1A beautiful woman lowers her eyes demurely beneath a hat. In an earlier era, her gaze might have signaled a mysterious allure. But this is a 2003 advertisement for Zoloft, a selective serotonin reuptake inhibitor (SSRI) approved by the FDA to treat social anxiety disorder. “Is she just shy? Or is it Social Anxiety Disorder?” reads the caption, suggesting that the young woman is not alluring at all. She is sick.

2But is she?

3It is possible that the lovely young woman has a life-wrecking form of social anxiety. There are people too afraid of disapproval to venture out for a job interview, a date or even a meal in public. Despite the risk of serious side effects—nausea, loss of sex drive, seizures—drugs like Zoloft can be a godsend for this group.

4But the ad’s insinuation aside, it’s also possible the young woman is “just shy,” or introverted—traits our society disfavors. One way we manifest this bias is by encouraging perfectly healthy shy people to see themselves as ill.

5This does us all a grave disservice, because shyness and introversion—or more precisely, the careful, sensitive temperament from which both often spring—are not just normal. They are valuable. And they may be essential to the survival of our species.

Shyness and introversion...are not just normal. They are valuable. And they may be essential to the survival of our species.

6Theoretically, shyness and social anxiety disorder are easily distinguishable. But a blurry line divides the two. Imagine that the woman in the ad enjoys a steady paycheck, a strong marriage and a small circle of close friends—a good life by most measures—except that she avoids a needed promotion because she’s nervous about leading meetings. She often criticizes herself for feeling too shy to speak up.

7What do you think now? Is she ill, or does she simply need public-speaking training?

8Before 1980, this would have seemed a strange question. Social anxiety disorder did not officially exist until it appeared in that year’s Diagnostic and Statistical Manual, the DSM-III, the psychiatrist’s bible of mental disorders, under the name “social phobia.” It was not widely known until the 1990s, when pharmaceutical companies received FDA approval to treat social anxiety with SSRI’s and poured tens of millions of dollars into advertising its existence. The current version of the Diagnostic and Statistical Manual, the DSM-IV, acknowledges that stage fright (and shyness in social situations) is common and not necessarily a sign of illness. But it also says that diagnosis is warranted when anxiety “interferes significantly” with work performance or if the sufferer shows “marked distress” about it. According to this definition, the answer to our question is clear: the young woman in the ad is indeed sick.

9The DSM inevitably reflects cultural attitudes; it used to identify homosexuality as a disease, too. Though the DSM did not set out to pathologize shyness, it risks doing so, and has twice come close to identifying introversion as a disorder, too. (Shyness and introversion are not the same thing. Shy people fear negative judgment; introverts simply prefer quiet, minimally stimulating environments.)

10But shyness and introversion share an undervalued status in a world that prizes extroversion. Children’s classroom desks are now often arranged in pods, because group participation supposedly leads to better learning; in one school I visited, a sign announcing “Rules for Group Work” included, “You can’t ask a teacher for help unless everyone in your group has the same question.” Many adults work for organizations that now assign work in teams, in offices without walls, for supervisors who value “people skills” above all. As a society, we prefer action to contemplation, risk-taking to heed-taking, certainty to doubt. Studies show that we rank fast and frequent talkers as more competent, likable and even smarter than slow ones. As the psychologists William Hart and Dolores Albarracin point out, phrases like “get active,” “get moving,” “do something” and similar calls to action surface repeatedly in recent books.

11Yet shy and introverted people have been part of our species for a very long time, often in leadership positions. We find them in the Bible (“Who am I, that I should go unto Pharaoh?” asked Moses, whom the Book of Numbers describes as “very meek, above all the men which were upon the face of the earth.”) We find them in recent history, in figures like Charles Darwin, Marcel Proust and Albert Einstein, and, in contemporary times: think of Google’s Larry Page, or Harry Potter’s creator, J. K. Rowling.

12In the science journalist Winifred Gallagher’s words: “The glory of the disposition that stops to consider stimuli rather than rushing to engage with them is its long association with intellectual and artistic achievement. Neither E = mc² nor Paradise Lost was dashed off by a party animal.”

13We even find “introverts” in the animal kingdom, where 15 percent to 20 percent of many species are watchful, slow-to-warm-up types who stick to the sidelines (sometimes called “sitters”) while the other 80 percent are “rovers” who sally forth without paying much attention to their surroundings. Sitters and rovers favor different survival strategies, which could be summed up as the sitter’s “Look before you leap” versus the rover’s inclination to “Just do it!” Each strategy reaps different rewards.

14In an illustrative experiment, David Sloan Wilson, a Binghamton evolutionary biologist, dropped metal traps into a pond of pumpkinseed sunfish. The “rover” fish couldn’t help but investigate—and were immediately caught. But the “sitter” fish stayed back, making it impossible for Professor Wilson to capture them. Had Professor Wilson’s traps posed a real threat, only the sitters would have survived. But had the sitters taken Zoloft and become more like bold rovers, the entire family of pumpkinseed sunfish would have been wiped out. “Anxiety” about the trap saved the fishes’ lives.

15Next, Professor Wilson used fishing nets to catch both types of fish; when he carried them back to his lab, he noted that the rovers quickly acclimated to their new environment and started eating a full five days earlier than their sitter brethren. In this situation, the rovers were the likely survivors. “There is no single best...[animal] personality,” Professor Wilson concludes in his book, Evolution for Everyone, “but rather a diversity of personalities maintained by natural selection.”

16The same might be said of humans, 15 percent to 20 percent of whom are also born with sitter-like temperaments that predispose them to shyness and introversion. (The overall incidence of shyness and introversion is higher—40 percent of the population for shyness, according to the psychology professor Jonathan Cheek, and 50 percent for introversion. Conversely, some born sitters never become shy or introverted at all.)

17Once you know about sitters and rovers, you see them everywhere, especially among young children. Drop in on your local Mommy and Me music class: there are the sitters, intently watching the action from their mothers’ laps, while the rovers march around the room banging their drums and shaking their maracas.

18Relaxed and exploratory, the rovers have fun, make friends and will take risks, both rewarding and dangerous ones, as they grow. According to Daniel Nettle, a Newcastle University evolutionary psychologist, extroverts are more likely than introverts to be hospitalized as a result of an injury, have affairs (men) and change relationships (women). One study of bus drivers even found that accidents are more likely to occur when extroverts are at the wheel.

19In contrast, sitter children are careful and astute, and tend to learn by observing instead of by acting. They notice scary things more than other children do, but they also notice more things in general. Studies dating all the way back to the 1960s by the psychologists Jerome Kagan and Ellen Siegelman found that cautious, solitary children playing matching games spent more time considering all the alternatives than impulsive children did, actually using more eye movements to make decisions. Recent studies by a group of scientists at Stony Brook University and at Chinese universities using functional MRI technology echoed this research, finding that adults with sitter-like temperaments looked longer at pairs of photos with subtle differences and showed more activity in brain regions that make associations between the photos and other stored information in the brain.

20Once they reach school age, many sitter children use such traits to great effect. Introverts, who tend to digest information thoroughly, stay on task, and work accurately, earn disproportionate numbers of National Merit Scholarship finalist positions and Phi Beta Kappa keys, according to the Center for Applications of Psychological Type, a research arm for the Myers-Briggs personality type indicator—even though their IQ scores are no higher than those of extroverts. Another study, by the psychologists Eric Rolfhus and Philip Ackerman, tested 141 college students’ knowledge of 20 different subjects, from art to astronomy to statistics, and found that the introverts knew more than the extroverts about 19 subjects—presumably, the researchers concluded, because the more time people spend socializing, the less time they have for learning.

21The psychologist Gregory Feist found that many of the most creative people in a range of fields are introverts who are comfortable working in solitary conditions in which they can focus attention inward. Steve Wozniak, the engineer who founded Apple with Steve Jobs, is a prime example: Mr. Wozniak describes his creative process as an exercise in solitude. “Most inventors and engineers I’ve met are like me,” he writes in “iWoz,” his autobiography. “They’re shy and they live in their heads. They’re almost like artists. In fact, the very best of them are artists. And artists work best alone.... Not on a committee. Not on a team.”

22Sitters’ temperaments also confer more subtle advantages. Anxiety, it seems, can serve an important social purpose; for example, it plays a key role in the development of some children’s consciences. When caregivers rebuke them for acting up, they become anxious, and since anxiety is unpleasant, they tend to develop pro-social behaviors. Shy children are often easier to socialize and more conscientious, according to the developmental psychologist Grazyna Kochanska. By six they’re less likely than their peers to cheat or break rules, even when they think they can’t be caught, according to one study. By seven they’re more likely to be described by their parents as having high levels of moral traits such as empathy.

23When I shared this information with the mother of a “sitter” daughter, her reaction was mixed. “That is all very nice,” she said, “but how will it help her in the tough real world?” But sensitivity, if it is not excessive and is properly nurtured, can be a catalyst for empathy and even leadership. Eleanor Roosevelt, for example, was a courageous leader who was very likely a sitter. Painfully shy and serious as a child, she grew up to be a woman who could not look away from other people’s suffering—and who urged her husband, the constitutionally buoyant F.D.R., to do the same; the man who had nothing to fear but fear itself relied, paradoxically, on a woman deeply acquainted with it.

24Another advantage sitters bring to leadership is a willingness to listen to and implement other people’s ideas. A groundbreaking study led by the Wharton management professor Adam Grant, to be published this month in The Academy of Management Journal, found that introverts outperform extroverts when leading teams of proactive workers—the kinds of employees who take initiative and are disposed to dream up better ways of doing things. Professor Grant notes that business self-help guides often suggest that introverted leaders practice their communication skills and smile more. But, he told me, it may be extrovert leaders who need to change, to listen more and say less.

25What would the world look like if all our sitters chose to medicate themselves? The day may come when we have pills that “cure” shyness and turn introverts into social butterflies—without the side effects and other drawbacks of today’s medications. (A recent study suggests that today’s SSRI’s not only relieve social anxiety but also induce extroverted behavior.) The day may come—and might be here already—when people are as comfortable changing their psyches as the color of their hair. If we continue to confuse shyness with sickness, we may find ourselves in a world of all rovers and no sitters, of all yang and no yin.

26As a sitter who enjoys an engaged, productive life, and a professional speaking career, but still experiences the occasional knock-kneed moment, I can understand why caring physicians prescribe available medicine and encourage effective non-pharmaceutical treatments such as cognitive-behavioral therapy.

27But even non-medical treatments emphasize what is wrong with the people who use them. They don’t focus on what is right. Perhaps we need to rethink our approach to social anxiety: to address the pain, but to respect the temperament that underlies it. The act of treating shyness as an illness obscures the value of that temperament. Ridding people of social unease need not involve pathologizing their fundamental nature, but rather urging them to use its gifts.

28It’s time for the young woman in the Zoloft ad to rediscover her allure.