It's not just human babies' heads that have difficulty passing through the relatively narrow birth canal. Researchers at UCLA have found, through 3D modelling, that several small primates face similar or even worse challenges.
A study published in Nature Ecology & Evolution shows that in squirrel monkeys, for example, the baby's head can be almost twice the size of the mother's pelvic space. Gorillas and orangutans have a larger space.
The researchers also discovered evolutionary adaptations. For example, in galagos, the pelvic bones never fuse, which facilitates passage.
