ABSTRACT
Humans are not the only species that is sensitive to outcome inequality. Other species, too, respond negatively to getting less than a social partner, and this breadth suggests a common biological foundation. Across species, negative responses to inequity are linked to the degree to which those species cooperate, and within cooperative tasks, subjects are sensitive to inequity, refusing to work with partners who do not equitably share rewards. Together, these results suggest that inequity aversion evolved because it provides a mechanism by which individuals can judge the relative value of their cooperative partners. In addition, humans and chimpanzees respond negatively to getting more than a partner, suggesting that they can inhibit this short term benefit for the long term gain of maintaining cooperative relationships. The comparative approach has been extremely useful in highlighting the roots of inequity responses and, thereby, helping us to better understand our own sense of fairness.
