Supplementary material from "Moralizing gods, impartiality and religious parochialism across 15 societies"

The emergence of large-scale cooperation during the Holocene remains a central problem in the human evolutionary literature. Among several contributing mechanisms, one hypothesis points to culturally evolved beliefs in punishing, interventionist gods that facilitate the extension of cooperative behaviour toward geographically distant co-religionists who are unlikely to reciprocate. Furthermore, another hypothesis points to such mechanisms being constrained to the religious ingroup, possibly at the expense of religious outgroups. To test these hypotheses, we administered two behavioural experiments and an extensive set of interviews to a sample of 2228 participants from 15 diverse populations. These populations included foragers, pastoralists, horticulturalists, subsistence farmers and wage labourers, practicing world religions such as Buddhism, Christianity and Hinduism, but also different forms of animism and ancestor worship. Using the Random Allocation Game (RAG) and the Dictator Game (DG) in which individuals allocated money between themselves, local and geographically distant co-religionists, and religious outgroups, we found that higher ratings of gods as monitoring and punishing reliably predicted decreased local favouritism (RAGs) and increased resource-sharing with distant co-religionists (DGs). The effects of punishing and monitoring gods on outgroup allocations revealed considerable between-site variability, suggesting that in the absence of intergroup hostility, some religious elements may be implicated in cooperative behaviour toward outgroup members as well. These results provide support for the hypothesis that beliefs in monitoring and punitive gods who care about human normative conduct help expand the circle of sustainable social interaction, and open new questions about how different traditions respond to religious outgroups.