Buttelmann et al (2017)

In the mid 1700s, Julien Offray de La Mettrie, the French doctor and philosopher, suggested that humans might be able to teach apes to learn a language. He justified his reasoning by simply highlighting the blurry line between humans and animals: “What was man before he invented words and learnt languages? An animal of a particular species.” Three hundred years after La Mettrie’s writing, Koko the gorilla was taught to use over 1,000 signs and can understand about 2,000 spoken words.

Over the past few decades, the scientific gap separating humans and animals has significantly closed, with research suggesting that many of the traits that we thought to be exclusively human are also experienced by those in the animal kingdom; these include behaviors like tool making, self-recognition, ideas of fairness, empathy, monogamy and love, and language (both auditory and sign language).

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And now, a study published in April in the journal PLOS ONE suggests that apes have an awareness that other people have thoughts that are different than their own. The study was based on a test originally developed for 16- to 18-month-old humans that involves helping a person locate an object. Just like the human babies, apes were more likely to help someone locate an object when that person thinks they know where the object is, but the ape knows they are mistaken. By investigating apes’ ability to attribute false beliefs to others, (to recognize that others can have beliefs about the world that are diverging and incorrect) the experiment aimed at answering whether great apes recognize that others have thoughts, experiences, and views of the world that are different than their own. This idea is generally known as “theory of mind.”

“For the last 30 or more years people thought that belief understanding is the key marker of humans and really differentiates us from other species – and this does not seem to be the case,” said David Buttelmann, co-author of the study and professor of Psychology the Max Planck Institute for Evolutionary Anthropology, in an interview with The Guardian.

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In the experiment, an ape (orangutan, bonobo, or chimpanzee) would watch a person (the experimenter) place an object in one of two boxes. Then a research assistant would take the object out of one box and put it into the other box. In one scenario, the experimenter stayed in the room the whole time, watching the assistant move the object; in the other scenario, the experimenter left the room during the switch, meaning that while they thought they knew in which box the object was, the ape knew they were mistaken.

In both cases, the experimenter would try to open the box that had originally contained the object but that was now empty. The team would watch to see whether, when given the chance, the ape would help the experimenter open the empty box, or instead open the box in which the object was now located.

Right before the response phase, the experimenter tries to open the box which he believes contains his object (false-belief condition) or which he knows is empty (true-belief condition). In both conditions this is the same empty box; all that differs is the experimenter’s belief about what is in it.
Buttelmann et al (2017)

The study found that, just like human infants, apes were significantly less likely to help a person who had been in the room during the box switch. The logic here is that the apes presumably knew that that person wasn’t confused as to the true location of the object. Similarly, the apes were more likely to help the experimenter find the object in the scenario where the person had a false belief about which box the object was in.

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“Great apes thus may possess at least some basic understanding that an agent’s actions are based on her beliefs about reality,”  explains the study. “Hence, such understanding might not be the exclusive province of the human species.” Buttelmann is currently working on redesigning the test to investigate how other members of the animal kingdom respond to false beliefs; he thinks that these continued experiments will lead to even deeper understanding regarding consciousness and the foundations of the theory of mind. "I would love to find out what factor might be the factor that drove the evolution of theory of mind," he said to in an interview with Smithsonian.