Robin Dunbar

Animal Minds - Knowing Primates


Can you guess what I'm thinking?

New Scientist vol 182 issue 2451 - 12 June 2004, page 44

Reading the minds of others comes as naturally to us as breathing, and we know some animals can do it too. The big question, says Robin Dunbar, is just how accomplished they are.

WE humans are naturally inclined to attribute minds to other animals because mind-speak is so deeply embedded in our everyday thinking about other people. Philosopher Daniel Dennett refers to this as the "intentional stance": we assume that other minds are like our own, which allows us to reflect intuitively, even if not explicitly, on our own mind-states. But what kinds of minds do animals have, and how do they compare with ours?

Psychologists have spent the past century or so exploring the mind. In the course of this, we have learned a great deal about memory and learning, how animals solve problems or find their way around mazes. And the burden of all this effort is that most animals are pretty much of a muchness when it comes to basic cognitive processes, with the possible exception of humans.

I don't think we should be satisfied with this conclusion. It is like being handed a list of the all the bricks and mortar, wood and windows that make up a house, but without the breath of a mention of what the building looks like or why it is there.

Monkeys and apes can get us out of this bind. They turn out to be a bit different from the run-of-the-mill mammal and bird because they can handle social complexity. This ability depends on a peculiar kind of cognition known as "social cognition". Monkeys and apes differ from other animals in the intrinsic complexity of their social relationships.

The important thing here is not that they behave in ways that other animals cannot, but rather how they do it. There is something about the intensity of their social relationships that seems different from the relationships found in other species.

Some years ago, Dick Byrne and Andy Whiten, of the University of St Andrews, UK, showed that primates engage in unique behaviours, one of which turned out to be tactical deception. Essentially, this involves misleading someone else, but the important issue seemed to be that they do this by mind-reading.

Primates are able to appreciate how what they do will be misinterpreted by another individual, and thus manipulate them into behaving in a way that is beneficial to the actor.

However, the idea that monkeys and apes read minds rather than behaviour in the way that humans do has faded with time. There is simply no evidence that any primates other than us have a generalised capacity in this respect. Indeed, the only evidence for any kind of non-human mind-reading comes from chimpanzees, and even then it is equivocal.

One study found that chimps failed the critical kind of mind-reading task - the "false belief" task - that young children pass with ease. A second study showed that, although chimpanzees do better than autistic humans (who lack mind-reading capacities by definition), they only did about as well as 4-year-old children. At this age, children are still acquiring the capacity to mind-read and do so imperfectly.

But it's worth reminding ourselves that there is something intense and personal about the social relationships of monkeys and apes that marks them out from the relationships exhibited by other species. As far as I can see, domesticated dogs are the only exception. They seem to have been bred explicitly to show the intense social commitment that primates have. Whether dogs' capacity to behave in this way is merely a superficial behavioural analogy of monkeys' capabilities or whether the same kind of psychological mechanisms underlie the canine behaviours remains to be seen.

Considering mind-reading abilities does give us a grip on just what the differences between humans and other animals actually are. Intentionality is the capacity to reflect on the contents of one's mind, as reflected in the use of verbs such as suppose, think, wonder (whether), believe and so on. The capacity to use these words defines first-order intentionality: such an animal is capable of knowing its own mind. Most mammals and birds probably fall into this category.

More interesting are those cases in which the individual is capable of reflecting on someone else's mind state: I suppose that you believe. This defines a higher level of intentionality, and is conventionally referred to as second order. It is equivalent to the stage that children reach at about the age of 5 years when they acquire what is known as "theory of mind" or, less formally, the ability to mind-read. More interesting still, is whether this sequence of intentionality can be extended reflexively to yet higher orders.

At the University of Liverpool, UK, we have shown experimentally that normal adult humans can aspire to fifth-order intentionality as a matter of course, but it turns out that this represents an upper limit for most people. Fifth order is the equivalent of being able to say: "I suppose [1] that you believe [2] that I want [3] you to think [4] that I intend [5]..."

Here, successive orders of intentionality are marked in square brackets.

It is the hierarchical nature of intentionality that gives us a natural metric for scaling species' social cognitive abilities. If the human limit is fifth order, chimpanzees - and perhaps other great apes - second order, and monkeys stop at first order, then it turns out that these capacities are a linear function of the relative size of the frontal lobe of the brain (and only of the frontal lobe).

This physical correlative to mental capabilities is interesting for two reasons. The first is that the brain has evolved from back - where visual processing occurs - to front. The same is true of the neocortex, the thin outer sheet that is both a mammalian speciality and the seat of most of the complex behaviours we associate with "thinking". The frontal lobe is particularly associated with those capacities that psychologists refer to as "executive function" or, in crude terms, conscious thought.

Secondly, large neocortices in general - and large frontal lobes in particular - are a primate speciality, suggesting that primates are likely to be especially well endowed with whatever psychological capacities are underpinned by these neural structures. They may even be unique to primates.

What are these capacities that monkeys and apes have? In my view, it is not so much the capacities that differ between monkeys, apes and humans, but the scale at which each species can exercise them.

These capacities are those basic to the lives of all mammals and birds. Minimally, they include the ability to reason causally, to reason analogically, to run two or more models of the world simultaneously, and the length of time into the future that any such model can be run. When these individual capacities are brought together on a large enough scale, mind-reading pops out as an emergent property.

So mind-reading looks like something special, but it is not some kind of specialised primate or even human capacity. Rather, it may simply reflect the capacity to compare the consequences of several behavioural options further into the future or handle the contents of several minds simultaneously without getting them confused.

In short, the differences between species of mammals on the scale of rats to humans is simply one of what might be termed the computational advantages of scale.

Robin Dunbar

Robin Dunbar is professor of evolutionary psychology at the University of Liverpool, UK. His research focuses on the evolution of cognition and social networks, and the behavioural ecology of primates, ungulates and humans. His latest book, The Human Story, was published by Faber & Faber last month