For behavior geneticists like Eaves, who do the nitty-gritty work in the nature-nurture debate, twins are the perfect people on whom to test hypotheses about what is molded by life's pressures and what is inborn. But such scientists wage the battle from a distance, using statistics to describe the behavior of populations -- of aggregates, in other words -- rather than individuals.
These statistics have shown that on average, identical twins tend to be around 80 percent the same in everything from stature to health to IQ to political views. The similarities are partly the product of similar upbringing. But evidence from the comparison of twins raised apart points rather convincingly to genes as the source of a lot of that likeness. In the most widely publicized study of this type, launched in 1979, University of Minnesota psychologist Thomas Bouchard and his colleagues have chronicled the fates of about 60 pairs of identical twins raised separately. Some of the pairs had scarcely met before Bouchard contacted them, and yet the behaviors and personalities and social attitudes they displayed in lengthy batteries of tests were often remarkably alike.
The first pair Bouchard met, James Arthur Springer and James Edward Lewis, had just been reunited at age 39 after being given up by their mother and separately adopted as 1-month-olds. Springer and Lewis, both Ohioans, found they had each married and divorced a woman named Linda and remarried a Betty. They shared interests in mechanical drawing and carpentry; their favorite school subject had been math, their least favorite, spelling. They smoked and drank the same amount and got headaches at the same time of day.
Equally astounding was another set of twins, Oskar Stohr and Jack Yufe. At first, they appeared to be a textbook case of the primacy of culture in forming individuals -- just the opposite of the Lewis-Springer pair. Separated from his twin six months after their birth in Trinidad, Oskar was brought up Catholic in Germany and joined the Hitler Youth. Jack stayed behind in the Caribbean, was raised a Jew and lived for a time in Israel. Yet despite the stark contrast of their lives, when the twins were reunited in their fifth decade they had similar speech and thought patterns, similar gaits, a taste for spicy foods and common peculiarities such as flushing the toilet before they used it.
Bouchard's collection of twins-raised-apart is unique in American behavior genetics. In most twin studies, including Eaves's research, scientists are comparing the similarities between identical twins and fraternal twins; in other words, they compare comparisons. To test the assumption that genes play a role in IQ, for example, scientists ask whether the IQs of identical twins (who share all their genes) are more similar than those of fraternal twins (who share an average of 50 percent). To have any statistical validity, such studies must examine thousands of twin pairs. But enough studies have been done to show that identical twins are roughly 85 percent similar for IQ, fraternal twins about 60 percent. Crunching the numbers, behavior geneticists say about half the variation in IQ, whether among twins or non-twins, may be due to genes.
It was this figure that provided the grist for the controversial 1994 book The Bell Curve, whose conservative authors argued that little could be done to help the poor because they suffered from low IQs that were fixed, for the most part, by their genes. The book has been disputed by many critics, including those who deny that IQ is a worthy measure of intelligence. Even if it is, though, the genetic component of IQ that The Bell Curve trumpets is not an overwhelming factor: Even if half of IQ variation is due to genes, that leaves room for plenty of average kids to be born to brilliant parents, and vice versa. And when children of smart parents are smart, it is nearly impossible to know whether this is due to the "smart" genes they inherited, or the "smart" environment their parents provided.
When it comes to social policy, genetics provides no worthy pretext for neglecting the disadvantaged, as geneticist and child development expert Sandra Scarr has pointed out. Scarr, a former University of Virginia professor, is considered a hard-liner for nature; she believes that if a child's basic needs are met, genes become the dominant control on how far the child will go in life. But she also has called for massive intervention to help underprivileged children. Infants and toddlers lacking the basics in food, shelter and affection, she says, are likely to be stunted in ways that outweigh genetic considerations.
When journalists first began interviewing Bouchard's twins-raised-apart, they focused on the spectacularly similar pairs, like the Springer-Lewis twins. But those twins turned out to be outliers in the Minnesota study. Most of the other twins weren't nearly as alike. Furthermore, since no one is claiming there is a gene for flushing the toilet before you use it, or a gene for marrying women named Betty, such coincidences are statistical anomalies, as Bouchard is quick to acknowledge. The quirky cases strengthen our sense of the power of nature, but they don't provide enough data to make a scientific case. "There probably are genetic influences on almost all facets of human behavior," Bouchard says today, "but the emphasis on the idiosyncratic characteristics is misleading. On average, identical twins raised separately are about 50 percent similar -- and that defeats the widespread belief that identical twins are carbon copies. Obviously, they are not. Each is a unique individual in his or her own right."
Geneticist humor: A little joke is posted on the bulletin board of the clinical genetics department at Johns Hopkins Hospital in Baltimore. It's a diagram of the X chromosome, with the names and descriptions of imaginary genes scribbled at intervals along it: "visa" -- the gene for shopping addiction; "klutz" -- the inability-to-manipulate-mechanical-objects gene; "blab" -- the gene for prolonged telephone conversation; "eek" -- the fear-of-bugs gene. There's even a gene for emotional instability -- "shrill" -- and one for learned helplessness: "honey . . ."
Variations on this joke can be found at labs around the country, pushpinned next to the job notices and 401(k) plan announcements and postcards from colleagues at the beach in Aruba. Like the "You want it when?!" posters on the walls of auto repair shops, the joke map parodies popular perceptions of the profession but contains a kernel of truth. Scientists have made some pretty remarkable claims recently about the impact of particular molecules on behavior. In journals such as Science and Nature Genetics, they publish news of genes for neuroticism and thrill-seeking and risk-taking, genes for alcoholism and aggression and anxiety. In 1993, a National Cancer Institute researcher reported the location -- on chromosome X, as it happens -- of a gene that seemed to cause homosexuality.
It must be said, however, that the meanings of such discoveries shed their precision as they travel from the scientific literature to the popular culture. Genes don't really make homosexuals or violent kids or depressed adults, and no reputable scientist would claim that they do. Genes make proteins that contribute to chemical pathways that play a role in complex neurological and existential events. But that's a long story, so spare us the details. Something inside us -- a "fatalism" gene, perhaps? -- makes us want to believe that the genetic blueprint holds the secrets of who we are.
Something of this fatalism imbues the folklore of twins. In the books and magazine articles and Web sites about their lives, twins tell uncanny stories of wordless understandings, of moments of grief or joy communicated at a distance without benefit of a phone, by some kind of genetic magnetism. On one Web site, a woman named Gilia Angell recalls wandering into the St. Patrick's Cathedral gift shop in New York and buying a postcard of an airbrushed Jesus, which she mailed to her twin sister in Olympia, Wash. A few days later, she says, a letter postmarked the same day arrived from Olympia. Enclosed was a refrigerator magnet "with the same filmy airbrushed picture of Jesus!" Then there are those twin pranks, adding to our general sense of wonderment over their doubleness -- duped boyfriends and confused motor vehicles officials, cheating on SAT tests -- and the good twin/bad twin dichotomies, exemplified by Jeen Han, a California 23-year-old who was recently convicted of trying to kill her twin.
Yet for all of that synergy stuff, natural-born clones don't have to be told they are separate individuals -- they know it. "You could take 50 cells from my leg and make 50 other people who look and sound like me, but they won't be me," says Richard Bausch, a novelist, short-story writer and George Mason University writing instructor. "To any twin, the idea that human clones would be the same is absurd. When you're a twin you know that. People are much too complicated to be replicated, no matter how many genes they discover."
On the face of it, Bausch's convictions seem undercut by his biology. His identical twin, Robert, is also a fiction writer, and also a writing instructor, at Northern Virginia Community College in Woodbridge. But these are writers, of course, whose job is to be finely aware of nuances. Robert is the more intellectual one; Richard is more religious. Their take on cloning is similar, but Robert's analogies are Jesuitic. "If everything that we call the will is just genetics and chemistry," he asks, "then who in the hell are we talking to when we try to remember something that's on the tip of our tongue?"
At 51, the Bausch twins see less of each other than they used to. They each have their own work and their own children to worry about. They have been profiled too often to really enjoy being a novelty act anymore. Neither feels that being a clone is what defines him. But Richard will say this: "How people react to life is determined by their nature, but I don't think nature is biological. I still believe in good and evil, and that there is such a thing as sin.
" 'Genes' is just the word we use to describe God."
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