Abstract: Nonhuman primates behave fairly in both captive and natural settings, indicating that they, like humans, seem to have sense of fairness. By analyzing current literature concerning non-human primate grooming behavior, we conclude that non-human primate behavior is consistent with cost-benefit symmetry, which is the essence of inequity aversion. Recent experimental studies indicate that non-human primates are not only concerned about their own cost-benefit symmetry, but also compare themselves with their partners. Some researchers infer from results of their experiments that the expectation hypothesis or frustration effect can account for nonhuman primate behavior. The present article analyzes living experiments and points out that the reason why these experiments yield inconsistent results is that many researchers have not taken into account the “effort” which exerts great influence on subjects’behaviors. We summarize the discussion and put forward three potential directions for future research.

Key words: Nonhuman primate; Sense of fairness; Grooming; Experiment