Three million years ago, Lucy and her fellow australopithecines had the same difficult births as modern humans, giving birth to particularly vulnerable newborns, according to digital simulations.
It is believed that childbirth in humans is more difficult than in other primates. In female chimpanzees, giving birth is “almost an event,” said Pierre Frémondier, lead author of the study, published Wednesday in the journal Communications Biology.
The shape of the female pelvis, which makes the exit of the human fetus dangerous, is questionable. The only solution to easily overcome the obstacle: to have a small skull and therefore be born a little prematurely.
The size of his skull, very small compared to the size of his future adult, makes him a particularly “immature” newborn, unable to survive unaided. The unusualness of mammals, which, apparently, is associated with the acquisition of bipedalism: having begun to walk on two legs, the first people would see how the architecture of their pelvis changed, and in women the birth canal narrowed.
To test this hypothesis, scientists returned to Australopithecus, an extinct species of hominin that lived in Africa between 3.2 million years and 1.8 million years ago.
Made famous by the discovery of Lucy’s fossil in 1974, this very ancient group of people were mostly bipedal but still had small brains as adults. “It’s almost comparable to chimpanzees, so we imagine primitive creatures living in very simple lineages,” Pierre Frémondier, an anthropologist and lecturer in obstetrics at the University of Aix-Marseille, explains to AFP.
To reconstruct the scenario, he and his team used digital simulations with software commonly used for automotive crash testing but adapted to the “biomechanics” of childbirth.
– “Parent Investments” –
The goal was to calculate the ratio between the skull size of newborns and the skull size of adult Australopithecus: this parameter is still unknown, paleontologists have only adult skull fossils of three Australopithecus species.
So they proposed different neonatal sizes, corresponding to brain masses of 110 grams, 145 grams (close to chimpanzees) and 180 grams (close to modern humans). On each simulation, the program had to calculate the size to find the correct path in the virtual births.
Result: only brains weighing between 110 and 145 grams passed through the channel without incident – what is called eutotic delivery, that is, normal. The big ones got stuck.
“With this smallest option, we calculated a ratio of 28% to 30%, which is very close to the configuration of Homo sapiens,” the researcher in the field of biocultural anthropology elaborates. This proportion, almost identical to ours, suggests that the baby Australopithecus also had a small skull compared to the adult, which was the only way to get out of the mother’s shrunken pelvis.
The authors of the study conclude that immaturity at birth was already present in Australopithecus, and that it comes from upright posture.
From this vulnerability they deduce the need to care for the infant in order to protect it from the cold, since it cannot regulate its own temperature, and from predators, since it is still far from being able to walk … the more deprived the child and the more important the postnatal contribution of the parents, both from the side of the mother and from the side of the group,” analyzes Pierre Frémondier.
It was this practice of “assisting childbirth that allowed people to socialize at an early stage.” And they mobilized higher cognitive functions, which led to an increase in brain size during human evolution.