Monkeys reject unequal pay.
Level 5 - mechanism / opinion, no new human data
Animal behavioral study with no human data.
PubMed 13679918 · doi:10.1038/nature01963
What was done
Brown capuchin monkeys (Cebus apella) engaged in reward-exchange tasks with a human experimenter while observing the rewards given to a conspecific partner. The study evaluated their behavioral responses when observing a partner receive a more attractive reward for equal effort or for no effort at all.
What was found
The abstract reports no numerical data, sample sizes, or test statistics. Qualitatively, monkeys refused to participate in exchanges when a conspecific received a more attractive reward for equal effort, and this refusal effect was amplified when the partner received the reward without expending any effort.
Why it matters
These findings suggest that inequity aversion is not unique to humans, pointing to an early evolutionary origin for fairness-related behaviors linked to cooperation.
Limits
The abstract omits the sample size, specific reward types, trial numbers, baseline refusal rates, and quantitative effect sizes. Furthermore, findings from captive animals interacting with human experimenters may not fully generalize to natural conspecific interactions in wild populations.
Cited by
- supports In behavioral experiments on capuchin monkeys, a monkey receiving a lower-value food reward reacts with anger and shakes the cage bars when a neighboring monkey receives a higher-value treat (a grape) for performing the same task.