David Reimer[1] showed pretty convincingly that there are a lot of hard-wired traits in the genes. Is it 100% of the difference? Of course not. Is it at least

David Reimer[1] showed pretty convincingly that there are a lot of hard-wired traits in the genes. Is it 100% of the difference? Of course not. Is it at least 50%? I think the evidence points to that being the case. Personally, I was always surprised at the difference in play between my boys and girls, even at VERY early ages. You can see the differences at under a year old, even if you are attempting to balance for societal pressures. I've spoken to enough parents who have experienced the same thing to firmly believe it is more than anecdotal. [1] http://en.wikipedia.org/wiki/David_Reimer http://en.wikipedia.org/wiki/David_Reimer