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Here's an environmental question for you, but it's not about recycling or species preservation; it has more to do with us as human beings and what makes us what we are.

The question is: how much of our talents, personality and interests come from our upbringing and environment, and how much comes from the genes that we inherited from our parents?Up until recently, that seemed like an impossible question to answer. How could you separate the influence of the environment and the influence of heredity?

Surprisingly, there is a way. And Dr. Tom Bouchard and his colleagues at the University of Minnesota have spent the last 17 years working on it.

Their technique involves taking advantage of an outmoded adoption practice. Today, adoption officials almost never separate twins. But up until a generation ago it was a common practice. Hundreds and hundreds of twins both in this country and in England were separated in infancy and reared apart.

To understand why twins who were reared apart are important to the nature-nurture question, keep in mind that identical twins come from a single fertilized egg that split in half. Coming from the exact same sperm cell and the exact same egg, their heredity is identical.

Fraternal twins, on the other hand, each come from a separate egg and a separate sperm. Genetically, fraternal twins are no more alike than other siblings who happened to be born in different years rather than at the same time.

So in the case of identical twins reared apart, because their heredity is the same, the differences between them come from their environment.

In the years since Bouchard began his research, he has found and studied more than 120 sets of twins, including fraternal and identical twins, who were reared apart. Many of them were separated at birth. The twins who are part of this study have undergone at least a week of testing, including answering more than 15,000 questions.

Some of the results are what you'd expect. Identical twins are almost always closer to each other in weight than fraternal twins. Genetics plays a large role in body weight. But identical twins are also close in areas that you wouldn't expect.

Frequently twins who have never met before coming to Bouchard's laboratory share eerily similar personality traits. In one set of twins, for instance, each had a fear of water and they handled their fear the same way: both of them always backed into a lake or a pool.

Often identical twins have similar personality traits. They usually have similar scores on tests that measure sense of well-being, ability to deal with stress, acceptance of traditional values and ability to exercise self-control. Fraternal twins, in contrast, are less alike in all these areas.

With surprising frequency, identical twins, even when reared apart, also have the same hobbies and choose similar lines of work. Bouchard has seen many cases like the identical twin brothers who hadn't seen each other since infancy, yet each became a volunteer fire captain.

Bouchard believes that genes and heredity play a far more powerful role in making us what we are than we previously suspected. Our heredity can strongly predispose us towards certain talents, interests and personality traits.

However, Bouchard emphasizes that a predisposition is not the same thing as being predetermined. The environment still plays a very major role.

If you are a separated twin and would like to participate in these studies or would like assistance in finding your twin, write to Dr. Thomas Bouchard, University of Minnesota, Elliott Hall, Minneapolis, MN, 55455.