Three million years ago, Lucy and her fellow australopithecines had births as complex and arduous as modern humans, bringing especially vulnerable newborns into the world, according to the results of a digital simulation.
Human births are known to be difficult compared to chimpanzees, whose births are hardly an “event,” said Pierre Frémondière, lead author of the study published Wednesday in the journal Communications Biology.
The reason is the shape of the pelvis, which makes it dangerous for the fetus to come out. The only solution to succeeding in the task is to have a small skull, which occurs when the baby is slightly premature, so the newborn is “immature” and unable to survive unaided any longer.
This is a particularity among mammals that seems to be linked to bipedalism, the ability to walk on two legs, which for early humans represented a modification of the pelvis, reducing the birth canal for females.
To test this hypothesis, the scientists returned to the australopithecines, an extinct species of hominid that lived in Africa between 3.2 and 1.8 million years ago.
This human ancestor, made famous by the discovery in 1974 of a fossil named Lucy, was mostly bipedal, but had a small brain when it reached adulthood.
“It’s almost comparable to that of a chimpanzee, so you imagine primitive beings with simple births,” Frémondière, an anthropologist and birth nurse at the University of Aix-Marseille, told AFP.
The specialist and his research team carried out simulations with a computer program used for car accidents, but adapted to the “biomechanics” of childbirth.
The aim was to calculate the ratio between the size of a child’s skull and the diameter of an adult’s head in australopithecines. This parameter was hitherto unknown, as paleontologists only had adult fossils.
Different fetal head sizes were used, corresponding to brains of 110, 145 (close to chimpanzee) and 180 grams (like the modern human). In each simulation, the software should calculate which dimension allows a viable exit from the birth canal.
The study showed that only brains between 110 and 145 grams were able to exit without problems. “With the smaller option, a proportion of 28% to 30% was calculated, which is very close to the configuration of the Homo sapiens“, said the researcher.
Thus, the authors assume that at birth this species had a small skull compared to the adult stage. The conclusion, therefore, is that immaturity at birth was already present in australopithecines and is due to bipedalism.
From this vulnerability derives the need to take care of the baby, protect it from the cold and from predators. Such a practice “allowed humans to socialize at an early stage” and mobilize higher cognitive functions, which led to an increase in brain size throughout human evolution.
