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Will we become an 'artificial' species?

Scientific discovery and discussion
XFool
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Re: Will we become an 'artificial' species?

#223522

Postby XFool » May 21st, 2019, 10:39 pm

mc2fool wrote:
XFool wrote:
mc2fool wrote:The perhaps more surprising ('twas to me at least) and less obvious case of genetic isolation is Africa. The Neanderthal genome project found that the Out-of-Africa migrations interbred with Neanderthals, and then kept going, the upshot of which is that everybody of the rest of the world populations today has 1-4% Neanderthal DNA (and a smattering of Denisovan) in them. However, not so for sub-Saharan African populations, in which Neanderthal DNA is generally absent.

I can't see why that should be "surprising", surely by present understanding it's pretty well required!

AFAIK, as a species "Neanderthals" evolved outside of Africa (although in turn their ancestors, like us, evolved in Africa) so it would only be subsequent 'Out of Africa' species that could have cross bred with them.

Yes, but that's besides my point. My comment was about what happened after that.

The lack of Neanderthal DNA in sub-Saharan African groups indicates that the descendants of the Out-of-Africa groups didn't -- in the 40,000 years following the last possible interbreeding with Neanderthals -- spread back into sub-Saharan Africa and promulgate their acquired Neanderthal DNA there. Some, sure, but not in any significant numbers at least.

That I find a little surprising, seeing they managed to spread to pretty much every other corner of the planet and, unlike the Americas and Australia, there was no significant geographical barrier that would have prevented some making a "return" over the last 40,000 years.

Are you sure? I have little real knowledge here but, again, Neanderthals evolved in Europe and spread to Asia, not back to Africa. Possibly the climate and the Sahara prevented intermixing with sub-Saharan African Homo Sapiens or even the return of significant numbers of Homo Sapiens who had interbred with Neanderthals? But if the movement of Sapiens was out of Africa and further afield, why would there be a significant population return (until historical times) when the territory was already occupied by Homo Sapiens? OK some small groups may have in time, but how could their Neanderthal genes really be important in a presumably then already significant African Sapien population - wouldn't they just get diluted away? - or a significant presence in the modern day African population? I just don't see it.

https://en.wikipedia.org/wiki/Neanderth ... _and_range

"No Neanderthal has ever been found outside Central to Western Eurasia, namely neither to the south of 30°N (Shuqba, Levant), nor east of 85°E (Denisova, Siberia).
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Total Neanderthal effective population size has been estimated at close to 15,000 individuals (corresponding to a total population of roughly 150,000 individuals), living in small, isolated, inbred groups.
"

Then again, there are possibly other factors: https://en.wikipedia.org/wiki/Neanderth ... ern_humans

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Re: Will we become an 'artificial' species?

#223530

Postby XFool » May 21st, 2019, 10:56 pm

mc2fool wrote:
mc2fool wrote:The lack of Neanderthal DNA in sub-Saharan African groups indicates that the descendants of the Out-of-Africa groups didn't -- in the 40,000 years following the last possible interbreeding with Neanderthals -- spread back into sub-Saharan Africa and promulgate their acquired Neanderthal DNA there. Some, sure, but not in any significant numbers at least.

Actually, I guess it's possible that they did but the Neanderthal DNA conferred some evolutionary disadvantage that made those lines with it in Africa die out.

But it's difficult to imagine what environmental challenge would select against them that would be unique to sub-Saharan Africa (a big place with a very wide range of environments) that wouldn't also have existed somewhere else on the planet. Yet Neanderthal DNA is universally present in all non-sub-Saharan African populations....

Surely, unless those Neanderthal genes actually conferred an advantage on the existing African Sapien populations, why would they be expected to spread through an existing contemporary population? Outside Africa, the presumably originally small number of migrating Sapiens encountered Neanderthals on their way to moving into Europe and Asia. So their descendants, who went on to spread around the world, would have simply inherited them - if not disadvantageous. A simple numbers game?

Or am I talking rubbish? ;)

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Re: Will we become an 'artificial' species?

#223538

Postby mc2fool » May 21st, 2019, 11:38 pm

XFool wrote:Are you sure? I have little real knowledge here but, again, Neanderthals evolved in Europe and spread to Asia, not back to Africa. Possibly the climate and the Sahara prevented intermixing with sub-Saharan African Homo Sapiens or even the return of significant numbers of Homo Sapiens who had interbred with Neanderthals?

The Sahara desert is new, only about 5000 years old and Neanderthals couldn't go "back" to Africa 'cos they never came from there in the first place. I was referring to the Out-of-Africa Homo Sapiens. The term "sub-Saharan Africans" refers to population groups and their ancestors rather than to ancient geography. It's to distinguish from what are now the northern African populations (Morocco to Egypt), who are returnees.

But if the movement of Sapiens was out of Africa and further afield, why would there be a significant population return (until historical times) when the territory was already occupied by Homo Sapiens? OK some small groups may have, but how could their Neanderthal genes really be important in a presumably already significant African Sapien population - wouldn't it just get diluted away?

We're talking about a time when the whole human population would have been just hundreds of thousands, so the idea of "occupied" would be pretty sparse, a group could have returned there and only rarely encountered anyone else, it's a big place. But in any case, that's exactly the point I was making, that it seems that no significant numbers of Out-of-Africans returned.

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Re: Will we become an 'artificial' species?

#223542

Postby mc2fool » May 22nd, 2019, 12:00 am

colin wrote:mc2fool wrote
Agreed to a lot of that, except that it isn't exponential, and the sparseness of population groups and the difficulty of travel until recently makes it entirely possible that Leif Erikson's genes have never crossed with any Patagonian's, and even if they had those lines could have died out or remained within relatively small groups. Numbers aren't the only limiting factor nor the guaranteeing one.

If the figures I quoted from Rutherford's book are correct then Leif Erikson, assuming he has left surviving descendants is one of the ancestor's of every European alive today, we are all descendants of him as we are all descendants of Charlemagne, Patagonia is populated by people who all share European descent to varying extents, there are even Romany Gypsies selling sprigs of the closest thing they have there to heather. I have met them in Puerto Mont. The indigenous natives who survived contact with the Spanish colonizers have been having children with people of Spanish descent for so long that I would find it hard to believe that there could be some enclave of indigenous people who do not share genes of European origin. That would just be a huge ethnographic story. So Leif Erickson's bloodline must stretch to Patagonia. They might have got there at the dawn of Spanish colonization as the Vikings were heavily into trading Anglo Saxon slaves on Spanish markets but there has been a constant influx of Europeans since the Spanish conquest at least and European Genes have spread throughout the surviving population of indigenous people.

I was talking about the challenges for Leif Erikson's genes infiltrating down to Patagonia through the Americas from his landing in Newfoundland 1000 years ago, rather than them being re-injected more directly several hundred years later.

In any case, I have suspicions and doubts about claims of "every" and "all". "Many" or even "most" I could buy (and didn't your op say 80%), but "every" and "all" just sound like the result of some mathematical model that doesn't (and to be fair, really can't) take into account real life events. Random stuff happens. And any "confirmatory" DNA evidence can only be statistical, not exhaustive.

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Re: Will we become an 'artificial' species?

#223545

Postby ursaminortaur » May 22nd, 2019, 1:13 am

mc2fool wrote:
XFool wrote:Are you sure? I have little real knowledge here but, again, Neanderthals evolved in Europe and spread to Asia, not back to Africa. Possibly the climate and the Sahara prevented intermixing with sub-Saharan African Homo Sapiens or even the return of significant numbers of Homo Sapiens who had interbred with Neanderthals?

The Sahara desert is new, only about 5000 years old and Neanderthals couldn't go "back" to Africa 'cos they never came from there in the first place. I was referring to the Out-of-Africa Homo Sapiens. The term "sub-Saharan Africans" refers to population groups and their ancestors rather than to ancient geography. It's to distinguish from what are now the northern African populations (Morocco to Egypt), who are returnees.


The Sahara is millions of years old but has swung between dry and wet periods.

https://www.worldatlas.com/articles/what-was-the-sahara-before-it-was-a-desert.html

The exact age of the desert is unknown although most experts argue that it was formed between two and three million years ago. Some experts claim to have evidence that supports the theory that the desert has been in existence for at least seven million years although nothing has been substantiated.
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Based on historical evidence, experts in the field are almost sure that the desert will be full of vegetation again in the future. The reason for this expectation can be explained by the Sahara pump theory, which explains the cycle that the desert goes through. According to the theory, the desert experiences alternating periods of wetness and dryness every 41,000 years. After this period, the earth’s tilt usually changes. Regardless of the change, the tilt is usually between 22° and 24.5°. Currently, the desert is experiencing a season of dryness. However, according to the theory, the desert will experience wet conditions after 15,000 years or so. In 15,000 years, the North African monsoon winds should be strong, which would bring about an increase in the region’s precipitation.


https://en.wikipedia.org/wiki/Prehistoric_North_Africa#Saharan_Climate_and_Human_Migration

In terms of human evolution, the Saharan pump has been used to date four waves of human migration from Africa, namely

Homo erectus (ssp. ergaster) into Southeast and East Asia
Homo heidelbergensis into the Middle East and Western Europe
Homo sapiens sapiens "Out of Africa theory"
The spread of Afro-Asiatic languages (Berber and Egyptian to North Africa and Semitic to the Arabian Peninsula and Middle East).

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Re: Will we become an 'artificial' species?

#223546

Postby ursaminortaur » May 22nd, 2019, 1:22 am

XFool wrote:
mc2fool wrote:
mc2fool wrote:The lack of Neanderthal DNA in sub-Saharan African groups indicates that the descendants of the Out-of-Africa groups didn't -- in the 40,000 years following the last possible interbreeding with Neanderthals -- spread back into sub-Saharan Africa and promulgate their acquired Neanderthal DNA there. Some, sure, but not in any significant numbers at least.

Actually, I guess it's possible that they did but the Neanderthal DNA conferred some evolutionary disadvantage that made those lines with it in Africa die out.

But it's difficult to imagine what environmental challenge would select against them that would be unique to sub-Saharan Africa (a big place with a very wide range of environments) that wouldn't also have existed somewhere else on the planet. Yet Neanderthal DNA is universally present in all non-sub-Saharan African populations....

Surely, unless those Neanderthal genes actually conferred an advantage on the existing African Sapien populations, why would they be expected to spread through an existing contemporary population? Outside Africa, the presumably originally small number of migrating Sapiens encountered Neanderthals on their way to moving into Europe and Asia. So their descendants, who went on to spread around the world, would have simply inherited them - if not disadvantageous. A simple numbers game?

Or am I talking rubbish? ;)


It appears that many of the Neanderthal genes which survive provided protection against diseases that Homo Sapiens encountered outside of Africa. Hence they would probably have died out in any populations which later returned to Africa since they would no longer have provided any advantage in that environment.

https://www.independent.co.uk/news/science/neanderthals-breeding-early-humans-diseases-flu-hepatitis-dna-genetics-a8568446.html

Homo sapiens, by contrast, would have been suited to the savannahs of Africa and crucially to the diseases that thrived there.
So as humans began to interact with Neanderthals, they would have been easy targets for harmful viruses as their immune systems would have been unable to defend them.

Interbreeding between these ancient human groups has left many modren Europeans and Asians with 2 per cent Neanderthal DNA.
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Research conducted by Professor Enard while he worked under Professor Dmitri Petrov at California's prestigious Stanford University has revealed this protection is part of the reason snippets of Neanderthal DNA have survived thousands of years after the species vanished.
“Many Neanderthal sequences have been lost in modern humans, but some stayed and appear to have quickly increased to high frequencies at the time of contact,” said Professor Petrov. “We believe that resistance to specific RNA viruses provided by these Neanderthal sequences was likely a big part of the reason for their selective benefits.”

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Re: Will we become an 'artificial' species?

#223604

Postby XFool » May 22nd, 2019, 10:28 am

mc2fool wrote:
XFool wrote:Are you sure? I have little real knowledge here but, again, Neanderthals evolved in Europe and spread to Asia, not back to Africa. Possibly the climate and the Sahara prevented intermixing with sub-Saharan African Homo Sapiens or even the return of significant numbers of Homo Sapiens who had interbred with Neanderthals?

The Sahara desert is new, only about 5000 years old...

Maybe. Maybe not:

https://en.wikipedia.org/wiki/Sahara#History

"It was long believed that the region had been this way since about 1600 BCE, after shifts in the Earth's axis increased temperatures and decreased precipitation, which led to the abrupt desertification of North Africa about 5,400 years ago. However, this theory has recently been called into dispute, when samples taken from several seven-million-year-old sand deposits led scientists to reconsider the timeline for desertification."

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Re: Will we become an 'artificial' species?

#223614

Postby XFool » May 22nd, 2019, 11:16 am

mc2fool wrote:
XFool wrote:Are you sure? I have little real knowledge here but, again, Neanderthals evolved in Europe and spread to Asia, not back to Africa. Possibly the climate and the Sahara prevented intermixing with sub-Saharan African Homo Sapiens or even the return of significant numbers of Homo Sapiens who had interbred with Neanderthals?

...Neanderthals couldn't go "back" to Africa 'cos they never came from there in the first place.

Quite correct. Here I was falling into the very error I usually try to avoid when trying to understand these things. Human, and of course all evolution, occurs over vast periods of time, involving differing groups, sub groups, changes in the Earth's motion through space, geology and climate in the unimaginably distant past. Trying to explain or get a handle on these things with everyday, ordinary language can result in misinterpretation or may very easily lead one astray.


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