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Michael Tomasello, one of the biggest and best primatologists out there, recently published a paper in Science on chimpanzee rationality. He and his colleagues setup a game where a human or chimpanzee receives something of value, and is able to share it with another.

He found some interesting results. Generally speaking, humans made offers close to 50 percent of the reward, but chimpanzees almost consistently made offers of substantially less than 50 percent, and accepted offers of any size, no matter how small. Tomasello and crew concluded that chimpanzees do not show a willingness to make fair offers and reject unfair ones. In this way, they protect their self interest and are unwilling to pay a cost to punish someone they perceive as unfair.

Here’s a link to the publication along with the abstract, “Chimpanzees Are Rational Maximizers in an Ultimatum Game,”

“Traditional models of economic decision-making assume that people are self-interested rational maximizers. Empirical research has demonstrated, however, that people will take into account the interests of others and are sensitive to norms of cooperation and fairness. In one of the most robust tests of this finding, the ultimatum game, individuals will reject a proposed division of a monetary windfall, at a cost to themselves, if they perceive it as unfair. Here we show that in an ultimatum game, humans’ closest living relatives, chimpanzees (Pan troglodytes), are rational maximizers and are not sensitive to fairness. These results support the hypothesis that other-regarding preferences and aversion to inequitable outcomes, which play key roles in human social organization, distinguish us from our closest living relatives.”