So a final experiment that I want to mention to you is our fairness study. This became a very famous study, and there are now many more, because after we did this about 10 years ago, it became very well known.

We did that originally with capuchin monkeys, and I'm going to show you the first experiment that we did.

It has now been done with dogs, with birds, and with chimpanzees.

We started out with capuchin monkeys. So what we did is we put two capuchin monkeys side by side. Again, these animals they live in a group, they know each other.

We take them out of the group, put them in a test chamber, and there's a very simple task that they need to do.

And if you give both of them cucumber for the task, the two monkeys side by side, they're perfectly willing to do this 25 times in a row.

So cucumber, even though it's really only water in my opinion, but cucumber is perfectly fine for them.

Now, if you give the partner grapes—the food preferences of my capuchin monkeys correspond exactly with the prices in the supermarket—and so if you give them grapes, it's a far better food than, you create inequity between them.

So that's the experiment we did. Recently, we videotaped it with new monkeys who had never done the task, thinking that maybe they would have a stronger reaction, and that turned out to be right.

The one on the left is a monkey who gets cucumber, the one on the right is the one who gets grapes. The one who gets cucumber, note that the first piece of cucumber is perfectly fine, the first piece he eats, and then she sees the other one getting grape, and you will see what happens.

So she gives a rock to us—that's the task—and we give her a piece of cucumber, and she eats it.

The other one needs to give a rock to us, and that's what she does, and she gets a grape.

And she sees the other one—she gives a rock to us, and now gets again cucumber. She tests her rock now against the wall, she needs to give it to us, and she gets cucumber again.

So, this is basically the Wall Street protest that you see here.

Two Monkeys Were Paid Unequally: Excerpt from Frans de Waal's TED Talk

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