Are humans cooperative breeders?

There is evidence to suggest that human female reproduction is assisted by other members of her family. In particular studies show that fathers and grandmothers are important in supporting her reproductive success. In this paper, we examine the effects of specific kin on specific components of fitness, and show that the contributions of matrilineal and patrilineal kin are very different. Fathers contributions to child survival are mixed, possibly being more significant in monogamous societies. Maternal grandmothers and other matrilineal kin tend to improve child survival but not female fertility, whereas patrilineal grandparents and male kin tend not to he lp child survival but do enhance the mothers rate of birth. We argue that these different strategies emerge as a response to different relatedness to the mother, because the costs of maternal mortality differ between the two lineages: patrilineal kin are less concerned about women paying the high costs of reproduction associated with high fertility. Models of the grandmother hypothesis for the evolution of menopause generally find that the magnitude of grandmother effects is not large enough to compen sate for the loss of later life fertility. However recent developments in modelling approaches do highlight the importance of transfers (be it of care or resources) in the evolution of human longevity and fertility schedules. These remain the most plausible explanation for the unusual features of the human female life history, including high birth rates and menopause.