The natural human response to unfairness most likely evolved to support long-term cooperation.
Researchers have spent the past decade studying primate behavioral responses to unequal versus equal rewards, Georgia State University reported.
"This sense of fairness is the basis of lots of things in human society, from wage discrimination to international politics," said Dr. Sarah Brosnan of Georgia State's departments of Psychology and Philosophy, the Neuroscience Institute and the Language Research Center.
"What we're interested in is why humans aren't happy with what we have, even if it's good enough, if someone else has more. What we hypothesize is that this matters because evolution is relative. If you are cooperating with someone who takes more of the benefits accrued, they will do better than you, at your expense. Therefore, we began to explore whether responses to inequity were common in other cooperative species," she said.
Brosnan and colleague Dr. Frans de Waal of the Yerkes National Primate Research Center and the Psychology Department at Emory University started testing how monkeys respond to fairness back in 2003 and were the first to report on the subject.
In this recent study the researchers observed brown capuchin monkeys got upset and refused to perform assigned tasks if their peer received a more desirable reward for completing the same activity. Inequity responses have now been tested in nine different primate species, humans included. The study's results suggest species only respond to "unfairness" if they are working with others.
Brosnan and de Waal hypothesized individuals should be willing to sacrifice a personal reward if it means their group will solidify long-term cooperative relationships; this phenomenon was only observed in apes and humans.
"Giving up an outcome that benefits you in order to gain long-term benefits from the relationship requires not only an ability to think about the future, but also the self-control to turn down a reward," Brosnan said. "These both require a lot of cognitive control. Therefore, we hypothesize that lots of species respond negatively to getting less than a partner, which is the first step in the evolution of fairness, but only a few species are able to make the leap to this second step, which leads to a true sense of fairness."
The findings were published recently in the journal Nature.
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