Abstract
Fertility has a strong biological component that has been long ignored by economists who study family decisions. We study to what extent genetic endowment affects women’s fertility behaviour and the role of gene-environment interactions in shaping these processes. We use data from UK Biobank on about 165,000 women born between 1939 and 1969. We analyze four outcomes (i.e., age at first sexual intercourse, age at first birth, completed family size, and childlessness), for each one of which we construct different polygenic risk scores. As measures of the environment we consider the diffusion of the birth control pill in the local area where women grew up. We find that fertility is powerfully shaped by both genetic predispositions and societal environmental risks, making the sharp distinction between nature and nurture obsolete. As the contraceptive pill becomes more widely used, we observe an anticipation of sexual debut and a postponement of motherhood, as well as, a reduction in completed family size, and an increased likelihood of childlessness. Each one of these environmental effects is stronger for women with higher polygenic scores. This means that environments with gender-equal social norms better allow women’s genetic potential to unfold. Our results are confirmed once (i) we consider female education as a measure of the environment, and (ii) when we exploit family-based random genetic variation among sisters.