Are Caesarean sections making us evolve to have bigger babies (and have smaller pelvises)?

Scientists are saying that regular C-sections are having an impact on human evolution

Traditionally, caesarean sections helped women with narrow pelvises be able to give birth without risking their own or their child’s life.

And, if we’re going to be particularly Darwin-esque about it, this would mean that the more successful caesarians there were, the more future generations were likely to have narrow pelvises (as the genes for it would be passed onto them) and this would lead to even more C-sections in future. Yes, stay with us here…

This explains why extreme cases where the baby is physically unable to fit down the birth canal (fetopelvic disproportion) has risen in the past 50 years. The rate has increased to around 3.3-3.6% (36 in 1,000 births) which is a 10-20% increase to the former 3% in 1960.

Historically, these mothers, and children would have died in labour, but now, thanks to modern medicine and practices, they are surviving and passing down the genes that would have been ‘selected’ out previously. Austrian researchers say this trend is likely to continue but at a slow rate.

So, does that mean that C-sections are altering the course of human evolution? Actually, maybe it does.

Nowadays, C-sections are also given to women who are expecting twins, babies who are breached, premature babies or to women who either have a low-lying placenta or an STI such as HIV, hepatitis or herpes. It can also occur as an emergency C-section if vaginal bleeding during labour occurs.

But, data from the World Health Organisation and other large birth studies, have found that there is also a trend towards modern women having healthier, larger newborns and so the selective force towards having smaller babies is also diminishing.

Commenting on the results, paleoanthropologists have cited other biological and cultural issues that factor into the increase of the Caesarean sections rate, which vary across the developed and developing world, and include factors such as diabetes and obesity in women of reproductive age (which would affect the size of your baby, too). Fascinating stuff!

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