I would think it's much more indirect than that. We know women have much more robust immune systems than men do, presumably partly because of the rigors of preg

I would think it's much more indirect than that. We know women have much more robust immune systems than men do, presumably partly because of the rigors of pregnancy, dangers of child birth, and demands of child rearing. And this is true across species. What was immediately fascinating to me about this article was the relationship between the immune system and pain sensitivity. Women suffer from autoimmune disorders much more than men because of their stronger immune systems. Makes one wonder if differences in the pain pathways are adaptive to the stronger immune system. Regarding painful child birth, from an evolutionary perspective it would only matter if the pain itself resulted in less reproduction. The pain is rather fleeting, all things considered, and worst for the first child. And there are many ways for natural selection to mitigate any negative impact on reproduction, such as flooding the woman with hormones that make her forget it, increasing sexual desire, etc.