A spatial evolutionary version of the ultimatum game as a toy model of income distribution

In the standard ultimatum game, two individuals, usually called the proposer and the responder, must agree on how to split a certain sum of money. The proposer makes an offer. If the responder takes this offer, the money is divided as proposed; however, if the responder rejects it, they receive nothing. In this work, a spatial evolutionary version of this game is used to investigate the income distribution in a society, as a consequence of employer-employee bargaining process. The two main modifications introduced here are: (1) the money does not disappear when an offer is not taken; (2) the survival of the players depends on the acceptance of proposals. There are four kinds of players, because each individual adopts one of two strategies as a proposer and one of two strategies as a responder. By performing numerical simulations, the long-term dynamics is determined and the Gini coefficient is computed in function of the model parameters. The results are interpreted from a socioeconomic perspective. (C) 2019 Elsevier B.V. All rights reserved.