The demographic stability of small human populations

Abstract

of birth and death which prevail in the population over a long time period. We have two basic kinds of data. There are aged skeletal series from large burial sites, and there are censuses from living primitive populations. The former give us direct information from past populations, and the latter give us information from living populations generally assumed to be representative of cultures during the long period of human evolution. Hence, both sources are used to reconstruct human demographic evolution. Most populations of these types are small ones which are not literate and do not keep records sufficient for demographic analysis. We generally have but a single census (or aged skeletal series) and only minor scraps of other information. There is almost never any actual data on age-specific rates of mortality, yet these rates are the fundamental parameters of demography and must be known. With standard theoretical approaches, it has been shown that the age distribution of small groups is unstable from year to year, and may be unreliable as a source from which to determine age-specific death rates (e.g., Moore, Swedlund & Armelagos, 1975; Angel, 1969). It is also known that populations are so subject to extinction, due to statistical fluctuations in births and deaths, that they are too transitory and unstable for useful study (this is based on statistical theory, which can be found in Bartlett, 1960; Pielou, 1969; Keyfitz, 1968). If this is true, then we must avoid the use of typical anthropological data, and are to a great extent prevented from gaining a reasonable knowledge of past demographic patterns. The mathematical models on which these assertions are based use fixed age-specific birth and death rates. Yet there is a wealth of biological and anthropological information to show that these vital processes of a population vary according to population size or density in a negative-feedback way. A population which becomes crowded suffers higher mortality and lowered fertility, and one which is uncrowded enjoys higher fertility and lower mortality. These facts must be incorporated into a realistic demographic model.