Spend enough time reading gossip magazines and famous women’s can start to look like a game of -blind musical chairs. Anne Heche had a three-year romance with Ellen DeGeneres—then left her for a male cameraman. Julie Cypher left her husband, Lou Diamond Philips, to pursue a relationship with Melissa Etheridge. Years later, she split with Etheridge and married another man. Cynthia Nixon was in an opposite-sex —until she met her current partner, a woman.

What’s going on here?

Both anecdotally and in the lab, women display greater sexual fluidity than men. Yet women aren’t always consciously aware of the variety of things that might turn them on—especially, studies show, when they consciously identify as heterosexual. In a new Archives of Sexual Behavior paper, University of Cardiff researchers Robert J. Snowden and Nicola S. Gray report that not only are straight women aroused by both male and female erotica, but—at least on a level—they consider both genders’ faces equally enticing.

“We can’t say their sense of their own sexuality is somehow wrong,” Snowden reported, “but what heterosexual women automatically appraise as arousing is not in line with their stated orientations.”

Press One for Straight

Snowden and Gray had men and women of all orientations press one button when a picture of a man or a sexually positive word (sensual, erotic) showed up on their screens, and another when they saw pictures of women or sexually negative words (ugly, repulsive). The test was then repeated with the opposite conditions: one button for females and sexy words, the other for males and unsexy words.

As expected, straight men and lesbians had the quickest reaction times when female images were paired with words like “arousing” and “stimulating,” while men responded fastest when the conditions were flipped. The surprise? “Heterosexual females did not show the expected preference for males over females,” Snowden explained. The results indicate that they most had either a mild to women or comparable reactions to both sexes.

Adaptive Attraction

Why are so many women aroused by a greater variety of stimuli than men? Part of the answer may be evolutionary: “Lubricating in response to all kinds of situations may have protected a woman’s organs from damage,” especially in the event of a nonconsensual encounter, suggests Florida State University psychologist Roy Baumeister. Having a more malleable sex drive, he adds, may also have enabled a woman to better adapt to changing circumstances, like shifts in mate availability or the loss of a partner.

Meredith Chivers, a sexuality researcher at the University of Toronto, notes that throughout history men have been more likely to take the lead in sexual encounters. So while men must have evolved a clear and steady attraction toward women, the reverse might not be true.

Still, capacity does not predict : A wide range of women can be attracted to members of the same sex, yet the vast majority still identify as straight and choose male partners. “Something is orienting their sexuality,” Chivers says, “but we still don’t fully understand what or why.”

One more clue: Behavioral plasticity isn’t exclusive to the realm of sexuality—female identity seems to be more malleable in general. In a 2003 study, Susan Turk Charles and Monisha Pasupathi found that, over the course of a single week, women were far likelier than men to report identification with conflicting traits, like submissive and argumentative, compliant and forceful. If women’s conceptions of themselves can be so fluid, it’s no wonder their sexualities are less fixed and more responsive to outside stimuli—whatever the stimuli might be.

Historically Heteroflexible?

Snowden and Gray’s findings are especially pronounced, but they aren’t the first indication that straight women’s attractions may diverge from their professed orientations. A uniquely female fluidity has coursed through just about every major sexuality study since Kinsey’s work in 1940.

Sociologist Edward O. Laumann found in 1994 that heterosexual women were more likely than men to have had a sexual encounter with the same gender, and in 2003, Nigel Dickson noted that a quarter of straight women admitted that they had experienced a romantic inclination toward a member of the same sex, compared to about 10 percent of straight men. In a 2005 study, Chivers discovered that heterosexual females were physiologically aroused by straight, gay, and lesbian alike.

Do male social taboos explain the gender divide? Not entirely. “Being somewhat attracted to both sexes seems to be the default for women,” says Chivers. “It’s as if this flexibility is built into females’ mating psychology.”

Neither Straight Nor Narrow

Straight women may be particularly ambidextrous in their attractions, but gay women seem to share at least some of the inclination to ambiguity. While the results might be different if repeated today, two studies—one in 1990 by Ritch C. Savin-Williams and another by Margaret Rosario six years later—found similar results: About 80 percent of gay women had had sex with a man, while just over half of gay men had had sex with a woman.