We examine a novel hypothesis that roots human prosociality in the need to elicit and sustain help from others for the purpose of raising children. Cross-cultural ethnographic data suggests a positive association between societal trust and allomaternal care, i.e., care coming from individuals other than the mother. In this study, we test the relationship between allomaternal care and cooperative behavior among a sample of 820 individuals in the Solomon Islands through a series of dictator games using a within-subject design that enables us to account for unobserved heterogeneity across subjects, as well as several observed and unobserved characteristics of the relationship between individuals and specific people in their network (relatives, acquaintances, and strangers). Our results show that receiving help with child care predicts heightened proso-ciality. This relationship remains strong even after accounting for other forms of mutual help. Moreover, help from non-relatives is associated with prosociality toward strangers, suggesting an important foundation for the development of impersonal prosociality. As evidence of a mechanism sustaining the prevalence of allomaternal care, we document large socio-cognitive benefits to children who receive care from non-relatives, based on stress data and daylong vocalizations of 200 children analyzed using a multilingually-trained neural network.
JEL Codes: I15, O15, Z13