My first year in graduate school, studying cooperation in monkeys, I spent a lot of time outside, just watching our groups of capuchin monkeys interact.
One afternoon, I was out back feeding peanuts to one of our groups, which required distracting one of our males, Ozzie, enough so that the other monkeys could get some. Ozzie loved peanuts, and he always tried to do anything he could to grab some.
On that day, however, he began trying to bring other things from his enclosure to me and trade them with me in order to get a peanut. Now, capuchins are smart, so this wasn't necessarily a surprise.
But what was a surprise was that some of the things that he was bringing me, I was pretty sure he liked better than peanuts. First, he brought me a piece of monkey chow, which is like dried dog food — it was even made by Purina — and for a monkey, is about as worthless as it gets.
Of course, I didn't give him a peanut for that. But he kept trying, and eventually, he brought me a quarter of an orange and tried to trade it with me for a peanut. Now, oranges are a valuable monkey commodity, so this trade seemed, shall I say, a little bit nuts? Now you may be wondering how we know what monkeys prefer.
Well, we ask them, by giving them a choice between two foods and seeing which one they pick. Generally speaking, their preferences are a lot like ours: the sweeter it is, the more they like it. So, much like humans prefer cupcakes to kale, monkeys prefer fruits, like oranges or grapes, to vegetables like cucumbers, and all of this to monkey chow.
And peanuts are not bad. However, they definitely don't prefer them to a chunk of orange. So when Ozzie tried to trade a quarter of an orange for a peanut, it was a surprise, and I began to wonder if he suddenly wanted that peanut because everybody else in his group was getting one.
In case you're wondering, I did give Ozzie his peanut. But then I went straight to my graduate adviser, Frans de Waal, and we began to design a study to see how the monkeys would respond when somebody else in their group got a better reward than they did for doing the same work.
It was a very simple study. We took two monkeys from the same group and had them sit side by side, and they would do a task, which was trading a token with me, and if they did so successfully, they got a reward.
The catch was that one monkey always got a piece of cucumber, and the other monkey sometimes got a piece of cucumber, but sometimes got a grape. And if you'll recall, grapes are much preferred to cucumbers on the capuchin monkey hierarchy.
These are two of my capuchin monkeys. Winter, on the right, is trading for a grape, and Lance, on the left, is trading for a cucumber. You can see that she — and yes, Lance is actually a female — is at first perfectly happy with her cucumber, until she sees Winter trading for a grape.
Suddenly, Lance is very enthusiastic about trading. She gets her cucumber, takes a bite and then — throws it right back out again. Meanwhile, Winter trades again and gets another grape and has Lance's undivided attention while she eats it.
This time, Lance is not so enthusiastic about trading. But eventually, she does so. But when she gets the cucumber this time around, she doesn't even take a bite before she throws it back out again.
Apparently, Lance only wants a cucumber when she hasn't just watched Winter eat a grape. And Lance was not alone in this. All of my capuchins were perfectly happy with their cucumbers as long as the other monkeys were getting cucumbers too.
But they often weren't so happy with their cucumbers when other monkeys were getting a grape. The obvious question is why? If they liked those cucumbers before, what changed? Now, I'm a scientist, and scientists are famously shy about reading too much into our studies, especially when it comes to what other animals are thinking or feeling, because we can't ask them.
But still, what I was seeing in my monkeys looked an awful lot like what we humans would call a sense of fairness. After all, the difference in that cucumber was that it came after Winter got a grape, rather than before.
We humans are obsessed with fairness. I have a younger sister, and when we were little, if my sister got a bigger piece of the pie than me, even by a crumb, I was furious. It wasn't fair. And the childhood me is not alone.
We humans hate getting less than another so much that one study found that if humans were given a hypothetical choice between earning 50,000 dollars a year while others earned 25,000 dollars, or earning 100,000 dollars a year while others earned 250,000 dollars, nearly half the subjects prefer to earn 50,000 dollars a year less money to avoid earning relatively less than someone else.
That's a pretty big price to pay. What drives people to this sort of apparently irrational decision-making? After all, throwing away your cucumber because someone else got a grape only makes sense if it makes things more fair.
Otherwise, Winter has a grape, and you have nothing. Of course humans are not capuchin monkeys. But on the surface, sacrificing 50,000 dollars because somebody else is going to earn more money than you makes no more sense than throwing away that cucumber.
Except maybe it does. Some economists think that the sense of fairness in humans is tied to cooperation. In other words, we need that sense of fairness when we're working with somebody else to know when we're getting the short end of the stick.
Think about it this way. Let's say you have a colleague at work who's having a hard time and needs a little extra help. You're probably more than happy to help out, especially if she does the same for you when you need it.
In other words, if things even out. But now, let's say that colleague is always slacking off and dumping extra work on you. That's infuriating. Or worse, what if you're doing all the work, and she's getting paid more.
You're outraged, right? As well you should be. That righteous fury is your sense of fairness telling you that, well, it's not fair. You need to get your fair share from the people you're working with, or it's exploitation, not cooperation.
You may not be able to leave every job where you're treated unfairly, but in a perfect world, one without racism and sexism and the frictions associated with finding a new job, it's your sense of fairness that would let you know when it was time to move on.
And if you couldn't? Well, that smoldering frustration might make you throw your cucumbers too. And humans are not alone in this. In the previous study, there was nothing Lance could do about it, but what if there had been? It turns out that capuchins simply refuse to cooperate with other capuchins who don't give them their share after they worked together.
And refusing to work together with another monkey is a pretty straightforward way of leveling the playing field. Apparently, no monkey getting anything at all is better than another monkey getting more.
But much like you and your coworker, they're perfectly happy with a little short-term inequality as long as everything evens out over the long run. This economic connection between fairness and cooperation makes sense to me as an evolutionary biologist.
After all, your ancestors didn't get to pass on their genes because they did well in some absolute sense, but because they did better than others. We don't call it survival of the fit, we call it survival of the fittest.
As in more fit than others. It's all relative. OK. So my capuchins don't like it when they get less than another. And they're perfectly happy to sacrifice their cucumbers to level the playing field.
That's great. But what we would call a sense of fairness in humans also means that we care when we get more than someone else. What about my monkeys? It turns out that primates do notice when they get more than others, or at least some of them do.
My capuchins do not. But in one of my studies, my chimpanzees would sometimes refuse a grape if another chimpanzee in their group got a cucumber, which is pretty impressive, given how much my chimpanzees like grapes.
However, they were still more upset when they got less than another chimp as compared to when they got more. You may not think it's fair when you have more than your neighbor, but you really don't think it's fair when your neighbor has more than you.
Here's an important question, though. Why do we care about inequality or unfairness when we are the ones who are unfairly benefiting? If evolution is about survival of the fittest, wouldn't it make sense to grab any advantage you can get? Here's the thing though.
I do better if I get more than you, sure. But best of all is if you and I can work together and get more than either one of us could have gotten on our own. But why would you work with me if you don't think I'm going to play fair? But if you think I'm going to notice when I've got more than you and do something about it, then you will work with me.
Evolution has selected us to accept the occasional short-term loss in order to maintain these all-important long-term relationships. This is true in chimpanzees, but it is even more important in humans.
Humans are incredibly interconnected and interdependent, and we have the advanced cognitive abilities to be able to plan far into the future. And to recognize the importance of maintaining these cooperative partnerships.
Indeed, if anything, I think we are likely underplaying how important the sense of fairness is for people. One of the biggest differences between humans and capuchin monkeys is the sheer magnitude and ubiquity of cooperation in humans.
In other words, we're a lot more cooperative than capuchin monkeys are. Legal and economic systems literally only exist if we all agree to participate in them. And if people feel left out of the rewards and benefits of those systems, then they stop participating, and the whole system falls apart.
Many of the protests and uprisings we're seeing, both in the US and around the globe, are explicitly framed in terms of fairness, which is not surprising to me. Whether it's about disproportionate access to resources, or that some groups are being disproportionately impacted by the legal system or the effects of a virus, these protests are the logical outcome of our long evolutionary tendency to reject unfairness combined with our long history of social stratification.
And the systemic inequalities that have resulted from that stratification. Layer on top of this the fact that by many measures economic inequality is skyrocketing. Chris Boehm wrote a book called "Hierarchy in the Forest," in which he argued that humans have reverse hierarchies in which those at the bottom band together to keep those at the top from taking advantage of them.
Perhaps these protests are simply the latest manifestation of humans' tendency to rebalance the hierarchy. Perhaps the biggest difference between us and capuchin monkeys is that we can recognize this problem and actively work to do something about it.
Of course we recognize when we're disadvantaged. But we can and we must also recognize when we're advantaged at the expense of someone else, and recognize fairness as the balance between these two inequalities, because our society literally depends upon it.
Indeed, my research shows that not all primate species care about inequality. It's only those that rely on cooperation, which most definitely includes humans. We evolved to care about fairness because we rely on each other for our cooperative society.
And the more unfair the world gets, and the less we care about each other, the more peril we will face. Our issues are more complex than grapes and cucumbers, but as the capuchins have taught us, we will all do better when we all play fair.