To be honest, I don't think I can begin to answer any of your questions... I just don't know. I was always lead to believe that this was the case. I noticed evidence in real life that suggested that it was true, therefore did not question its validity, etc.
Hey, does that sound familiar?
I thought that the stress that childbirth puts on women's bodies leads them to being, in general, better able to recover from illness or injury. Also they would be able to handle more intense levels of pain for the same reason. It makes some kind of sense - especially when you think about it from the view of evolution - but it's still unsupported assertation really. Anyway, I'm no biologist, so I'm more than prepared to be enlightened.
The Rock Hound