294 THE KEGULATION OP NUMBEKS 



The question of the effectiveness of adjustment in this period 

 has been touched upon. In general it may be said that under- 

 population is rare. Under-population seldom arises and then 

 generally as a result of the abnormal incidence of war or disease. 

 It sometimes happens that for a long period an area once densely 

 populated maintains but a sparse population and this is not 

 infrequently taken to indicate under-population. But such 

 situations generally arise when for one reason or another such 

 as the destruction of capital during prolonged war, or the break- 

 down of artificial works upon which the food-supply depends 

 there has been a decrease in the density desirable. Thus the 

 Mesopotamian watercourses were neglected by the Mongol 

 conquerors in the thirteenth century and in consequence the 

 optimum number for that area declined. Such a situation should 

 therefore not be taken as indicating, without further inquiry, 

 under-population. 



Over-population is less rare. It may be due to the neglect 

 of ancient practices having as their effort the restriction of 

 increase without the taking into use at the same time of new 

 practices. This sometimes happens when a higher and a lower 

 civilization come into contact and has been one of the causes of 

 over-population in India. It may also arise when on the passing 

 away of old practices some influence may militate against the 

 taking up of new practices. In this manner the influence of the 

 Catholic Church, which has been directed against contraceptive 

 practices, may have tended to produce over-population in Ireland. 

 More commonly, however, over-population arises in this period 

 as the result of a spirit of apathy and listlessness. Under such 

 circumstances, which are usually the result of social oppression 

 or political misfortunes, no effort is made to keep up the standard 

 of living and in consequence the machinery designed to restrict 

 increase breaks down. 



Taking the third period in more detail, we have as regards 

 the last section of- that period definite evidence to the effect 

 that approximation is fairly close. There are minor fluctua- 

 tions in the nearness of approach to the desirable number. 

 That, however, which it is in any broad view of the whole 

 problem of quantity desirable to emphasize, is the nearness of 

 approach the fact that in any country at any given time 

 within this period the numbers present are, roughly speaking, 



