Сьюзан Кейн - Quiet [The Power of Introverts in a World That Can't Stop Talking]

Other studies of personality also support the premise that extroversion and introversion are physiologically, even genetically, based. One of the most common ways of untangling nature from nurture is to compare the personality traits of identical and fraternal twins. Identical twins develop from a single fertilized egg and therefore have exactly the same genes, while fraternal twins come from separate eggs and share only 50 percent of their genes on average. So if you measure introversion or extroversion levels in pairs of twins and find more correlation in identical twins than in fraternal pairs—which scientists do, in study after study, even of twins raised in separate households—you can reasonably conclude that the trait has some genetic basis.

None of these studies is perfect, but the results have consistently suggested that introversion and extroversion, like other major personality traits such as agreeableness and conscientiousness, are about 40 to 50 percent heritable.

But are biological explanations for introversion wholly satisfying? When I first read Kagan’s book Galen’s Prophecy , I was so excited that I couldn’t sleep. Here, inside these pages, were my friends, my family, myself—all of humanity, in fact!—neatly sorted through the prism of a quiescent nervous system versus a reactive one. It was as if centuries of philosophical inquiry into the mystery of human personality had led to this shining moment of scientific clarity. There was an easy answer to the nature-nurture question after all—we are born with prepackaged temperaments that powerfully shape our adult personalities.

But it couldn’t be that simple—could it? Can we really reduce an introverted or extroverted personality to the nervous system its owner was born with? I would guess that I inherited a high-reactive nervous system, but my mother insists I was an easy baby, not the kind to kick and wail over a popped balloon. I’m prone to wild flights of self-doubt, but I also have a deep well of courage in my own convictions. I feel horribly uncomfortable on my first day in a foreign city, but I love to travel. I was shy as a child, but have outgrown the worst of it. Furthermore, I don’t think these contradictions are so unusual; many people have dissonant aspects to their personalities. And people change profoundly over time, don’t they? What about free will—do we have no control over who we are, and whom we become?

I decided to track down Professor Kagan to ask him these questions in person. I felt drawn to him not only because his research findings were so compelling, but also because of what he represents in the great nature-nurture debate. He’d launched his career in 1954 staunchly on the side of nurture, a view in step with the scientific establishment of the day. Back then, the idea of inborn temperament was political dynamite, evoking the specter of Nazi eugenics and white supremacism. By contrast, the notion of children as blank slates for whom anything was possible appealed to a nation built on democracy.

But Kagan had changed his mind along the way. “I have been dragged, kicking and screaming, by my data,” he says now, “to acknowledge that temperament is more powerful than I thought and wish to believe.” The publication of his early findings on high-reactive children in Science magazine in 1988 helped to legitimize the idea of inborn temperament, partly because his “nurturist” reputation was so strong.

If anyone could help me untangle the nature-nurture question, I hoped, it was Jerry Kagan.

Kagan ushers me inside his office in Harvard’s William James Hall, surveying me unblinkingly as I sit down: not unkind, but definitely discerning. I had imagined him as a gentle, white-lab-coated scientist in a cartoon, pouring chemicals from one test tube to another until— poof! Now, Susan, you know exactly who you are . But this isn’t the mild-mannered old professor I’d imagined. Ironically for a scientist whose books are infused with humanism and who describes himself as having been an anxious, easily frightened boy, I find him downright intimidating. I kick off our interview by asking a background question whose premise he disagrees with. “No, no, no!” he thunders, as if I weren’t sitting just across from him.

The high-reactive side of my personality kicks into full gear. I’m always soft-spoken, but now I have to force my voice to come out louder than a whisper (on the tape recording of our conversation, Kagan’s voice sounds booming and declamatory, mine much quieter). I’m aware that I’m holding my torso tensely, one of the telltale signs of the high-reactive. It feels strange to know that Kagan must be observing this too—he says as much, nodding at me as he notes that many high-reactives become writers or pick other intellectual vocations where “you’re in charge: you close the door, pull down the shades and do your work. You’re protected from encountering unexpected things.” (Those from less educated backgrounds tend to become file clerks and truck drivers, he says, for the same reasons.)

I mention a little girl I know who is “slow to warm up.” She studies new people rather than greeting them; her family goes to the beach every weekend, but it takes her ages to dip a toe into the surf. A classic high-reactive, I remark.

“No!” Kagan exclaims. “Every behavior has more than one cause. Don’t ever forget that! For every child who’s slow to warm up, yes, there will be statistically more high-reactives, but you can be slow to warm up because of how you spent the first three and a half years of your life! When writers and journalists talk, they want to see a one-to-one relationship—one behavior, one cause. But it’s really important that you see, for behaviors like slow-to-warm-up, shyness, impulsivity, there are many routes to that.”

He reels off examples of environmental factors that could produce an introverted personality independently of, or in concert with, a reactive nervous system: A child might enjoy having new ideas about the world, say, so she spends a lot of time inside her head. Or health problems might direct a child inward, to what’s going on inside his body.

My fear of public speaking might be equally complex. Do I dread it because I’m a high-reactive introvert? Maybe not. Some high-reactives love public speaking and performing, and plenty of extroverts have stage fright; public speaking is the number-one fear in America, far more common than the fear of death. Public speaking phobia has many causes, including early childhood setbacks, that have to do with our unique personal histories, not inborn temperament.

In fact, public speaking anxiety may be primal and quintessentially human, not limited to those of us born with a high-reactive nervous system. One theory, based on the writings of the sociobiologist E. O. Wilson, holds that when our ancestors lived on the savannah, being watched intently meant only one thing: a wild animal was stalking us. And when we think we’re about to be eaten, do we stand tall and hold forth confidently? No. We run. In other words, hundreds of thousands of years of evolution urge us to get the hell off the stage, where we can mistake the gaze of the spectators for the glint in a predator’s eye. Yet the audience expects not only that we’ll stay put, but that we’ll act relaxed and assured. This conflict between biology and protocol is one reason that speechmaking can be so fraught. It’s also why exhortations to imagine the audience in the nude don’t help nervous speakers; naked lions are just as dangerous as elegantly dressed ones.

But even though all human beings may be prone to mistaking audience members for predators, each of us has a different threshold for triggering the fight-or-flight response. How threateningly must the eyes of the audience members narrow before you feel they’re about to pounce? Does it happen before you’ve even stepped onstage, or does it take a few really good hecklers to trigger that adrenaline rush? You can see how a highly sensitive amygdala would make you more susceptible to frowns and bored sighs and people who check their BlackBerrys while you’re in mid-sentence. And indeed, studies do show that introverts are significantly more likely than extroverts to fear public speaking.