Do Chimps Share Our Sense of Fairness?

In a new paper, primate researcher Sarah Brosnan and her colleagues report finding the first evidence that chimpanzees won’t tolerate unfairness that is directed at others.

The scientists decided to see what happened when they gave pairs of chimps different rewards in exchange for the same tokens—one got a carrot while the other got a grape (a sweeter, better deal). As expected, the chimps were more likely to reject the carrot when they saw their partner get a grape. This kind of “inequity aversion,” primatologist Frans de Waal has argued, is a rational response that’s linked to the fact that:

in a cooperative system, one needs to watch what kind of investment one makes and what one gets in return. If your partners always ends up getting a greater share, this means that you’re being taken advantage of. So, the rational thing to do is withhold cooperation until the reward division improves (The New York Times).

But the researchers discovered something even more interesting: The chimps were more likely to reject a grape when their partner only got a carrot. In other words, the chimps didn’t only respond negatively when they got the short end of the stick, but also when their partner got a raw deal.

So are chimps as sensitive to unfairness as humans are? Given the choice, will they make fair offers and reject unfair ones? Researchers at the Max Planck Institute of Evolutionary Anthropology don’t think so. A couple of years ago, they showed that unlike humans—who will reject an unfair division of money, even at a cost to themselves—chimpanzee responders accepted any nonzero offer, whether it was unfair or not. The only offer that was reliably rejected was the 10/0 option (responder gets nothing) (Max Planck Society).

And clearly the chimps were willing to propose unfair deals to their partners. Yet it’s worth pointing out that they were also separated from one another by cage mesh. Perhaps Brosnan’s animals rejected their “undeserved” grapes in part because they sat right next to their less fortunate partner and may have feared retaliation for their windfall, the researchers suggest (New Scientist).

Category: Animal Studies

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