A new study shows that the number of successful Caesarean births in recent decades is having an effect on human evolution.
The study by the department of theoretical biology at the University of Vienna showed that the rate of cases where the baby can’t fit through the birth canal has jumped from 30 out of 1,000 in the 1960s to about 36 out of 1,000 in the present day, an increase of about 20 percent, according to the BBC.
“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 researcher Dr. Philipp Mitteroecker, the BBC reported.
“Without modern medical intervention such problems were often lethal and this is, from an evolutionary perspective, selection.”
Scientists have wondered why the pelvis hasn’t grown larger to accommodate babies’ large heads, or why babies’ heads haven’t grown smaller. New Scientist speculates that there must be a balance between larger babies, which tend to be healthier, and narrower pelvises, which allow easier upright walking and also reduce premature births.
Although evolution sometimes takes longer, the trend toward doing Caesarean sections has increased rapidly in order to reduce possible complications to the mother and sometimes, just for convenience.
While Caesareans were rare before the 1950s because they were much riskier, now more than 1 in 4 babies are born this way. Another factor in the increase is that women are having babies later in life, when the chance of complications naturally increases, New Scientist reported.
Researchers expected the trend to continue to increase, but only slightly, the BBC reported.
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