A new analysis shows that childbirth difficulties affect numerous primate species, often more severely than in humans. Researchers found that many primates must deliver large-headed infants through narrow pelvises, a challenge that may date back to the earliest primates over 50 million years ago.
The study reassessed birth canal shapes in 29 primate species alongside newborn skull data. It revealed that small primates such as bush babies and tamarins experience the greatest mismatch, with infant heads nearly twice the size of the birth canal.
Previous assumptions stemmed from a flawed 1940s study by anthropologist Adolph Schultz. That work used human pelvis landmarks that do not accurately measure other primate birth canals, leading to overestimates of canal size.
Nicole Torres-Tamayo and Lia Betti at University College London led the research, published in Nature Ecology and Evolution. They suggest birth difficulties represent an ancestral condition in primates, though great apes show fewer issues due to their larger size.
Nicole Webb at the University of Zurich noted that even chimpanzees may face close fits, prompting further study of the methods.