The Evolution of Metaphorical Language: Robert Sapolsky on Our Ability to Think in Symbols
Professor Robert Sapolsky, a biologist and neuroscientist at Stanford University, explains how humans developed metaphorical language, why figures of speech, comparisons, and parables have such power over us, and how our brain’s limited ability to distinguish between metaphorical and literal meanings helped us create art, learn to feel others’ pain, and experience shame when we act immorally.
Humans are used to thinking of themselves as unique in many ways. We’re the only species that invented various tools, killed each other, and created culture. But each of these supposed distinguishing features is now found in other species as well. We’re not as special as we once thought. However, there are other manifestations that do make us unique. One of the most important is our ability to think in symbols. Metaphors, comparisons, parables, and figures of speech all have tremendous power over us. We kill for symbols, we die for them. Yet, symbols have also given rise to one of humanity’s greatest inventions: art.
In recent years, scientists from leading universities, including University College London and Yale, have made remarkable progress in understanding the neurobiology of symbols. Their main finding: the brain isn’t very good at distinguishing between the metaphorical and the literal. In fact, research shows that symbols, metaphors, and the morality they generate are products of clumsy processes in our brains.
How Symbolic Language Evolved
Symbols serve as simplified stand-ins for complex things (for example, a rectangle of cloth with stars and stripes represents all of American history and its values). This is extremely useful. To understand why, start by considering “basic” language—communication without symbolic content. Suppose you’re threatened by something terrible and you scream at the top of your lungs. Someone hearing this doesn’t know what the scary “Aaaaah!” means—is it a comet, a death squad, or a giant lizard? Your cry just means something is wrong—a general alarm with no specific message. This is a fleeting expression, a form of communication used by animals.
Symbolic language brought huge evolutionary advantages. You can see this in how children—and even some other species—learn symbolism. For example, when vervet monkeys spot a predator, they don’t just make a generic alarm call. They use different vocalizations, different “proto-words,” where one means “Predator on the ground, climb the trees,” and another means “Predator in the air, get down from the trees.” Evolution was needed to develop the cognitive abilities to make these distinctions. Who would want to climb up when the predator is flying right at you?
Language separates the message from its meaning, and, like our hominid ancestors, we continue to benefit from this separation—it brings great individual and social advantages. We became able to recall past emotions, anticipate future ones, and imagine things unrelated to emotions. We evolved the ability to separate message from meaning and purpose: lying. And we invented aesthetic symbolism. After all, those 30,000-year-old images of horses in the Chauvet Cave aren’t actually horses.
Our early use of symbols helped form powerful bonds and rules of interaction, and human communities became increasingly complex and competitive. A recent study of 186 indigenous societies led by Ara Norenzayan (University of British Columbia) and Azim Shariff (Oregon State University) found that the larger the typical social group, the more likely their culture was to create a god who monitors and judges human morality—the ultimate symbol of rule enforcement.
The Brain’s Clumsy Path to Symbolic Thinking
How did our brains evolve to mediate this difficult task? In a rather clumsy way. As mentioned, evolution isn’t an inventor—it’s a tinkerer, working with whatever parts are available. While a squid can’t swim as fast as most fish, it swims pretty fast for a creature descended from mollusks. Similarly, the human brain processes symbols and metaphors in a rather rough way, but it does a pretty good job for an organ that evolved from one that could only handle literal information. The best way to shed light on this clunky process is with metaphors for two senses critical to survival: pain and disgust.
Consider this example: you stub your toe. Pain receptors send messages to your spinal cord and then to your brain, where different areas kick into action. Some of these areas tell you about the location, intensity, and nature of the pain. Is it your right toe or your left ear? Was your toe bruised or crushed by a tractor? This vital pain-processing system is found in all mammals.
But there are more sophisticated, much later-evolved parts of the brain in the frontal cortex that assess the meaning of pain. Is it good news or bad? Does your bruise signal the start of a nasty disease, or are you just about to earn a certificate for walking on hot coals, and that’s what the pain is about? Many of these assessments happen in the anterior cingulate cortex, a part of the frontal cortex. This structure is heavily involved in “error detection,” noting discrepancies between what was expected and what’s happening. And pain out of nowhere is definitely a mismatch between a pain-free expectation and a painful reality.
Empathy and the Anterior Cingulate Cortex
Let’s look at the work of Naomi Eisenberger at UCLA. Imagine you’re lying in a brain scanner, playing a virtual ball game: you and two others in another room toss a cyber-ball on a computer screen (in reality, there are no other people—just a computer program). In the control condition, you’re told mid-game that there’s a computer glitch and you’ll be temporarily disconnected. You watch as the virtual ball is tossed between the remaining two players. In the experimental condition, you’re playing with two others, and suddenly they start ignoring you and only toss the ball to each other.
Hey, why don’t they want to play with me anymore? Middle school problems come rushing back. And the brain scanner shows that at this moment, neurons in your anterior cingulate cortex are activated.
In other words, rejection hurts. “Well, sure,” you might say. “But it’s not the same as stubbing your toe.” But that’s the point: abstract social pain and real physical pain activate the same neurons in the brain’s anterior cingulate cortex.
Tania Singer and Chris Frith at University College London took this further. While a subject was in a brain scanner, they received a mild electric shock to their fingers. All the usual brain areas lit up, including the anterior cingulate cortex. Then the experiment was repeated, but this time the subjects watched their loved ones receive the same mild shock. The brain areas that ask “Are my fingers hurting?” stayed quiet, since it wasn’t their problem. But the subjects’ anterior cingulate cortex lit up, and they began to “feel someone else’s pain”—and this isn’t just a figure of speech. They actually felt as if they were in pain too. Evolution did something special with humans: the anterior cingulate cortex became (metaphorically) a stage for creating the context of pain as the basis for empathy.
But we’re not the only species capable of empathy. Chimpanzees show empathy, for example, when they care for someone who’s been attacked by another chimp. We’re also not the only species with an anterior cingulate cortex. However, research shows that the human anterior cingulate cortex is more complex than in other species, more connected to abstract and associative brain areas—regions that can focus our attention on global suffering, not just toe pain.
And we feel others’ pain like no other species. We feel it across great distances, which is why we’re willing to help a refugee child on another continent. We feel it across time, experiencing the horror that gripped people left behind in Pompeii. We even feel empathetic pain when seeing certain symbols, rendered in pixels. “Oh no, poor Na’vi!” we cry when the great tree is destroyed in “Avatar.” Because the anterior cingulate cortex has trouble remembering that “it’s just a figure of speech,” it functions as if your heart is literally breaking.
Metaphors, comparisons, parables, and figures of speech—they have enormous power over us. We kill for symbols, we die for them.
Morality and the Power of Disgust
Let’s look at another area where our weak ability to manage symbols adds enormous power to a uniquely human trait: morality.
Imagine you’re in a brain scanner and, thanks to a disturbingly persuasive scientist, you eat some rotten food. Something rancid, foul-smelling, and clearly inedible. This activates another part of the frontal cortex, the insula, which, among other things, is responsible for taste and smell disgust. The insula sends signals to your facial muscles to reflexively contract so you can spit it out, and to your stomach muscles to induce vomiting. All mammals have an insula involved in taste aversion. After all, no animal wants to eat poison.
But we’re the only creatures for whom this process serves something more abstract. Imagine eating something disgusting. Imagine your mouth full of centipedes, chewing and trying to swallow them as they squirm, wiping their legs from your lips. At that moment, your insula fires up and sends signals of disgust. Now, think about something terrible you once did, something truly shameful. The insula activates. These processes gave rise to a key human invention: moral disgust.
Isn’t it remarkable that the human insula is involved in both physical and moral disgust? Not when human behavior can make us feel stomach cramps, bad tastes, and even smell stench. When I heard about the Newtown school shooting, I felt a pain in my stomach—and it wasn’t just a figure of speech to show how upset I was. I felt nauseous. The insula doesn’t just urge the body to purge toxic food—it asks our stomach to purge reality of this nightmare. The gap between symbolic message and meaning shrinks.
Chen-Bo Zhong (University of Toronto) and Katie Liljenquist (Brigham Young University) found that if you’re forced to reflect on your moral wrongdoing, you’re more likely to go wash your hands afterward. But they demonstrated something even more provocative. After reflecting on your moral failings, you’re put in a situation where you can respond to someone’s request for help. If you’re still wallowing in your moral filth, you’re more likely to help. But not if you’ve had a chance to wash up after your moral soul-searching. In that case, you’ve “compensated” for your crime—you’ve washed away your sins and rid yourself of those dark stains. Pontius Pilate and Lady Macbeth could give lectures at scientific conferences on this topic.
Interestingly, the way our brains use symbols to distinguish between physical and moral disgust also applies to political ideology. Research by Kevin Smith (University of Nebraska) shows that, on average, conservatives have a lower threshold for physiological disgust than liberals. Look at pictures of feces or open wounds filled with maggots—if your insula goes wild, you’re likely a conservative, but only on social issues like same-sex marriage (if you’re heterosexual). If your insula can get past the disgust, you’re probably a liberal. In a study by Yoel Inbar (Tilburg University), David Pizarro (Cornell), and Paul Bloom (Yale), participants placed in a room with a trash can emitting a terrible stench “showed less warmth toward gay men compared to straight men.” In a control room with no smell, participants rated gay and straight men equally. In a clever real-life example, Tea Party candidate Carl Paladino sent out campaign flyers scented with garbage during his 2010 Republican primary run for New York governor. His campaign slogan: “Something really stinks in Albany.” Paladino won the primary (but lost badly to Andrew Cuomo in the general election).
Our shaky, symbol-dependent brains are shaped by personal ideology and culture, influencing our perceptions, emotions, and beliefs. We use symbols to demonize our enemies and wage war. In Rwanda, Hutus depicted Tutsis as cockroaches. Nazi propaganda posters portrayed Jews as rats carrying disease. Many cultures “inoculate” their members—creating repulsive symbols that sharpen and strengthen specific neural pathways—from cortex to insula—that you’ll never find in other species. Depending on who you are, these pathways may be triggered by a swastika or two men kissing. Or perhaps by thoughts of abortion or a 10-year-old Yemeni girl forced to marry an old man. Our stomachs clench, we feel on a biological level that it’s wrong, and we give in to that feeling.
The same brain mechanism works with symbols that help us empathize, connect, and embrace others. This is most powerfully embodied in art. We see the skill of a talented photojournalist—a photo of a child whose home was destroyed by a natural disaster—and we reach for our wallets. If it’s 1937, we look at Picasso’s “Guernica” and see not just a menagerie of anatomically deformed mammals. Instead, we see devastation and feel the pain of a defenseless Basque village doomed during the Spanish Civil War. We want to stand up to the fascists and Nazis who carried out the air raid. Today, we may feel compelled to care about animals when we see a simple artistic symbol—the panda logo of the WWF.
Our brains, constantly generating metaphors, are unique in the animal kingdom. But clearly, we’re dealing with a double-edged sword. We can use the dull side—to demonize—or the sharp side, which inspires us to do good.