Humans aren’t the only great apes capable of guessing what others are thinking – chimpanzees, bonobos, and orangutans have also demonstrated the predict another’s beliefs, even in instances when they know that said belief is mistaken, according to research published on Friday.
As Science explained in a separate report, the study authors conducted a classic experiment to see if non-human primates had a trait known as the “theory of mind”, or the ability to attribute desires, knowledge, or intentions to others.
In such experiments, children see someone hide a chocolate bar and then leave the room. Once they exit, a second individual sneaks in and hides it elsewhere, then guesses where the first person will look for the bar. If they predict that the first individual will look in the original hiding place, they pass the test and demonstrate an ability to understand a person’s thought processes.
This ability, which involves predicting another person’s beliefs even when they are false and do not match reality, has long been believed to be a distinctly human characteristic. However, in the new study, researchers from Duke University and an international team of colleagues show how three other species of great apes also appear to grasp the concept of “false belief.”
More than half passed the experiment, according to the researchers
Lead author Christopher Krupenye, who works as an evolutionary anthropologist at Duke, and his colleagues filmed a scene featuring a man in a generic apelike costume stealing a rock from a man, then hiding it in one of two boxes and scaring off his victim. Once the victim left, the costumed man first moves it to the other box, then leaves with it. Check it out here:
Normally, people involved in such experiments would predict that when the victim returned, he would search for the rock in the first box, which is where it was when he originally left, Science explained. To determine whether or not other species of primates would do likewise, the authors showed them the footage while using high-tech eye-tracking technology to follow their gazes.
A total of 30 animals (14 chimpanzees, nine bonobos, and seven orangutans) were shown the video, and 22 of them looked directly at the two boxes when the victim came back to the scene after being chased off. More than half (17) of the subjects stared directly at the first box, where the costumed man had originally hidden the rock. These eye movements revealed that the apes correctly guessed that the man would open the box where he had last seen the rocks, even when they knew that it was no longer there, Krupenye’s team told the journal.
Similar results were obtained when the researchers had another group of 40 apes view a second, slightly different film. The apes “reliably look in anticipation of an agent acting on a location where he falsely believes an object to be, even though the apes themselves know that the object is no longer there,” the authors wrote. “Our results suggest that great apes also operate, at least on an implicit level, with an understanding of false beliefs.”
However, as Krupenye told Science, while he and his fellow researchers have demonstrated that nonhuman primates “can predict others’ behaviors, which is a sophisticated ability” that had not been attributed to their species before, there is still work to do before they can definitively claim that apes are capable of understanding the concept of false beliefs. The researchers said that they plan to devise a behavioral scenario that calls upon the apes to put this knowledge to the test.
Image credit: Thinkstock
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