McAuliffe Katherine, Shelton Natalie, Stone Lauren
Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA,
Anim Cogn. 2014 Nov;17(6):1289-301. doi: 10.1007/s10071-014-0764-x. Epub 2014 Jun 4.
The human sense of fairness entails sensitivity not just to equality, the equal division of resources, but also to merit, the relationship between an individual's share of resources and how hard they worked for their share. Recent evidence suggests that our sensitivity to equality has deep phylogenetic roots: several nonhuman animal species show an aversion to unequal reward distributions. However, the extent to which nonhuman animals share sensitivity to merit remains poorly understood, largely because previous studies have failed to properly manipulate work effort in inequity aversion tasks. Here, we tested whether cotton-top tamarins (Saguinus oedipus) would exhibit a differential response to inequity when acquiring rewards was either (1) effortful or (2) effortless. Subjects engaged in a pulling task in which they had an opportunity to deliver a disadvantageously unequal distribution of food to themselves and a partner (one piece for self, four pieces for partner). We made delivery effortful by adding a weight to the pulling handle. Critically, effort was calibrated to each individual. Results show that individuals varied markedly in their response to effort, highlighting the importance of manipulating work effort at the individual level. Overall, subjects showed little aversion to inequity. However, subjects were slightly less likely to accept inequity when doing so was effortful, although this effect was pronounced in only one individual. Our findings suggest a new method for capturing individual variation in effort and for studying the roots of the concept of merit in nonhuman animals.
人类的公平感不仅涉及对平等（资源的平均分配）的敏感，还涉及对功绩（个人资源份额与其为获取该份额所付出努力之间的关系）的敏感。最近的证据表明，我们对平等的敏感有着深厚的系统发育根源：几种非人类动物物种表现出对不平等奖励分配的厌恶。然而，非人类动物对功绩的敏感程度仍知之甚少，这主要是因为以往的研究未能在不公平厌恶任务中恰当地操控工作努力程度。在此，我们测试了棉顶狨猴（Saguinus oedipus）在获取奖励时（1）需要努力或（2）无需努力的情况下，是否会对不公平表现出不同的反应。实验对象参与了一项拉动任务，在该任务中，它们有机会给自己和同伴分配到不利的不平等食物（自己一份，同伴四份）。我们通过在拉柄上加重物使分配变得费力。关键的是，努力程度是根据每个个体进行校准的。结果表明，个体对努力的反应差异显著，这凸显了在个体层面操控工作努力程度的重要性。总体而言，实验对象对不公平几乎没有厌恶感。然而，当这样做需要努力时，实验对象接受不公平的可能性略低，尽管这种效应仅在一个个体中较为明显。我们的研究结果提出了一种新方法，用于捕捉个体在努力方面的差异，并研究非人类动物功绩概念的根源。
