Great apes can tell when a person is mistaken and help to set them straight.

A study published in the journal Plos One Wednesday found that great apes know when a person is holding a false belief.

The experiment was conducted at the Leipzig Zoo in Germany and led by David Buttelmann from Max Planck Institute for Evolutionary Anthropology and the University of Bern.

Chimpanzees, bonobos and orangutans watched while an actor placed an object in one of two boxes. For the test, the person left the room and a second person took the object out of the first box, put it into another box and locked both boxes.

When the first person returned and attempted to retrieve the item from the original box, the apes — who had learned how to unlock the boxes — could decide accurately which box to open in order to assist.

The apes unlocked the correct box more often than they had in tests where the actor had demonstrated he knew the correct box. 

It's been established for a while that humankind's nearest primate relatives can understand some things about the psychological states of others. They can read expressions to interpret food preferences, for example. 

But understanding when someone else has a false belief is a mark of advanced social cognition, and researchers previously thought great apes lacked that capacity. "Finding evidence of belief-tracking in great apes was kind of a surprise to all of us," said Buttelmann.

A study published in the journal Science last year established the possibility that great apes had some awareness of false belief. That study tracked the eye movements of apes who knew an object had been moved, but understood a human believed it was in the original location.

Buttelmann and his colleagues "were not satisfied" with that methodology, though, he said in an interview with CBC News. "We thought if apes indeed have an understanding of false belief they should be able to use it."

These new results build on those earlier findings and establish that great apes "not only understand others' beliefs, they plan and execute their social interactions according to this understanding," he said.

Understanding ourselves

The point of investigating social cognition in apes is not just to get to know our close evolutionary cousins, but to help us understand how our own cognitive abilities evolved — essentially, what makes humans human.

"The main idea of why we do those studies, not just because they're fun, but is to find out how theory of mind in humans evolved," said Buttelmann.

Theory of mind is the understanding that others have thoughts, beliefs and knowledge that might be different from our own. We can better appreciate our own cognitive evolution if we compare ourselves to animals who share some characteristics with us, he said.

The experiment was originally designed for human toddlers 16 to 18 months old, and conducted with toys in the boxes, the study says. The test was applied to the great apes in close fashion to the tiny humans.

"Our studies show that there is at least some precursors of theory of mind in great apes," said Buttelman. 

From here scientists can explore whether it's because we live in large groups that we evolved to have advanced social cognition, or whether that hinged on our roots as hunters, for example, he said.

Another possible distinction? Where great apes may use their social cognition competitively — to mate with a desirable female while a dominant male is seeking food in another area, for example — early humans may have put theirs to work for "pro-social" reasons like sharing knowledge of how to cook a potato, said Buttelmann.