Twins Double Psychologists’ Insight

April 6, 1986

by James Plourde of The Register-Guard

Despite their prominence in the zodiac and occasional mention in the titillating headlines of supermarket tabloids, most twins lead relatively normal lives.

But normal or not, twins provide scientists with unique research opportunities, and Hill Goldsmith, a University of Oregon psychology professor, believes the study of twins may offer a means of understanding genetic influences in human behavior.

There are two types of twins–identical and fraternal. Identical twins are 100 percent alike genetically. Fraternal twins, like any other group of siblings, are 50 percent alike genetically.

Identical twins share a carbon-copy genetic structure because their lives begin as one fertilized egg in their mother’s womb. Within the first few days of pregnancy, for reasons not fully understood, the egg divides and both parts evolve into separate human beings. In the extremely rare case of Siamese twins, the egg never divides completely, and the babies are born fused together at one part of the body.

Fraternal twins are formed when a woman releases two eggs in her ovulation cycle, and each egg is fertilized by separate sperm. The separate fertilized eggs allow the possibility of a boy-girl combination, which is impossible in a set of identical twins.

Twins make ideal test subjects for Goldsmith because they are reared in the same environment by the same parents under almost identical circumstances.

“That (the environment) gives you a sort of control,” Goldsmith says. “You can compare the similarity in the identical twins to the similarity in the fraternal twins. . .If the identical twins are more similar than the fraternal twins, there is at least some suggestive evidence that there are certain genetic differences influencing whatever you’re studying.”

What Goldsmith is usually studying is the effect genes have on activity levels and on personality, in particular how youngsters respond to stress.

“The results seem to suggest moderate genetic influences on those characteristics, but I stress that they’re only moderate,” Goldsmith says.

In one of Goldsmith’s laboratory studies, he compared how identical and fraternal twins reacted to stress. The twins were individually exposed to a mildly stressful situation, such as having a stranger walk into the room. Goldsmith said the identical twins tested reacted more similarly than did the fraternal twins.

Using this and other studies, researchers are able to surmise that genetic make-up is a factor in human behavior.

These types of studies not only point to genetic influences on behavior, they also lend credence to the long-held belief that identical twins are more alike and share a closer bond than do other siblings or even fraternal twins.

That comes as no surprise to Portland researcher Betty Jean Case. A fraternal twin herself, Case is writing a book based on information she has gathered in a five-year, nationwide survey of twins.

The 66-year-old Case said she never gave much thought to how being a twin influenced her life until the birth five years ago of her twin grandsons, Andy and Tony Case of Springfield. Shortly after their birth, Case launched an intensive exploration into the attitudes of twins.

She began her search at a twins convention in Springfield, Ill., handing out copies of a three-page questionnaire to every twin she could find. She also asked conference members to contact other twins interested in being a part of the survey, and she took out ads in newspapers to generate responses.

Case has accumulated 750 completed questionnaires from twins all over the United States.

Her survey focuses on twins’ relationships with their parents and with their fellow twin and explores their feelings about growing up as a twin. It also gives respondents a chance to offer some advice through questions such as: “What would be the most important advice you could give to parents raising twins?” and “How do you think society can help twins develop their individuality?”

Through the multitude of questions and responses, Case said, one major theme has emerged.

“The main thing I see is that twins want to be recognized as individuals,” she said, adding that twins tend to share a closer bond than that shared by other siblings and most twins said they wouldn’t change the circumstances of their birth.

But along with the security and love of having a live-in playmate comes the struggle most twins experience of asserting their independence and of trying not to measure their worth against the accomplishments of their twin.

Identical twins, primarily female identicals, share the closest bond of the twin groups. Identicals also reported more instances of shared thoughts and experiences, Case said.

“Identicals often experience a great deal of feeling similar thoughts, similar dreams,” Case said. “One pair of brothers stopped giving each other Christmas gifts because they kept giving each other the same thing.”

When one woman went to have her ears pierced, her identical twin sister recalled feeling pain in her ear lobes, which had turned beet red. Another woman reported feeling abdominal pain when her twin sister went into labor.

The survey also indicated that identical twins tended to experience less jealousy and competition with each other than did fraternals.

One frequent complaint from the twins was their objection to being talked to as one person both within and outside of the family. This has led to problems in later life for some twins in separating from their sibling.

“Some twins said that it wasn’t until they went to college that they realized they were a person,” Case said.

One twin answering the study reported being cruelly treated by other children in school.

“They tried to knock out a tooth so they could tell who each one was,” Case said.

Nothing that drastic ever happened to Pam Starling or her identical twin sister, Rhonda, but both experienced some of the stresses chronicled in Case’s research. Neither participated in the research effort, however.

Pam Starling, 27, of Springfield, said she and her sister are “best friends,” but their greatest conflict as children arose over asserting their own identities.

“Besides being close, we struggled for our own identities. So when we fought, we really fought very strongly and most of our fights were over Rhonda using my things or wearing my clothes or vice versa,” she said.

Being the youngest in a family of five, they often were blamed as a unit if one of them did something wrong.

“The twins got blamed for something. They automatically lumped us together,” she said.

She doesn’t recall any psychic experiences with her sister, such as being able to sense her thoughts or feel her pain.

“I look at it in a very practical way. Because we were so close and because we had so much in common that if something sort of strange did happen, or we sort of knew what each other was thinking, it’s just because of that kind of closeness, which you can have with anyone you know really well,” she said.

And if she were some day to give birth to twins?

“I would stress that they are two unique individuals,” she said. “I wouldn’t get into the whole twin trip of dressing them alike. Having the same expectations of them isn’t very healthy either. Because they look so much alike and talk alike you have to be more conscientious about looking at the differences and respecting that.”

“Don’t force them to do the same thing because it’s convenient.”

But despite some drawbacks, Starling said she is glad to be a twin, especially because of the close relationship she has with her sister.

“I don’t ever remember feeling like, Gosh, I wish I wasn’t a twin,'” she said. “I thought it was neat. We did get a certain amount of special attention because we were twins, and I think it was a positive thing.”

Reprinted with permission. Copyright 1986, The Register-Guard,