Perhaps I am a fool for placing this in GQ. I readily admit there may be no GQ answer, and a move to GD may be forthcoming.
But it seems to me that this is a factual question that is susceptible to a factual answer, so here it starts:
Is the percentage of homosexuals the same, or roughly similar, in all human cultures? I imagine there’s a higher percentage of gay men in downtown San Francisco than in Billings, Montana, of course, but that’s because a gay-friendly environment self-selects people. But that’s not what I’m asking.
Being that homosexuality is illegal in India, they either have to suppress or turn to mutilation. Being the case, the number of gays in probably much large than stats suggest.
But unfortunately you can’t ignore this as a gay-friendly culture also self-selects, in that it influences how many people are willing to be identified as gay. As there is no known way of finding out who’s gay and who’s not without asking, you’re always going to have a way of accounting for the percentage that lie and the cultural influences that may cause them to lie.
So your OP is unanswerable unless you either even out the cultural differences, which kind of negates the whole point , or find a way of determining sexuality through a objective medical test rather than interview.
Besides that, if we are to accept that homosexuality is determined before birth (A GD debate right there), then there is no reason to assume that percentages should differ between cultures. Unless you can prove that cultural aspects (like, say, food) influence pre-natal development.
Seeing as there’s no agreement on the frequency of homosexuality in our culture, I don’t think you’re likely to get a (supportable) answer for its frequency across other cultures as well. It will mostly depend on the agenda of the person you are asking.
Reportage of a given behaviour at similar values across cultures is interpreted as a reflection of biogenecity. I gathered that was what the OP was asking.
Generally, studies of humans and other animals suggest that if you could watch everyone over the course of their whole lifetimes, you’d see 3-10% of all sexually dimorphic creatures displaying same-gender targeted sexual behaviors. Note that even in humans, these behaviors are not always correlated with gay “identity.” There are certainly human environments more conducive to the expression of homosexual sexual behavior and identify, both positive (e.g., San Francisco) and negative (e.g., prison).
You also have to take into account the fact that homosexuality is not an all-or-nothing trait. Relatively few people are absolutely 100% homosexual or heterosexual in orientation, and some people are essentially bisexual.
On top of that, even if we presume that basic orientation is innate (present at birth, whether genetic or developmentally determined), how that orientation is expressed will depend strongly on how tolerant a particular culture is toward homosexuality.
Some people’s innate orientation may be 100% homosexual, and they will be homosexual in any culture (although they may not practice homosexuality out of fear in the most repressive cultures). But someone who is innately 75% homosexual and 25% heterosexual, and whose behavior would reflect this in a tolerant culture, may end up being exclusively heterosexual in behavior in a repressive culture.
, or find a way of determining sexuality through a objective medical test rather than interview.