Why men invest in non-biological offspring: paternal care and paternity confidence among Himba pastoralists

Paternal investment is predicted to be a facultative calculation based on expected fitness returns and modulated by a host of social predictors including paternity uncertainty. However, the direct role of paternity confidence on the patterns of paternal investment is relatively unknown, in part due to a lack of research in populations with high levels of paternity uncertainty. Additionally, much of the work on paternity certainty uses cues of paternity confidence rather than direct assessments from fathers. We examine the effect of paternity assertions on the multiple measures of paternal investment in Himba pastoralists. Despite a high degree of paternity uncertainty, Himba have strong norms associated with social fatherhood, with men expected to invest equally in biological and non-biological offspring. Our behavioural data show patterns that largely conform to these norms. For domains of investment that are highly visible to the community, such as brideprice payments, we find no evidence of investment biased by paternity confidence. However, more private investment decisions do show some evidence of sex-specific titration. We discuss these results in light of broader considerations about paternal care and the mating-parenting trade-off.