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  • Stephanie wrote a new post, Caesarean births 'affecting human evolution' 3 years, 7 months ago

    By Helen Briggs

    The 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 […]

    • Bulldogs, and some other breeds of dog, are now mostly incapable of giving birth naturally, following many generations of caesarian births and pedigree breeding for peculiar characteristics.
      https://www.ncbi.nlm.nih.gov/pubmed/20136998

    • Odd to limit the discussion to C-sections, though. All of medicine “overrides” selection processes. Our NICU saves extremely premature babies. Antibiotics save countless millions every year. Trauma surgeons save victims of knife and gun fights. and on and on. Social programs both save people who might have starved or frozen to death, and perhaps encourage greater fecundity. greater education results in lower reproductive rates. But speaking of the c/s rate: Tiny Asian ladies marry NBA basketball players and have babies too large for their pelvis. Fast foods and obesity have resulted in the average baby weighing a pound more than a decade ago- without any change in the size of the birth canal. Fetal monitoring results in more frequent C-sections- and, we hope, saves babies who otherwise would have never lived to the age of reproduction.

      Practically every aspect of modern society affects survival/reproduction in ways that alter the definition of reproductive fitness for humans.

    • @Brian, huh?
      who is limiting the discussion? I’ll grant every point you make, but it’s a story about a study of the effect of caesarean births. Perfectly reasonable to keep the talk to the evidence being presented.

    • There is a focus on a narrow pelvis in this article. But isn’t it possible that baby’s heads have become larger? I think the same evolutionary logic can be applied here. In fact it seems more logical to me. Partner choice and intelligence are probably linked. A big head means on average more intelligence. So there is a positive evolutionary pressure for big heads, I think. An evolutionary pressure for small pelvises does not seem as likely to me.

    • hfaber #5
      Dec 6, 2016 at 4:21 pm

      There is a focus on a narrow pelvis in this article. But isn’t it possible that baby’s heads have become larger? I think the same evolutionary logic can be applied here. In fact it seems more logical to me. Partner choice and intelligence are probably linked. A big head means on average more intelligence. So there is a positive evolutionary pressure for big heads, I think. An evolutionary pressure for small pelvises does not seem as likely to me.

      These competing selection pressures are explained on the BBC link.

      ▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬

      @BBC link – Opposing forces

      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.

      “One side of this selective force – namely the trend towards smaller babies – has vanished due to Caesarean sections,” said Dr Mitteroecker.

      “Our intent is not to criticise medical intervention,” he said. “But it’s had an evolutionary effect.

    • Just point out that this all appears a little arrogant coming from the West. I’m sure it is having this impact in the West, but there are many millions who still starve to death every year, millions in poverty who die still during childbirth without the benefits of modern medicine. All of these people are being selected for or against by natural selection. I don’t know what level of immigration we need to accept to reduce the our modern impacts on our western genomes but I image it wouldn’t take to many refugees to strengthen our gene pool again (of course that is if we didn’t insist as my country to my shame is – in locking them up in poor surrounding nations). Our empathy and social welfare systems will need to get one hell of a lot better I think before this becomes a real issue globally.

    • 30 to 36 in a thousand in a fifty year period is not massively significant is it? I think the headline is slightly overblown / clickbait.
      The rise in caesareans (in the west at least) in mainly due to women being older mothers and therefore more likely to have complications and therefore doctors often go down the caesarean route as its safer on average for this age group (38+). This was the case with my daughter who was at huge risk of being breech.
      Rising obesity is also a reason for more caesareans.

    • @ MrDNA,

      Yes, C’ sections are a bit of a political issue as well.

      The midwifes at the hospital where my son was delivered were excellent in many ways but were also peppered with woo in others (for example- they promoted a variety of natural remedies). It made it difficult for us to make decisions about which way to act they outlined the benefits of natural birth (which I do not doubt are real) but it was clear that they had issues with doctors over using it. I wanted the numbers. It was looking like my son was going to be breech and our hospital does not do breech births if they can avoid it they will scheduled a C section. So we needed to make a decision, the midwifes where encouraging us to try different things from some woo candle thing (burning smelly candles on your feet) they claimed there had been studies supporting the effectiveness of this so I found the paper read it found it was a small study which did indeed find there was some success in turning babies with this method it appears whatever was in the candles was inducing massive abdominal contractions which in some patients succeeded in turning the baby but in two cases (there were 12 or so in the trial so not a big study) resulted in detached placates and emergency trips to the hospital to get an emergency c section others stopped the treatment because of the pain and the trail was canceled at that point. The midwives were surprised when it handed them over the evidence of what they’d be advocating.

      They then suggested to my wife that we could try to get the baby turned with physical manipulation. I asked the question of what could go wrong and how often does it go wrong so we could have some basis on which to make a judgement. They knew exactly what could go wrong (detached placenta again) and in which case they would perform an emergency C section. Okay so how often does this happen? That they could not tell me, I pushed for them to find out and eventually one of the doctors told me about 1 in 200. That was enough for me and my wife and we singed in for a c section the next day.

      My wife would have preferred the natural child birth at the time and she felt guilty afterwards for not going through this right of passage. For me though its all about the relative risks all going well it would appear that natural birth is better but given safety of certain complications it’s unlikely we are going to be mandating natural child birth.