Human evolution is a continuous process with many factors affecting how future generations develop and one of these factors is said to be Caesarean births.
Researchers at University of Vienna in Austria have suggested through their study that advances in medical science and the resulting development of caesarean sections to deliver babies is having a huge impact on human evolution. Researchers have pointed out that more and more mothers are now requiring surgery for delivery of babies and the primary reason for this is narrow pelvis size.
According to researchers, if the child would have been larger than normal before birth, both the child and mother would have died during labour during the days when caesarean sections were not an option. However, with that mode of birth now a very commonly used option, researchers say that genes of narrow pelvis size are being passed from mothers to the child as they both are now surviving thanks to c-sections. According to estimates by the researchers over the course of five decades the number of 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.
Researchers question the reason behind such a high rate of fetopelvic disproportion – basically that the baby does not fit through the maternal birth canal? The answer boils down to the fact that we humans have been making use of medical intervention – c-section – and evolutionary measure – selection.
Just 100 years ago it would have been impossible for women with very narrow pelvis to survive during labour. However, that has changed and with more and more women with narrow pelvis surviving, they are passing these genes to their daughters and this effectively provides us with an answer to the long standing evolutionary question as to why the human pelvis has not grown wider over the years.
In contrast over the years heads of human babies are getting larger with each generation and this is basically a indication that there are opposing evolutionary forces at play. 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. Researchers point out that one of the side effects of the selection force – c-sections – has eliminated the trend of smaller babies.