Overview

• In human embryos, the ilium’s cartilage growth flips 90 degrees around day 53 of gestation, producing a pelvis that is shorter and wider than in other primates.
• Iliac ossification begins near the sacrum and is delayed by up to 16 weeks compared with other primates, preserving the remodeled shape and supporting births of larger‑brained infants.
• The Nature study integrates histology, CT imaging, and single‑cell and spatial transcriptomics on 128 human embryonic samples alongside nearly two dozen primate species from museum and research collections.
• Researchers implicate hundreds of regulatory elements, highlighting SOX9 and PTH1R in the growth‑plate reorientation and RUNX2 in the ossification timetable.
• Authors infer the growth‑plate reorientation arose roughly 5–8 million years ago and the ossification delay within the last ~2 million years, consistent with pelvic traits in Ardipithecus and Australopithecus fossils.