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The
other day I fixed something—a rarity for me. The flotation device in the toilet
water tank was rubbing against the side, getting stuck halfway up so that the
tank didn’t fill completely. I own a hammer and know how to operate it. But I
couldn’t fit it into the tank to whack the device back into place. Ditto for
owning and using a wrench. It wouldn’t fit either. But fortunately I also own a
plunger and I used its handle to push the floating thing back the other way,
using the side of the tank as a fulcrum. It worked, although the device got
bent so that the top of the tank didn’t quite fit. That overwhelmed me, so I
called it a good day’s work.

I
was proud of myself. “There,” I thought smugly. “It’s not just chimps who can
use tools.”

Humans
used to be unique in lots of ways. We were the only species who made tools,
murdered each other, passed on culture. And each of those supposed defining
features has now been demonstrated in other species. We’re not so special after
all. But there are still ways that humans appear to stand alone. One of those
is hugely important: the human capacity to think symbolically. Metaphors,
similes, parables, figures of speech—they exert enormous power over us. We kill
for symbols, die for them. Yet symbols generate one of the most magnificent
human inventions: art.

In
recent years scientists from leading universities, including UCLA, University
College London, and Yale, have made remarkable insights into the neurobiology
of symbols. A major finding from their work is that the brain is not very good
at distinguishing between the metaphorical and literal. In fact, as scientists
have shown us, symbols and metaphors, and the morality they engender, are the
product of clunky processes in our brains.

Symbols
serve as a simplifying stand-in for something complex. (A rectangle of cloth
with stars and stripes represents all of American history and values.) And this
is very useful. To see why, start by considering basic language—communication
without a lot of symbolic content. Suppose you are being menaced by something
terrifying and so scream your head off. Someone listening can’t tell if the
blood-curdling “Aiiiii!” means an approaching comet, right-wing death squad, or
Komodo dragon. It just means that things are majorly not right, a generic
scream where the message is the meaning. This present-tense emotionality is
what communication by animals is mostly about.

Symbolic
language brought huge evolutionary advantages. This can be seen even in the
baby steps of symbolism of other species. When vervet monkeys, for instance,
spot a predator, they don’t just generically scream. They use distinct
vocalizations, different “proto-words,” where one means, “Aiiiiii!, predator on
the ground, run up the tree,” and the other means, “Aiiiiii!, predator in the
air, run down the tree.” It’s mighty useful to have evolved the cognitive
capacity to make that distinction. Who would want to guess wrong and dash up to
the top of a tree when the problem is a raptor swooping down?

Language
pries apart a message from its meaning, and as our hominid ancestors kept
getting better at this separation, great individual and social advantages
accrued. We became capable of representing emotions in the past and possible
emotions in the future, as well as things that have nothing to do with emotion.
We evolved a uniquely dramatic means of separating message from meaning and
intent: lying. And we invented asthetic symbolism; after all, those
30,000-year-old paintings of horses in Chauvet cave are not really horses.

Our
early use of symbols helped forge powerful bonds and rules of cooperation, as
human societies grew increasingly complex and competitive. A recent study by
Ara Norenzayan of the University of British Columbia and Azim Shariff of the
University of Oregon revealed that, across 186 societies, the larger the
typical social group, the more likely it was the culture created a god who
monitored and judged human morality—perhaps the ultimate symbol of rule
enforcement.

How did our brains evolve to mediate this complexity? In an awkward way. As has been said, evolution is not an inventor, it’s a tinkerer, making do with the pieces at hand. While a squid can’t swim as fast as many fish, it swims pretty fast for something that evolved from mollusks. Similarly, while the human brain turns out to handle symbols and metaphors in an inelegant way, it still does a pretty good job for something that evolved from brains that only processed the literal. The best way to shine a light on this unwieldy process is through metaphors for two feelings critical to survival: pain and disgust.

Consider the following: you stub your toe. Pain receptors there send messages to the spine and on up to the brain, where various regions kick into action. Some of these areas tell you about location, intensity, and quality. Is it your left toe or right ear that hurts? Was your toe stubbed or crushed by a tractor-trailer? This is the meat-and-potatoes of pain processing, found in every mammal.

But there are fancier, more recently evolved parts of the brain in the frontal cortex that assess the meaning of the pain. Maybe it’s bad news: your stubbed toe signals the start of some unlikely disease. Or maybe it’s good news: you’re going to get your firewalker diploma because the hot coals made your toes throb. Much of this assessing occurs in a frontal cortical region called the anterior cingulate. This structure is heavily involved in “error detection,” noting discrepancies between what is anticipated and what occurs. And pain from out of nowhere surely represents a discrepancy between the pain-free setting that you anticipate versus the painful reality.

Now let’s go a little deeper, based on work by Naomi Eisenberger at UCLA. While lying in a brain scanner, you play a game of virtual catch, where you and two people in another room toss a cyberball around on a computer screen. (In reality, there aren’t two other people, only a computer program.) In the control condition, you’re informed mid-play that there’s a computer glitch and you’re temporarily off-line. You watch the virtual ball get tossed between those two people. Now in the experimental setting, you’re playing with the other two and suddenly they start ignoring you and only toss the ball between them. Hey, how come they don’t want to play with me anymore? Junior high all over again. And the brain scanner shows that the neurons in your anterior cingulate activate.

In other words, rejection hurts. “Well, yeah,” you might say. “But that’s not like stubbing your toe.” It is to your anterior cingulate. Both abstract social and literal pain impact the same cingulate neurons.

We take things a step further with work by Tania Singer and Chris Frith at University College London. While in a brain scanner, you’re administered a mild shock, delivered through electrodes on your fingers. All the usual brain regions activate, including the anterior cingulate. Now you watch your beloved get shocked in the same way. The brain regions that ask, “Is it my finger or toe that hurts?” remain silent. It’s not their problem. But your anterior cingulate activates, and as far as it’s concerned, “feeling someone’s pain” isn’t just a figure of speech. You seem to feel the pain too. As evolution continued to tinker, it did something remarkable with humans. It duct-taped (metaphorically, of course) the anterior cingulate’s role in giving context to pain into a profound capacity for empathy.

We’re not the only empathic species. Chimps show empathy when, for example, they become more likely to groom someone who has been unfairly thrashed by an aggressive jerk of a chimp. And we’re not the only species with an anterior cingulate. But studies show the human anterior cingulate is more complex than in other species, with more connections to abstract, associational parts of the cortex, regions that can call your attention to the pains of the world, rather than the pain in your big toe.

And we feel someone else’s pain like no other species. We extend it over distance to help a refugee child on another continent. We extend it over time, feeling the terror of what are now mere human remains at Pompeii. We feel it embodied in words, as we contemplate George’s sadness that Lennie is never going to get his rabbits. (That part of Of Mice and Men never failed to leave me a sopping, tearful mess when I’d reread it obsessively as a kid.) We even feel empathic pain prompted by symbols encompassed in pixels. “Oh no, the poor Na’vi!” we cry, when Home Tree is destroyed in Avatar. Because the anterior cingulate has trouble remembering “it’s only a figure of speech,” it functions as if your heart is literally being torn out. 

Metaphors, similes, parables, figures of speech—they exert enormous power over us. We kill for symbols, die for them.

Let’s consider another domain where our brains’ shaky management of symbols adds tremendous power to a unique human quality: morality.

You’re in a brain scanner and because of the scientist’s weirdly persuasive request, you bite into some rotten food. Something rancid and fetid and skanky. This activates another part of the frontal cortex, the insula, which, among other functions, processes gustatory and olfactory disgust. It sends neuronal signals to face muscles that reflexively spit out that bite, and to your stomach muscles that make you puke. All mammals have an insula that processes gustatory disgust. After all, no animal wants to consume poison.

But
we are the only animal where that process serves something more abstract. Think
about eating something disgusting. Think about a mouthful of centipedes,
chewing and swallowing them as they struggle, wiping off the little legs that
you’ve drooled onto your lips. Whammo goes the insula, leaping into action,
sending out its usual messages of disgust. Now think about something awful you
once did, something deeply shameful. The insula activates. It has been co-opted
into processing that human invention: moral disgust.

Is
it a surprise that the human insula is involved in processing moral disgust
along with gustatory disgust? Not when human behaviors can make us feel sick to
our stomachs, can leave bad tastes in our mouths, can stink. When I heard about
the massacre at Newtown, “feeling sick to my stomach” wasn’t
just some symbolic figure-of-speech way of saying that I felt distressed. I
felt nauseous. The insula not only prompts the stomach to purge itself of toxic
food; it prompts our stomach to purge the reality of that nightmarish event.
The distance between the symbolic message and the meaning shrinks.

As
shown by Chen-Bo Zhong of the University of Toronto and Katie Liljenquist of
Brigham Young University, if you’re forced to ruminate on a moral transgression
of yours, you’re more likely to clean your hands afterward. And the scientists
showed something even more provocative. They ask you to ruminate on your moral
failings; afterward, you’re put in a position where you can respond to
someone’s request for help. Wallow in your moral turpitude and you’re more
likely to help. Unless you had a chance to wash post-wallowing. Then that urge
to compensate for your transgression is gone; you’ve washed away your sins and
gotten that damn spot out. Pontius Pilate and Lady Macbeth could lecture at
scientific conferences about this one.

Remarkably,
the way our brains use symbols to discern disgust and morality also contributes
to political ideology. Work by scientists such as Kevin Smith of the University
of Nebraska reveals that on the average conservatives have a lower threshold
for visceral disgust than do liberals. Look at pictures of excrement or open
sores undulating with maggots, and if your insula goes atypically berserk,
chances are that you’re a conservative—but only about social issues, say, gay
marriage, if you’re heterosexual. And if your insula just takes those maggots
in stride, chances are you’re a liberal. In a study by Yoel Inbar of Tilburg
University, David Pizarro of Cornell and Paul Bloom of Yale, participants,
placed in a room with a wastebasket marinated in a stink spray (note to self: never do research in that lab)
“showed less warmth toward gay men relative to heterosexual men.” In a control room,
without the stink, participants evaluated gay and heterosexual men equally. In
a nutty, smart, real world example, Tea Party candidate Carl Paladino mailed
out campaign flyers impregnated with the smell of garbage during his GOP
primary campaign for New York governor in 2010. His campaign trumpeted,
“Something really stinks in Albany.” Paladino won his primary. (He stunk,
however, in the general election, losing by a large margin to Andrew Cuomo.)

We evolved a uniquely dramatic means of separating meaning from intent: lying.

Our
wobbly, symbol-dependent brains are molded by personal ideology and culture,
shaping our perceptions, emotions, and convictions. We use symbols to demonize
our enemies and wage war. The Hutu of Rwanda portrayed the enemy Tutsi as
cockroaches. In Nazi propaganda posters, Jews were rats who carried dangerous
microbes. Many cultures inculcate their members into acquiring symbols that
repel, doing so by strengthening specific neural pathways from the cortex to
the insula, pathways that you’d never find in another species. Depending on who
you are, those pathways could be activated by the sight of a swastika or of two
men kissing. Or perhaps by the thoughts of an abortion, or of a 10-year-old
Yemeni girl forced to marry an old man. Our stomachs lurch, and we feel the
visceral certainty of what is wrong. And we belong.

The
same brain apparatus is behind symbols that move us to our most empathic,
inclusive, and embracing. It is often art that does this most powerfully. We
see the artistry of a skillful photojournalist—a photo of a child whose home
was devastated by a natural disaster— and we reach for our wallets. If it is
1937, we don’t look at Picasso’s “Guernica” and see a menagerie of anatomically
deformed mammals. Instead we see the devastation and feel the pain of a
defenseless Basque village immolated during the Spanish Civil War. We feel
moved to act against the Fascists and Nazis who conducted the aerial attack.
Today we can feel moved to care about the fate of animals when we look at the
simple artistic symbol, like a panda logo, of an environmental group.

Our
metaphor-making brains are unique in the animal kingdom. But clearly we are
dealing with a double-edged sword. We can dull the edge that demonizes, and
sharpen the one that urges us to good acts. 

Robert
Sapolsky is a professor of biology and neurology at Stanford University. He is
the author of a number of books, including
Why
Zebras Don’t Get Ulcers, Monkeyluv, and A
Primate’s Memoir

This article was originally published in our “What Makes You So Special” issue in April, 2013.