February 21, 2012

How much does family matter? A comparative study of kin influences on fertility

Rebecca Sear, London School of Economics

The question of why people have the number of children that they do has still not been fully answered, despite decades of research on this topic. Recently, the hypothesis that humans are cooperative breeders has emerged in evolutionary anthropology, which suggests that the support women receive in raising children from other individuals (particularly kin) may be a key part of the answer. Here, I investigate whether the presence of kin influences a woman's fertility, using evidence from a wide range of populations. I first present the results of a systematic review of all published studies which have investigated correlations between kin availability and female fertility. This review demonstrates substantial evidence that the presence of family members is correlated with fertility, but these results do not always show consistent relationships. In some cases, particularly in high fertility societies and particularly for a woman’s in-laws, kin increase fertility rates. In other analyses, particularly of the influence of a woman's own parents in low fertility societies, kin slow down fertility. This literature is, however, very varied, with different studies using different methodologies and different measures of fertility and kin availability. More comparative work is needed to elucidate exactly how kin might influence fertility rates. I conclude by outlining my current research programme which aims to investigate kin influences on fertility using existing large-scale demographic datasets, using comparable methodologies in all datasets to facilitate comparisons between populations, and to explore the pathways through which kin may influence fertility.