Explaining fairness in complex environments

This article presents the evolutionary dynamics of three games: the Nash bargaining game, the ultimatum game, and a hybrid of the two. One might expect that the probability that some behavior evolves in an environment with two games would be near the probability that the same behavior evolves in either game alone. This is not the case for the ultimatum and Nash bargaining games. Fair behavior is more likely to evolve in a combined game than in either game taken individually. This result confirms a conjecture that the complexity of our actual environment provides an explanation for the evolution of fair behavior.