I wanted to let you all know about a new book I think is an important contribution to the scientific understanding of the relative roles of heredity and environment: ENTWINED LIVES: TWINS AND WHAT THEY TELL US ABOUT HUMAN BEHAVIOR (1999, Dutton) by Dr. Nancy Segal, a professor of psychology at California State University, Fullerton. Nancy spent nearly a decade working at the famous Minnesota Center for Twin and Adoption Research with Thomas Bouchard, Jr., and has been a contributing editor for TWINS magazine. (She is also a twin--fraternal.)

Nancy and her book were the subject of a Dateline NBC special report on twins a couple of weeks ago and this pushed her book up toward the top of the Amazon.com list (where you can order it, or it should be in most bookstores by now). She will be on my radio show this Wednesday from 6-7pm, 89.3 FM, KPCC, followed by a book signing at Borders bookstore at 475 South Lake Blvd. in Pasadena, next to Macy's.

What is especially interesting about Nancy's work is that she has developed an extensive database of not only maternal and fraternal twins, but of what she calls "pseudotwins"--adopted children of the same age raised in the same home. That is, they share no genetic relationship at all but they do share the same environment (since they are the same age there will be no birth order effects ala Frank Sulloway's research that shows how siblings of different ages compete for parental attention with different strategies and thus develop different attitudes, beliefs, and personalities). The bottom line to this study is fascinating: identical twins reared apart are more similar on almost any measurable behavioral trait or personality characteristic than these pseudotwins. So, as we continue to see over and over again, heredity matters in a big way.

This is just one part of Nancy's research. The book is a complete study of twins, including all the amazing and almost freaky similarities between identical twins reared apart, like the Jim twins Jim Lewis and Jim Springer. These identical twin brothers were separated at birth and reunited at age 39. In addition to having the same jobs, cars, hobbies, and health histories, they both married a first wife named Linda, and a second wife named Betty (apparently when one of them separated from his wife the other wife got worried), they named their sons the same name of James Alan (the other James Allan--maybe the letter l is not genetically programmed), both drove a light blue Chevrolet when they met, both worked as sheriffs, both smoked Salems and drank Miller Lite, and, most amazingly, they both used the same brand of toothpaste--and I don't mean Crest--it was an obscure imported Swedish toothpaste called Vademecum. Nancy's explanation for the latter is that genes code for taste preferences. Still, this is darn right spooky. And the book is filled with such stories, as well as a LOT of good, solid research data. Check it out right away.