The conventional wisdom is that as people progress in life they become set in their ways. But new research suggests that women have great potential to change in middle age — at least with respect to their sexuality. Researchers say it's increasingly common for women, often after being married to a man for years, to start their first lesbian relationship later in life. Here's a quick guide to what's happening:

What have these studies found?
The phenomenon is more common than many people think. Christan Moran, a researcher at Southern Connecticut State University, interviewed more than 200 women over 30 who were married to men but found themselves attracted to a woman, and concluded that heterosexual women can "experience a first same-sex attraction well into adulthood." Utah University professor Lisa Diamond has, for 15 yearss, followed a group of 79 women who reported some same-sex attraction. Every two years, 20 to 30 percent change the way they describe themselves — gay, straight, or bi-sexual. Seventy percent have changed since the study began. In August, at the American Psychological Association's annual convention, research by Moran and others will be showcased in a session called "Sexual Fluidity and Late-Blooming Lesbian."

Were "late-blooming lesbians" always gay, but closeted?
Not always. In some instances, women may come out after repressing or hiding their feelings. But Diamond, as quoted in the Guardian, says that often "women who may have always thought that other women were beautiful and attractive would, at some point later in life, actually fall in love with a woman, and that experience vaulted those attractions from something minor to something hugely significant." In these cases, Diamond says, "it wasn't that they'd been repressing their true selves before; it was that without the context of an actual relationship, the little glimmers of occasional fantasies or feelings just weren't that significant."

Why might this happen later in life?
Diamond thinks it might be a combination of factors. Women's minds and bodies change with age, and their circumstances and priorities shift. "People become more expansive in a number of ways as they get older," Diamond says. "I think a lot of women, late in life, when they're no longer worried about raising the kids, and when they're looking back on their marriage and how satisfying it is, find an opportunity to take a second look at what they want and feel like."

Is this a new phenomenon?
No, but researchers say declining homophobia is making it easier for women to explore a new sexual identity. And some late-blooming celebrity lesbians are encouraging even wider social acceptance. Sex and the City's Cynthia Nixon was in a heterosexual relationship for 15 years before she became involved with her current partner, Christine Marinoni, in 2004. Actress Portia de Rossi was married to a man before she married Ellen DeGeneres in 2008. Comedian Carol Leifer, who was the inspiration behind the Elaine character on "Seinfeld," dated men, including Jerry Seinfeld, until the age of 40. Then she fell for a woman. "My feelings for men were very real and powerful, but I fell in love with my partner," she told ABC News. "It's been the best relationship of my life." 

Sources: Guardian, Daily Mail, Telegraph, ABC News, Zimbio