According to current medical knowledge (as reported in various peer-reviewed journals, including The International Journal of Transgenderism, The Journal of Clinical Endocrinology & Metabolism, and a whole lot of others I'm not gonna dig up my notes to list off) there's a whole lot that goes into what we lump under "sex" and "gender".
Chromosomes are important, but they're more of a guideline than a rule. XX and XY are the most common, but there's a lot more variation than anyone covers in 8th grade biology. And XX doesn't always mean "female" nor does XY always mean "male" even in basic physical development. It's one of the reasons that "genetic female only" line cracks me up. Unless they're karyotyping at the door, you can't tell what chromosomes someone has from their anatomy, their endocrinology, or any method other than genetic karyotyping. In addition, assigned-female individuals cannot be assumed to all posses uteri, vaginas or differentiated vulvae, assumed to menstruate, or assumed to anything else commonly claimed to be universal to women. Gasp! Some women - including some "genetic women" - even have cliterophalluses! Teh shock!
There's a lot of statistically-common variation out there. I sometimes love to get in the middle of some of these debates and point out that my wife, who was assigned male at birth, has XX chromosomes (and XXY ones - she's a mosaic variation of Klinefelter syndrome). I'm the one who has given birth, and my karyotype is XoXY. I have conceived (multiple times, on birth control even), birthed healthy children, breastfed - and yet I had testes as well as ovaries well into adulthood. And the two of us are not all that rare.
According to the folks that study such things, there are three major contributors to sex during development - the influence of the chromosomes contributed by the two parents, the hormone balance in the fetus (and, to a lesser extent, in the mother) during brain development, and the hormone balance in the fetus (again, and to a lesser extent in the mother) during gonadal definition an development. The latter two are considered to be the largest influences, and usually they "line up" and the hormone balances at the two different points influence development in the same direction. But not always, and there are an infinite number of variations possible.
All of that was just about sex. Gender is a whole other fettle of kish, and probably has just as much complexity. Ditto to gender presentation.
How much is innate, and how much is societal? I think that's going to vary dramatically depending on the individual. Some folks are rather fluid in one or both, some folks have strong innate preferences that influence their gender identity and/or presentation, and others (probably the majority) have some areas that are "natural" to them and others they pick up and still others they don't even have a thought about.
For me, I'm mostly read as female, and mostly anatomically female. I generally ID as intersex, and either genderqueer or soft butch. I would like to be able to mod my body in some ways (and remove some feminine markers) that are not possible for me, yet there are some aspects of a female body I really like. There are some ways I wish I could be more masculine, but I do not want a male body. Queer I am.
#s 3-7 to follow.
This entry was originally posted at http://sanacrow.dreamwidth.org/9780.htm