And yet for all the variability in the ancient environments that shaped the human brain, there were constants. We hunted and gathered. We lived in small bands. We mated and raised children. These are the universals that shaped the brain’s developments.
The rather uncomfortable feeling most of us have when we’re around snakes is evidence of how this ancient experience continues to influence us today. Throughout the long prehistory of our species and those that preceded it, snakes were a mortal threat. And so we learned our lesson: Beware snakes. Or, to be more precise, some of us learned that lesson. Others didn’t, but they had a nasty habit of dying. So natural selection did its work and the rule—beware snakes—was ultimately hardwired into every human brain. It’s universal. Go anywhere on the planet, examine any culture. People are wary of snakes. Even if—as in the Arctic—there are no snakes. Our primate cousins shared our long experience and they feel the same way: Even monkeys raised in laboratories who have never seen a snake will back away at the sight of one.
Of course not everyone is wary of snakes, much less afraid of them, and some people like snakes enough to keep a twelve-foot Burmese python in the basement. It’s also possible to be terrified of much cuddlier animals, even dogs, which our ancient ancestors created by selectively breeding wolves for the traits they desired. Psychologists describe the natural human wariness of snakes as merely an inclination to be afraid of snakes. If a person has positive experiences with snakes early in life, the phobia will not develop. Negative experiences will easily bring it out. People can also learn to be afraid of dogs, but those fears are not promoted by ancient hardwiring. The difference in the two fears is revealed when psychologists attempt to treat phobias with “positive conditioning” (bringing the patient together with the feared animal in a safe and pleasant environment). Dog phobias typically disappear quickly. But snake phobias are often impossible to erase—thanks to lessons learned tens of thousands of years ago.
Our troubled relationship with snakes is an obvious example of how the environment of our ancient ancestors shaped the brain that is reading this sentence. It’s also a fairly trivial one. More profound examples of ancient hardwiring are not so easy to spot, but, in many cases, they are also vastly more important to the operations of the brain.
One bit of very old wiring is sometimes called the Law of Similarity. In the late nineteenth century, anthropologists noticed that traditional cultures assumed that causes resembled their effects. The Zande people of Africa,for example, believed that ringworm was caused by fowl excrement because fowl excrement looks like ringworm. In European folk medicine, foxes were felt to have great stamina and so their lungs were used to treat asthma, while Chinese folk medicine treated eyesight ailments with ground-up bat eyes because it was (quite wrongly) believed that bats had superior eyesight. The fact that this same assumption—like causes like—could be found in culture after culture, all over the world, is a very strong indication that it has biological origins.
The Law of Similarity comes in an even more basic form: Appearance equals reality. If it looks like a lion, it is a lion. Or, to put it in the modern vernacular, if it walks like a duck and quacks like a duck, it’s a duck. That may seem more like common sense than ancient wiring, but it is quite ancient. And it’s not always so sensible.
Psychologists found that when they asked students to eat a piece of fudge shaped like dog feces, the students were—shall we say—reluctant. The students knew the fudge was fudge. But it looked like dog feces and that triggered a feeling of disgust—another bit of ancient hardwiring—that they couldn’t shake. The researchers got the same results when they asked people to put a piece of rubber shaped and colored like vomit in their mouths. And when they asked students to choose an empty container, fill it with sugar, and label it SODIUM CYANIDE, POISON, the students shrank from consuming the sugar. “In these studies,” wrote psychologists Paul Rozin and Carol Nemeroff, “subjects realized that their negative feelings were unfounded, but they felt and acknowledged them anyway.”
The appearance-equals-reality rule often surfaces in magical beliefs. Want to hurt someone? In voodoo, you torment a doll that looks like the target. The same connection was made when isolated tribes first encountered photographs and were terrified: These images were duplicates of the people they depicted, and that must mean cameras steal the spirit of the person being photographed.
Of course, I know that a photo of my children is not my children. On one level, that’s easy to understand. I said so over and over as I stumbled around an African slum looking for that picture of my kids. But my inner caveman couldn’t grasp this. For millions of years, he and his ancestors followed the appearance-equals-reality rule. If it looks like a deer, it is a deer: There’s your lunch. If it looks like a lion, it is a lion: Run, or you will be lunch. That rule worked well. It worked so well it was wired into every human brain, where it remains to this day.
But the appearance-equals-reality rule clearly leads to the conclusion that a photograph of my children is my children. This is why my inner caveman panicked. I’ve lost my children! I can’t abandon my children! And so off I went in a place where I stood a good chance of being robbed or killed or both, in search of a worthless scrap of chemical-covered paper.
This seems absurd only from the perspective of a modern human. For Paleolithic man, the appearance-equals-reality rule was useful and reliable. He could be quite confident that if he saw something that looked like his children, it was his children. Only when the environment changed as a result of the invention of photography would humans see images that looked like their children but were not their children—and that happened only 180 years ago.
Of course, our world is awash in photographic images that, presumably, could trigger ancient wiring and confuse our sense of reality. And yet that’s not happening. A photo is not the thing it depicts. Most people don’t have to think hard to get that. The reader may understandably conclude that it’s only the author who’s got faulty wiring, not the species.
Not so. To understand why, we must return to the two systems of thought introduced earlier.
System One is the more ancient. It is intuitive, quick, and emotional. System Two is calculating, slow, and rational. I’ll call the two systems Gut and Head, because that’s how we usually talk about them. “I have a gut feeling, ” someone may say when she has a vague sense that something is true for reasons she cannot quite explain. “Use your head,” her friend may respond—meaning, that can’t be true, so stop and think carefully. (Bear in mind, however, that this is only a metaphor. Poets may say feelings come from the heart or the stomach, but in reality the brain alone generates all thoughts and feelings.)
System Two, or Head, is conscious thought. When we examine the statistics and decide that the odds of being killed in a terrorist attack are far too small to worry about, Head is doing the work. Head is our best bet for accurate results, but it has limitations. First, Head needs to be educated. We live in a world of complex information, and if Head doesn’t learn the basics of math, stats, and logic—if it doesn’t know the difference between an increaseof 5 percent and an increase of 5 percentage points, say, or that correlation does not prove causation—it can make bad mistakes. Head also works very slowly. That may not be a problem when you are reading the newspaper at the breakfast table, but it’s a little troublesome when you see a shadow move in long grass and you have to decide what to do without consulting an encyclopedia to determine the prevalence and hunting habits of lions.