Human childbirth may not be complicated due to our need for large brains and pelvises suitable for upright walking, referred to as the “obstetrical dilemma”, according to research published in the journal Nature Ecology & Evolution. The human birth canal is framed by the bones of the pelvis which is barely larger than the baby’s head. During labour, the joint between pubic bones softens a little, allowing the baby’s head to make its way out into the world. But despite the slight evolutionary tweaks, the childbirth is a difficult process – much more difficult than in most other animal.
The study analysed chimpanzee pelvic bones and found that females had human-like pelvic characteristics despite having easier births due to small brains, which surprised the scientists. Using three-dimensional simulations, the researchers also found that apes had “similarly constricted midpelvis as in humans, with even narrower outlet dimensions”.
Based on the findings, the study posited that substantial obstetric constraints “did not arise abruptly in humans but evolved gradually through a series of obstetric compromises from an already constricted birth canal shared across anthropoid primates” over millions of years.
“It is not primarily an adaptation to giving birth to large-brained infants because we show in this study that these changes happen prior to significant brain expansion,” study lead author Nicole Webb, a paleoanthropologist at the University of Zurich was quoted as saying by Live Science.
“Our ancestors the australopithecines likely were already susceptible to the birth complications that we encounter today. and they may have even required some sort of birth assistance like us,” Webb added.
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What do the study findings suggest?
Apes have small fetal heads which aids in the uncomplicated birth. In contrast, in modern humans, the fetal head is 10 per cent longer than the anteroposterior inlet diameter, whose length is reduced compared to that of apes. Webb stated that akin to humans, chimpanzees may be “subtly trending towards this pattern” as well where human babies are born helpless but their brains continue to grow afterwards.
If the research stands true, the scientists may have found an explanation as to why some of our ancestors seemingly had a challenging time giving birth despite having small brains. They may have faced the same birthing challenges as that common ancestor shared with chimpanzees.