There are few issues as hotly contested — and as poorly understood — as the question of what makes a person gay or straight. It's not only a political, social, and religious question but also a scientific question, one that might someday have an actual, provable answer.
The handful of scientists who work in this under-funded and politically charged field will tell you: That answer is a long way off. But as Lesley Stahl reports, their efforts are already yielding tantalizing clues. One focus of their research is twins.
The bedrooms of 9-year-old twins Adam and Jared couldn't be more different. Jared's room is decked out with camouflage, airplanes, and military toys, while Adam's room sports a pastel canopy, stuffed animals, and white horses.
When Stahl came for a visit, Jared was eager to show her his G.I. Joe collection. "I have ones that say like Marine and SWAT. And then that's where I keep all the guns for 'em," he explained.
Adam was also proud to show off his toys. "This is one of my dolls. Bratz baby," he said.
Adam wears pinkish-purple nail polish, adorned with stars and diamonds.
Asked if he went to school like that, Adam says, "Uh-huh. I just showed them my nails, and they were like, 'Why did you do that?'"
Adam's behavior is called childhood gender nonconformity, meaning a child whose interests and behaviors are more typical of the opposite sex. Research shows that kids with extreme gender nonconformity usually grow up to be gay.
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Danielle, Adam and Jared's mom, says she began to notice this difference in Adam when he was about 18 months old and began asking for a Barbie doll. Jared, meanwhile, was asking for fire trucks.
Not that much has changed. Jared's favorite game now is Battlefield 2, Special Forces. As for Adam, he says, "It's called Neopets: The Darkest Faerie."
Asked how he would describe himself to a stranger, Jared says, "I'm a kid who likes G.I. Joes and games and TV."
"I would say like a girl," Adam replied to the same question. When asked why he thinks that is, Adam shrugged.
"To me, cases like that really scream out, 'Hey, it's not out there. It's in here.' There's no indication that this mother is prone to raise very feminine boys because his twin is not that way," says Michael Bailey, a psychology professor at Northwestern University and a leading researcher in the field of sexual orientation.
Bailey says he doesn't think nurture is a plausible explanation.
Psychologists used to believe homosexuality was caused by nurture — namely overbearing mothers and distant fathers — but that theory has been disproved. Today, scientists are looking at genes, environment, brain structure and hormones. There is one area of consensus: that homosexuality involves more than just sexual behavior; it's physiological.