BIOLOGY IN ITS WIDER ASPECTS . 1275 



genuine law of population if we could only translate it into the 

 concrete. 



As the density of an animal population begins to be very marked, 

 a check to further multiplication steps in, and we can understand 

 that automatic check because it means less food. The density of the 

 population has so increased that there is less food available, and not 

 only less food but less space to move about in. Pearl found that the 

 space at the disposal of the hens in his poultry yard made a great 

 difference. And it has been shown for various ranks of animal life 

 that the check put by the densit}^ of population on further multipli- 

 cation can be understood in terms of reduced food, lessening space, 

 and the accumulation of toxic waste products. Especially when the 

 animals are aquatic is the accumulation of toxic waste products 

 in the water an important factor. And without pursuing the subject 

 further at present, we may say that biologists are beginning to 

 understand why there should be an automatic check when a certain 

 density of population is reached . 



But what about man? Whenever we think of man we see that 

 for civilised countries density of population cannot mean the same 

 as among animals. Among animals density of population usually 

 implies scarcity of food, but man is not entirely dependent on the 

 area in which he lives. Indeed, it may be easier to feed people in 

 a crowded urban area than in a sparsely populated rural area. Thus 

 density of population does not mean the same thing for mankind 

 as among animals. Among animals the number per acre would at 

 once affect the food supply; in man this need not follow except in 

 primitive rural conditions. In fact, everything points to the con- 

 clusion that the decline of the population rate which occurs in 

 mankind is not due to biological factors except to a slight extent; 

 it is due to psj^chological and other factors of a subtler kind. 



What is to be said for the restriction of the size of the human family ? 

 In the animal kingdom the restriction of the family is always 

 associated with increased parental care and affection. So that is a 

 good lead. The lesson to be drawn from the reduction of the animal 

 family is that it tends towards a higher pitch of life, more parental 

 care, more affection, more family life in the true sense. Here is a 

 suggestion of the benefit that might follow a restriction of the size 

 of the human family: there would be more parental care and a 

 better send-off in life; there would be greater freedom of life for the 

 mother. A reduction of the population rate would also work against 

 war, for most wars have been due to over-population. It would 

 alwaj^s be working against the debacle that will be involved if the 

 world becomes over-full. Moreover, if the family were in process of 

 greater restriction than at present, more attention would be paid 

 to the serious problem of the entailment of defects. If people were 

 deliberately restricting their families, they would be a little more 



