Role polarization and its effects in the spatial ultimatum game.

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Human society is believed to be becoming increasingly polarized, yet it remains unclear how role polarization influences the evolution of fairness. In addition, little is known about role adaptation, despite the fact that altering the roles of players can often change the outcome of the ultimatum game. Unlike earlier static, random, symmetric role assignment, here I suggest a succeed-reinforce-fail-slacken role adaptation rule that encourages successful proposers in the present round to propose again in the next round and vice versa. The results demonstrate that this simple rule can tip the scales in favor of fair strategies when it comes to the proposer advantage, and therein lies the key to promoting fairness. Depending on its pace, notably, role adaptation can direct the system to equilibrium states that bear variable degrees of role polarization, with two consequences incidentally. Not only does it favor fairness, it also fosters empathy. Noise associated with role adaptation often reduces role polarization and thus has a negative impact on fairness and empathy. The comparison of experiments with various networks validates the substantial resilience of role polarization to structural changes. These findings add to the evidence for role polarization and highlight the centrality of role adaptation in the evolution of fairness.