How We Become What We Are

New studies suggest that some aspects of human personality are inborn and resistant to change. Ironically, this makes the role of environment all the more important in shaping individual lives

AN offspring of Cry Havoc and One Tough Cookie, Slick Willy is the second bull terrier fortunate enough to belong to David Lykken, a psychologist interested in temperament. Temperament, which is reflected in a creature's manner of behavior, is personality's biological, enduring, and heritable aspect. It greatly contributes to but does not entirely explain personality, much as innate intelligence contributes to but cannot entirely explain ability. Willy's temperament originated when the English bulldog was deliberately crossed with the white English terrier, almost 200 years ago. The nature of the resulting fearless, tenacious fighting machine requires a different sort of nurture than that of dogs bred for complaisance. When Willy can't resist chomping through a plastic jug with his powerful jaws or taking a few extra laps before responding to a summons, Lykken mostly just grumbles, reserving sterner measures for more serious infractions. Harsh treatment would render the feisty animal vicious; permissiveness or neglect would produce an uncontrollable bully. Willy's good behavior depends on an appreciation of his innate disposition and a judicious balance of carrot and stick.

In a postindustrial culture that holds up a workaholic Mr. Nice Guy as its temperamental ideal, the heroic spirit defined by Alexander the Great has fallen from grace. Time and technology have shrunk the number of acceptable outlets for the daring, aggressive nature that swung the sword and mapped the unknown, until it has come to be associated primarily with criminals. This saddens but doesn't surprise Lykken, a professor of psychology at the University of Minnesota; his work, some of it conducted with subjects behind bars, convinces him that "the psychopath and the hero are twigs of the same branch."

The history of another bull-terrier owner, Captain Sir Richard Francis Burton, the legendary nineteenth-century explorer, spy, scholar, and soldier, brings Lykken's observation to life. By the age of nine, the boy who would be the first white man in many parts of Africa and Asia, and who would translate the Kama Sutra, was, according to his biographer Edward Rice, "virtually a hard-core delinquent," more or less ignored by his parents and known for fighting, shooting at tombstones and church windows, lewdness—and enduring toothache. A prodigy who spoke twenty-nine languages, Burton preferred the army to Oxford. His temperament is summed up by his rationale for visiting the forbidden Muslim city of Harar: no European had successfully entered the city, so visiting it was "therefore a point of honor with me." Had he been born in the gutter rather than in a milieu that provided suitable channels for his aggressiveness, "Ruffian Dick" might have followed his proclivities to the gallows rather than to knighthood. The superficially odd similarity between guys in white hats and guys in black ones, vividly portrayed in Clint Eastwood's recent film Unforgiven, illustrates Freud's observation that although a particular instinct always has the same aim, it may have different objects. What worries Lykken is not the inclination to prevail but how it is directed.

As America reels from a wave of lawlessness, research on the temperamental underpinnings of violence has become increasingly controversial. Because black men compose only six percent of the general population but about half of the imprisoned one, the issue particularly concerns the black community, which is understandably suspicious of biological explanations for behavior. In 1992 a firestorm of protest caused Frederick Goodwin, a psychiatrist and the director of the federal Alcohol, Drug Abuse and Mental Health Administration, and the world's authority on manic depression, to resign his job and return to his previous position as director of the National Institute of Mental Health after he drew a parallel between inner-city violence and primate studies showing that young males in the wild were more violent and more sexually active when they had to compete for scarce resources. Black political leaders and others also successfully lobbied the National Institutes of Health to withhold money for a conference, to be held that year at the University of Maryland, on possible genetic components of violent behavior.

From the archives:

"Growing Up Scared" (June 1990)
Spurred on by family instability, violent crime now touches millions of young lives. The control of crime in the streets, in the schools, and in the home ought to be the pre-eminent "children's issue." By Karl Zinsmeister

Despite the apprehension that research on violence could stigmatize individuals or groups, what it actually shows is that, particularly where natures like Slick Willy's and Richard Burton's are concerned, nurture is the best predictor of good or bad behavior. The demise of the nineteenth-century bourgeois conscience makes no difference to some types of people, but it makes a big one to others. Mostly because of a large increase in illegitimacy since 1970, Lykken says, "across the land, but mainly in the inner cities, thousands of children aren't being brought up by, but only domiciled with, parents who are indifferent, incompetent, or unsocialized themselves." He continues, "We're running a crime factory that turns out little sociopaths." One reason why this white academic chooses to speak out on a socially sensitive issue becomes clear when he gestures toward photographs of two particularly robust babies displayed in his office. "My grandsons are going to be big African-American males, so they're going to face a high risk of attracting violence themselves and of frightening other people. Because of them, and the fact that crime is threatening to destroy all the great improvements in race relations that have come about in my lifetime, I get kind of steamed up about this problem." He concedes that "there's not a prayer in the world" that the solution he favors—the licensing of people for biological parenthood according to the same criteria that are used for adoption—will be tested in the near future: "My purpose in making an extravagant suggestion is to start a discussion. The problem is so real, and nobody is talking about the solution."


AS personal rights and freedoms have expanded during this century, there has been less and less talk about temperament. Throughout most of history, however, people have been regarded less as unique individuals than as variations on a few basic human types. In the fifth century B.C. Hippocrates described four temperaments, which he considered to be linked to various predominant bodily fluids, or humors: the sanguine temperament is optimistic and energetic, the melancholic is moody and withdrawn, the choleric is irritable and impulsive, and the phlegmatic is calm and slow. However quaint this theory may seem, Hippocrates anticipated modern linkages of biochemistry with behavior and astutely described types of people as familiar today as they were in antiquity.

By the 1940s two powerful ideologies diverted scientists' age-old interest in the biological dimensions of personality. First, Freud asserted the overwhelming importance of personal history in determining what his followers called character. Second, revulsion at Nazism's proclamation of inferior and superior genetic types converged with the spread of democratic ideas to focus academe on racial equality and the formative power of environment. Among the few scientists to express interest in temperament was I. P. Pavlov, the dark prince of conditioning, who observed of his dogs that "the final nervous activity present in the animal is an alloy of the features peculiar to the type and of the changes wrought by the environment." "Excitatory," choleric dogs, like Slick Willy, were by nature "pugnacious, passionate, and easily and quickly irritated," while the "inhibitory," or melancholic, animal "believes in nothing, hopes for nothing, in everything he sees the dark side." Of the two stabler sorts that Pavlov observed, one was "self-contained and quiet; persistent and steadfast," and the other "energetic and very productive" but easily bored. Such insights, however, were dwarfed by mountains of literature on what our mothers did to us.

Over the past decade modern genetics has made research into temperament intellectually acceptable again, though it is not well loved in some circles, where it is regarded as a right-wing theory of predestination. Even those who study temperament can be defensive or vaguely apologetic about their findings. Lykken rolls his eyes over his reputation as a "biological fascist." Jerome Kagan, a Harvard developmental psychologist pre-eminent among temperament researchers, and the author of the recently published Galen's Prophecy: Temperament in Human Nature, observes, "Because of my training, politics, and values, in my work I once muted the power of biology and maximized the environment's." Twenty years ago, when he observed a shy toddler, Kagan saw a child influenced by unpleasant social experience; today he sees one who has a certain type of neurochemistry. "I have been dragged, kicking and screaming, by my data to acknowledge that temperament is more powerful than I thought and wish to believe," he says. "That' s where I am, not out of prejudice but out of realism."

Fear, Aggression, Boldness

LIKE the ghost in the machine or the mind in the brain, temperament is best glimpsed in action. To discern it, watch a person communicate, says Hagop Akiskal, the senior science adviser on affective and related disorders at the National Institute of Mental Health: "It's not just a matter of personality but something more basic that has to do with rhythm, reactivity, emotion." Of all species, Homo sapiens has the most feelings. Just as drives such as hunger and sleep are more flexible than reflexes like the eye blink and the knee jerk, emotions, which are physiological as well as psychological events, give us more behavioral options than do drives. Some emotions are so basic and universal that the psychologist Hans Eysenck, a pioneer of the modern biological study of personality, who conducts research in London at the Institute of Psychiatry, believes that they're nothing less than the lowest common denominators of human experience. "We've done our studies in thirty-six countries," he says, "and everywhere we find the same three ways in which behavior can differ." To varying degrees all people express fear, which helps us avoid danger; aggression, which enables us to fight it; and extraversion, or sociability, which enables us to face it with equanimity. Fundamentally, our temperaments are distinguished by the traits of anxiety, irritability, and elan.

That our natures are organized around our habitual reactions to threat has given Philip Gold, a research psychiatrist who is the chief of the neuroendocrinology branch of the NIMH, a "tragic view of the human condition." Physical or emotional, real or perceived, danger lurks everywhere, and from an evolutionary perspective our species' great asset and, sometimes, liability is an extremely sensitive emotional and physiological arousal system that detects and reacts to it. This is the stress, or "fight or flight," response. The stable sorts of people whom modern researchers describe as uninhibited, bold, or relaxed can cope with life's vicissitudes—from a snake in the jungle to a fire-breathing boss—in a manner Gold describes as "philosophical," because their stress response isn't triggered by every little thing and doesn't stay on red alert longer than necessary. These resilient people are innately disposed, Gold says, "to celebrate the beauty of existence and the wonders of an interior life and external connections despite being surrounded by unanswerable questions, ambiguous dilemmas, and the certainty of loss and death."

Those who naturally react to the threatening or the merely unfamiliar with an excess of either the flight or the fight response are in for more trouble. Because their stress response spikes frequently and ebbs slowly, Hippocrates' melancholics, whom scientists now describe as anxious, inhibited, or reactive, are so worn down that they are apt to behave in what Gold calls a depressive way: "Faced with a setback, for example, they say it occurred because they're worthless." To protect themselves, the flight-prone often cultivate an avoidant way of life that worsens their plight. "They're likelier to survive in truly threatening situations," Gold says, "but they have less comfortable lives." Hippocrates' cholerics, like Willy and Burton, respond to stress by going into fight mode. To these people, whom researchers variously call aggressive, impulsive, or irritable, the dark possibility of pain and defeat is so intense, Gold says, "that they can't bear to be accountable for it in a depressive way." Instead they blame it on others, and strike out. Although the bias toward one of these fundamental emotional tones, or temperaments, "has to do with what a person has learned he has to be in order to be loved," Gold says, "it also has to do with genetic factors that biologically predispose him to respond in a certain way to the paradigmatic human situations of pleasure and opportunity, danger and loss." He continues, "In the blood-and-guts world of challenges, these differences in the stress response account for the fundamental parameters of what people are like."

Although some people are so colored by a single emotional tone that they're said to be the inhibited, uninhibited, or aggressive type, most temperaments aren't primary yellow, blue, or red. Their many subtle shades include greens, oranges, and violets blended from lots of different genetic proclivities. Kagan predicts that future research will define many more dispositions and traits, or temperamental characteristics, each with its own physiological substrates; a likely example is a familiar permutation of the reactive temperament known as the obsessive type. What most people consider occasional thoughts or pursuits rivet the neural arousal system of the genius, the collector, and the artist, who vent their obsessions in compulsive activity. Reflecting on Benny Goodman's notorious social insensitivity, a wise musician from his band observed that the celebrated clarinetist, who practiced his instrument eight hours a day, thought not about people but about fingering.

Although scientists disagree about the ultimate number of traits and the temperaments they color, most of the research concerns the three most obvious qualities: fearfulness, boldness, and aggressiveness. Just as the scars that laced Burton's body speak of the way aggressive people operate in the world, the lives of two of his eminent Victorian contemporaries say something about the approaches of the inhibited and uninhibited temperaments. The Queen whose name is synonymous with the effort to dampen arousal described the clockwork progress of an ideal day in the company of her beloved husband: "We walked in the garden. ... At twelve o'clock we had prayers in the drawing-room, which were read by a young clergyman, who preached a good sermon. ... I read to Albert the first three cantos of The Lay of the Last Minstrel, which delighted us both; and then we looked over some curious, fine old prints by Ridinger" Yet even Victoria had days when novelty intruded on her careful plans, trying her sensitive nerves. Despite the efforts of maids and courtiers in a posh Highlands lodge, some missing luggage caused her a rougher night than Burton would have passed in a pestilent swamp: "I disliked the idea of going to bed without any of the necessary toilette," she wrote in her diary. "However, some arrangements were made which were very uncomfortable; and after two I got into bed, but had very little sleep at first; finally, fatigue got the better of discomfort, and after three I fell asleep."

The nocturnal arrangements of Victoria's subject the Honorable Jane Digby El Mezrab, who also doted on her husband—at least, on her fourth one—would have greatly perturbed Victoria. With Sheikh Medjuel El Mezrab, this well-traveled, much-married lady passed half each year in a Bedouin tent in the Syrian desert. Arab robes flying and blue eyes rimmed with kohl, she raced camels and horses, went falconing, and even accompanied her lord and master into battle; in quieter moments she served him at meals and washed his feet. After more than a decade of this flared-nostril life, taken up well past the point at which Victoria had abandoned herself to inconsolable widowhood, Jane wrote, "Sixty-two years of age, and an impetuous romantic girl of seventeen cannot exceed me in ardent passionate feelings." Like her Queen, Jane focused on her domestic life, but how she did so throbs with the uninhibited temperament.

"Nature-Nurture" Experiments

As Hippocrates intuited, such contrasting dispositions reflect very different chemistries. Scientists are just beginning to develop the technology that allows them to eavesdrop on the whisperings of neurotransmitters, the brain' s chemical agents of communication, and learn how these are translated into modulations of behavior. For the most part, the links between particular traits and transmitter levels remain tentative, partly because the former can involve neurochemical choruses, not just solos. So far, the principle that who we are involves our biological as well as our social heritage rests mostly on two types of research. At the University of Minnesota' s Center for Twin and Adoption Research and elsewhere, scientists have established certain traits as genetically rooted by comparing the characteristics of pairs of identical and fraternal twins who have been reared together or adopted separately in infancy and raised apart; the relatively few observed differences in the identicals' personalities must be caused by environment. In longitudinal studies Kagan and others monitor developmental changes in their subjects from infancy in order to search for the biopsychological consistencies that suggest temperamental origins.

Some of the most important, if indirect, insights into human temperament come from classical nature-nurture experiments in which generations of animals are selectively bred for particular traits and then closely monitored in different settings. The research psychologists Stephen Suomi, of the National Institute for Child Health and Human Development, and J. D. Higley, of the National Institute on Alcohol Abuse and Alcoholism, have produced strains of rhesus monkeys that are variously inhibited, uninhibited, or aggressive, and have then tracked their neurobiology through their neurotransmitters' metabolites, or end products, in cerebrospinal fluid. "When you observe groups of primates, they look a lot alike initially," Higley says. "Within a few minutes, though, you identify the solitary, inhibited one, who peeks at you around a corner, and the bold one, who leaves the group and approaches in hopes of a treat. Our monkeys show big differences in these traits, which tend to be the most enduring ones in humans as well."

Like hot and cold or hard and soft, inhibited and uninhibited seem to be extremes on a single spectrum, and scientists who study one trait also study the other. Anxious monkeys have high levels of norepinephrine; bold monkeys have low levels of the same transmitter. It makes sense that the inhibited have lots of something the uninhibited have little of, but that may be too simplistic an etiology for boldness. Suomi and Kagan maintain that uninhibitedness includes but is more than not being anxious, especially at its extreme, and that the other ingredients in its formula have thus far eluded detection. Although the inhibited and the uninhibited, which account for about 10 and 20 percent of the primate population respectively, can be arranged on a continuum of stress responsivity and norepinephrine level, Kagan says that the exercise and its implications are a bit like "putting Mozart on a spectrum with your daughter who's taking piano lessons. He's just better in music?"

Because he works with human babies and children rather than monkeys, Kagan can't examine temperamental neurology as directly as Suomi can. He infers something of how his subjects' nervous systems operate, however, by periodically measuring their behavioral and physiological responses, such as heart rate and blood pressure, to mild stressors such as noise, sour tastes, unfamiliar objects and people, even a mother's frown. Regarding infancy, he has proved what every parent knows: each baby is born with a characteristic mood and style of responding. By the second and third years of life, he has found, some clearly express one of two great temperamental extremes.

About 15 percent of youngsters are plainly inhibited. They differ physiologically from other children in many ways, from their greater incidence of allergies and constipation to their higher heart rates and levels of cortisol, a stress related hormone. They tend to have blue eyes and narrow faces, and slightly more of them are girls. Psychologically, they're constrained and fretful, and have unusual fears—fears, say, of kidnapping rather than of monsters. The stimuli that swamp their sensitive nerves barely stir those of another group of children. Most of the 30 percent of uninhibited youngsters are boys, and boys account disproportionately for the very boldest. Their physiological hallmark is their very low heart rate; their behavior is marked by energy and spontaneity. To these emerging portraits Nathan Fox, a professor of psychology at the University of Maryland, adds that very anxious and bold children have stable patterns of right-brain and left-brain activity, as measured by electroencepbalograms. Either type of EEG, he says, is "a very good fingerprint of a particular temperament."

Evidence from twin studies and his subjects' family histories has convinced Kagan that the inhibited and uninhibited natures begin with genes. Yet, at least at the individual level, nature's contribution cannot be quantified; too many parts of the equation, such as epistasis, or the process whereby one gene suppresses the expression of another, elude measurement. When scientists compare personalities within a group, their guesstimates of how much of the variation among individuals is due to biology and how much to learning generally range from 20 percent and 80 percent respectively to 50-50, as the Minnesota team believes. One study has suggested that 40 percent of the difference in inhibition among a group of middle-class children depended on genes, but, Kagan says, "to ask what proportion of personality is genetic rather than environmental is like asking what proportion of a blizzard is due to cold temperature rather than humidity." What the distinctive genetic heritages of anxious and bold children bring about, however, are neurochemical differences in the functioning of the amygdala—a brain structure that assigns emotion to experience—and its connections. Thus the same loud noise that scares an inhibited child will intrigue an uninhibited one. As Fox says, "Some children are by and large, across many situations, very fearful, while others, no matter what you throw at them, are happy-go-lucky and approach the world with gusto."

Finding an Adaptive Niche

THE sensitivity of the inhibited nature to things not only threatening but also merely novel makes life an uphill affair. At least one inhibited person is known to have projected this aversion to the unfamiliar into the after-life. For the public celebration of Queen Victoria' s Diamond Jubilee, a statue of one of her predecessors, Queen Anne, was scheduled to be moved from its accustomed position. "Most certainly not!" said Her Majesty. "Why, it might some day be suggested that my statue should be moved, which I should much dislike." Some of the inhibited have an easier time than others, however, because they're not socially constrained, or shy. Although inhibition is linked to norepinephrine, what Higley calls the "nerdiness" of the loner who can't get along goes with low levels of the transmitter serotonin. A person could have a high level of norepinephrine, and so be nervous, yet also have a high level of serotonin, and thus be sociable. The garrulous worrywart that Higley evokes is a familiar character—think of Victoria or Miles Silverberg on Murphy Brown. Medical literature shows, Higley says, that the capacity of such people to reach out, which many anxious people don't have, helps them counter the effects of stress. He says, "If you're wired to elicit and respond to social stimuli, you may get a lot of support that helps get you through that rotten, worried feeling inside."

To the many parents in the trenches concerned about their offspring's shyness, brashness, or other untoward tendencies, Kagan offers a few pragmatic insights. First, he says, children are born with different temperaments, so new mothers and fathers shouldn't assume that they're mishandling a baby who's neither pleased nor pleasing. Second, a child's disposition is malleable: "Parents shouldn't say, 'God gave me this type of kid—that's it!' They should acknowledge that some things are harder for the child to control, but should assume he can still exert some control." Finally, Kagan says, "remember that in a complex society like ours, each temperamental type can find its adaptive niche."

Few would wish to be the anxious type, but in an environment filled with predators, or their modern equivalents, having some worriers around is adaptive, at least for the species; that's why they remain in the gene pool. Hans Eysenck, a famously iconoclastic Freud-basher who has scored a zero on his own test of inhibition, says that his wife accuses him of not being afraid enough. "She is exceedingly careful, driving defensively and letting others get ahead. From the point of view of survival, her style is much better."

Again, another name for the anxious or inhibited temperament is "reactive." Among various good things associated with such a quiet, reflective nature, the foremost is intellectual achievement. Inhibited seven-year-olds excel at what Nathan Fox calls "executive functioning"; when they're asked how kids who have only one toy should share it, they offer a strategy such as "Alphabetize their last names, and let the person closest to A go first." Putting theory into practice is hard for them, however, because their sensitive natures and elaborate schemes are unsuited to the heterogeneous rigors of the school yard. Most do not end up with social or psychological problems, and the more fortunate find niches where they can operate successfully, becoming scientists, say, or poets.

A party animal doesn't dash off a Paradise Lost. The same high-strung families much afflicted by moodiness and depression are more likely than others to include writers and dancers, painters and composers. Happily, this strain is hypersensitive not only to stress and danger but also to art and nuance: as Byron wrote, "Of its own beauty is the mind diseased." Hagop Akiskal, after investigating (in collaboration with his wife Kareen Akiskal) what he calls "the romantic idea that mental illness is related to creativity," discovered a link not with disease per se but with a variation on the reactive disposition which he calls the "cyclothymic temperament." People of this type alternate rapidly between high and low levels of mood and activity which are far less marked than those of manic depressives. The "down" spells foster contemplation and reflection; during the "up" spells surging energy, ambition, confidence, and mental puissance drive hard work.

Unlike those burdened with an inhibited nature, the uninhibited have few complaints. Stress that breaks more sensitive spirits merely stimulates theirs. For example, one in five fighter pilots will at some point have eject from his plane, and one in twelve will die in the line of duty exclusive of combat, yet the most elite fliers zealously compete for this hair-raising job. David Lykken has an insight why dare-devils not only cope with but thrive on what most people consider appalling risks. When he tested a group of prison inmates, he found that the boldest didn't readily learn how to escape an avoidable electric shock; they felt it, all right, but they didn't fear it.

The adaptive potential of steel nerves is summed up by a line of dialogue that frequently figures in action-adventure movies: "It's a tough job, but someone's got to do it." Ulysses S. Grant "was not excited by [danger], but was simply indifferent to it, was calm when others were aroused," according to his military secretary. "I have often seen him sit erect in his saddle when everyone else instinctively shrank as a shell burst in the neighborhood." A Union soldier put it thus: "Ulysses don't scare worth a damn." The uninhibited can manifest this same sangfroid in situations, from boardroom conferences to political debates, that entail social rather than physical risk. Grant was equally unperturbed by "the greatest moral emergencies," his aide wrote. "At the surrender of Lee, he was as impassive as on the most ordinary occasion." The insensitivity that is the dark side of boldness can squelch intimate relations. This wasn't so in the case of Grant—the general was devoted to Mrs. Grant and she to him. Among fighter pilots, however, nine out of ten separations and divorces are initiated by wives.

Having a nervous system that reads "threat" as "thrill" means you might die young, but you'll have fun. It has been said that Jane Digby, a famous equestrian, met a dashing sheikh (who may or may not have been Medjuel) while trying to buy a supposedly untamable horse from him. After she broke it, the Bedouin said his price could not be paid in coin. Jane agreed to be his if he would put away his other wives; should the arrangement turn out to be satisfactory, she said, it could be renewed in three years. Lykken recalls a trapper and bush pilot from northern Minnesota "who had adventures that made my jaw drop," he says. "He didn't brag, but just talked about these things he did that were so interesting, like going to a bear den and pulling out the cubs."

The Fighting Spirit

NEITHER Queen Victorias nor Jane Digbys, most people have the middling levels of inhibition that best ensure survival. "That's how biology works," J. D. Higley says. "Not too many temperaments are extreme." The one that seems most extreme is the disposition Hippocrates called choleric and his modern successors call irritable. To Higley, "if inhibition and boldness are the north and south of temperament, equanimity and irritability are the east and west." Although the irritable temperament is the hardest to define, Akiskal says, it's the easiest to see. We in fact pay to see it whenever we watch a movie actor who specializes in portraying restless characters who "express intense, unmodulated emotion that, seemingly out of nowhere, comes on like an avalanche, stirring everyone," Akiskal says. "That's what temperament does, and the irritable one does it most intensely." He deplores the prissy tendency to look askance at the hot-blooded temperament: "Civilized Western behavior assumes its relative absence, but its impact is very useful in some circumstances—say, in getting a point across quickly. Many people can't express such vivid feelings because they just don't have them—they lack the color that the intense supply." Although this disposition is potentially the most pathological, it's the least studied, Akiskal says, partly because "it evokes a lot of negative feelings in people."

Some of those negative feelings spring from the fact that although irritability—the tendency to be easily annoyed—is not the same as aggressiveness, the two are far from incompatible. As Richmond Lattimore observed, the tragedy of Achilles, the supreme warrior, was that his will was "disturbed by anger." Sir Richard Burton shared the hero's psychic heel: at one Point in his youth he had no fewer than thirty-two affairs of honor pending violent settlement.

Throughout history mankind has deliberately bred the fighting spirit. Slick Willy and the bulls of the corrida are obvious examples of an effort perhaps not limited to animals. From the time of Atreus and his son Agamemnon the aristocracy has traditionally taken more pride in its warriors than in its scholars. In Shakespeare's Henry V the French King Charles VI cautions his overconfident nobles that despite the erstwhile Prince Hal's reputation as a wastrel, the young invader "is bred out of that bloody strain/That haunted us in our familiar paths./... This is a stem/Of that victorious stock; and let us fear/The native mightiness and fate of him."

Having bred a strain of aggressive rhesus monkeys, Higley finds that their defining characteristic is in early life irritability, and in later life the unsociability that correlates with the low level of serotonin they've inherited. Although it shows the stability of a temperamental characteristic, appearing early in development and staying late, aggressiveness seems less a single trait than an explosive combination of several. Thus the monkeys who acquire the most wounds over a lifetime—a pragmatic gauge of a belligerent nature—are quick-tempered loners who both attract and instigate attacks. Richard Burton was a higher primate of this type; his spectacular gifts brought him little advancement largely because of his flair for provoking the lesser mortals who were his bureaucratic superiors. This explanation makes sense to Higley, who finds that a troop's most aggressive primate isn't usually the leader. That popular figure is apt to be a pacific, high-serotonin back-slapper who knows how to work a crowd. "In stable settings a monkey who tries to run things with force gets kicked out," Higley says. "If the females don't like a male, he's gone."

Partly because the genesis of aggressiveness is more complex than that of inhibition or boldness, Jerome Kagan is uncomfortable with the notion that there is an aggressive temperament per se. In his view, aggressive children are fundamentally characterized by fearlessness; they're bold but badly brought up, so that they become bullies. Nathan Fox was surprised to discover that a few members of a group of unruly young research subjects headed perhaps toward what psychologists call "conduct problems" were described by their mothers as inhibited or anxious. Higley, too, finds some inhibited sorts among his scarred bad actors. Once again, he traces aggressiveness to the tendency to act first and reflect later. Despite the fearfulness associated with these inhibited monkeys' high levels of norepinephrine, Higley says, they are impulsive, a trait that correlates with their low serotonin levels and that means "they don't think way ahead, so they end up in encounters that might have been avoided."

For practical reasons, much of the research on aggressiveness involves people who commit violent crimes. That 90 percent of such people are men implicates masculinity itself, wrought by the hormone testosterone, as a major biological factor in violent behavior. Although they are by no means a homogeneous group, many of the imprisoned have a few sad biographical features in common, including a history of inappropriate aggression from early childhood, an impulsive, angry personality, and a lower-than-average verbal IQ. Some of their troubles may be inherited. An impressive Danish study comparing twins revealed that if one male identical twin was found guilty of a crime, the other was five times as likely as the average Danish man to be a criminal as well; a fraternal twin in the same situation was three times as likely to be a criminal.

Saying that violently aggressive behavior has a genetic component is a far cry from saying there's a "crime gene." In fact the only shred of evidence for such a thing concerns a rare mutation that affects violence-prone males from a single Dutch family. The strongest hypothesis for the way in which genes could help to bring about a violently aggressive disposition rests on considerable data from Scandinavia, where governments keep careful public-health records and social influences such as poverty and drugs figure less in crime. This evidence suggests that people involved in violent crimes that are "hot," or impulsive, rather than "cold," or premeditated, tend to have low levels of serotonin. The finding provides a clue to one type of aggression, but not an explanation for it.

It may have a poor image in the modern world, but Hippocrates' choleric temperament is, like all dispositions, neither good nor evil per se. General Norman Schwarzkopf's family may not relish playing board games with him, but in certain settings Schwarzkopf is the ideal companion. Even in prosaic settings "aggressiveness can be beneficial if it helps you pound the table and say, 'I want justice!" Higley observes. "If a society wants variability, which is what ours espouses, it needs different kinds of individuals."

How Experience Tempers Physiology

RATHER than asking how much of identity derives from genes and how much from learning, Kagan would pose "a better question: What combination of inherited physiology and experience makes a person, say, fearful, or bold?" Because they gloss over half of that combination, sensational headlines about genes that purportedly account for this or that proclivity—recently, toward violence or homosexuality—annoy thoughtful researchers, who recognize that experience channels biological proclivities. "This biological-predisposition business has become ridiculous," Kagan says. "Even if there's a genetic component to a person' s behavior, that doesn't mean he has no control over it." Male primates, for example, are biologically predisposed to be promiscuous; because most men can curb that strong urge, Kagan says, wives rarely sanction husbands' adultery. "Many scientists hope to win the Nobel Prize for finding the circuit in the brain responsible for the fact that I can start to do something and then stop," he says. "That's will, which is a special quality of Homo sapiens that allows us to control our behavior—and it' s part of nature." Although Kagan's research has made him "more permissive" regarding certain human foibles, he says, "this is the most important thing to understand: Don't assume that just because a person has a temperamental quality, he has no conscious control over it. There's always a window of nondeterminism. Think about a species of monkeys, some of whom are raised in the zoo and others in the wild. They have the same genes, but they're very different monkeys. And that's only monkeys."

That a temperamental tendency can be described as genetic doesn't mean it's fixed, or rigidly predictable. Behavior, because it's so complicated to orchestrate, is polymorphic—it requires the action of many genes in concert. Even in experiments with insects in which both heredity and environment are rigidly controlled, scientists are unable to program behavior uniformly. Human behavior is vastly more baroque, though, and a predisposition to be, say, shy, doesn't mean a person must be reserved but only that he's likelier than others to be.

Although there's no single gene for inhibition, boldness, or aggressiveness, what scientists call gene-environment correlation means that people who inherit those biopsychological tendencies will gravitate toward the kinds of experiences that reinforce the traits. The naturally fearless, for example, live in the fast lane from their diaper days. As soon as they can crawl, they're everywhere at once, exploring, falling, pushing the limits. Later "they climb a few fences, become desensitized, and climb up on the roof," Lykken says. "They'll have all sorts of experiences that other kids won't. Chuck Yeager [the test-pilot hero of The Right Stuff, and the first flier to break the sound barrier] could step down from the belly of the bomber into the rocket ship and push the button not because he was born with that difference between him and me, but because for the previous thirty years his temperament impelled him to work his way up from climbing trees through increasing degrees of danger and excitement. Genes affect the mind indirectly, creating formative experiences."

The long-standing view that early experience in the home inscribes personality on a blank mind has recently been challenged. Research suggesting that the personalities of siblings are hardly more similar than those of unrelated children implies that if the mighty family can't even out more of the differences among those who have half their genes in common, then environment does not much affect temperament. Lykken illustrates the flip side of the point with anecdotes from the University of Minnesota research on identical twins reared separately from birth. Such pairs are eerily alike not only in IQ and traits such as inhibition, boldness, and aggressiveness, but also in idiosyncrasies, such as the way two sisters count themselves to sleep, or the way two brothers have come to prefer the same cologne, hair cream, and imported toothpaste.

To say that nurture doesn't usually remodel nature does not mean that it can't. "Most families are custodial," Lykken says, "so nothing interferes with children's genetic proclivities." Fox agrees that the hands-off spirit of modern mothers and fathers means that children change less than they otherwise might. "Parents usually say, 'This is who my child is," he explains. "Depending on what they do or don't do, that child's biology is either going to express itself or be moderated. Because they're too busy and it's too hard, most parents today don't intervene, so biology mostly creates the kids' environments. But if you expect boys to play football, you're not going to say it's okay for your son to be fearful." Parental intervention, researchers say, is what changes the children who change.

At the cutting edge of research, scientists are learning that certain social experiences that cause juices to surge or subside can change not only behavior but also physiology—a discovery that means the traditional concept of temperament as inborn must be redefined. When Suomi gives a genetically uninhibited infant monkey to an inhibited foster mother, her potentially upsetting ways just roll off his back and he remains fearless; similarly, uninhibited children rarely become inhibited over time. When a monkey bred to be inhibited is reared by a bold, easygoing foster mother, however, the youngster develops not only her ways but even her low-norepinephrine chemistry. And an infant raised by inept juveniles rather than competent adults will eventually resemble, both behaviorally and physiologically, a troubled monkey selectively bred for a low serotonin level. "Experience can push genetic constitution around," Suomi says. "Its effect is so profound that I'd call it temperament."

So would Megan Gunnar, a psychologist at the University of Minnesota's Institute of Child Development, who defines temperament as "a set of behavioral predispositions that have physiological substrates and experiential components." When toddlers and their mothers encounter a clown in her lab, she says, "Some go 'Whoopee!' and others 'Oh, no!" The uninhibited children forget about their mothers and play with the clown. If an inhibited child has what Gunnar describes as a "secure" relationship with a mother who accepts his fearful reaction, his stress response, measured through the amount of cortisol in his saliva, ebbs, and he too might play. If an inhibited child has an "insecure" tie with an unaccepting mother, however, his agitation is fed by her discomfort; the more she urges him to play with the clown, the greater his stress.

Over time, repeated stressful experiences can literally, not just figuratively, alter the nervous systems of the temperamentally vulnerable. Animal research has shown that when a rat is given a small shock, it shows no marked reaction; when exposed to such stressors for five consecutive days, it shows signs of the stress response; when exposed for seven or eight days, the rat has a seizure, and thereafter this "kindled" animal will seize with little or no provocation. Experiments of this kind are of course not done with people, but Philip Gold and other neuroscientists now think that in human beings, too, by triggering a cascade of chemical reactions, serious chronic stress, particularly in early life, causes changes in the way genes within a brain cell function, permanently altering the neuron's biology. Because they require a particular type of input to turn on or off, only some of a neuron's thousands of genes, each of which is involved in some aspect of cellular structure or communication, are activated at any given moment. When a temperamentally vulnerable person is constantly bombarded with upsetting stimuli, Gold says, the genes that get turned on are those involved in the cellular components of the stress response. Over time the person's nervous system is configured accordingly, becoming a kind of two-way radio that specializes in receiving and transmitting unhappy signals. The concluding chapters in what Gold calls "the natural history of an affective disorder" chronicle the repeated struggles of such people with anxiety or what some call its chronic form, depression.

Many more women than men suffer from these so-called mood disorders, and explaining why is a tricky business. Although similar numbers of males and females are inhibited as infants, more of the latter stay that way. Among human beings, some of the discrepancy could be due to the fact that society discourages the tendency in boys. Primate research suggests that a biological explanation applies as well. After the onset of adolescence, females generally have higher levels of serotonin than males, which correlates with their greater sociability; for them, the greatest stress continues to be trouble with relationships. "After puberty, male monkeys have a much bigger set of challenges to deal with," Stephen Suomi says. "They have to leave home and get into a new troop. To help them do what they must do to survive, evolution may have blunted their response to social stress." In short, many males may be physiologically, not just psychologically, less sensitive to the social issues that upset females.

Young Troublemakers

FORTUNATELY, the type of nervous system likeliest to be kindled by a poor environment can be strengthened by a supportive one. Kagan predicts that seventy-five out of a hundred inhibited two-year-olds will eventually have normal social lives. It's probably no coincidence that three quarters of Gunnar' s reactive children, in her estimate, have the secure relationships that will enable them to "learn to be kind to themselves and back off a little in a stressful situation, neither negating nor overdoing their anxiety, until we can't even see the stress response anymore." Gunnar says, "You may be a certain way for the rest of your life, but the big issue is how you manage it—or not." Gold says about innately inhibited individuals, "In their quiet, introverted way, they can acquire the skills that allow them to be resolute and to endure anxiety and pain. They might look timid but be like a rock. If the fate of the Western world depended on someone not giving up a secret under torture, I'd rather put it in such hands than in those of a seemingly bold person who hadn't had to learn those complex skills." Fox suspects that when inhibited children learn to handle stress, the physiological marker associated with fearfulness might disappear from their EEGs: once again, it appears that experience can modify the brain.

That message is particularly important where the aggressive are concerned. Gene-environment correlation virtually guarantees that raising aggression-prone children in settings that impose few limits—and such settings have proliferated since the 1950s—will create mayhem. When so-called "difficult" babies, who are so cranky, demanding, and hard to please that they strain even model parents, are paired with negligent mothers, for example, their risk of developing behavioral problems soars. Where the etiology of crime is concerned, even a "biological fascist" like Lykken blames nurture—specifically, the sort provided by escalating numbers of incompetent single parents. A few of the young troublemakers who are destroying schools and neighborhoods are psychopaths whose psychobiological peculiarities would challenge the civilizing skills of any parents; but the vast majority, Lykken says, have relatively normal temperaments that are simply unsocialized. "Many little boys are potential criminals who find it perfectly natural to take things, break things, and beat up on people. It's their parents' responsibility to stomp some of that out—to inhibit antisocial behavior, instill prosocial values, and cultivate the work ethic. Because it's such a tough job, it takes two people. Adoption agencies usually give babies to mature, self-supporting, sane married couples who have no criminal records. Why should there be fewer criteria for starting off a biological child?"

Temperament research shows that good parenting can have potent effects. If it can alter a hypersensitive physiology, Higley reasons, it could affect a belligerent one, too. He plans to rear impulsive, ornery young monkeys with adults "who demand that they behave appropriately, and punish them when they don't," and to monitor changes in their neurochemistry along with changes in their behavior. He suspects that he'll see their low serotonin levels rise. Like many of his biology-minded colleagues, Higley often argues from the other side of the ideological fence, "trying to convince people that having a genetically modified trait doesn't mean that you're programmed." He says, "Someone could be disposed to respond with inappropriate aggression but learn early in life that if he does, he'll get into trouble. He may also learn to like the reinforcement he gets from positive interactions."

As is the case with Slick Willy, praise can sometimes inspire better behavior than punishment, which only makes some tough kids tougher. "If your temperament is such that fear doesn't play a big role in your life," Lykken says, "you're less likely to pay attention to punishment, which depends on the desire to avoid anxiety. That kind of child may care if people stop admiring him, though, so the way to socialize him is by giving him a sense of pride, as successful coaches do."

At a time of fractured families and communities, research on the modification of temperament has very practical applications. Some so-called "resilient" children, who turn out well amid the neglect and poverty that stunt so many others, inherit some of their strength. If early social support can override biology, however, the resilient can be made as well as born.

Time and Direction

TINKERING with adult temperament is more difficult—so much so that one might consider simply making the best of what one has got. Even if that's not so bad, the satisfaction afforded by a disposition depends greatly on milieu. The inhibition that America finds sissified is part of the national character of Japan, for example, and it has been said that Lord Byron, the hero of the Romantic era, would have been regarded as a madman in the previous Age of Enlightenment. In Twilight of the Golds, a recent Broadway play, characters debate whether a fetus destined to be homosexual should be aborted. When the Human Genome Project is finished, in ten or fifteen years, temperamental traits could inspire similarly chilling discussions. As Kagan says, "When the masses can use genetic information to mate selectively, society will face a big ethical problem."

Partly because social influences have such a profound effect on how we regard temperament, Kagan feels that "whether you should try to change or accept yourself is a political question." He says, "There are many good things about being, say, introverted—think of Wittgenstein. But now the cultural ideal is Bill Clinton. If you happen to have an unfashionable personality, you suffer the consequences." Sometimes a deeper understanding of why one is the way one is brings peace. Once, after Kagan gave a talk at a scientific conference, the scientist who had spoken before him invited him to lunch. "For sixty years I've been blaming my mother for my introversion,' he said, 'and now I see that it's temperament," Kagan recalls. "Suddenly, he saw his life differently and felt better about it."

The no-frills approach to coping with one's temperament is choosing settings that suit it. Richard Burtons and Jane Digbys don't belong on assembly lines, nor Queen Victorias in used-car lots. "If you have brittle bones," Eysenck says, "there's not a lot you can do about it other than to avoid risky activities like skiing. If you're inclined to be anxious, you can avoid the situations that produce those symptoms."

Sometimes a disposition can be neither accepted nor accommodated. "Temperament casts its longest shadow in those who have a very dour tone," Kagan says. "There are some people who never feel good inside. If we could enter deep into Sylvia Plath's limbic system, and listen, and feel what she felt ..." Kagan allows that psychotherapy—particularly the behavioral kind, in which the client learns new responses to old stimuli—has "some modest success in helping people change certain qualities." Akiskal is a bit more positive about the open-ended psychodynamic therapy so often criticized these days. Although its results resist quantification, "the more leisurely treatment helps those who want to be more reflective and insightful," he says. "We may simply not know how to measure its efficacy."

As Peter D. Kramer observes in the bestseller Listening to Prozac, drugs designed to alter the transmitter imbalances linked to depression and other disorders are increasingly touted as temperamental tune-ups for people who are not ill in the conventional sense but want to be bolder, say, or more energetic. Gold dismisses the notion that such medicines can be used as psychic vitamins to pep up a normal personality. "People whose arousal systems are not perturbed do not respond to these agents. The idea that healthy people who take Prozac feel better is absolutely ridiculous." He finds repellent as well as unrealistic the notion that psychiatry will someday provide painless living through chemistry. "To respond to the loss of a loved one or a cherished dream casually is grotesque. To 'feel better' means to feel one's feelings better, including sadness or anger, without getting stuck in them."

The easiest way to experience a change in temperament is to wait. From childhood through old age, our psyches alter along with our bodies, according to inexorable schedules set by our biological clocks. Toddlers and teenagers offer flamboyant examples of this phenomenon, and subtler manifestations may include what Margaret Mead called "post-menopausal zest." Although middle-aged men don't undergo the well-defined endocrinological shift that women do, Auke Tellegen, a psychologist at the University of Minnesota, who devised the Multidimensional Personality Questionnaire, suspects that they experience something similar, albeit more gradual. "For lack of hormones," he says, "perhaps a man will be a Zen monk at seventy." Even thrill-seeking psychopaths lose some of what Lykken calls their "lustful vigor" in their forties. Some develop respectable ways of walking on the wild side. After spending much of his earlier life in prison, one of Lykken's subjects succeeded in business and bought a plane. "I set off to go flying with him," Lykken says, "thinking, 'What am I doing? He's going to stand the plane on end and scare me to death.' But he flew like a transport pilot, because his self-esteem is now involved with being licensed to fly jets and do all sorts of things the average amateur can't."

As the high-flying ex-con illustrates, one's mode of involvement may not change much, but one's focus can, creating the possibility of a different kind of life with the same old temperament. Religious conversions are Tellegen's favorite example: "Charles Colson would have beat his grandmother to death when he was with Nixon, but then he was 'born again.' He probably always had a very emotional, intense temperament, but now he has different enemies and friends. His nature didn't change—he just does something else with all that zeal."