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The Nature vs. Nurture Controversy
George Howe Colt
IT'S NOT JUST BROWN EYES. YOUR INHERITANCE COULD ALSO INCLUDE INSOMNIA, OBESITY AND
OPTIMISM. YET SCIENTISTS ARE SAYING THAT GENES ARE NOT--QUITE--DESTINY.
IN THE DEBATE OVER THE RELATIVE POWER OF nature and nurture, there may be no more devout believers in nurture than new parents. As my wife and I, suffused with a potent mix of awe, exhaustion and ego, gazed down at our newborn daughter in the hospital, it was hard not to feel like miniature gods with a squirming lump of figurative putty in our hands. We had long believed that people could make the world a better place, and now we firmly believed that we could make this a better baby. At home our bedside tables were swaybacked by towers of well-thumbed parenting manuals. A black-and-white Stim-Mobile, designed to sharpen visual acuity, hung over the crib. The shelves were lined with books, educational puzzles and IQ-boosting rattles. Down the line we envisioned museum visits, art lessons, ballet. And if someone had tapped us on the shoulder and told us that none of this would matter that in fact we could switch babies in the nursery and send our precious darling home with any other new parents in the hospital, and as long as those parents weren't penniless, violent or drug addicted, our daughter would turn out pretty much the same., well, we would have thwacked that someone with a Stim-Mobile. DOES THE KEY TO WHO WE ARE LIE IN OUR genes or in our family, friends and experiences? In one of the most bitter scientific controversies of the 20th century--the battle over nature and nurture--a wealth of new research has tipped the scales overwhelmingly toward nature. Studies of twins and advances in molecular biology have uncovered a more significant genetic component to personality than was previously known. Far from a piece of putty, say biologists, my daughter is more like a computer's motherboard, her basic personality hardwired into infinitesimal squiggles of DNA. As parents, we would have no more influence on some aspects of her behavior than we had on the color of her hair. And yet new findings are also shedding light on how heredity and environment interact. Psychiatrists are using these findings to help patients overcome their genetic predispositions. Meanwhile, advances in genetic research and reproductive technology are leading us to the brink of some extraordinary--and terrifying--possibilities. PHOTO (COLOR): THRILL-SEEKING - Being a TV stuntman may have genetic roots. Certainly, Kent Karieva has been happily falling out of trees since early childhood. Now, 28, he sets himself on fire, crashes cars and sky-dives for a living. Twin studies gauge thrill-seeking to be 59 percent heritable; biologists have found that people who crave excitement often carry a longer version of one gene on chromosome 11. That gene influences the brain's response to dopamine, a chemical linked to pleasure and euphoria, whose release may be triggered by new, exciting-and risky-experiences. The moment the scales began to tip can be traced to a 1979 meeting between a steelworker named Jim Lewis and a clerical worker named Jim Springer. Identical twins separated five weeks after birth, they were raised by families 80 miles apart in Ohio. Reunited 39 years later, they would have strained the credulity of the editors of Ripley's Believe It or Not. Not only did both have dark hair, stand six feet tall and weigh 180 pounds, but they spoke with the same inflections, moved with the same gait and made the same gestures. Both loved stock car racing and hated baseball. Both married women named Linda, divorced them and married women named Betty. Both drove Chevrolets, drank Miller Lite, chain-smoked Salems and vacationed on the same half-mile stretch of Florida beach. Both had elevated blood pressure, severe migraines and had undergone vasectomies. Both bit their nails. Their heart rates, brain waves and IQs were nearly identical. Their scores on personality tests were as dose as if one person had taken the same test twice. Identical twins raised in different families are a built-in research lab for measuring the relative contributions of nature and nurture. The Jims became one of 7,000 sets of twins studied by the Minnesota Center for Twin and Adoption Research, one of half a dozen such centers in this country. Using psychological and physiological tests to compare the relative similarity of identical and fraternal twins, these centers calculate the "heritability" of behavioral traits the degree to which a trait in a given population is attributable to genes rather than to the environment. They have found, for instance, that "assertiveness" is 60 percent heritable, while "the ability to be enthralled by an aesthetic experience" is 55 percent heritable. Studies of twins have produced an impressive list of attributes or behaviors that appear to owe at least as much to heredity as to environment. It includes alienation, extroversion, traditionalism, leadership, career choice, risk aversion, attention deficit disorder, religious conviction and vulnerability to stress. One study even concluded that happiness is 80 percent heritable--it depends little on wealth, achievement or marital status. Another study found that while both optimism and pessimism are heavily influenced by genes, environment affects optimism but not pessimism. A third study claimed a genetic influence for the consumption of coffee but not, it seems, of tea. Critics accuse researchers of confusing correlation with causation, yet they admit the data suggest a strong genetic influence on behavior. Far less dear is how it all works. Is there a gene for becoming an astronaut? For enjoying symphonies? MOLECULAR BIOLOGISTS AROUND THE world are trying to answer such questions, searching for specific bits of DNA that may contribute to particular behaviors. In a small, windowless laboratory cluttered with bottles of chemicals, back issues of scientific journals and bags of sterile rubber gloves, there sits an aged Sears Kenmore Coldspot refrigerator. Inside are 21 plastic trays labeled with Magic Marker: College Students. Gay Men. Smokers. Shy Kids. Each tray contains 96 almond-size plastic vials. Each vial contains a smidgen of DNA. These are Dean Hamer's study subjects, his "people," as he refers to them. The refrigerator holds the blueprints for nearly 2,000 people, a database that Hamer, chief of Gene Structure and Regulation at the National Cancer Institute in Bethesda, Md., hopes will help him find the keys to why we smoke, why we get anxious, why we take risks. In what he describes as "a giant fishing expedition," Hamer is working his way through the human genome, tracking down any variation that may affect personality. PHOTO (COLOR): OBESITY - Student Paula Sylvester (left) weighed nine pounds at birth. At 26, she weighs 265. Her mother, Rosetta (right), weighs 215. Paula's grandmother reached 650 pounds. Twin studies show body mass to be 70 percent heritable. Biologists believe that in rare cases, obese people have a gene mutation that doesn't allow them to produce leptin, the hormone that tells the brain when to stop eating. That may be why, after Rosetta diets, the weight always returns. "Obesity is most likely due to a strong genetic push in a permissive environment," says David Allison of the Obesity Research Center in New York City. "That doesn't mean it's unalterable. It just means it's hard to change." Even for someone like Hamer, who admits to genetic propensities for both optimism and risk-taking behavior, it is a daunting prospect. The human body has 100 trillion cells, each equipped with a complete set of DNA distributed among 23 pairs of chromosomes. (DNA is microscopic yet sizable: If set out in a continuous strand, the DNA from a single cell would be six feet long.) Each cell's DNA is made up of some three billion nucleic components. Most of these seem to be nonfunctioning--"junk" DNA, biologists call them--but about 3 percent are working genes. The total number of working genes is believed to be 80,000, give or take 20,000. The task: to pinpoint the one-in-three-billion bit that might contribute to a particular behavior. Using DNA from groups of people with a high incidence of a certain trait, Hamer's lab has scanned hundreds of thousands of amplified strands of DNA, hoping to come across a variation common to those with the trait but absent in those without it. In 1993 his lab isolated a stretch of genes on the X chromosome that may be linked to male homosexuality. Three years later a gene on chromosome 11 was found to be consistently longer in people with a taste for novelty-seeking. Last year his lab linked anxiety to a gene involved in regulating levels of serotonin, a brain chemical affected by the antidepressant Prozac. The hoopla with which these discoveries have been greeted-"GAY GENE!" the headlines blared--has obscured the fact that other institutions have had mixed results when trying to replicate the findings. It has also made it seem as if single genes dictate specific behaviors. The reality is more complicated. Genes don't make men gay or children timid. They make proteins, which kindle complex neurological events. Biologists now believe that any given trait is shaped by a constellation of different genes. "From twin studies, we know that anxiety is 40 to 50 percent genetic," explains Hamer. "And from our data we know that the gene we isolated accounts for about 5 percent of the effect. We think there may be ten genes altogether that influence anxiety. But there may be a hundred or a thousand." In any case, he says, different people can have different combinations of those genes. People with just a few of those anxiety genes might feel nervous when they have to give a speech. Those with a few more might cringe when the phone rings. And those with a full complement might be so timid they rarely leave the house. If, as twin studies suggest, the heritability of most personality traits is about 50 percent, that still leaves 50 percent to the environment--an environment, say behavioral geneticists, whose influence works far differently from what we once thought. Until recently the family was assumed to be the crucible in which personality was formed. In fact, children may shape parents' behavior as much as parents shape theirs. "If you are genetically a responsive, happy infant, you are going to get different mothering than if you are an irritable or rejecting child," says University of Minnesota psychologist David Lykken. The older a child gets, the more power he has to mold his own environment. "People seek out experiences and environments," Lykken says, "that are compatible with their genetic nature." Studying adolescents adopted in infancy, University of Virginia psychologist Sandra Scarr was surprised to find that children adopted by well-educated, professional parents performed no better in school or on intelligence tests than children who had been adopted into working-class homes. "Providing children with super environments--private schooling, museum visits, lessons and so on--made no difference in their intelligence, adjustment or personality development," says Scarr. She concludes that if a child has "good enough parenting"--parents who aren't abusive or neglectful and provide a basic level of support--one set of parents is as good as another. The child will develop along paths set out by his genes. "It doesn't matter whether you take the kids fishing or to a Mozart concert," says Scarr. "As long as you do it with love, almost anything you do is going to be fine and functionally equivalent." But don't throw out those Spock and Brazelton manuals. Even the most zealous behavioral geneticists admit that genes are not-quite-destiny. "Depending on the other genes you inherit, and on your biology and on your in utero experience, the genes will have full force or less force," explains Harvard psychologist Jerome Kagan. Upbringing and circumstance may steer someone born with a predisposition for shyness to grow up into an agoraphobe-or a great poet. Someone with a propensity for aggression might become an Adolf Hitler, but he might become a General Patton. In any case, if genes are not commands but nudges, we can nudge back. We are the only animals on earth that can overrule our genes. And we do so constantly--whenever an alcoholic chooses not to drink or an obese person diets. How important is it to understand our genetic makeup? Does it matter that our anxiety can be traced to a snippet of nucleic matter and not to the time Mommy spanked us for spilling our juice? Psychologist Thomas Bouchard, director of the Minnesota twin study, believes it does: "A lot of books say you can do anything you want, but we have real doubts about that. It's not that you can't, but we suspect it's done at a cost." He suggests that we not push kids in directions they're not inclined toward. "The job of a parent," says Bouchard, "is to look for a kid's natural talents and then provide the best possible environment for them." PHOTO (COLOR): HOMOSEXUALITY - In 1993 biologists found a variation on the X chromosomes of 33 out of 40 pairs of brothers who were gay--evidence that genes might play a part in sexual orientation. (A comparable marker has not been found in lesbians.) Some denounced the findings as part of a homophobic conspiracy. Others said the genetic link showed homosexuality is natural. "It makes sense there might he a gene for this," says Michael Joseph Kay. McGrail (below, left, with Michael John Kay. McGrail, his partner of 10 years). "I'm left. handed. I'm also gay. I see them on the same level--that I was created this way." Bethesda psychiatrist Stanley Greenspan is one of a growing number of therapists who have incorporated the findings of behavioral genetics into their practice. "When a trait appears to be influenced by genes, people assume it's not changeable," he says. "Well, we can't change the genes, but we can change the way genes express themselves. We can change behavior." Greenspan works with children and their parents to rechannel a child's genetic propensities. For a sensitive girl, so fearful of new sights and sounds that at age three she still clung to her mother for dear life, Greenspan prescribed rhythmic rocking, as well as extra doses of imaginative play. The rocking soothed the child; the play helped her to gradually become more assertive. For an aggressive girl who pushed, punched and bit her classmates--"she so craved sensory input that she literally attacked her world," says Greenspan he designed games of dancing, shouting and beating on drums, but part of the exercise was to gradually go from fast and loud to slow and soft. "We gave her socially appropriate ways to satisfy her needs, but we taught her how to learn control." Greenspan's work illustrates an idea at the heart of behavioral genetics today--that heredity and environment are entwined, always reacting to and building on each other. "It's not a horse race between nurture and nature," he says. "It's a dance." ============================================================================== BY THE YEAR 2005, SCIENTISTS ARE EXPECTED to have mapped the entire sequence of the human genome. It will be many years before they know the functions of those 80,000 genes, but ways to take advantage of this information are already being developed. Within a few decades, people who feel ill will go to physician-geneticists who will run DNA scans to check the relevant genes, make pinpoint diagnoses and prescribe drugs targeted to precise genetic needs. This will be true for depression, phobias and life-threatening obesity, as well as for less crippling traits. Just as Mary Poppins had a magic bottle from which she dispensed spoonfuls of strawberry-flavored liquid to cure Michael's fussiness, parents may supply a pill to embolden their shy child before the school dance. Before my wife and I had our daughter, genetic counselors were able to tell us whether she had the genes for Down syndrome or Tay-Sachs disease. By the time she is ready to be a mother, genetic counselors will be able to tell her whether her fetus is genetically inclined toward depression or addiction. Such knowledge will surely lead to an ethical morass. "Where does it stop?" asks a character in The Twilight of the Golds, a recent play in which a couple decide to abort a fetus whose genes suggest it will be gay. "What if you found out the kid was going to be ugly, or smell bad, or have an annoying laugh, or need really thick glasses?" (Not such a far- fetched question, given that three quarters of young couples in a recent survey said they would choose abortion if told their fetus had a 50 percent chance of growing up to be obese.) The morass will become still stickier when we have the technology to tinker with the genes themselves. Clinical trials are already under way using gene therapy--the introduction of healthy new genes to counteract a mutated or missing gene--to repair disorders such as cystic fibrosis, cancer and AIDS. Most of us would welcome treatment that might eliminate these afflictions. But what about depression? Aggression? Timidity? By the time my daughter's grandchild is ready to give birth, prospective parents may design their children at the computer, scrolling through genetic menus to pick and choose, from their own DNA pools, specific gene clusters for height, weight and eye color, as well as for assertiveness, extroversion, happiness and so on. "The question is not whether the science will happen it will," says Princeton molecular geneticist Lee Silver. "The question is, will people use it?" Have we ever been able to restrain ourselves? The first person to study twins, 19th century anthropologist Francis Galton, finding that "nature prevails enormously over nurture," recommended breeding quotas to weed out the "unfit." The eugenics movement gathered force from 1907 to 1965, some 60,000 people were sterilized in the U.S. for such conditions as pauperism and "feeblemindedness"--and led to the extermination programs of the Third Reich, a horror that shadows the nature-nurture debate today. Critics of behavioral genetics say the risk of misuse should preclude further research. But that, journalist William Wright argues, "makes as much sense as rejecting electricity because of daytime television." Weighed against the potential benefits--might we end war by getting rid of aggressive genes?--is a Pandora's box of misuse. After the discovery of the so-called gay gene, for example, religious fundamentalists called for techniques to "correct that genetic defect." Caution is needed. "Do we know enough to know what we are changing?" asks Ronald Green, director of the Ethics Institute at Dartmouth. "Are we going to be wise enough to do it well, in such a way that we don't impoverish the future? In trying to avoid a Ted Kaczynski, might we destroy an Einstein?" A FEW NIGHTS AGO, WATCHING my daughter arrange her 37 Beanie Babies by color and species, I felt a shock of recognition--and glanced over at my wife, who wears the same expression when she arranges Shakespeare's plays in chronological order. My lump of putty is eight now, and I don't need a DNA scan to tell me she has inherited her mother's intelligence, her father's stubbornness, her grandfather's wit. The genes may be familiar, but the mix--thank heavens--is unique. Warts and all, she is exactly the child I want. When I look at her, I see a part of me. When I look at myself, it seems there's less of me than there once was. At a recent party, schmoozing with one last guest on my way out the door, I suddenly thought, I'm acting exactly like my father! Having spent my youth fighting to forge my own identity, I find, increasingly, that I resemble the very parent against whom I worked so hard to rebel: his social ease, his sense of humor--and, now that I am in my forties, his thinning hair and slight potbelly. Indeed, as I get older, I feel that instead of adding layers, I am shedding skins. In becoming more like my parents, I am becoming more myself. I am surprised but delighted that it all feels so comfortable--not an imprisoning but a homecoming. GENES AND VIOLENCE
No genetic link to criminality--other than being born male--has been proved. But that hasn't stopped people from making a connection. "The place to fight crime is in the cradle," says psychologist David Lykken, who has a controversial proposal: that biological parents be licensed. Lykken believes that a lot of crime is due to genetic predispositions for aggression and impulsiveness combined with incompetent parenting and the breakdown of the nuclear family. "We wouldn't let a crack addict, a teenager or a criminal adopt a child," he says. "Why not make the same minimal requirements for people having children biologically?" One Minnesota state representative is trying to write a version of Lykken's views into law, while detractors have called Lykken a fascist. Indeed, when it comes to the subject of violence, behavioral genetics is particularly prickly. In 1992 a lawyer tried to stage a conference on genetics and crime, but civil rights groups forced its postponement. When it was finally held three years later, the symposium was disrupted by protesters, and a handful of attendees signed a statement labeling the proceedings "racist pseudoscience." Critics say that linking genes and violence is blaming the victims and shifting the focus away from the real culprits: poverty, racism and unemployment. Brain research has shown that violent males tend to have low levels of the chemical serotonin, levels associated with depression, aggression and impulsivity--all traits with high heritabitity. But adoption studies show that children whose biological parents had trouble with the law have a far greater likelihood of having similar problems if their adoptive family had those problems too. Biology may contribute to antisocial behavior, the studies suggest, but environment helps tip the balance. In the same way, crime may be more pervasive in inner cities, not because of the genes of the people who live there but because inner cities tend to be fragmented, impoverished and racially polarized environments. Neurobiologist Evan Balaban sees Lykken's proposal as a throwback to the early 1900s, when 15 states had laws permitting the sterilization of criminals. "The predominantly academic people making these suggestions seem to be ignorant of what attempts have been made to solve these problems by people on the firing line, It might behoove them to put some effort into learning what the real issues are."

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