Kin networks and opportunities for reproductive cooperation and conflict among hunter-gatherers

Abstract

Little is known about the potential for reproductive conflict among hunter-gatherer populations, who are characterized by bilateral kinship ties, flexible residential mobility, and high offspring mortality. To assess the potential for reproductive conflict, we use longitudinal residence and reproductive history data for two bands of South American foragers. Using multilevel logistic regressions (N = 44 women, N = 712 person years), we examine how yearly measures of (i) camp composition, (ii) distribution of female kin and (iii) a woman's position in a female kinship network impact the likelihood of giving birth or experiencing a child's death. We compare conflict models to a demographic model that accounts for the proportion of women giving birth in a given year. Contrary to conflict models, results show that the odds of giving birth increase with the presence of highly related women. However, the odds of experiencing an offspring death are insensitive to the presence of coresident women. Network measures of closeness and centrality in the female kin network also show no significant effect on reproductive outcomes. Furthermore, chances of both births and deaths increase in years when proportionally more women are giving birth. We argue that demographic stochasticity relating to ecological conditions best predicts reproductive outcomes for women. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.

Keywords: cooperative breeding; hunter–gatherers; reproductive conflict.

Figure 1.

Average relatedness, distribution of primary kin and camp size (panels bottom to top) of two Savanna Pumé bands (DA and YA) across all census years. (Online version in colour.)

Figure 2.

Total number of reproductive-age women, births and offspring deaths in a given year for each camp (top panels). Joint distribution of age at first birth and age at first marriage (bottom left), showed a strong positive association, indicating marriage and first birth are tightly linked. Dashed lines indicate the mean ages for first marriage and first birth. Age at first birth by year of first marriage (bottom right) showed no evidence of a secular trend of increasing age at birth with time. (Online version in colour.)

Figure 3.

Odds ratios from each of the models. Error bars represent 95% confidence intervals. (Online version in colour.)

Figure 4.

Total number of births and deaths in a given year by proportion of Savanna Pumé women giving birth. (Online version in colour.)