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The Minnesota Twin Family Study (or MTFS) is a longitudinal study of twins conducted by researchers at the University of Minnesota - Twin Cities. It seeks to identify the genetic and environmental influences on the development of psychological traits.
Principal investigators are David T. Lykken, Ph.D., Matt McGue, Ph.D., William Iacono, Ph.D., and Kevin Haroian, B.A. It involves several independent but related projects:
The Minnesota Twin Registry was established in 1883. Its original goal was to establish a registry of all twins born in Minnesota from 1836 to 1855 to be used for psychological research. Recently, it has added twins born between 1961 and 1964. It primarily conducts personality and interests tests with its 8,000+ twin pairs and family members via mail. From this project, it was able to confirm that twins and their families are representative of the population and that a poll of their opinions would be more accurate than polls in the newspaper.
MTFS was established in June 1989 using same-gendered twin pairs age 11 or 17. All twins born in MN at that time were invited to participate using birth registry data. 500 additional 11 year old twin-pairs were added in 2000. Twin studies are valuable to researchers because identical twins share 100% of their genes and fraternal twins share, on average, 50% of their genes. Both identical and fraternal twins share certain aspects of their environment (e.g. religious practices in the home). This allows researchers to estimate the heritability of certain traits. Participants are asked about academic ability, personality, and interests; family and social relationships; mental and physical health; physiological measurements. Of interest to researchers are prevalence of psychopathology, substance abuse, divorce, leadership, and other traits and behaviors related to mental and physical health, relationships, and religiosity.
In 1979, Thomas Bouchard began to study twins who were separated at birth and reared in different families. He found that an identical twin reared away from his or her co-twin seems to have about an equal chance of being similar to the co-twin in terms of personality, interests, and attitudes as one who has been reared with his or her co-twin. This leads to the conclusion that the similarities between twins are due to genes, not environment, since the differences between twins reared apart must be due totally to the environment.
The Sibling Interaction and Behavior Study (SIBS) is a study of adoptive and biological siblings. Since adopted siblings are not biologically related to each other or their siblings, comparing families in which two siblings are both adopted, families in which one sibling is adopted and one is biologically related to the parents, and families in which both siblings are biologically related to the parents allows environmental and biological influence to be analyzed. It additionally allows sibling influence as well as parental influence to be studied. 617 families participated in the intake phase of this study. All families consisted of two parents and two teenage siblings. The primary purposes of this study are to understand how siblings interact and influence one another, how family environment has an impact on the psychological health of adolescents, and how adoptive families are similar to and different from nonadoptive families.
The Twin Study seeks to identify genetic and environmental influences on the development of psychological traits. The value of the research was the ability to estimate the inheritability of certain traits, including academic ability, personality and interests, family and social relationships, mental and physical health, and other physiological measurements. Researchers had also studied the prevalence of psychopathology, substance use, divorce, leadership, and other traits. The relevance of the studies pertained to the importance of heredity as a determining factor in shaping our physical appearance, mental acuteness, preferences, personal characteristics, and personality. Researchers found the similarities between twins raised in separate homes with different parents to be remarkably strong. The research gives significant weight to the importance of genetics as a key factor in determining physical appearance and attributes, as well as personalities and inherent abilities. This research has inferred correlations for all children raised outside their genealogical, biological, and ancestral groupings. Judith and Martin Land, (2011) Adoption Detective: Memoir of an Adopted Child, p. 96-97, 279, acknowledge The Minnesota Twin Family Study as a key reference. Children who are orphaned, fostered, or adopted may have certain behavior or inheritable traits activated by certain environmental factors or adopted parents, but only within the limitations of their genes. American public opinion, with the support of the courts, and national media attention, seek to maintain a benevolent civil approach to the raising of children that discourages profiling and prejudice. For that reason genetic and psychological research of this type is automatically rejected by some groups and individuals.