As modern humans, we have evolved the ability to walk upright on two legs and have exceptionally large brains. While these traits might help us to solve puzzles and reach the top shelf, they come at a price: narrow hips and large heads make giving birth a slow, extremely painful experience that often requires medical assistance. But what was it like for our ancient relatives?
Researchers led by Boston University recently took a look at what birthing might have been like for Australopithacus sediba, an ancient hominin belonging to the same genus as the famous Lucy. Based on fossil evidence of this species, we know it lived about 2 million years ago, around the same time as two ancient humans, Homo rudolfensis and Homo habilis.
Turning to fossil bones, the researchers digitally reconstructed what the pelvis of a female A. sediba might have looked like, allowing them to work out how it would have given birth. They found that the process would have been quite a bit easier for the ancient species than it is for women today.
When human babies are born, they have to rotate several times to fit through the birth canal, but for A. sediba, this probably wasn’t the case, even though the species shared some pelvic features, like birth canal shape, with its human relatives. The researchers estimate that for rotation to be required, the head of an A. sediba baby would have to increase by 28-42 percent. However, they note that some level of rotation may still have occurred in the species.
"The foetal head and shoulder breadth have ample space to pass through even the tightest dimensions of the maternal birth canal," lead researcher Dr Natalie Laudicina at Boston University told BBC News. It’s still not clear exactly when the need to rotate to exit the birth canal first evolved in humans.
The obvious conclusion might be that as ancient hominins adapted to upright walking and larger brains, birthing became more and more difficult. However, the new research actually adds complexity to the story. For example, Lucy, who belonged to the species Australopithecus afarensis, would have had a more difficult birthing process than A. sediba, as it would have been a tighter squeeze for the infant to move through the birth canal. Despite this greater challenge when giving birth, Lucy and her kin actually lived about a million years earlier than A. sediba, suggesting that the evolution of birthing is tricky and complex.
“The interspecific differences in fossil hominin pelvic morphology and fetal dimensions show that there is not a linear, gradual change from an ‘easy’ birth to a ‘difficult’ birth,” the researchers write in PLOS ONE. “Instead, the morphology of each specimen exhibits its own set of obstetric challenges.” They note that the shape of the A. sediba pelvis is likely partially the result of how the hominin moved, rather than being adapted solely to birthing.