How does a reciprocal communal sharing system come into existence in a sustainable form in human societies? The anthropological literature has provided two explanations for the origin of communal sharing under uncertainty: risk reduction by social sharing (Kaplan & Hill, 1985) and tolerated theft (Blurton Jones, 1984, 1987; Winterhalder, 1986, 1996). In this paper, we aim to develop a third explanation focusing on the emergence of a communal sharing norm. A communal sharing norm here refers to a social norm designating uncertain resources as common properties. A series of computer simulations based on an evolutionary game framework suggests that such a communal sharing norm is indeed evolvable. We argue that the evolutionary game analysis can be a powerful tool in cognitive science to derive empirical hypotheses concerning various cognitive and behavioral mechanisms.
