If one twin is gay, the odds that his identical twin will also be gay is higher, indicating some genetic or hormonal link. But since it’s an odd rather than a given, that would seem to demonstrate that there’s more going on.
It also would seem strange, to me at least, that a man would get a specific feminine trait (attraction to men) or vice versa, without all of the other gender traits. Certainly, it could happen, but predominantly if there was a hormal/genetic issue with confusion between male and female, I would expect it to have a greater overall effect than just adjusting sexual attraction. I would expect gay men to look more feminine - wider hips, narrower shoulders, a longer index finger, less rugged features, etc. But overwhelmingly, that is not what we see. Gay men seem to be just as big, burly, and manly as any other man. Gay women can tend to look a bit masculine, but I suspect that, that’s more due to weight, makeup, haircut, and clothing choice than anything innately physical.
I would also question how this attraction actually works? In most other mammalian species, on Earth, attraction is very straightforward. Generally, the female has a scent that she releases and that scent causes the male to get turned on and want to mount her. Humans do have scent glands, but on the whole we don’t seem to be terribly scent-driven. Our sense of smell isn’t very good and, so far as I am aware, scents don’t generally cause men to become erect. Often we start noticing our desired sex early in life, before puberty, when it is unlikely that either gender would be emitting sexy odors via their scent glands.
That would imply that we are visually driven. But image recognition, targeted to specific images, seem like something that’s far harder to encode into DNA than instictual reactions to a particular chemical hormone. Animal bodies are largely operated via hormones already, so making us susceptible to them is pretty easy. But specific visuals? Much harder.
And then getting back to what I had previously mentioned, we often find ourselves first noticing and talking about our desired gender before we hit puberty. And before puberty, the physical differences between male and female is pretty minute. So what we are meant to be recognizing, visually, to turn us on to one gender or the other seems pretty questionable, let alone whether our DNA can really encode that level of specificity into us.
Whereas, we know that Bonobos - one of the animals in closer relation to us - are pretty much free-wheeling when it comes to sexual behavior. For them, it’s just a more-the-merrier sort of thing, regardless of gender. We can also look back at ancient Greece and Rome and find ancient societies which seemed to think that, while marriage between man and woman was necessary as a means to create children, it was entirely reasonable (or even preferred) to have male lovers.
Scientifically, what evidence we have that homosexuality is linked to anything in particular is pretty limited. Personally, I don’t think that that’s because homosexuality isn’t genetic nor epigenetic. Rather, it’s because human sexuality is probably, by default, pansexual. Via logic, social cues, who the first person was when you thought of after finding out about sex, or who-knows-what, we mostly just learn to favor one sex or the other early on. And then, based on how poorly re-programming therapy has done, the assumption would be that our gender preference becomes locked in during our development phase and cannot be readily changed afterwards.
For some of us, there may be more to it than that (based on the twin studies). But currently, I would take the lack of evidence as a lack of evidence for innate sexuality overall, rather than as evidence of a lack of inborn homosexuality.
