CSUF News Service

Psychology Professor Debunks Popular 'Twin Mythconceptions'

Nancy Segal

Nancy L. Segal, professor of psychology

Can twins communicate telepathically? Should twins be separated in school? Do twins skip generations?

In her latest book, "Twin Mythconceptions: False Beliefs, Fables and Facts About Twins," Cal State Fullerton professor of psychology Nancy L. Segal separates fact from fiction on more than 70 commonly held beliefs about the origins and development of twins.

Segal — one of the world's leading experts on twin research, director of the Twin Studies Center and the 2016 recipient of the California State University's Wang Family Excellence Award — is committed to mentoring the next generation of researchers. Twin-family relations, twin loss, personality similarity, general intelligence and twins raised apart are among the topics she and her students continue to explore.

What inspired you to write "Twin Mythconceptions"?

I was struck by the many misconceptions and false beliefs about twins among both professionals and the general public, and decided to provide the best current scientific information possible.

Can you share a few examples of false beliefs about twins, and the truths behind them?

Most people assume that identical twins communicate telepathically, but there is no scientific evidence to support this. I believe twins sometimes appear to communicate this way, but the behavior is grounded in their matched genes, which predispose them to process information alike and to think in very similar ways.

Most schools routinely separate young twins for fear that they will not develop their own identity and individuality. There is no research basis for this. In fact, evidence suggests that many young twins perform better when they are kept together in the early years. There should be no policy; each pair should be handled on a case-by-case basis.

Many people believe twins skip generations. This is not the general rule, although it could happen in some families. Both identical and fraternal twinning appear to have genetic components, but the mechanisms behind them are uncertain.

What's new or different about this book from your previous works?

The structure is unique: I address about 70 'mythconceptions' organized into different chapters. Each is followed by a reality check of each one (e.g., true; false; possibly), then I provide a brief answer for people who want information quickly, followed by a longer more scientific explanation.

What can the study of twins teach us about human health and behavior?

Comparing the degree of similarity between identical and fraternal twins with respect to traits of interest shows us that genetic influence on health and behavior is more pervasive than we would have thought — it affects just about everything. We know this since identical twins, who share all their genes, are generally more alike than fraternal twins, who share 50 percent of their genes, on average, by descent. Of course, the environment plays a key role as well and affects some traits more than others — no trait is affected only by the genes, or only by the environment.

Upcoming talks: Segal will discuss her latest book at a Sunday, Sept. 17, event in Pasadena, hosted by Michael Shermer, a CSUF alumnus and founder of the Skeptics Society and Skeptic magazine. She also will deliver a TEDx Talk Saturday, Nov. 4 at Mira Costa High School in Manhattan Beach.

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