Insights into the evolution of the sense of fairness

A sense of fairness has long been considered purely human — but animals also react with frustration when they are treated unequally by a person. In a study with long-tailed macaques (Macaca fascicularis), researchers have now confirmed an alternative explanatory approach. A combination of social disappointment with the human experimenter and some degree of food competition best explains their behavior in an ‘inequity aversion’ experiment.