And that, she says, is how some women develop sexual desires for their friends. She says most people are sexually attracted to both sexes, even if the attraction is as lopsided as 95 percent for one sex and 5 percent for the other. "I do think that there's a lot more wiggle room with regard to desire and love than most people are usually comfortable acknowledging." She says she has studied cases of women who fall hopelessly in love with a female friend, and even though both women are heterosexual, they will date and have sex and feel fully satisfied. But yet, they are not lesbians, she says. Their interest is only in each other, spurred by an emotional bond that turned sexual -- and if the relationship ends, as she has seen happen, the women both go back to happily dating men.

One woman she studied had lived with a female friend for over a year, and the woman would spend hours walking along streets, trying to decide if she was attracted to other women or not. It turns out, she never was. "People can experience strong sexual attractions that are totally unusual to the rest of their experience," Diamond says. "They're situational. In one setting and one circumstance, it may seem possible."

So if this is true, why are straight women turned on by lesbian porn? Bailey has a number of theories, and he feels he'll get closer to the answer once his research team repeats the study -- but this time, they'll monitor brain waves instead of genitals. He said there's a chance the women aren't actually being turned on by the porn, but that their stimulation is a hard-wired biological defense. Much like a woman who becomes genitally aroused while being raped, Bailey said, women may only be creating lubricant so that they are not damaged by something penetrating them -- something his probes had registered as a sexual stimulation. "Genital arousal in women is not the same thing as being in the mood," he says.

Or, he says, it could be something quite different: All women may be naturally bisexual, and society shapes most of them into heterosexuals. He says this could be an evolutionary trait, because women didn't have to develop a sexual orientation when men, as the historically dominant species, were the ones always seeking out mates.

But as some skeptics of the study suggest, women may not be guided by their biology at all, but only by the sexual images and stereotypes around them. American culture, for what it's worth, is a drooling teenage boy. It is obsessed with the female body, sprinkling a busty silhouette or a seductive midriff on any object that needs extra pizzazz. The country will tolerate a male sexual figure every so often, with his remarkably hairless torso and abs like a plate of chicken nuggets, but the penis is categorically off-limits. Where Americans see sex, they see only breasts -- at the movies, in magazine ads, through the perky shreds of fabric that pass as bikinis. And therefore, both American men and women have come to associate the very essence of sex with the female form, according to sex therapist Wendy Maltz, coauthor of "Private Thoughts: Exploring the Power of Women's Sexual Fantasies." So, she says, when the straight women in the study were becoming aroused by watching lesbian porn, they were only responding to a culturally programmed symbol of sex. "Let's take both men and women who had never been exposed to any visual imagery of sex, and then let's hook them up and see what goes on, and I think you'd find different reactions."

But while society is never short on ingrained sexual suggestion, a growing collection of writing claims that women are more susceptible to cultural influences than men. In "Gender Differences in Erotic Plasticity: The Female Sex-Drive as Socially Flexible and Responsive," psychologist Roy F. Baumeister argues that women's sexual behavior is less consistent than men's, because women's sexuality is more strongly linked to changing variables such as education and religion. For instance, the feminist movement of the 1970s is often cited as influencing the sexual orientation of the women most closely involved, turning straight women into lesbians because of what writer Sarah Pearlman called a "choice as much on politics as on sexual interest in other women."

Maltz says that men are also a slave to society, and their response to the porn in the study proves it. Just as straight women were turned on by women because of the female body's cultural implications, straight men were turned off by other men because of America's severe homophobia. Men are taught to avoid the male body, to be borderline repulsed by it, and the straight men in the study did just that, she said. Meanwhile, since women are open to seeing another woman's body, they're free to identify with that woman -- to see her orgasm on screen and physically feel it for themselves, just as they might cry upon seeing people enrapt in sorrow. On a surface level, they are being aroused by the woman on the screen, but Maltz says the real response is deeper than that. "It's not necessarily a desire to be with that woman. It's probably a celebration of their own female sexuality. It's an identification with the woman rather than a lusting after her."

That's not to say that women respond to sexual situations the same way that men do, though. While Maltz contests that the porn study reveals anything about a woman's biology, she does concede that women are inherently different in their sexual interests. Where men want sex, women want relationships -- even in their deepest fantasies. "Women's hearts are very connected with their sexual response," she says. In the marketplace, this manifests itself most in romance novels, a forum where the sex may be hot but the emotions are heavy. And while men may scoff, these books capture so many women because they portray men at their sexiest: devoted, adoring and there in the morning. Men are anchored to the flesh, it seems, but women need their lovers in context. "A lot of women are aroused by the ideal of a man being very faithful and drawn to a particular woman, and that they have found each other, that she maybe has been the answer he was looking for in life."

But to one porn industry veteran, the study really only captures how women respond to porn, not to sexual situations. Annie Sprinkle, a porn star turned sexual performance artist, has seen a lot of changes since she entered the industry 30 years ago and one of those changes was the growth of a female audience. For decades, centuries even, men were the prominent consumers of porn, and so they've learned to filter and nit-pick the bits of pornography that turn them on, she says. For women, though, porn is something relatively new and generally untamed. Since women haven't become as selective yet, she says, they're being turned on by, well, just about anything.

Sprinkle has seen the porn industry drag American culture along, redefining what people think is sexy by blindly guessing its market value. She remembers porn in the 1970s, when the industry assumed women wanted to be loved in a soft, pink and fuzzy sort of way. Films were made to reflect that, and in due time, women's sexual preferences followed along. "People are very impressionable," she says. "In my experience, watching what's been made, I think people have a gut reaction to what they like and don't like, but they also are very conditioned by what's out there. The porn industry thinks it knows sometimes, and they don't necessarily always know. They think they know, and that's what they make, and then people start to like what they make."

If there really is a difference between what arouses men and women, she says, it's probably based on hormones. Most women she meets are aroused more from the head and heart, but her transsexual friends are unpredictable, she says. One friend in particular exhibited a stunning transformation when she started taking testosterone pills. Now, Sprinkle says, the former cuddle-loving woman is "a lot more about fucking than romance."

So then, what is it about female sexuality that seems so elusive? Why are men so predictable, so pathetically easy to forecast and satisfy, when women are being aroused by the unexpected and falling in love with the previously unthinkable? Why does light seem to travel slower than the development of a man's erection, and yet women, according to Florida-based sex therapist Miriam Davis, can take up to 45 minutes of stroking and kissing to become fully aroused? (The time delay is for multiple reasons, Davis says, be they reservations due to poor body image or unresolved anger or anxiety that are easy distractions from sexual pleasure.)

Whatever it is, Sprinkle says we'll never know. And while she appreciates the scientific inquiries into such questions, she says the conclusions will never be concrete explanations, but only tiny snapshots of our sexuality today. Tomorrow, though, everything could change. The past 50 years have been nothing short of a sexual revolution, she says, and she expects nothing less of the next 50. "It's nice to generalize, but it's important to remember, with human sexuality, it's so multifaceted. It's like trying to say 'What is life?' What's the difference between men and women in life in general? You can't really pinpoint it. Sex, there's so many levels to it. That's the beauty of it."

And that's the message Katie likes to hear. A college student in Chicago who asked that her real name not be used, Katie stopped looking for answers years ago. She says she always thought girls were beautiful, even if she once considered herself straight. Then, in her sophomore year of high school, she developed a crush on a girl. And then another. And now, years later, even as she's been dating her boyfriend for a year and a half, she has a hopeless crush on his sister. She still hasn't actually touched another girl, but she expects to one day, and none of this ever confuses her. Even when she developed her first crush on a girl, she merely shrugged it off. "She was gorgeous, had this awesome body, awesome funny personality. I really liked her," she says. "I just figured, if this is the stuff I like in a person, so what if she's not a guy? What does it matter?"

These days, Katie actively rejects any label. She's not straight, but she's not bisexual, and she believes that, at their very core, women don't even have a sexual preference. "We like what we like, and we'll do what we need to get it," she says. She's told her boyfriend this, and he said that as long as she doesn't cheat on him, he doesn't care who she gets turned on by. That's good to know, she says, because the people on her radar are many and multicolored, and she doesn't want them to stop coming. "A woman's body is an extremely sexual thing that can arouse anyone," she says. "I don't think I'd ever limit myself to one gender. I don't think it matters."

Private Life Romance, relationships, and the personal side of Table Talk