Humans certainly have a sense of fairness, but can an animal feel taken advantage of by another animal?

Researchers Sara Brosnan and Frans de Waal at Yerkes National Primate Research Center trained capuchin monkeys to give tokens in exchange for food. Then, working with pairs of monkeys, Brosnan gave one monkey a grape in exchange for a token while only exchanging a less-tasty cucumber with the second monkey.

As the bartering progressed, the second monkey began to refuse to trade its token or rejected the cucumber. When the first monkey was given a grape with no request for a token in trade, the second monkey became uncooperative and stopped working entirely, sometimes even throwing things.

This experiment implies that the human sense of fairness is evolved rather than learned, and is shared by others in the animal kingdom.

Do our pet species also have this sense of fairness? Only future research will tell.

– Dr. Marty Becker is co-author of the new book “Chicken Soup For The Horse Lover’s Soul.”