Word: dna
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...identical twins. For example, psychologist Michael Bailey of Northwestern University famously demonstrated that if one identical twin is gay, there is about a 50% likelihood that the other will be too. Seven years ago, Hamer picked up where the twin studies left off, homing in on specific strips of DNA that appear to influence everything from mood to sexual orientation...
...decision to switch fields was Charles Darwin's The Descent of Man, and Selection in Relation to Sex. "I was fascinated to learn that Darwin seemed so convinced that behavior was partially inherited," he remembers, "even though when he was writing, genes had not been discovered, let alone DNA." Homosexual behavior, in particular, seemed ripe for exploration because few scientists had dared tackle such an emotionally and politically charged subject. "I'm gay," Hamer says with a shrug, "but that was not a major motivation. It was more of a question of intellectual curiosity--and the fact that...
...results of Hamer's first foray into behavioral genetics, published by the journal Science in 1993, ignited a furor that has yet to die down. According to Hamer and his colleagues, male homosexuality appeared to be linked to a stretch of DNA at the very tip of the X chromosome, the chromosome men inherit from their mothers. Three years later, in 1996, Hamer and his collaborators at NIH seconded an Israeli group's finding that linked a gene on chromosome 11 to the personality trait psychologists call novelty seeking. That same year Hamer's lab helped pinpoint another gene, this...
Hunting down the genes that influence personality remains a dauntingly difficult business. Although DNA is constructed out of a mere four chemicals--adenine, guanine, cytosine, thymine--it can take as many as a million combinations to spell out a single human gene. Most of these genes vary from individual to individual by only one chemical letter in a thousand, and it is precisely these minute differences that Hamer and his colleagues are trying to identify. Of particular interest are variations that may affect the operation of such brain chemicals as dopamine and serotonin, which are well-known modulators of mood...
Over the coming decade, Hamer predicts, scientists will identify thousands of genes that directly and indirectly influence behavior. A peek inside the locked freezer in the hallway outside his own lab reveals a rapidly expanding stash of plastic tubes that contain DNA samples from more than 1,760 volunteers. Among them: gay men and their heterosexual brothers, a random assortment of novelty seekers and novelty avoiders, shy children and now a growing collection of cigarette smokers...