Twins Reared Apart: The Best Natural Experiment

Psychology June 09, 2012 / By Nancy L. Segal

SYNOPSIS

Twins reared apart allow new insights into nature and nurture. A new book about the Minnesota Study of Twins Reared Apart tackles this topic.

I was very privileged to have spent my first post-doctoral years associated with the Minnesota study of Twins Reared Apart, directed by University of Minnesota professor Thomas J. Bouchard, Jr. Meeting the twins and observing their behaviors over the course of a week was a thrilling experience. And watching their relationships with one another evolve was also exciting. Most of the twins were adoptees and were so gratified to finally meet a biological family member, especially a twin.

I have just documented the origins, methods, findings, implications and controversies of this study in a book titled, BORN TOGETHER-REARED APART: THE LANDMARK MINNESOTA TWIN STUDY (Harvard University Press, 2012). The book includes marvelous pictures of some of the twins we studied, as well as the amazing life history events responsible for their separation and eventual reunion.

The reared apart twin design provides one of the best approaches to studying genetic and environmental influence on behaviors involves the rare pairs of identical and fraternal twins reared apart and reunited. The size of the correlation between reared apart identical co-twins offer scientists a pure estimate of genetic influence on behavioral and physical traits. The size of the correlation between reared apart fraternal co-twins provides an informative comparison. Greater resemblance between identical than fraternal twins is consistent with genetic influence on the traits under study.

The Minnesota study began in 1979 and continued for twenty years. The volume of material that accumulated was too vast to include in a single volume. I have, therefore, included some supplementary material in a web site: drnancysegaltwins.org. Information about my other books can also be found there.

It is amazing that twins continue to be separated today, given the increased appreciation for family ties. In the past, twins were separated mostly due to illegitimacy or maternal death. Today, the new assisted reproductive technologies that may yield several babies, not just one, have caused some families to relinquish one or more of their multiple birth children; these families may lack the resources to properly care for them. China’s One-Child Policy was also indirectly responsible for the separation of pairs of mostly female twins. In fact, I am studying those twins, as well. And new cases occasionally cross my desk from unexpected sources. These cases are all scientifically informative in their own way, but bringing the twins together is the most satisfying part of the process.

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Author

Nancy L. Segal

Dr. Nancy L. Segal received a B.A. degree in psychology (with distinction) and English literature from Boston University (1973), and M.A. (1974) and Ph.D. (1982) degrees in Social Sciences and Behavioral Sciences from the University of Chicago. She is currently Professor of Psychology at California State University, Fullerton (CSUF) and Director of the Twin Studies Center which she founded in 1991. Dr. Segal is the CSUF 2004-5 Distinguished Professor in Humanities and Social Sciences and the 2004-5 Outstanding Professor of the Year. She also received the 2005 James Shields Award for Lifetime Contributions to Twin Research, from the Behavior Genetics Association and International Society for Twin Studies and the 2006 “international Making a Difference” Award from Multiple Births Canada. Dr. Segal is the author of Someone Else’s Twin: The True Story of Babies Switched at Birth (Amherst, NY: Prometheus Books, 2011), Indivisible by Two: Lives of Extraordinary Twins (Cambridge: Harvard University Press, 2005) and Entwined Lives: Twins and What They Tell Us About Human Behavior (NY: Dutton, 1999, NY: Plume 2000), and the senior editor of Uniting Psychology and Biology: Integrative Perspectives on Human Development (Washington, D.C.: APA Press, 1997). Her newest book, Born Together-Reared Apart: The Landmark Minnesota Twin Study (Cambridge: Harvard University Press), will be released in May 2012. Dr. Segal received a 2003-2004 American Fellowship from the American Association of University Women for completion of Indivisible by Two. She was also co-principal investigator of a 2003-2005 NIMH supported study “Twins, Virtual Twins and Friends: Peers and Adjustment.” Dr. Segal has authored approximately 120 scientific articles and book chapters in addition to her three books. A recent paper won a 2007 Award for Excellence in Research from the Mensa Foundation. She is also an Associate Editor of Twin Research and Human Genetics, the official journal of the International Society for Twin Studies. Dr. Segal’s guest television appearances include the Martha Stewart Show, Good Morning America, 20/20, the Oprah Winfrey Show, Discovery Health and the upcoming series Our America (OWN). Her radio interviews include NPR (Fresh Air, AirTalk, Diane Rehm Show) and numerous local stations. She has been a consultant for the media (National Geographic Magazine), the law (twins’ wrongful death and custody cases) and the arts (theater and film). She frequently addresses both professional and general audiences concerning her work. Her current recent interests include behavioral and physical development of twins, the nature of twins’ social relationships, Korean twins separated at birth. the behavioral development of Chinese twins adopted internationally, the behavioral consequences of twin loss and the personality similarity of unrelated look-alikes.

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