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 article provides an illustrative model about how a norm emerges in a society. We focus on the "communal-sharing norm" in primordial societies, a norm designating uncertain resources as common properties to be shared with other members. Based on anthropological findings, 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 dominate 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 of norm construct for analyzing the dynamic relation between minds and society.