Getting right down to business, she informs us that she has five different subtopics she can discuss, and asks us to raise our hands to vote for our first, second, and third choice of subjects. Then she performs, rapid-fire, an elaborate mathematical calculation from which she determines the three subtopics for which we've collectively voted. The crowd settles down amiably. It doesn't really matter which subtopics we've chosen; we know that Aron is here to talk about sensitivity, and that she's taking our preferences into consideration.

Some psychologists make their mark by doing unusual research experiments. Aron's contribution is to think differently, radically differently, about studies that others have done. When she was a girl, Aron was often told that she was "too sensitive for her own good." She had two hardy elder siblings and was the only child in her family who liked to daydream, and play inside, and whose feelings were easily hurt. As she grew older and ventured outside her family's...o...b..t, she continued to notice things about herself that seemed different from the norm. She could drive alone for hours and never turn on the radio. She had strong, sometimes disturbing dreams at night. She was "strangely intense," and often beset by powerful emotions, both positive and negative. She had trouble finding the sacred in the everyday; it seemed to be there only when she withdrew from the world.

Aron grew up, became a psychologist, and married a robust man who loved these qualities. To her husband, Art, Aron was creative, intuitive, and a deep thinker. She appreciated these things in herself, too, but saw them as "acceptable surface manifestations of a terrible, hidden flaw I had been aware of all my life." She thought it was a miracle that Art loved her in spite of this flaw.

But when one of her fellow psychologists casually described Aron as "highly sensitive," a lightbulb went on in her head. It was as if these two words described her mysterious failing, except that the psychologist hadn't been referring to a flaw at all. It had been a neutral description.

Aron pondered this new insight, and then set out to research this trait called "sensitivity." She came up mostly dry, so she pored over the vast literature on introversion, which seemed to be intimately related: Kagan's work on high-reactive children, and the long line of experiments on the tendency of introverts to be more sensitive to social and sensory stimulation. These studies gave her glimpses of what she was looking for, but Aron thought that there was a missing piece in the emerging portrait of introverted people.

"The problem for scientists is that we try to observe behavior, and these are things that you cannot observe," she explains. Scientists can easily report on the behavior of extroverts, who can often be found laughing, talking, or gesticulating. But "if a person is standing in the corner of a room, you can attribute about fifteen motivations to that person. But you don't really know what's going on inside."

Yet inner behavior was still behavior, thought Aron, even if it was difficult to catalog. So what is the inner behavior of people whose most visible feature is that when you take them to a party they aren't very pleased about it? She decided to find out.

First Aron interviewed thirty-nine people who described themselves as being either introverted or easily overwhelmed by stimulation. She asked them about the movies they liked, their first memories, relationships with parents, friendships, love lives, creative activities, philosophical and religious views. Based on these interviews, she created a voluminous questionnaire that she gave to several large groups of people. Then she boiled their responses down to a constellation of twenty-seven attributes. She named the people who embodied these attributes "highly sensitive."

Some of these twenty-seven attributes were familiar from Kagan and others' work. For example, highly sensitive people tend to be keen observers who look before they leap. They arrange their lives in ways that limit surprises. They're often sensitive to sights, sounds, smells, pain, coffee. They have difficulty when being observed (at work, say, or performing at a music recital) or judged for general worthiness (dating, job interviews).

But there were also new insights. The highly sensitive tend to be philosophical or spiritual in their orientation, rather than materialistic or hedonistic. They dislike small talk. They often describe themselves as creative or intuitive (just as Aron's husband had described her). They dream vividly, and can often recall their dreams the next day. They love music, nature, art, physical beauty. They feel exceptionally strong emotions-sometimes acute bouts of joy, but also sorrow, melancholy, and fear.

Highly sensitive people also process information about their environments-both physical and emotional-unusually deeply. They tend to notice subtleties that others miss-another person's shift in mood, say, or a lightbulb burning a touch too brightly.

Recently a group of scientists at Stony Brook University tested this finding by showing two pairs of photos (of a fence and some bales of hay) to eighteen people lying inside fMRI machines. In one pair the photos were noticeably different from each other, and in the other pair the difference was much more subtle. For each pair, the scientists asked whether the second photo was the same as the first. They found that sensitive people spent more time than others looking at the photos with the subtle differences. Their brains also showed more activity in regions that help to make a.s.sociations between those images and other stored information. In other words, the sensitive people were processing the photos at a more elaborate level than their peers, reflecting more on those fenceposts and haystacks.

This study is very new, and its conclusions still need to be replicated and explored in other contexts. But it echoes Jerome Kagan's findings that high-reactive first graders spend more time than other children comparing choices when they play matching games or reading unfamiliar words. And it suggests, says Jadzia Jagiellowicz, the lead scientist at Stony Brook, that sensitive types think in an unusually complex fashion. It may also help explain why they're so bored by small talk. "If you're thinking in more complicated ways," she told me, "then talking about the weather or where you went for the holidays is not quite as interesting as talking about values or morality."

The other thing Aron found about sensitive people is that sometimes they're highly empathic. It's as if they have thinner boundaries separating them from other people's emotions and from the tragedies and cruelties of the world. They tend to have unusually strong consciences. They avoid violent movies and TV shows; they're acutely aware of the consequences of a lapse in their own behavior. In social settings they often focus on subjects like personal problems, which others consider "too heavy."

Aron realized that she was on to something big. Many of the characteristics of sensitive people that she'd identified-such as empathy and responsiveness to beauty-were believed by psychologists to be characteristic of other personality traits like "agreeableness" and "openness to experience." But Aron saw that they were also a fundamental part of sensitivity. Her findings implicitly challenged accepted tenets of personality psychology.

She started publishing her results in academic journals and books, and speaking publicly about her work. At first this was difficult. Audience members told her that her ideas were fascinating, but that her uncertain delivery was distracting. But Aron had a great desire to get her message out. She persevered, and learned to speak like the authority she was. By the time I saw her at Walker Creek Ranch, she was practiced, crisp, and sure. The only difference between her and your typical speaker was how conscientious she seemed about answering every last audience question. She lingered afterward with the group, even though, as an extreme introvert, she must have been itching to get home.

Aron's description of highly sensitive people sounds as if she's talking about Eleanor Roosevelt herself. Indeed, in the years since Aron first published her findings, scientists have found that when you put people whose genetic profiles have been tentatively a.s.sociated with sensitivity and introversion (people with the gene variant of 5-HTTLPR that characterized the rhesus monkeys of chapter 3) inside an fMRI machine and show them pictures of scared faces, accident victims, mutilated bodies, and polluted scenery, the amygdala-the part of the brain that plays such an important role in processing emotions-becomes strongly activated. Aron and a team of scientists have also found that when sensitive people see faces of people experiencing strong feelings, they have more activation than others do in areas of the brain a.s.sociated with empathy and with trying to control strong emotions.

It's as if, like Eleanor Roosevelt, they can't help but feel what others feel.

In 1921, FDR contracted polio. It was a terrible blow, and he considered retiring to the country to live out his life as an invalid gentleman. But Eleanor kept his contacts with the Democratic Party alive while he recovered, even agreeing to address a party fund-raiser. She was terrified of public speaking, and not much good at it-she had a high-pitched voice and laughed nervously at all the wrong times. But she trained for the event and made her way through the speech.

After that, Eleanor was still unsure of herself, but she began working to fix the social problems she saw all around her. She became a champion of women's issues and forged alliances with other serious-minded people. By 1928, when FDR was elected governor of New York, she was the director of the Bureau of Women's Activities for the Democratic Party and one of the most influential women in American politics. She and Franklin were now a fully functioning partnership of his savoir faire and her social conscience. "I knew about social conditions, perhaps more than he did," Eleanor recalled with characteristic modesty. "But he knew about government and how you could use government to improve things. And I think we began to get an understanding of teamwork."

FDR was elected president in 1933. It was the height of the Depression, and Eleanor traveled the country-in a single three-month period she covered 40,000 miles-listening to ordinary people tell their hard-luck stories. People opened up to her in ways they didn't for other powerful figures. She became for Franklin the voice of the dispossessed. When she returned home from her trips, she often told him what she'd seen and pressed him to act. She helped orchestrate government programs for half-starved miners in Appalachia. She urged FDR to include women and African-Americans in his programs to put people back to work. And she helped arrange for Marian Anderson to sing at the Lincoln Memorial. "She kept at him on issues which he might, in the rush of things, have wanted to overlook," the historian Geoff Ward has said. "She kept him to a high standard. Anyone who ever saw her lock eyes with him and say, 'Now Franklin, you should ...' never forgot it."

The shy young woman who'd been terrified of public speaking grew to love public life. Eleanor Roosevelt became the first First Lady to hold a press conference, address a national convention, write a newspaper column, and appear on talk radio. Later in her career she served as a U.S. delegate to the United Nations, where she used her unusual brand of political skills and hard-won toughness to help win pa.s.sage of the Universal Declaration of Human Rights.

She never did outgrow her vulnerability; all her life she suffered dark "Griselda moods," as she called them (named for a princess in a medieval legend who withdrew into silence), and struggled to "develop skin as tough as rhinoceros hide." "I think people who are shy remain shy always, but they learn how to overcome it," she said. But it was perhaps this sensitivity that made it easy for her to relate to the disenfranchised, and conscientious enough to act on their behalf. FDR, elected at the start of the Depression, is remembered for his compa.s.sion. But it was Eleanor who made sure he knew how suffering Americans felt.

The connection between sensitivity and conscience has long been observed. Imagine the following experiment, performed by the developmental psychologist Grazyna Kochanska. A kind woman hands a toy to a toddler, explaining that the child should be very careful because it's one of the woman's favorites. The child solemnly nods a.s.sent and begins to play with the toy. Soon afterward, it breaks dramatically in two, having been rigged to do so.

The woman looks upset and cries, "Oh my!" Then she waits to see what the child does next.

Some children, it turns out, feel a lot more guilty about their (supposed) transgression than others. They look away, hug themselves, stammer out confessions, hide their faces. And it's the kids we might call the most sensitive, the most high-reactive, the ones who are likely to be introverts who feel the guiltiest. Being unusually sensitive to all experience, both positive and negative, they seem to feel both the sorrow of the woman whose toy is broken and the anxiety of having done something bad. (In case you're wondering, the woman in the experiments quickly returned to the room with the toy "fixed" and rea.s.surances that the child had done nothing wrong.)

In our culture, guilt is a tainted word, but it's probably one of the building blocks of conscience. The anxiety these highly sensitive toddlers feel upon apparently breaking the toy gives them the motivation to avoid harming someone's plaything the next time. By age four, according to Kochanska, these same kids are less likely than their peers to cheat or break rules, even when they think they can't be caught. And by six or seven, they're more likely to be described by their parents as having high levels of moral traits such as empathy. They also have fewer behavioral problems in general.

"Functional, moderate guilt," writes Kochanska, "may promote future altruism, personal responsibility, adaptive behavior in school, and harmonious, competent, and prosocial relationships with parents, teachers, and friends." This is an especially important set of attributes at a time when a 2010 University of Michigan study shows that college students today are 40 percent less empathetic than they were thirty years ago, with much of the drop having occurred since 2000. (The study's authors speculate that the decline in empathy is related to the prevalence of social media, reality TV, and "hyper-compet.i.tiveness.")

Of course, having these traits doesn't mean that sensitive children are angels. They have selfish streaks like everyone else. Sometimes they act aloof and unfriendly. And when they're overwhelmed by negative emotions like shame or anxiety, says Aron, they can be positively oblivious of other people's needs.

But the same receptivity to experience that can make life difficult for the highly sensitive also builds their consciences. Aron tells of one sensitive teen who persuaded his mother to feed a homeless person he'd met in the park, and of another eight-year-old who cried not only when she felt embarra.s.sed, but also when her peers were teased.

We know this type of person well from literature, probably because so many writers are sensitive introverts themselves. He "had gone through life with one skin fewer than most men," the novelist Eric Malpa.s.s writes of his quiet and cerebral protagonist, also an author, in the novel The Long Long Dances. "The troubles of others moved him more, as did also the teeming beauty of life: moved him, compelled him, to seize a pen and write about them. [He was moved by] walking in the hills, listening to a Schubert impromptu, watching nightly from his armchair the smashing of bone and flesh that made up so much of the nine o'clock news."

The description of such characters as thin-skinned is meant metaphorically, but it turns out that it's actually quite literal. Among the tests researchers use to measure personality traits are skin conductance tests, which record how much people sweat in response to noises, strong emotions, and other stimuli. High-reactive introverts sweat more; low-reactive extroverts sweat less. Their skin is literally "thicker," more impervious to stimuli, cooler to the touch. In fact, according to some of the scientists I spoke to, this is where our notion of being socially "cool" comes from; the lower-reactive you are, the cooler your skin, the cooler you are. (Incidentally, sociopaths lie at the extreme end of this coolness barometer, with extremely low levels of arousal, skin conductance, and anxiety. There is some evidence that sociopaths have damaged amygdalae.)

Lie detectors (polygraphs) are partially skin conductance tests. They operate on the theory that lying causes anxiety, which triggers the skin to perspire imperceptibly. When I was in college, I applied for a summer job as a secretary at a large jewelry company. I had to take a lie detector test as part of the application process. The test was administered in a small, dingily lit room with linoleum floors, by a thin, cigarette-puffing man with pocked yellow skin. The man asked me a series of warm-up questions: my name, address, and so on, to establish my baseline level of skin conductance. Then the questions grew more probing and the examiner's manner harsher. Had I been arrested? Had I ever shoplifted? Had I used cocaine? With this last question my interrogator peered at me intently. As it happens, I never had tried cocaine. But he seemed to think I had. The accusing look on his face was the equivalent of the old policeman's trick where they tell the suspect that they have the d.a.m.ning evidence and there's no point denying it.

I knew the man was mistaken, but I still felt myself blush. And sure enough, the test came back showing I'd lied on the cocaine question. My skin is so thin, apparently, that it sweats in response to imaginary crimes!

We tend to think of coolness as a pose that you strike with a pair of sungla.s.ses, a nonchalant att.i.tude, and drink in hand. But maybe we didn't choose these social accessories at random. Maybe we've adopted dark gla.s.ses, relaxed body language, and alcohol as signifiers precisely because they camouflage signs of a nervous system on overdrive. Sungla.s.ses prevent others from seeing our eyes dilate with surprise or fear; we know from Kagan's work that a relaxed torso is a hallmark of low reactivity; and alcohol removes our inhibitions and lowers our arousal levels. When you go to a football game and someone offers you a beer, says the personality psychologist Brian Little, "they're really saying hi, have a gla.s.s of extroversion."

Teenagers understand instinctively the physiology of cool. In Curtis Sittenfeld's novel Prep, which explores the adolescent social rituals of boarding-school life with uncanny precision, the protagonist, Lee, is invited unexpectedly to the dorm room of Aspeth, the coolest girl in school. The first thing she notices is how physically stimulating Aspeth's world is. "From outside the door, I could hear pounding music," she observes. "White Christmas lights, currently turned on, were taped high up along all the walls, and on the north wall they'd hung an enormous orange and green tapestry.... I felt overstimulated and vaguely irritated. The room I shared with [my roommate] seemed so quiet and plain, our lives seemed so quiet and plain. Had Aspeth been born cool, I wondered, or had someone taught her, like an older sister or a cousin?"

Jock cultures sense the low-reactive physiology of cool, too. For the early U.S. astronauts, having a low heart rate, which is a.s.sociated with low reactivity, was a status symbol. Lieutenant Colonel John Glenn, who became the first American to orbit the Earth and would later run for president, was admired by his comrades for his supercool pulse rate during liftoff (only 110 beats per minute).

But physical lack of cool may be more socially valuable than we think. That deep blush when a hard-bitten tester puts his face an inch from yours and asks if you've ever used cocaine turns out to be a kind of social glue. In a recent experiment, a team of psychologists led by Corine Dijk asked sixty-odd partic.i.p.ants to read accounts of people who'd done something morally wrong, like driving away from a car crash, or something embarra.s.sing, like spilling coffee on someone. The partic.i.p.ants were shown photographs of the wrongdoers, who had one of four different facial expressions: shame or embarra.s.sment (head and eyes down); shame/embarra.s.sment plus a blush; neutral; or neutral with a blush. Then they were asked to rate how sympathetic and trustworthy the transgressors were.

It turned out that the offenders who blushed were judged a lot more positively than those who didn't. This was because the blush signified concern for others. As Dacher Keltner, a psychologist at the University of California, Berkeley, who specializes in positive emotions, put it to the New York Times, "A blush comes online in two or three seconds and says, 'I care; I know I violated the social contract.' "

In fact, the very thing that many high-reactives hate most about blushing-its uncontrollability-is what makes it so socially useful. "Because it is impossible to control the blush intentionally," Dijk speculates, blushing is an authentic sign of embarra.s.sment. And embarra.s.sment, according to Keltner, is a moral emotion. It shows humility, modesty, and a desire to avoid aggression and make peace. It's not about isolating the person who feels ashamed (which is how it sometimes feels to easy blushers), but about bringing people together.

Keltner has tracked the roots of human embarra.s.sment and found that after many primates fight, they try to make up. They do this partly by making gestures of embarra.s.sment of the kind we see in humans-looking away, which acknowledges wrongdoing and the intention to stop; lowering the head, which shrinks one's size; and pressing the lips together, a sign of inhibition. These gestures in humans have been called "acts of devotion," writes Keltner. Indeed, Keltner, who is trained in reading people's faces, has studied photos of moral heroes like Gandhi and the Dalai Lama and found that they feature just such controlled smiles and averted eyes.

In his book, Born to Be Good, Keltner even says that if he had to choose his mate by asking a single question at a speed-dating event, the question he would choose is: "What was your last embarra.s.sing experience?" Then he would watch very carefully for lip-presses, blushing, and averted eyes. "The elements of the embarra.s.sment are fleeting statements the individual makes about his or her respect for the judgment of others," he writes. "Embarra.s.sment reveals how much the individual cares about the rules that bind us to one another."

In other words, you want to make sure that your spouse cares what other people think. It's better to mind too much than to mind too little.

No matter how great the benefits of blushing, the phenomenon of high sensitivity raises an obvious question. How did the highly sensitive manage to survive the harsh sorting-out process of evolution? If the bold and aggressive generally prevail (as it sometimes seems), why were the sensitive not selected out of the human population thousands of years ago, like tree frogs colored orange? For you may, like the protagonist of The Long Long Dances, be moved more deeply than the next person by the opening chords of a Schubert impromptu, and you may flinch more than others at the smashing of bone and flesh, and you may have been the sort of child who squirmed horribly when you thought you'd broken someone's toy, but evolution doesn't reward such things.