Genetic Influences on Fertility Behavior: Findings from a Danish Twin Study, 1910--23
Hans-Peter Kohler and Kaare Christensen
Abstract: Whereas most research focuses on how variations in socioeconomic conditions contribute to the diversity in fertility behavior within a population, this paper analyzes the fertility of Danish twins in order to find possible genetic influences on an individual's fertility decisions. The analyses reveal that male monozygotic twins have a significantly higher correlation of completed fertility than their dizygotic counterparts, which suggests a (dominant) genetic influence on male fertility behavior. For females, an important gene-environment interaction emerges: the difference in the correlation of completed fertility between mono- and dizygotic twins changes over time. Only for later cohorts is there evidence for a greater similarity of completed fertility among female monozygotic twins as compared to dizygotic twins. This means that the genetic influence on the fertility of females increases over the sample period.