Scientific Director at the University of Utah Brain Institute
Not Clearly Pro or Con to the question "Is Sexual Orientation Determined at Birth?"
"The reason males and females behave differently is that the same nerve cells have been rewired to alter sexual preference. Our conclusions are narrow in that they are about worms and how attraction behaviors are derived from the same brain circuit. But an evolutionary biologist will consider this to be a potentially common mechanism for sexual attraction.
We cannot say what this means for human sexual orientation, but it raises the possibility that sexual preference is wired in the brain. Humans are subject to evolutionary forces just like worms. It seems possible that if sexual orientation is genetically wired in worms, it would be in people too. Humans have free will, so the picture is more complicated in people."
"The Sensory Circuitry for Sexual Attraction in C. elegans Males," Current Biology, Nov. 6, 2007