Like humans, marmosets – small monkeys with Einstein-like ears from Brazil – listen to conversations between others and prefer to approach individuals they look at positively, a study in the journal Scientific advances showed Wednesday.
While behavioral research has gained knowledge about the social life of primates, it has tended to lack reliable ways to determine an individual’s “inner perspective” or inner functioning of his or her mind.
Marmosets are an ideal species to study due to their close-knit 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 trustworthy and who is not?
A team led by Rahel Brugger of the University of Zurich (UZH) presented 21 adult yachts born in captivity, with recordings from a hidden speaker of an opposite-sex adult, making either calls for food or aggressive calls from chat in response to begging infants.
As a control, they also played pot calls made by a single person.
The scientists then pointed the infrared cameras at the faces of hell to record nasal temperatures – looking for drops to indicate that the monkeys are alert and engaged.
Tests found that marmosets answered only combined and not individual calls, indicating that they understood when real conversations took place.
After playing the recordings, the team let the shores into a room full of toys and a mirror.
The thugs did not recognize their own reflection and believed that it represented the monkey that made the recorded call.
The researchers found that, overall, the yachts preferred to approach when records indicated that the individual was helpful.
“This study adds to the growing evidence that many animals are not only passive observers of third-party interactions, but that they also interpret them,” said Judith Burkart, lead author and professor of anthropology at UZH.
The team intends to use this temperature mapping approach for future investigations, such as the origin of morality.
© Agence France-Presse