Warfare and reproductive success in a tribal population

Significance The reasons why warriors in small-scale societies participate in war are poorly understood. Evolutionary anthropologists have argued that individuals can benefit from participating in warfare despite the risks they face. Unfortunately, field data to evaluate this hypothesis are exceedingly rare. Here we present the first quantitative study on warfare and reproductive success among a pastoralist population. Participation in warfare for elders is associated with a greater number of wives and children. Ethnography suggests this result is because greater warriorship gives men increased access to bridewealth over the life course. Our results appear to apply to similar pastoralist populations and provide support for the expectation that warriors in small-scale societies benefit from participating in warfare. Intergroup conflict is a persistent feature of many human societies yet little is known about why individuals participate when doing so imposes a mortality risk. To evaluate whether participation in warfare is associated with reproductive benefits, we present data on participation in small-scale livestock raids among the Nyangatom, a group of nomadic pastoralists in East Africa. Nyangatom marriages require the exchange of a significant amount of bridewealth in the form of livestock. Raids are usually intended to capture livestock, which raises the question of whether and how these livestock are converted into reproductive opportunities. Over the short term, raiders do not have a greater number of wives or children than nonraiders. However, elders who were identified as prolific raiders in their youth have more wives and children than other elders. Raiders were not more likely to come from families with fewer older maternal sisters or a greater number of older maternal brothers. Our results suggest that in this cultural context raiding provides opportunities for increased reproductive success over the lifetime.