Compared to most other primates, humans are characterized by a tight fit between the maternal birth canal and the fetal head, leading to a relatively high risk of neonatal and maternal mortality and morbidity. Why the human birth canal has not evolved to be larger and reduce these risks has long been a topic of debate. A new study, published in PNAS and co-led by Dr. Nicole Grunstra, affiliated scientist in the Mammal Collection at the Natural History Museum of Vienna, highlights the role of the pelvic floor in constraining human pelvic evolution.