Like humans, marmosets – tiny monkeys with Einstein-like ear tufts native to Brazil – overhear conversations between others and prefer to approach individuals who see them positively, a study in the journal Science Advances it turned out Wednesday.
While behavioral research has built up knowledge about the social life of primates, it often lacked reliable ways to determine a person’s “inner perspective” or the inner workings of his or her mind.
Marmosets are an ideal species to study because of their close social structure: they live in highly cooperative groups of about 15 family members, with the entire extended clan responsible for raising children.
How do they decide who is reliable and who is not?
A team led by Rahel Brugger from the University of Zurich (UZH) presented 21 captive-born adult marmosets with recordings of a hidden speaker of an adult of the opposite sex making either food offering calls or aggressive chatter in response to begging infants.
As a control, they also played the calls of the marmosets made by one person.
The scientists then focused infrared cameras on the marmosets’ faces to record nasal temperatures – looking for droplets that indicate the monkeys were alert and engaged.
The tests showed that the marmosets only responded to combined calls and not individual calls, indicating that they understood when real calls were taking place.
After playing the recordings, the team had the marmosets enter a room full of toys and a mirror.
Marmosets did not recognize their own reflection and thus believed it to represent the monkey making the recorded call.
The researchers found that the marmosets generally preferred to approach when the recordings indicated that the individual was helpful.
“This study adds to the growing evidence that many animals are not only passive observers of interactions with third parties, but also interpret them,” said Judith Burkart, senior author and professor of anthropology at UZH.
The team plans to use this approach to temperature mapping for future research, such as on the origins of morality.
© Agence France-Presse