This would explain how men are biologically homosexual, but it doesn't for women. It seems very possible then, that there's an entirely different process by which women become gay (perhaps this also happens to men and they're a "different" type of gay male). That would explain why women in general have (anecdotally) a much more fluid sexual expression, because the process in entirely different. Perhaps we're all attracted to males in the womb, and only exposure to certain proteins/chemicals makes us attracted to females, and those proteins are more prevalent on the Y chromosomes than X.

If there's a protein on the Y chromosome that somehow creates male gayness.
How does that explain lesbians? Or bisexuals for that matter?

I appreciate your pointing out the fact that it's mostly *not* genetics or birth order, but I wish you could get your headline writer on board. A classic science journalism fail in the headline.

Who should I @ on for that?

Biology is not genetics; genetics is not biology. DNA is a complex of organic chemistry that excretes ribosomes, which fold (i.e., shape) proteins, which determine (and are) cell function. Biology is the (study of) living organisms, i.e., the life processes made possible by DNA - both individually and in groups broadly construed as 'species' (which are not absolute categories of living things, but generalizations of interbreeding populations), but also as 'cultures' (from Petri dishes to opera houses). The behavior of bats, bacteria, and late-night customers at Taco Bell - this is all biology. And it is not a simple product of genetic determinism, it is an expression of DNA. These are not the same thing. The behavior of the complex chemistry that is DNA is modified (i.e., 'switched' 'on' and 'off' and thus cell function is altered) by 'epigenetic markers' (generally methyl group molecules or histones/alkaline proteins) which are not genetic, but environmental factors that alter the expression of the DNA (shape and function of the living body. See, for example: https://www.ncbi.nlm.nih.gov/pmc/article…

So what does this have to do with homosexuality, well, everything. Here, for example, is a fairly definitive study of the argument, which avoids the genome centered (and also Darwinian) problems inherent in the study Dan mentions: https://www.ncbi.nlm.nih.gov/pubmed/2517…

Again, the expression of DNA (i.e., life) is not genetically determined: genetics is about the coding of life, which is not life, but the heritage of past life (which does, of course, play a huge role in the shaping of todays life). If you want to make (biological) sense out of the expression of that heritage, whether it means chickens with teeth or guys with mesh thongs, epigenetic biology is the way (just be sure to avoid the new-agy quacks who have attempted to hijack the term). And remember, biology is not genetically derived as a hierarchy of chemical imperialism, but a really cool heterarchy: by tweaking the environment of a fertilized egg, we can get chickens with teeth. And the the crazy doesn't stop there! Gut bacteria 'determines' (joke) a persons IQ: and protozoan parasites cause traffic accidents: http://onlinelibrary.wiley.com/doi/10.11…, and https://bmcinfectdis.biomedcentral.com/a….

The gist is simple, biology is not. Homosexuality, like all sorts of behavior from geeking out on biology to adrenaline addiction, is not simply a product of DNA, it is a consequence of a fascinating complex of interactions. And it is a feature of classic Darwinian evolutionary theory - which is not about individual reproduction, but about population group (species, nation, family) reproduction.
If you are lucky enough to have a homosexual uncle or aunt (who isn't thrown out of the family dynamic due to cultural/religious insanity), you are likely to have an extra adult in the group. One who isn't producing offspring, but helping the offspring of their siblings (and maintaining a biologically healthy sex life all the while). It's like having a rich uncle pay for your marriage, or (better yet) university, or a gap year, or first flat. Works the same for penguins as for people. So homosexuality is a positive darwinian adaptation, i.e., a naturally evolved phenomena (which, like many such phenomena, functions epigenetically).

I should only add the caveat: isn't 'likely to be' producing offspring, instead of 'isn't' producing offspring. However, with the penguins and other 1400 plus non-human species that enjoy getting their gay on, this caveat is not necessary. People are weird.

I'm really glad this article had engendered such intelligent comments, and somehow evaded right-wing attention.