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Author Notes:

To whom correspondence may be sent at the present address: Sarah F. Brosnan, Department of Psychology, Georgia State University, P.O. Box 5010, Atlanta, GA 30302-5010., Email: sbrosnan@gsu.edu.

To whom correspondence may be addressed: Frans B. M. de Waal, Email: dewaal@emory.edu.

M.v.W., S.F.B., and F.B.M.d.W. designed research.

M.v.W. performed research.

M.v.W., S.F.B., and F.B.M.d.W. analyzed data.

M.v.W., S.F.B., and F.B.M.d.W. wrote the paper.

We thank J. Andreoni and L. Santos for helpful comments on an earlier version of this manuscript, M. Dindo for assistance with testing, and the animal care and veterinary staff for maintaining the health of our study subjects.

The Yerkes Primate Center is fully accredited by the American Association for Accreditation of Laboratory Animal Care.

The authors declare no conflict of interest.

Subjects:

Research Funding:

This work was supported by Grant IBN-0077706 from the National Science Foundation (to F.B.M.d.W.) and Basegrant RR-00165 from the National Institutes of Health (NIH) (to the Yerkes National Primate Research Center).

S.F.B. was supported in part by NIH Institutional Research and Academic Career Development Grant K12 GM00680–05 (to Emory University).

Keywords:

  • capuchin monkey
  • Cebus apella
  • cooperation
  • frustration
  • fairness

Inequity responses of monkeys modified by effort

Tools:

Journal Title:

Proceedings of the National Academy of Sciences

Volume:

Volume 104, Number 47

Publisher:

, Pages 18854-18859

Type of Work:

Article | Post-print: After Peer Review

Abstract:

Without joint benefits, joint actions could never have evolved. Cooperative animals need to monitor closely how large a share they receive relative to their investment toward collective goals. This work documents the sensitivity to reward division in brown, or tufted, capuchin monkeys (Cebus apella). In addition to confirming previous results with a larger subject pool, this work rules out several alternative explanations and adds data on effort sensitivity. Thirteen adult monkeys exchanged tokens for rewards, showing negative reactions to receiving a less-favored reward than their partner. Because their negative reaction could not be attributed to the mere visibility of better rewards (greed hypothesis) nor to having received such rewards in the immediate past (frustration hypothesis), it must have been caused by seeing their partner obtain the better reward. Effort had a major effect in that by far the lowest level of performance in the entire study occurred in subjects required to expend a large effort while at the same time seeing their partner receive a better reward. It is unclear whether this effort–effect was based on comparisons with the partner, but it added significantly to the intensity of the inequity response. These effects are as expected if the inequity response evolved in the context of cooperative survival strategies.

Copyright information:

© 2007 by The National Academy of Sciences

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