Modeling NLSY Fertility Patterns Longitudinally and Biometrically: Evolutionary, Genetic, and Social Interpretations

Joseph L. Rodgers, University of Oklahoma
David Bard

Using fertility patterns and kinship information from the National Longitudinal Survey of Youth (NLSY), we fit biometrical models to partition genetic, shared environmental, and nonshared environmental variance associated with fertility differences in the NLSY females. Those females -- who were aged 35-42 in the 2000 data -- have mostly completed childbearing. Our model is a multivariate longitudinal model linking early fertility, early middle fertility, middle fertility, and late middle fertility. Our analysis shows different genetic sources underlying early and later fertility, and strong shared environmental influences only for early fertility. These findings are interpreted in relation to Fisher's Fundamental Theorem of Natural Selection, and also in relation to a theory developed by Udry (1995) explaining how the amount of reproductive choice constrains the link between fertility preferences and the biological expression of those preferences.