Final Report Summary - FAMMAT (Family Matters: Intergenerational Influences on Fertility)
Do women have more children in the presence of helpful family members? This is the overarching question which the ERC-funded project FAMMAT aimed to answer. This research question was motivated by the hypothesis developed in the human evolutionary sciences that humans are cooperative breeders, and that mothers require help to raise children. To answer this question, the ERC-funded team analysed secondary datasets from all over the world to determine: (1) whether kin influence fertility?; (2) why do they influence fertility?; and (3) when do they influence fertility the most?
A review of existing literature showed that kin often do influence women’s fertility, but that the presence of kin does not always increase women’s fertility, and may sometimes even be associated with lower fertility. Further, there are differences in which kin matter. Parents-in-law are more likely to be associated with higher fertility than a woman’s own parents, for example. Moreover, the presence of parents is sometimes associated with later first births on the parts of both daughters and sons (suggesting parents may lower the fertility of their children under some circumstances).
Our detailed empirical analyses of individual datasets allowed us to explore why parents and parents-in-law should matter for women’s fertility. In lower and middle income contexts, our results suggest that kin influences on fertility are plausibly driven by direct influences of kin, rather than being the result of spurious correlations between kin availability and fertility. In Indonesia, for example, parents-in-law are associated with higher fertility for women, but only when they provide help to women, supporting the cooperative breeding hypothesis that women will be able to increase their fertility in the presence of helpful kin.
In high income contexts, the picture is somewhat more complicated. While there are some indications that parents and parents-in-law, particularly emotional support from parents and in-laws, is positively correlated with fertility, the provision of substantial material resources appear to lower women’s fertility, at least in some contexts. We suggest this is because the substantial provision of material resources is linked to the need of recipients for resources. The provision of material resources is therefore an indicator that individuals may be in a relatively poor situation to reproduce, rather than an indicator that an excess of resources is available, which may be used to enhance fertility.
Finally, we showed that not all interactions within a family surrounding reproduction are cooperative, but that conflict within the family may also influence fertility. Parents often, though not always, have a delaying effect on the age at first birth of both sons and daughters. We proposed a new hypothesis to help explain this finding: if parents and offspring both require help to raise children, then there may be conflict within the family for reproductive opportunities. The presence of parents may therefore indicate intergenerational conflict within a household. We developed a mathematical model to establish the plausibility of this hypothesis. We also tested this hypothesis empirically, by using a database containing data on parental influences on age at first birth from 20 small-scale societies, from low income, high fertility contexts. This analysis supported our hypothesis by demonstrating that the greatest parental delays to age at first were seen in contexts where intergenerational conflict was likely to be most severe. It should be noted, however, that such conflict is only seen because families are cooperative, such conflict would not be seen if families did not cooperate over the raising of children.
A review of existing literature showed that kin often do influence women’s fertility, but that the presence of kin does not always increase women’s fertility, and may sometimes even be associated with lower fertility. Further, there are differences in which kin matter. Parents-in-law are more likely to be associated with higher fertility than a woman’s own parents, for example. Moreover, the presence of parents is sometimes associated with later first births on the parts of both daughters and sons (suggesting parents may lower the fertility of their children under some circumstances).
Our detailed empirical analyses of individual datasets allowed us to explore why parents and parents-in-law should matter for women’s fertility. In lower and middle income contexts, our results suggest that kin influences on fertility are plausibly driven by direct influences of kin, rather than being the result of spurious correlations between kin availability and fertility. In Indonesia, for example, parents-in-law are associated with higher fertility for women, but only when they provide help to women, supporting the cooperative breeding hypothesis that women will be able to increase their fertility in the presence of helpful kin.
In high income contexts, the picture is somewhat more complicated. While there are some indications that parents and parents-in-law, particularly emotional support from parents and in-laws, is positively correlated with fertility, the provision of substantial material resources appear to lower women’s fertility, at least in some contexts. We suggest this is because the substantial provision of material resources is linked to the need of recipients for resources. The provision of material resources is therefore an indicator that individuals may be in a relatively poor situation to reproduce, rather than an indicator that an excess of resources is available, which may be used to enhance fertility.
Finally, we showed that not all interactions within a family surrounding reproduction are cooperative, but that conflict within the family may also influence fertility. Parents often, though not always, have a delaying effect on the age at first birth of both sons and daughters. We proposed a new hypothesis to help explain this finding: if parents and offspring both require help to raise children, then there may be conflict within the family for reproductive opportunities. The presence of parents may therefore indicate intergenerational conflict within a household. We developed a mathematical model to establish the plausibility of this hypothesis. We also tested this hypothesis empirically, by using a database containing data on parental influences on age at first birth from 20 small-scale societies, from low income, high fertility contexts. This analysis supported our hypothesis by demonstrating that the greatest parental delays to age at first were seen in contexts where intergenerational conflict was likely to be most severe. It should be noted, however, that such conflict is only seen because families are cooperative, such conflict would not be seen if families did not cooperate over the raising of children.