Now, researchers have mapped the key structural changes in the pelvis that enabled early humans to first walk on two legs and accommodate giving birth to a big-brained baby. The study, published in Nature on 27 August, compared the embryonic development of the pelvis between humans and other mammals. They found two key evolutionary steps during embryonic development - related to the growth of cartilage and bone in the pelvis - which put humans on a separate evolutionary path from other apes.