doing doubles duty
Tammie and Tapatha Rodgers of Fullerton sometimes have the exact same dream. They realize it the following morning when, talking about their dreams, they start to finish each other’s sentences. They’re college classmates, roommates, sisters. They share nearly everything; Tapatha says they even take turns being dominant.
They’re identical twins, each with 100% of the other’s genes.
“We’re as close as two people can get,” says Tapatha, 21. “The most we ever spent apart is 48 hours. It was a weekend trip.”
The psychology of the Rodgerses and thousands of other twins is the life’s work and life’s fascination of Nancy L. Segal, a nationally known twins expert who teaches at Cal State Fullerton.
Public interest in twins has never been higher, says Segal, 46. In the past year, she has been swamped with requests for speeches, magazine articles, TV documentary consulting work, expert-witness appearances and research. The recent brouhaha over cloning only added to her scientific celebrity.
Interest in twins is such that Segal, a behavioral geneticist and professor of developmental psychology, has been asked to write a book aimed at the public. “Friendship Extraordinaire: Twins and What They Tell Us About Human Development and Personality” is scheduled to be published next year by Dutton Press.
Much of the curiosity is from twins themselves, who are eager to learn about one another and who promote their interests with their own magazine, Web sites, clubs, support groups and even an annual festival (held not in the Twin Cities but in the next best place--Twinsburg, Ohio). Thanks to greater longevity, along with more births of multiples due to advances in reproductive technology, twins represent an increasing percentage of the population.
In the five-year history of Segal’s Twins Study Center at Cal State Fullerton, more than 100 pairs of twins have participated in research ranging from olfactory perception to bereavement levels.
Segal’s overriding goal: to help solve the nature-vs.-nurture riddle--that is, to determine which of our behavior is influenced by our genes and which by our home environment.
In basic twin research, similarities between twins raised separately indicate the power of heredity. Conversely, similarities between unrelated siblings reared together point to the influence of home life.
The science of behavioral genetics hit its nadir with Josef Mengele’s murderous Auschwitz experiments and other Nazi studies in eugenics. Theories opposing such biological determinism then came into vogue, advanced by behaviorists John B. Watson and B.F. Skinner. They argued that environment, not heredity, was paramount and that humans could be conditioned to act in nearly any fashion.
“Now there’s been a movement to middle ground,” Segal says. Nazi experimentation “gave the whole field of medical genetics a negative cast,” she says. “But [genetic] studies still were done . . . and data just became so abundant and persuasive that it couldn’t be ignored [by mainstream psychology]. And people were getting disenchanted with the wholly environmental point of view.”
For research into genetics, twins are the ideal subjects--”a natural living laboratory,” as Segal says. By studying twins, Segal sees potential answers to behavioral questions that can’t otherwise be answered, not even by human clones, since clones would not have shared the womb and early upbringing.
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Twins separated at birth can show eerily similar behavior. Segal participated in a follow-up study of one such identical pair--Jim Lewis and Jim Springer.
The Jim twins, adopted by separate Ohio families a few weeks after birth, were reunited 39 years later, in 1979. What they discovered about each other’s history, beyond being given identical first names by their adoptive families, reveals the powerful grip of their shared genes:
Both had been part-time sheriff’s deputies and had worked at McDonald’s and gas stations. Each enjoyed carpentry as a hobby. Each used the same slang. Each chain-smoked Salems and drank Budweisers (and crushed the empty cans).
It gets better: Each Jim had a son named James and a boyhood dog named Toy. Both married women named Linda and later married women named Betty. Each drove the same-model blue Chevy to vacation at the same three-block stretch of beach in Florida. Each suffered migraines and even used the same words to describe the pain.
Says Segal, who emphasizes that the Jim twins are prototypal: “If identical twins are more alike than fraternal twins [who have different genetic makeups], this indicates that genetic influences probably affect the trait under study.
“This helps non-twins understand the way that they are, and why their children develop as they do.”
About a third of all twins are identical, having formed when a fertilized egg split. Other twins are fraternal, formed when two eggs are fertilized by separate sperm.
Identical twins’ similarities can sometimes be hard for singletons to accept. A few years ago, Segal says, a pair of twins missed the same answers on a college test and were accused of cheating. Segal was asked to verify that it was indeed plausible that the two might score the same. She did, and the cheating charges were dropped.
Segal has studied the bond between identical twins and has found it strong. The level of grief a twin experiences when the other twin dies is, in fact, greater than that experienced after the death of a mother, father or other sibling and equals the bereavement felt when a spouse dies, her research has found.
Such data have proved attractive to lawyers trying to maximize damage awards in wrongful death cases, and Segal has appeared as an expert witness in such trials about a dozen times.
In the current Orange County case pitting Jeen Han of El Cajon against her identical twin, Sunny Han, Segal says it was understandable that Sunny Han came to the defense of her sister at one point during the trial, even though Jeen Han is accused of conspiring to murder her.
“It doesn’t surprise me because they are identical and have a history of shared experiences,” Segal says. “If this were an ordinary friend, that would never happen. It’s key in [Sunny’s] new take on the case.”
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Central to Segal’s research is documenting how twins interact with each other.
“Her specialty, perhaps the only person in the world to do it, is to use twins to study the genetics of cooperation and competition,” says Thomas Bouchard, director of one of the nation’s oldest twin research centers, at the University of Minnesota. “She uses twins in a broader way than any other investigator I know and is quite imaginative, full of energy.”
Like many enthusiastic researchers, Segal tends to live and breathe her specialty. In her case, the study of twins, it is literally so--she is a twin.
Segal says that growing up in New York, she was always interested in why she and her fraternal twin, Anne, weren’t very much alike.
“We are temperamentally very different, yet we had the exact same upbringing. And that’s what got me thinking of nature and nurture,” Segal says.
“Then, when I got to college and became interested in psychology, this whole area was fascinating to me because it provided answers to questions I’d had growing up. Why is it that two related people can be so different?”
She began finding answers at the University of Minnesota, where she was assistant director of the Minnesota Center for Twin and Adoption Research.
Her studies benefit not only twins but also non-twins, she says.
As an example, she cites her research into cooperation and competition, part of which involved observing about 60 pairs of twins on school playgrounds.
“In that experiment, I found that identical twins get along better than fraternals. This tells us . . . it’s genetically based,” she says. “So parents who have ordinary siblings, and wonder why some get along better than others, know that part of it may be personality. Their tastes are just not compatible. So parents shouldn’t feel it’s something they did wrong.”
Twin research is not without its critics. They say it’s hard to pinpoint how much of twins’ behavior is in fact due to genes and how much is a result of their having had common treatment--the same bedspreads, the same clothes, the same birthday gifts.
As a partial response, Segal is completing research she says is “precisely the reverse” of studying identical twins who were raised apart, such as the Jim twins.
Her study, to be published in June in the Journal of Educational Psychology, looks at unrelated siblings of the same age who are reared together. If being raised by the same parents produces similar behavior, Segal reasons, these types of children would show it.
“My argument is, let’s look at kids who are reared together but who have no genes in common, such as a boy and his adopted brother of the same age. So far, the data suggests they’re not very much alike at all.”
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To parents, Segal’s studies offer welcome tips for raising twins--who can be more than twice the work of singletons.
A Costa Mesa-based group, Orange Coast Mothers of Twins, has 131 members, double its membership of four years ago, says president Elaine Markley.
“Nancy’s work has helped us figure out what things are inborn [among twins] and what things we affect as a parent,” Markley says. “She has done studies with twins and how they relate . . . to tell us things that can impact their whole future.”
Among parents’ concerns is whether identical twins should be put into different classrooms at school (Segal says it should be decided on a case-by-case basis). Another issue is whether it’s OK to label one twin, with fingernail polish or a pierced ear, to help identification even though the twin might resent it (the alternative--calling a twin “Hey, you” or by no name at all--could have even worse psychological consequences, Segal says).
One of Segal’s most helpful presentations, Markley says, was on twin loss and how it can devastate the surviving twin and the family.
“If your twin has to go through anything like that, it’s tough,” Markley says. “At a meeting we had two 35-year-old, very macho guys. One of them said he hopes he dies before his twin because he would have no idea how he’d live. He would miss him even more than his spouse.”
The lifelong bond is illustrated by identical twins Debbi Apodaca and Terri Bugbee, both of whom have participated in research at the Twins Study Center.
“We’ve always lived together,” says Apodaca, 33, of Placentia. “There’s never been any question.”
Their husbands could scarcely disagree--the two couples, each with children, live in the same house.
