The ultimatum game is one of the most replicated experiments in behavioral economics and social psychology. It tests whether humans behave as rational, self-interested agents — or whether fairness overrides self-interest.

The Setup

Two players. Player 1 receives $10 and must offer Player 2 some portion of it. Player 2 can accept (both keep the money) or reject (both get nothing).

What Rational Theory Predicts

Player 2 should accept any offer above zero — something is better than nothing.

What Actually Happens

Offers below about 30% are rejected roughly 50% of the time. People are willing to sacrifice real money to punish perceived unfairness. The emotional drive to punish injustice overrides rational self-interest.

Cross-Cultural Findings

The threshold for rejection varies across cultures — some societies show much higher tolerance for low offers, others lower. But the basic phenomenon — rejection of unfair offers at personal cost — appears to be universal.

Evolutionary Explanation

In repeated social interactions, punishing exploitation maintains long-term cooperative relationships. The emotion of fairness outrage is an evolved enforcement mechanism, not an irrational quirk.

Reference:

Wikipedia: Ultimatum Game

https://en.wikipedia.org/wiki/Ultimatum_game