One of the most surprising findings of behavior genetics has been that, statistically speaking, family environment plays no consistent role in determining personality or intelligence. Some family environments, in fact, tend to exaggerate the differences among siblings -- even identical twins -- rather than making them more the same.
"In my more cavalier mode I would have said that all that stuff psychology and sociology are made of -- you know, parents influencing their kids -- doesn't amount to squat," says Eaves, a bluff Briton who speaks in the clotted burr of his native Birmingham. Upon further reflection, Eaves found it hard to characterize the boundary between genetics and environment. "If a parent is saying to the kid, `For Christ's sake stop peeling the wallpaper and go outside and play,' you might find a correlation between parental shouting and conduct disorder. But where is the causality? Was it the parent yelling at the kid, or the kid's intrinsic need to peel wallpaper?"
Kendler spells out the gene-environment interplay like this: A person with a predisposition to depression may be hard to get to know. When something bad happens to that person -- say, the death of a parent -- he or she probably won't have supportive people to turn to, and this social isolation deepens the depression. The lack of friends is a "genetically selected" environment, which ends up deepening the original genetic effect.
The scientists in Richmond have shown that correlations for marijuana and cocaine use are nearly the same between fraternal and identical twins, suggesting that social environment is the main cause of drug experimentation. But the identical twin of a drug addict is far more likely to be an addict than is the fraternal twin of an addict. That suggests that genes play a major role when it comes to the biochemistry of drug dependence. In other words, "environment" may lead you to fool around with drugs, but genes hook you. Neurological studies point in the same direction -- to the idea that addicts' brains are wired differently.
All the same, Kendler is wary of psychiatrists who disregard environment altogether. "Over the last 15 years we've suddenly switched to a biological emphasis, so that some of my colleagues now really doubt that stressful life events have anything to do with depression," Kendler says. "From our data, that's simply absurd. It's as bad as it used to be when people blamed mothers for everything."
Some of this complexity is reflected in a substance-abuse study that Charlene Woodard, a clinical psychologist on Eaves's team, is conducting with a National Institute on Drug Abuse grant. Previous studies have shown that while African Americans tend to get into drug abuse later than whites, they end up suffering greater health consequences. Woodard's study, which reflects her experience as a counselor for drug addicts, incorporates factors such as a sense of racial identity, religiosity and perceived discrimination as correlates of drug abuse among African American adolescents. "There may be genetic contributions to alcoholism, but the protective and risk factors are different depending on cultural factors," she says. Woodard's hope is that once she finds attitudes that correlate with low drug abuse, the knowledge can be incorporated into prevention programs.
An African American researcher like Woodard treads a delicate path in behavior genetics. After all, leading behavior geneticists such as Arthur Jensen and the late Hans Eysenck -- a German-born Briton with whom Eaves worked -- have been accused of racism for suggesting that genes accounted for the lower IQ scores of blacks (and the Irish). The Bell Curve drew heavily on the work of these scholars. "Using the term genetics in the same sentence with African American is very sensitive," says Woodard. "All I can do as a researcher is consciously recognize that there is some scientific value in answering the question, `Why are we dying at an earlier age than whites? Why is our health worse?' "
Adds Carol Prescott, "Traditionally, the `What good is it?' of twin studies was to convince the people who thought everything in human behavior was nurture. I think we've come beyond that and maybe are swinging in the other direction, to everything being genetic." From her perspective, once scientists can determine that a genetic disposition puts someone at risk for a problem, it enables society to attack environmental causes that push that person over the edge. "If you look at the co-twin of someone who has a history of depression, what predicts whether or not they will get it? What might protect them? What increases the risk?" says Prescott. One of the Richmond group's studies is looking at identical twins in which one is an alcoholic and the other is not. The idea is to understand what differences in environment may have protected the sober twin. If we knew which individual genes were responsible for psychiatric ailments, environments presumably wouldn't matter as much. But molecular techniques have thus far failed to find the genetic causes for any complex mental illness or condition. "There's been lots of talk and lots of hope," says Kendler, "but no concrete widely replicated results."
Lots of hope -- and lots of hype. One striking trend in molecular genetics at the moment is the frustration scientists are encountering in isolating genetic components of traits such as schizophrenia. After the identification of one-gene defects such as cystic fibrosis and Huntington's disease, scientists had expected to quickly identify the more complex genetic components of psychiatric conditions. Some widely publicized discoveries have been announced, but few have been reproduced. After the 1996 discovery of a "novelty seeking" gene was splashed on the front page of the New York Times, three follow-up studies failed to duplicate the finding. If there is such a gene, geneticist David Cox of Stanford prophesies, its overall contribution to personality is likely to be small.
Which is why some scientists, like Evan Balaban of the Neurosciences Institute in San Diego, argue that hunts for behavioral genes are almost a waste of time.
It's not that Balaban doesn't think behavior has biological roots -- he's a scientist who manipulates behavior for a living, transplanting brain cells from quails to chickens in such a way that makes the chickens sing like quails. Behavior originates in the brain -- he knows that -- but he also knows what else goes on in the brain: a random movement of particles that can have unpredictable results, particularly during fetal development, when the odd molecular bounce can cause a lifetime's worth of effects. "Labeling something genetic doesn't explain the process by which it happens," says Balaban. "You have to see how the genes interact. And there are so damn many and they interact in so many ways. As a science this is going to take us a long time to sort out."
So many mysteries, and Lindon Eaves knows them as well as anyone. Not only does he oversee twin studies, he also once designed a computer program to test a biological application of chaos theory -- the theory that small changes can lead to enormous changes in complex systems. In his case, the complex system was a pair of twins, and by the time he finished running his program he had seen that a tiny alteration in the developing embryos of identical twins would end up making them different in half their characteristics by the time they were adults.
As intriguing as that result was, though, Eaves has even bigger mysteries on his mind one Sunday evening as he heads not to his office, but to his church. On this night he is wearing the black shirt and collar of the Rev. Eaves, weekend Episcopalian minister, and he is preaching evensong at St. James's Episcopal Church in Richmond. The reading for the evensong sermon comes from the seventh chapter of Luke, in which Jesus's touch revives a dead man in the town of Nain.
But those who have come to church this evening expecting a pious service from a minister instead get a sermon from a minister who is part scientist as well. God talk is mostly "mumbo-jumbo" and "gibberish," he thunders. Did the man in Nain really rise from the dead? "That's too far off the wall," he says. Yet there was a miracle, and it was this: Jesus reached out to the man in the coffin. "Jesus approached while others shrank away. Jesus touched the untouchable. He went into the space where the rule book ends, the place where science fails."
Later, at a small gathering of students in a church meeting house, a plate of potluck stew balanced on his stomach, Eaves expands on the topic of genes and religion. "Science deals with humans in an essentially deterministic way," he says. "Whether we talk about genes or environment, we're talking about people being caused. And that's a little bit different than when we talk about ourselves as centered, acting, creating beings. How do we reconcile that with the idea that we're carrying around a code that when it unpacks has a strong impact on us? I mean, I have a paper out there that shows there may be some genetic effects on whether we go to church."
But if going to church is just a biological imperative, an impulse selected by evolution, one student asks, "How do you explain Mother Teresa?" After all, Mother Teresa and her genes apparently sacrificed their future so that the genes of others might live. That didn't make sense from an evolutionary viewpoint, because if it were so, the genes for saintly sacrifice would never have survived.
"The trouble with Mother Teresa -- I mean God love her," says Eaves, chewing a mouthful of food, "is that she may have been a mutant."
"And what about Jesus?" asks the student.
"Whoa! Whoa!" says Eaves. "Excellent question."
Sherry Clark's answer: "I was very angry at God when my father died," she is saying one night, sitting in a kitchen in somebody else's Gaithersburg house where she's been a live-in housekeeper for a few months. She's talking not only about God and her dear departed father, but also her genes.
"I felt betrayed," she says. "But eventually I realized that God isn't a murderer. People make certain choices in their lives and you get points taken off for being stupid. Father had a bad heart. Not a smoker or drinker but he didn't eat well. Part of it was genetic, and part of it was his emotions and attitudes. He used food for a purpose it wasn't intended to be used for, for comfort. He abused food. That's where I get it from, and my twin, too."
Maybe yes, and maybe no.
In fact, the only definitive truth about identical twins is that they're not identical at all. On the subject of nature and nurture, it turns out that Sharon and Sherry Clark disagree.
"I would say 75 percent of personality is genetic and 25 percent is environment," says Sherry. "Right down the line."
"What you are comes from your parents, other siblings and their perceptions of you," says Sharon. "The first three years of a child's life are so important in terms of whether they become secure or insecure."
Whatever created the Clarks' separate natures -- nature, nurture or some blend -- it has held true through their lives so far. At age 16, Sharon won a statewide singing contest, and two years later she enrolled at the Berklee School of Music in Boston. Sherry, also a talented singer but not quite as gifted as her sister, went off with a friend to North Hollywood, Calif., where she worked the odd job and partied a lot.
A year later they were back together, living with their mother at the family home on Dade Lane in Alexandria. Sherry was an international operator for AT&T for seven years. Later she went to culinary school and started housekeeping, saving money to start a catering business. In November she got fired from the Gaithersburg gig, just as she was about to quit.
Sharon has held a series of retail jobs while attending the academy of the clubs -- listening to hundreds of hours of music at D.C.-area bars. In September, she finally cut the CD she hoped would set her career on fire. "Finally," it was called. Success led to more success: After a Blues Alley performance in November she met some Democratic Party officials, and got invited to sing at the White House in the spring.
For all the good fortune, untimely death gnaws at the Clark family. The twins' oldest sister, Sylvia, succumbed to leukemia in 1980, leaving two sons, Curtis and Israel. Rejected by their father, the boys grew up essentially parentless. After a short life that involved several years in prison, Curtis Lamont Clark was slain over a drug deal on Mother's Day 1996, age 21. He was found in D.C. in a car, shot so full of holes that Sharon, who identified the body, barely recognized him. "He was a big guy, maybe 230 pounds, but he looked tiny in that coffin," she says.
Maybe Curtis's life carries its own small point to the nature-nurture debate. Sharon thinks so. "He didn't get the adult love he needed to form himself without going to the streets to be accepted," she says. "And the street whipped him."
And maybe the larger point was this: Nothing in the genetic blueprint puts you out on the street, a young man shot full of holes, just as nothing in the blueprint arranges for you to sing at the White House.
Genes, in other words, aren't everything. Just ask any identical twin.
Arthur Allen last wrote for the Magazine about medical ethics and the use of painkillers.
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