order that natural selection should be 

 effective, it is necessary that successful survival 

 should be accompanied by preponderating repro- 

 duction. From the point of view of the race, it is 

 of no use for the higher types of men to survive if 

 they do not leave children to inherit their qualities. 

 Hence the power of voluntarily restricting the birth- 

 rate, which has become a marked feature of European 

 civilization since 1876, has modified fundamentally 

 the biological problems of sociology. The thrifty and 

 far-seeing in all ranks of life now tend to restrict closely 

 the number of their children. Their average family 

 has sunk from over six to about three, and shows 

 signs of further diminution. On the other hand, the 

 careless and improvident, and, still more ominous, 

 the mentally weak, still breed at nearly their old 

 natural rate ; while, owing to the advance of modern 

 scientific hygiene, they have a greatly diminished 

 death-rate, and rear a high proportion of decadent 

 citizens. The good hereditary qualities of the race are 

 threatened with decay. It is probable that nothing 

 short of the religious motive, which is certainly 

 effective among many Jews and Roman Catholics, 

 will suffice to reverse these tendencies of the better 

 stocks. In this way, religion would acquire once more 

 an effective survival value. 



When we pass to the bearing of Darwin's work on 

 theories of politics, no consensus of opinion has been 



