Dr. Darby Proctor, Emory University – Fairness in Chimpanzees

Apr 4, 2013

In today’s Academic Minute, Dr. Darby Proctor of Emory University shares research indicating a innate sense of fairness in chimpanzees.

Darby Proctor is a postdoctoral fellow at the Yerkes National Primate Research Center at Emory University where her research examines the decision-making processes of nonhuman primates under circumstances of risk. She is currently working on a series of gambling style tasks to elucidate risk preferences in chimpanzees. She holds a Ph.D. from Georgia State University.

About Dr. Proctor

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Dr. Darby Proctor – Fairness in Chimpanzees

Why do humans behave fairly? Most people can’t answer this question. Instead they will respond by saying “it is just fair.” But, a more interesting question is why, in evolutionary terms, do we have this sense of fairness. In order to examine the evolutionary roots of fairness, my colleagues and I adapted a traditional task for testing fairness in humans, the ultimatum game, for chimpanzees. The reason chimpanzees are of interest is because they are one of our two closest living relatives. If a sense of fairness is not unique to humans, chimpanzees seem an ideal candidate for also having this sense.

In the ultimatum game, the proposer is given some amount of money. This individual is told to divide the money in any way they choose with a partner. If the partner accepts the offer, both players are rewarded with the proposed split. However, if the partner rejects the offer, neither individual is rewarded. In humans, the most frequent offer is 50% of the money and offers of less than 20% are routinely rejected. Thus, it is in the interest of the proposer to be fair in order for offers not to be rejected.

We simplified this game for chimpanzees by only allowing them two possible offers – one an equal split of the rewards and the other a selfish offer favoring the proposer. What we found is that, like humans, chimpanzees preferentially made equitable offers. In other words, they behaved fairly. We believe this indicates an evolutionary continuity between humans and chimpanzees and suggests that last common ancestor between the two species also had a sense of fairness.

It is likely that the evolution of this sense was tied to the evolution of cooperation. When two individuals cooperate, they need some mechanism to ensure that they are getting a “fair” share, otherwise it would be more beneficial to work alone. Thus, we show for the first time that chimpanzees, who are highly cooperative, seem to recognize that making fair offers is more beneficial than being selfish in a cooperative task.

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