Warfare and reproductive success in a tribal population

Abstract

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.

Keywords: human behavioral ecology; pastoralists; reproductive success; status; warfare.

Fig. 1.

Histogram of stealth raid participation during the study period for 91 nonelders.

Fig. 2.

Scatterplot of the relationship between age rank and raid participation for nonelders with number of wives indicated by shape. Age rank ranges from 1 to 91, with 1 being the oldest individual in the sample and 91 being the youngest. Number of wives indicated by shape: = two wives; ∆ = one wife; ○ = unmarried.

Fig. 3.

Boxplots comparing the number of wives and children for battle raid leaders and prolific vs. nonprolific raiders. Prolific raider status of elders and (A) number of wives: nonprolific n = 18, prolific n = 11; (B) number of children: nonprolific n = 14, prolific n = 10. Battle-raid leadership and (C) number of wives: nonleaders n = 20, leaders n = 9. (D) Number of children: nonleaders n = 16, leaders n = 8.

Fig. 4.

Histogram of distribution of the number of wives of study participants. Nonelders, solid bars (n = 91); elders, striped bars (n = 29).