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timmy
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Has no life at all |
Location: UK, in Devon
Registered: February 2003
Messages: 13828
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Gay and Straight Men React Differently to Sexual Odors
By NICHOLAS WADE
Published: May 9, 2005
Using a brain-imaging technique, Swedish researchers have shown that
men and women respond differently to two odors that may be involved in
sexual arousal, and that homosexual men respond in the same way as women.
The two chemicals, one a testosterone derivative produced in men's
sweat and the other an estrogen-like compound found in women's urine,
have long been suspected of being pheromones, chemicals emitted by one
individual to trigger some behavior in another of the same species.
The role of pheromones, particularly in guiding sexual behavior, has
been well established in animals but experts differ as to what
importance, if any, they have retained in human mating.
The new research may open the way to studying human pheromones as well
as the biological basis of sexual preference. The study, by Dr. Ivanka
Savic and colleagues at the Karolinska Institute in Stockholm, is
being reported in Tuesday's issue of the Proceedings of the National
Academy of Sciences.
Most odors cause specific, smell-related regions of the human brain to
light up when visualized by a PET scanner, a form of brain imaging
that tracks blood flow in the brain and hence, by inference, the
presence of suddenly active neurons in need of extra glucose. Several
years ago, Dr. Savic and colleagues showed that the two chemicals
activated the brain in a quite different way from ordinary scents. The
estrogen-like compound, though it activated the usual smell-related
regions in women, lit up the hypothalamus in men. This is a brain
center that governs sexual behavior and, through its control of the
pituitary gland lying just beneath it, the hormonal state of the body.
The male sweat chemical, on the other hand, did just the opposite; it
activated mostly the hypothalamus in women and the smell-related
regions in men. The two chemicals seemed to be leading a double life,
playing the role of odor with one sex and of pheromone with another.
Dr. Savic has now repeated the experiment but with the addition of
homosexual men as a third group. The gay men responded to the two
chemicals in the same way as did women, she reports, as if the
hypothalamus's response is determined not by biological sex but by the
owner's sexual orientation.
Dr. Savic said she had also studied homosexual women, and had gathered
"very interesting and somewhat complicated preliminary data." Another
researcher said that it did not matter that gay women were not
included in Dr. Savic's final report because they do not respond in
the same way as gay men do.
The report by Dr. Savic and her colleagues recalls a 1991 report by
Dr. Simon LeVay that a small region of the hypothalamus was twice as
large in straight men than in women or gay men. The PET scanning
technique used by Dr. Savic lacks the resolution to see the region
studied by Dr. LeVay, which is a mere millimeter or so across. But
both findings suggest that the hypothalamus is organized in a way
related to sexual orientation.
The new finding, if confirmed, would break new ground in two important
directions, those of human pheromones and human sexuality. Mice are
known to influence each other's sexual behavior through emission of
chemicals that act like hormones on the recipient's brain and are
known, by derivation, as pheromones. Hopes, by the fragrance industry
among others, of finding human pheromones were dashed several years
ago when it emerged that the vomero-nasal organ, a tiny structure in
the nose through which mice detect many pheromones, has largely lost
its innervation in humans.
Researchers interpreted that to mean that humans, as they evolved to
rely more on sight than on smell, had no need of the primitive cues
that pass for sexual attractiveness among mice. But a role for human
pheromones could not be ruled out, especially in light of findings
that women living or working together tend to synchronize their
menstrual cycles.
Dr. Savic's work is seen by some researchers as strong evidence in
favor of human pheromones. "The question of whether human pheromones
exist has been answered. They do," Dr. Noam Sobel, a neuroscientist at
the University of California, Berkeley, wrote in commenting on Dr.
Savic's report of 2001.
Dr. Catherine Dulac, a Harvard University biologist who studies
pheromones in mice, said that if a chemical modified the function of
the hypothalamus, that might be sufficient to regard it as a
pheromone. She said the Swedish study was extremely interesting, even
though "humans are a terrible experimental subject," but noted the
researchers had used a far higher dose of the armpit chemical than
anyone would be exposed to in normal life.
If human pheromones do exist, Dr. Savic's approach may allow insights
into how the brain is organized not just for sexual orientation but
for sexuality in general. "The big question is not where homosexuality
comes from but where does sexuality come from," said Dr. Dean Hamer, a
geneticist at the National Institutes of Health.
The different pattern of activity that Dr. Savic sees in the brains of
gay men could be either a cause or an effect of their sexual
orientation. If sexual orientation has a genetic cause, or is
influenced by hormones in the womb or at puberty, then the neurons in
the hypothalamus could wire themselves up in a way that shaped which
sex a person is attracted to. Alternatively, Dr. Savic's finding could
be just be a consequence of straight and gay men using their brain in
different ways.
"We cannot tell if the different pattern is cause or effect - the
study does not give any answer to these crucial questions," Dr. Savic
said. But the technique might provide an answer, Dr. Hamer noted, if
it were applied to people of different ages to see when in life the
different pattern of response developed.
Dr. LeVay said he believed from animal experiments that the size
differences in the hypothalamic region he had studied arose before
birth, perhaps in response to differences in the circulating level of
sex hormones. Both his finding and Dr. Savic's suggest the
hypothalamus is specifically organized in relation to sexual
orientation, he said.
Some researchers believe there is likely to be a genetic component of
homosexuality because of its concordance among twins. The occurrence
of male homosexuality in both members of a twin pair is 22 percent in
non-identical twins but rises to 52 percent in identical twins. On the
other hand, gay men have fewer children, meaning that in Darwinian
terms any genetic variant that promotes homosexuality should be
quickly eliminated from the population. Dr. Hamer believes such genes
may nevertheless persist because, although they reduce descendants in
gay men, they increase fertility in women.
Could Dr. Savic's technique be used as a way of assessing a person's
sexual orientation? She said it had not be shown to have the
specificity necessary for a test. Other researchers said that
observing people's reactions to erotic images was a simpler way of
doing the same thing, so the brain scanning technique raised no new
issues.
Author of Queer Me! Halfway Between Flying and Crying - the true story of life for a gay boy in the Swinging Sixties in a British all male Public School
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