C-Sections Could Affect Genetics Of Your Pelvis

As the number of C-sections is on the rise, does it have a significant effect on human evolution? Researchers in Austria have found that quite a few number of mothers now have narrowed pelvic size compelling them to deliver their baby via a Caesarean section.

It turns out that the number of cases where a baby does not pass through the birth canal has gone up from a 3% rate (that is 30 out of 1,000 births) in the 1960s to 3.6% (that is 36 out of 1,000 births) today. This birth rate has been taken on a global scale with a 10-20% increase over 50-60 years show due to evolutionary effect.

While more women now have narrow birth canals, it is not likely to have been transmitted genetically from mother to daughter, because both would not have survived during childbirth.

The question as to why the rate of fetopelvic disproportion (or the baby not fitting through the birth canal) is high now can help shed light on human evolution, according to Dr. Phillipp Mitteroecker at the department of theoretical biology at the University of Vienna. He adds that if there were no medical intervention, birth complications such as very narrow pelvis can be a deadly problem. But from the evolutionary point of view, very narrow pelvis has become a matter of natural selection.

Dr. Mitteroecker adds that over a century ago, women with very narrow size of the pelvis would not live on. But with advanced medical intervention available now, they survive and their daughters inherit their genes encoding for a narrow pelvis.

The natural selection for very narrow pelvis has been met by opposing forces too. While researchers wondered as to why more mothers now have narrow pelvises, the contradictory evolutionary question that arises is why the human pelvic size has not become wider over the years.

When compared to other primates, the head of human babies is large. Therefore other primates can birth more easily.

The scientists made studies using mathematical models gathered from WHO data besides taking into account other studies on large birth.

The studies led them to opposing evolutionary forces in the theoretical research. One evolutionary force was found to be trending towards bigger newborns who are healthier. But if the baby grows too large, it can get blocked in the birth canal during labor which could be fatal for both the mother and the baby. In this case, the genes would not be inherited.

The other evolutionary force is that trending towards smaller babies which has nearly vanished owing to increasing number of C-sections.

Dr. Mitteroecker says that while they don’t criticize medical intervention in childbirth, it has gone on to show its impact on human evolution.

The looming question now is as to what it could hold for the future. Dr. Mitteroecker expects that this evolutionary phenomenon is likely to continue although slightly and gradually. Therefore it is less likely that majority of the children will arrive through C-sections.

The study appeared in the Proceedings of the National Academy of Sciences.

Smithsonian paleoanthropologist Dr. Briana Pobiner commented on the study saying that several other cultural and biological issues could determine the C-section rates which could vary across various sections of the world.

Consultant obstetrician and spokesperson for the Royal College of Obstetricians, Daghini Rajasingam, says that factors such as obesity and diabetes could influence the number of C-sections. Given that diabetes is more prevalent in the younger generation now, increasing number who are of the age to bear children are likely to have diabetes, leading them to have a C-section. Also, with more women now being obese around the reproductive age, you can expect a high BMI necessitating C-section rates, according to Dr. Rajasingam.

(Courtesy: BBC News)

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