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Bigger and bigger brains
Adapting to variation provides a context for symbolic reasoning, but it hardly explains our unique ability to invent calculus and write romance novels. After all, many animals create a database of knowledge, and many of them make tools, which they use creatively. Still, it is not as if chimpanzees write symphonies badly and we write them well. Chimps can’t write them at all, and we can write ones that make people spend their life savings on subscriptions to the New York Philharmonic. There must have been something else in our evolutionary history that gave rise to unique human thinking.
One of the random genetic mutations that gave us an adaptive advantage involved walking upright on two legs. Because the trees were gone or going, we needed to travel increasingly long distances between food sources. Walking on two legs instead of four both freed up our hands and used fewer calories. It was energy-efficient. Our ancestral bodies used the energy surplus not to pump up our muscles but to pump up our minds.
This led to the masterpiece of evolution, the region that distinguishes humans from all other creatures. It is a specialized area of the frontal lobe, just behind the forehead, called the prefrontal cortex. What does the prefrontal cortex do? We got our first hints from a man named Phineas Gage, who suffered the most famous occupational injury in the history of brain science.
Gage was a popular foreman of a railroad construction crew. He was funny, clever, hardworking, and responsible, the kind of guy any father would be proud to call “son-in-law.” On September 13, 1848, he set an explosives charge in the hole of a rock using a tamping iron, a three-foot rod about an inch in diameter. The charge blew the rod into Gage’s head. It entered just under the eye and destroyed most of his prefrontal cortex. Miraculously, Gage survived. But he became tactless, impulsive, and profane. He left his family and wandered aimlessly from job to job. His friends said he was no longer Gage.
When damage occurs to a specific brain region, we know that any observed behavioral abnormality must in some way be linked to that region’s function. I describe several such cases throughout the book for this reason. Gage’s case was the first real evidence that the prefrontal cortex governs several uniquely human cognitive talents, called “executive functions”: solving problems, maintaining attention, and inhibiting emotional impulses. In short, this region controls many of the behaviors that separate us from other animals (and from teenagers).
Three brains in one
The prefrontal cortex, however, is only the newest addition to the brain. Three brains are tucked inside your head, and parts of their structure took millions of years to design. Your most ancient neural structure is the brain stem, or “lizard brain.” This rather insulting label reflects the fact that the brain stem functions the same way in you as in a Gila monster. The brain stem controls most of your body’s housekeeping chores: breathing, heart rate, sleeping, waking. Lively as Las Vegas, these neurons are always active, keeping your brain buzzing along whether you’re napping or wide awake.
Sitting atop your brain stem is your “mammalian brain.” It appears in you the same way it does in many mammals, such as house cats, which is how it got its name. It has more to do with your animal survival than with your human potential. Most of its functions involve what some researchers call the “four Fs”: fighting, feeding, fleeing, and … reproductive behavior. Several parts of the mammalian brain play a large role in the Brain Rules.
The amygdala allows you to feel rage. Or fear. Or pleasure. Or memories of past experiences of rage, fear, or pleasure. The amygdala is responsible for both the creation of emotions and the memories they generate. We’ll explore the powerful effects of emotions, and how to harness them, in the Attention chapter.
The hippocampus converts your short-term memories into longer-term forms. The Memory chapter covers the surprising way that happens, and the key to remembering.
The thalamus is one of the most active, well-connected parts of the brain—a control tower for the senses. Sitting squarely in the center of your brain, it processes and routes signals sent from nearly every corner of your sensory universe. We’ll return to this bizarre, complex process in the Sensory Integration chapter.
Folded atop all of this is your “human brain,” a layer called the cortex. Unfolded, this layer would be about the size of a baby blanket, with a thickness ranging from that of blotting paper to that of heavy-duty cardboard. It is in deep electrical communication with the interior. Neurons spark to life, then suddenly blink off, then fire again. Complex circuits of electrical information crackle in coordinated, repeated patterns, racing to communicate their information along large neural highways that branch suddenly into thousands of exits. As we’ll see in the Wiring chapter, these branches are different in every single one of us. Each region of the cortex is highly specialized, with sections for speech, for vision, for memory.
You wouldn’t know all this just by looking at the brain. The cortex looks homogenous, somewhat like the shell of a walnut, which fooled anatomists for hundreds of years. Then World War I happened. It was the first major conflict where medical advances allowed large numbers of combatants to survive shrapnel injuries. Some of these injuries penetrated only to the periphery of the brain, destroying tiny regions of the cortex while leaving everything else intact. Enough soldiers were hurt that scientists could study in detail the injuries and the truly strange behaviors that resulted. Eventually, scientists were able to make a complete structure–function map of the brain. They were able to see that the brain had, over eons, become three.
Scientists found that as our brains evolved, our heads did, too: They were getting bigger all the time. But the pelvis—and birth canal—can be only so wide, which is bonkers if you are giving birth to children with larger and larger heads. A lot of mothers and babies died on the way to reaching an anatomical compromise. Human pregnancies are still remarkably risky without modern medical intervention. The solution? Give birth while the baby’s head is small enough to fit through the birth canal. The problem? You create childhood. Most mammals reach adulthood within months. Our long childhood gave the brain time to finish its developmental programs outside the womb. It also created a creature vulnerable to predators for years and not reproductively fit for more than a decade. That’s an eternity when you live in the great outdoors, as we did for eons.
But the trade-off was worth it. A child was fully capable of learning just about anything and, at least for the first few years, not good for doing much else. This created the concept not only of learner but, for adults, of teacher. Of course, it was no use having babies who took years to grow if the adults were eaten before they could finish their thoughtful parenting. We weaklings needed to out-compete the big boys on their home turf, leaving our new home safer for sex and babies. We decided on a strange strategy. We decided to try to get along with each other.
We cooperated: You scratch my back …
Trying to fight off a woolly mammoth? Alone, and the fight might look like Bambi vs. Godzilla. Two or three of you together—coordinating behavior and establishing the concept of “teamwork”—and you present a formidable challenge. You can figure out how to compel the mammoth to tumble over a cliff, for one. There is ample evidence that this is exactly what we did.
This changes the rules of the game. We learned to cooperate, which means creating a shared goal that takes into account our allies’ interests as well as our own. In order to understand our allies’ interests, we must be able to understand others’ motivations, including their reward and punishment systems. We need to know where their “itch” is. To do this, we constantly make predictions about other people’s mental states. Say we hear news about a couple: The husband died, and then the wife died. Our minds start working to infer the mental state of the wife: The husband died, and then the wife died of grief.
We create a view, however brief, into the psychological interior of the wife. We have an impression of her mental state, perhaps even knowledge about her relationship with her husband. These inferences are the signature characteristic of something called Theory of Mind. We activate it all the time. We try to see our entire world in terms of motivations, ascribing motivations to our pets and even to inanimate objects. The skill is useful for selecting a mate, for navigating the day-to-day issues surrounding