Why Haven't Humans Evolved Easier Childbirth? Our Organs Get In The Way

We might've gotten away with it if it wasn't for our pesky organs. Image credit: Gorodenkoff/Shutterstock.com

Thanks to modern medicine there are a range of ways for a human to come into the world, from a tight squeeze to a trip out the sunroof via caesarean. Parents' experiences can range from seamless to fraught, and those who have been through a traumatic birth may struggle to come to terms with it long after it’s over. Given that it can have fatal consequences for both the parent and the baby, you might think we as a species could've evolved in favor of a safer and easier way of giving birth. Unfortunately, according to a recent study published in the journal Proceedings of the National Academy of Sciences, this is probably as good as it gets.

Engineers at the University of Texas at Austin and University of Vienna took a closer look at the anatomical underpinnings of childbirth, which revealed the series of evolutionary trade-offs that left us with the current system. One of the complications of human birth is the comparatively narrow birth canal when you consider the size of babies' heads, but this complication has remained owing to the protection it provides the parent’s other organs.

The head-to-head of the baby's easy exit versus the safety of the mother’s vital organs is apparently what prevents the birth canal from becoming a smoother, more spacious ride for those involved. In vying for two opposing life-preserving agendas the two competing biological imperatives persevere in the face of evolution.

"Although this dimension has made childbirth more difficult, we have evolved to a point where the pelvic floor and canal can balance supporting internal organs while also facilitating childbirth and making it as easy as possible," said lead researcher and assistant professor Krishna Kumar in a statement.

For a quick refresher, the pelvic floor is a muscle group (not to be confused with the magical placenta) that stabilizes the spine and supports the uterus, bowel, and bladder. To establish its role in childbirth, and better understand how its influence would change depending on size or thickness, the researchers carried out multiple finite element analyses using computerized pelvic floor models.

Their results showed that while an increase in pelvic floor size might make for an easier birth, without the bony structures to support it, other organs slump downwards. No good. Increasing the pelvic floor thickness (which might prevent this) actually increased the pressure needed to push the baby out. Also, no good.

"We found that thicker pelvic floors would require quite a bit higher intra-abdominal pressures than humans are capable of generating to stretch during childbirth," said Nicole Grunstra of the University of Vienna's Unit for Theoretical Biology in a statement. "Being unable to push the baby through a resistant pelvic floor would equally complicate childbirth, despite the extra space available in the birth canal, and so pelvic floor thickness appears to be another evolutionary 'compromise,' in addition to the size of the birth canal."

For now, it seems, evolution has given as good as it's getting.


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