Page 10 of 11 --With imprinted genes, there is no backup engine.
So if
there's something atypical in the copy from mom, the copy from
dad
cannot be turned on. The UCLA lab is now collecting DNA from
identical
twins in which one twin is straight and the other is gay. Because
the
twins begin as genetic clones, if a gene is imprinted in one twin,
it
will be in the other twin as well. Normally, as the fetuses
are
developing, each time a cell divides, the DNA separates and makes
a
copy of itself, replicating all kinds of genetic information. It's
a
complicated but incredibly accurate process. But the coding to keep
the
backup engine shut down on an imprinted gene is less
accurate.
So how might imprinted genes help explain why one identical twin
would
be straight and the other gay? Say there's an imprinted gene
for
attraction to females, and there's something atypical in the copy
the
twin brothers get from mom. As all that replicating is going on,
the
imprinting (to keep the copy from dad shut down) proceeds as
expected
in one twin, and he ends up gay. But somehow with his brother,
the
coding for the imprinting is lost, and rather than remain shut
down,
the fuel flows to fire up the backup engine from dad. And that
twin
turns out to be straight.
IN THE COURSE OF REPORTING THIS STORY, I EXPERIENCED A good deal
of
whiplash. Just when I would become swayed by the evidence
supporting
one discreet theory, I would stumble onto new evidence casting
some
doubt on it. Ultimately, I accepted this as unavoidable terrain in
the
hunt for the basis of sexual orientation. This is, after all,
a
research field built on underfunded, idiosyncratic studies that are
met
with full-barreled responses from opposing and well-funded
advocacy
groups determined to make the results from the lab hew to the
scripts
they've honed for the talk-show circuit.
You can't really blame the advocacy groups. The stakes are high. In
the
end, homosexuality remains such a divisive issue that only
thoroughly
tested research will get society to accept what science has to
say
about its origin. Critics of funding for sexual orientation
research
say that it isn't curing cancer, and they're right. But we devote a
lot
more dollars to studying other issues that aren't curing cancer
and
have less resonance in society.
Still, no matter how imperfect these studies are, when you put them
all
together and examine them closely, the message is clear:
While
post-birth development may well play a supporting role, the roots
of
homosexuality, at least in men, appear to be in place by the time
a
child is born. After spending years sifting through all the
available
data, British researchers Glenn Wilson and Qazi Rahman come to an
even
bolder conclusion in their forthcoming book Born Gay: The
Psychobiology
of Sex Orientation, in which they write: "Sexual orientation
is
something we are born with and not `acquired' from our social
environment."
