Are apes inequity averse? New data on the token‐exchange paradigm

Recent studies have produced mixed evidence about inequity aversion in nonhuman primates. Brosnan et al. Proceedings of the Royal Society of London. Series B. Biological Sciences 272:253-258, 2005 found inequity aversion in chimpanzees and argued that effort is crucial, if subjects are to evaluate how they are rewarded in comparison to a competitor for an identical performance. In this study we investigated inequity aversion with chimpanzees, bonobos and orangutans, using the method of Brosnan et al. Proceedings of the Royal Society of London. Series B. Biological Sciences 272:253-258, 2005 after introducing some methodological improvements. Subjects always received a less-preferred food in exchange for a token, whereas the competitor received either the same type of food for their token (equity) or a more favored food for it (inequity). Apes did not refuse more of the less-preferred food when a competitor had received the more favored food. Thus, with an improved methodology we failed to reproduce the findings of Brosnan et al. Proceedings of the Royal Society of London. Series B. Biological Sciences 272:253-258, 2005 that apes show inequity aversion.