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.

当实验者先前向同种个体提供偏好食物时，黑猩猩会拒绝非偏好食物，这一现象此前被视为公平感感知的佐证。本文提出一种全新假说——社会失望假说（social disappointment hypothesis），该假说认为黑猩猩的拒食行为实则表达了其对人类实验者未能给予其同等优渥奖励的失望情绪。我们采用2×2实验设计对该假说展开检验，实验设置包含两个变量维度：食物分配主体为人类实验者或机器，以及场景中是否有同伴在场。结果显示，相较于机器分配食物的情境，黑猩猩在人类实验者分配食物时更易出现拒食行为；而同伴在场与否并未显著提升其拒食概率。上述研究结果表明，黑猩猩对非偏好食物的拒食行为源于其对实验者的社会失望情绪，而非公平感感知。