The ability to understand false beliefs has long been thought to be unique to human consciousness, but a recent study revealed for the first time that great apes are capable of making this distinction as well.

Researchers at Duke found that great apes understood the false belief of others, which is simply a notion about the surrounding world that is not true. From chipmunks to college students, every animal is capable of holding a false belief. However, it was previously thought that only humans were able to understand when someone else held a false belief.

“Doing so in the most complete sense requires imagining another individual's perspective and understanding exactly how that individual construes the world to be different than it actually is,” said Christopher Krupenye, a researcher in developmental and comparative psychology at the Max Planck Institute for Evolutionary Anthropology in Germany, who co-led the study with Fumihoro Kano, a comparative psychologist at Kyoto University. Krupenye received his Ph.D. in evolutionary anthropology from Duke this May.

The presence of such ability in apes—such as chimpanzees, bonobos and orangutans—means that their understanding of others as mental beings is more complex than was previously assumed.

Pinpointing false belief has given scientists a better look into the ways apes interact with one another.

“What it means is when apes are competing with others, they can do it more effectively. Apes have evolved this ability to compete based on not just who is there, but on what the other one knows and believes about the world,” said Michael Tomasello, senior author of the study, co-director of the Max Planck Institute and Trinity '72.

Tomasello added that humans can still be distinguished from apes because of humans' ability to engage in cooperation. 

For the study, the researchers created a video with a point of conflict that would engage the attention of the apes. In the video, a man expresses interest in a rock, before a second man dressed in a gorilla suit nicknamed “King Kong” angrily takes the rock away and hides it under a box.

The man leaves the room, and King Kong transfers the rock to a second box. He then takes the rock away entirely. When the man walks back into the room, scientists wanted to test whether the apes could predict where the man would—incorrectly—think the rock was.

Eye tracking technology was used to locate where the chimps looked during the video. The apes spent the longest time looking at the box where the man had last seen the object, indicating that they knew the man would think to search for the rock there, even though the object had been removed. The “anticipatory looking” of the apes was then recorded by the eye-movement tracking devices.

This particular method of testing distinguished the study from other literature in the field that attempts to have chimps react to a detection of false belief with a simple task, similar to the way children over the age of four are tested on their understanding of the same topic. All of these studies have had negative conclusions, Tomasello explained. However, this most recent study was designed to be simpler and based on the way infants under the age of 24 months are tested.

“Previous studies imposed a lot more demands on the apes, in terms of what they had to remember and how much self control they had to exercise," Krupenye said. "It may well be that our task was successful simply because it was less demanding for the participants.” 

Although these results represent a milestone in the field, the findings stop short of putting apes and humans on an even playing field when it comes to an understanding of mind theory.

“Apes can do it when it’s just a matter of looking, but when it’s a matter of incorporating that knowledge into intelligent, strategic action, there is no evidence so far of them doing that,” Tomasello said.

Future tests are necessary to ensure that the apes are not simply reacting to and memorizing patterns of behavior, the researchers noted.