Apes have a human-like ability to guess what others are thinking according to research that supports the view that other primates can empathise and have complex inner lives.
In a fresh take on a classic psychology experiment, the apes were able to correctly anticipate that someone would look for a hidden item in a specific location, even if the apes knew that the item was no longer there.
The ability to predict that someone holds a mistaken belief – which psychologists refer to as a “theory of mind” – is seen as a milestone in cognitive development that children normally acquire by the age of five. The findings also overturn the view that the ability to place oneself in another’s shoes is unique to humans.
“This cognitive ability is at the heart of so many human social skills,” said Christopher Krupenye of Duke University. “I think our findings start to suggest that maybe apes have a deeper understanding of each other than we previously thought.”
Previously, primatologists have shown that apes are remarkably skilled at understanding what others want, empathising and even deceiving others to gain advantage for themselves. But when it came to predicting what someone else was thinking, even when they were wrong, apes consistently failed the test.
Krupenye and Fumihiro Kano, a comparative psychologist at Kyoto University who co-led the study, re-examined the question using a creative approach that involved showing the apes videos of a capering actor dressed in a King Kong suit.
“Our challenge was really in making TV that apes would want to watch,” said Krupenye. “Apes are obsessed with social information, and so we created social conflicts that would engage them and encourage them to track the key false belief information.”
The video features an actor dressed as King Kong, who hits a man holding a long pole before darting under one of two haystacks while the human looks on. In some scenarios, the King Kong character switches haystack while the human disappears out of view behind a door.
The man then reappears and smacks the haystack he thinks his assailant is hidden under – presumably to get his own back.
By using eye-tracking technology, the scientists showed that 17 out of 22 apes tested switched their gaze to show they had correctly anticipated when the man would target the wrong haystack.
“King Kong is somewhat ape-like but also unfamiliar and novel, and we knew that these elements would enhance apes’ attention,” said Krupenye. “The movies are silly and comical to humans, but they actually depict the kind of social information that’s really meaningful within ape societies.”
Having an insight into the beliefs of others is essential for getting along socially, predicting what people might do and even tricking someone. Being unable to infer what others are thinking or feeling is considered an early sign of autism.
Prof Frans de Waal, a primatologist at Emory University in Atlanta, Georgia, who was not involved in the study, said that the findings confirm that theory of mind is not an exclusively human ability. “Increasingly, we see their inner lives as very similar to that of humans,” he said. “This is hardly surprising given the brain similarity and the close genetic connection between humans and apes.”
De Waal said the latest findings build on a growing body of evidence pointing to primate cognition being closer to that of humans than once thought. “Our brains are bigger, true, which means that we have a more powerful computer, but its fundamentals, its hardware, is the same as that of other primates,” he said.