What the Monkeys Can Teach Humans About Making America Fairer

The capuchin monkey study, published last week in Nature, has generated a lot of interest for a scant three-page report buried in the journal's letters section. There is, certainly, a risk of reading too much into the feeding habits of 10 research monkeys. But in a week when fairness was so evidently on the ropes — from the World Trade Organization meeting in Cancún, which poor nations walked out of in frustration, to the latest issue of Forbes, reporting that the richest 400 Americans are worth $955 billion — the capuchin monkeys offered a glimmer of hope from the primate gene pool.

The study's implication that we are, to some extent, hard-wired for fairness speaks with special force to the legal system. American law has undergone a transformation in recent years, led by conservative Supreme Court justices and scholars, away from a focus on broad principles of fairness and toward a willingness to subject people to treatment that might be unjust, on the grounds that it is legal. The monkey study suggests, however, that fairness might be more than a currently unfashionable legal concept. It may be integral to who we are.

Sarah Brosnan and Frans de Waal, researchers at the Yerkes National Primate Research Center at Emory University, chose capuchin monkeys because capuchins are among the few primates — along with men and chimpanzees — that hunt cooperatively. Team hunting has evolutionary advantages, allowing a species to capture prey, like squirrels, it otherwise could not. In many monkey societies the dominant male eats what he wants, and the others fight over the scraps. But in societies like those of capuchins — and humans — in which hunting is done cooperatively, food is more equitably distributed.

The reason for the sharing is obvious. Cooperative primates will be reluctant to engage in a group hunt if they cannot be assured that their reward will be properly related to their efforts. The capuchin monkeys in the study did not care merely about rules: it was not enough that they were given a cucumber slice when that was what they expected. They also wanted the rule that was applied to them to be, in a larger sense, fair.

In Stanley Kubrick's "2001: A Space Odyssey," an ape-man throws a bone he has just used as a weapon into the air and it is transformed into a spaceship. The discovery of weapons was certainly, as the movie indicates, one of our key evolutionary moments. But the capuchin monkey study is a welcome reminder that the first time an ape-man angrily picked up his food allotment and threw it into the air because it was unjust was no less pivotal to the emergence of what it means to be human.