inequity aversion
(in.ek.wuh.tee uh.VUR.zhun) n. An innate tendency to resist or react negatively to inequitable or unfair situations.
inequity-averse adj.

Example Citations:
Attention bosses: Even monkeys seem to know the value of equal pay for equal work.

When rewarded similarly for the same task — in this case, exchanging a small rock with a scientist — capuchin monkeys worked happily for a slice of cucumber. But after they witnessed a partner getting a coveted, succulent grape for the bit of granite, the cucumber-paid monkeys took offense.

Some went on strike. Some kept halfheartedly doing the work, but refused to accept the stinkin' cucumber.

"There were none that didn't care," said Sarah Brosnan, a graduate student at Emory University in Atlanta. A description of her experiment, conducted with Emory's Frans de Waal, appears Thursday in the journal Nature.

If primates offer a window to the origin of human behavior, the findings suggest that people may be born with a strong, primal reaction to unfair rewards. The researchers even have a term for it: "inequity aversion."
—Laura Beil, "Monkeys show sense of fairness about work, rewards in experiment," Knight-Ridder, September 18, 2003

During the evolution of cooperation it may have become critical for individuals to compare their own efforts and pay-offs with those of others. Negative reactions may occur when expectations are violated. One theory proposes that aversion to inequity can explain human cooperation within the bounds of the rational choice model, and may in fact be more inclusive than previous explanations. Although there exists substantial cultural variation in its particulars, this 'sense of fairness' is probably a human universal that has been shown to prevail in a wide variety of circumstances. However, we are not the only cooperative animals, hence inequity aversion may not be uniquely human. Many highly cooperative nonhuman species seem guided by a set of expectations about the outcome of cooperation and the division of resources. Here we demonstrate that a nonhuman primate, the brown capuchin monkey (Cebus apella), responds negatively to unequal reward distribution in exchanges with a human experimenter. Monkeys refused to participate if they witnessed a conspecific obtain a more attractive reward for equal effort, an effect amplified if the partner received such a reward without any effort at all. These reactions support an early evolutionary origin of inequity aversion.
—Sarah F. Brosnan and Frans B. M. de Waal, "Monkeys reject unequal pay," Nature, September 18, 2003

Earliest Citation:
We model fairness as self-centered inequity aversion. Inequity aversion means that people resist inequitable outcomes; i.e., they are willing to give up some material payoff to move in the direction of more equitable outcomes. Inequity aversion is self-centered if people do not care per se about inequity that exists among other people but are only interested in the fairness of their own material payoff relative to the payoff of others. We show that in the presence of some inequity-averse people "fair" and "cooperative" as well as "competitive" and "noncooperative" behavioral patterns can be explained in a coherent framework.
—Ernst Fehr and Klaus M. Schmidt, "A theory of fairness, competition, and cooperation," Quarterly Journal of Economics, August 1, 1999

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