Humans have been fighting against unequal pay for centuries. Our natural sense of fairness rejects unequal pay for doing the same tasks or work. What’s interesting, is that humans aren’t the only creatures who reject unequal pay.

In this video, Dr. Frans De Waal shares with us an experiment he did with Dr. Sarah Brosnan on Capuchin Monkeys. The experiment was to find if Capuchin monkeys reacted to unequal pay the same way humans do, or if the rejection of unequal pay is purely a human reaction. The scientists took two Capuchins out of their normal family group and put them in a test chamber. The monkeys were given a very simple task to complete, if they completed the task they were given a reward. The task throughout the experiment was the same, hand the experimenter a rock from inside the test chamber. In the control group, both monkeys were given cucumbers as the reward. If the both monkeys are given cucumber for their reward, the monkeys are perfectly willing to continue doing the task twenty five times in a row. Where the experiment gets interesting, however, is when the scientists begin to give one of the monkey unequal pay.

In the experimental group, the scientists ask the Capuchin monkeys to perform the same task, but one monkey receives cucumbers, and the other monkey receives grapes. Grapes are considered a better, more delicious food by the monkeys. The difference in reaction is startling. The monkey who is given cucumbers, while initially happy to perform the task, becomes enraged when it sees the monkey in the other cage being payed in grapes, not cucumbers. The monkey immediately begins throwing the cucumbers at the experimenter and demanding grapes after it has completed it’s task. Eventually the monkey will even stop performing the task it does not get equal pay for.

This fantastic experiment shows that the rejection of unequal pay is not just a human trait. Other animals also have an innate sense of fairness and will reject the inherent inequality of unequal pay as well.