>Our bodies are designed to handle prolonged environmental stressors better because that's sort of what having a second human using all of your organs for 9 months will demand.

I read a book about the Donner Party disaster which focused on the women, and at the end they tallied up the survivors versus those who died. I don't remember the specific numbers, but women vastly outnumbered the men as survivors. And when researchers even adjusted for those who had children (who would have a much stronger survival instinct to stick around to protect them), even childless women outlasted the men at least two-fold (and no, the men weren't sacrificing for them or anything).