SGN Page 12

Solitary gene in fruit flies causes same-gender attraction

Solitary gene in fruit flies causes same-gender attraction
by Lisa Keen A solitary gene is capable of causing a fruit fly to sexually pursue other fruit flies of the same gender, according to a study published in the June 3 issue of the scientific journal Cell. While that finding does not prove that sexual orientation in humans is determined by a single master gene, it contributes a significant piece of evidence to support that growing scientific consensus. This latest study comes from a two-year-old research center in Austria led by a former post-doctoral student from the University of California-Berkeley. The researcher, Australian (sic) Barry Dickson, bred a female fruit fly to carry a single male-type gene and then observed that fly interact with other male and female fruit flies. While female fruit flies normally remain very passive sexually, the altered female was sexually assertive with other female fruit flies. A similar observation was noted when a male fruit fly was bred to carry a single female-type gene. Dean Hamer, a respected geneticist at the National Institutes of Health who does similar research, said the new study was very well done. Theres no arguing with the data, its completely clean, said Hamer, in an interview. They had two flies identical in every atom of their DNA except this one gene. Hamer noted, however, that just because this single gene plays a master switch role in determining the object of the fruit flys sexual attractions does not rule out the possibility that other genes are also involved. And it doesnt suggest that theres a master switch in humans, said Hamer. The studys real significance, he said, is that it demonstrates that a behavior as complex as sexuality can be under the simple and direct control of a single gene. In 1991, Hamer and a team of researchers at the National Cancer Institute, reported finding identical sequences of DNA on the X-chromosome of most Gay brothers. Earlier this year, in a study that received little media attention, Hamers group reported narrowing its search down to three areas on non-sex chromosomes (chromosomes other than the X and Y chromosomes which determine gender). Hamer said that as early as next year, he expects the specific gene to be identified; that work, he said, is being conducted by one of his former graduate students. Other studies have pointed to biological causes of sexual orientation. One, published just last month in the Proceedings of the National Academy of Sciences, found that Gay men react differently than straight men to a chemical substance called pheromones. While its not certain what role these chemicals play in humans, in animals, they appear to cause odors that stimulate the sexual interest of other animals. These chemicals pheromones are testosterone based in men and estrogen based in women. The estrogen-based pheromones in women caused a reaction in the hypothalamus of straight men, but not in Gay men. The hypothalamus is a gland under the brain that regulates body temperature, heart beat, and other reactions to such stimuli as fear and sexual arousal. The new pheromone study found that the hypothalamus of Gay men was not stimulated by the female estrogen-based pheromone but was stimulated by the male testosterone-based pheromone. Warren Throckmorton, a proponent of sexual re-orientation recently named to the advisory council of the nations largest provider of mental health care, took issue with the Austrian studys reference to sexual orientation. Fruit flies exhibit mating behavior, said Throckmorton, but I doubt they experience desire or attraction or longing. They simply do what they are programmed to do, whether in male bodies or female bodies. Humans are nothing like this and any analogies to humans are completely inadequate. Other researchers, including Hamer, said they would hope findings such as these would influence the arguments advanced by opponents of equal rights for Gays that homosexuality is a matter of choice and morality. As one biologist told the New York Times, in reaction to the Austrian study, Hopefully this will take the discussion about sexual preferences out of the realm of morality and put it in the realm of science.