title: What Explains the Heritability of Completed Fertility? Evidence from Two Large Twin Studies.
abstract: In modern societies, individual differences in completed fertility are linked with genotypic differences between individuals. Explaining the heritability of completed fertility has been inconclusive, with alternative explanations centering on family formation timing, pursuit of education, or other psychological traits. We use the twin subsample from the Midlife Development in the United States study and the TwinsUK study to examine these issues. In total, 2606 adult twin pairs reported on their completed fertility, age at first birth and marriage, level of education, Big Five personality traits, and cognitive ability. Quantitative genetic Cholesky models were used to partition the variance in completed fertility into genetic and environmental variance that is shared with other phenotypes and residual variance. Genetic influences on completed fertility are strongly related to family formation timing and less strongly, but significantly, with psychological traits. Multivariate models indicate that family formation, demographic, and psychological phenotypes leave no residual genetic variance in completed fertility in either dataset. Results are largely consistent across U.S. and U.K. sociocultural contexts.
authors: Department of Psychology, University of Illinois at Urbana-Champaign, 603 E. Daniel Street, Champaign, IL, 61820-6232, USA. dabriley@illinois.edu.
authors: Daniel A
authors: DA
authors: Briley
authors: Department of Sociology and Nuffield College, University of Oxford, Oxford, UK.
authors: Felix C
authors: FC
authors: Tropf
authors: Department of Sociology and Nuffield College, University of Oxford, Oxford, UK.
authors: Melinda C
authors: MC
authors: Mills
mesh_terms: D000328:Adult; D000368:Aged; D001519:Behavior; D003710:Demography; D005260:Female; D005298:Fertility / Q000235:genetics*; D056726:Genetic Association Studies; D006801:Humans; D040582:Inheritance Patterns / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010641:Phenotype
keywords: Behavior genetics; Cognitive ability; Family formation; Fertility; Personality