45

A REPORTER AT LARGE

DOUBLE MYSTERY
Recent research into the nature of twins is reversing many of our most fundamental convictions about why we are who we are. I BY LAWRENCE WRIGHT

of identical-twin girls were surrendered to an adoption agency in New York City in the nineteen-sixties . The twins, who are known in psychological literature as Amy and Beth, might have gone through life in obscurity had they not come to the attendon of Dr . Peter Neubauer, a prominent psychiatrist at New York University's Psychiatric Institute . Neubauer, who was also an adviser to the adoption agency, believed at the time that twins posed such a burden to parents, and to themselves in the form of certain developmental hazards, that adopted twins were better off being reared apart from each other. It was clear that such a separation would also offer Neubauer exceptional research possibilities . Studies of twins reared apart are the most powerful tool that scholars have for analyzing the relative contributions of heredity and environment to the makeup of individual human natures . Identical twins are rare, however, and twins who have been separated and brought up in different families are particularly unusual . Neubauer knew of only a handful of studies examining twins reared apart, and in many cases the twins being studied had been separated late in their childhood and reunited at some point long before the study began . Amy and Beth presented an opportunity to look at twins from the moment they were separated and to trace them through childhood, observing at each stage of development the parallel or diverging courses of their lives . Such a study might not lay to rest the ancient quarrel over the relative importance of nature and nurture, but one could imagine few other experiments that would be more relevant to understanding the mystery of the human condition .
SET

By the time Amy and Beth were sent to their adoptive homes, an extensive team of psychologists, psychiatrists, pediatricians, and observers was waiting to follow them as they moved from infancy to adolescence . Every step of childhood would be documented through psychological tests, tests of skills and abilities, school records, parental and sibling interviews, films, and the minutes of several hundred weekly conferences . Because the twins had identical genetic constitutions, the team could evaluate the effects of the environment on their personalities, their behavior, their health, their intelligence. Broadly speaking, the differences between the girls as they grew older would be a measure of the validity of the most fundamental assumption of analytical psychology, which is that experience and, in particular, our family background shapes us into the people that we become. The agency that placed the children shortly after their birth informed each set of potential adoptive parents that the girl they were adopting was already involved in a study of child development, and strongly urged the adoptive parents to continue it, however, neither the adoptive parents nor the girls themselves were ever told that the subject of the study was twins . The sisters were fair-skinned blondes with small oval faces, blue-gray eyes, and slightly snub noses . Amy was three ounces heavier and half an inch longer than Beth at birth, an advantage in height and weight that persisted throughout their childhood . The girls were adopted into families that were, in certain respects, quite similarboth were Jewish, and lived in New York State . The mothers stayed at home, and in each family there was a son almost exactly seven years older than the twin . (In

Beth ' s family, there was an older daughter as well.) In other respects, the environments were profoundly different ; notably, Amy's family was lower middle class and Beth 's was well off. Amy's mother was overweight, low key, and socially awkward . Although she had a compassionate side to her nature, she was an insecure mother, who felt threatened by her daughter' s attractiveness. Beth' s mother, on the other hand, doted on her daughter and spoke positively of Beth' s personality and her place in the family. The team described Beth's mother as pleasant, youthful, slim, chic, poised, self-confident, dynamic, and cheerful . Whereas Amy's mother seemed to regard Amy as a problem, a stubborn outsider, Beth 's mother treated her daughter as " the fun child . " She went out of her way to minimize the differences between herself and Beth, to the extent of dyeing her own hair to emphasize their similarity . The girls ' fathers were alike in many respects confident, relaxed, at ease with themselvesbut were as different as the mothers in their treatment of the girls . Amy' s father came to agree with his wife that Amy was a disappointment, whereas Beth 's father was more available and supportive. All in all, the research team characterized Amy' s family as a well-knit threesome -mother, father, and sonplus an alienated Amy. It was a family that placed a high value on academic success, simplicity, tradition, and emotional restraint. Beth 's family, on the other hand, was sophisticated and full of energy "frenetic" at times and it tended to put more emphasis on material things than on education . Clearly, Beth was more in the center of her home than Amy was in hers. And how did these identical twins in such contrasting environments turn out?

Separated-twins stories feed the fantasy that we might have someone who is not only our mirror but who understands us perfectly .

46

As might be expected, Amy's problems began early and progressed in a disturbing direction. As an infant, she was tense and demanding . She sucked her thumb; she bit her nails ; she clung to her blanket; she cried when left alone ; she wet her bed ; she was prone to nightmares and full of fears . By the time she was ten, she had developed a kind of artificial quality that manifested itself in role-playing, madeup illnesses, and confusion over her sexual identity. Shy, socially indifferent, suffering from a serious learning disorder, pathologically immature, she was a stereotypical picture of a rejected child . If only Amy had had a mother who was more empathic, more tolerant of her limitations, more open and forthcoming (like Beth's mother), Amy's life might have turned out far better. If only her father had been more consistently available and affectionate (like Beth's father), she might have been better able to negotiate the Oedipal dramas of latency and might have achieved a clearer picture of her own sexual role . If only her brother had been less strongly favored (like Beth ' s brother), Amy would have been spared the mortifying comparisons that were openly drawn in her family . In theory, if Amy had grown up in Beth ' s family, the sources of her crippling immaturity would have been erased, and she would be another kind of personhappier, one presumes, and more nearly whole. And yet in almost every respect Beth's personality followed in lockstep with Amy's dismal development. Thumbsucking, nail-biting, blanket-clenching, and bed-wetting characterized her infancy and early childhood . She became a hypochondriac and, like Amy, was afraid of the dark and of being left alone. She, too, became lost in role-playing, and the artificial nature of her personality was even more pronounced than Amy's . She had similar problems in school and with her peers . On the surface, she had a far closer relationship with her mother than Amy had with hers, but on psychological tests she gave vent to a longing for maternal affection which was eerily the same as her identical sister's . Beth did seem to be more successful with her friends and less confused than Amy, but she was also less aware of her feelings. The differences between the girls seemed merely stylistic ; despite the differences in their environments, their pathology was fundamentally the same .

Did their family lives mean so little? Were they destined to become the people they turned out to be because of some genetic predisposition toward sadness and unreality? And what would psychologists have made of either girl if they did not know that she was a twin? Wouldn't they have laid the blame for the symptoms of her neurosis on the parents who raised her? Finally, what did all this say about the fundamental presumptions of psychology?

been a tidal wave of twin-based scholarship . There are now so many scientists seeking to study twins that every August researchers set up booths under a huge tent at the Twins Day Festival in Twinsburg, Ohio, where some three thousand browsing identicals and fraternals stop to take blood-pressure tests or fill out questionnaires . Recent studies of twinship have challenged our most entrenched views of human development and have capsized cherished beliefs about human naturein particular, the bedrock notion HE separated-twins story is a chestthat character is created by experience. nut of American journalismone But then twins have been confounding that is guaranteed to gain national expo- humanity from the earliest timesalsure, along with stories of pets that have most as if they were a divine prank detrekked across the country to find their signed to undermine our sense of indimasters . The appeal of the separated- viduality and specialness in the world. twins story is the implicit suggestion that Twins are both an unsettling presence, it could happen to anyone. Babies actu- because they sabotage our sense of perally do get lost or separated, and, how- sonal uniqueness, and a score-settling ever rare such an event may be, it feeds presence, because their mere existence althe common fantasy that any one of us lows us to pose questions we might not might have a done, a doppelganger- have thought to ask if we lived in a world someone who is not only a human mir- without them. ror but also an ideal companion, someIn the United States today, at least one who understands us perfectly. It is eleven births out of every thousand are not just the similarity that excites us but twins, which is to say that about one perthe difference : the fantasy of an identical son in fifty has a twin (about one-third twin is a projection of ourselves living an- of those are identical) . That constitutes other life, finding other opportunities, a virtual epidemic. Between 1973 and choosing other careers, sleeping with 1990, twin births shot up at twice the rate other spouses ; an identical twin can ex- of singletons, and triplets and higherperience the world and come back to re- multiple births increased at seven times port about choices we might have made. the single-birth ratepartly because But the story has a darker and more many women are waiting until later in threatening side, and this may be the real life to have children, and multiple births secret of its grip on our imagination . We are more frequent among older mothers. think we know who we are. We struggle Last year, fully a third of all first births to build our characters through experi- in this country were produced by women ence ; we make ourselves unique by deter- over the age of thirty-five . "But that's mining what we like, what we don 't like, only part of it," says Dr. Louis Keith, a 6 and what we stand for . The premise of professor of obstetrics at Northwestern free will is that we become the people we University Medical School, and the choose to be . Suppose, then, we meet an president of the Center for the Study of Other who is, in every outward respect, Multiple Birth . "The real increase in ourself. It is one thing to imagine an twins and triplets in the United States identical Other who, having lived a sepa- did not occur until 1985, when we rate and distinct life, has been marked by learned how to superovulate women. it and become different from us . But Now doctors are prescribing ovulationwhat if, in spite of all the differences, we enhancing agents as if they were prescriband the Other arrive at the same place? ing bubble gum at a children' s birthday Isn' t there a sense of loss? A loss not only py.a"rt If twins are important to science beof identity but of purpose? We are left wondering not only who we are but why cause they allow us to ask how much of we are who we are. our nature arises from our genes and how The Neubauer twin study is just one much from our circumstances, the anamong thousands that have raised these swers have equally profound implicaquestions . Over the last decade, there has tions for social policy. The hallmark of

 48 THE NEW YORKER., AUGUST 7, 1995

liberalism is that changes in the social twin studies to be largely under genetic environment produce corresponding influence. All this comes after several decades of changes in human development . But if people ' s destinies are written in their heightened political struggle between genes, why waste money on social pro- those who believe that people are largely grams? Much of the ferocious argument the same, with differences imposed upon over individual and group differences in them by their environment, and those intelligence (which has recently been who conclude that people differ mainly rekindled by Richard Herrnstein and because of their genes, and that their enCharles Murray' s " The Bell Curve " ) vironments are largely of their own makdraws upon the fact that there is a closer ing. Obviously, the roots of liberal and correlation between I .Q test scores of conservative views are buried in such contrary presumptions about human naidentical twins than between those of fraternal twinsthe difference being an in- ture . The broad movement from envidication of how much of what we call in- ronmental determinism to behavioral getelligence is inherited . Even matters that netics which has transformed psychology would seem to be entirely a reflection of over the last thirty years has also dramatione' s personal experience, such as politi- cally altered society' s view of human decal orientation or depth of religious com- velopment and become a part of the inmitment, have been shown by various visible substratum of American politics .

This can he demonstrated by comparing the climates of opinion that produced the Great Society, in 1965, and the Contract with America, in 1995. These days, even the most dogmatic environmentalist is willing to admit that nature influences nurture . The debate has evolved into a statistical war over percentageshow much of our personality or behavior or intelligence or susceptibility to disease is attributable to our genes, as compared with such environmental factors as the family we grow up in or the neighborhood we live in or how long we attend school . (What the statistics measure is genetic differences in populations, not in individuals . We cannot infer from the statistics that, say, fifty per cent of any one individual's personality is genetically acquired .) The fulcrum upon which one side rises while the other falls is the concept of heritability. Heritability, decreed the animal geneticist J . L . Lush in 1940, is the fraction of the observed variation in a population that is caused by differences in heredity. For instance, laboratory rats that arc bred for their intelligence in escaping mazes will grow smarter over the generations, just as maze-dumb rats will grow dumber when they are bred together. Since there is no difference in their environments, the difference between the two populations must be inherited . It is easy to demonstrate the transmission of traits in plant and animal populations ; in fact, the manipulation of observable genetic traits is the basis of selective breeding. In human beings, however, matters are more complex . Since selective breeding is morally out of the question, scientists must rely on the chance data that society sends their way . One of the principal sources of information about human heritability is twin studies . Theoretically, if a trait is highly heritable then it will approach a hundred per cent concordance in identical twins and fifty per cent in fraternal twins and other siblings . But environmental factors can also affect traits that are genetically transmitted . Height, for instance, is a heritable trait, and in well-nourished Western populations most of the variation in stature is an expression of the genes . But the genes require a supportive environment in order to be expressed in the first . What are 'congressional ethics ' ? " "You've been around here longer than I have

 LIBERALS, CONSERVATIVES, AND NATURE 49

place . A population that exists on the brink of starvation can have little variation in height, because growth is arrested; there is no way of telling who has tall genes and who has short ones . If one group within a population enjoys an abundant diet while the rest are starving, the variation in height is largely environmental. Identical, or monozygotic (MZ), twins are thought to result from the splitting of a single fertilized egga zygote in a form of asexual reproduction . Fraternal, or dizygotic (DZ), twins are thought to be the product of two separate eggs, independently fertilized . Thus, identical twins are clones, having identical genes, whereas fraternal twins share only fifty per cent of their genes on average. The existence of these two types of twins creates a statistical opportunity that has contributed to the expanding field of behavioral genetics, which is built on heritability estimates. Behaviors as diverse as smoking, insomnia, marriage and divorce, choice of careers and hobbies, use of contraceptives, consumption of coffee (but not, oddly enough, of tea), menstrual symptoms, and suicide have all been found to have far higher rates of concordance for identical than for fraternal twins a finding that suggests these traits to be more influenced by genes than was previously suspected. A survey of Australian twins in the early nineteen-eighties also found a surprisingly significant genetic component for attitudes toward such wide-ranging political and social issues as apartheid, the death penalty, divorce, working mothers, and some forty other subjects . Only on a motley assortment of topicscoeducation, the use of straitjackets, and pajama partieswas there no meaningful genetic influence on individual attitudes . An especially interesting, and ongoing, Swedish study of elderly twins, begun in 1984 by Professor Robert Plomin, a behavioral geneticist at the Institute of Psychiatry in London and at Pennsylvania State University, looked at life events such as divorce, retirement, illness, the death of a child, the mental illness of a spouse, and financial reversesmany of which might seem, almost by definition, to be accidents of the environment. The researchers concluded that, in many respects, identical twins who had been reared apart were even more alike in terms of their major life events than identical twins who had been reared together.

Underlying these startling findings is an insistent unanswered question : How? Is there a gene for neurosis or Alpine skiing or traditional values? Nothing in molecular biology suggests anything of the sort. It is more likely that configurations of genes shape behavior than that a single gene exercises autonomous control over certain kinds of actions . This is especially true of complex functions such as intelligence. Because supporting molecular evidence has been slow in coming, in most cases the only proof of genetic influence on personality and behavior still comes from twin and adoption studies, which examine unrelated individuals reared together (thus complementing studies of twins reared apart) . Numerous twin studies have shown that alcoholism is an inherited disorder; for example, identical twins are much more alike in their drinking patterns than fraternals, and if these patterns lead to alcoholism it's more likely that both twins will be alcoholics. But even if alcoholism is genetically rooted it is clear that environment plays a significant role in much of drinking behavior . Alcoholism is rarely a problem in religious cultures where drinking is forbidden. Homosexuality appears to be moderately heritable among males and less so among females . A stretch of X chromosome has been implicated in some instances of male homosexuality, but it leaves open the question of what, exactly, is inherited . "The fairest thing to say is that nobody knows, " Richard C . Pillard, a professor of psychiatry at the Boston University School of Medicine, says . "Is it a propensity to like somebody who is sort of the same as you versus somebody who ' s different, or to like a man versus a woman, or to be very sensitive, or what? To me that's the payoff question. What is that little brain up there doing that ' s making you different? " One reason for the dearth of such knowledge is that research involving the genetic underpinnings of behavior has often been discouraged. When Dutch scientists announced, two years ago, that they had found a connection between a genetic defect and a form of familial aggression, they were denounced for even considering a genetic basis for violent behavior . In this country, the National Institutes of Health, facing charges of racism, pulled the rug out from under a

planned 1992 conference on " Genetic Factors in Crime" and scaled hack research into the causes of violence. Again and again, when genetic research turns toward human nature, and away from simple biology, politics swamps the discussion and often sinks the research efforts.

T been reared apart, and the most inioral genetics are of twins who have
fluential of these studies have been conducted at the University of Minnesota by Professor Thomas J. Bouchard, Jr . A tall, shambling man of fifty-seven, Bouchard wears suspenders and looks as if he'd be more at home sharing a cup of coffee with the local dairy farmers than sorting through the computerized data bank in the university' s Center for Twin and Adoption Research, which he founded . Largely because of Bouchard and his team, the University of Minnesota has been the epicenter of twin studies since 1979 . It was then that Bouchard read a newspaper story about Jim Lewis and Jim Springer, identical twins who had been separated at birth and reunited thirty-nine years later. Each of the Jim twins, as they were called, was six feet tall and weighed a hundred and eighty pounds ; they looked as much alike as any other identical pair. At their reunion, they discovered that each had been married twice, first to a woman named Linda and then to a woman named Betty . Jim Lewis had named his firstborn child James Alan, and Jim Springer had named his James Allen . In childhood each twin had owned a dog named Toy. They had enjoyed family vacations on the same beach in Florida and had worked part time in law enforcement. They shared a taste for Miller Lite beer and Salem cigarettes. At the time, only nineteen cases of reunited identical twins had been reported in the United States . Few had been reared by families who were not biologically related, and that made the Jims all the more exceptionalalmost perfect for a behavioral geneticist who had spent his career trying to tease apart the influences of nature and nurture on the human personality. Bouchard excitedly persuaded university officials to provide grant money to initiate a study of the Jim twins. "It was just sheer scientific curios-

THE most powerful studies in behav-

50

ity, " Bouchard says now . "I thought we were going to do a single study of a set of twins reared apart. We might have a little monograph . " The morning the tests were to begin, Bouchard took the Jims to breakfast . He intended to brief them on the particulars of the study, but it was the first time he had ever worked with twins, and he found himself obsessing over little things about themthe way each one had bitten his nails, for example . Each of the Jims had a peculiar whorl in his eyebrow, and Bouchard started absently counting the number of hairs in their brows. "You ' re staring at us," one told him. Bouchard apologized . He had been staggered by the similarities of their gestures, their voices, and the morphology of their bodies . These two men had lived entirely separate lives, and yet if Bouchard closed his eyes he couldn't tell which Jim was talking. Since the Jims ' first visit, more than a hundred other reared-apart twins have come to the Twin Cities to spend a week in Bouchard ' s laboratories, in Elliott Hall . In the tests, which usually start on Sunday afternoon and go through the following Saturday, twins undergo a variety of personality assessments and medical examinations, including X-rays, cardiograms, and blood tests. They have their fingerprints taken and their allergies evaluated . They submit to a sexualhistory questionnaire that is so intimate that some twins decline to finish it . By the end, Bouchard 's team will know as much about each of the twins as it is possible to measure in fifty hours of testing. The researchers will know what both twins eat, the books they read, their sexual orientation and predilections, the television shows they watch, how much their hands quiver when they hold a stick in a hole, their musical tastes and talents, their fears and phobias, their childhood traumas, their pulse rates at rest and under stress, their hobbies, their values, the amount of decay in their teeth, the way they sit in a chair . Because of the Minnesota project, separated twins have become one of the most densely studied populations in the history of psychology. Besides the Jims, many memorable personalities have passed through Elliott Hall. Among the early pairs were Daphne Goodship and Barbara Herbert, who, like the Jims, had been adopted separately as infants and lived apart for

UPON WINNING ONE'S FLIGHT IN THE SENIOR FOUR-BALL

Oh, where have they gone tothe eight-iron stiff to the pin, after two less fortunate shots, setting up a par, the calmly stroked putt that snatched a win away from the staggered opponents ; the heroic long drive that cleared the brook on the fly by a foot or two; the bravely slashed wedge that lifted the plugged ball up in a sea-spray of sand to bobble blindly toward the hole? How can these feats matter so little, so soon after they mattered so much? The blood thrumming in the temples, the rushes of love for one ' s doughty, erratic partner, the murderous concentration upon imaginary abstractions carved in the air by sheer sinew and boneboiled down to a trinket of silver, a tame patter of applause in the tent, a pleasantry, a loss.
-JOHN UPDIKE

thirty-nine years . Barbara had gone to a Oskar Stohr . They were born in Trinmodest home in Hammersmith, a bor- idad in 1933 and were split apart a few ough of London, as the daughter of a city months later by a bitter divorce, brought gardener . Daphne had a middle-class on by their father' s violent behavior . Jack childhood north of London, in the town stayed in Trinidad with their father, a of Luton, where her father was a metal- Jewish merchant in Port of Spain. Oskar lurgist. When they finally met, at King's went to live in the all-female household Cross Station in London, in May of of their German maternal grandmother. 1979, each was wearing a beige dress and While Oskar was preparing to become a a brown velvet jacket . Right away, they member of the Hitler Youth, Jack was noticed they had identical crooked little exploring his Jewish identity. At the age fingersa small defect that had kept of sixteen, he was sent to Israel to work both of them from ever learning to type on a kibbutz. In 1954, he decided to emior to play the piano . There were other grate to the United States, and stopped commonalities that were harder to ex- off in Germany to meet his brother for plain . Both had the eccentric habit of the first time since their separation . The pushing up their noses, which they called reunion was chilly and brief. Then, "squidging . " Both had fallen down the twenty-five years later, Jack's wife read stairs at the age of fifteen and had weak about the Jim twins and the Minnesota ankles as a result . At sixteen, each had studies, and Jack decided that it might be met at a local dance the man she was go- a good idea to meet his twin again, this ing to many. The twins suffered miscar- time on neutral ground . He got in touch riages with their first children, then pro- with Bouchard, and the professor eagerly ceeded to have two boys followed by a agreed to fly them both to Minneapolis. girl. And both laughed more than anyBouchard was standing with Jack at one else they knew, prompting them the Minneapolis airport when Oskar got to be nicknamed the Giggle Twins. off the plane . "I remember Jack pulling Bouchard was interested in the fact that in his breath, because Oskar walked exeach fell silent whenever the conversation actly the same way he did," Bouchard turned to provocative subjects, like poli- says . "They have a kind of swagger to tics . In fact, neither had ever voted, ex- their bodies." Each sported rectangular cept once, when she was employed as a wire-rimmed glasses, a short, clipped mustache, and a blue two-pocket shirt polling clerk Among other twins who came to with epaulets. They shook hands but did Minnesota to be quizzed and probed and not embrace. Bouchard thought that they bled and recorded were Jack Yufe and would be an ideal pair for detecting en-

51

environmental influence . The contrasts in their upbringing, their cultures, and their family lives were overwhelming . Moreover, they didn ' t seem to like each other enough to mythologize their similarities, as critics of twin studies have suggested that twins tend to do. As it turned out, Jack and Oskar were full of quirky habits in common, such as storing rubber bands on their wrists, reading magazines from back to front, flushing the toilet before using it, and dipping buttered toast in their coffee. They also enjoyed startling people by sneezing in crowded places . They differed in certain obvious respects ; Oskar, for instance, was married, while Jack was divorced, but Jack noticed that Oskar expected his wife to take care of all his needs without questionmuch as he himself had done when he was married. Jack regarded himself as a liberal Californian, and he saw his brother as "very traditionalistic, typically German . " Oskar was a skier, Jack was a sailor. Oskar was a devoted union man, Jack a self-employed entrepreneur . Of course, they had lived profoundly different lives, so they differed completely in their memories, their experiences, their religious and political orientations in other words, their interior worlds, the raw stuff of selfhood . And yet their personality profiles were strikingly similar. Bouchard observed that their tempos, their temperaments, their characteristic mannerisms were far more alike than differentsimilarities that were all the more surprising because Oskar had been reared entirely by women and Jack had grown up with their father. The mountain of data compiled by the Minnesota team, along with ongoing twins research in Boulder, Stockholm, and Helsinki, has stunningly tipped the balance in the natureversus-nurture debate. Bouchard and his team have assessed a variety of personality characteristics, such as sense of well-being, social dominance, alienation, aggression, and achievement, which they described in an important article in the journal of
Personality and Social Psychology

much alike as identicals reared together. Moreover, there was not a single one of those personality traits in which fraternal twins reared together were more alike than identicals reared apart . How could this be? Wouldn ' t twins who had grown up in the same family, gone to the same schools and churches, and been exposed to the same values and traditions have been similarly shaped by those influences? If, as the Minnesota team was claiming, half of the variance in personality in a population was genetic in origin and the other half was environmental, why wouldn' t identical twins reared together be far more alike in their personalities than identicals reared apart? The answer to this paradox had been suggested before, but not with the force of so much data . The Minnesota team asserted that almost none of the environmental variance was due to sharing a common family environment ; rather, most of the differences that could be attributed to environmental causes arose from unshared experiencesin other words, the lives the twins led outside the home . Bouchard and his colleagues repeated this assertion in a disturbing 1990 article in Science . "The effect of being reared in the same home is negligible for many psychological traits, " the Minneso-

tans wrote . " We infer that the diverse cultural agents of our society, in particular most parents, are less effective in imprinting their distinctive stamp on the children developing within their spheres of influenceor are less inclined to do sothan has been supposed . "

C about human nature from studying twins, it's astonishing to realize how

ONSIDERING

all that we've learned

little we know about the twinning process itself. In spite of the burst of twinbased scholarship in recent years, much that is commonly believed to be true about twinning is either wrong or in dispute. It is not clear, for instance, whether twinning is a kind of birth defect or, contrarily, whether birth defects are caused by twinning (or if, indeed, either has anything to do with the other) . We don't know what significance, if any, to attach to the elevated incidence of left-handedness among both kinds of twins. It is not even certain whether fraternal twins always come from two eggs or sometimes from one that has split before fertilization . We are just now learning that twins are different in particular ways from singletons (their teeth are more symmetrical, for example), but we don't know why or what that means . In sum, we don't know who twins are or how twins happen . We only

in 1988 . They concluded that identicals reared apart were as

"Josephine, my man!"

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THE NEW YORKER, AUGUST 7, 1995

presume to know what they tell us about who we are. So much depends on a phenomenon about which we know so little . Even the prevalence of twins is a subject of puzzlement and controversy . With the increasing use of ultrasound to detect early pregnancies, we now know that twinning is a far more common occurrence than anyone had previously imagined . Although only about one out of eighty or ninety live births produces twins, at least one-eighth of all natural pregnancies begin as twins. Many of us singletons, in other words, began life as something more as part of a pair. Doctors equipped with color-Doppler and vaginal ultrasounds and high-speed scanners have been able to observe multiple pregnancies as early as five weeks after conception. " People are picking up twin pregnancies the size of garden peas, " says Professor Charles E . Boklage, a developmental biologist at the East Carolina University School of Medicine and a well-known maverick in the world of twin biology. "They're seeing a lot more twins than they ever knew were there. " Many doctors have undergone the unnerving experience of spotting twin embryos one month, only to find a singleton the next time they looked . What was happening? At the Third International Congress on Twin Studies, held in Jerusalem in 1980, this question was raised, and one of the participants cried out, "Vanishing twins! "thus giving a name to a phenomenon that has caused as much confusion as excitement. Boklage studied reports of three hundred and twenty-five twin pregnancies and found that sixty-one ended as twins, a hundred and twenty-five as singletons, and the remainder a hundred and eighty-sixas a complete loss : a measure of how risky twin pregnancies are . Often the only external sign of a vanishing twin is vaginal bleeding. "The so-called phenomenon of the `vanishing-twin syndrome' is neither phenomenal nor a syndrome," Boklage contends . "It is much too common to be considered phenomenal, and it occurs for too many reasons to be considered any kind of syndrome . " He says that most pregnancies, whether multiple or single, fail anyway, so it is not as surprising as it seems that twins often disappear . " Somewhere in the vicinity of ten to fifteen per cent of us and that's a minimum estimate--ate walking around

thinking we ' re singletons when in fact we 're only the big half," Boklage says . He estimates that for every set of twins born live there are at least six singletons who are survivors of twin conceptions. Twins are far more susceptible to the birth defects, spontaneous mutations, and vascular problems that threaten early life . Simply being a twin is stressful and raises the odds against survival. Because all twins battle in the womb for space and nutrition, the experiences of twins before birth may be considerably different from those of singletons . " Twins compete physically," says Dr . Louis Keith, of Northwestern . Several years ago, one of the doctors on his staff observed twin fetuses fighting. " One punched the other and the other looked startled, " Dr . Keith recalls . "On another occasion, a doctor was looking with the ultrasound at triplets, and two of them were kissing, as clear as day . Among multiples, there is intrauterine life. They do fight . They do kiss . " There is considerable evidence that when one twin dies the survivor can suffer lifelong feelings of guilt . "When someone loses a twin, the intensity of grief tends to be higher than with many other relatives," says Nancy L . Segal, a professor of developmental psychology and the director of the Twin Studies Center at California State University, Fullerton . "It' s a loss that only another twin can understand." Six years ago, Dr. Elizabeth Bryan, who is the medical director of the Multiple Births Foundation, in London, helped set up the Lone Twin Network, to provide support for survivors coping with their grief. "I 've met quite a number of people who only discovered their twin was stillbornthat is, they only discovered that they were a twin at allat some adult occasion such as when they were about to get married, or their first child was on the way, and their mother suddenly said, ` Your twin died and I never told you, '" Dr. Bryan says. "Several of them said that the news came as a profound relief. For the first time, they understood the loss they'd felt all their lives . " Dr. David Teplica, a plastic surgeon in Chicago, has been photographing twins since 1988 . " Since my early teens, I've been obsessed with the idea of twinning, " the thirty-six-year-old Teplica says . "I read everything I could about twins ." Five years ago, he got to know

Dr . Keith and his identical twin, Donald, who is a Pentagon defense contractor . At their urging, Dr . Teplica turned his hobby into a more formal project, and he has already compiled an archive of approximately six thousand twin portraits. "There have been fascinating things that have come up as part of the whole process of collecting these images," he says. "It' s now clear to me that almost all secondary skin characteristics on the head and face, and probably elsewhere, are genetically predetermined . Freckle patterns, hair whorls, the first gray hairs, the first wrinkles on the human face, even the development of acne in the same location on the nose at exactly the same time all these things seem to be in some way genetically predetermined . Why else would a set of identical twins from upstate New York get exactly the same three little crow 's-feet at the corners of the eyes? Why would two women from Texas develop basal-cell carcinoma in exactly the same spot on their left cars within a year of each other? How can it he that two cells that were separated just after conception can carry enough genetic information to predetermine where your blackheads will develop when you are fifty or sixty years old? It ' s really very scary ." After a year or so of collaboration, Donald Keith asked Teplica, " David, why are you so fascinated with twins? Maybe you are one." Teplica laughed and replied, "Donald, I 'm not a twin ." But the next time his mother came to visit Teplica asked her if there was any chance that he was a twin . " She turned white," he recalls, " and proceeded to tell me how she had tried to get pregnant for many years, and when she finally became pregnant she was so large, put on so much weight so quickly, that her physician told her she would be delivering twins . But then in the fourth month she had some cramping, passed some tissue, had some bleeding . She spent the rest of her pregnancy in bed, and delivered only me. Now, that was before the days of ultrasound, but every indication was that she did have a twin pregnancy." Charles Boklage cites another interesting phenomenon, which, though it has rarely been detected, may not be at all uncommon . " Possibly some of us are twins who are walking around in a single body, " Boklage says . Such a creature is called a chimera, after the mytho-

INTRAUTERINE PUNCH-UPS

logical Greek monster that had the head of a lion, the body of a goat, and the tail of a serpent . Chimeras are easily produced in laboratory experiments with animals, and sometimes occur in nature within a single species when littermates fuse together early in their development in the uterus . Occasionally, blood donors are found to be carrying two different blood types : it could mean that fraternal twins merged in the womb . Of course, there is no way to determine whether identical twins have merged, since their genes and blood types are the same . In those cases, the twins don ' t vanish; they amalgamate.

Benvironmentalist belief that people the last thirty years waging war on the
are fundamentally alikethat they are made different only by their families, their schooling, the traumas of life . Now, after decades of persuasive twin studies showing how similar identical twins are, even when they have been raised in separate families, behavioral geneticists must face the question of why identical twins differ at all. In 1981, an unusual set of twin girls found their way to the office of John Bum, who was at the Hospital for Sick Children in London and is now a professor of clinical genetics at the University of Newcastle Upon Tyne . Katy and Jenny were friendly, easygoing eightyear-old girls, who both wore their dark hair in pigtails . Both had distinctive dark round eyes, slender lips, and long faces that finished in jutting chins . Katy, a gifted gymnast, had a lively expression and a bouncy, athletic gait. Jenny was notably shorter and weaker . Her calves were swollen, giving a false impression of muscularity; in fact, she had difficulty standing, and she walked with an obvious waddle. Her scores on verbal-intelligence tests were also significantly lower than Katy's, reflecting the duller expression in her eyes . Further tests demonstrated something that Professor Burn suspected but could scarcely believe : the shorter, weaker, less intelligent twin was suffering from muscular dystrophy, the other twin showed no sign of the disease . And yet, according to DNA tests, the twins were identical. The twins presented, as it were, twin mysteries . Like hemophilia and redgreen color blindness, muscular dystro-

EHAVIORAL

geneticists have spent

55 phy is carried on the X chromosome. Specifically, it is a flaw in the dystrophene gene, which gives integrity to the muscle membranes and allows them to contract and relax. The form of the disease manifested in Jenny, called Duchenne, is particularly savage, and what surprised Bum was that it is a genetic disorder normally seen only in boys . A progressive wasting illness, it almost always leads to death by the age of twenty . Since few males with Duchenne muscular dystrophy live long enough to reproduce, the flaw is carried through the maternal line. Yet here was a young girl with all the marks of full-bore Duchenne, which did in fact continue its remorseless progression over the next several years, confining her to a wheelchair by the age of eleven and killing her at sixteen . Why, Bum wondered, did this girl suffer from a disease that is supposed to be found only in boys? Even stranger, how was it that her identical-twin sister was spared this appalling destiny? When Bum looked in the scientific literature, he discovered that this wasn 't the first time that one of a set of identicaltwin girls had exhibited signs of muscular dystrophy and the other had not. Because the disease is carried on the X chromosome, Bum reasoned, the discordance between the two girls must have something to do with X-chromosome inactivation. Females, of course, carry two X chromosomes, whereas males have an X and a Y. When a female zygote discovers that it has twice as many X chromosomes as it requires, an interesting process follows : half of its X chromosomes are turned off. One way of understanding this is by looking at calico cats, which are exclusively female. Genes for fur colors are carried on the X chromosome : there is one gene for black-and-white coat colors and another gene for the orange-marmalade color. A male cat may be either black-and-white or orange, but the female, through X inactivation, may choose one or the other X chromosome from each pair. "If you took a normal girl and looked at a thousand cells, you'd expect five hundred of those cells to be using the mother's X and five hundred to be using the father's X-just like tossing coins," Bum reasoned. " Now and again, very rarely, a . girl will toss heads in every cell, and not tails, and switch off all her good copies. " As it turned out, Burn was right: the afflicted twin was using only the mother's X, whereas her unaffected sister was us-

 56 THE NEW YORKER, AUGUST 7,1995

we shouldn't try to explain everything at once ." Clearly, some identical twins are more identical than others . " Some of the differences are traceable to the very early prenatal stagesunequal nutrition, unequal blood supplies, " Nancy Segal says . "Twills never have identical fingerprints . One twin may be right-handed, one left-handed. One may dominate in certain situations and one may be more submissive . There ' s a spectrum along which twins differ . " Identicals can be dramatically discordant for facial and other physiological features, such as cleft lip or cleft palate . An MZ twin who is the product of a placenta that was only marginally attached to the womb may develop into a miniature version of his siblingas in the Hollywood gag that brought together Danny DeVito and Arnold Schwarzenegger as long-lost twins . There have even been instances at least three are knownof genetically identical twins who were of different gender. In each case, one of the pair was born with only one X chromosome and no Y . (It takes a Y chromosome to make an embryo male.) Somehow, possibly because of the twinning process, that twin grew from cells that didn't have the Y There's still something about a Yalie-Smithie ` chromosome, and so had become a fe." wedding that gives me major goose bumps male by default . "None of the characteristics of identical twins correlate perfectly," Segal says . "Even among idening only the father's X. Could this differ- mother' s and some of the father ' s, or all ticals, there are differences in virtually ence in the two girls, which explained of the mother'sit didn' t seem to mat- everything ." why one of them had muscular dystro- ter . Yet the MZ girls as a group showed About twenty-five per cent of all idenphy, also be a cause of twinning? That more skewing than DZ girls . "Whatever tical twins show signs of mirror imagmight account for the excess of girls causes identical twinning, these studies ing a reversal of laterality that is most show that even though identical twins commonly detected when twins have among identical twins in general. Burn and a colleague, Judith Good- share the same genes, a genetic trait opposite-handedness . They may have opship, arranged to collect the placentas of does not have to be shared, " Burn says . posite hair whorls, opposite dental patall twin girls born in the Newcastle re- "The English language is misleading in terns, and opposite birthmarks and gion over a period of two years . DNA calling these twins identicalperhaps we moles . In its mildest form, mirror imagtests of the umbilical cords determined should use the German term eineiige, ing can be a matter of, say, on which side of the mouth the first tooth appears, but whether the twins were MZ or DZ. `one egg .' Burn had predicted what the survey "We still need to understand why it can also be more dramatic, as in rare showed : that identical-twin girls were monozygous twinning is so common in instances of twins whose organs have more likely to have skewed distribution humans and so exceptionally rare in other been found on the wrong side of their patterns of the X chromosome . The rest species, " he continues . "I now think that bodies . This condition appears in Siof his theory, however, posited that if one it has something to do with chronology . amese twinsa circumstance that has led twin had an excess of the mother ' s X, If you start messing around with the ex- most researchers to conclude that mirror then the other would mirror her by hav- act timing of ovulation, and fertilization, imaging is characteristic of MZ twins only, ing an excess of the father ' s that it was and implantation, then you may end up and especially those who have separated something about the tug-of-war that had creating the conditions that allow MZ later in development . It became an article caused the zygote to break apart in the twinning to occur . No single magic bul- of faith that twins who had oppositefirst place . What he and Goodship found let will explain everything . It may be a handedness must be identicaleven was that if one twin had an excess of the fundamental law of physics that the very when there were obvious differences in mother' s X, the other was just as likely to things that hold cells together will every eye and hair color . " It turns out that there have only the father's, or some of the now and again just come apart . So maybe is no difference between identical and

 CRIMINALITY IN GENES 57

fraternal twins in the frequency of lefthandedness, " Charles Boklage says . And he speculates that mirror imaging is just as common among fraternal twins as among identicals . "My own twin daughters---I used to think that they were monozygotic twins . I found out not long ago that they're not. They always looked practically identical, but there were impressionistic differences, and one day I discovered why . I held one child up in front of the mirror. Now, I ' m used to seeing my face in a mirror, but I wasn ' t used to seeing hers . What it did, of course, was reHer verse the asymmetries in her face ." eyes metamorphosed into the image of her sister' s. Twins of both kinds have a higher rate of left-handedness . Some scientists, like Luigi Gedda, the director of the Gregor Mendel Institute, in Rome, have suggested that all left-handed singletons may be survivors of a vanished-twin pair. Like twins, lefties are a puzzling minority whose origins have never been satisfactorily explained . Their brains develop differently from those of right-handers; for instance, right-handers tend to rely on the left hemisphere of their brain for language, whereas left-handers are more diffuse in their neurological organization. They are disproportionately likely to be alcoholics, psychotics, epileptics, and dyslexics, and to suffer from allergies and auto-immune disorders . Some evidence suggests that they are also more likely to be gifted and precocious, especially in mathematics, presumably because of their more enriched right hemisphere. Boklage believes that because " non-righthandedness" (a term he uses to include ambidexterity) is found at a higher rate not only in twins of both types but also in their family members, there must be a highly heritable factor that both forms of twinning have in common. After infancy, most identical twins are sufficiently distinct that they can easily be told apart by their parents and close friends. A few identical twins are so different that they don't resemble each other any more closely than ordinary siblings. Some researchers suspect that certain differences, particularly in behavior, result from their separating early in embryogenesis, and therefore coming to term in separate placentas . "There is evidence now from four studies that placentation does make a difference in twin resemblance, " says Richard J . Rose, a professor

of psychology and medical genetics at Indiana University, in Bloomington . Rose was speaking of behavioral characteristics. "There ' s no genetic variationthey're all monozygotic but our new data suggest that the early-separating twins are significantly less alike in many dimensions of personality . I don't know quite what that represents . It could be a consequence of differences in the in-utero environment, or it could simply be a consequence of the actual timing of the embryological splitting in the twinning process . We certainly do know that genetic differences are not the cause of these behavior differences, because they ' re all genetic replicas . " So environment does matter, after all. But what is it in the environment that affects us and makes us different from each other and different from the selves we might have been if genes alone controlled who we are? The differences between identical twins may turn out to be more informative than the similarities.

and environment acting in concert. For more than ten years, Dr . Thomas Mack, an epidemiologist at the University of California in Los Angeles, has been amassing a registry of adult twins with chronic diseases, and he has now identified more than fifteen thousand sets of twins with cancer, multiple sclerosis, and Lou Gehrig ' s disease, among others . According to Mack's data, a twin whose identical twin has multiple sclerosis is more than ten times as likely to get the disease as a fraternal twin whose sibling is afflicteda finding that demonstrates how powerfully genetic M .S . is. On the other hand, out of five hundred sets of twins in which melanoma occurred, there are only ten instances of both twins' having the disease, indicating that despite the genetic contribution of inherited traits such as light skin, an overwhelming environmental influence is at work. If you are an identical twin with breast cancer, which is known to be a familial disease, the chances that your twin will also get the disease is about five times NE of the most provocative questions in the entire nature-versus- as high as the average. Although the vast nurture debate concerns the influence of majority of the twins get the disease, the genes on criminal behavior . Twin stud- likelihood of getting breast cancer is ies in Nazi Germany confidently placed affected by the age of first menstruation: the heritability of criminality at between the younger you are, the higher your sixty and seventy per cent, and that be- chances for breast cancer in the future. came part of the rationale for sterilizing Mack found that not all identical twins criminals . Although more recent Ameri- get their period at the same time, so there can studies tell us that there is a genetic must be an environmental element trigconnection to the anti-social behavior of gering the hormones . Breast-cancer rates also rise with a woman's age very young children, they also point out that from adolesat her first pregnancy and with her age at menopause. In each cence on the environment plays an increasingly imporcase, environmental factors create differences between tant role . A Swedish adopidentical twins, and those diftion study in 1982 found that the rate of criminality in ferences influence the health of women who are equally adopted children was 2 .9 per cent when neither their biosusceptible to the disease. One of the most puzzling logical nor their adoptive parents had committed a crime ; the features of identical twins is their love figure rose to 6 .7 per cent if their adop- lives . When David Lykken and Matt tive parents were criminals and to 12.1 McGue, colleagues in the University of per cent if their biological parents were Minnesota Psychology Department, criminals . That might seem to be a dear conducted a study of fifteen hundred sets demonstration of the relative weight of of twins, they found that if one identical environment and genetics in determining twin had been divorced the chances that anti-social behavior . If both sets of par- the other twin had also been divorced ents were criminals, however, the chance were forty-five per cent, which is twentyof the child's being criminal as well was five per cent above the average divorce forty per cent . Together, genes and en- rate among Minnesotans. Lykken postuvironment appear to be several times as lates that genes influence divorce rates powerful as either force acting alone. through personality characteristics that Cancer also shows the effects of genes contribute to or detract from marital har-

 58

THE NEW YORKER, AUGUST 7, 1995

mony . Identical twins tend to have their first dates at about the same time and to date with equal frequency . Their sexual dysfunctions also tend to be very similar. They marry and begin having children at roughly the same points in their lives. The only real difference between identical twins lies in whom they choose to many. When Louis Keith was in medical school, in Chicago, he had a friend named Phyllis Markuson . They dated a couple of times but were never more than friends . On New Year's Eve of 1960, Phyllis bumped into Louis 's identical twin, Donald, at the ballet . Louis and Donald were as physically alike as identical twins can beboth of them darkeyed, long-lashed, full-lipped Latin-lover types . Donald, who was home from the Army on leave, was wearing his dress blues . " There was just something different about him, like a spark," Phyllis recalls . "They were both very good-looking. I think Louis has softer features, especially around the mouth . Donald is more angular. His jaw is more set and refined, which reflects his personality . But who knows what one sees in another personphysically, emotionally, or intellectuallythat makes him different from everybody else? " Phyllis was instantly smitten, and so was Donald . Immediately after the ballet, he called his brother and asked if he had any romantic inten-

tions toward Phyllis . "Most twins know that this area is a big, fat hot potato," Donald says . Louis told his brother that he liked Phyllis a lot but wasn't romantically interested . "Arc you sure?" Donald asked . "I don't want you to say ten years from now that I stole a girl you were interested in ." Donald and Phyllis have now been married for thirty-two years. "It's lucky Louis and I don ' t have the same taste in women, " Donald says . "It would be very difficult going through life wanting the same spouse . " Although twins competing for the same mate is a staple of television talk shows, the relationship between the Keiths and Phyllis is more typical . Two years ago, Lykken and Auke Tellegen, who is also a member of Minnesota's Psychology Department, reported the results of a study of a thousand middleaged twins and their spouses, which examined various widely held assumptions about mate selection . One such assumption is that people tend to choose mates similar to themselves . When the researchers compared sets of twins with the people they had chosen to marry, they found that there was a strong correlation between twins and their spouses in regard to height, physical attractiveness, education, and traditionalism but over all the twins and their spouses had too little in common to explain their selection of

EVERYTHING

MUST

each other . A second assumption is that we are all looking for someone special, someone who has certain qualities that we admire . Presumably, identical twins who have been raised together will have the same criteria; after all, they do tend to make very similar choices about clothes and furniture and vacations . But, when Lykken and Tellegen compared the spouses of identical twins, they resembled each other even less than the spouses resembled the twins they were married to ; they were hardly more alike than people who were married to unrelated individuals . Another surprise was the fact that when the twins were asked to evaluate their twin' s spouse, in more than half the cases they expressed merely neutral feelings . The spouses, for their part, returned the favor although one might have expected them to be at least somewhat attracted to the identical twin. And, while nearly twice as many husbands of identical twins approved of the other twin as did the wives of identical twins, even among the husbands twentyfive per cent were not attracted at all to the identical twin, and only thirteen per cent said that they "could have fallen for her myself." Among the wives, the figure was only seven per cent. "We are left with a curious and dis quieting conclusion," Lykken and Tellegen wrote . " Although most human choice behavior . . . reflects the characteristics of the chooser and of the choice, the most important choice of allthat of a mate seems to be an exception. Although we do tend to choose from among people like ourselves, another person who is remarkably like ourselves (our MZ twin) is not likely to be drawn to the same choice we make . " The authors concluded that human pairing is inherently random : " Romantic infatuation, we suggest, like imprinting, forms an initial bond almost adventitiously and then sustains it long enough, in most instances, for an enduring bond to be forged by the slower processes of learning and adaptation that result in compassionate love . " Several other recent twin studies have begun to look at what makes people happy. The findings so far point to two independent components of happiness one called extraversion, or positive emotionality, and the other called neuroticism, or negative emotionality . Curiously, the two traits appear to operate

 TWINS AND LOVERS 59

independently of each other and not, as might be expected, like a seesaw, in which the rise of one marks the decline of the other . A person who is free of negative moods is not necessarily happy, just as a person who never experiences positive moods is not necessarily unhappy . Some researchers have proposed that both extraversion and neuroticism arise out of particular situations, with positive experiences leading to positive emotionality, and negative experiences to negative emotionality. This is a basic environmentalist position: that an accumulation of pleasant experiences will endow a person with a happy nature, while unpleasant experiences have the opposite effect . Other researchers assert that both extraversion and neuroticism are genetically driven. To test these theories, in 1992 a team directed by Laura Baker, a professor of psychology at the University of Southern California, who heads the Southern California Twin Project, recruited some fifty sets of twins from the Los Angeles area, who ranged in age from sixteen to seventy-two . This twin study was done in conjunction with a family study comprising three generations of two hundred and twenty families . What the two studies found was that the more closely family members were related, the more similar they were in experiencing negative emotionality, that is, levels of this trait were more similar among DZ twins and siblings, who share, on the average, fifty per cent of their genes, than among grandparents and grandchildren, who share about twenty-five per cent of their genes . This finding suggests the presence of a marked genetic effect where neuroticism is concerned . Predictably, MZ twins were even more alike in this respect than DZ twins. But a different conclusion emerged when positive emotionality was measured. There the differences between MZ twins and DZ twins were not nearly so great, suggesting that shared experiences, instead of genetics, may influence levels of positive emotionality. Unhappy natures, as we might as well call those with negative emotionality, seem to pass through the generations in the genes of descendants . Yet happiness

"Rest assured, society will always prefer B-2 bombers ."

seems to be largely a gift of the environmentincluding the family environment . Although countless twin studies have now documented the paucity of influence that ordinary families have on children, Baker's study suggests that one thing a good family can do is to make a child happy.

0.hung about it, " David Lykkcn said talk as he up the phone . The state leg-

K., Senator, we'll have lunch and

islator on the other end of the line wanted to talk about Lykken' s proposal to require the licensing of parents . "We already have criteria for parents who adopt a child," Lykken told me as he sat in his office in Elliott Hall amid piles of books and research papers . Lykken, who is the head of the Minnesota twin registry, has gray hair and a Vandyke beard, and often talks in a quiet voice with his eyes closed, as if he were in a reverie. " Typically, the parents have to be mature, " he continued . "There has to be a father and a mother, and they have to have means of support, and they can 't be actively psychotic or seriously criminal . I say that our problems are not going to be

mitigated until we establish similar criteria for those who would produce children biologically . " Although even Lykken considers it very unlikely that his licensing plan will become law anytime soon, it is social engineering like that that causes people to be terrified of behavioral genetics . " A lot of social scientists are so scandalized by my proposals that they think I must be a Fascist, " Lykken says . " But I consider myself a political atheist. " I,ykken is a well-respected researcher who is known for taking authoritarian positions on public policy. He has just published a new book, "The Antisocial Personalities," in which he contends that what turns children into sociopaths is not genes but environment, and particularly the environment of a fatherless home and an illiterate mother . "It has become part of the received knowledge from twin studies in recent years that being reared together in the same home does not make siblings more alike, and that puzzles people," Lykken said. "The one real exception to that is socializationlearning how to avoid breaking the rules that are necessary for living together . We know

60

that criminality runs in families . Thirty per cent of arrestees have a brother already in the slammer . There's no question that the small group of chronic criminals who are responsible for sixty per cent or more of crime in this country tend to come from the same areas, the same social classes, the same families . When you look at the sorts of environments in which the typical juvenile delinquent grows up, you don 't need a study in order to be convinced that this is a pathogenic environment . It' s mind-boggling, the kinds of homes in which several million American adolescents are currently developing into little sociopaths." Lykken acknowledges that under his plan a disproportionate number of the unlicensed parents would be black, since he says that illegitimacy is some six times as high among blacks as among whites . "I think that this is the explanation for the difference between black and white crime, " he said. "One-eighth of the population is responsible for about half the violent crime . That is because such a high proportion of black males arc reared without fathers . So, if we could accomplish, by some magic, a reduction to a very low level of illegitimacy in both races, crime rates would plummet and would equalize between the races, and even 1 .Q differences would be smaller than they are . " Race and I .Q. are the bugbears of behavioral genetics, because of historically lower I .Q. scores among blacks . At the center of the I .Q controversy is Sandra Scarr, a former colleague of Lykken and Bouchard at the University of Minnesota, who is now a professor of psychology at the University of Virginia. Scan was one of the first researchers to conduct twin studies in minority racial populations. Brilliant and dauntingly prolific, much praised and often damned, Scarr has divided the academy because she has insisted on applying the insights of behavioral genetics to developmental psychology. Early in her career, Scarr began studying why so many black children did poorly on tests and in school achievement . She wondered whether it was a result of sociocultural disadvantage or genetically based racial differences . This was a forbidden question in 1967, when Scarr first started studying the records of black and white twins in the Philadelphia public schools . Two years later, the Berkeley psychologist Arthur Jensen stirred up a

LIZARD AND I
The early sun skins us . He's crept from beneath an ivy cover to stretch beside me, a twig in straw, rock wedge, sack of breath. The sun hazes the ground straight across, a trained spotlight casting all nearby in silhouette : field, poplar, ridgeline. I'm counting out days like coins, a hoard. I' m presuming nothing but this bright effusion outside the bicker and crush, the should and hurry. Our airwaves play Disaster other hours. I 've raised him five . He's seen me. No one cares. We 're alive at the start . The lavender nods with bees. SANDY SOLOMON

nasty debate by airing his theory, based on I .Q-test scores, that whites arc genetically superior to blacks in intelligence. Two years later, Richard J . Herrnstein, a Harvard psychologist, followed with an article in The Atlantic on I .Q, in which he disowned his previous environmentalist stance . (That article was widely discussed and became the basis of "The Bell Curve, " which was published last year, shortly after his death.) Having observed the public pillorying of Jensen and HerrnScar stein when their articles appeared, decided that if her data supported a substantial relationship between African ancestry and low intellectual skills she was prepared to leave the country . "There was no point in documenting yet again that on average blacks score lower than whites," Scarr says . "So I turned to testing black twins in order to look at the genetic and environmental variation within the black community. " One of the most striking findings of Scarr ' s early work on twins was that, while studies had shown a closer correlation between the I .Q scores of white identical twins than between those of white fratenals, the scores of both identical and fraternal black twins were similar. A set of black fraternal twins was less likely to range widely in intelligence; there was less likely to be one clever and one slow twin. Scan speculated that the differences were suppressed by the deprivations of the black children ' s environment. When she compared the I .Q

scores for white children at the bottom of the socioeconomic ladder, it turned out that environmental differences were just as important for them . Scarr' s findings suggested that inner-city black children (and white children in the same severely deprived circumstances) could have the genes for a higher intelligence than their environment permitted them to express . In 1972, soon after Scar- began teaching at the University of Minnesota (a move that seems almost inevitable for anyone interested in twin studies), she and one of her students, Andrew Pakstis, decided to test Jensen 's theory that intelligence differences between blacks and whites were genetic in origin . Scarr and Pakstis reasoned that if Jensen was right children of mixed black and white ancestry (as is the case with most African-Americans) would score higher on intelligence tests according to their proportion of white ancestry . But subsequent tests of Philadelphia twins found no relation between intellectualperformance scores and degree of white genetic background. Then Scarr, along with Richard A. Weinberg, a psychologist who worked with her at Minnesota ' s Institute of Child Development, went on to study a hundred and thirty black and mixed-race children, ranging in age from four to twelve, who had been adopted by welloff white families . The average I .Q of these children was 106, which was higher than the average white I .Q, and well

GI

above the average score of 90 for black children in the region . The earlier the children had been adopted, the better they fared . Scarr and Weinberg estimated that the scores of these earlyadopted children could be as much as twenty points higher than those of children of comparable age who had been reared in the black community . It seemed clear to the two researchers that environment influenced I .Q considerably: specifically, being reared and educated in the culture of the tests apparently made a large difference in achievement. At the same time, however, Scarr and Weinberg were studying a group of-white adolescents who had been adopted in early infancy by white families across the middle range of the socioeconomic spectrum . 'We were interested in seeing the cumulative effects of the family environment on I .Q scores, " Scarr says . "We were astonished at the results ." The hypothesis of the study was that if family environment mattered, then at the end of the child-rearing period adopted children should show the maximum effects of the advantages and disadvantages of the families that had taken them in. But what the Scarr-Weinberg adoptedI.Q adolescent study found was that the scores of the adopted adolescents bore no relation at all to those of the other children reared in the same family or to those of their adoptive parents . "We had expected the children reared in the same family to resemble one another more in IQ and personality than the young children in our transracial study, but we were dead wrong on both counts," Scarr says. The adopted young black children in the other study were more similar to their white siblings than the adopted adolescents in the new study were to their siblings, despite the fact that the adolescents had spent their entire childhood with their adopted families and were of the same race . "This was really interesting," Scarr says . "First, we were amazed that in an adolescent-adoption study we did not find any resemblances among people unless they were genetic relatives . This did not jibe with previous adoption literature or with our own transracial adoption study . We tried to figure out why adolescents bore so little resemblance to their adoptive families. " Scan found that children in the same family who were genetically unrelated were alike in their early years but grew to

be different over time . They became more like their biological parents, whom they didn't know, than like the adoptive parents who raised themnot only in social attitudes, vocational interests, and certain personality features, such as prejudice and rigidity of belief, but also in I .Q A follow-up study of the black and mixed-race children who were adopted into white homes found that by adolescence their I .Q scores had fallen to a point slightly above what would be the average for their racial and ethnic mixture in the area . It was similar to the progression of mental development observed in MZ and DZ twins : the two types start out life being almost equally alike but diverge as they pass through childhood, with the MZ twins becoming even more similar and the DZ twins going their separate ways. One lesson from the adopted-adolescent study seemed to be that genetic differences caused individuals to respond differently to similar rearing conditions. Another was that adopted children reared in rural or working-class homes did not differ significantly in their intelligence from adopted children reared by parents who were professionals . From these two findings, Scarr concluded that black and white children were essentially alike in their inherent intelligence and in their ability to achieve in schools, provided that they were given realistic opportunities to become part of the culture of the tests and of the schools . As long as children in a population were reasonably nurtured, Scarr observed, the individual

differences between them must be genetic . ' l 'herefore, efforts to improve intellectual or academic performance should concentrate on rescuing those who were living on the far margins of society who were genuinely deprived and were unable to gain the skills or knowledge needed to compete in the mainstream culture. Over the last fifteen years, Scarr has been refining a new theory of development, based largely on her conviction that environments do influence the intellects of young children . At early stages of life, she observes, enriched environments, such as day-care centers with stimulating programs, can boost a deprived child' s achievement . Even young children, however, are genetically programmed to create certain experiences for themselves . For instance, a smiling, gregarious baby is more likely to be cuddled and petted than a fussy and undemonstrative one . If these two dissimilar infants are siblings, their experiences of living in the same home can be quite different. As children mature, they gain more and more control over their environment, and actively select from the superabundance of opportunities and experiences those which conform to their genetic disposition . The distinction between genes and environment becomes less and less clear. " The dichotomy of nature and nurture has always been a bad one, not only for the oft-cited reasons that both are required for development, but because a false parallel arises between the two," Scarr wrote (in collaboration

"It's always poor you, isn 't it, Albert?"

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with her student Kathleen McCartney) in 1983 in the journal Child Development. "We propose that development is indeed the result of nature and nurture but that genes drive experience . Genes arc components in a system that organizes the organism to experience the world . " That is why MZ twins become more similar over time and DZ twins less so. Identical genes compel MZ twins to experience the world in a similar manner, thus reinforcing the similarities of their natures, whereas the genetic variation of DZ twins awakens different interests and talents, which inevitably pull the twins apart into more distinct individuals. Identical twins who have been reared separately may live in different families, and even in different cultures, but they evoke similar responses from their environment and are disposed by their natures to make similar choices and to build similar niches for themselves. In this school of thought, environment and genes do not represent separate, countervailing forces . To some, it may not even make sense to allocate percentages of heritability to, say, IO or personality traits, because after one reaches a certain age the environment is itself a heritable reflection of one' s genetic disposition. We make our environments, rather than the other way aroundthat is, as long as the environment we find ourselves in is not so impoverished or abusive that normal development cannot occur. "Good enough " parents, who provide an average environment to support development, will have the same effects on their children as "superparents, " who press upon their children every cultural advantage. "The statement that parents have few differential effects on children does not mean that not having parents is just as good as having parents, " Scarr said, in a 1991 presidential address to the Society for Research in Child Development . "It may not matter much that children have different parents, but it does matter that they have parent(s) or some supportive, affectionate person who is willing to be parent-like . To see the effects of having no parents (or parent surrogates), one would have to return to the orphanages of long ago . . . or see children trapped in crack houses of inner cities in the United States, locked in basements and attics by vengeful, crazy relatives. Really deprived, abusive, and neglectful environments do not support normal devel-

opment for any child . " Despite these caveats, Scarr' s speech was bitterly attacked by developmental psychologists who oppose her views, believing that they discourage efforts to improve the welfare of childrenespecially black children and fail to hold parents accountable for their children' s behavior . In fairness, Scarr concedes that parents can have important effects on children ' s motivation and self-esteem, but she insists that, beyond a minimum level of nurturing, they have little measurable impact on intelligence, interests, and personality. has tumult Tthewhichthreehad academe inonly refor last decades, has cently begun to affect politics and social policy, having captured a place in the popular culture . Although twin studies are rarely a conspicuous feature of policy debates, they do exert an underlying force, through the altered understanding of human development which they have engendered. Clearly, we have moved from being a country that believes in the equality of human nature and the effectiveness of government to being one that not only doubts the ability of government to improve people's lives but also denies the possibility of personal transformation. This shift in perspective is reflected in the retreat from the social activism of our recent past . One can look at the cuts in welfare and job-training programs, the attacks on affirmative action, and the erosion of tax support for public education as strong evidence that Americans no longer embrace the ideal that it is possible to change people substantially by improving their circumstances. Given the consequences, it's not surprising that there has been so much resistance to the portrait of human nature which has been drawn from twin studies . When we read about twins who were separated at birth and are reunited in middle age only to discover that in many respects they have become the same person, it suggests to us that life is somehow a charade: that we only seem to react conHE

assault of behavioral genetics,

sciously to events ; that the life experiences we think have shaped us are little more than ornaments or curiosities we have picked up along the way; and that the injunctions of our parents and the traumas of our youth which we believed to be the lodestones of our character may have had little more effect on us than a book we have read or a show we have seen on televisionthat, in effect, we could have lived another person' s life and still be who we are. And yet twins may have a different lesson to teach us . "A philosopher who was talking about twins said that maybe it' s freedom that makes identical twins different, " says Lindon J . Eaves, who is a human geneticist at the Virginia Commonwealth University School of Medicine . " Frankly, I don ' t believe that for a minute. It could be freedom that makes them alike. " Eaves runs one of the largest twin studies in the world, known as the Virginia 30,000, which surveys fifteen thousand twins and their relatives . He is also an Anglican priest, and has consequently reflected on the implications of behavioral genetics for the doctrine of free will. "I think freedom means something about the capacity of the human organism not to be pushed around by external circumstances, " he says . "I would argue that evolution has given us our freedom, that natural selection has placed in us the capacity to stand up and transcend the limitations of the environment. So I think the quest for freedom is genetic . I can ' t prove it, but I think it' s a way forward . " It may be threatening to see ourselves as victims of our genes, but that may be preferable to being victims of our environment. To a major extent, after all, our genes are who we are . A trait that is genetically rooted seems somehow more immutable than one that may have been conditioned by the environment. This seems to leave aside the possibility of free choice or even consciousness of choice at all . And yet people who are aware of their natures are constantly struggling with tendencies they recognize as ingrained or inborn. It makes little difference how such tendencies were acquiredonly how they are managed . If it is true that our identical clone can sort through the world of opportunity and adversity and arrive at a similar place, then we may as well see that as a triumph of our genetic determination to become the person we ought to be .