Professor of Psychiatry at the Boston University School of Medicine
Pro to the question "Is Sexual Orientation Determined at Birth?"
"A problem for those of us who favor a genetic basis for sexual orientation is why, from an evolutionary point of view, gay attractions should exist at all. My suggestion is that both orientations are genetically programmed, that both appeared during the evolutionary history of our species and therefore may exist at least in rudimentary form in our close primate relatives...
Behavior genetics applied to sexual orientation encounters a variety of criticisms. In this debate, I feel like a detective who's presenting his case to the district attorney. I have scraps and clues, hypothesis and sometimes hang together but that also have gaps. But the DA must be a skeptic. He has to put my case before a jury whom he must convince beyond a reasonable doubt. The standard of proof rises as the investigation proceeds. The most I can say is that no one has yet put forward evidence that is devastating to my case."
"The Genetic Theory of Sexual Orientation," Harvard Gay and Lesbian Review, Winter 1997