Some scientists are theorizing that homosexuality is caused by
epi-marks — extra layers of information that control how certain genes are expressed. These epi-marks are usually, but not always, "erased" between generations. In homosexuals, these epi-marks aren't erased — they're passed from father-to-daughter or mother-to-son, explains William Rice, an evolutionary biologist at the University of California Santa Barbara and lead author of the study.
Jason Koebler writes about the findings in US News & World Report.
Rice and his team created a mathematical model that explains why homosexuality is passed through epi-marks, not genetics. Evolutionarily speaking, if homosexuality was solely a genetic trait, scientists would expect the trait to eventually disappear because homosexuals wouldn't be expected to reproduce. But because these epi-marks provide an evolutionary advantage for the parents of homosexuals: They protect fathers of homosexuals from underexposure to testosterone and mothers of homosexuals from overexposure to testosterone while they are in gestation.
"These epi-marks protect fathers and mothers from excess or underexposure to testosterone — when they carry over to opposite-sex offspring, it can cause the masculinization of females or the feminization of males," Rice says, which can lead to a child becoming gay. Rice notes that these markers are "highly variable" and that only strong epi-marks will result in a homosexual offspring.
Homosexual behavior has been observed in black swans, penguins, sheep, and other animals, he says.
Rice's model still needs to be tested on real-life parent-offspring pairs, but he says this epigenetic link makes more sense than any other explanation, and that his team has mapped out a way for other scientists to test their work. [RELATED: Supreme Court Will Hear Gay Marriage Cases] "We've found a story that looks really good," he says. "There's more verification needed, but we point out how we can easily do epigenetic profiles genome-wide. We predict where the epi-marks occur, we just need other studies to look at it empirically. This can be tested and proven within six months. It's easy to test. If it's a bad idea, we can throw it away in short order."
Read more here: http://www.usnews.com/news/articles/2012/12/11/scientists-may-have-finally-unlocked-puzzle-of-why-people-are-gay