The natural sex drive is simply the desire to stroke one's genitalia. What they are to be stroked against is determined, among humans, mostly by social constructions. Animals have pheromones, which serve as a means to further reproduction, but among humans it's scientifically documented that pheromones are much weaker than in most animal species.
By socially constructed, I don't simply mean based on norms of social acceptability. The two things can even be opposite. Actually, homosexuality was constructed as such in the 19th century mostly as a way to place a stigma on this behavior whereas before the stigma didn't really exist or take different forms. It's not that men having sex with other men didn't exist, it simply means that this wasn't considered as a fundamental category per se.
I doubt the last word has been said on human pheromones and, in any case, even if the influence of pheromones is weaker in humans, the fact of reacting before them and the predisposition to be attracted by those of the same or opposite sex may indicate some kind of biological orientation of the sex drive... if human pheromones exist. They probably do as they exist in other mammals, though apparently there's only indirect evidence of their existence.
It's true that "heterosexuality" and "homosexuality" are modern constructs, but the stigma on relationships between men obviously existed before in many societies under the names of "sodomy" or "bestialism". There wasn't a "category" or an "identity" around such relationships, but they were reprehensible behaviours harshly punished by intolerant societies.
Also, the sex of angels and their ability to dance in reduced spaces are essential questions.
