A Research Note on the Demographic Potential of Polygyny: Evaluating an Age-Related Summary Indicator

This research note discusses one underexplored aspect of the study of polygyny, namely, the extent to which the practice remains viable from a purely demographic standpoint. Using data from the United Nations World Population Prospects 2022 covering 48 countries in sub-Saharan Africa (SSA), I evaluate a simple indicator-gamma-for capturing the "demographic potential" of polygyny, that is, the fraction of men who can have two wives with no other man pushed out of the marriage market. I estimate how this indicator has evolved between 1950 and 2021 across regions of SSA and show how the measure correlates with polygyny estimates from available men's and women's Demographic and Health Surveys. Gamma shows inverted U-curve patterns aligned with stages of the demographic transition, from modestly low levels to high levels during periods of rapid population growth and then declining again. Recent declines are starkest in South SSA, while potential remains moderate elsewhere. Gamma correlates positively with polygyny estimates from Demographic and Health Surveys-particularly in Central and South SSA-and can explain up to 50‒70% variation in polygyny, albeit not everywhere. Findings primarily hold within regions, suggesting this is one of manifold factors at play. I conclude by outlining fruitful directions for the study of polygyny.