monkeys like things fair and square

Just like humans, capuchin monkeys have been found to have a sense of fairness, say researchers from the Yerkes National Primate Research Center of Emory University in Atlanta. In their study, published in the Sept. 18 Nature, Sarah Brosnan and Frans de Waal taught brown capuchin monkeys, a social primate, to exchange tokens for food. Cucumber would normally be considered an acceptable treat, and the capuchins were happy to exchange a token for a piece. But if a monkey saw another monkey getting a grape — a more-favored food — in exchange, an interesting thing happened. Some would then refuse to hand over a token at all; others would refuse the cucumber, and some would take the cucumber, but refuse to eat it. The monkeys also appeared to get upset if another monkey received a treat for doing nothing at all. While the researchers acknowledge that their data can’t give the precise motivation for why the capuchins reacted as they did, they think that just like humans, the monkeys may hold “emotionally charged expectations about reward distribution and social exchange.” According to the authors, the capuchins’ reactions also “support an early evolutionary origin of inequity aversion.”

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 9/23/2003.