I'm rather fond of the Hormonal Wash theory, and I expect that there's a genetic component, too. However, just because we got a different hormone mix than usual, doesn't mean that we are flawed or faulty in any way. Just different.
It's pointless to debate nature vs nurture, IMHO. Certainly, nurture influence how & when one's gender diversity will manifest, but you can't make a girl out of a boy. The sad case of David Reimer shows us that. And remember, the major proponent of the theory that gender identity is learned was Dr John Money, David Reimer's specialist. And David was the main evidence he used to "prove" how correct his theory was.
Occasionally, people start threads here claiming that they are a crossdresser because of their upbringing. But the curious thing is that these four possible reasons for becoming a CDer are given by various people: excessive female influence, insufficient female influence, excessive male influence, or insufficient male influence. This indicates to me that none of these are actually causative of CDing, although they may influence a CDers actions, thoughts & feelings.
Robin
