Page 9 of 11 --There is, however, a towering question that
Sanders's
study will probably not be able to answer. That has to do
with
evolution. If a prime motivation of all species is to pass genes on
to
future generations, and gay men are estimated to produce 80
percent
fewer offspring than straight men, why would a gay gene not have
been
wiped out by the forces of natural selection? This
evolutionary
disadvantage is what led former Amherst College biologist Paul
Ewald to
argue that homosexuality might be caused by a virus - a pathogen
most
likely working in utero. That argument caused a stir when he and
a
colleague proposed it six years ago, but with no research done to
test
it, it remains just another theory. Other scientists have
offered
fascinating but unpersuasive explanations, most of them focusing
on
some kind of compensatory benefit, in the same way that the
gene
responsible for sickle cell anemia also protects against malaria.
A
study last year by researchers in Italy showed that female
relatives of
gay men tended to be more fertile, though, as critics point out,
not
nearly fertile enough to make up for the gay man's lack of
offspring.
But there will be plenty of time for sorting out the
evolutionary
paradox once - and if - researchers are able to identify actual
genes
involved in sexual orientation. Getting to that point will
likely
require integrating multiple lines of promising research. That
is
exactly what's happening in Eric Vilain's lab at the University
of
California, Los Angeles. Vilain, an associate professor of
human
genetics, and his colleague, Sven Bocklandt, are using gay
sheep,
transgenic mice, identical twin humans, and novel approaches to
human
genetics to try to unlock the mystery of sexual orientation.
Instead of looking for a gay gene, they stress that they are
looking
for several genes that cause either attraction to men or attraction
to
women. Those same genes would work one way in heterosexual women
and
another way in homosexual men. The UCLA lab is examining how
these
genes might be turned "up" or "down." It's not a question of what
genes
you have, but rather which ones you use, says Bocklandt. "I have
the
genes in my body to make a vagina and carry a baby, but I don't
use
them, because I am a man." In studying the genes of gay sheep,
for
example, he's found some that are turned "way up" compared with
the
straight rams.
The lab is also testing an intriguing theory involving imprinted
genes.
Normally, we have two copies of every gene, one from each parent,
and
both copies work. They're identical, so it doesn't matter which
copy
comes from which parent. But with imprinted genes, that does
matter.
Although both copies are physically there, one copy - either from
the
mom or the dad - is blocked from working. Think of an airplane with
an
engine on each wing, except one of the engines is shut down. A
recent
Duke University study suggests humans have hundreds of imprinted
genes,
including one on the X chromosome that previous research has tied
to
sexual orientation.
