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Both from CNN:
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Scientists have found new evidence that suggests male homosexuality has a genetic link. The research supports a similar study two years ago.
Researchers studied pairs of homosexual brothers, focusing on the X chromosome, which men inherit from their mothers. The new study suggests a particular portion of that chromosome helps influence whether a man is gay.
"Our result says that genes are involved in male sexual orientation, although they certainly do not determine a person's sexual orientation," said Dean Hamer, a researcher at the National Cancer Institute and author of the study. "There probably are other biological factors like hormones, for example, and other variables we simply don't know anything about yet."
Previous studies also have suggested a biological influence in sexual orientation, but scientists still can't explain what makes a person gay, heterosexual or bisexual. The study does not identify any specific gene. Hamer said there was no way to know how strongly the gene influences the development of male homosexuality.
Hamer worked with colleagues at the National Institute of Health, the University of Colorado at Boulder and the Whitehead Institute for Biomedical Research. They examined 32 pairs of exclusively or mostly gay brothers from unrelated families. Twenty-two pairs, or two-thirds, shared the same version of the genetic material, suggesting that it contains a gene predisposing the men to homosexuality.
Researchers looked for a similar effect in women but found no evidence to support the theory. The study appears in the November issue of the journal Nature Genetics.
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The possibility that sexual orientation may be predisposed before birth gained new support in a research project being published this week that tested how women respond to sound.
Scientists at the University of Texas, Austin, say they have found the first strong evidence of a physical difference between lesbians and straight women -- a finding that the inner ears of gay women work more like those of men.
The study is to be published Tuesday in the Proceedings of the National Academy of Sciences.
The origin of homosexuality has long been a matter of contention. Some believe it to be a matter of choice, but others -- including many gay people -- say it is not choice but biology.
Previous research has found that two parts of the brain are different in gay and heterosexual men. Other studies have found that some genes differ between gay and straight men.
Excess exposure to male hormones before birth cited
The Texas scientists said they found the inner ears of lesbians have undergone "masculinization," probably from excess exposure to male hormones before birth.
"Their auditory centers have been masculinized and the presumption is that so have the sites in the brain that direct sexual preference," said Dennis McFadden, the lead author of the study.
It has yet to be proven, however, that there is a specific site in the brain that directs women to be lesbians, he said.
Dr. Michael Bailey of Northwestern University said the research is "compelling" and may be "consistent with the biological origin of lesbianism."
"The most likely interpretation," he said, "is that this represents some kind of effect of early hormones on the developing fetus."
Test results considered tentative
Bailey cautioned, however, that the research will not be accepted as valid until other scientists replicate the experiment.
Sandra Witelson, an expert on brain anatomy and sexual orientation at McMaster University in Ontario, Canada, said the study supports the theory that lesbianism may be "related to early factors in brain development."
Researchers stress that while science can measure trends among groups, it cannot predict sexual orientation for individuals, a caution that lesbian Laura Brown of Atlanta agrees with. The prospect that women might be tested and given hormones to control their sexuality is "frightening," says Brown. 119K / 9 sec. AIFF or WAV sound
How test was conducted
The inner ear difference between homosexual and heterosexual women was detected using a test that measures the function of the cochlea, a key sound amplifier in the inner ear, said McFadden, a professor of experimental psychology.
The cochlea amplifier in women is more sensitive than that of men, giving women an increased ability to detect very soft sounds in a very quiet room. The test measures a very slight sound the cochlea makes when responding to a soft clicking sound.
Females, with their more sensitive cochlea, respond more powerfully to this test than do men, said McFadden. This is true even among infants.
To test for differences between the sexes, the researchers recruited more than 200 adults divided into four groups: homosexual women and men, and heterosexual women and men.
Some from each of the four groups were later identified as bisexual. The sexual orientation of the subjects was determined by questionnaire.
The results, McFadden said, indicated that lesbians had click-responses that were significantly weaker than those of heterosexual women.
The signal was weaker still for all males, both gay and straight. Bisexual men and women were in the middle, although McFadden said there were not enough of these to draw firm conclusions.
What is clear, he said, is that there is a dramatic difference in the development of the hearing systems of lesbians and heterosexual women. It also is known that development of the inner ear is affected before birth by androgens, a male hormone.
Androgens, said McFadden, may also "alter the brain centers that produce sexual orientation." But he said researchers have yet to find a brain structure that determines sexual orientation in women.
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