Chimps thinking about thinking

Jesse Bering has an excerpt from his upcoming book The Belief Instinct over at Slate in which he explains, quite handily, theory-of-mind (theory-of-mind is essentially inferring the mental states of others – thinking about what someone else is thinking.  For an excellent but succinct explanation, read Bering’s article).  He goes on to suggest that attributions of theory-of-mind to inanimate objects is something that we do all the time, telling us,

“As a direct consequence of the evolution of the human social brain, and owing to the importance of our theory-of-mind skills in that process, we sometimes can’t help but see intentions, desires, and beliefs in things that haven’t even a smidgeon of a neural system. In particular, when inanimate objects do unexpected things, we sometimes reason about them just as we do for oddly behaving—or misbehaving—people. More than a few of us have kicked our broken-down vehicles in the sides and verbally abused our incompetent computers.”

Especially computers, that have something akin to overt behaviour, I would add.  But I digress.

Bering’s thesis is that misapplication of theory-of-mind has led to the universality of belief in God [the latest in what is becoming a cottage industry of putting forth evolutionary theories of religiosity.]  What I find most intriguing is the juxtaposition of the pitch for Bering’s new book and a paper that has just showed up (online before publication) in PNAS which suggests that chimpanzees have a much better developed theory-of-mind than previously documented.

The experiment is straightforward.  If you put a flat piece of wood on the table before a chimp, he or she will know the difference between that situation and one in which a piece of food is under the wood, causing it to sit at a bit of an angle.  Of course, a chimp has to have some experience to learn about this trick, but that sort of learning is old hat in the field of primate research.  What is new and remarkable in the paper from Michael Tomasello’s group is that chimps are able to infer if another chimp understands the same thing.

The way the experiment is set up is that a pair of chimps have access to unequal information.  Basically, 2 pieces of wood can be seen: one has a piece of food under it, so that it sits on an angle, while the other covers a secret hole that contains food, and therefore sits flat.  Chimp #1 can see that food has been placed under both, while chimp #2 only gets to view the scene after the food is put in place.  Now is where things get interesting.

The game that the chimps learn is that one of the two of them get to go first, and the other follows.  But they cannot see what the other actually does, and if one chooses the food under the slanted board, a non-food object replaces it so that when the second chimp views the scene, they can’t ‘know’ if the slanted board covers food or not.

When Chimp #1 (who saw the food being placed in both spots) goes first, she almost always picks the slanted board.

When Chimp #2 goes first, on Chimp#1 turn she picks the flat board ~50% of the time.

The final paragraph of the paper is worth quoting in its entirety.

Several studies have shown that chimpanzees know what others currently see, and what they saw just a few minutes before (and so now know about) . Here we demonstrated that chimpanzees also know that others go beyond direct perception and immediate memory to make inferences about nonperceived realities. In the current study subjects could not have been reacting to the behavior of the competitor (as they could not see her at the key points in the procedure), nor did they learn their best response during the test (and any influences from first being competitors in the social condition would have been the same for subjects choosing first or last in the test), thus obviating two key criticisms leveled at studies of animal social cognition in the past. If we define thinking as going beyond the information given in perception to make inferences, we may conclude that not only is thinking not the exclusive province of human beings, but thinking about thinking is not either.

What is most interesting about this brief report is that it suggests, once again, that aspects of what was once considered to be unique to humans is not.  Of course, if theory-of-mind is of evolutionary value (and there are very good reasons why inferring the mental states of others would be advantageous – just consider competition for mates), there is no reason to expect that it arose de novo in humans.  As with many other adaptations that our minds have made over the millennia, it is interesting to see just where our thinking about thinking has taken us.

Link to Jesse Bering’s article in Slate

Link to Schmelz et al.’s article in PNAS