Tools and Alliances

Without tools, hominids could not have spread so far. But what evolutionary force made it possible for those hominids to make their tools in the first place? Throughout hominid evolution, their brain expanded in fits and starts. As they gained bigger and more complex brains, hominids presumably became able to handle the challenge of making tools. That still leaves a question unresolved: How did these big brains arise?

The answer may have its roots in the social lives of apes and monkeys. Compared to other animals, primates are a particularly social bunch, spending their lives in bands, making alliances, and struggling up the social hierarchy. Primates are keenly aware of the shifting reality of their social world–often even more than of the physical world. Vervet monkeys, for example, are terrified of pythons, but they can’t recognize a fresh python track. On the other hand, they can keep track of the genealogy and history of their band. If two vervets get in a fight, their relatives will bear the grudge and may harass one another days later.

In some cases, primates have such a keen awareness of their fellow primates that they can deceive them. Andrew Whiten, a primatologist at St. Andrews University in Scotland, once watched a chacma baboon named Paul sneak up on an adult female named Mel. Mel was digging into the ground to get her hands on a nutritious plant bulb. Paul looked around and saw that there were no other baboons in sight. Suddenly he let out a yell, and within seconds his mother came running. Assuming that Mel was harassing her son, she drove Mel off a small cliff. Paul then took Mel’s bulb for himself.

And of all the nonhuman primates, the most deceptive and crafty are our closest relatives, the great apes. “It’s as if the apes have been reading Machiavelli,” says Whiten. “They’re very concerned to climb up the social hierarchy, and make the right allies to enable them to do that. But at the same time if the occasion is right, just as Machiavelli would have advised, they’ll deceive those friends and ditch them.”

Neuroscientists once assumed a keen social intelligence was nothing special in itself. They thought that the brain was a general‑purpose information processor, and it used the same strategies to solve any problem it encountered, social, physical, or otherwise. But evidence now suggests that our brains do not work in a general‑purpose way. They appear to be a collection of modules–distinct networks of neurons, each of which is dedicated to solving a particular task.

Our brains contain many modules for carrying out specialized mental tasks, such as filling in the edges of objects we see. The optical illusion above reveals these edge‑building‑neurons at work.

To see a module at work, look at the optical illusion above. Even though this picture consists of three circles with wedges cut out of them, you see a triangle. That’s because in the visual centers of your brain, there’s a module whose job is to perceive edges on objects, even when those edges aren’t completely visible. Instead of a random collection of lines, your brain can recognize them as the boundaries of an object. The signals carried from your eyes to your brain are massaged by many different modules, each dedicated to its own image‑processing job, and once they’re done, your brain merges the information together into a three‑dimensional image of the world you

You didn’t have to go to school to develop these visual modules; they began to form when you were an embryo and matured as you began using your eyes. Many biologists see them as adaptations created by natural selection–organs as distinct as an elephant’s trunk or a bird’s beak–which evolved as solutions to problems our ancestors regularly faced. Visual modules may have evolved as our distant primate ancestors struggled to recognize their favorite fruits or navigate through trees. Instead of building up a new picture of the world 60 times a second from scratch, our brains use modules to extract the chunks of information that really matter.

Just as we see with special modules, we may use other modules for perceiving our social world. Simon Baron‑Cohen, a psychologist at Cambridge University, has traced the outlines of these social‑intelligence modules by studying people with different brain disorders. One group of subjects has a condition known as Williams syndrome. They typically have low IQs between 50 and 70, they may have trouble telling their left from their right, and they can’t perform simple addition. And yet people with Williams syndrome often turn out to be gifted musicians and voracious readers. They are fascinated by other people and are remarkably empathetic.

To study the social intelligence of people with Williams syndrome, Baron‑Cohen invented a test. He looked through magazines for pictures of particularly expressive faces and cut out a strip that included their eyes. He then showed these strips to people with Williams syndrome and asked them to tell him what the people in the pictures were feeling, based only on their eyes. The answers his subjects offered tended to be the same as those of a control group of normal adults. Although people with Williams syndrome may be brain‑damaged, that damage did not harm their ability to look through the windows of the soul.

Baron‑Cohen got a mirror‑image result when he performed the same tests on autistic children. Autism does not automatically produce a low IQ; in rare cases autistic people may even be brilliant. But they consistently find it difficult to grasp the rules of society or understand what other people are thinking and feeling. When BaronCohen had autistic subjects look at pictures of eyes, they failed miserably at guessing the states of mind of the people in the pictures. Something about their brains keeps them from putting themselves in other people’s places.

Baron‑Cohen’s work may expose the outlines of the modules that give us social intelligence. If these social‑intelligence modules are damaged–as in the case of autistic people–other forms of intelligence may escape unharmed. People with Williams syndrome demonstrate that brain damage can harm some forms of intelligence while leaving social intelligence untouched.

The evolution of social intelligence may have been one of the most important factors in the rise of humans, not to mention the evolution of primates in general. The evidence is in the weight of primate brains. Robin Dunbar, a psychologist at the University of Liverpool, has compared the size of brains–particularly the neocortex, the outermost layer of the brain, in which high‑level thought processes take place. Some primates, such as lemurs, have a relatively small neocortex for their body size, while other primates, such as baboons and chimps, have big ones. Dunbar discovered a striking pattern: the size of a primate’s neocortex is tightly correlated with the average size of the groups in which it lives. The bigger the group, the bigger the neocortex.

When primates live in larger groups, Dunbar concludes, it puts bigger demands on their social intelligence. They need to keep track of their alliances and grudges, of relatives and acquaintances. Mutations that produce a bigger, more powerful neocortex are favored in these species because they make it possible for a primate to enhance its social intelligence. Not surprisingly, primates with a bigger neocortex engage in more deception than primates with smaller ones.

If we humans follow the primate rule–which only makes sense, given that we are primates–then the evolution of social intelligence must have played a crucial part in the development of our extraordinarily big brains.