Facts So Romantic

Was the Golden Rule Born in the Mind of a Monkey?

As economic inequality increased in many wealthy nations in recent years, a debate has developed around the question of whether inequality is bad for national economies—and bad for their citizens. A captivating video clip of monkey behavior (see below), taken from a 2011 TED talk by primatologist Frans de Waal, has become a surprising piece of ammunition in this discussion.

The video illustrates a famous 2003 experiment by de Waal and his colleague Sarah Brosnan. It begins with a capuchin monkey being rewarded with a cucumber slice for handing a rock to the experimenter. The monkey happily performs this task and collects her payment—until the monkey next to her is given a more desirable reward, a grape, for the same job. The first monkey then flings the unappetizing cucumber from her cage. In the study, the monkeys often refused to hand over a rock if they saw the other monkey get grapes while they themselves continued to get cucumbers.

Frans de Waal says that his research with primates shows that “instead of fairness and justice being intellectual products, something we have arrived at through reason, they are embedded in basic emotions, some of which are found in other primates,” possibly through a shared evolutionary history. “This is basically the [Occupy] Wall Street protest that you see here,” de Waal says at the end of the video clip. If his point about fairness is right, then arguments about inequality take on a biological imperative—greater equality can be seen as the “natural order” of things, and inequality as an inherently destructive force. As de Waal himself has argued in his most recent book, The Age of Empathy, our capacity for building a stable society rests in part on knowing what kind of animals we humans are. (For more on de Waal’s thinking on primate morality, see “The Cosmopolitan Ape,” his Q&A with Nautilus last year.)

For a social-justice activist, the message from the monkeys may seem clear: Equal effort deserves equal pay, and any society that ignores this simple principle is messing with a deeply rooted instinct for fairness. But within the scientific world, far from settling the nature of fairness, Brosnan and de Waal’s classic study has prompted a stream of research that shows just how complex and fragile fairness can be in primate and human interactions.

If you watch the video of the capuchin monkeys (especially if it’s in the context of a blog post on income equality), it may seem obvious that the underpaid monkey is objecting to unfair treatment. But a sense of fairness may not be what’s driving the monkey’s behavior. Imagine that there was no second monkey in the experiment, just one monkey and an experimenter with a bowl full of cucumbers and another full of grapes. If the monkey were given the cucumber as a reward in that case, she might also object to it—not because it was unfair, but just because the cucumber doesn’t seem very appealing once the monkey knows there are grapes to be had. The monkey who rejects cucumbers may be less like a political protester and more like a two-year-old swatting away a proffered apple slice when a well-stocked candy jar is in full view.

To show that fairness is involved, the experiments need to demonstrate that monkeys are more reluctant to do the task when another monkey actually receives better payment, as compared with a situation in which the better reward is simply clearly visible. When such controls have been applied, the results of the studies have been mixed: Some primate species, like the highly social capuchin monkeys, do show sensitivity to social inequity, but chimpanzees generally seem less preoccupied with fairness.

“This is basically the [Occupy] Wall Street protest that you see here.”

On the whole, evidence for fairness in other primates is much more limited than it is in adult humans. Monkeys and apes don’t reject an unequal distribution if the food is freely given rather than paid out in exchange for a task. In the lab, they generally act in their own interest when choosing how to dole out resources, while people are more likely to share equally with a partner. And they don’t turn down unequal offers in a task known as the “ultimatum game,” in which one partner decides how to divide up some resources and the other partner either accepts the offer or decides that neither partner will get anything. People often sacrifice resources in order to express contempt for an unequal offer, whereas chimps typically take what they can get, fair or not.

Experimental comparisons between humans and other animals are notoriously tricky, and there may be many reasons why primates don’t respond to unfairness in the particular ways that are measured in experiments. In some cases, the animals may have noticed an unequal outcome, but the experimental setup doesn’t offer the option for a useful response—and since they can’t verbally object to the injustice, we may never know how they really feel about it. In other cases, the experimental tasks may be so complicated that the animals fail to fully grasp their consequences. So while there’s some evidence that equity plays a role in animal behavior, scientists continue to debate whether this really shows that fairness is an instinct that we share with other animals.

Another way of approaching the question is to look at how fairness shapes the behavior of human children; a very early sensitivity to fairness would support the idea that it’s at least partly innate rather than entirely the product of cultural indoctrination. 

And indeed, babies distinguish between fair and unfair behavior in others at a very young age. In a study by Alessandra Geraci and Luca Surian, 12- to 18-month-old babies watched short videos in which one “fair” animated character gave a toy to each of two other characters, while another “unfair” character handed two toys to a single character, leaving the other empty-handed. Afterwards the children were offered pictures of the fair and unfair characters and were told to pick one of them. Fourteen of 17 babies chose the fair character rather than the unfair one, suggesting that infants value fairness in others long before they’re capable of having conversations about morality and ethics.

But studies show that it takes a surprisingly long time for children to incorporate fairness into their own actions. Three- and 4-year-olds do readily object to an unequal distribution of resources if they’ve received the short end of the stick. But, like non-human primates, they rarely protest when they’re on the winning end of an unequal distribution. This makes it hard to know whether it’s unfairness that they dislike, or simply getting less than others.

As children become aware of their social reputations, they start to behave in ways that they know are valued by others.

In fact, in deciding how to distribute resources, preschoolers strongly favor divisions in which they come out ahead of others; not only are they likely to claim more than their own share, they even show a spiteful tendency to sacrifice resources if it means that they can have more than someone else. A recent study by Mark Sheskin and colleagues showed that when given a choice between allotting two prize tokens each to themselves and another child and claiming one for themselves while giving none to the other, 5- and 6-year-olds preferred the latter. If humans come predisposed to value fairness—and the study with young babies suggests that’s true—then it would appear that the abstract notion of fairness has to battle other, more self-serving impulses.

It’s not until closer to 8 years of age that children show a robust tendency to divide resources equally. And even then, they may be more concerned with appearing fair to others than with actually being fair. In a forthcoming study led by Alex Shaw, children between 6 and 11 years of age had to decide how to allocate a nice prize and a lesser prize between themselves and another child. They were told that they could either just choose who got which prize, or they could flip a coin to determine the outcome. The older children (ages 9 to 11) chose to flip the coin 53 percent of the time, as opposed to 37 percent among the younger group. But when they were given the option to flip the coin in private and report the outcome, the “impartial” coin flip magically landed in their favor 62 percent of the time. This suggests that even for the older children, unfairness itself doesn’t necessarily cause distress—at least, not enough to make them give up the good prize. But as children become aware of their social reputations, they start to behave in ways that they know are valued by others.

As they approach adulthood, children show a steadily increasing tendency to distribute resources equally or even altruistically. But paradoxically, they may become less egalitarian in certain ways over the course of their development. Ernst Fehr and his colleagues found that children were more likely to deprive their peers of resources, even at a cost to themselves, if they were told that the other children came from a different school than if they were told that they belonged to the same school. This bias against members from a different group increased with age into the teen years, even though on the whole, teens were much less likely than younger kids to behave selfishly. In other words, they behaved more generously overall, but treated in-group and out-group members more unequally. For example, at ages 8 and 9, children made spiteful choices 41 percent of the time with in-group members and 44 percent of the time with out-group members, as compared with 17 versus 33 percent for 12- and 13-year-olds.

This growing body of research points toward conclusions that are much more nuanced than simply, “We are wired for equality.” Ultimately, knowing what kind of animals we are may help us better understand to what degree fairness is really an innate, primate value, as opposed to a product of our exceptional modern moment.


Julie Sedivy teaches at the University of Calgary. She is the author of Language in Mind: An Introduction to Psycholinguistics and the co-author of Sold on Language: How Advertisers Talk to You and What This Says About You.


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