Questioning 30 years of research that attributes the differentiation between male and female brains to the influence of sex hormones, a study by researchers at the University of California, Los Angeles claims to have identified 54 genes that may trigger the differences between male and female brain development long before birth.
The authors of the study claim that their findings may offer physicians a tool for gender assignment for babies born with ambiguous genitalia and may lend support to theories of biological determination of gay and lesbian identity.
The findings are included in the October issues of "Molecular Brain Research," a scholarly journal.
Researchers hope to use their research to answer broad questions about gender identity, said research leader Dr. Eric Vilain, assistant professor of human genetics and urology at the David Geffen School of Medicine at UCLA, in a press release.
"Our findings may help answer an important question -- why do we feel male or female," Vilain said. "Sexual identity is rooted in every person's biology before birth and springs from a variation in our individual genome."
In their study, Vilain and his team attempted to determine whether genetic influences could explain variations between male and female brains. To do so they compared the production of genes in male and female brains in embryonic mice that had not yet developed sex organs, which control hormone production.
The researchers found that 54 genes were produced in different quantities between the male and female mice. Eighteen genes were produced at higher levels in the male mice and 36 in the females.
Because the brains of the test subjects appeared to be developing in different ways prior to hormonal influence, the study shows that hormones are not solely responsible for organizing the brain, Vilain said.
"We believe that one's genes, hormones and environment exert a combined influence of sexual brain development," he added.
Further research will attempt to distinguish the specific roles in sexual maturation for each of the 54 genes. The results of these studies may help scientists determine how humans form their concept of gender identity, Vilain said.
"Our findings may explain why we feel male or female, regardless of our actual anatomy," Vilain said. "From previous studies, we know that transgender persons possess normal hormonal levels. Their gender identity likely will be explained by some of the genes we discovered."
The findings also may aid physicians in assigning gender to babies born with ambiguous genitalia.
About three million children a year -- 1 percent of all live births -- are born with mild cases of malformed genitalia each year. Cases in which doctors cannot physically determine the infant's sex occur less frequently -- about one in 3,000 deliveries.
"If physicians could predict the gender of newborns with ambiguous genitalia at birth, we would make less mistakes in gender assignment," Vilain said.
Additionally, the study may add weight to the argument that gay and lesbian identities are linked to biology.
"It's quite possible that sexual identity and physical attraction is 'hard-wired' by the brain," Vilain said.
Determining that sexual orientation is biologically controlled should lead to political and social changes, he said.
"We must dismiss the myth that homosexuality is a 'choice' and examine our civic legal system," Vilain said.
Queer Student Union President Adrienne Patton said she hoped the study would encourage people who believe that being gay is a "choice" that can be "corrected" to take a second look.
"Hopefully this will be convincing to people who believe being gay and lesbian is a disease," Patton said.
However, she said she was slightly pessimistic about how influential it would be.
"There have been lots of studies that show there is a biological aspect of gay identity, but I don't think it's ever going to be proven that it's completely biological," Patton said.
However, she said it is important not to wait for such proof to begin to materialize for gays and lesbians to secure rights.
"Whether being gay is a choice or biological, people still need to have their rights," Patton said.
Lambda Law Alliance Co-President David Laibstain agreed that while the research may have scientific value, it has and should not have any relevance on policy formation.
Individuals should have equal rights in the marketplace and in marriage whether or not gender is "hard-wired" as the study suggests, Laibstain said.
The research "doesn't really matter" with respects to the law, he said.
The Lambda Law Alliance is a U.Va. student group representing lesbian, gay, bisexual and transgendered people at the Law School.
The UCLA study was supported by the National Institute of Child Health and Human Development, the National Science Foundation and with start-up funds from the UCLA Department of Urology. Vilain's co-authors included Phoebe Dewing, Steve Horvath and Tao Shi, all of UCLA.
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