Abstract

Cooperative animals often find themselves in situations in which they need to monitor and compare pay-offs received from joint ventures. They can compare their pay-offs with a) the history of giving to and receiving from the same partner, b) the effort they put into the venture, or c) what others are getting. There is ample observational evidence that monkeys and apes follow rules of social reciprocity. There is also evidence for market effects of supply and demand. In a series of experiments we have further shown that monkeys show payment for labor and reject income inequality. The latter finding, first reported by Brosnan & de Waal, is directly relevant to the origin of the human sense of fairness. I will discuss how the two relate.