The Impact of Intergenerationally-Transmitted Fertility and Nuptiality on Population Dynamics in Contemporary Populations

Abstract

There are intergenerational continuities in contemporary fertility, mortality and partnership behaviors due to genetic and environmental factors. If persistent, these would be expected over time to lead to a proportionate increase in those with a higher than average propensity to reproduce, and consequently to lead to higher population growth (or lower decline) than would otherwise be the case. We use three scenarios of fertility transmission to investigate the differences in long run population dynamics under models of intergenerationally correlated fertility and partnership behaviors: (1) fertility is not heritable; (2) daughters’ fertility is partly correlated with mother’s fertility; (3) daughters have the same fertility propensity (fecundability) as their mothers. Positive correlations increase population growth rates substantially, even though the correlation coefficients between completed fertility of mothers and daughters may be modest with the assumptions of these models. This suggests that large samples are required to detect such effects in historical populations, and that the widely-held assumption that fitness was not heritable is questionable. The demographic regime is based on that of England and Wales from 1750 to 2050 and so covers typical long-term experiences of now-developed societies as they moved from pre- transitional to contemporary patterns of below-replacement level cohort fertility. The methodology is based on microsimulation of full kinship networks based on the Berkeley SOCSIM program. 209