SOME ASPECTS OF THE BIOLOGY OF HUMAN POPULATIONS 523 



In the last period of life, from age fifty on, females are 

 rather considerably in excess of males in most hving popula- 

 tions. The exceptions to this rule, among the populations 

 listed in Table ii are Samoa, United States, Australia, 

 Canada, Union of South Africa (whites), British India, 

 Brazil Bulgaria. The fact that, in general, females 

 have a greater longevity than males accounts for their 

 usually greater frequency in the living population at ages 

 from fifty years on. 



Turning now to the age distribution of living populations 

 it appears that, on the average, approximately a half of the 

 population of living males falls between the ages fifteen and 

 forty-nine inclusive. Thirty five per cent are under fifteen 

 years of age and 15 per cent are fifty years of age or over. 

 For females the corresponding average percentages are 

 51, 33, and 16. 



Among the different populations the greatest variation is 

 found in the percentage of the total population under fifteen 

 years of age. In this age group the effects of differences in 

 both natality and mortality are directly felt. 



The age distribution of living populations has much more 

 than merel}^ statistical interest. Figure i shows in graphic form 

 the average situation documented in Table 11. 



Practically no children below the age of fourteen are 

 completely self-supporting by their own effort. A large 

 proportion of persons above fifty also are not, by their own 

 efforts at those ages. The half of the population between the 

 ages of fifteen and forty-nine has to support a large part 

 of the rest of the population as well as themselves. This 

 burden includes both direct expenditure at the time, that is 

 while they are under fifty, and also savings for their own 

 old age, when they can no longer work. This extraordinary 

 overlapping of generations characterizes human populations 

 to an extent perhaps not equalled in any other living form. 

 It is a factor of profound importance in their biology. The 

 tremendous burden depicted in Figure i is borne by mankind 

 for reasons in part emotional. We (in a statistical sense) 

 care for our offspring and our parents beyond the time 

 limits of biological necessity in good part because we want to. 

 But for this satisfaction we pay a high price. 



