How primates (including us!) respond to inequity.

Purpose: Responding negatively to inequity is not a uniquely human trait. Some of our closest evolutionary ancestors respond negatively when treated less well than a conspecific. Comparative work between humans and other primates can help elucidate the evolutionary underpinnings of humans' social preferences.

Methodology/approach: Results from studies of nonhuman primates, in particular chimpanzees and capuchin monkeys, are presented in comparison to human results that have been collected during economic game studies in humans, such as in the Ultimatum Game or Impunity Game.

Findings: Among nonhuman primates, a frequent behavioral reaction to inequity is to refuse to continue the interaction. While in some cases this response appears to be caused by the inequitable distribution, in others, it seems to be caused by another individual's inequitable behavior. While these reactions are similar to those of humans, this reaction does not appear to be a sense of fairness in the way that we think of it in humans. Neither nonhuman primate species alters their behavior when they are the benefited individual, and in an experimental situation, chimpanzees do not alter their behavior to obtain food for their partner as well as for themselves.

Originality/value of the chapter: Although there are differences between human and nonhuman primate responses, such studies allow us to better understand the evolution of our own responses to inequity. Given the strong behavioral reactions that even monkeys show to inequitable treatment, it is not surprising that humans are concerned with equity. Such comparisons increase understanding of issues such as healthcare disparities in humans.