Kin influences on fertility: a theoretical framework tested with a review of the literature

Cristina Moya, London School of Hygiene and Tropical Medicine (LSHTM)
Rebecca Sear, London School of Hygiene and Tropical Medicine (LSHTM)

Far from being an asocial process, reproductive decision-making in humans is affected by family and other social networks. However, the direction and strength of kin effects is inconsistent across studies. Explaining this variation requires a better understanding of what various fertility outcomes mean functionally and of each individual’s strategic interests. A previous review demonstrated that kin have a beneficial impact on one aspect of childbearing: the survival of a woman's children. The influence of family on fertility is a little more complicated to study, however, since decisions regarding age at first birth, the pace of reproduction, and total number of births can be made independently of one another. Further complicating matters, woman and her kin do not always have the same strategic considerations, so that kin may hinder, rather than help, fertility. In this paper we develop a framework for comparing various accounts of why kin affect fertility. We test these possibilities by compiling and analyzing a database of kin effects on fertility from the literature. Focusing on how parents and in-laws might affect different fertility outcomes, we find that parents are more likely than in-laws to have anti-natal effects on a woman’s total fertility, and age at first birth, but not on inter-birth intervals.