One key hallmark of being human is walking on two legs. chimpanzees, bonobos, and gorillas, have upper hipbones (ilia) that are tall, narrow, and oriented flat front to back which anchor large muscles for climbing.Unlike blades when viewed from the side, human hipbones have rotated to the sides to form a bowl shape. https://www.nature.com/articles/s41586-025-09399-9/figures/6A new paper analyzed 128 samples of embryonic tissues from humans and nearly two dozen other primate species from museums in the United States and Europe along with human embryonic tissues collected by the Birth Defects Research Laboratory at the University of Washington. They took CT scans and analyzed histology (the microscopic structure of tissues) to reveal the anatomy of the pelvis during early stages of development and found that evolution reshaped the human pelvis in two major steps. First, a growth plate by 90 degrees to make the human ilium wide instead of tall.