This new research and meta-research, summarized here, indicating that tendencies toward being gay or lesbian are a matter of epigenetics more than genetics in general, and ruling out the idea of a “gay gene,” makes a lot of sense to me.
The idea that it has at least a fair amount to do with epigenetic issues in the womb makes HUGE sense to me, as statistical studies show consecutive male births (no intervening females) increase the likelihood of each successive male being gay:
Here’s the key info:
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.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.Moreover, epi-marks are usually produced from scratch with each generation — but new evidence is showing that they can sometimes carryover from parent to child. It's this phenomenon that gives the impression of having shared genes with relatives.
That said, at the same time, the io9 story looks like a bit of oversell, past the headline. I wouldn't go so far as to say homosexuality is not genetic; I would certainly say it's not solely genetic, and might say it's not primarily genetic.
And, just because you rule in epigenetic influences, you can’t rule out genetic ones by fiat.
At the same time, this theory is hugely explanatory for why a trait that reduces evolutionary fitness continues to perpetuate, too.
And, it also relates to other issues, such as gender identity problems.
Epigenetics in general also undercuts the ideas of Pop Evolutionary Psychology, especially its vaunted Enivironment of Evolutionary Adaptedness.
That’s because epigenetic influences are themselves subject to outside environmental influences. And, as the io9 story notes, and as we’ve seen in other issues like obesity, epigenetic influences can be passed on from generation to generation.
So between heredity of nongenetic factors that are environmentally determined, and such factors rapidly shifting, the EEA is all wet, again.