THE JERUSALEM GAME: CULTURAL EVOLUTION OF THE GOLDEN RULE

It has often been noted that most of the major world religions espouse a version of the "golden rule." In this paper we consider the cultural evolution of such a doctrine, where the responsibility to act altruistically towards others applies universally, not just to other members of the same society. Using a game-theoretical model, we find that societies over a critical size benefit from adopting a mode of universal altruism. These "golden-rule societies" must justify violence against outsiders by formulating exceptions to this universal rule. For smaller groups, it is more efficient to adopt a rule that simply requires cooperation within the group. Data from the ethnographic record supports a correlation between group size and societal norms of universal cooperation. Our results provide an explanation for the prevalence of the golden rule among contemporary cultures. We find that universal altruism arises due to cultural selection for greater ingroup bias, and is a natural byproduct of the emergence of large-scale societies.