Evolving a Theory of Mind

The earliest hominids were distinctly chimplike–in the shape of their body, in the sorts of habitats they made their home, and even in the size of their brain. Their social life was probably chimplike as well, demanding a social intelligence on a par with that of living chimps. To explore that potential connection, scientists have tested chimpanzees to see just how much they understand about their fellow chimps. Does their Machiavellian behavior come from a capacity to understand that other chimpanzees have a mind like their own? Do they have what psychologists would call a “theory of mind”?

Studies of chimpanzees suggest that they have only the rudiments of one. They know, for instance, what their fellow chimps can and cannot see. Brian Hare, a primatologist at Harvard, and his colleagues demonstrated this with a series of experiments with dominant and subordinant chimps. Whenever chimps come into conflict over food, the dominant ones win. In Hare’s experiments, a dominant chimp and a subordinate one would be released at the same time into a cage from opposite sides. Hare placed two pieces of fruit in the cage, and the subordinate chimp could tell that the dominant chimp could see only one of the pieces of fruit, because her view of the second one was blocked by a piece of PVC tubing. Knowing this, the subordinate chimp consistently went for the hidden fruit, so as to avoid a confrontation with the dominant chimp over the visible one.

“We’re increasingly realizing that chimpanzees do have the beginnings of the elements of a theory of mind,” comments Harvard chimp expert Richard Wrangham. “So we now know that a chimp can look at another chimp, see what it sees, and then base its own strategies on what that other chimp has seen. We don’t know of any other species, other than humans and chimpanzees, that can do that.”

But chimpanzees don’t seem to be able to put themselves fully in the minds of other chimps. Daniel Povinelli, a primatologist at the University of Southwestern Louisiana, performed an experiment comparing the social intelligence of chimps with 2‑year‑old children. He had his subjects gesture to one of two observers to ask for a piece of food–one observer wore a gag, the other a blindfold. The 2‑year‑old children understood that the blindfolded person could not see the gesture and asked the gagged person instead. The chimps, on the other hand, were just as likely to gesture to the blindfolded person as the gagged person.

Hare’s experiment shows that chimpanzees understand some basic facts about seeing–that barriers, for example, can prevent other chimpanzees from seeing things. But Povinelli’s experiment suggests that chimpanzees don’t understand the full scope of vision–that there is a mind on the other side of those eyes perceiving the images that enter it.

These findings suggest that the common ancestor of chimps and humans could not actually conceive of the other members of its species as having minds of their own, capable of thinking as they did. They did not, in other words, have a theory of mind. Our hominid ancestors must have evolved one only after they split from chimpanzees 5 million years ago.

Andrew Whiten and Robin Dunbar have both argued that hominids began evolving a theory of mind as our ancestors gradually shifted from living in dense jungles to open woodlands and finally to savannas. They began coming in regular contact with big, dangerous predators like lions and leopards, and they could no longer hop into trees for safety. These hominids had to stick together in even bigger numbers than their ancestors had. Life in bigger groups would encourage the evolution of more social intelligence, which required bigger brains. In the process, hominids evolved into mind readers. By looking at the eyes of their fellow hominids, they could tell not only what they could or could not see but what they were thinking. They could read body language and reflect on the past actions of other people. In the process, hominids began to do a better job of deceiving one another, making alliances, and keeping track of one another.

Whiten suspects that once this sort of social evolution got started, it spiraled out of control. Any individual hominid born with a keener theory of mind would be able to deceive the rest of his or her band and ultimately might enjoy more reproductive success. “Now that creates a selection pressure in everybody else to be better at detecting deception,” says Whiten. “And really, detecting deception means having a better notion of what’s going on in the other’s mind. That’s mind reading.”

Hominid evolution may have become a feedback loop of ever‑increasing social intelligence, producing our ever‑expanding brains. Ultimately, this evolutionary spiral transformed hominid society itself. It eventually became too hard for a dominant male to enforce a hierarchy in his band because his subordinates had become too clever. Hominid society shifted from a chimplike hierarchy to an egalitarian structure. Each individual used his or her theory of mind to keep track of everyone else, making sure no one cheated the group or tried to dominate it.

Only when hominids began to live in an egalitarian society, Whiten argues, could they fully take advantage of the hunter‑gatherer way of life. Men could work together to plan a hunt, and they could leave the women and children behind without being paralyzed by suspicion. Likewise, women could organize expeditions of their own to find tubers and other plants. With tools and cooperation, hominids carved themselves a new ecological niche in the savanna.

“A theory of mind makes us as sublime as we are because we can feel for others so much,” says Whiten. “At the same time, it allows us to be that much more sneaky than any other species on the planet.”