Although I'm not certain this is a "GLBT" issue per se, this seemed like the best place to put it. We no longer have our Humanities forum...
Insisting there are only two human sexes erases the existence of intersexuals.
Two Sexes Are Not Enough
http://www.pbs.org/wgbh/nova/gender/fs.html
European and American culture is deeply devoted to the idea that there are only two sexes. Even our language refuses other possibilities; thus to write about Levi Suydam I have had to invent conventions -- s/he and h/er to denote individuals who are clearly neither/both male and female or who are, perhaps, both at once. Nor is the linguistic convenience an idle fancy. Whether one falls into the category of man or woman matters in concrete ways. For Suydam -- and still today for women in some parts of the world -- it meant the right to vote. It might mean being subject to the military draft and to various laws concerning the family and marriage. In many parts of the United States, for example, two individuals legally registered as men cannot have sexual relations without breaking antisodomy laws.
But if the state and legal system has an interest in maintaining only two sexes, our collective biological bodies do not. While male and female stand on the extreme ends of a biological continuum, there are many other bodies, bodies such as Suydam's, that evidently mix together anatomical components conventionally attributed to both males and females. The implications of my argument for a sexual continuum are profound. If nature really offers us more than two sexes, then it follows that our current notions of masculinity and femininity are cultural conceits. Reconceptualizing the category of "sex" challenges cherished aspects of European and American social organization.
Indeed, we have begun to insist on the male-female dichotomy at increasingly early stages, making the two-sex system more deeply a part of how we imagine human life and giving it the appearance of being both inborn and natural. Nowadays, months before the child leaves the comfort of the womb, amniocentesis and ultrasound identify a fetus's sex. Parents can decorate the baby's room in gender-appropriate style, sports wallpaper -- in blue -- for the little boy, flowered designs -- in pink -- for the little girl. Researchers have nearly completed development of technology that can choose the sex of a child at the moment of fertilization. Moreover, modern surgical techniques help maintain the two-sex system. Today children who are born "either/or -- neither/both" -- a fairly common phenomenon -- usually disappear from view because doctors "correct" them right away with surgery. In the past, however, intersexuals (or hermaphrodites, as they were called until recently), were culturally acknowledged.
In 1993 I published a modest proposal suggesting that we replace our two-sex system with a five-sex one. In addition to males and females, I argued, we should also accept the categories herms (named after "true" hermaphrodites), merms (named after male "pseudohermaphrodites"), and ferms (named after female "pseudohermaphrodites"). [Editor's note: A "true" hermaphrodite bears an ovary and a testis, or a combined gonad called an ovo-testis. A "pseudohermaphrodite" has either an ovary or a testis, along with genitals from the "opposite" sex.] I'd intended to be provocative, but I had also been writing tongue in cheek and so was surprised by the extent of the controversy the article unleashed. Right-wing Christians somehow connected my idea of five sexes to the United Nations-sponsored Fourth World Conference on Women, to be held in Beijing two years later, apparently seeing some sort of global conspiracy at work. "It is maddening," says the text of a New York Times advertisement paid for by the Catholic League for Religious and Civil Rights, "to listen to discussions of 'five genders' when every sane person knows there are but two sexes, both of which are rooted in nature."
[snip]
How many genders are there? (I am differentiating gender as a cultural role from sex as a biological category.)
Many cultures had three or four or five, besides the two we normally think of.
http://en.wikipedia.org/wiki/Third_gender
Examples of third genders in many cultures include the Hijras of India, the Kathoeys of Thailand, the Winktes/Two-Spirits/"Berdaches" of Lakota Culture, and the Fa'afine of Polynesia.
Binary thinking limits our understanding. There are more than two sexes, and more than two genders.

