Recently Jason Collins became the first current athlete in major professional sports in the US to come out as gay. This earned him the cover of Sports Illustrated and more attention than he ever received for actually playing basketball. Reaction of other athletes and the general public to the announcement seems to be extremely supportive.

A less covered aspect of this story is that Jason has an identical twin brother, Jarron, who is also an NBA veteran and who spent many years underperforming for my Utah Jazz. Jarron is straight and claims to have had no idea whatsoever that his twin brother is gay until very recently. Jarron and Jason have never publicly confirmed or disproven that they are monozygotic (identical) twins. My understanding of twins is that, especially as they grow older, identical twins prefer to emphasize their individuality rather than their genetic commonality, causing them to reject the “identical” moniker. For a variety of reasons, identical twins have slight variations in appearance that usually allow them to be differentiated by people who are paying attention, even though they have the same genes. But most people who have watched the Collins over the years would find it shocking if they were not monozygotic (more shocking than one of them being gay, actually).

There is a long history of studying variation in genetic phenotypes with twin studies . Homosexuality has always proven a genetic puzzle because it lowers reproductive fitness and, therefore, should die out over time. A recent study in the Quarterly Review of Biology (University of Chicago Press) says, “Pedigree and twin studies indicate that homosexuality has substantial heritability in both sexes, yet concordance between identical twins is low and molecular studies have failed to find associated DNA markers.” Thus, if the “born this way” mantra is true, it is clearly more complicated than a simple genetic story.

This same study offers a different account of the biological origins of homosexuality. The authors propose an epigenetic model of sexual orientation. Epigenetic studies (which try to understand how genes are expressed) are all the rage now (just last week I was at an NBER conference where there was an interesting paper on epigenetics and cognitive development in rhesus monkies), and many biosocial phenomena are thought to result from the combination of genes and the environment, where the prenatal environment of the developing fetus is particularly important. It seems that epi-markers are often heritable, which would account for observed heritability in the absence of DNA markers.

I have read a variety of twin research over my career, since twin studies are quite common in economics. Dabbling into this genetic research on homosexuality, I am struck by how little there has been in the past couple of decades, especially given the importance of gay rights as a social concern. But perhaps the politics explains the lack of science. It would be disconcerting, at least, to embark on a field of study where an increasingly large group of politically motivated, influential and often angry people are already convinced they know the answer: sexual orientation is innate and immutable. The activist community wants acceptance, not understanding. Hence, most people will avoid doing science that will cause people to hate them if they get unpopular answers (or, even worse, label them as hateful for even asking the questions).

Both the innate and immutable claims might prove to be true, but as more and more people buy the hype, the science gets harder and harder to do. What if, perchance, this new epigenetic research leads to a medical or other treatment (perhaps prenatal hormonal therapies) that could “turn off” the development of homosexual orientation in utero or sometime thereafter? How would this affect the gay rights movement?

Shouldn’t even people who are gay rights activists be in favor of the development of knowledge that might lead to such a discovery? A consistent theme I hear when homosexuals tell their stories about coming out is how hard it was to admit, first to themselves and then to others, that they are gay. Many of them tell stories of great pain and anguish prior to coming out (and sometimes thereafter). Wouldn’t eliminating that pain be wonderful?

The obvious response to this is that it isn’t homosexuality that causes the pain, but is instead the “homophobic culture” we live in. Fair enough. But consider the thought experiment where the culture is completely accepting of homosexuality. It seems that even in this homophilic wonderland, there are compelling reasons to prevent homosexuality. First of all, the desire to create biological children that are related to both parents seems a powerful (and biologically rooted) urge. Second, mate selection is much harder for homosexuals purely for statistical reasons. Third, the social self-sorting of homosexuals into urban environments, where mate selection is easier, can be costly, especially for individuals who don’t like those environments for other reasons. Finally, there is always stress (sometimes a lot) for growing up as a minority, whether minority status is defined, by race, religion, ethnicity, or sexuality.

In short, a central claim of the gay rights movement is that homosexuals do not choose to be gay. But if they could, would they? If there were a simple treatment that their mothers could have chosen, wouldn’t it be desirable? Sure, many activists are going to say, “No Way. Gay life is wonderful. We are proud of who we are.” I believe they are sincere. Yet I wonder, even for that group, what they would tell their mothers to do if they could go back in time. Would not even people who are completely accepting of homosexuality choose heterosexuality for their children if given the option? Certainly some would not, but I wager that the overwhelming majority would.

I know this language of “prevention” drives many people nuts. Homosexuality is not a deviation, not abnormal, not a disease, not something that needs to be fixed, etc., etc. Yes, yes, I know this rhetoric. But that’s what it is: political rhetoric. It used to be that large majorities of people (including scientists) had never even entertained the notion that homosexuality could have biological origins. Indeed, Franz Kallman, one of the earliest (and widely cited) advocates of genetic origins began his 1952 study in The American Journal of Human Genetics with the claim that “an allusion to a possible relationship between sex and organic inheritance is unlikely to provoke more than a polite smile of skepticism.” Yet his findings comparing monozygotic and dizygotic twins were quite striking, suggesting strongly that genetic origins are important. As most do, Kallman concludes his study with a plea for more research: “The urgency of such work is undeniable as long as this aberrant type of behavior continues to be an inexhaustible source of unhappiness, discontentment, and a distorted sense of human values” (p. 146). This from the guy who is fighting to get people to take genetic origins of sexual orientation seriously!

Since that time, public and scientific opinion has shifted considerably. But it is important to note that the science has never followed a pathway that supports the “innate and immutable” story. That mantra is political, not scientific. As the study cited earlier reminds us, the genetic concordance of homosexuality in identical twins is low, much less than 50% in most studies. The new epigenetic story is at its heart an environmental story, and environments can be changed (genes can, too).

My worry is that the quest to understand will be squashed before it really gets started. It would be a shame if acceptance and tolerance crowd out inquiry. When politics drives out scientific inquiry, nobody wins.