Caesarean births 'affecting human evolution'(bbc.com)
bbc.com
Caesarean births 'affecting human evolution'
http://www.bbc.com/news/science-environment-38210837
65 comments
The way we live is very unnatural. That's why it is only logical that also our evolution is unnatural. Since we no longer have any natural enemies, we ourselves set up the rules, that decide over life and death. And these rules are wrong in many ways. You could write a whole book about it.
One chapter could be devoted to the resulting overpopulation that causes a variety of problems. Instead of letting politics, medicine and capitalism dictate our evolution, we should give nature more freedom. And if we further succeed in reducing the world population to 3 or 4 billions, a certain equilibrium could be reestablished in this world. I am ready to help.
One chapter could be devoted to the resulting overpopulation that causes a variety of problems. Instead of letting politics, medicine and capitalism dictate our evolution, we should give nature more freedom. And if we further succeed in reducing the world population to 3 or 4 billions, a certain equilibrium could be reestablished in this world. I am ready to help.
Humans have been evolving more in the last 50,000 years that in the previous million (by bone records). This is nothing new. Social organizations (tribe/village/town/city) have put new pressures on us to adapt to.
Never mind caesarean; why do so many people need glasses? Why do so many get depressed in winter? It may all be ad-hoc sledgehammer adaptations to get (most of) us to settle down in villages and specialize. And use less calories per capita so the village thrives, even at the expense of the comfort of individuals.
Never mind caesarean; why do so many people need glasses? Why do so many get depressed in winter? It may all be ad-hoc sledgehammer adaptations to get (most of) us to settle down in villages and specialize. And use less calories per capita so the village thrives, even at the expense of the comfort of individuals.
Modern anything affects human evolution - food production, social programs, culture, etc.
Main stream journalists can not get science right.
In the normal course of evolution women with narrower pelvis die a painful death while delivering a baby (or the baby dies). Thus the genes that give women a narrower pelvis do not get passed on.
We can not let these women die this horrible death. This is a good outcome.
In the normal course of evolution women with narrower pelvis die a painful death while delivering a baby (or the baby dies). Thus the genes that give women a narrower pelvis do not get passed on.
We can not let these women die this horrible death. This is a good outcome.
"Women with a very narrow pelvis would not have survived birth 100 years ago. They do now and pass on their genes encoding for a narrow pelvis to their daughters."
and
"Our intent is not to criticise medical intervention," he said. "But it's had an evolutionary effect."
The article said everything you said, and more, in what way did it "not get science right"?
and
"Our intent is not to criticise medical intervention," he said. "But it's had an evolutionary effect."
The article said everything you said, and more, in what way did it "not get science right"?
To be fair, aside from the preschool formatting of the article (one sentence per paragraph, a concerning recent BBC trend), the journalist didn't actually say anything incorrect.
But she did not answer the main question that was asked: why the human pelvis has not grown wider over the years? She said that there were two opposing forces, one for larger babies (they have more chance of survival), and the other was natural selection preventing them getting too large (by killing them both in childbirth).
Maybe I'm missing something, but neither of those answer the question of why the pelvis has not got larger.
All I can assume is that it is (a) an evolutionary trend of men to be attracted to younger and potentially, on average, slimmer and more healthy or fertile women, and (b) cultural, since there is evidence that in historic times and possibly also in less technologically advanced societies, larger hips are considered desirable (which makes total sense in a society with no access to modern medicine).
I'm sure some anthropologists will beat me up for these terrible generalisations, but in general, on average, it seems these forces may have an impact on pelvis size over generations?
But she did not answer the main question that was asked: why the human pelvis has not grown wider over the years? She said that there were two opposing forces, one for larger babies (they have more chance of survival), and the other was natural selection preventing them getting too large (by killing them both in childbirth).
Maybe I'm missing something, but neither of those answer the question of why the pelvis has not got larger.
All I can assume is that it is (a) an evolutionary trend of men to be attracted to younger and potentially, on average, slimmer and more healthy or fertile women, and (b) cultural, since there is evidence that in historic times and possibly also in less technologically advanced societies, larger hips are considered desirable (which makes total sense in a society with no access to modern medicine).
I'm sure some anthropologists will beat me up for these terrible generalisations, but in general, on average, it seems these forces may have an impact on pelvis size over generations?
Men are indeed attracted to relatively wide-hipped women, but there is an upper limit on hip width. There is a biomechanical tradeoff between pelvic shape and locomotor efficiency. The width of the pelvis affects the energy needed for a bipedal gait, since it alters the shape of the largest bones of the lower skeleton and their associated musculature (compare the angle of the femur in men v women and imagine how it affects joint stress). So there's a three way evolutionary arms race between the needs of the large-brained infant, the need to successfully expel said infant, and the need to be able to walk and run efficiently and without musculoskeletal damage.
[deleted]
> one sentence per paragraph, a concerning recent BBC trend
3 of your 5 paragraphs are a single sentence.
3 of your 5 paragraphs are a single sentence.
There's two sides to this coin. By allowing normally lethal genes to be passed on were likely to cause more death in the future. This is definitely something that should be screened and prevented, whether through gene editing, surrogacy, or just selecting for embryos that are either male or lack the undesired trait.
Nobody has to die to voluntarily select this out of the population. The Jewish community has been on the forefront of this for a long time. On the border of eugenics I guess, but self selecting against genes that will cause suffering or death.
Nobody has to die to voluntarily select this out of the population. The Jewish community has been on the forefront of this for a long time. On the border of eugenics I guess, but self selecting against genes that will cause suffering or death.
Why should we avoid those genes? We have the technology to deal with the situation when it arises. What would be the problem with, eventually, all women giving birth by Caesarean?
There are plenty of other instances where our advancements have likely influenced our evolution. For one, the ease at which we can today travel between continents means that there's far more breeding between different races than we've ever had in human history. Should that be stopped? We also don't run/walk nearly as much as we used to thanks to harnessing hydrocarbons...should we continue to try to select for the long-distance running abilities that helped our ancestors kill animals for food during persistence hunting? And I'm betting that certain people are genetically more predisposed to catching measles, polio or any of the other diseases for which we've developed effective vaccines...would we want to make sure that those genes don't get passed on?
In short...why optimize for a world that doesn't exist? Unless you subscribe to a belief in a post-apocalyptic future where modern technology regresses and mankind is forced to live in a more primitive state, there's really no need for us to actively do anything...the magic of evolution is that it just happens naturally. Now, evolution can be an uncaring bitch to individuals, so there's plenty of reason why an individual would want to screen their offspring for certain genetic traits, but at the societal level, it's just swimming against a really strong current.
There are plenty of other instances where our advancements have likely influenced our evolution. For one, the ease at which we can today travel between continents means that there's far more breeding between different races than we've ever had in human history. Should that be stopped? We also don't run/walk nearly as much as we used to thanks to harnessing hydrocarbons...should we continue to try to select for the long-distance running abilities that helped our ancestors kill animals for food during persistence hunting? And I'm betting that certain people are genetically more predisposed to catching measles, polio or any of the other diseases for which we've developed effective vaccines...would we want to make sure that those genes don't get passed on?
In short...why optimize for a world that doesn't exist? Unless you subscribe to a belief in a post-apocalyptic future where modern technology regresses and mankind is forced to live in a more primitive state, there's really no need for us to actively do anything...the magic of evolution is that it just happens naturally. Now, evolution can be an uncaring bitch to individuals, so there's plenty of reason why an individual would want to screen their offspring for certain genetic traits, but at the societal level, it's just swimming against a really strong current.
> What would be the problem with, eventually, all humans needing glasses to see, or born with cornea defects? We know how to fix that.
We should optimize for a world that works, instead of one we believe we'll be able to fix forever, and constantly requires purposeful effort to work. Would you like to carry your Fix The Generalized Imbalance Pills (FTGIMP, f-gimp how we call it, as in: "Hold on love, the trekking has been fun, but know I gotta take the f----gimp") when you decide to go for a bike ride? Or will you tell me "but how many people do you know that go on bike rides for more than 10 minutes?". How many people travel the world on a shoestring? Should they stop doing that?
Would you like to go to space? How large should the infirmary be? With all these things that "we know how to do" and will be required to do, if we don't get a better vessel.
I agree the world has changed. But this vessel is still better when it is self sufficient to the max. Instead of long distance running, we will need low maintenance living. Requiring vaccines, failing joints, birth complications will not help. The resources are limited. It helps no one, in the long run, to make living more complex.
We should optimize for a world that works, instead of one we believe we'll be able to fix forever, and constantly requires purposeful effort to work. Would you like to carry your Fix The Generalized Imbalance Pills (FTGIMP, f-gimp how we call it, as in: "Hold on love, the trekking has been fun, but know I gotta take the f----gimp") when you decide to go for a bike ride? Or will you tell me "but how many people do you know that go on bike rides for more than 10 minutes?". How many people travel the world on a shoestring? Should they stop doing that?
Would you like to go to space? How large should the infirmary be? With all these things that "we know how to do" and will be required to do, if we don't get a better vessel.
I agree the world has changed. But this vessel is still better when it is self sufficient to the max. Instead of long distance running, we will need low maintenance living. Requiring vaccines, failing joints, birth complications will not help. The resources are limited. It helps no one, in the long run, to make living more complex.
The advances you seem to think are bad lead to those who benefit from treatments being productive. They build stuff and contribute and this helps society. It helps everyone when you help those who are infirm/unwell/unlucky. But say we took the view that intervention was bad - who chooses who dies?
> What would be the problem with, eventually, all women giving birth by Caesarean?
It needs significantly more resources (time, labor, medication) and therefore should negatively affect host's fitness but in most developed countries it does not. NOW we optimize for a world that does not exist.
It needs significantly more resources (time, labor, medication) and therefore should negatively affect host's fitness but in most developed countries it does not. NOW we optimize for a world that does not exist.
It requires a lot less resources than a painful death uses. It also uses less resources than a vaginal delivery that should have been a ceasar. How are we optimising for a world that doesn't exist?
It is blindingly obvious from an evolutionary standpoint that this is happening. I have thought about it a fair bit, as it has directly impacted my own family, and I've no doubt it will continue to do so in subsequent generations.
I don't think it's something to worry much about, as the much broader benefits of modern medicine (namely, antibiotics) have had so much impact on our survival rate that this would pale into insignificance.
Which may be borne out (pun intended) by the numbers: 3% to 3.3% or 3.6% in 50-60 years - is that statistically significant? The error there is in the same order as the overall increase, so it's hard to believe it's even measurable at this stage.
Because it is so obviously going to happen, I suspect there may be some curve-fitting going on here?
I don't think it's something to worry much about, as the much broader benefits of modern medicine (namely, antibiotics) have had so much impact on our survival rate that this would pale into insignificance.
Which may be borne out (pun intended) by the numbers: 3% to 3.3% or 3.6% in 50-60 years - is that statistically significant? The error there is in the same order as the overall increase, so it's hard to believe it's even measurable at this stage.
Because it is so obviously going to happen, I suspect there may be some curve-fitting going on here?
> 3% to 3.3% or 3.6% in 50-60 years - is that statistically significant?
The growth rate is likely to be geometric.
> Historically, these genes would not have been passed from mother to child as both would have died in labour.
How do we know that? As the name implied, Caesar was born this way, a little over 2000 years ago. It's likely the procedure is much much older, too. So what timeframe are we talking about?
What we didn't know how to do 100 years ago was how to save mother and child once birth had begun and the baby's head had started to go into the canal and got stuck. But humanity have known how to do caesarean birth for a very long time (there are even cases of women doing it to themselves).
Also, from an evolutionary perspective it doesn't matter if the mother survives birth; it only matters whether the baby lives. So it's at best incorrect to phrase the problem this way:
> Women with a very narrow pelvis would not have survived birth 100 years ago. They do now and pass on their genes encoding for a narrow pelvis to their daughters.
How do we know that? As the name implied, Caesar was born this way, a little over 2000 years ago. It's likely the procedure is much much older, too. So what timeframe are we talking about?
What we didn't know how to do 100 years ago was how to save mother and child once birth had begun and the baby's head had started to go into the canal and got stuck. But humanity have known how to do caesarean birth for a very long time (there are even cases of women doing it to themselves).
Also, from an evolutionary perspective it doesn't matter if the mother survives birth; it only matters whether the baby lives. So it's at best incorrect to phrase the problem this way:
> Women with a very narrow pelvis would not have survived birth 100 years ago. They do now and pass on their genes encoding for a narrow pelvis to their daughters.
> Also, from an evolutionary perspective it doesn't matter if the mother survives birth; it only matters whether the baby lives.
Wouldn't it though? A mother that lives can go on to give birth to more children.
Not to mention that a mother's survival might affect her child's chance of survival.
Wouldn't it though? A mother that lives can go on to give birth to more children.
Not to mention that a mother's survival might affect her child's chance of survival.
The previous comment was probably written in an extremely patriarchal context... a king's offspring would be taken care of even if the mother died. Though even there, the chances of being stabbed in the back might have been increased without motherly protection.
Things I learned from QI: The word Caesarian does not come from Caesar, but from Cadere, meaning to cut.
Well I stand corrected but so should you: Caesar was named this way because it was said one of his ancestors had a Caesarian birth.
Wiki says it's an ancient urban legend.
https://en.wikipedia.org/wiki/Gaius_Julius_Caesar_(name)#The...
https://en.wikipedia.org/wiki/Gaius_Julius_Caesar_(name)#The...
It is probably just a myth that Caesar was born this way.
At the time, the mother most likely couldn't survive a section, because the resulting infections would kill anyone who had such surgery performed. And Caesar's mother lived to old age.
At the time, the mother most likely couldn't survive a section, because the resulting infections would kill anyone who had such surgery performed. And Caesar's mother lived to old age.
People have performed all sorts of surgeries for thousands of years, and while yes, the percentage of them getting infected and resulting in death was probably very high, it doesn't mean that every single surgery ended that way - in the end, people have been amputating limbs or getting wounded on the battlefield and surviving without any sterilization. So while it's rather unlikely, it's possible that Caesar's mother survived the operation.
True, but deep wounds in the abdomen are much, much more difficult regarding infections than e.g. limb amputation. Surviving that was very extremely unlikely. Roman law said that the child must be cut out of a dead mother's womb, to bury it separately, but by that time the woman was dead or dying.
As far as I could find, the earliest written source claiming Caesar was born with C-section is from about 1000 years later.
As far as I could find, the earliest written source claiming Caesar was born with C-section is from about 1000 years later.
This is the first Cesar that is born by cesarian is name is Scipio Africanus[1]
[1] https://en.wikipedia.org/wiki/Scipio_Africanus
[1] https://en.wikipedia.org/wiki/Scipio_Africanus
I also have a lots of doubt about this study, the article says '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.'
1960 -> 2016 = 56 years, can natural evolution show signs so fast? Also 'cases where the baby cannot fit down the birth canal' is a subjective, standards may have evolved, maybe babies are also bigger?
> can natural evolution show signs so fast?
Yes, in fact, I think the accepted dominant manifestation of natural evolution is rapid change in trait distribution in response to significant change in enviromental pressure, and near stasis otherwise, not continuous slow change.
Changing a trait from near certain death of mother and child to one which, while it has some increased risk, is normally survivable without lasting adverse consequences for either mother or child is an enormous change in terms of the degree of selective pressure against the trait.
That's not to say there aren't other potential contributors, but it's not unreasonable for natural evolution to have measurable effects in the timeframe in question in those circumstances.
> maybe babies are also bigger?
The article expressly calls that out as a contributing evolutionary trend that was itself limited by the fact that beyond a certain point, that becomes fatal. So, that's certainly true, but in no way a contradiction to the point in the article.
Yes, in fact, I think the accepted dominant manifestation of natural evolution is rapid change in trait distribution in response to significant change in enviromental pressure, and near stasis otherwise, not continuous slow change.
Changing a trait from near certain death of mother and child to one which, while it has some increased risk, is normally survivable without lasting adverse consequences for either mother or child is an enormous change in terms of the degree of selective pressure against the trait.
That's not to say there aren't other potential contributors, but it's not unreasonable for natural evolution to have measurable effects in the timeframe in question in those circumstances.
> maybe babies are also bigger?
The article expressly calls that out as a contributing evolutionary trend that was itself limited by the fact that beyond a certain point, that becomes fatal. So, that's certainly true, but in no way a contradiction to the point in the article.
>maybe babies are also bigger?
Well adults are bigger. Average height has been increasing worldwide and better nutrition is the accepted cause. So maybe(most definitely) a pregnant well-fed mother will produce a larger baby than a mother eating more like those in generations past. We've been evolving for safe delivery of babies while teetering on starvation, not when so well fed that 25% of the US population is obese.
Well adults are bigger. Average height has been increasing worldwide and better nutrition is the accepted cause. So maybe(most definitely) a pregnant well-fed mother will produce a larger baby than a mother eating more like those in generations past. We've been evolving for safe delivery of babies while teetering on starvation, not when so well fed that 25% of the US population is obese.
Evolution is a ultimate rat race.
FYI offtopic: Kid can be mingled in umbilical cord and natural birth is not possibile then. Only way is caesarean. Dont pull the baby by the head.
FYI offtopic: Kid can be mingled in umbilical cord and natural birth is not possibile then. Only way is caesarean. Dont pull the baby by the head.
Going to potentially be controversial, but we need (might be a strong word here) genetic manipulation with strong ethical and humanist values attached to it (and a lot more knowledge).
If we are to deny natural selection its role, then we might want to still prevent people from passing on genes which effectively handicap them when they don't have access to certain facilities and technology. Prevention in this case is not eugenics, but gene manipulation/therapy.
Having said this, what we most certainly don't want is genetic standardisation (good path for extinction) and even the manipulation of genes, that seem to cause "problems" (today's problems might be tomorrow's cure), needs a deep understanding of implications, which at the moment we probably don't have.
P.S.: Hold the similar view regarding GMO in food.
If we are to deny natural selection its role, then we might want to still prevent people from passing on genes which effectively handicap them when they don't have access to certain facilities and technology. Prevention in this case is not eugenics, but gene manipulation/therapy.
Having said this, what we most certainly don't want is genetic standardisation (good path for extinction) and even the manipulation of genes, that seem to cause "problems" (today's problems might be tomorrow's cure), needs a deep understanding of implications, which at the moment we probably don't have.
P.S.: Hold the similar view regarding GMO in food.
That already happens sometimes: it's called IVF with PGD (pre-implantation genetic diagnosis). Before an embryo is implanted a cell is taken from it and tested for genetic defects.
It's an expensive and convoluted process, so it's only done when one or both of the parents are carriers of a serious genetic mutation.
It's an expensive and convoluted process, so it's only done when one or both of the parents are carriers of a serious genetic mutation.
> it's only done when one or both of the parents are carriers of a serious genetic mutation
I have friends who have done PGD simply to select the gender of their child. Once researchers identify reliable genetic markers for height and intelligence, expect PGD to become rapidly more popular among the upper class.
I have friends who have done PGD simply to select the gender of their child. Once researchers identify reliable genetic markers for height and intelligence, expect PGD to become rapidly more popular among the upper class.
Well you can just pick a spouse who is tall and smart?
Then how do you deal with people who did not get a tall and smart spouse?
I'm no evolutionary scientist, but haven't we as a species already denied natural selection long ago?
For evolution you need physical separation. With our level of globalisation that's not going to work.
For evolution you need physical separation. With our level of globalisation that's not going to work.
> For evolution you need physical separation. With our level of globalisation that's not going to work.
Global empires are nature's way to shuffle some genes around and reduce inbreeding. Then individual nations start to exploit the empire for their selfish benefit, everything falls apart and nature runs an iteration of competitive evolution for a change. Rinse, repeat.
Disclaimer: talking out of my ass :)
Global empires are nature's way to shuffle some genes around and reduce inbreeding. Then individual nations start to exploit the empire for their selfish benefit, everything falls apart and nature runs an iteration of competitive evolution for a change. Rinse, repeat.
Disclaimer: talking out of my ass :)
For speciation you need some kind of separation, which does now sometimes happen within a generation (e.g. one social group refusing to date another social group), but is very unlikely to persist across many generations.
Evolution by natural or sexual selection within a single species can still occur.
Evolution by natural or sexual selection within a single species can still occur.
haven't we as a species already denied natural selection long ago?
No, how could we? We have influenced external pressures such as predators on our selection, at most.
No, how could we? We have influenced external pressures such as predators on our selection, at most.
It's a very complex issue, but my gut feeling is we should not allow germline editing on humans. It's a Pandora's box and the goal posts will keep moving with fundamental consequences to our species. Also like you say we are dealing with extremely complex systems, where uninteded effects might become apparent only generations later
Couldn't this be said about medicine in general?
Yes. The better medicine gets, the feebler we all become. This is a pity, but the alternative is worse[1].
[1] https://www.quora.com/Are-we-eliminating-natural-selection-b...
[1] https://www.quora.com/Are-we-eliminating-natural-selection-b...
It's not a pity at all. Everyone who is around that wouldn't be without modern medicine imparts something to those around them. To give an extreme example, Stephen Hawking.
What I've realized is that sapiens is the first species to fall off of the evolution gradient. The more intellectual we become, the less dependent we will be on a random optimization function. We are scared about how AI would leap ahead of biology, don't neglect that we are leaping ahead of the rest of biology because we have biological intelligence.
We're just not making good use of our intelligence yet.
We're just not making good use of our intelligence yet.
There is not only one alternative.
The other medical intervention that is affecting evolution is ICSI (https://en.wikipedia.org/wiki/Intracytoplasmic_sperm_injecti...) iVF treatment where the man has low quality sperm.
I've heard that the doctors who perform this joke that they are breeding future clients for themselves.
I've heard that the doctors who perform this joke that they are breeding future clients for themselves.
madaxe_again(4)
I personally blame advertisment photography, with their models with ridiculously close-to-one waist/hip ratios.
>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.
This could easily be explained by doctors being more willing to perform Caesareans than they were previously. No evidence is cited that the average width of women's pelvises has actually changed, so this is all wild speculation as far as I can see.
Of course, it is no surprise to see the HN crowd latching on to the idea that we should let more women die in childbirth.
This could easily be explained by doctors being more willing to perform Caesareans than they were previously. No evidence is cited that the average width of women's pelvises has actually changed, so this is all wild speculation as far as I can see.
Of course, it is no surprise to see the HN crowd latching on to the idea that we should let more women die in childbirth.
Call me a sceptic.. since the invention of farming women have had little evolutionary pressure to run fast to catch food nor outrun predators. Why then haven't evolution widen the canal to reduce fatalities during childbirth? And this has been going on for much longer than caesarean procedures.
In a different context it has been discussed how we have used up our easily accessible energy and may not be able to restart civilization on this planet. So why keep lowtech genes around? Make way for large brains and large heads!