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Some bisexual women travel a similar path. Sarah Listerud, a member of a large Catholic family, arrived at Oberlin College believing marriage for her was a "given." During her sophomore year, she fell in love with a woman. She had subsequent lesbian liaisons but remained attracted to men. "I thought bisexuality was a phase I was going through before joining the lesbian community," recalls Listerud, now 29 and living in Chicago. But then, she would "bump into a guy in the cafeteria who was really cute or get a crush on a guy. Finally, it was like a little light bulb went off. I thought maybe bisexuality is real. I was absolutely terrified. It was undesirable; it was not politically correct. I was sure to be ostracized from the lesbian community."
For other women, bisexuality is a late discovery. "Many never had any sexual attraction to other women," notes psychiatrist Tim Wolf of San Diego. "But now they are in their 30s or 50s, and they fall in love with a particular woman." Lani Kaahumanu was a typical San Mateo, Calif., housewife, wed to her high school sweetheart for 11 years and the mother of two children. With the women's movement of the '70s, "all of a sudden there was this freedom to love women," says Kaahumanu, 48. She divorced and for four years lived what she calls a "very public lesbian life." But by 1980 Kaahumanu had fallen in love with a man. Wolf speculates that women come to a realization of their bisexuality later than men do because women tend to be more physically affectionate with each other throughout their lives and this closeness camouflages the sexual desire. Women also seem to show more sexual flexibility than men and switch their sexual focus more often, he adds.
What causes the duality of desire? Most experts believe sexual orientation develops from a mix of nature and nurture, but the recipe remains a mystery. Gender may be fixed prenatally by a chromosome and a wash of hormones, but does a flood of chemicals prime the fetus for a particular sexual preference?
Scientists are discovering differences in brain structure -- at least between straight and gay men. UCLA researchers reported this month that autopsies showed that the anterior commissure -- a bundle of nerves that connects the left and right hemispheres of the brain -- appears to be about a third larger in homosexuals than in heterosexuals. Another study, published last year, revealed that a segment of the hypothalamus, which influences sexual activity, seems to be half as large in gay men as it is in straight men. A recent survey found that when one twin is gay, an identical sibling is three times as likely as a fraternal twin to be gay as well.
Although such findings suggest a strong biological influence, they are hardly conclusive. One problem: Are the differences in brain tissue the cause or the result of differences in behavior? "You've always got to keep in mind that experience changes the brain," stresses June Reinisch, director of the Kinsey Institute. And if nature is paramount, why don't identical twins always have the same sexual orientation?