Caesarean Sections Could Alter Human Evolution, May Result to Bigger Babies?

A new research reveals that the frequency of mothers opting for Caesarean births could greatly impact human evolution, resulting to narrow pelvis and bigger babies.

The study, published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), says that the regular use of C-sections has decreased the mortality rate during childbirth but could also increase the rate of fetopelvic disproportion. Fetopelvic disproportion is the discrepancy between a large fetus and a narrow maternal pelvic canal.

In order to know if C-sections have indeed affected the rise of obstructed labor, the researchers said that the amount of fetopelvic disproportion -- where the baby does not fit the birth canal -- has increased dramatically. The numbers went up from 30 in 1,000 births in the 1960s to 36 in 1,000 births today.

But how does the C-section affects this? BBC notes that without a Caesarean birth, the genes responsible for fetopelvic disproportion would have not been passed on as the mother and the baby would die.

"Without modern medical intervention such problems often were lethal and this is, from an evolutionary perspective, selection. 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," said Philipp Mitteroecker from the department of theoretical biology at the University of Vienna.

Though natural birth will not be entirely obsolete, the researchers said that this evolutionary trend due to C-sections will increase "slightly and slowly."

"The pressing question is what's going to happen in the future? There are limits to that. So I don't expect that one day the majority of children will have to be born by [Caesarean] sections," Mitteroecker said.