Caesarean section and evolution

In December 2016, a BBC News item (Briggs, 2016) summarised an academic article by a team of Austrian theoretical biologists with the headline: ‘Caesarean births “affecting human evolution”’.

According to the biologists (Mitteroecker et al, 2016), fetopelvic disproportion—where the fetal head is too big to pass through the maternal pelvis—accounts for most cases of obstructed labour in humans. The authors note that women with narrow pelvises would not have survived birth a century ago, and suggest that the increasingly regular use of caesarean section (CS) has resulted in an evolutionary increase of fetopelvic disproportion rates by 10–20%.

Given the media impact that ensued when the story was reported, one might infer that the relationship between CS and evolution was being aired for the first time. However, a 2003 paper—citing CS rates of around 22% in England and Wales—suggested the reason for humans' poor performance during natural childbirth is that cultural evolution has surpassed biological evolution. According to Liston (2003: 560), dietary habits favouring sugar and fat over protein, less exercise and changes in reproductive behaviour have contributed to primigravid women being typically shorter, older and fatter than is ideal for first childbirth, yet ‘some audits… have ignored these factors and their importance is not widely appreciated by either the medical professions or the general public.’