As there is no such thing as a free lunch, Sammy and Bias had to work for theirs. The two capuchin monkeys (the species once employed by organ grinders) sat in side-by-side cages separated by a mesh barrier while just beyond the bars was a tray holding two cups of food. It was counterweighted so that both monkeys had to pull a bar to haul in lunch, moving the tray snugly against the cage in such a way that Sammy could reach one cup and Bias the other.
But Sammy was in such a hurry to chow down that after grabbing the apple in her cup, she let go of the tray before Bias could dig into her own. The tray snapped out of reach, causing Bias to scream bloody murder. After half a minute, Sammy understood. She reached out for the tray and helped Bias reel it in.
Anyone who has been around toddlers will recognize Bias's reaction as a simian, "That's not fair!"
The concept of equity -- and fury when it is violated -- lies deep in the human psyche. But scientists have long wondered whether it is a product of learning or something innate, from deep in our evolutionary past. That question has taken on added importance as behavioral economists probe why people sometimes make "irrational" decisions, such as rejecting a payoff that would leave them quantitatively better off if a rival unfairly benefits.
Sammy's reaction, righting the inequity, hints at something even more intriguing: Animals other than humans are not only sensitive to unfairness, but are driven to rectify it. Philosophers have long argued that this ability underlies much of our human morality.
The search for the roots of our sense of equity began, as
science often does, with casual observations. Primatologist
Frans de Waal of the
Treat me unfairly? Take that!
Capuchins, too, know unfairness when they see it. They prefer grapes to cucumbers, and when a scientist gave a grape to one capuchin and a cucumber to another, the latter threw it onto the ground and stalked away rather than acquiesce to this injustice.
Now, the research is moving from observations to experiments, such as the pull-tray that triggered Bias's tantrum. To test how sensitive capuchins are to inequity, Prof. de Waal and colleagues counterweighted the tray so that it required only one monkey to reel it in. In this case, the monkey almost never shares its apple with the monkey who hasn't helped. No work, no pay is fair.
When pulling the tray requires two monkeys' efforts, but only one cup is filled, the lucky monkey often shares its spoils. "Winners were, in effect, compensating their partners for received assistance," Prof. de Waal writes. It was the fair thing to do.
To be sure, a saintly commitment to fairness isn't the only thing going on here. By being magnanimous, the monkey who shares his reward with a hard-working but unrewarded partner makes it more likely that when the tables are turned, she will be treated with equal generosity.
Paired with a relative, monkeys are even more willing to pull the tray, even if their own cup (which they can see from afar) is empty. "Fair," it seems, covers a family member reaping the rewards of your labors even if you don't.
Even when little or no effort is required, chimps and capuchins
balk at unfair situations, says anthropologist Sarah Brosnan
A sense of fairness underlies irrational choices by humans, too. Economists assume that economic decisions are rational, but in many cases people prefer to gain less in order to punish someone who is behaving unfairly. If a partner proposes a $7/$3 split of $10 offered in an experiment, many people reject it outright, gaining nothing rather than accepting the inequity. "People are willing to give up their own potential gain to block someone else from unfairly getting more than themselves," says Ms. Brosnan, who points to resistance to globalization and free trade as current examples.
It isn't hard to see the survival value of being able to detect inequity. Cooperation requires a grasp of fairness. You need to be able to detect (and punish) freeloaders to keep a cooperative society running. "Fairness counts," she says. "Humans and other animals are able to detect unfairness because doing so is beneficial."
And, it seems, it's an ancient attribute of the primate mind.
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