WHAT MAKES THEM DO IT

By Anastasia Toufexis

DO YOU GET A KICK OUT OF DANGEROUS sports like skydiving and whitewater rafting? Do you jump eagerly from job to job or even get a thrill from rearranging the furniture? If so, you are probably what psychologists call a "novelty seeker." The exact origins of personality types have eluded scientists for years. But it now appears that a craving for exciting new experiences can be credited, in part at least, to a single gene.

So say teams of researchers from Israel and the U.S. who announced independently last week that they have linked novelty seeking to a gene on chromosome 11. This marks the first time a normal personality trait has been firmly linked to a particular gene. Says Dr. Robert Cloninger, professor of psychiatry and genetics at Washington University in St. Louis, Missouri: "Eventually we are going to be able to genetically map personality traits as precisely as we will physical characteristics like height and weight."

In the two studies published in the current Nature Genetics, people filled out personality questionnaires and had blood taken for genetic analysis. The scientists found that those whose answers showed them to be exploratory and excitable--two hallmarks of novelty seeking--have a longer version of a gene known as D4DR, compared with those who are more reserved and reflective.

The gene helps regulate dopamine, a chemical messenger in the brain that mediates pleasure and emotion. Researchers have yet to figure out exactly how the longer gene affects behavior. What they do know, says Dr. Jonathan Benjamin, an Israeli visiting scientist at the U.S. National Institute of Mental Health and co-author of the study, is that "when a molecule of dopamine arrives knocking on the door to a cell, the cell reacts a little bit more strongly in the people with the long version."

Does this mean the D4DR gene alone compels people to take up bungee jumping or air surfing? Emphatically not. Researchers suspect that another four or five dopamine-related genes also contribute. Moreover, behavior ultimately depends as much on upbringing and opportunity as it does on innate temperament. Someone with the thrill-seeking gene might turn out to be a serial murderer, observes behavioral geneticist Irving Gottesman of the University of Virginia. "Under a different scenario and in a different environment," he says, "that person could become a hero in Bosnia."

And that has ethicists worried. As scientists fill in knowledge about the genes of personality, will employers and insurers use genetic work-ups to deny jobs to those inclined to love thrills? Will parents demand prenatal testing to weed out children who have the "wrong" personality genes? "They are big issues," admits Dr. Richard Ebstein, a molecular biologist who led the research team at Jerusalem's S. Herzog Memorial Hospital, "and they will come up."

--By Anastasia Toufexis. With reporting by Jenifer Mattos/New York and Eric Silver/Jerusalem

With reporting by JENIFER MATTOS/NEW YORK AND ERIC SILVER/JERUSALEM