Chimps play fair in the Ultimatum Game

From Woodruff Health Sciences Center

Chimpanzees have a sense of fairness that was previously seen as uniquely human, finds a study by Emory's Yerkes National Primate Research Center and Georgia State University. The researchers played the Ultimatum Game with the chimpanzees to determine how sensitive the animals are to the reward distribution between two individuals if both need to agree on the outcome.

The findings, published by the Proceedings of the National Academy of Sciences (PNAS), suggest a long evolutionary history of the human aversion to inequity, as well as a shared preference for fair outcomes by the common ancestor of humans and apes.

Click here to watch a video of the experiment.

“We used the Ultimatum Game because it is the gold standard to determine the human sense of fairness," says lead author Darby Proctor, a post-doctoral fellow at Yerkes. "In the game, one individual needs to propose a reward division to another individual and then have that individual accept the proposition before both can obtain the rewards. Humans typically offer generous portions, such as 50 percent of the reward, to their partners, and that’s exactly what we recorded in our study with chimpanzees.”

"Until our study," adds co-author Frans de Waal, "the behavioral economics community assumed the Ultimatum Game could not be played with animals, or that animals would choose only the most selfish option while playing. We've concluded that chimpanzees not only get very close to the human sense of fairness, but the animals may actually have exactly the same preferences as our own species."

For purposes of direct comparison, the study was also conducted separately with human children.

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