Illustration of a female Australopithecus sediba carrying an infant
JOHN BAVARO FINE ART/SCIENCE PHOTO LIBRARY
Childbirth was difficult and dangerous for our ape-like ancestors, much as it is for women today. A new study of the pelvises of Australopithecus suggests that labour exerted powerful forces on their pelvic floors – meaning Australopithecus mothers risked perineal tearing.
“We show that Australopithecines are quite similar to modern humans,” says Pierre Frémondière, a midwife at Aix-Marseille University in France. “If they had lots of deliveries, probably they would have a greater risk of pelvic floor disorder.”
For modern humans, vaginal childbirth requires a lot of force, as a large-headed baby is forced through a relatively narrow pelvis. One region that is prone to damage is the pelvic floor, a sheet of muscles that links the left and right halves of the pelvis. Many women tear their pelvic floor during labour, and it’s been estimated that 1 in 4 women experience pelvic floor disorders such as incontinence or organ prolapse.
Frémondière and his colleagues wanted to find out if similar difficulties afflicted our extinct ancestors. They focused on Australopithecus, which lived in Africa between about 2 million and 4 million years ago. These early hominins walked upright but were also still adapted to spend time in trees, and may have made and used stone tools. They may have been the ancestors of Homo, the genus to which we belong.
Based on the handful of Australopithecus pelvises that have been found, the team knew that the Australopithecus birth canal was oval: it was wide from left to right, but narrow from front to back. Non-human primates like chimpanzees have the opposite set-up, whereas the modern human birth canal is more circular.
To investigate what would happen in Australopithecus labour, the team simulated the pelvises of three individuals from different species: Australopithecus afarensis, Australopithecus africanus and Australopithecus sediba. To model the pelvic floor muscles, the researchers took an MRI scan of a pregnant woman, extracted the three-dimensional image of the pelvic floor, and morphed it to fit the Australopithecus pelvises. Then they simulated a baby being pushed through the pelvises, and estimated how much force would be exerted on the pelvic floor.
They found that the Australopithecus pelvic floor experienced forces of 4.9 to 10.7 megapascals, similar to the 5.3 to 10.5 MPa exerted on the human pelvic floor during labour.
The team did well to use multiple Australopithecus pelvises, and to make the comparison to data from a live human birth, says Lia Betti at University College London. “This is a really good way of checking that your model is robust.”
Despite that, Betti is cautious about the results. She says we don’t know if the pelvic floor muscles of Australopithecus differed from ours, which could have made them more or less resilient to tearing. Also, as a check, the team modelled two modern human births, and in one case the baby did not rotate in the birth canal as they do in real life. This indicates that the simulations are missing key factors, she says.
“The problem is just we do not have a huge amount of evidence,” says Betti. Three Australopithecus pelvises – all from different species – is a small dataset. There are no known pelvises from earlier hominin species.
“I think that we are just at the beginning of this kind of study,” says Frémondière.
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