Some excerpts from the outstanding article http://www.fordham.edu/halsall/med/thorp.asp
One of the most seductive claims to issue from this work is the claim that the very category "homosexual" is a social construct which is scarcely more than a hundred years old. This claim is made of course by Foucault himself
But the book's most important and striking claim -- its recurrent underlying thesis -- is that homosexuality is not a natural but a social category.
On the surface homosexuality is extremely odd; "nature does nothing without a purpose," said Aristotle, and we are inclined to believe him.
To put it in Aristotelian language, homosexuality is produced when efficient causality fails to push in the direction that final causality seems to pull -- as in an automatic pilot that is broken. The general tradition of psychoanalytic theories of homosexuality falls into this line, it seems to me. Arrested maturation, unresolved Oedipal complexes, and the like all depict homosexuality as something that in each individual case should not have happened; homosexuality arises because a fundamental psychic development that normally does occur, in this case, for some reason did not.
I also think that the whole project of understanding homosexuality as genetically based does not get over an initial hurdle of implausibility: each of these theories would require homosexuality to run in families in ways that nobody would seem to have any prima facie reason to think that it does.
And if homosexuality has not got there either by the oversight of nature or by a ruse of nature, how has it got there? Into this puzzling dilemma steps Foucault with a sort of Copernican revolution, proposing that homosexuality got there because we put it there. We created the category and gave it the importance which it seems to have; we drew together a series of practices and tastes, gave them a single name, and postulated their psychic depth.
And now we seem to be mystified as to how this strange creature got there. Foucault writes: "homosexuality appeared as one of the forms of sexuality when it was transposed from the practice of sodomy into a kind of interior androgyny, a hermaphrodism of the soul. The sodomite had been a temporary aberration; the homosexual was now a species." The very word "homosexual" came into English only in 1892, formed after a German neologism coined about twenty years earlier. Homosexuality, then, is a social construct of our own culture, and virtually even of our own century. What we mean by "homosexuality" did not exist in Greece; there is no such thing as Greek homosexuality;
Foucault, in the striking remark which I quoted above, claims that what had been merely the practice of sodomy got transformed, in the thought of the nineteenth century, into an interior androgyny, a hermaphrodism of the soul. What Foucault seems to be suggesting is that sexual preference may itself be nothing more than a superficial matter of taste and practice, like the practice of opening breakfast eggs at the big or the little end, or the preference for white or dark meat of fowl, and that it need have no deeper roots in the soul than we generally suppose these cases to have. If this is true, it is no wonder that the quest to understand the deep cause of homosexual preference has been unsuccessful: it is a quest for something that isn't there.
A citizen may penetrate whom or whatever he pleases, but a citizen must not be penetrated. However that may be, our symmetrical concept of homosexuality contrasts rather starkly with the Greek asymmetrical concept of pederasty.
Another Article http://www.nickyee.com/ponder/social_construction. which compliments the above.