Over at the Advocate, geneticst Dean Hamer takes this on. The whole thing is worth reading.
[T]he scientific community has long regarded sexual orientation – whether gay, straight, or somewhere in between – as a phenotype: an observable set of properties that varies among individuals and is deeply rooted in biology. For us, the role of genetics in sexual behavior is about as “disputable” as the role of evolution in biology. Come to think of it, pretty much the same folks are opposed to both ideas.
The empirical evidence for the role of genetics in sexual orientation has steadily mounted since I first entered the field in the early 1990s. Back then, the only quantitative data was derived from studies of unrepresentative and potentially biased samples of self-identified gay men and lesbian. But in the intervening 20 years, studies of twins – the mainstay of human population genetics – have been conducted on systematically ascertained populations in three different countries. These studies are notable because they have large sample sizes that are representative of the overall population, they’re conducted by independent university-based investigators using well-established statistical methods, and the results are published in the peer-reviewed literature.
Each of these studies has led to the same fundamental conclusion: genes play a major role in human sexual orientation. By contrast, shared environmental factors such as education, parenting style, or presumably even exposure to Lady Gaga, have little if anything to do with people's orientation. While there is a substantial amount of variation that cannot be ascribed to either heritable or shared environment, the differences might also be due to biological traits that are not inherited in a simple additive manner.....
Another criticism frequently brought up by politically motivated critics of the research is that there is still no single identified "gay gene." However, the same is true for height, skin color, handedness, frequency of heart disease and many other traits that have a large inherited component but no dominant gene. This doesn't mean that sexual orientation is a choice; it simply confirms that sexual orientation is complex, with many genes contributing to the phenotype...
There is good reason for their opposition to the scientific findings. Studies in college classrooms have shown that exposure of students to information about the causes of sexual orientation has a direct, positive influence on their opinions about LGBT civil rights. This fits with polling data showing that people who believe that gays are "born that way" are generally supportive of full equality, whereas more than two thirds of those who believe it is "a choice" are so opposed that they favor the re-criminalization of same-sex relations.
....t it is essential to acknowledge that lack of scientific knowledge can actually result in having our rights and freedoms taken away through the actions of misinformed voters, legislators and judges.