Well,it may not be so settled after all. Studies of identical twins seem to suggest that it is not genetic at all -- at least not in any way, shape, or form that we can recognize or understand now. It appears that these studies tilt the balance to choice. Gays are made and not born. I am sure that this probably will not change many minds. We tend to settle into our own opinions rather comfortably. But... you might want to read up on it here.
Let me quote a couple of pertinent paragraphs:
Eight major studies of identical twins in Australia, the U.S., and Scandinavia during the last two decades all arrive at the same conclusion: gays were not born that way. “At best genetics is a minor factor,” says Dr. Neil Whitehead, PhD. Whitehead worked for the New Zealand government as a scientific researcher for 24 years, then spent four years working for the United Nations and International Atomic Energy Agency. Most recently, he serves as a consultant to Japanese universities about the effects of radiation exposure. His PhD is in biochemistry and statistics.
Identical twins have the same genes or DNA. They are nurtured in equal prenatal conditions. If homosexuality is caused by genetics or prenatal conditions and one twin is gay, the co-twin should also be gay.
“Because they have identical DNA, it ought to be 100%,” Dr. Whitehead notes. But the studies reveal something else. “If an identical twin has same-sex attraction the chances the co-twin has it are only about 11% for men and 14% for women.”
Because identical twins are always genetically identical, homosexuality cannot be genetically dictated. “No-one is born gay,” he notes. “The predominant things that create homosexuality in one identical twin and not in the other have to be post-birth factors...”
Still, many misconceptions persist in the popular culture. Namely, that homosexuality is genetic – so hard-wired into one’s identity that it can’t be changed. “The academics who work in the field are not happy with the portrayals by the media on the subject,” Dr. Whitehead notes. “But they prefer to stick with their academic research and not get involved in the activist side.”