Romantic opportunities appear to influence women's sexual identities, but not men's

"This indicates that women's sexuality may be more flexible and adaptive than men's," said study author Elizabeth Aura McClintock, an assistant professor of sociology at the University of Notre Dame.

McClintock's study relies on data from the National Longitudinal Study of Adolescent to Adult Health (Add Health) and considers its first (1994-1995), third (2001-2002), and fourth (2007-2008) waves. More specifically, she tracked 5,018 women and 4,191 men as they moved from adolescence to young adulthood. On average, they were 16-years-old in Wave I, 22 in Wave III, and 28 in Wave IV.

Confirming previous research, McClintock found that women were more likely than men to report bisexuality, while men were more likely to report being either "100 percent heterosexual" or "100 percent homosexual." She also found that women were three times more likely than men to change their sexual identities from Wave III to Wave IV of Add Health. Add Health participants, who were not asked about their sexual identities until Wave III, could identify as 100 percent heterosexual, mostly heterosexual, bisexual, mostly homosexual, and 100 percent homosexual.

In each wave of Add Health that McClintock used for her study, participants were also asked if they had ever experienced same-sex attraction or participated in same-sex sexual activity.

"Women have a greater probability than men of being attracted to both men and women, which gives them greater flexibility in partner choice," said McClintock. "Having flexible sexual attractions may grant greater importance to contextual and experiential factors when it comes to sexual identity."

McClintock's research showed that women with more education and women who were more physically attractive (as rated by their Add Health interviewers) had higher probabilities of identifying as "100 percent heterosexual" than other women in Waves III and IV of Add Health. In addition, women who had a child by Wave III were less likely than other women to identify as "100 percent heterosexual" in Wave IV.

McClintock speculated that women who avoided young motherhood, were physically attractive, or had high levels of education may have been less likely to explore relationships with same-sex partners because they had more romantic opportunities with male partners. In other words, their social position facilitated a hetero-conformist identity and thus discouraged alternative sexual identities, according to McClintock.

"Women with some degree of attraction to both males and females might be drawn into heterosexuality if they have favorable options in the heterosexual partner market," McClintock said. "Women who are initially successful in partnering with men, as is more traditionally expected, may never explore their attraction to other women. However, women with the same sexual attractions, but less favorable heterosexual options might have greater opportunity to experiment with same-sex partners. Women who act on same-sex attraction are more likely to incorporate same-sex sexuality into their sexual identities."

Interestingly, for men: higher levels of education were associated with a lower likelihood of identifying as "100 percent heterosexual" in Waves III and IV of Add Health, physical attractiveness had no clear association with sexual identity, and those who became fathers by Wave III were more likely to identify as "100 percent heterosexual" in Wave IV.

"Men are less often attracted to both sexes," McClintock said. "Men's sexuality is, in this sense, less flexible. If a man is only attracted to one sex, romantic opportunity would little alter his sexual identity."

McClintock said sexual identity is a social construct. "It is important to emphasize that I am not suggesting that same-sex unions are a second-best option to heterosexual unions," McClintock said. "And I do not think that women are strategically selecting an advantageous sexual identity or that they can 'choose' whether they find men, women, or both sexually attractive. Rather, social context and romantic experience might influence how they perceive and label their sexual identity."