superfluous mathematics. Besides, when game theory math incorporates the economists’ belief in selfish rationality, it doesn’t even predict human behavior correctly.

Actually, though, game theory provides a more sophisticated and quantitative tool for describing human nature than the intuition of criminals. Looked at in the right way, the ultimatum game does not disprove game theory, but expands it. Fairness, trust, and other social conditions do affect how people play games and make economic choices. But that just means that the standard economic notion of self-interest is too restrictive—life is more than money. Game theory’s math doesn’t really tell you what people want, but rather how people should behave in order to achieve what they want.

As economist Jörgen Weibull observes, reports of game theory’s death have been exaggerated. “It has many times been claimed that certain game-theoretic solutions—such as Nash equilibrium … —have been violated in laboratory experiments,” Weibull writes. “While it may well be true that human subjects do not behave according to these solutions in many situations, few experiments actually provide evidence for this.”2

Early experiments with tests such as the ultimatum game merely assumed that people wanted to maximize their money—which they often failed to do when playing the game. Such tests do not disprove game theory, though; instead, they suggest that something is wrong with the experimenter’s assumptions. Later versions of the ultimatum game attempted to include things like fairness, or, more generally, test how a player’s social preferences (that is, concerns for others) influence game decisions. Such factors as altruism and spite, Weibull notes, affect the outcome that players prefer to reach, and they make their choices accordingly.

“Indeed, several laboratory experiments have convincingly— though perhaps not surprisingly for the non-economist—shown that human subjects’ preferences are not driven only by the resulting material consequences to the subject.”3 In some cases, social context (say, the norms of a person’s peer group) dictates choices that appear inconsistent with both personal self-interest and con-



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