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.