Just like humans, apes may have the ability to guess what others are thinking, even in cases when someone holds a mistaken belief, according to a new study.
The study shows that great apes watching a video like that of ninja swords and ape costumes can process false beliefs, which is the notion that someone's understanding of a situation may not be congruent with reality.
The research challenges the view that the ability to understand unobservable mental states is unique to humans.
In the video, a human and a person dressed in an ape suit are engaged in a hide and seek-like scenario. An eye-tracker on a TV monitor follows an observing apes' gaze, recording where the ape anticipates the action will occur next.
The video was adapted from a typical false-belief test that indicates whether someone can understand that another's actions are not driven by reality, but by beliefs about reality, even when those beliefs are false.
"Human infants only start understanding the concept of false beliefs after they're about four years old," said Fumihiro Kano of Kyoto University in Japan.
"Despite their excellent social cognitive skills, great apes consistently failed the false-belief test in previous studies that required them to physically retrieve an object," said Kano.
The videos and eye-trackers used for this study, on the other hand, were simplified from a version of the test used previously for human infants and great apes; with this design the great apes need only to sit, stare at the screen, and be passive spectators of test videos.
The team, led by Kano and Christopher Krupenye at Duke University, showed this video to chimpanzees, bonobos, and orangutans at Kyoto University's Kumamoto Sanctuary and the Max-Planck Institute in Leipzig, Germany.
"The apes performed very well, even when compared to human infants and adults," said Kano.
"The results indicate that the great apes can predict how the human in the video will make the wrong choice. This shows that apes understand reality-incongruent beliefs, at least when the test subject only needs to watch the video," he said.
"These findings suggest that this essential human skill - to recognise others' beliefs - may be at least as old as humans' last common ancestor with the other apes, which lived 13 to 18 million years ago," said Krupenye.
"This certainly puts to question the notion that the human psyche is unique and superior to other animals," added Satoshi Hirata, senior author of the study.
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