The Nature vs. Nurture Controversy
George Howe ColtLIFE MAGAZINE: SPECIAL REPORT
IT'S NOT JUST BROWN EYES. YOUR INHERITANCE COULD ALSO INCLUDE INSOMNIA, OBESITY ANDOPTIMISM. 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 devoutbelievers 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 feellike miniature gods with a squirming lump of figurative putty in our hands. We had long believedthat people could make the world a better place, and now we firmly believed that we couldmake this a better baby. At home our bedside tables were swaybacked by towers of wellthumbedparenting 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 onthe shoulder and told us that none of this would matter that in fact we could switch babies in thenursery and send our precious darling home with any other new parents in the hospital, and aslong as those parents weren't penniless, violent or drug addicted, our daughter would turn outpretty 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 oneof the most bitter scientific controversies of the 20th century--the battle over nature and nurture--awealth of new research has tipped the scales overwhelmingly toward nature. Studies of twins andadvances in molecular biology have uncovered a more significant genetic component topersonality than was previously known. Far from a piece of putty, say biologists, my daughter ismore like a computer's motherboard, her basic personality hardwired into infinitesimal squiggles ofDNA. As parents, we would have no more influence on some aspects of her behavior than wehad on the color of her hair. And yet new findings are also shedding light on how heredity andenvironment interact. Psychiatrists are using these findings to help patients overcome theirgenetic predispositions. Meanwhile, advances in genetic research and reproductive technologyare leading us to the brink of some extraordinary--and terrifying--possibilities.PHOTO (COLOR): THRILL-SEEKING - Being a TV stuntman may have genetic roots. Certainly, KentKarieva 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 geneon chromosome 11. That gene influences the brain's response to dopamine, a chemical linked topleasure 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 steelworkernamed Jim Lewis and a clerical worker named Jim Springer. Identical twins separated five weeksafter birth, they were raised by families 80 miles apart in Ohio. Reunited 39 years later, they wouldhave strained the credulity of the editors of Ripley's Believe It or Not. Not only did both have darkhair, stand six feet tall and weigh 180 pounds, but they spoke with the same inflections, movedwith the same gait and made the same gestures. Both loved stock car racing and hatedbaseball. 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 halfmilestretch of Florida beach. Both had elevated blood pressure, severe migraines and hadundergone vasectomies. Both bit their nails. Their heart rates, brain waves and IQs were nearlyidentical. Their scores on personality tests were as dose as if one person had taken the same testtwice.Identical twins raised in different families are a built-in research lab for measuring the relativecontributions of nature and nurture. The Jims became one of 7,000 sets of twins studied by theMinnesota Center for Twin and Adoption Research, one of half a dozen such centers in thiscountry. Using psychological and physiological tests to compare the relative similarity of identicaland fraternal twins, these centers calculate the "heritability" of behavioral traits the degree towhich a trait in a given population is attributable to genes rather than to the environment. Theyhave found, for instance, that "assertiveness" is 60 percent heritable, while "the ability to beenthralled by an aesthetic experience" is 55 percent heritable.Studies of twins have produced an impressive list of attributes or behaviors that appear to owe atleast as much to heredity as to environment. It includes alienation, extroversion, traditionalism,leadership, career choice, risk aversion, attention deficit disorder, religious conviction andvulnerability to stress. One study even concluded that happiness is 80 percent heritable--itdepends little on wealth, achievement or marital status. Another study found that while bothoptimism and pessimism are heavily influenced by genes, environment affects optimism but notpessimism. A third study claimed a genetic influence for the consumption of coffee but not, itseems, of tea. Critics accuse researchers of confusing correlation with causation, yet they admitthe data suggest a strong genetic influence on behavior. Far less dear is how it all works. Is there agene for becoming an astronaut? For enjoying symphonies?MOLECULAR BIOLOGISTS AROUND THE world are trying to answer such questions, searching forspecific bits of DNA that may contribute to particular behaviors. In a small, windowless laboratorycluttered with bottles of chemicals, back issues of scientific journals and bags of sterile rubbergloves, there sits an aged Sears Kenmore Coldspot refrigerator. Inside are 21 plastic trays labeledwith Magic Marker: College Students. Gay Men. Smokers. Shy Kids. Each tray contains 96 almondsizeplastic 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, adatabase that Hamer, chief of Gene Structure and Regulation at the National Cancer Institute inBethesda, Md., hopes will help him find the keys to why we smoke, why we get anxious, why wetake risks. In what he describes as "a giant fishing expedition," Hamer is working his way throughthe human genome, tracking down any variation that may affect personality.PHOTO (COLOR): OBESITY - Student Paula Sylvester (left) weighed nine pounds at birth. At 26, sheweighs 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 hormonethat tells the brain when to stop eating. That may be why, after Rosetta diets, the weight alwaysreturns. "Obesity is most likely due to a strong genetic push in a permissive environment," saysDavid 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 risktakingbehavior, it is a daunting prospect. The human body has 100 trillion cells, each equippedwith a complete set of DNA distributed among 23 pairs of chromosomes. (DNA is microscopic yetsizable: If set out in a continuous strand, the DNA from a single cell would be six feet long.) Eachcell's DNA is made up of some three billion nucleic components. Most of these seem to benonfunctioning--"junk" DNA, biologists call them--but about 3 percent are working genes. The totalnumber of working genes is believed to be 80,000, give or take 20,000. The task: to pinpoint theone-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 hasscanned hundreds of thousands of amplified strands of DNA, hoping to come across a variationcommon to those with the trait but absent in those without it. In 1993 his lab isolated a stretch ofgenes on the X chromosome that may be linked to male homosexuality. Three years later a geneon 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 brainchemical 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 thefindings. It has also made it seem as if single genes dictate specific behaviors. The reality is morecomplicated. Genes don't make men gay or children timid. They make proteins, which kindlecomplex neurological events. Biologists now believe that any given trait is shaped by aconstellation of different genes. "From twin studies, we know that anxiety is 40 to 50 percentgenetic," explains Hamer. "And from our data we know that the gene we isolated accounts forabout 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 havedifferent combinations of those genes. People with just a few of those anxiety genes might feelnervous when they have to give a speech. Those with a few more might cringe when the phonerings. 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 stillleaves 50 percent to the environment--an environment, say behavioral geneticists, whoseinfluence works far differently from what we once thought. Until recently the family was assumedto be the crucible in which personality was formed. In fact, children may shape parents' behavioras much as parents shape theirs. "If you are genetically a responsive, happy infant, you are goingto get different mothering than if you are an irritable or rejecting child," says University ofMinnesota psychologist David Lykken. The older a child gets, the more power he has to mold hisown environment. "People seek out experiences and environments," Lykken says, "that arecompatible with their genetic nature."Studying adolescents adopted in infancy, University of Virginia psychologist Sandra Scarr wassurprised to find that children adopted by well-educated, professional parents performed nobetter in school or on intelligence tests than children who had been adopted into working-classhomes. "Providing children with super environments--private schooling, museum visits, lessons andso on--made no difference in their intelligence, adjustment or personality development," saysScarr. She concludes that if a child has "good enough parenting"--parents who aren't abusive orneglectful and provide a basic level of support--one set of parents is as good as another. Thechild will develop along paths set out by his genes. "It doesn't matter whether you take the kidsfishing or to a Mozart concert," says Scarr. "As long as you do it with love, almost anything you do isgoing to be fine and functionally equivalent."But don't throw out those Spock and Brazelton manuals. Even the most zealous behavioralgeneticists 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 someoneborn with a predisposition for shyness to grow up into an agoraphobe-or a great poet. Someonewith a propensity for aggression might become an Adolf Hitler, but he might become a GeneralPatton.In any case, if genes are not commands but nudges, we can nudge back. We are the onlyanimals on earth that can overrule our genes. And we do so constantly--whenever an alcoholicchooses not to drink or an obese person diets.How important is it to understand our genetic makeup? Does it matter that our anxiety can betraced to a snippet of nucleic matter and not to the time Mommy spanked us for spilling ourjuice? Psychologist Thomas Bouchard, director of the Minnesota twin study, believes it does: "A lotof books say you can do anything you want, but we have real doubts about that. It's not that youcan't, but we suspect it's done at a cost." He suggests that we not push kids in directions they'renot inclined toward. "The job of a parent," says Bouchard, "is to look for a kid's natural talents andthen provide the best possible environment for them."PHOTO (COLOR): HOMOSEXUALITY - In 1993 biologists found a variation on the X chromosomes of33 out of 40 pairs of brothers who were gay--evidence that genes might play a part in sexualorientation. (A comparable marker has not been found in lesbians.) Some denounced thefindings as part of a homophobic conspiracy. Others said the genetic link showed homosexualityis 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 alsogay. 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 haveincorporated the findings of behavioral genetics into their practice. "When a trait appears to beinfluenced by genes, people assume it's not changeable," he says. "Well, we can't change thegenes, 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 asensitive girl, so fearful of new sights and sounds that at age three she still clung to her mother fordear life, Greenspan prescribed rhythmic rocking, as well as extra doses of imaginative play. Therocking soothed the child; the play helped her to gradually become more assertive. For anaggressive girl who pushed, punched and bit her classmates--"she so craved sensory input thatshe literally attacked her world," says Greenspan he designed games of dancing, shouting andbeating on drums, but part of the exercise was to gradually go from fast and loud to slow andsoft. "We gave her socially appropriate ways to satisfy her needs, but we taught her how to learncontrol."Greenspan's work illustrates an idea at the heart of behavioral genetics today--that heredity andenvironment are entwined, always reacting to and building on each other. "It's not a horse racebetween nurture and nature," he says. "It's a dance.
BY THE YEAR 2005, SCIENTISTS ARE EXPECTED to have mapped the entire sequence of the humangenome. It will be many years before they know the functions of those 80,000 genes, but ways totake advantage of this information are already being developed. Within a few decades, peoplewho 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 truefor depression, phobias and life-threatening obesity, as well as for less crippling traits. Just as MaryPoppins had a magic bottle from which she dispensed spoonfuls of strawberry-flavored liquid tocure Michael's fussiness, parents may supply a pill to embolden their shy child before the schooldance.Before my wife and I had our daughter, genetic counselors were able to tell us whether she hadthe 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 towarddepression or addiction. Such knowledge will surely lead to an ethical morass. "Where does itstop?" asks a character in The Twilight of the Golds, a recent play in which a couple decide toabort a fetus whose genes suggest it will be gay. "What if you found out the kid was going to beugly, or smell bad, or have an annoying laugh, or need really thick glasses?" (Not such a farfetchedquestion, given that three quarters of young couples in a recent survey said they wouldchoose abortion if told their fetus had a 50 percent chance of growing up to be obese.) Themorass 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 tocounteract 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 aboutdepression? Aggression? Timidity?By the time my daughter's grandchild is ready to give birth, prospective parents may design theirchildren at the computer, scrolling through genetic menus to pick and choose, from their ownDNA 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 centuryanthropologist Francis Galton, finding that "nature prevails enormously over nurture,"recommended breeding quotas to weed out the "unfit." The eugenics movement gathered forcefrom 1907 to 1965, some 60,000 people were sterilized in the U.S. for such conditions as pauperismand "feeblemindedness"--and led to the extermination programs of the Third Reich, a horror thatshadows the nature-nurture debate today. Critics of behavioral genetics say the risk of misuseshould preclude further research. But that, journalist William Wright argues, "makes as much senseas rejecting electricity because of daytime television."Weighed against the potential benefits--might we end war by getting rid of aggressive genes?--isa Pandora's box of misuse. After the discovery of the so-called gay gene, for example, religiousfundamentalists called for techniques to "correct that genetic defect." Caution is needed. "Do weknow enough to know what we are changing?" asks Ronald Green, director of the Ethics Instituteat Dartmouth. "Are we going to be wise enough to do it well, in such a way that we don'timpoverish 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 whenshe arranges Shakespeare's plays in chronological order. My lump of putty is eight now, and Idon't need a DNA scan to tell me she has inherited her mother's intelligence, her father'sstubbornness, her grandfather's wit. The genes may be familiar, but the mix--thank heavens--isunique. 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 thereonce was. At a recent party, schmoozing with one last guest on my way out the door, I suddenlythought, I'm acting exactly like my father! Having spent my youth fighting to forge my ownidentity, I find, increasingly, that I resemble the very parent against whom I worked so hard torebel: his social ease, his sense of humor--and, now that I am in my forties, his thinning hair andslight potbelly. Indeed, as I get older, I feel that instead of adding layers, I am shedding skins. Inbecoming more like my parents, I am becoming more myself. I am surprised but delighted that itall feels so comfortable--not an imprisoning but a homecoming.GENES AND VIOLENCENo genetic link to criminality--other than being born male--has been proved. But that hasn'tstopped people from making a connection. "The place to fight crime is in the cradle," sayspsychologist 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 andimpulsiveness 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 makethe same minimal requirements for people having children biologically?"One Minnesota state representative is trying to write a version of Lykken's views into law, whiledetractors 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 ongenetics and crime, but civil rights groups forced its postponement. When it was finally held threeyears later, the symposium was disrupted by protesters, and a handful of attendees signed astatement labeling the proceedings "racist pseudoscience."Critics say that linking genes and violence is blaming the victims and shifting the focus away fromthe real culprits: poverty, racism and unemployment. Brain research has shown that violent malestend to have low levels of the chemical serotonin, levels associated with depression, aggressionand impulsivity--all traits with high heritabitity. But adoption studies show that children whosebiological parents had trouble with the law have a far greater likelihood of having similarproblems if their adoptive family had those problems too. Biology may contribute to antisocialbehavior, the studies suggest, but environment helps tip the balance. In the same way, crime maybe more pervasive in inner cities, not because of the genes of the people who live there butbecause 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 15states had laws permitting the sterilization of criminals. "The predominantly academic peoplemaking these suggestions seem to be ignorant of what attempts have been made to solve theseproblems by people on the firing line, It might behoove them to put some effort into learning whatthe real issues are."
View Less >>