Empathy leads to fairness.

In the Ultimatum Game, two players are asked to split a prize. The first player, the proposer, makes an offer of how to split the prize. The second player, the responder, either accepts the offer, in which case the prize is split as agreed, or rejects it, in which case neither player receives anything. The rational strategy suggested by classical game theory is for the proposer to offer the smallest possible positive share and for the responder to accept. Humans do not play this way, however, and instead tend to offer 50% of the prize and to reject offers below 20%. Here we study the Ultimatum Game in an evolutionary context and show that empathy can lead to the evolution of fairness. Empathy means that individuals make offers which they themselves would be prepared to accept.