Twin Studies Actually Show Genetic Link to Sexual Orientation

CHICAGO– Truth Wins Out condemned a scientifically inaccurate billboard placed on a section of Interstate 95 in Richmond, Virginia by the “ex-gay” political organization Parents and Friends of Ex-Gays (PFOX). The PFOXTWINSbillboard proves that PFOX is a purveyor of junk science and its affiliated therapists are unqualified practice legitimate therapy.

The offensive billboard reads: “Identical Twins: One gay. One Not. We believe twins research studies show, Nobody is born gay.” It is important to point out that PFOX’s billboard uses the words “we believe,” which show that the group’s leaders view science as a matter of faith rather than fact, to be distorted and twisted for political ends, notes TWO.

“PFOX’s billboard underscores the groups scientific illiteracy and shows that ‘ex-gay’ activism is about demagoguery and marketing, rather that truth and results,” said Truth Wins Out’s Executive Director Wayne Besen. “In reality, twin studies prove that there is a genetic link to sexual orientation. It is stunning that PFOX would pay for a billboard to showcase its ignorance and incompetence.”

Unfortunately, anti-gay activists consistently distort research. They point to twin studies and say, “if homosexuality was truly genetic, the concordance rate for identical twins would be 100-percent.” Scientists say that this is a gross misunderstanding of the research. According to Dr. Eric Vilain, Professor of Human Genetics, Pediatrics and Urology at UCLA, and the Director of the Institute for Society and Genetics:

“All sorts of traits that are clearly genetic do not show 100% concordance [in twins]. I’ll give you examples, if people look at obesity. Or autism, looking at twins. There is undeniably, no one will even challenge that there is a genetic cause for both obesity and autism.

The twin studies do not show that it is 100% genetic. They just demonstrate that there is a genetic influence. There could be other influences on sexual orientation. Some of them might be environmental. For instance, the older brother effect [studies showing the more older brothers a boy has, the more likely he is to be gay] is an environmental influence. That’s what has happened in the past, in the same womb seems to influence the sexual orientation of future pregnancies. So, it is certainly not an all or nothing phenomenon.”

Dr. Marc Breedlove, Michigan State University, Rosenberg Professor of Neuroscience says that sexual orientation is likely to be influenced by several genes, although more research needs to be done to identify them:

The example I like to use is, to talk about height. The estimates are there are 150 different genes that influence height. So, is there a gene for being tall? A gene, if you get that gene you will be tall no matter what? No, there probably isn’t a gene for being tall. But, does that mean there is no genetic influence on height? Of course not, that would be silly. Of course, there is a genetic influence on height. Of course there is a genetic influence on sexual orientation. The data are really completely firm.

Dr. Simon LeVay, author of “Gay, Straight, and the Reason Why: The Science of Sexual Orientation” had this to say:

“The evidence that genes play a role comes from comparing the similarity in sexual orientation between monozygotic, or so-called identical twins, and dizygotic, or so-called fraternal twins. And these identical twins share pretty much 100% of the same genes. Where as the fraternal twins, who are just like regular brothers and sisters, they share about half their genes, and to the extent a trait like sexual orientation is genetically influenced, you should see a higher agreement in sexual orientation between those pairs of twins who are identical compared with those who are fraternal. And that’s what you find. So, it’s certainly not the case that every pair of identical twins share the same sexual orientation, but they do so at a much higher rate than those twins who are fraternal. You can sort of go through the arithmetic from those numbers and derive a measure of what proportion of the total causation of that person’s sexual orientation is genetic.”

You can learn more about the science of sexual orientation at Here is what real scientists have to say about sexual orientation:

Truth Wins Out (TWO) is a non-profit organization that works to demolish the very foundation of anti-gay prejudice. Our philosophy is simple: We attack the underpinnings of homophobia by debunking harmful lies, discrediting hateful myths, and countering anti-gay organizations. By chipping away at the underlying ignorance that fuels anti-LGBT attitudes, we can ultimately win our fight for fairness and achieve full equality for gay, lesbian, bisexual, and transgender people worldwide.