Twins: And What They Tell Us About Who We Are (18 page)

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Authors: Lawrence Wright

Tags: #Family & Relationships, #Siblings, #Science, #Life Sciences, #Genetics & Genomics, #test

BOOK: Twins: And What They Tell Us About Who We Are
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In psychological literature, the child is known as John/Joan. It was Money's belief at the time, which John/Joan reinforced, that gender differences were not inborn, they are created by the environment. "You were born with something that was ready to become your gender identity," he wrote in a later account. "You were wired but not programmed for gender in the same sense that you were wired but not programmed for language. Your gender identity couldn't differentiate as male or female without social stimulation any more than the undifferentiated gonad you started out with could have become testicles or ovaries without the stimulation of your Y or X chromosomes." The varying expectations that family and society place on boys and girls, Money believed, cause them to differentiate into masculine and feminine roles. The twins offered an intriguing opportunity to test this theory.
There is, unfortunately, very little in the literature about the unaffected boy twin, who seems to have developed as a normal heterosexual man. As for John/Joan, Money was able to report that by the age of five, "the little girl already preferred dresses to pants, enjoyed wearing her hair in ribbons, bracelets and frilly blouses, and loved being her daddy's little sweetheart." From birth, John/Joan had always been the dominant twin, but now her dominance expressed itself in a stereotypically feminine manner, and she fussed over her brother "like a mother hen," according to the mother. "Although this girl is not yet a woman," Money wrote in 1975, ''her record to date offers convincing evidence that the gender identity gate is open at birth." We are born sexually neutral, in other words, and are pushed by social forces into one camp or the other. "This dramatic case,"
Time
magazine reported in 1973, "provides strong support for a major contention
 
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of women's liberationists: that conventional patterns of masculine and feminine behavior can be altered. It also casts doubt on the theory that major sex differences, psychological as well as anatomical, are immutably set by the genes at conception."
Was John/Joan an exception to the genetic argument? A rebuttal? How could behavioral geneticists account for such an anomaly? In 1980 BBC television sought to update the story of John/Joan. Money agreed to participate, and then withdrew after psychiatrists working on the case reported that John/Joan was having "considerable ambivalence" over her role as a female.
In 1997 Milton Diamond at the Department of Anatomy and Reproductive Biology, University of Hawaii-Manoa, and H. Keith Sigmundson, a psychiatrist at the Ministry of Health in Victoria, British Columbia, revisited the John/Joan saga. They were aided by the fact that Dr. Sigmundson supervised the therapists involved in the case. They learned that, contrary to the impression Money gavethat Joan was a rather typical little girleven as a young child she declared that she wasn't a girl. She would rip off dresses her mother tried to put on her, and she refused to mimic putting on makeup and lipstick like her mother; instead, she put on shaving cream and pretended to shave. She knew instinctively that something was wrong. Later, John/Joan recalled: "I looked at myself and said I don't like this type of clothing. I don't like the type of toys I was always being given. I like hanging around with the guys and climbing trees and stuff like that and girls don't like any of that stuff. I looked in the mirror and [saw] my shoulders [were] so wide, I mean there [was] nothing feminine about me . . . that was how I figured it out. [I figured I was a guy] but I didn't want to admit it. I figured I didn't want to wind up opening a can of worms."
 
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Each year, the twins were taken to Johns Hopkins to be examined by the doctors. The children were made to stand naked for inspection by the clinicians and were encouraged to inspect each otheran experience that John/Joan's twin recalls with outrage. At the age of thirteen, Joan ran away from the hospital. She was eventually found hiding on the roof of a nearby building.
When puberty arrived, Joan's problems with peers became unbearable. She was friendless. Girls teased her cruelly, especially when she repeatedly tried to urinate standing up in the girls' bathroom. Sometimes, Joan went to the boys' bathroom. Eventually she was expelled from school when she retaliated against her tormentors forcibly. She became suicidal. Finally she announced her intention to become a boy. Her father then broke down and admitted what had happened fourteen years before. "All of a sudden everything clicked," John/Joan recalls.
The child insisted on receiving male hormone injections. He received a mastectomy, and a phallus was surgically constructed. John soon became accepted as a boy as Joan had never been as a girl. He worked out with weights. At the age of sixteen, he acquired a windowless van with a bed and a bar. "He wanted to lasso some ladies," Diamond told the
New York Times
. Sexual relations were problematic, but possible. John married at twenty-five and adopted his wife's children. According to Diamond, John is happy with life as a man. Certainly his case will no longer be cited as evidence that environment controls sexual identity; indeed, the story of John/Joan will probably be recorded as an example of the forcefulness of nature, which powerfully exerts itself even when good intentions conspire to deceive it.
There may be an important difference between identical twins who separated early in embryogenesis (and
 
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therefore came to term in separate placentas) and those who separated later. "There is evidence now from four studies that placentation does make a difference in twin resemblance," says Richard Rose, a psychologist at Indiana University in Bloomington. "There's no
genetic
variationthey're all monozygoticbut the early separating twins are significantly less alike for many dimensions of personality. Neither I nor anyone else knows quite what that represents. It could be a consequence of differences in the in utero environment, or it simply could 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."
The most dramatic examples of late-separating twins, of course, are conjoined twins, who are notorious for their conflicting personalities. Chang and Eng Bunker occasioned the term Siamese twins because of their birth in 1811 in Siam (modern Thailand). Joined at the abdomen, the Bunker brothers toured the United States with the P. T. Barnum circus, eventually becoming quite wealthy and retiring to a farm in North Carolina. There they married two sisters and succeeded in fathering twenty-two children, none of whom were twins. Chang had a reputation for an explosive temper, and he became an alcoholic when his health began to fail. Eng, the calmer brother, was a lifelong teetotaler. He was so alarmed by his brother's drinking that he sought to be surgically separated, but no doctor would attempt the operation. Masha and Dasha, a pair of Russian twins born during the Second World War, have a single lower body and an upper body that is entirely separate. They spent their childhood in vigorous, some-times violent disagreements, warring over their differ-
 
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ing tastes in music, television, and exercise. Abigail and Brittany Hensel, who were born in 1990, are unusual even among conjoined twins, having only two legs and an undivided torso (only four such sets have been recorded). Although one is a hearty eater, and the other picks at her food, so far they don't seem to have developed the oppositional personalities that have characterized other well-known conjoined sets.
About twenty-five percent of identical twins show features of mirror imaging, a reversal of laterality that is most commonly detected when twins have opposite-handedness. In its mildest form, mirror imaging can be a matter of which side of the mouth the first tooth appears on, but it can also be more dramatic, as in twins whose organs are actually found on the wrong side of their bodies. This condition appears frequently in conjoined twins, a circumstance that has led most researchers to conclude that mirror imaging is characteristic of late-separating MZ twins only. It became an article of faith that twins who had opposite-handedness must be identical, even when there were obvious differences in eye and hair color. "It turns out that there is no difference between identical and fraternal twins in the frequency of left-handedness," says Charles Boklage. "The mirror image thing is a cute idea that came from the 1920s, before there was blood typing. Now, there is such a thing as mirror imaging. My own twin daughtersI used to think that they were monozygotic twins. I found out not long ago they're not. They always looked practically identical, but there were impressionistic differences. One day I discovered why. I held a 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 was reverse the asymmetries in her face." Her face metamorphosed into the image of her sister. Boklage contends
 
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that mirror imaging is just as frequent in DZ twins, such as his daughters, as it is with MZs.
Twins of both kinds have a higher rate of left-handedness, and some scientists, such as Luigi Gedda, the director of the Mendel Institute in Rome, have suggested that 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 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 more likely to be alcoholics, psychotics, epileptics, dyslexics, and to suffer from allergies and autoimmune disorders. Some evidence suggests they tend to be gifted and precocious, especially in mathematics. The higher rate of non-right-handedness among twins is often accounted for as "birth stress," but that wouldn't explain why there are more lefties among their non-twin relatives. Nancy Segal thinks that left-handedness may have two causes, birth trauma and late separation, that give rise to separate problems or talents. Boklage believes that because non-right-handedness (a term he uses to include ambidexterity) is found at a higher rate in twins of both types and their family members, there must be a highly heritable factor that both forms of twinning have in common.
Few studies have examined the phenomenon of mirror imaging, and those that do have largely failed to show a significant difference between opposite-handed pairs. Boklage, however, decided to examine the data for schizophrenia in identical twins, a major battlefield in the war against environmentalists. If you are a twin who has schizophrenia, the chances that your identical
 
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sibling has it as well are about thirty to fifty percent, according to various studies. For a fraternal twin, the odds fall to about ten percentabout the same as for a non-twin sibling. Obviously, there is a genetic contribution, even if it is modest. But if schizophrenia is inherited, why don't both twins suffer from it simultaneously? Perhaps there are certain environmental triggers that set off the disease in a vulnerable individual, for instance, one twin might experience a trauma or a stressful event that the other does not. The problem with this appealing theory is that nothing in the environment has ever been demonstrated to cause schizophrenia. Boklage noticed that if one looked only at right-handed twins who are schizophrenic, the chances of an identical sibling suffering from schizophrenia jumped to ninety-two percent. When one member of a twin pair is schizophrenic and the other is not, one or both of them is left-handed. Moreover, left-handed schizophrenics tended to be less severely ill than the right-handers.
In 1990 the Keith twins (along with Alexander Golbin, an assistant professor of psychiatry at the University of Illinois, and Irene Golbin, his research assistant) surveyed twenty-seven mirror-image MZ twins, fifty-three non-mirror-image twins, and twenty-four DZ twins (four of whom showed mirroring) at the annual Twins Day Festival in Twinsburg, Ohio. The researchers were particularly interested in finding certain sleep irregularities, such as bedwetting, teeth grinding, apnea, insomnia, sleepwalking, and nightmares. They discovered startling differences among the mirror-image "identicals," who seemed to be quite polarized in their sleeping habits, compared with the non-mirroring MZ and the DZ group. The researchers postulated that there may be a psychological mirroring that goes along with the physical, each
 
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reflecting a profound biological polarization. It could possibly explain opposing tendencies in personality, sex orientation, and susceptibility to disease.
Behavior geneticists have spent the last thirty years waging war against the environmentalist belief that people are fundamentally alike, and are made different only by their families, their schooling, the traumas of lifeby their environments, in other words. Now, after decades of persuasive twin studies showing how similar identical twins are to each other, even when they have been raised in separate families, behavior geneticists must face the question of why identical twins should differ at
all
. They have the same genes, and studies have shown again and again that the influence of common family background on intelligence, personality, and behavior is modest to negligible for most measurable traits. And yet identical twins do differ from each other, often quite stunningly. For instance, several studies have shown that an identical twin who is homosexual stands a fifty percent chance of having a gay twin. But if homosexuality is genetically determined, why wouldn't the chances be closer to one hundred percent? Does the environment play a role after all? And if so, how? What is it in the environment that affects us and makes us different from each other, and different, in some respects, from ourselves, the selves we might have been if genes alone control who we are? The differences in identical twins may turn out to be more informative than their similarities.

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