SOME BIOLOGICAL ASPECTS OF THE POPULATION PROBLEM

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Abstract
Summary: 1. The logistic curve which Pearl has applied to the growth of populations of the fruit fly is the law of an experiment carried out under certain restrictions. The assumptions from which the law can be deduced are assumptions whose biological significance is problematical. Their sociological relevance is obscure. There is no sound reason to believe that the decline in European birth‐rate is the expression of a universal law governing the growth of populations. No known biological data conflict with the view that the declining fertility of European communities is a phenomenon sui generis.2. Occupational, statistics from all countries where the birth‐rate has fallen indicate a differential decline. To estimate the genetic significance of differential fertility existing methods are inadequate, and new methods for the detection of genetic differences in social behaviour are required. There are some indications that differential fertility is an ephemeral feature of present‐day conditions because the decline of the birth‐rate is extending to the labouring classes. On this view civilisation appears to be faced with the alternative of devising new incentives to parent‐hood or facing extinction through a progressive decline of population.3. There is insufficient reason to believe that improvement in infant welfare has significantly diminished the expectation of life in the later age groups—or that it is likely to do so in the immediate future.