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 Nature Vs Nurture In Worms
by The Canadian Press
Posted: October 29, 2007 - 1:00 pm ET
(Toronto, Ontario) Using genetic manipulation, U.S. scientists altered the brains of
nematode worms, causing them to become attracted to wrigglers of the same sex.
While the scientists can't say what this means for sexual orientation in
humans, it does raise the possibility that sexual preference is wired in an
organism's brain.
Biologist Erik Jorgensen and his research team at the University of Utah took
female nematodes with normal reproductive organs and activated genes that
determine ``maleness,'' thereby converting female brains to male brains.
``So we did that and now the females are attracted to other females,''
Jorgensen said from Salt Lake City. ``That told us that the brain was sufficient
for all of the sex-specific behaviors, for sexual attraction.''
In other words, co-author Jamie White, a postdoctoral researcher in
Jorgensen's lab, said in a statement: ``They look like girls, but act and think
like boys. The (same-sex behavior) is part of the nervous system.''
Nematodes, or C. elegans, are millimeter-long worms that live in soil and eat
bacteria. Many of the same genes found in nematodes are also found in other
animals - including people - making them a good model for human research.
Because the worms have no eyes, sexual attraction is based only on their
sense of smell. Male nematodes are drawn to sex-attractant odors, called
pheromones, produced by the females.
The researchers, whose work is published in the most recent issue of Current
Biology, first tested pheromones on male nematodes.
``We put a spot of that beautiful odor on a plate and we put the males down
on the plate,'' said Jorgensen. ``They went straight . . . for the source of
that pheromone.''
``And when we make these transgendered
females, they do the same thing. As soon as she detects that there are other
females on the plate from the odors, she zips right up there,'' he said.
``Normally a female would avoid that spot. They actually have an active
repulsion.''
But the scientists found there is more to the mating ritual than just sexual
attraction.
``The females that are now attracted to other females, they get there and
they don't know what to do,'' said Jorgensen, pointing out that there are other
brain cells involved in the actual mechanics of sex.
Under certain adverse conditions - what Jorgensen calls ``life on the prairie
. . . when there are no boys around'' - female nematodes can become
hermaphrodites, producing both sperm and eggs to ensure propagation. Those used
in this experiment were ``absolutely female,'' he said.
While not published in the current paper, preliminary results from subsequent
experiments show sexual preference of male nematodes can also be altered using
genetic manipulation. Rewired male wrigglers avoided female pheromones.
Still, Jorgensen said he's reluctant to make strong inferences about human
behavior from studies of worms.
``Humans are animals and humans are subjected to the same evolutionary
pressures as any organism, so there will be a strong genetic component to
sexuality in humans as well as worms, flies, mice,'' he said.
``But in addition, our brains are very complex. And because our brains are so
large, an emergent property has arisen, which is consciousness and will. We can
make choices. So to say that personal choice or free will doesn't play a role in
human sexuality is a simplification.''
Furthermore, the issue of human sexual orientation is politically loaded, he
said, with the gay community for the most part favoring the
idea that genes underlie sexual preference, while religious conservatives deem homosexuality
a choice that goes against God's will.
In his personal view, deciding the truth of the matter ``is really an
inappropriate pressure on science.''
What the researchers are more interested in is what their results say about
how the brain functions overall.
``We understand electricity: you put these components together and you can
get a light to turn on,'' Jorgensen said. ``But how does the brain work? This is
biological tissue. How do we sense the things we sense? How do we remember the
things we remember? And how do we think the things we think?''
The worm attraction studies lay some of the groundwork for figuring out how
the brain's wiring translates into such behaviors, he said.
``What this gives us for future studies is a circuit and
behavior that we
can pick apart and say: `Look, these are the connections.' That is our goal
really, to understand how the brain works.''
©365Gay.com 2007
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