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7. In looking for the causes of this differential increase as 

 between various sections of the population, we have to remember 

 that, in accordance with what has been said in the last chapter, 

 we suppose the position in regard to population in the nation as 

 a whole to be ruled by economic factors. If there is an increase, 

 then we suppose that increase to be somewhere about that which 

 the economic situation demands in order that the greatest income 

 per head should be gained. It follows that generally speaking 

 the conditions we find among the mass of the industrial population 

 excluding the lowest class approximate to those which are de- 

 manded ; but it is possible that, just as the increase among the 

 lowest class is excessive, so the increase among the higher social 

 class may be too small judging from the economic standpoint. 

 We have here to ask what factors there are which bring about 

 a lower fertility among the upper classes, recollecting that this 

 low fertility may not be wholly due to an approximation to 

 economic requirements, but may represent a failure in adjusting 

 increase to the economic situation. 



Among the factors which bring about a low fertility in these 

 classes, those connected with differences in education and the age 

 at which the maximum income is obtained are the most important. 

 Education is continued in these classes up to an age at which 

 men in the industrial classes are earning almost the maximum 

 wage to which they will ever attam. Even when education in 

 the ordinary sense of the word is finished, there usually follows 

 a period when the salary gained is low, or when perhaps a premium 

 has to be paid in order to obtain a start in whatever profession 

 is chosen. Doctors and barristers seldom begin to earn until some 

 years after their education is complete. Further, when they do 

 begin to earn, the income is often for many years low, and may 

 in some cases not reach the maximum until late in life. Among 

 the industrial population conditions are wholly different, and 

 the maximum rate of wages is soon reached. Whatever forces, 

 therefore, may be playing upon the industrial population, 

 there are in addition the above forces playing upon the 

 professional classes which account for the lower rate of increase 

 among them. 



There are also many other factors at work in the same direction. 

 In the life led by the upper social classes there are more numerous 

 ways in which the desire for relaxation, change, and pleasure may 



