Data from: Social disappointment explains chimpanzees' behaviour in the inequity aversion task

Chimpanzees’ refusal of less-preferred food when an experimenter has
previously provided preferred food to a conspecific has been taken as
evidence for a sense of fairness. Here, we present a novel hypothesis—the
social disappointment hypothesis—according to which food refusals express
chimpanzees' disappointment in the human experimenter for not
rewarding them as well as they could have. We tested this hypothesis using
a two-by-two design in which food was either distributed by an
experimenter or a machine and with a partner present or absent. We found
that chimpanzees were more likely to reject food when it was distributed
by an experimenter rather than by a machine and that they were not more
likely to do so when a partner was present. These results suggest that
chimpanzees’ refusal of less-preferred food stems from social
disappointment in the experimenter and not from a sense of fairness.