Comparisons of embryonic pelvic development between humans and other mammals reveal two key developmental shifts in cartilage and bone growth that redirected human pelvic morphology. Those shifts produced a wide, bowl-shaped pelvis optimized for upright, two-legged locomotion while preserving a birth canal suitable for large-brained infants. Anatomical, histological and genomic analyses across developmental stages identify changes in growth patterns that separate human pelvic development from that of other apes. The resulting pelvic architecture affected whole-body alignment from skull base to toes, and similar features are observable in ancient hominin fossils, informing functional genomic inquiries into bipedalism and childbirth adaptations.
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.
"Everything from the base of our skull to the tips of our toes has been changed in modern humans in order to facilitate bipedalism," says Tracy Kivell, a palaeoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Kivell says the study offers a new understanding of how some of those changes came about, not just in living humans, but also in fossils from ancient hominins such as Denisovans.
As modern humans evolved, our pelvises developed the wide, bowl-like shape needed to allow upright, two-legged walking - but it is unclear exactly how that happened. "The human pelvis is dramatically different than what you see in chimpanzees and gorillas, so we wanted to set out to try and understand what's happening there," says study co-author Terence Capellini, a developmental geneticist at Harvard University in Cambridge, Massachusetts.
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