CHAPTER VI 



THE PRINCIPLE AS MANIFESTED IN 

 HUMAN SOCIETY 



IN applying the principle to human society it will be well 

 to set forth certain general rules embodying the results 

 we should expect to find. The principle is that the 

 degree of fertility at any given moment will be inversely 

 proportional to the intensity of the nervous charge. 

 This requires a qualification similar to that found necessary 

 in applying it to the vegetable world ; but in human 

 society the qualification is only likely to become operative 

 in actual famine conditions. As these are very rare, it 

 will be possible, for practical purposes, to ignore the 

 qualification and consider the degree of fertility as varying 

 inversely with the development of nervous energy. We 

 have seen that the factors which make for a high develop- 

 ment of nervous energy are 



A moderate amount of physical exertion. 



A plentiful diet rich in nutriment in proportion to its 

 bulk, and rich in proteids. 



A bright and bracing climate. 



A bright and cheerful environment generally, with 

 plenty of mental stimulation. 



From these may be deduced the following general 

 rules to which we may expect the facts to conform, 



Generally speaking, the birthrate and the deathrate 

 should rise and fall together. 



