The latest salvo in this longstanding debate comes not from philosophers, economists or priests, but from the lab. After a four-month study of capuchin monkeys, Frans de Waal and Sarah Brosnan of Emory University came to a startling conclusion: these primates have a rudimentary sense of justice, and in some cases are willing to take a stand against injustice even at the cost of their own well-being. The findings, published last week in the scientific journal Nature, suggest that justice is not so much a product of nurture, a lesson taught by parents and community, as an evolved trait. For humans, the implications are clear: if lower primates have an inborn sense of justice, humans probably do, too. Does this mean that Thomas Hobbes and Adam Smith were wrong about our selfish natures? “Economists have always disregarded the sense of fairness because it’s not considered to be a rational behavior,” says Brosnan. “Now it looks like it was there long before advanced cultural institutions came about.”
So how did Brosnan and de Waal find the sense of fairness in primates? They began with a pair of brown capuchin monkeys, chosen precisely because they’re extremely interdependent creatures known to be good at cooperating with one another. They gave the monkeys tokens, and then, with outstretched hand, palm up, asked for the token in exchange for a slice of cucumber. The monkeys at first seemed happy with this barter arrangement, willingly giving up a token for a reward.
Things really got interesting when the scientists began treating the monkeys unfairly. They gave one monkey, in full view of her partner, a sweet, juicy grape. Then they turned to the partner and offered not a grape but a plain old cucumber. Often, the reaction was emotional and decisive: she spurned the cucumber–even though she had no reason to expect that her action would prod the experimenters into giving her a grape. (All monkeys in the experiment were female; males apparently didn’t care as much about who received what kind of food.) The researchers tried the experiment in different variations on five female monkeys more than 50 times, and got a self-destructive, rebellious response 40 percent of the time. When the scientists took the experiment a step further, offering one monkey a grape for no reason, resistance in the other monkey doubled: four times out of five, she either refused to hand over a token or spurned the cucumber. Sometimes the aggrieved monkey even went so far as to toss the token out of the test chamber.
To de Waal, such self-righteous indignation in a primate suggests that “human behavior has very old evolutionary roots.” The aggrieved monkeys seemed to recognize the unfairness of their position, and their reactions were telling precisely because they were irrational. The cucumber-holding monkey, after all, gave up a reward for no apparent reason other than to demonstrate disgust at being badly treated. It suggests that a sense of fairness is as primal as base emotions, and that both may have been passed down through eons of evolution.
Studies of humans also support the notion that justice is deeply ingrained. Economist Ernst Fehr of the University of Zurich has shown that under certain circumstances people will often reject an unfair offer even if it means both parties are worse off. Recently a group of Princeton researchers used imaging tools to find out what went on in the brain when such an offer was spurned. They found significantly more activity in the parts of the brain associated with negative emotions such as anger and disgust, suggesting that fairness is not a higher, rational function at all. “This is ultimately about the correct view of human nature,” says Fehr. “Mainstream economics is built on this assumption that people are completely selfish, but what happens if employers want to cut wages?” Just like the monkeys, the humans might rebel and quit, even if it meant no money rather than less.
Perhaps what de Waal and Brosnan have observed in their capuchin monkeys is the early stirrings of a system of morals. It’s not clear if scientists will ever succeed in tracing how the fairness instinct grew into the even more enlightened sense that, as John Donne wrote, “any man’s death diminishes me, because I am involved in mankind.” But on the other hand, that may not matter so much. There’s probably no need for monkeys to share all of our virtues.
