SOME ASPECTS OF THE BIOLOGY OF HUMAN POPULATIONS 525 



tioii of the burden is altered, not its total drag. Consider, for 

 example, the population of France, which is not far from 

 the condition technically called "stationary" by statisticians. 

 France has shghtly less than a quarter of its living population 

 under fifteen, in place of the average 35 per cent. But on the 

 other hand she has almost exactly 25 per cent of her popula- 

 tion aged fifty or over. So once more each of the potentially 

 actively working fifty per cent has one extra mouth to feed 

 besides his or her own, in whole or in part. 



Consider another case. The native population of Greenland 

 is not particularly soHcitous about keeping its old people 

 aHve after they are unable to fend for themselves and earn 

 their own keep. Eskimos of advanced age are hard to find, 

 on the testimony of all Arctic travellers. But does this materi- 

 ally reduce the burden in total on the workers? It does not. 

 For while, according to the figures of Table 11, only about 

 8.5 per cent of the living population of Greenland is fifty 

 years or over in age, something over 40 per cent are children 

 under fifteen. 



The figures of Table 11 give us a glimpse of one of the 

 most important elements of the biology of human groups 

 or populations. This is the principle of self-regulation. 

 Self-regulation of the individual organism, in its regeneration 

 and in its physiological and morphological processes gener- 

 ally, has long been familiar to the student of biology. It is 

 also one of the most striking and important phenomena in 

 group biology, or the biology of populations. 



In the next section we shall consider this matter more 

 particularly. 



THE SELF-REGULATION OF HUMAN POPULATIONS IN SIZE 



The primary biological variables involved in the growth 

 of population are two in number; natality, measured by the 

 birth rate, on the one hand; and mortality, measured by 

 the death rate, on the other hand. These primary elements 

 are fundamental to the discussion of the growth of popu- 

 lations of any and all organisms whatever, from ameba to 

 man. In most of the lower organisms hving in a state of nature, 

 whether plant or animal, these are the only first-order 



