Human fertility and population equilibrium.
In preindustrial settings, biological, economic, and social mechanisms caused fertility to respond to feedback signals from population size variation in such a way as to steer populations toward equilibrium levels. It is unlikely that the relevant signal was population density; more plausibly the signal was economic well being, which in turn responded to population density, among other influences. Numerous empirical studies provide persuasive evidence for such a fertility response. However, the response was relatively weak, so that populations responded only slowly to shocks. The half life of a shock-induced deviation from equilibrium was probably on the order of 70 years. Dynamic behavior of population size was discernibly affected only in the long run. Because of the presence of environmental external costs to childbearing, and because fertility response mechanisms were not necessarily intentional, the equilibrium population size and corresponding welfare need not have possessed any desirable properties. In developed countries, these equilibrating mechanisms are no longer in effect.
Lee
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University of California, Berkeley 94720.
D000818:Animals; D002980:Climate; D004463:Ecology; D005260:Female; D005298:Fertility; D006801:Humans; D008297:Male; D015233:Models, Statistical; D011157:Population Dynamics; D012098:Reproduction; D012424:Rural Population; D013269:Stochastic Processes; D014505:Urban Population