In a recent interview, Tim Pawlenty was asked "Is being gay a choice?" The presidential hopeful replied that "the science in that regard is in dispute."
As a working molecular biologist, that was certainly a surprise to me.
In fact, the 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.
One criticism frequently leveled at my work was that sexual orientation couldn't possibly be inherited because "gays don't have kids." As the gay father of a daughter with lesbian mothers, I always had to shake my head in disbelief - but now there is a solid scientific explanation for how genes that increase same-sex attraction might persist or even increase in the population. Careful family studies by two groups of investigators show that the same inherited factors that favor male homosexuality actually increase the fecundity of female maternal relatives, and that this effect is sufficient to balance out the decreased number of offspring for gay men and maintain the genes over the course of natural selection. This explanation may not be the only one, but it serves to show that the evolutionary paradox is not necessarily overwhelming.
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.
In certain animal model systems, the precise genes involved in sexual partner choice have in fact been identified and their neuro-biochemical pathways have been worked out in detail. Humans may be more socially and culturally complex, but it is likely that some of these mechanisms are preserved, as they are for every other behavioral trait we know.
Given the accumulated evidence, why might Pawlenty assert that the scientific community is still debating the role of biology in sexual orientation? Probably because that's what the religious fundamentalist groups that vehemently oppose LGBT rights want people to think, and have spent considerable time, effort and money trying to promote.
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.
I would never want my life, liberty, or pursuit of happiness to be subject to a DNA test or any other sort of scientific analysis. Basic rights are just that - basic. But 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.
At least Pawlenty acknowledged that science has some role to play. I doubt that would be the case for his competitor Michele Bachman, who considers sexual orientation to be so malleable that people can "pray away the gay". She's hopeless. With Pawlenty, it might just take some education - and plenty of Lady G, of course.
Dean Hamer is a molecular biologist who works on human genetics and HIV prevention and is the author of several scientific books including The Science of Desire. When he's not in the lab, he is visiting small towns and rural communities with his husband Joe Wilson on the Out In The Silence campaign.