A new study in Nature shows that women have backs and hips that help them carry the weight of a growing baby without falling over. They have another vertebra that helps them lean back more to balance the growing baby's weight. They have wedge-shaped vertebra in the crucial spot, rather than square ones, to help bear the weight like a keystone. And women's wider hip joints let them bear the torque of walking with a big weight in their abdomens with less strain. Pregnant women are still subject to more back problems than other people, but they would hurt even more, and even more often, if they were built like men. The scientists who did the study report these nifty bones are found in ancient australopithecine women as well as modern women.
However you think people got that way, this is a fine piece of engineering. I myself think this is further evidence of providentially guided evolution, but even if you think people were designed this way from the get-go, or evolved this way by random mutation and natural selection, we end up in the same place: pregnant women are ingeniously configured to walk with babies.