Great apes may have shown proof of a 'theory of mind', once thought uniquely humans

A 2019 study starts to prove the intelligence of primates. Great apes would have a 'theory of mind', something thought to be peculiar to humans.

© Getty Images

It is undeniable that we still have a lot to learn about our cousins the great apes. An international study sheds new light: some apes have acquired a theory of mind.

Discover our latest podcast

In cognitive science, this term defines the ability to understand the intentions of others, and to attribute non-visual states of mind to yourself and others, something which was thought to be exclusively reserved for humanity's overgrown brains. But more and more studies, including one published in the Proceedings of the National Academy of Sciences in 2019, have come to prove that our primate cousins can also do it, as well as smarter bird species like some parrots and crows.

To prove it, the researchers gave 29 chimpanzees, 4 orang-utans and 14 bonobos a visual test. First, they divided the apes into two groups: one was able to inspect some kind of transparent panel or screen. The other was shown the same screen but more opaque. They then showed them a short video, featuring a fairly elaborate plot.

A complex scenario

In this video, the primates were able to see a man observing from a distance an actor in an ape disguise. He placed an object in a box. The man stood behind a screen that each of the groups could associate with the screen they had inspected. Behind this screen, the man waited for the actor to transfer the object to a second box, before hiding it. After the actor's departure, the observer man went to get the box from a place in between.

According to the scientists, the natural reaction of the apes would have been to expect that the person who had not seen the subterfuge and the change of box, would immediately look to the place of origin. By the same logic, the apes having seen the transparent screen would necessarily think that the person knew that the object had changed box.

The intelligence of primates

Using technology to track eye activity, researchers were able to analyse the apes' deduction path. It appears that they looked more at the box the object was hidden in when the human appeared to be stuck.

In conclusion, our study shows that great apes can use their past visual experience to assign perception and potentially infer beliefs about others.

As the researchers point out, additional research will be necessary to prove or not this theory. But with the growing number of scientific studies looking into the subject of animal intelligence, it is becoming increasingly difficult to ignore that humans are not the only species capable of questioning someone else's actions.

Animal behaviour is affected by human noise Animal behaviour is affected by human noise