Caesarean births 'affecting human evolution'
bbc.com
bbc.com
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.
For evolution you need physical separation. With our level of globalisation that's not going to work.
Evolution by natural or sexual selection within a single species can still occur.
No, how could we? We have influenced external pressures such as predators on our selection, at most.
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 :)
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.
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've heard that the doctors who perform this joke that they are breeding future clients for themselves.
[1] https://www.quora.com/Are-we-eliminating-natural-selection-b...
We're just not making good use of our intelligence yet.
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!
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.
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.
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.
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?
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.
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.
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.
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.
As far as I could find, the earliest written source claiming Caesar was born with C-section is from about 1000 years later.
https://en.wikipedia.org/wiki/Gaius_Julius_Caesar_(name)#The...
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.
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.
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.
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"?
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.
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.
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.
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.
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?
3 of your 5 paragraphs are a single sentence.