Thoughts on Gender Identity

A couple of posts back, I spoke about the puzzle of Gender Identity, specifically relating to transgendered persons. One commenter was kind enough to provide some informational links (I'm writing this on the fly and I apologize for not posting internal links).

The gist is that human gender identity seems to be established in utero and that it's fixed. The cells of the human brain have different degrees of sensitivity to sexual hormones, primarily estrogen and testosterone, and that determines whether an individual sees himself or herself as male or female.

If the results of this research is correct doesn't this contradict the feminist argument that gender is primarily cultural?

How does an honest feminist researcher into gender identity resolve this?

Based on my own, extremely limited, personal experience, I think that gender identity has a strong biological basis, but there is a certain flexibility due to cultural influences. (Much as genes can determine your maximum height, but nutrition and environment determines if you actually achieve it.) On a purely personal note, I can't remember if I ever didn't know that I was female, although my interests have not always followed "traditional" patterns, as understood by my grandmothers.