The effect of similarity on the evolution of fairness in the ultimatum game.

• An ultimatum game model with similarity between players is proposed. • The evolution of fairness under such model and the underlying reason are studied. • A toy model for quantitatively analysis is given. • Effect of different distribution of similarity on our result is also studied. The ultimatum game (UG) is a useful game model for investigating the evolution of fairness. In this paper, considering the similarity between individuals, we introduce a similarity parameter into the spatial UG and focus on the evolution of the average offer and acceptance threshold. Under this mechanism, individuals can be either more generous or stingier to those who they are similar to. The simulation result shows that the fairness of the system decreases when the strategy is affected by the similarity between players. The greater the influence of similarity, the more fairness is decreased. Equal treatment, hence, is the best way to obtain fairness. Our results may provide some critical insights into the effect of similarity and favoritism on fairness among people. [ABSTRACT FROM AUTHOR]