system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does giving birth hurt, even though it harms reproduction? why was it not removed through natural selection?

don't give me stories about the first woman eating a weird fruit please.
gpt
Human reproduction is limited by two of humanity's most useful advantages: We stand upright and are very intelligent.

Standing upright requires a relatively narrow pelvis. Being very intelligent requires a relatively large brain, and therefore skull. Yet the skull must fit through the pelvis at birth! So a middle ground is found and we are adapted to have babies born relatively undeveloped, so their skull bone plates are not fused yet and their brain is smaller. It hurts, but pain isn't a limiting factor on reproductive success.

A consequence of being born undeveloped is that human children are vulnerable and delicate. They need constant care and protection to survive, and so have frequent cries that their parents are biologically wired to respond to.

So we have covered why childbirth is painful and babies are annoying little shits.