Background: The influence of family and friends on an individual’s fertility has long been an important topic within demography. Researchers who focus on social network effects and evolutionary demography have shown a renewed interest in this issue in recent years. However, only a few studies have been conducted in contemporary low-fertility, resource-rich settings.

Objective: This study investigates whether a British woman’s entry into motherhood (i.e., her first birth) is influenced by the kin orientation of her close social network. Specifically, we test the prediction derived from evolutionary theory that individuals with a kin-oriented network will have higher fertility than those with fewer relatives in their close social networks. We consider two potential proximate mechanisms by which kin may influence fertility. First, relatives could provide practical resources, such as childcare, which reduce the costs of reproduction, thereby increasing fertility. Second, family members might communicate relatively pro-natal messages that could help to "persuade" childless women to become mothers.

Methods: We use data from the British Household Panel Study (1992 to 2003), and base the degree of kin orientation on the number of relatives a woman includes when identifying her three closest non-household associates. We conduct a discrete-time event history analysis to measure the risk of first birth, controlling for household composition and socio-economic background.

Results: We find that when a woman has more kin in her close social network, her risk of having a first birth increases at all ages. This suggests that relatives may influence fertility behaviour in this contemporary resource-rich population. Both of our proposed proximate mechanisms may be important in driving this effect.