Capuchin Monkey Experiment

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

A famous experiment which demonstrated the Norm of Equity.

In the experiment, capuchin monkeys were given tasks to complete. When one monkey completed the task and received a cucumber slice as a reward, it was content. However, when another monkey completed the same task and received a grape (a more desirable reward), the first monkey became visibly upset upon seeing the unequal treatment.

In fact, it began to reject its cucumber slice, throwing it back at the experimenter.