The logic of social sharing: An evolutionary game analysis of adaptive norm development

Although norms can potentially serve useful constructs to understand human minds, being fundamentally social in evolutionary as well as cultural senses, there are as yet no useful psychological theories of adaptive norm development. This ar-ticle provides an illustrative model about how a norm emerges in a society. We fo-cus on the "communal-sharing norm " in primordial societies, a norm designating uncertain resources as common properties to be shared with other members. Based on anthropologicalfindings, we develop a theory about how the communal-sharing norm emerges and is maintained. Then, using evolutionary computer simulations, we test several hypotheses about the conditions under which the norm will domi-nate social resource sharing. We further test behavioral implications of the norm, demonstrating that uncertainty involved in resource acquisition is a key factor that triggers the psychology of sharing even in highly industrialized societies. Finally, we discuss the importance ofnorm constructfor analyzing the dynamic relation be-tween minds and society. The notion of "social norm " has a distinctive sta-tus in modem psychology. Although the concept has been one of the most central constructs in other social sciences such as sociology, law, political science, and anthropology (e.g., Axelrod, 1986; Coleman, 1990; Cooter & Ulen, 1996), its theoretical status in psy-chology has been less firm. Despite an early empha-sis on this notion (Asch, 1952; Jacobs & Campbell, 1961; Sherif, 1936), even in modern social psychol-ogy, the role of social norm construct for explaining behavior is often criticized. Some theorists argue that in many realistically complex social contexts, a vari-ety of social norms are potentially applicable to a given social situation, some of which are mutually in-compatible. Thus, unless we can tell which norm is actually operating in the situation in advance, th