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Biologists at the University of Utah have engineered worms that are attracted to worms of the same sex, bolstering evidence that sexual orientation may be hard-wired in the brain.

The researchers isolated the nerve cells responsible for sexual attraction in nematode worms, then "flipped" a genetic switch in the brains of female worms so they became attracted to other females.

"They look like girls, but act and think like boys," said Jamie White, a postdoctoral fellow at the U. and lead author of the study, which will be published in the November issue of Current Biology.

The research does not provide solid answers about human sexuality - "that's going to be more complicated than what's happening with worms," said White.

But it does lend support to the notion that people are born with a sexual orientation.

"It seems possible that if sexual orientation is genetically wired in worms, it would be in people, too," biology professor Erik Jorgensen said in a news release.

Nematode worms are millimeter-long creatures that live in soil all around the globe, feeding off compost. They have no eyes and use scent to attract sexual partners. Most of the worms are hermaphrodites, and produce both sperm and eggs so they can reproduce alone. But the hermaphrodites - commonly referred to as female by the researchers - get a bonus from mating with a male: many times more eggs and a more diverse gene pool, said White.

The biologists identified scent-detecting cells that help males find and home in on the females' pheromones.

Then they "flipped a switch" in the females' nervous system so that they behaved like males - swarming to the scent of another female - but their gender remained chromosomally the same.

According to a related study from the University of Rochester Medical Center to be published in the same journal, the female worms also picked up other traits associated with males, not just sexual behavior.

At first, White and Jorgensen suspected that neurons found only in male brains determined male sexual attraction.

To their surprise, they discovered that neurons in female brains, when activated, did the same thing. Female nematodes that were never previously drawn to the pheromones of other females were suddenly swarming to the scent.

"It is the mind only - not the mind and body - that needs to be male to have male behavior," White said.

Other research projects have engineered changes in the sexual orientation of mice and flies before.

"Everything is kind of pointing in the same direction," White said. To duplicate a behavior that is associated with one gender or another, "it's not like you have to grow a whole new area of the brain. . . . You can basically take a female brain and make a few minor tweaks."

Marina Gomberg, a spokeswoman for the Utah Pride Center, said she had mixed feelings about the research.

On the one hand, science like this is a good thing for the gay, lesbian and transgendered community if it makes more people accepting of others.

But, "to be very honest, it sort of saddens me that we would have to rely on genetics to make our society recognize us as normal, healthy individuals."

White conducted his research along with Jorgensen, who is the scientific director of the Brain Institute at the U.; technician Jeff Gritton; and three U. undergraduate students, Thomas Nicolas, Long Truong and Elliot Davidson. It was funded primarily by the National Science Foundation.