Kin influence on the decision to start using modern contraception: A longitudinal study from rural Gambia.

In earlier work in rural Gambia, we found that kin influence reproductive success: matrilineal kin, especially mothers, maternal grandmothers and unmarried older sisters all helped to promote the survival and nutrition of young children; in contrast patrilineal kin, especially husband's mother, promoted fertility. These differing influences of maternal and paternal lineage are predicted on the basis of kin selection and sexual conflict theory, because the costs of reproduction fall more heavily on the mother than the father. These studies covered the period 1950-1975, when this population was essentially "natural fertility, natural mortality." It is not possible to tell whether these effects were due to kin influencing active reproductive decision-making, or due to indirect effects such as kin improving nutrition by helping. Since 1976, modern contraception has become available in this community. In an analysis of the behavioral ecology of the decision to start using modern contraception, we found that high parity for your age was a key determinant of the decision, as was village and calendar year. Here, we examine whether the presence or absence of kin and also whether the contraceptive status of kin influenced the decision to start using contraception. We find little evidence that kin directly influence contraceptive uptake, either by their presence/absence or as models for social learning. However, death of a first husband (i.e., widowhood) does accelerate contraceptive uptake. We discuss our results from an evolutionary demography perspective, in particular regarding theories of sexual conflict, biased cultural transmission, and social learning. 2009 Wiley-Liss, Inc.