Why do chimpanzees react when their partner gets a better deal than them? Do they note the inequity or do their responses reflect frustration in response to unattainable rewards? To tease apart inequity and contrast, we tested chimpanzees in a series of conditions that created loss through individual contrast, through inequity, or by both. Chimpanzees were tested in four social and two individual conditions in which they received food rewards in return for exchanging tokens with an experimenter. In conditions designed to create individual contrast, after completing an exchange, the chimpanzees were given a relatively less-preferred reward than the one they were previously shown. The chimpanzees’ willingness to accept the less-preferred rewards was independent of previously offered foods in both the social and individual conditions. In conditions that created frustration through inequity, subjects were given a less-preferred reward than the one received by their partner, but not in relation to the reward they were previously offered. In a social context, females were more likely to refuse to participate when they received a less-preferred reward than their partner (disadvantageous inequity), than when they received a more-preferred reward (advantageous inequity). Specifically, the females’ refusals were typified by refusals to exchange tokens rather than refusals to accept food rewards. Males showed no difference in their responses to inequity or individual contrast. These results support previous evidence that some chimpanzees’ responses to inequity are mediated more strongly by what others receive than by frustration effects.
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We thank Bart Wilson and an anonymous reviewer for their insightful and constructive feedback on this manuscript. We also thank all the staff at the UT MD Anderson Cancer Center for their help and for providing the highest quality of care for the chimpanzees housed there. This research was funded by a NSF CAREER grant award to SFB (SES 0847351). At the time of writing, LMH was supported by the Leo S. Guthman Fund. The chimpanzee colony is supported by NIH U42 (OD-011197).
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Hopper, L.M., Lambeth, S.P., Schapiro, S.J. et al. Social comparison mediates chimpanzees’ responses to loss, not frustration. Anim Cogn 17, 1303–1311 (2014). https://doi.org/10.1007/s10071-014-0765-9
- Individual contrast
- Social contrast