Study Concludes Epigenetic Cause of Homosexuality

Study Concludes Epigenetic Cause of Homosexuality December 15, 2012

A new study in the Quarterly Review of Biology by a group of international researchers has concluded what I have long assumed to be true, that the primary cause of homosexuality is epigenetic and it is largely locked in during gestation.

Writing in The Quarterly Review of Biology, researchers William Rice, a professor at the University of California, Santa Barbara, and Urban Friberg, a professor at Uppsala University in Sweden, believe that homosexuality can be explained by the presence of epi-marks — temporary switches that control how our genes are expressed during gestation and after we’re born.

Specifically, the researchers discovered sex-specific epi-marks which, unlike most genetic switches, get passed down from father to daughter or mother to son. Most epi-marks don’t normally pass between generations and are essentially “erased.” Rice and Friberg say this explains why homosexuality appears to run in families, yet has no real genetic underpinning…

To reach this conclusion, Rice and Friberg created a biological and mathematical model that charted the role of epigenetics in homosexuality. They did so by applying evolutionary theory to recent advances in the molecular regulation of gene expression and androgen-dependent sexual development…

Normally, sex-specific marks that are triggered during early fetal development work to protect boys and girls in the womb from undergoing too much natural variation in testosterone, which should normally happen later in a pregnancy. Epigenetic processes prevent female fetuses from becoming masculinized when testosterone exposure gets too high, and vice versa for males.

Moreover, epi-marks also protect different sex-specific traits from swinging in the opposite direction; some affect the genitals, and others may affect sexual orientation. These epi-marks can be transmitted across generations from fathers to daughters, or mothers to sons.

Two caveats: First, I haven’t read this study and I’m not the best person to evaluate its validity if I had. I’d be very curious to hear the opinions of geneticists who have seen the study and can lend some expertise in understanding and evaluating it. Second, I would bet that this is hardly the end of the matter. I doubt that there is a single cause to homosexuality, though it has long seemed obvious to me that when someone says “well if homosexuality is genetic, why haven’t we found the gene that causes it” to be vastly oversimplified. With my admittedly limited understanding, it has long made sense that epigenetics is more important here than the idea of finding a specific gene that determines whether a person is gay or straight.

One more caveat: Ultimately, I don’t care whether the cause is genetic, epigenetic or otherwise. Even if the bigots were right and homosexuality was entirely a personal choice, like whether to wear bell bottoms or learn how to speak Spanish, it wouldn’t change my conclusion that everyone should be treated equally regardless of their sexual orientation or gender expression.


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