The effects of kin on female fertility in rural Gambia

Human females reproduce relatively rapidly throughout their reproductive years compared to the other great apes. It has been suggested that women are able to sustain this rapid pace by co-opting family members to help raise their children. We tested the hypothesis that the presence of kin will increase the reproductive rates of women using a longitudinal database collected from rural Gambia. We found that both the husband's mother and, to a lesser extent, the husband's father increased the probability that a woman would give birth. A woman's parents, however, had no effect on her fertility rate, nor did her elder sisters or co-wives. The presence of a woman's elder brothers even decreased her probability of giving birth. There was no evidence that elder children acted as 'helpers at the nest', as the existence of living elder children slowed down rather than increased birth rates. We suggest that the increased fertility in the presence of mothers-in-law may be due to these women helping out their daughters-in-law with domestic and subsistence duties. Given that it is paternal, rather than maternal, relatives who increase fertility, social pressures on women from older kin to bear many children may also be important.