There are some intriguing developments in our so-far long failure to understand the origins of homosexual emotional and sexual orientation. Evolutionary scientists William Rice and Urban Friberg believe that they may have "solved the evolutionary riddle of homosexuality" by tracing homosexuality not to genes, but instead to the molecular coding that influences how genes are expressed. George Dvorsky breaks down in more detail what this coding, known as "epi-marks," does:
Epigenetic mechanisms can be seen as an added layer of information that clings to our DNA. Epi-marks regulate the expression of genes according to the strength of external cues. Genes are basically the instruction book, while epi-marks direct how those instructions get carried out. For example, they can determine when, where, and how much of a gene gets expressed.
Elizabeth Norton explains what the researchers were studying:
According to the hypothesis, homosexuality may be a carry-over from one's parents' own prenatal resistance to the hormones of the opposite sex. The "epi-marks" that adjusted parental genes to resist excess testosterone, for example, may alter gene activation in areas of the child's brain involved in sexual attraction and preference. "These epigenetic changes protect mom and dad during their own early development," Rice says. The initial benefit to the parents may explain why the trait of homosexuality persists throughout evolution, he says.
Still, the theory has so far been confined to a mathematical model, as one of the researchers emphasizes to Jason Koebler:
"We've found a story that looks really good," [Rice] 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."