The Minnesota Twin Registry started in 1983 on the premise that all human research is more interesting and informative if twins participate. Its original goal was to establish a registry of all twins born in Minnesota from 1936 to 1955 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, we were 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.
The Minnesota Twin Study of Adult Development began in 1986 to identify what causes individual differences in aging. Study of identical (MZ) and fraternal (DZ) twins allows for estimation of how genes and environment affect the aging process. Some of its preliminary findings are the following: (1) Genetic factors appear to influence personality, mental, and activity-level changes as adults become older; (2) Maintaining an active lifestyle will contribute to more successful aging; (3) Continuing to engage in intellectual activities will help adults retain cognitive functioning as they age; and (4) Keeping an active social life will contribute to stronger feelings of happiness and well being. This study is directed by Dr. Matt McGue.
In 1979, T.J. Bouchard began to study twins who were separated at birth and raised in different families. We have 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 finding leads us to believe that the similarities between twins are due to genes, not environment. Given that the differences between twins reared apart must be due totally to the environment, and givne that these twins are just as similar as twins reared together, we can conclude that the environment, rather than making twins alike, makes them different.
One example of the amazing similarity of twins reared apart is the so-called “Jim twins”. These twins were adopted at the age of four weeks. Both of the adopting couples, unknown to each other, named their son James. Upon reunion of the twins when they were 39 years old, Jim and Jim have learned that:
- Both twins are married to women named Betty and divorced from women named Linda.
- One has named his first son James Alan while the other named his first son James Allan.
- Both twins have an adopted brother whose name is Larry.
- Both named their pet dog "Toy."
- Both had some law-enforcement training and had been a part-time deputy sheriff in Ohio.
- Each did poorly in spelling and well in math.
- Each did carpentry, mechanical drawing, and block lettering.
- Each vacation in Florida in the same three-block-long beach area.
- Both twins began suffering from tension headaches at eighteen, gained ten pounds at the same time, and are six feet tall and 180 pounds.