Nonhuman Species’ Reactions to Inequity and their Implications for Fairness

It is well known that humans respond negatively to inequity, but until recently little has been known about such responses in animals. Previous observational research in animals has shown hints that animals do respond to inequity. Chimpanzees respond with temper tantrums if they do not get what they desire, social canids refuse to play with individuals who violate social rules, and ravens show third party intervention against norm violations. Recent experimental work with nonhuman primates has given us a more detailed understanding. Capuchin monkeys and chimpanzees both respond negatively to distributional inequity. Moreover, chimpanzees show significant variation in response depending upon the social group they inhabit, with those from a short-term group or a relatively asocial living situation showing a much greater response to inequity than those from a long-term stable group. This mirrors human variation in responses to inequity, which are based upon the quality of the relationship. In this paper, I attempt to define ‘‘fairness’’ in a way that is useful for nonhuman studies and clarify what aspects are being examined in animal societies. I then place the animal work in the context of the studies on humans, especially as related to research in social psychology and economics. I conclude that studying the inequity response in animals is useful for a number of reasons, including the opportunity to gain insight into how this response functions in less complex organisms and social systems and clarification of our understanding of the evolution of this behavior.