Capuchin monkeys (Cebus apella) are sensitive to others’ reward: an experimental analysis of food-choice for conspecifics
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The issue whether non-human primates have other-regarding preference and/or inequity aversion has been under debate. We investigated whether tufted capuchin monkeys are sensitive to others’ reward in various experimental food sharing settings. Two monkeys faced each other. The operator monkey chose one of two food containers placed between the participants, each containing a food item for him/herself and another for the recipient. The recipient passively received either high- or low-value food depending on the operator’s choice, whereas the operator obtained the same food regardless of his/her choice. The recipients were either the highest- or lowest-ranking member of the group, and the operators were middle-ranking. In Experiment 1, the operators chose the high-value food for the subordinate recipient more frequently than when there was no recipient, whereas they were indifferent in their choice for the dominant. This differentiated behavior could have been because the dominant recipient frequently ate the low-value food. In Experiment 2, we increased the difference in the value of the two food items so that both recipients would reject the low-value food. The results were the same as in Experiment 1. In Experiment 3, we placed an opaque screen in front of the recipient to examine effects of visual contact between the participants. The operators’ food choice generally shifted toward providing the low-value food for the recipient. These results suggest that capuchins are clearly sensitive to others’ reward and that they show other-regarding preference or a form of inequity aversion depending upon the recipients and the presence of visual contact.
KeywordsOther-regarding preference Prosocial behavior Inequity aversion Food sharing Social sensitivity Capuchin monkeys
This study was supported by the Research Fellowships of the Japan Society for the Promotion of Science (JSPS) for Young Scientists (No. 21264 to Ayaka Takimoto), the Grant-in-Aid for Scientific Research (Nos. 17300085 and 20220004 to Kazuo Fujita) from JSPS, by the 21st Century COE Program, D-10, to Kyoto University, from Japan Ministry of Education, Culture, Sport, Science, and Technology (MEXT) and by the MEXT Global COE Program, D-07, to Kyoto University. The subject monkeys were originally provided by the Cooperation Research Program from the Primate Research Institute, Kyoto University, with Tetsuro Matsuzawa as the counterpart. We also gratefully acknowledge James R. Anderson, Monica Rankin, Kazuhiro Goto for various suggestions on our manuscript, and the editor and three anonymous reviewers for their helpful comments on an earlier version of this article.
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