Puppycow
Penultimate Amazing
I think that you should add "a different mix of hormones affecting the embryonic brain." Based on the theories I've heard, this seems to be essential. Nowadays, both male-to-female and female-to-male transsexuals describe what happens to them emotionally and mentally when they undergo sex-change hormonal therapy, but they are already at the outset the opposite gender of what we would expect them to be based on their bodies and genetics. The hormones of the amniotic fluid seem to contribute to gender identity and sexual orientation.
That may be true, although it isn't what I meant. I think that your brain and mine are being affected by hormones right now, not just in the past. That is not to say that we are ruled by our hormones (although some people may be) but we are influenced by them at least.