Primate researchers might have to watch for union uprisings among their subjects. Well, not quite, but a new study shows that capuchin monkeys have a sense of fairness about work they've done and will refuse a reward for their toil if other monkeys get paid better. The results indicate that a sense of equity goes far back in primate evolution.
In the last decade, behavioral scientists have found that humans will reject pay--to their own detriment--if they perceive that they are being treated unfairly. Researchers have debated whether this response was unique to humans, whose cultures often promote equality and cooperativity, or whether it arose earlier in primate evolution.
To determine whether other primates also have a sense of equality, biopsychologists Susan Brosnan and Frans de Waal at Emory University in Atlanta tested capuchin monkeys, whose evolutionary path diverged from ours some 4.5 million years ago. They used a simple task-and-reward experiment: Brosnan handed a token to one monkey in a pair, and if the monkey gave it back to her, she gave it either a piece of bland cucumber or a yummy grape as a reward. If one monkey earned a grape, and the second monkey in the pair was only offered a cucumber chunk as compensation, it would often refuse the cucumber.
If one monkey received a grape in the absence of any token-swapping work, the presumably indignant second monkey would sometimes throw its own token away instead of enduring the humiliation of performing work only to be underpaid. Whereas monkeys almost always gave back the token when they were both paid equally, more than 50% of the time they didn't when the reward was unfair, the researchers report in the 18 September issue of Nature.
Behavioral economist Ernst Fehr of the Massachusetts Institute of Technology in Cambridge says this sense of equality in human culture is the reason salaries in companies are not made public. "Why not? Everyone would think they were underpaid." He says this is the first time that researchers have shown the concept of equity to exist in nonhuman primates. The fact that "even monkeys" reject unequal pay means the sense of fairness is "deeply evolutionarily rooted."