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Apes may be even more like us than we thought. They appear to anticipate that a person’s actions will follow his or her beliefs, even when they know the person is wrong – an ability never before demonstrated in non-human primates.

The capacity to infer what others might be thinking, known as theory of mind, is central to what makes us human, and is reflected in the ways we cooperate and communicate, says at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Humans, for example, possess an awareness of false beliefs held by other individuals, recognising that the thoughts of others don’t necessarily reflect reality.

To see whether apes have this same type of awareness, Krupenye, at Kyoto University in Japan, and their colleagues filmed scenarios designed to stimulate apes. The videos involve conflict between pairs of human actors, one of whom is dressed in a King Kong costume. “The apes are curious; they want to know what’s going on,” says Krupenye.

King Kong in a haystack

In one video, the fake ape hits a person, and then hides in one of two haystacks while the person watches. After the human leaves the scene, “King Kong” exits the haystack and runs off screen. The person then reappears, apparently looking for the attacker.

Because humans and other animals will look at a location where they anticipate action, the haystack that the apes glanced at first when they watched the video might indicate the one they expected the human to approach.

The researchers used a camera to track the eyes of 40 apes, including chimpanzees, bonobos and orangutans. Of the 30 apes that focused on the haystacks, two-thirds looked first at the one where the human falsely believed the character was hiding.

The scientists also tested the apes with a similar scenario, in which the King Kong character hides a stone in one of two boxes as a person watches, but then steals it when they leave. When the person returns to look for the stone, about three-quarters of apes that paid attention to the boxes glanced first at the one that the human should open.

To test that the apes weren’t just looking at the last place where they saw an object or character, the researchers filmed different versions of the videos. In these, King Kong briefly hides in the other haystack after the person leaves before dashing away, or transfers the stone to the other box without a person watching.

“They can anticipate that an individual will search for an object where they last saw it, even though the apes know that it’s no longer there,” Krupenye says. “That is a really important human skill that has never been shown before in apes.”

This means that one of our most sophisticated and significant skills – reading the minds of others – is not unique to us, but also possessed by some of our evolutionary relatives, says Kano. Just like us, he says, great apes have complex social lives bolstered by mutual understanding.

Infant-like understanding

Although the study demonstrates an exciting new method for testing apes’ understanding, it raises more questions than it answers, says at Yale University.

“We don’t yet have a reason why primates fail other false-belief studies while succeeding on this,” says Santos.

One possibility is that tested for conscious understanding, whereas the new one demonstrates implicit knowledge similar to the kind that , says at Victoria University of Wellington in New Zealand.

Krupenye agrees that the study doesn’t necessarily mean apes are explicitly aware of others’ false beliefs – but points out that even an implicit awareness implies a high level of social understanding.

Martin says the case might be strengthened by a comparison of a situation in which, for example, apes need to anticipate how someone who is aware of the true situation might behave. If apes are able to understand what others are thinking, she says, we should see signs of them using that skill.

“Can we find any evidence of it in their behaviour?” asks Martin.

The answer is yes, according to at the University of St Andrews in the UK. For decades, researchers have watched apes demonstrate behaviours that suggest complex social understanding, such as deceiving their peers, he says. “To me, this is another nice block slotting into place where it should,” says Byrne.

This paper adds to the growing body of evidence that great apes – which are endangered in the wild – are deeply similar to humans, Krupenye says.

Conservation measures to combat habitat destruction and direct killing of apes are sorely needed, says Byrne. “They are too much like us to be treated just as animals,” he adds.

The findings suggest that an ability to recognise false beliefs in others has existed in the primate family tree for at least 13 to 18 million years, and was present in the last common ancestor of great apes and humans.

Journal reference: Science, DOI:

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