[Kaunisenkeli]

Coda: Absolutely! This past summer, I took a Psychology of Gender class that was being offered at my college. At the end of the last class, the prof asked us each if our opinion on the biological/societal divide in gender had changed at all. All but maybe two said that the class really had changed the way they viewed gender. It's such an incredibly complex thing, and it isn't pure anything.
Also, I actually know a trans-woman through Gaia who nobody questions the fact of her being a woman, but she could be seen as a complete butch lesbian stereotype in how she dresses and acts (I'm kind of a half-femme/half-butch lesbian, myself). For people who have challenged me on some of my behaviors, I just tell them that I've been through everything I have to finally be myself, so why would I turn around and start acting like a stereotype (feminine, masculine, or otherwise).

Also, Tiva: There has been some work done in genetics that suggests even the old sex chromosome dynamic most people know (X-Y, et al), and we aren't even getting into intersexed folks (people with XXY, men with XX, women with XY... and on into complication). The last I heard on it was several years ago, but according to what I read there were several more genes involved in keeping even adult bodies towards one side or the other, physically speaking. More studies need to be done on this, but it's interesting all the same.