How equity norms evolve? - An evolutionary game theory approach to distributive justice

A Nash demand game (NDG) has been applied to explain moral norms of distributive justice. In NDG, two players simultaneously make demands and receive them unless the sum of the demands exceeds the amount of the resource. Otherwise, they obtain nothing. This paper proposes the demand-intensity game (D-I game), which adds an "intensity" dimension to NDG in order to discuss various scenarios for the evolution of norms concerning distributive justice. We show basic analyses of the D-I game in game theory and then evolutionary simulations. Descriptive/evolutionary approaches show that three types of norms could evolve mainly dependent on the conflict cost in the game: egalitarianism, "wimpy" libertarianism and libertarianism in decreasing order of the cost. Although the wimpy libertarianism is classified as the libertarianism in the sense of claiming the full resource, it can achieve an egalitarian division without conflict cost as a result.