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Animal Seem to Have an Inherent Sense of Justice

Animals Seem to Have An Inherent Sense Of Fairness and Justice

November 10, 2006

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

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 Yerkes
National Primate Research Center, Atlanta, once saw a female chimp, Puist,
help her male friend, Luit, chase off a rival. The rival took it out on
Puist. Although Puist reached out her hand to Luit in a plea for backup,
Luit "did not lift a finger to protect her," recalls Prof. de Waal in a
recent paper. You could imagine the "that's not fair!" module in her mind
turning on. Once the rival left, Puist "turned on Luit, barking furiously.
She chased him across the enclosure and pummeled him."

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

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 of Emory University. In
a series of experiments, the animals learned to trade a "token" (a rock or
plastic pipe) with a trainer for food. If they saw a cagemate trade for a
delectable grape, but were offered a cucumber in exchange for their own
token, they were much more likely to refuse to hand it over for the stupid
vegetable. Better to go hungry than to give in to this unfairness.

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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