快猫短视频

SOME parents cannot stomach the news that their son has embraced a gay
lifestyle. But when Roger Gorski tells them that their sons have inherited 鈥渁n
immutable, behaviourally expressed, bimodal trait鈥� rather like left-handedness,
homosexuality assumes a whole new mantle of respectability.

鈥淚 recently spoke at a seminar for Mormon parents of gay children in Salt
Lake City and it was amazing,鈥� says Gorski. 鈥淚 felt like I was talking in a
vacuum, with every word sucked up. It was the parents who were coming out.鈥�

Such meetings are all in a day鈥檚 work for the neurobiologist from the
University of California in Los Angeles. He welcomes the chance to tell
angst-ridden parents a few biological facts: that homosexuality is a normal
genetic variant, that it is not a lifestyle choice, a disease, or a mental
illness, and that in all probability it was passed down from the person鈥檚
mother.

Vindicated

Everyone leaves these cosy assemblies smiling鈥擥orski has dispensed some
soothing news, gay men feel vindicated, parents can go back to loving their
homosexual sons unconditionally. And Dean Hamer, the molecular geneticist from
the National Institutes of Health near Washington DC, who, in 1993, discovered
where in the genome the gay gene nestles, can pat himself on the back for
fostering goodwill on earth.

Gorski has also contributed to the idea that gayness is biological in origin.
In 1992, he showed that the anterior commissure, a bundle of nerves that
connects a small region of the right and left sides of the brain鈥檚 cortex, is
larger in gay men than in straight. All the same, Gorski is the first to
acknowledge that in the name of community spirit, the scientific fellowship is
quietly blending fact with biological theory. For in reality, today鈥檚 scientists
are about as baffled by homosexuality as they have ever been.

In the intervening three years, Hamer鈥檚 spectacular finding has started to
look shaky. Some geneticists have poked holes in his original methodology, and
others have failed to confirm the existence of the gay gene with their own
studies.

But those disappointments have done nothing to dull the intense scientific
and public interest in what triggers gayness. And if human genetics has drawn a
blank in the past few years, new studies of fruit fly courtship are reinforcing
the idea that, in the end, homosexuality will come down to the difference of a
gene or two. Meanwhile, one Cornell psychologist has introduced a fresh twist to
the ancient argument that homosexuality is an acquired rather than innate
behaviour鈥攚ith his controversial 鈥渆xotic to erotic鈥� theory of sexual
orientation.

That gayness is at least partly genetic is just about indisputable. A man
with a gay identical twin brother鈥攖hat is a brother who to all intents and
purposes shares all his genes鈥攈as a 52 per cent chance of being gay, and a
man with a gay non-identical twin only a 22 per cent chance, according to a 1991
study from psychologist J. Michael Bailey at Northwestern University in
Chicago.

X-rated

In their study, Hamer鈥檚 team showed that specific genetic markers on a region
of the X chromosome called Xq28 were shared by 33 of 40 pairs of gay brothers.
Chance dictates that the brothers inherit either of their mother鈥檚 X chromosomes
at the same rate, that is that only 20 pairs of brothers should have shared the
markers. Hamer concluded that within a region of 4 million DNA base pairs on the
tip of the long arm of the X chromosome, lies a locus related to sexual
orientation. He calls this locus GAY-1.

Harvard biologist Evan Balaban loathes the over-simplification of the gay
gene topic by both scientists and journalists that accompanied Hamer鈥檚 original
identification of GAY-1. 鈥淚 wish that some of the work was done a bit more
carefully and presented more conservatively,鈥� said Balaban. 鈥淚t can only lead to
misunderstanding and disappointment.鈥�

Certainly, with the air still ringing from the trumpets and cymbals that
accompanied the release of Hamer鈥檚 original research paper, it comes as a great
anticlimax that other scientists have been unable to reproduce his findings.
George Ebers, a neurologist at the University of Western Ontario in London,
failed when he searched for the same genetic landmarks on Xq28 of 54 pairs of
gay Canadian brothers. Even Hamer seems to be having problems repeating his own
work with the same degree of conviction. In a recent repeat study of 33 pairs of
gay brothers, he found that only 67 per cent shared genetic markers on Xq28,
compared with the 82 per cent identified in his first study.

One of the most persistent criticisms of Hamer鈥檚 research has been his ready
acceptance, after interviews with the family members of gay men, that there were
considerably more gay relatives on the mother鈥檚 side of the families than the
father鈥檚. It was this observation that led him to confine his search to the
X-chromosome, instead of the other 22. But, says Balaban, 鈥渋f you ask about
medical history by interviewing family members, who knows more about it, men or
women? Women of course.鈥� But Hamer is quick to defend his methodology. 鈥淲e did
several controls. We asked the same people who the lesbians were in the family,
and from their answers we found they were evenly distributed between the two
sides of the family.鈥�

And even if Hamer is right, and GAY-1 does contain the key to male
homosexuality, the work is far from over. GAY-1 contains several hundred genes,
and only by teasing out the gene or genes responsible for sexual orientation
will there be a chance of working out the biochemical basis of why some men are
turned on by other men. Hamer refuses to say how far his search has
progressed.

But if the genetics of sexual orientation in humans has reached deadlock,
work on sexual orientation in fruit flies is winging ahead. Way back in 1963,
the gene responsible for same-sex courtship in the fruit fly (Drosophila
melanogaster) was tracked down to a region on the third chromosome (the
species only has four chromosomes) by Kulbir Gill, a visiting Indian scientist
to Yale University in New Haven, Connecticut. Jeffrey Hall, a geneticist at
Brandeis University in Waltham, Massachusetts, later named the genetic
variant fruitless.

Flies do it

Fruitless males court females as well as other males, making them
bisexual rather than gay. Now, Hall, molecular biologist Bruce Baker of Stanford
University in Palo Alto in California, and neurobiologist Barbara Taylor from
Oregon State University in Corvallis, have completed a three-year project that
created an array of reproductively dysfunctional cousins of the original
fruitless variant. The results are expected to show that one of the new
fruitless variants courts males, but not females, making it a true 鈥済ay鈥�
fruit fly.

The biochemical function of the fruitless gene remains a mystery.
Still, Hall has his suspicions. He believes that the unmutated version of the
fruitless gene that regular flies carry is central in setting up a
region in the nervous system that teaches male fruit flies to recognise the cues
from females and ignore other cues that are useless for reproduction. And
although he is quick to point out the risks of extrapolating from flies to
humans (鈥淵ou don鈥檛 have to treat human chromosomes with X-rays to get
homosexuality鈥攊t is found everywhere in nature in extremely high
percentages鈥�), Hall says it is conceivable that a DNA homologue to the
fruitless gene may exist in the human brain.

Over the past decade, scientists from Amsterdam to California have been
picking through brain matter in their search for structures that differentiate
gay men from their straight brothers. Three findings stand out. Gorski鈥檚 work on
the anterior commissure, and the discoveries that the superchiasmatic nucleus
(which contains the 鈥渂ody clock鈥�) is larger in gay men than straight men, and
that another region of the hypothalamus, usually referred to as INAH-3 and whose
function is a mystery, is smaller. Most researchers agree that it鈥檚 impossible
to say what any of those findings actually mean鈥攅xcept that they support
the idea that biology, in the shape of genes, hormones and brain structures,
correlates with gayness in some men.

Daryl Bem, a psychologist from Cornell University in Ithaca, New York, is not
impressed by that insight. 鈥淐orrelation is not cause,鈥� he says. 鈥淪exual
orientation is not transmitted by genes.鈥� Instead, Bem argues that when it comes
to sexual orientation, a child is born with a clean slate. Genetic inheritance
affects the child鈥檚 temperament and behaviour, and that, in turn, moulds their
final sexual orientation.

Bem takes his cue from a 1981 study of about 1000 gay men and women, and 500
straight men and women living in the San Francisco Bay area. That study, which
was run by researchers at the Kinsey Institute for Research in Sex, Gender and
Reproduction in Bloomington, Indiana, found that 63 per cent of gay men reported
that as children they disliked 鈥渂oys鈥� games鈥�, such as football, compared to 10
per cent of straight men. On the flip side, 48 per cent of gay men had enjoyed
鈥済irls鈥� games鈥�, such as playing house, compared to 11 per cent of straight men.
Those findings have been confirmed by studies that look at boyhood play, and
then wait and see who becomes gay and who straight, and also by a massive
鈥渕eta-analysis鈥� that pooled the data from 48 separate studies.

Bem speculates that a boys-will-be-boys boy who enjoys a bit of rough and
tumble will detach himself from the gentler, more introspective world of little
girls, and so will come to regard females as dissimilar and exotic. This
sentiment is translated into 鈥減hysiological tingles and jolts鈥� in the presence
of the opposite sex which at first seem offensive (hence the widely held view
among boys that 鈥済irls are yuck鈥�, and vice versa), but which during adolescence
fire up sexual desire. Genes may well help hard-wire a boy鈥檚 brain so that he
acts in a fashion that doesn鈥檛 conform to his gender, becomes distanced from
other boys and later finds them sexually attractive. 鈥淚t鈥檚 psychologically
determined,鈥� says Bem. 鈥淵ou can take a `sissy鈥� boy, make him play football, and
it will only serve to make him feel even more as if he doesn鈥檛 fit in.鈥�

Bem鈥檚 theory is all-encompassing. It explains both male and female
homosexuality (the Kinsey study also showed that lesbians tended to prefer boy鈥檚
games as children) and heterosexuality, as well as some long-standing
conundrums, such as why children who are not related, but are raised
together鈥攆or example adopted children and children raised on
kibbutzim鈥攏ever fancy one another as adults: the familiar is the
antithesis of the exotic.

Curious but cautious

Biologists are treating Bem鈥檚 theory with a mixture of caution and curiosity.
Hall says that there are at least two reasons why the theory should be
given due consideration. First, it leaves a role for genes. No one has ruled out
the idea that genes code for sexual orientation through a simple activity like
childhood play, says Hall. Second, science has far from ruled out an
experience-based element to homosexuality. After all, roughly half of men with
gay identical twin brothers are straight.

But Bem admits that there is a least one more vital piece of evidence he
needs to support his theory. Whereas most animals, be they rats or adult humans,
that are confronted with unfamiliar animals or objects become (non-sexually)
aroused鈥攈eart rate increases and breathing becomes more shallow, for
example鈥擝em has yet to show that the same thing happens when a boy who
does not conform to his gender norms is in the presence of other boys. 鈥淭hat鈥檚
the first experiment we plan to do,鈥� he says.

Meanwhile, whether Bem, and the eclectic bunch of geneticists,
neuro-anatomists and psychologists who are studying gayness, will ever
completely understand the forces that dictate sexual orientation remains to be
seen.

* * *

Do Gay Men Make Better Brothers?

When Zimbabwe president Robert Mugabe last year described homosexuals as
鈥渓ower than dogs鈥� he was reflecting a popular sentiment that gay sex is a
perversion because it breaks the laws of nature. In his lurid way, Mugabe was
disseminating the lay version of the notion that evolution could not possibly
select for a gay gene because homosexuality hampers reproduction.

On the contrary, argue geneticists like Dean Hamer of the National Institutes
of Health near Washington DC, who discovered the location of the gay gene,
nature may select for a gay gene because it carries a distinct gain for the
species as a whole. For instance, gay men may make better brothers, giving their
siblings鈥� children鈥攚ho share a fair chunk of their uncle鈥檚 genetic
material鈥攖he edge in the survival stakes.

The kinship theory reasons that natural selection works on averages, not on
individuals, picking the genes that help more people than they hurt. Thus a gay
gene could be perpetuated by the heterosexuals who carry it silently, and
selected for by the cumulative reproductive success of the tribe.

But there are alternative explanations for the persistence of the gay trait.
Perhaps the putative gay gene sits on a bit of the chromosome that is unstable,
so that fresh variants pop up to replenish the supply. Gayness may also be the
by-product of a gene whose primary impact is to increase the number of children
women have. That鈥檚 not such a far-fetched idea when you consider that women can
carry the identical gene to gay men (see
Diagram), and that the gene
is supposed to effect human sexual behaviour. There is even some evidence,
albeit tentative, for that idea. After studying several thousand homosexuals,
Ray Blanchard, a psychologist from the University of Toronto, concluded that a
man is more likely to be gay if he is the youngest in a longer than average line
of brothers鈥攚ith each additional older brother, the odds of homosexuality
increased by 33 per cent.

Other reading: 鈥淗omosexuality in men and number of older brothers鈥� by R.
Blanchard and A. F. Bogeart, American Journal of Psychiatry, 1996, vol
153, p 27-31.

* * *

The feminine mystique

While men鈥檚 sexual orientation is more or less bimodal鈥攇ay or
straight鈥攚ith very little gradation in between, women express their
sexuality across a wide range. Far more women than men categorise themselves as
bisexual, for instance. That complexity has needled science well-nigh into
pretending lesbianism does not exist.

So too has the small matter that most researchers in the field are men. 鈥淢ale
scientists are less interested in female sexuality,鈥� says psychiatrist Richard
Pillard of Boston University in Massachusetts. 鈥淭hey get impatient with the
苍耻补苍肠别蝉.鈥�

Finally, the research bias cannot be divorced from the political reality that
sexual liaisons between women, with their coy image of playful romps and gentle
caresses, incite less public intolerance than the thought of sexual encounters
between men. Lesbianism may have escaped scrutiny simply because scientists have
less incentive to find a biological justification for it.

With the dearth of reliable information, most scientists can only speculate
on the origins of female sexual attraction. 鈥淲hat is it that makes a woman more
responsive to the social context than the gender of a partner? Maybe women have
more genes than men relating to homosexuality, or maybe they can ignore their
genes more easily,鈥� says Pillard.

The few attempts to understand the biological basis of lesbianism do,
however, reveal that it has a strong genetic component. A woman has a 48 per
cent chance of being a lesbian if her identical twin is also a lesbian. The Xq28
locus, however, does not play a role in female homosexuality as it may in male
homosexuality, and unlike in men (see
Box), birth order has no
effect on a woman鈥檚 sexual preferences.

Only nature鈥檚 slip-ups provide a window on the biological processes that may
influence female sexuality. In congenital adrenal hyperplasia (CAH), a defective
gene causes male hormones to be pumped into the bloodstream of the female fetus.
The result is a baby girl who has the outside genitalia of a boy鈥攁n
aberration usually put straight by a series of operations between birth and the
end of puberty.

Sexologist John Money of Johns Hopkins University in Baltimore has found that
an incredible 37 per cent of CAH females identify themselves as lesbian or
bisexual, suggesting that male hormones may play a role in female
homosexuality.