Who Helps and Why? Cooperative Networks in Mpimbwe

Studies that examine how helping behavior varies among individuals shed light on both the extent and the variation of human cooperative tendencies and the potential fragility of genealogical kinship in structuring prosociality. Here we explore the importance of both reciprocal altruism and kin selection in structuring cooperation in a contemporary African village context (Mpimbwe, Tanzania), where ethnographic observations suggest that traditional patterns of cooperation are becoming deeply eroded. Our analysis of the various ways in which people assist each other reveals that levels of helping are low. Reciprocal altruism is the principal explanation for helping, and genealogical kinship is important with respect to directing unilateral aid to needy individuals. However, more nuanced analyses, in conjunction with ethnographic evidence of threats of supernatural sanctions on uncooperative kin, expose the fragility of biological kinship in structuring cooperation in Mpimbwe and a further preference for affinal relatives. Furthermore, the finding that wealthier individuals are less engaged in reciprocal dyads than are poorer individuals suggests that in developing rural communities cooperative networks weaken most readily among the wealthy. More generally, we demonstrate how entry into a market economy and increasing wealth inequalities have the potential both to change the way individuals manage risk and to alter their relationships with kin.