A woman brings a womb to the party. To have children, she must risk her life and endure discomfort and pain. What does the man bring? He pays for the gas. That's not really a lot to ask, is it?

Nature has "locked" women into the role of child-bearer, at least it has if we assume that having children is something a society values, if only to support us in our old age. From there on out, the rest is details.