Caesarean births 'affecting evolution'

[Nearly Sane]

Fascinating.

http://www.bbc.co.uk/news/science-environment-38210837

[SusanDoris]

Yes, it is a very interesting piece of information, isn't it. I can't think of any downsides to keeping mothers and babies alive and well, but if a time came when the super volcano erupted and extinction was very close, with only a few groups of very robust humans left alive, then  without medical facilities the species survival would depend on those females who were able to bear children easily and the harsh rule of survival would mean that many others would die. That is a very grim scenario though and I can't see it happening.

[ad_orientem]

Surely that isn't really evolution?

[Nearly Sane]

Surely that isn't really evolution?

why?

[BeRational]

Surely that isn't really evolution?

Surely that's exactly evolution.

[ad_orientem]

Isn't evolution about genetic mutations which give some sort of advantage over others of the same species? Over time the ones with the advantage survive and the others don't, that is, natural selection.

[Harrowby Hall]

Isn't evolution about genetic mutations which give some sort of advantage over others of the same species? Over time the ones with the advantage survive and the others don't, that is, natural selection.

Yes, and this instance is demonstrating natural selection in action. It is demonstrating the interaction between environment and inheritance at the heart of natural selection.

There is an environmental change: better antenatal care, nutrition etc may mean that foetuses grow faster and bigger. Those whose mothers do not have a sufficently large birth canal to accommodate larger heads die when mothers die trying to give birth them. The mothers with mutations giving them larger birth canals survive as do their offspring who carry the mutation.

Thus, in the long term, all women will be descended from those with large birth canals.

For evolution to work, there must be losing non-mutants as well as successful mutants.

[ad_orientem]

Eh? But they're not dying anymore.

[Harrowby Hall]

They would be if the super volcano went off ....


They are not dying any more because of surgical intervention. We shall have reached a very serious state if every human birth can only be enabled by caesarian section.

[Spud]

One reason this is interesting is that it gives a possible explanation for the worldwide population explosion. That reminds me of the plague of locusts on this week's David Attenborough programme: when they had eaten all the vegetation, apparently they all died.

[Spud]

It's not "survival of the fittest". There is a decrease in fitness.

[Nearly Sane]

It's not "survival of the fittest". There is a decrease in fitness.

If the environmental pressure is removed, then the fitness of the attribute becomes irrelevant.

[Nearly Sane]

One reason this is interesting is that it gives a possible explanation for the worldwide population explosion. That reminds me of the plague of locusts on this week's David Attenborough programme: when they had eaten all the vegetation, apparently they all died.

no, the numbers are comparatively small and the increase in population is related far more to better nutrition and medical advances.

[Spud]

no, the numbers are comparatively small and the increase in population is related far more to better nutrition and medical advances.

Thanks- yes, 36 cases of babies heads being too big for the birth canal in every1000 births is quite low. Interesting that the overall percentage of births by CS worldwide is apparently 18.6℅.

[Spud]

Yes, and this instance is demonstrating natural selection in action. It is demonstrating the interaction between environment and inheritance at the heart of natural selection.

There is an environmental change: better antenatal care, nutrition etc may mean that foetuses grow faster and bigger. Those whose mothers do not have a sufficently large birth canal to accommodate larger heads die when mothers die trying to give birth them. The mothers with mutations giving them larger birth canals survive as do their offspring who carry the mutation.

Thus, in the long term, all women will be descended from those with large birth canals.

For evolution to work, there must be losing non-mutants as well as successful mutants.

Is a large birth canal caused by a mutation?

[Walter]

Is a large birth canal caused by a mutation?

every development is caused by mutation

[Spud]

This lady seems to know what she's talking about:

https://m.youtube.com/watch?v=8X7OliY01qI

Notice, if women eat a lot of sugar while pregnant, babies grow bigger. Pelvic inlet circumference can be increased by 30℅ by doing exercises.

[jeremyp]

PZ Myers is sceptical.

http://freethoughtblogs.com/pharyngula/2016/12/07/c-sections-havent-been-shown-to-change-human-evolution/

His point is that no causal relationship between head size and frequency of C-section has been shown.

[john]

Evolution?

Nah Goddit he is factually proven to influence the birth process!

[Walt Zingmatilder]

PZ Myers is sceptical.

http://freethoughtblogs.com/pharyngula/2016/12/07/c-sections-havent-been-shown-to-change-human-evolution/

His point is that no causal relationship between head size and frequency of C-section has been shown.

And he's a new atheist......that clinches it.

[jeremyp]

And he's a new atheist......that clinches it.

What on Earth makes you think that?

Actually, don't answer that - it would derail the thread.

[Walt Zingmatilder]

What on Earth makes you think that?

Actually, don't answer that - it would derail the thread.

I don't. Why did you mention PZ Myers, the famous new atheist, in the first place?

[Walt Zingmatilder]

PZ Myers is sceptical.

http://freethoughtblogs.com/pharyngula/2016/12/07/c-sections-havent-been-shown-to-change-human-evolution/

His point is that no causal relationship between head size and frequency of C-section has been shown.

Are you and he suggesting that the theory of natural selection has no predictive power?

[jeremyp]

I don't. Why did you mention PZ Myers, the famous new atheist, in the first place?

Because he wrote a blog post (that I linked) which refutes the premise of this thread. Apart from being a "new atheist" he is also a biology professor.

[Spud]

https://www.google.co.uk/amp/medicalxpress.com/news/2015-04-large-women-pelvis-delivery-babies.amp?client=ms-android-huawei

"Large headed women [who are likely to have babies with larger heads] found to have pelvis shape to allow for delivery of large headed babies"