Abstract: At the crux of human bipedalism and childbirth is the ilium, which evolved to be shorter, broader, and parasagittally curved, compared to cranio-caudally tall, coronally-oriented ilia of other apes. Here, using histological, morphological, comparative genomic and functional genomic approaches on ethically collected human samples and museum-collected prenatal primates, we reveal that underlying this human iliac shape are two key developmental shifts. First, the human iliac growth plate underwent a spatial shift in orientation, residing perpendicular to that present in all other primate and mouse ilia and using molecular methods, we discovered human accelerated sequence changes in numerous molecular pathways, permitting undifferentiated iliac skeletal cells to shift the direction of their outgrowth. Second, the human ilium experienced a timing shift in bone ossification unlike that observed for human long-bones, or in non-human primate ilia and long-bones. Here, human iliac ossification initiates at the posterior border, then radiates anteriorly, but remains external with external cells contributing initially to the production of bone as compared to chimpanzees and other primates, where internal ossification of the ilium is like other long bones. Underlying this shift are regulatory changes in other molecular pathways. The consequence of these shifts is a human pelvis that can grow, permit proper muscle orientation and function, all-the-while retaining its complex unique human shape for walking and birthing functions later in life.