As I mention in this week's podcast on Anne Fauto-Sterling's "Five Sexes: Why Male and Female Are Not Enough," this question animates her early work on sex variation and intersexuality:
Why are "we" in the West so culturally invested in maintaining that there are only two sexes, even though this belief goes against the rather obvious and regular phenomena of natural sex variation?
But this question is misleading because "our" cultural investment isn't really in two sexes, but in maintaining the One. The sex/gender system establishes the primacy of the male/masculinity against which female/femininity is posited as sheer negation: Man is rational, woman is irrational (or emotional); man is physically strong, woman is physically weak. (As Beauvoir puts it, man occupies both the positive and neutral positions, woman the negative one. ) These statements may in fact not be true (for example, many women are stronger than many men) but exclusivity nonetheless structures our thinking where it comes to questions of sex and gender. (Exclusivity is where identity is created through the exclusion of the other, by way of negation.) As Luce Irigaray has argued, in this sex/gender system there is no "woman" but only man and not-man.
Our investment in the One is not limited to questions of sex and gender, but it is rather a metaphysical and logical commitment to the One that dates all the way back to Presocratic philosophy and debates between Parmenides & Zeno and Heraclitus & Empedocles, with followers on each side. That is how far back one has to go to find the origins of our decision, in the West, to go with the One and the logic it entails. The One won the day and has dominated ever since, but those who uphold the multiplicity and infinity of being have constituted and alternative history of philosophy. Questions of difference, alterity, and the Other/otherness are ways of thinking against the homogeneity policed by the logic of the One.
As I see it, the problem is not limited to the subjugation of women and repression of sex variation, but is the larger problem of a constitutive inability to think difference beyond negation and exclusivity. We can see the same logic of domination at work in enforcing racialized regimes, for example. But why do we refuse to "believe our own eyes" and the multiplicity of our experience in the phenomenal world, and insist on taming this experience through the creation of falsifying knowledges and dogma. Our experiences are always filtered through our systems of belief, so we learn to literally not see difference. But it takes a lot of effort to maintain this state of affairs - and that is the good news, politically speaking.
In the upcoming series of podcasts, we'll be discussing inter-subjectivity and the Other - join us starting next week!