Our extinct Australopithecus relatives may have had difficult births

Childbirth was difficult and dangerous for our ape-like ancestors, much as it is for women today. A new study of the pelvis to Australopithecus suggesting that labor exerted powerful forces on their pelvic floor—which means 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 many births, they would probably have a greater risk of pelvic floor disorders.”

For modern humans, vaginal birth requires a lot of force, as a large-headed baby is forced through a relatively narrow pelvis. One region prone to injury is the pelvic floor, a sheet of muscle that connects the left and right halves of the pelvis. Many women tear their pelvic floor during childbirth, and it is 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 befell our extinct ancestors. They focused on Australopithecuswho 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 Gaythe genus we belong to.

Based on a handful Australopithecus the stream that is found, the team knew that Australopithecus the birth canal was oval: it was wide from left to right, but narrow from front to back. Non-human primates such as chimpanzees have the opposite layout, while the modern human birth canal is more circular.

To investigate what would happen in Australopithecus birth, the team simulated the pelvis 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 modified it to fit Australopithecus the pelvis. They then simulated a baby being pushed through the pelvis and estimated how much force would be applied to the pelvic floor.

They found that Australopithecus the pelvic floor experienced forces of 4.9 to 10.7 megapascals, equivalent to the 5.3 to 10.5 MPa exerted on the human pelvic floor during childbirth.

The team did well to use more Australopithecus the pelvis, and to make the comparison with data from a live human birth, says Lia Betti at University College London. “This is a very good way to check that your model is robust.”

Despite that, Betti is cautious about the results. She says we don’t know about the pelvic floor muscles Australopithecus differed from ours, which could have made them more or less resistant to demolition. As a check, the team also modeled two modern human births, and in one case the baby did not rotate in the birth canal as they do in real life. It indicates that the simulations are missing key factors, she says.

“The problem is just that we don’t have a huge amount of evidence,” says Betti. Three Australopithecus the stream – all from different species – is a small data set. There are no known brooks from earlier hominin species.

“I think that we are only at the beginning of this type of study,” says Frémondière.

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