The study, published in Nature Communications, explains:
“We find that the monkeys accept food less frequently from those who persistently reject another’s requests for help. This negative social evaluation effect is robust across conditions, and tightly linked to explicit refusal to help. Evaluation of potential helpfulness based on third-party interactions may thus not be unique to humans.”
In the study, two humans acted out scenarios in which one of them refused to help the other open a glass jar that contained a toy. A group of seven capuchin monkeys watched the interactions after having been trained to receive food from only one person at a time.
When the two actors then offered food to the monkeys, the monkeys gravitated towards the human who had exhibited cooperative behavior.
But why did the monkeys reject the “selfish” human offering free food? The study suggests that selfish behavior may be seen by the monkeys as “dangerous” behavior.
“Explicit refusal to help is a signal that you’re dangerous, that you’re negative,” Kiley Hamlin, a developmental psychologist at the University of British Columbia in Vancouver, Canada, told Scientific American.
The capuchin monkeys are highly social and cooperative, so the study’s findings do not necessarily translate to all animals. But it does raise the possibility of the behavior being measured in other primates.
Another study published in January found that some chimpanzees have the ability to recognize fairness, another trait previously thought limited to humans.
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