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Although the Nyborg twins did not go separate ways—far from it—life stepped between them. Pam dated more, married sooner, quit college, had kids first, paid more attention to her looks and clothes. Tami stayed in college, was a bit more serious, a bit less social, and she got better jobs. Both were dynamos, to hear them tell it, mothers who took on a million things at once. Both had gathered weight in the hips, Pam more than Tami. Both were cheerful in spite of setbacks. Pam was the twin who developed chronic fatigue syndrome.
Over a week the twins were subjected to medical tests and psychological interviews. They rode stationary bicycles wearing lung monitors, they slept with electrodes on their skulls, and they plunged their arms into a cooler of ice water and (each twin out of hearing of the other) reported on the level of the pain. Pam appeared to be more sensitive to pain.
The beauty of the co-twin method is that the healthy twin serves as the control for the sick twin. Control in this context means to remove genes from the equation, in the way that two equal quantities cancel each other out. Also, differences in the twins’ childhood environment are removed, because it’s assumed that both women were reared in the same way and ate the same food. Buchwald, the lead investigator, explains: “It’s been very unclear what group is the best control for chronic fatigue syndrome. Everyone’s struggled with it. Other researchers have used healthy people, depressed patients, even multiple sclerosis patients. No one knew what group to use for comparison. And none of those groups were controlled for environment or for genetics.”
The ultimate goal is to grasp the underpinnings of the disorder. If chronic fatigue syndrome has a signal—a distinct biological or psychological feature—Buchwald and Goldberg hope that the co-twin experiments will detect the signal amid the noise of human variation. The note that is most revealing so far is the capacity to consume oxygen during exercise. The researchers learned that the ill twin of the pair couldn’t pedal the bike as long as the other. Of course, individual fitness has a role, yet a person’s maximum oxygen capacity is largely inherited, according to—what else?—studies of twins.
The surprising finding is that, on average, the monozygotic twins in the University of Washington study, both those with chronic fatigue and those without, fall below normal in exercise capacity. The stationary bike tests have produced a biological clue, but it still doesn’t explain why only one twin in each pair got sick.
The research by Buchwald and Goldberg is hands-on experimentation, entailing the physical manipulation of twins, as opposed to simply observing their behavior or questioning them about their health. The researchers are well aware of twin experimentation’s ugly past.
Before World War II, twin studies were conducted in the Soviet Union, England, and the United States, but Germany was the site of the most advanced work. The world’s leading twin scientist was Otmar von Verschuer. He wrote a book on tubercular twins, arguing that susceptibility to the disease had a genetic foundation. Von Verschuer compiled a large file of twins in the Berlin area, in effect the first twin registry, and he compared the children for features like lung capacity and intelligence.
In the 1930s Von Verschuer headed the Institute for Hereditary Biology and Racial Hygiene in Frankfurt, where his favorite graduate student was Josef Mengele. The German scientists believed in eugenics. Adolf Hitler’s rabid program of eugenics required the improvement of the so-called Aryan race and the elimination of other “races” that were deemed inferior, especially Jews. Thus Von Verschuer, Mengele, and their colleagues were commissioned to find measurable ways of telling the races apart.
Twin studies conducted at the Auschwitz concentration camp in 1943 and 1944 became a central part of this effort. Mengele personally picked pairs from the crowds of incoming prisoners and performed grisly experiments on them. He would subject one twin to X-rays, blood transfusions, or bacterial injections and not the other, and then look for differences in their organs. He listed the eye colors and other features of twins of several nationalities, trying to tell which traits were genetically fixed and which might be malleable. Geneticists now know this was a scientifically doomed project, since the genetic variation within any ethnic group far exceeds the variation between different groups.
Mengele’s notes and findings were lost. Good riddance, say those who work with twins today, most of whom cannot bear to talk about Mengele. In the aftermath of World War II, scientists shied away from a biological or inherited framework for people’s differences. The nature-nurture pendulum swung toward environmental causes of disease—industrial pollution for cancer, for example. Autism was believed to be caused by bad parenting—a failure of the home environment, not an innate deficit. Learning and conditioning were held to be the font of all behavior, not genes. Statisticians reexamined the body of work on heritability in general and declared the sample sizes too small to support the nature-nurture statistics. Worse, fraud appeared to sully a celebrated British study of twins’ intelligence.
Twin studies did not get back on their feet until 1979. Psychologist Thomas Bouchard of the University of Minnesota, fending off comparisons with Mengele, founded the Minnesota Study of Twins Reared Apart. Bouchard helped introduce a new study approach by systematically finding and following adult twins who had been separated since their early childhoods. The first pair to be scrutinized were the famous “Jim” twins, two identical brothers who reunited in 1979. Not only were both named Jim (a coincidence of their adoptions) but they also shared a taste for woodworking, bit their fingernails to the nub, had identically named sons, smoked the same brand of cigarettes, drove the same cars, and held the same kind of job. Growing up, these twins had no experiences in common, yet they had turned out intriguingly the same.
