Caesarean births 'affecting human evolution'By Helen Briggs BBC News 7 December 2016
http://www.bbc.com/news/science-environment-38210837
In the UK, about one in four babies is born by Caesarean THINKSTOCKThe regular use of Caesarean sections is having an impact on human evolution, say scientists.
More mothers now need surgery to deliver a baby due to their narrow pelvis size, according to a study.
Researchers estimate cases where the baby cannot fit down the birth canal have increased from 30 in 1,000 in the 1960s to 36 in 1,000 births today.
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It has been a long standing evolutionary question why the human pelvis has not grown wider over the years.
The head of a human baby is large compared with other primates, meaning animals such as chimps can give birth relatively easily.
The researchers devised a mathematical model using data from the World Health Organization and other large birth studies.
They found opposing evolutionary forces in their theoretical study.
One is a trend towards larger newborns, which are more healthy.
However, if they grow too large, they get stuck during labour, which historically would have proved disastrous for mother and baby, and their genes would not be passed on.
Historically, these genes would not have been passed from mother to child as both would have died in labour.
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