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article imageCesarean births are changing how we evolve

By Tim Sandle     Dec 10, 2016 in Science
Amsterdam - Cesarean sections (or C-sections) save the lives of mothers and babies, and they are also a ‘lifestyle’ choice for some expectant mothers. This area has been examined by researchers to see what the impact is upon human evolution.
The C-section procedure enables a baby to be delivered through incisions made to the mother’s lower abdomen. This is undertaken, for medical reasons, when the baby is too large to pass through the mother’s birth canal. There are also other medical reasons why this procedure may be undertaken.
According to Dr. Philipp Mitteroecker, from the University of Vienna, Austria, the process is a form of evolutionary selection. In that, according to the evolutionary biologist, the procedure does not take place ‘naturally’ (in that it requires a medical intervention.) One global estimate puts the annual number of cesareans at 1.3 million and it accounts for over 30 percent of births.
Where the evolutionary aspect comes in the rise in cesareans means that the genes associated with birth complications, such as those that influence the baby’s head size and the mother’s pelvis size, are then carried onto future generations.
Interviewed by Laboratory Roots, Dr. Mitteroecker adds: "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.”
To predict what might happen in the future, Dr. Mitteroecker constructed a computer model. Data was drawn from the World Health Organization and other large birth studies. This model looked back and shows how the proportion of cesareans has increased from 30 percent in 1960 to 36 percent today, and how that is likely to increase in the future due to genetic shifts. In doing so, Dr. Mitteroecker stated that his aim was not to pass comment on cesareans but rather to measure how an evolutionary effect is taking place.
One interesting outcome is that bigger babies, born via caesareans, tend to be healthier and have higher chances for survival. Such events are likely to rise given a tendency for women to have narrower pelvises.
It could be that, one day in the future, the majority of children will have to be born by cesarean sections. The research is published in the journal PNAS, in a paper titled “Cliff-edge model of obstetric selection in humans.”
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