The Washington Post Magazine


The Mysteries of Twins
(Page Three)
The Washington Post
Sunday, January 11, 1998

Geneticist Lindon J. Eaves
Geneticist Victor McKussick
(David Barry/The Post)




McKUSICK

DISAGREED

WITH THOSE

WHO WANTED TO SAY

THERE IS

NO

GENETIC

BASIS

FOR INTELLIGENCE.

"THAT'S

LIKE

DEFYING

GRAVITY,"

HE SAYS.





Anne Clark, born Anne Collins, believes in God and free will, but also that chance can affect how you exercise free will. How else to explain her own history?

Anne and her identical twin, Lynne Weindel, grew up middle-class in Fairfax County, like Sharon and Sherry Clark. They were quiet and mild-mannered girls with freckles and red corkscrew hair, neither deeply reflective nor entirely untroubled -- average students who played together and shared friends and looked very similar. There was no good twin/bad twin dichotomy that anyone noticed, and the proper young ladies didn't stage any mistaken-identity pranks because they didn't think they looked alike. "We thought we'd get caught," says Lynne, mildly.

When the girls were 8, their father died suddenly from the complications of a gallstone operation. Lynne's memory of the event is faint. So is Anne's, but she is convinced it was a defining moment, perhaps the defining moment, of her life. "I remember waiting for my mom at our aunt's house, playing in their basement," she says. "I remember my brother crying, the emptiness and fear. It was numbing." The next year the girls were split into separate classes at Laurel Ridge Elementary in Fairfax. Lynne loved her second-grade teacher; Anne recalls being lonely.

Together they attended Shepherd College in West Virginia, but Anne dropped out after the second year to marry a part-time DJ named Mike Clark, whom she'd met when he was lip-synching a Van Halen song at a talent show.

Lynne got her degree in education and became a teacher at a day-care center.

Anne had a daughter, broke up with Mike after two years, cobbled together jobs and living arrangements until Mike and she got back together in 1995. Their daughter, now 7, has been diagnosed with attention deficit disorder, and Anne blames herself. "They say ADD is genetic, but it could be the environment, too. They just don't know much about it." She fiddles with her hair. She's sitting in the living room of her twin's Herndon town house. Where she stayed for an entire year once, while she was getting her life back together.

What accounts for the different choices? "I think I was always more impulsive than Lynne. More rebellious."

Was her rebelliousness native or learned? "In school, it seemed like she always had a friend and I was pretty much on my own. I needed a male in my life more than Lynne did."

Genes? Environment? A distorted mirror of the past? Anne Clark shrugs. "Those were the choices I made in my life," she says. "My choices."

When it comes to sorting through the intricacies of environment, genes and free will, one could have no better guide than Victor McKusick, whose cluttered office at Johns Hopkins is down the hall from the bulletin board with the satirical chromosome map. At 76, McKusick is the father of medical genetics, a biological categorizer extraordinaire whose contribution to genetics recently won him the highest honor in American science, the 1997 Albert Lasker Award. McKusick, as an admirer noted recently, seems to have had his career mapped out "from the very instant he became unicellular." McKusick is not only a cloner of DNA, but also, a clone. He's an identical twin.

A few years ago, McKusick was on a government ethics panel that met to discuss The Bell Curve. The book troubled many scientists, who felt it misused behavior genetics data in the interest of making a political point. McKusick signed a statement condemning the book, but in the preceding discussion he disagreed with panel members who wanted to say there was no genetic basis for intelligence. "That's like denying gravity," McKusick says. His own experience contributed to this conviction. Born on a Maine dairy farm in 1921, Victor and his twin, Vincent, both displayed remarkable brain power that enabled them to climb to the peaks of their respective professions. At 13, Victor was treated at Massachusetts General Hospital for an infected arm, and emerged several weeks later with the certainty that he would make his career in medicine. Vincent, who managed to stay out of the hospital as a kid, went on to Harvard Law School and eventually became chief justice of the Maine Supreme Court.

In both men one senses a polite but adamantine intelligence and a genius for organization. They are similar in height and weight -- about six feet, 180 pounds; similar in their soft-spoken but intense speech patterns and mannerisms. There are the usual share of serendipities: On a recent summer vacation in Nova Scotia, Victor developed a dental abscess. His brother, sailing up from Maine to join him, had to make an emergency shore call after developing the same problem.

Still, "there were differences in the two of us right from the beginning," says Victor. All through their childhood, Vincent usually took the lead, Victor usually followed. As to what accounts for that, Vincent defers to his brother, and Victor is too careful a scientist to venture a guess. Perhaps it had to do with the random movement of the neurons as they migrated to the brain stems of the weeks-old McKusick fetuses. Perhaps it was a "runting effect" -- the tendency of one identical twin to suck up womb nutrition to the detriment of the other. Or perhaps the differences in identical twins can be explained by the expectations of parents and siblings, desperate to find some way to tell the twins apart. In any case, "a geneticist is really as much interested, if not more interested, in the differences between identical twins as they are in the similarities," says McKusick. "The differences give you information on non-genetic factors."

Behavior genetics -- concerned as it is with differences in sensitive matters such as intelligence, personality and sexuality -- is still a controversial field, even if its taint-by-association with eugenics has faded. Over the years, behavior geneticists have grown more careful and conscious of their biases. They are increasingly interested not so much in highlighting the power of biology as in studying the interaction of genes and environment -- the hyphen in the nature-nurture debate. They puzzle, for example, over issues like this: Since it's well known that there is a large genetic component to schizophrenia, why is it that only 50 percent -- and not all -- of the identical twins of schizophrenics are schizophrenics themselves? If they are clones, what makes them so different?

On a recent afternoon in the auditorium of the Virginia Institute for Psychiatric and Behavioral Genetics, a research center at Virginia Commonwealth University in downtown Richmond, psychiatric geneticist Kenneth Kendler is training 30 new interviewers for a survey on stress and coping. In 1979, the same year Bouchard began his path-breaking work in Minnesota, researchers at VCU began assembling some 15,000 fraternal and identical twin pairs in the Virginia Twin Registry, one of the world's largest data banks of its kind. Kendler is co-director of the institute along with Lindon Eaves. For the current study, some 5,500 twins will be interviewed for several hours each about such dicey topics as religious convictions, family tragedies, drug use and mental illness. The researchers will measure the similarity of the answers each twin gives, then compare the degree of sameness in identical twins with that of fraternal twins. Using complex statistical models, they intend to assess the genetic component of different behaviors and environmental risk factors that can send one twin over the edge into clinical depression, for example, while the other copes.

Critics of such studies contend that behavior geneticists confuse correlations with causation and underestimate the effects of environment. Plant grass seed in a desert and a meadow, these critics say, and the seed in one will thrive while the seed in the other perishes, whether or not the seeds are equally good. "Two twins who look like Christie Brinkley are going to have more similar life experiences than two who look like Roseanne," says Joseph L. Graves, a developmental biologist at Arizona State University West in Phoenix. Some critics also contend that the behavior geneticists bend statistics toward nature over nurture. "There's an old joke about statistics that says with two points I can draw you an elephant, with three points I can make it sing," says Andrew Futterman, a psychologist at Holy Cross College in Massachusetts.

The practitioners of behavior genetics say their aim is to discern differences, not to prove an ideological point. In the current survey, Kendler and Carol Prescott, another geneticist, are trying to get at some of the vagaries of genetic and social stress underlying particular types of drug abuse. "Why does somebody use alcohol and somebody else marijuana, and somebody else cocaine?" asks Kendler, a wiry man with a long gray beard that he strokes absent-mindedly while speaking. "Is it a matter of economics? Of drug availability? Of very specific brain receptors for certain drugs?"

(continued on Page Four)

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