Inter-group variation is greater in humans than in any other animal, and scholars continue to debate the cause of this diversity. Two competing explanatory models of human variation emphasize either (1) ecological differences and "evoked" culture or (2) population-level effects of cultural transmission. The former emphasizes mechanisms that operate within a single generation, while the latter emphasizes cumulative cultural history operating over many generations. To test these competing models, the authors measured the relative power of ecological variables as compared to culture history to predict behavioral variation in 172 western North American tribes. Culture history is subdivided into culture phylogeny (based on language phylogeny) and spatial distance.

In this study, the authors inspect the relationship between religion, morality, and cooperation by examining the extent to which people associate their deities with moral concern. Using data from 2,228 individuals in 15 different field sites, they find that on average, people tend to ascribe at least some moral concern to their deities, and this effect is stable even after controlling for the influence of explicitly moralistic deities that these societies also worship. The authors also find that ratings of moral concern are not necessarily very high, even for deities that are typically considered to be moralistic, and that there is individual-level variation in the degree of moral concern attributed to deities. In addition, there is an individual-level correlation between how morally interested two selected deities are conceived to be and that being male or more educated decreases the likelihood of associating deities with moral concern. These findings challenge the longstanding belief that belief in moralistic deities is unique to certain societies or religions and instead suggest that the association between deities and moral concern is more widespread and variable, and suggest that the moral character of gods may be tied to cooperation within societies.