The emergence of large-scale cooperation during the Holocene remains a central problem in the evolutionary literature. One hypothesis points to culturally evolved beliefs in punishing, interventionist gods that facilitate the extension of cooperative behaviour toward geographically distant co-religionists. 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 a set of interviews to a sample of 2228 participants from 15 diverse populations. These populations included foragers, pastoralists, horticulturalists, and wage labourers, practicing Buddhism, Christianity, and Hinduism, but also 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 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 between-site variability, suggesting that in the absence of intergroup hostility, moralizing gods may be implicated in cooperative behaviour toward outgroups. These results provide support for the hypothesis that beliefs in monitoring and punitive gods help expand the circle of sustainable social interaction, and open questions about the treatment of religious outgroups.
A fundamental puzzle of human evolution is how we evolved to cooperate with genetically unrelated strangers in transient interactions. Group-level selection on culturally differentiated populations is one proposed explanation. We evaluate a central untested prediction of Cultural Group Selection theory, by assessing whether readiness to cooperate between individuals from different groups corresponds to the degree of cultural similarity between those groups. We documented the normative beliefs and cooperative dispositions of 759 individuals spanning nine clans nested within four pastoral ethnic groups of Kenya-the Turkana, Samburu, Rendille and Borana. We find that cooperation between groups is predicted by how culturally similar they are, suggesting that norms of cooperation in these societies have evolved under the influence of group-level selection on cultural variation. Such selection acting over human evolutionary history may explain why we cooperate readily with unrelated and unfamiliar individuals, and why humans' unprecedented cooperative flexibility is nevertheless culturally parochial.
Scholars of religion have long sought to explain the persistent finding that women tend to report greater religiosity than men. However, the size of this 'gender gap' may depend on the measure of religiosity employed, the religious tradition being sampled, and socio-demographic factors.Here, we conduct a systematic cross-cultural investigation into the prevalence of, and explanations for, the religiosity gender gap in 2,002 individuals from 14 diverse societies.While variation exists across societies, women in general indicate greater mental commitment to (i.e. thinking and worrying more about) their community's moralistic god, more frequent participation in rituals for their community's moralistic god, and more frequent prayer. While we find that the gender gap extends beyond the Christian world, no such difference was seen in religious commitment towards more local gods, to which men tend to show greater commitment. Tentative support is provided for explanations relating gender differences in religiosity to lower formal education and greater mentalising among women, however an explanation for greater religious commitment to local gods among men remains elusive.Nevertheless, our data suggest that the moralising gods of some contemporary world religions, unlike local deities and traditions, have evolved in ways that make them more appealing to women.
The Turkana people inhabit arid regions of east Africa where temperatures are high and water is scarce and they practice subsistence pastoralism, such that their diet is primarily composed of animal products. Working with Turkana communities, we sequenced 367 genomes and identified 8 regions putatively involved in adaptation to water stress and pastoralism. One of these regions includes a putative enhancer for STC1 - a kidney-expressed gene involved in the response to dehydration and the metabolism of purine-rich foods such as red meat. We show that STC1 is induced by antidiuretic hormone in humans, is associated with urea levels in the Turkana themselves, and is under strong selection in this population (s~0.041). This work highlights that partnerships with subsistence-level groups can lead to new models of human physiology with biomedical relevance.
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