New York, Oct 7 (IANS) Just like us, apes can grasp complex mental states and have the ability to guess what others might be thinking, suggests new research.

Apes can correctly anticipate that humans will look for a hidden item in a specific location, even if the apes know that item is no longer there, a new study revealed. 

The results, which show that apes can grasp what others know even when it differs from their own knowledge, demonstrate that nonhuman primates can recognise others' beliefs, desires, and intentions -- a phenomenon called "theory of mind" (ToM), and one that has generally been believed as unique to humans. 

"This is the first time that any nonhuman animals have passed a version of the false belief test," said one of the lead researchers Christopher Krupenye from Duke University in Durham, US.

The capacity to tell when others hold mistaken beliefs is seen as a key milestone in human cognitive development. Such skills are essential for getting along with other people and predicting what they might do. 

The new findings, published in the journal Science, suggest the ability is not unique to humans, but has existed in the primate family tree for at least 13 to 18 million years, since the last common ancestors of chimpanzees, bonobos, orangutans and humans.

"If future experiments confirm these findings, they could lead scientists to rethink how deeply apes understand each other," Krupenye said.

In the study, the apes watched two short videos. In one, a person in a King Kong suit hides himself in one of two large haystacks while a man watches. Then the man disappears through a door, and while no one is looking the King Kong runs away. In the final scene, the man reappears and tries to find King Kong.

The second video is similar, except that the man returns to the scene to retrieve a stone he saw King Kong hide in one of two boxes. But King Kong has stolen it behind the man's back and made a getaway.

The researchers teased out what the apes were thinking while they watched the movies by following their gaze with an infrared eye-tracker installed outside their enclosures.

To pass the test, the apes must predict that when the man returns, he will mistakenly look for the object where he last saw it, even though they themselves know it is no longer there.

In both cases, the apes stared first and longest at the location where the man last saw the object, suggesting they expected him to believe it was still hidden in that spot.

Their results mirror those from similar experiments with human infants under the age of two.

The apes' correct anticipation of where the human expected the object to be suggests that they understand that person's perspective.