Feb 04 2025

Do Apes Have a Theory of Mind

Designing research studies to determine what is going on inside the minds of animals is extremely challenging. The literature is littered with past studies that failed to properly control for all variables and thereby overinterpreted the results. The challenge is that we cannot read the minds of animals, and they cannot communicate directly to us using language. We have to infer what is going on in their minds from their behavior, and inference can be tricky.

One specific question is whether or not our closest ancestors have a “theory of mind”. This is the ability to think about what other creatures are thinking and feeling. Typical humans do this naturally – we know that other people have minds like our own and we can think strategically about the implications of what other people think, how to predict their behavior based upon this, and how to manipulate the thoughts of other people in order to achieve our ends.

Animal research over the last century or so has been characterized by assumptions that some cognitive ability is unique to humans, only to find that this ability exists in some animals, at least in a precursor form. This makes sense, as we have evolved from other animals, most of our abilities likely did not come out of nowhere but evolved from more basic precursors.

But it is still undeniably true that humans are unique in the animal kingdom for our sophisticated cognitive abilities. Our language, abstraction, problem solving, and technological ability is significantly advanced beyond any other animal. We therefore cannot just assume that even our closest relatives possess any specific cognitive ability that humans have, and therefore this is a rich target of research.

The specific question of whether or not our ape relatives have a theory of mind remains an open research controversy. Previous research has suggested that they might, but all of this research was designed around the question of whether or not another individual had some specific piece of knowledge. Does the subject ape know that another ape or a human knows a piece of information? This research suggests that they might, but there remains a controversy over how to interpret the results – again, what can we infer from the animal’s behavior?

A new study seeks to inform this discussion by adding another type of research – looking at whether or not a subject ape, in this case a bonobo, understands that a human researcher lacks information. This is exploring the theory of mind from the perspective of another creatures ignorance rather than their knowledge. The advantage here, from a research perspective, is that such a theory of mind would require that the bonobo simultaneously knows the relevant piece of information and that a human researcher does not know this information – that their mental map of reality is different from another creature’s mental map of reality.

The setup is relatively simple. The bonobo sits across from a human researcher, and at a 90 degree angle from a “game master”. The game master places a treat under one of several cups in full view of the bonobo and the human researcher. They then wait 5 seconds and then the researcher reveals the treat and gives it to the bonobo. This is the training phase – letting the bonobo know that there is a treat there and they will be given the treat by the human researcher after a delay.

In the test phase an opaque barrier is placed between the human researcher and the cups, and this barrier either has a window or it doesn’t. So in some conditions the human researcher knows where the treat is and in others they don’t. The research question is – will the bonobo point to the cup more often and more quickly when the human researcher does not know where the treat is?

The results were pretty solid – the bonobos in multiple tests pointed to the cup with the treat far more often, quickly, and insistently when the human researcher did not know where the treat was. They also ran the experiment with no researcher, to make sure the bonobo was not just reaching for the treat, and again they did not point to the cup when there was no human researcher to communicate to.

No one experiment like this is ever definitive, and it’s the job of researchers to think of other and more simple ways to explain the results. But the behavior of the bonobos in this experimental setup matched what was predicted if they indeed have at least a rudimentary theory of mind. They seem to know when the human researcher knew where the treat was, independent of the bonobo’s own knowledge of where the treat was.

This kind of behavior makes sense for an intensely social animal, like bonobos. Having a theory of mind about other members of your community is a huge advantage on cooperative behavior. Hunting in particular is an obvious scenario where coordination ads to success (bonobos do, in fact, hunt).

This will not be the final word on this contentious question, but does move the needle one click in the direction of concluding that apes likely have a theory of mind. We will see if these results replicate, and what other research designs have to say about this question.

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