On the earlier comment that heterosexuality and homosexuality don't exist, I believe they absolutely do exist but that they take on different realities depending on time and place.
They DEFINITELY exist in 2011 America. WE LABEL. In fact, gays themselves are the most insistent in slapping on labels at a moment's notice. For example, "that guy is married and has six kids, but he did it with two or three guys when he was younger. So he is a closet homosexual!" Or - "look at those guys standing in front of Cutler at that bodybuilding competition. They've got to be gay!"
Even ancient Greece probably had some concept of homosexuality. Alexander the Great may not have been "gay", but a transvestite prostitute probably was considered homosexual, or whatever the word would have been at that time.
I read about two married men in a gay bar in Istanbul about ten years ago. One was a visiting American. The other was Turk. Even though their sexual behaviors were roughly the same, the American was a "closet homosexual". The Turk was "straight". The Turk was being helpful to the American and pointing out exactly which men in the bar he believed to be gay and which were not. Most were not. According to this Turk, you are gay if you are submissive, but not otherwise. An American might laugh at this distinction, but why is one man's reality "correct" and the other "incorrect"?
Different places, different realities.