[bermanoid]

The problem here is that culture determines gender.

Absolutely. I never claimed otherwise.

All I think is that some sort of robust signaling mechanism that displays a person's (or animal's) reproductive "team" should be expected to exist in any sexually dimorphic species. In many animals, this is hard coded, but I suspect that in humans that was generalized to a high level imperative, "figure out what sex you are, and clearly display the appropriate characteristics so that mates can find you".

Once we look at our own sexual taboos involving who and what we are forbidden to have sexual relations with, and we recognize that these are socially contextual, not innate taboos, things change a great deal.

But this is exactly my point: the fact that these social sexual taboos so often go against behaviors that reduce evolutionary fitness suggests that supporting those social behaviors may, in fact, be precisely the way that evolution ended up most easily controlling those behaviors.

To be very clear about this: the fact that behavior is influenced socially rather than genetically does not necessarily mean that it's an accident of history. It very well could be a direct evolutionary adaptation that leaned on social behavior to implement itself. Nature tunes nurture, and nurture tunes nature, so arguing for one to the exclusion of the other is usually wrong.

That doesn't, of course, mean that we shouldn't try to overcome such evolutionary imperatives. But we should be aware of the fact that in such cases, the social behaviors are not completely arbitrary, and that we have an uphill battle to fight.

[einhverfr]

Structuralists and Post-structuralists though tend to see most cultural constructs as arbitrary on an atomic level, and to the extent they are useful to a group that comes out of context with other cultural constructs. So for example the fact that we associate pink with girls and blue with boys is entirely arbitrary. It could be (and indeed historically has been until surprisingly recently) the other way around.

With humans though the linking of physical sex and gender is not as simple as you suggest. As I have said, some cultures (like ours) have two genders. Some have three, with children being genderless, and some have more genders than three. To pretend that gender is only about display of sex-based characteristics is to gloss over the fact that in most cultures it doesn't really work that way, nor does it really even in our own.

Gender is instead a social category and a social position. It affects division of labor and all sorts of other things. Different genders often have different taboos and these are often aimed at preventing gender-crossing, as well as maintaining a symbolic order between genders.

This is a very broad category of anthropology, and it's dangerous to assume that everyone structures their society around two genders fairly closely tied to biological sex, since this is not really the case.