(Phys.org) —A common species of monkey is underlining the message that it's nice to be nice.
New research has found that capuchin monkeys – once used by Victorian organ grinders – respond best to humans who are helpful to others, shunning "selfish" people.
Experts at the University of Stirling and Kyoto University in Japan have been studying these clever monkeys, native to Central and South America.
They placed the simians in front of actors and got the humans to act in helpful or unhelpful ways. They then studied the monkeys' readiness to accept food from the performers.
Dr Jim Anderson at the University of Stirling, who led the research team, said: "We found the monkeys accepted food less frequently from the human performers who persistently rejected the other person's requests for help.
"This research is significant as it provides evidence that social evaluation based on third-party interactions – the way we respond to others – is not unique to humans."
The researchers have shared their findings in the online journal Nature Communications this week.
Human beings start evaluating others through eavesdropping or the perceived reputation of others at an early age. However, there has been little experimental analysis of the "social evaluations" of other species.
Dr Anderson said: "The situations acted out in front of the monkeys were of no direct relevance to the animals. However, they judged the interactions of the humans and their disposition.
"This research complements another paper, recently published in journal Cognition, showing that capuchin monkeys also negatively evaluated humans who refused to fully reciprocate in an exchange of objects with another person.
"In other words, the monkeys tended to avoid people who behaved selfishly in interactions with others."
Capuchin monkeys were discovered by explorers to the Americas in the 15th century. They named them after members of a Catholic order – which wears brown robes with large hoods covering their heads.
Highly intelligent, the monkeys were used by old-fashioned organ grinders and were popular pets. More recently some of them have been trained as aides for paraplegic humans.
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More information: The full report is available at: dx.doi.org/10.1038/ncomms2495