"Adolescent monozygotic twins are quite similar, as would be expected, considering that they are the same age, gender, ethnicity, and social class, have the same parents, live in the same community, attend the same school, and share genetically based traits," write researchers Robert Crosnoe, Ph.D., of the University of Texas at Austin and Glen H. Elder Jr., Ph.D., of the University of North Carolina at Chapel Hill in the November-December issue of Child Development.
However, the authors note, "Considering the forces that promote twin similarity, one might be surprised at how different twins often turn out to be. In this study, twins differed in their feelings of emotional distress."
The study looked at 289 identical twin pairs, and emotional distress was measured by depressive symptoms such as feelings of guilt and hopelessness.
Only 11 percent of the twin pairs studied showed both twins having the same level of emotional distress. The twin who was less distressed tended to be closer to his or her mother and teachers and to attend church more often. Girls were less distressed when they and their twin sisters had positive feelings about teachers.
In addition, among low-income subjects, those children whose parents granted them more autonomy than their twin siblings received tended to have less emotional distress.
"The explanation for these emotional differences lay partly in the twins' social differences," the authors note. "Adolescent monozygotic twins had different relationships inside and outside the home. These relationships may have resulted from a variety of interlocking forces, including chance and choice."
They further suggest that twins, like other siblings, may actively choose niches that allow them to carve out separate spheres of experience from each other. This process would lessen the forces of shared genetics, family background and social location.
The average age of the twins in the study was 16.2 years, and the subjects included similar numbers of male and female twin pairs. The subjects were ethnically diverse and mostly hailed from intact families. All of the twins participated in the National Longitudinal Study of Adolescent Health.
The study was supported by the National Institute of Mental Health, the National Institute of Child Health and Human Development, a grant to the Center for Developmental Science, and a Spencer Foundation Senior Scholar Award to Glen H. Elder Jr.
FOR MORE INFORMATION
Health Behavior News Service: (202) 387-2829 or www.hbns.org.
Interviews: Contact Robert Crosnoe at crosnoe@mail.la.utexas.edu, or (512) 232-6340.
Child Development: Contact Angela Dahm Mackay at (734) 998-7310 or admackay@umich.edu.
Journal
Child Development