Genetic and Environmental Influences on Fertility Expectations and Outcomes Using NLSY Kinship Data

Abstract

There has been recent interest in the research literature concerning the potential for genetic influences on fertility-related behaviors. Fisher’s (1930) well-known theorem suggesting that the heritability of fertility-linked behaviors must eventually disappear (e.g., Plomin, DeFries, & McClearn, 1990) runs counter to a number of empirical findings concerning sexuality and fertility behaviors. Miller has recently developed a framework (Miller et al, 1999b) that casts fertility outcomes into the bigger context of fertility desires and expectations. We draw on this framework to investigate the role of broad genetic and environmental influences on a number of fertility attitudes, and link those to fertility outcomes. Our data come from recently defined kinship structure from the National Longitudinal Survey of Youth, and thus provide a large national sample in which to investigate these issues. Our findings suggest that both fertility expectations and desires have a heritable component, and virtually no shared environmental component. However, expectations have a systematically higher level of genetic influence than outcomes. These findings are both readily interpretable within previous frameworks, and also can be used to general future research agendas.