Left-wing humanities PhDs don't believe that biology influences society. They have a large stake in that idea because they want to study society and language, instead of biology because they don't know how to study biology. They have a bunch of dog-eared copies of Foucault books, not microscopes. So, no surprise that they want to say sexuality is completely a social construction. Obviously, that's garbage.
Let's also clarify what we mean by gay. There's sexually attracted to the same sex and there's identifying as gay. Even today, many people are married to opposite sex partners and identify as straight, but are attracted to the same sex and have sex with people of the same sex. Is that straight? When people talk about other cultures not having the concept of gay people, that's about semantics. Older cultures just treated gay people differently by forcing them into straight relationships or clergy/civil service or killing them.
I recommend
this article on the pitfalls of genetic determinance.
