By Julie Moreau

The children of lesbian parents are less likely to identify as heterosexual as adults and much more likely to report same-sex attraction, according to a long-term study by the Williams Institute at the UCLA School of Law, a think tank focused on sexual orientation and gender.

As many as 6 million children and adults in the U.S. have lesbian, gay, bisexual or transgender parents, according to the institute, and its study found that “the female and male offspring of lesbian parents were significantly more likely to report same-sex attraction, sexual minority identity, and same-sex experience.”

“Perhaps we should be celebrating that the culture has evolved enough that these young people feel free to explore who they are."

Dr. Nanette Gartrell, M.D.

“These findings suggest that adult offspring from planned lesbian families may be more likely than their peers to demonstrate diversity in sexual attraction, identity, and expression," the report said.

The study employs the National Longitudinal Lesbian Family Study (NLLFS), the longest-running, real-time study of sexual-minority-parent families in the world. Started in 1986, the study has been following the offspring of lesbian parents from conception into adulthood. For this latest report, 76 children of lesbian parents, now all adults in their mid-20s, were asked about their sexual attraction, identification and behavior. For comparison, researchers demographically matched these offspring with 25-year-old participants in the National Survey of Family Growth (NSFG).

‘FREE TO EXPLORE WHO THEY ARE’

Of the 76 children of lesbian parents, 70 percent of females and 90 percent of males identified as “heterosexual or straight,” compared to 88 percent of females and 98 percent of males in the demographically matched NSFG group.

Further, 54 percent of women and 33 percent of men with lesbian parents reported having a same-sex sexual experience between the ages of 17 and 25, compared to 38 percent of women and 9 percent of men in the NSFG group.

Dr. Nanette Gartrell, the report’s lead author and a visiting distinguished scholar at the Williams Institute, told NBC News there are multiple theories to explain sexual orientation — including hormones, genetics and the environment — but so far, she added, “the evidence suggests that there is no one factor that is a single determinant.”

When asked for her explanation as to why the sons and daughters of lesbians might be less likely to identify as straight, she noted they “may have more expansive perspectives on sexuality.”

“They were raised by parents who were nonjudgmental and may be more attuned to their own feelings because of the environments in which they were raised,” Gartrell said. “Perhaps we should be celebrating that the culture has evolved enough that these young people feel free to explore who they are.”

As for the big gender gaps among men and women from both the NLLFS and NSFG groups, Gartrell said these differences are consistent with previous research over the past 15 years that suggests women experience sexuality more fluidity than men.

The findings, she added, are also consistent with research that demonstrates “variability and fluidity in sexual development, expression and self-identification over time, particularly in the span from adolescence to early adulthood.”

‘ANCIENT STEREOTYPES AND FEARS’

About the broader National Longitudinal Lesbian Family Study, Gartrell said its motivation was to understand the first generation of children conceived by donor insemination in the U.S.

“At the time the study began, the world was a very different place,” she explained. “There was lots of speculation about the mental health and sexual orientation of these children.”

In a study published last year in the New England Journal of Medicine, Gartrell and her co-authors showed that from a mental health perspective, adult children with lesbian parents fared just as well as their peers with opposite-sex parents.

“They are doing very, very well,” she said of these adult offspring.

Gartrell added that her work “challenges ancient stereotypes and fears” that children would be psychologically harmed by growing up with same-sex parents and the vast majority would be gay themselves. These fears, she said, “hold no water whatsoever.”

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