The rise of Caesarean sections may be affecting human evolution, according to a new study published in the journal Proceedings of the National Academy of Sciences.
The study found that more mothers need the invasive surgery to deliver their babies due to a narrow pelvis size.
In the 1960s, 30 in 1,000 women underwent a Caesarean section due to a narrow pelvis, whereas 36 in 1,000 births are now done by C-section.
In the past, according to the BBC, women with narrow pelvic bones and their babies would have died during childbirth, thus preventing those genes from being passed on. C-sections have allowed for both those women and children to survive.
“Without modern medical intervention, such problems were often lethal and this is, from an evolutionary perspective, selection,” Dr. Philipp Mitteroecker of the University of Vienna said. “Women with a very narrow pelvis would not have survived birth 100 years ago. They do now and pass on their genes encoding for a narrow pelvis to their daughters.”
Dr. Mitteroecker went on to explain that the purpose of the study was not to criticize medical interventions during labour, rather to just understand its effect.
There are, however, opposing evolutionary theories to their theoretical study. For one, newborn babies are now larger and healthier. Historically, a larger baby would have gotten stuck during labor, which would have killed both the mother and the newborn.
“One side of this selective force — namely the trend towards smaller babies — has vanished due to Caesarean sections,” said Dr. Mitteroecker.
Dr. Mitteroecker explained that it’s very difficult to predict what the trend will be for future births.
“The pressing question is what’s going to happen in the future?” Dr. Mitteroecker said, according to the BBC. “I expect that this evolutionary trend will continue, but perhaps only slightly and slowly.”
However, he does not expect a time in the future where a majority of children will be born by Caesarean sections.