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Our Amazingly Recent Common Ancestry

posted 2 years ago by jriley555 (8551)
13 replies | jump to latest

Have just come across an assertion, evidently well founded among the experts but entirely implausible & non-intuitive, that everyone alive is related to the same set of ancestors going back to the 'genetic isopoint', estimated to be 7K years ago. Different modeling would yield different results, but in any case, vastly more recently than the arrival of modern [redacted] Sapiens in Europe circa 45K years ago.

I have a very hard time accepting this on the basis of Australia's or Tazmania's isolation alone. But this is the accepted science on the matter, believe it or not. I spoke about this issue with a fellow holding a PhD in Evolutionary Biology, and his response was that if there was even the slightest gene flow, the conclusion would hold.

Another way to look at this assertion is that any time then or before the genetic isopoint, any ancestor found to be related to anyone alive is related to everyone alive.

The basic idea is that after about 40 generations, there aren't 2**40 distinct ancestors available, and the ancestry tree collapses. Meaning, there is much in-breeding as we proceed back through the generations.

Chew on that one awhile...

https://www.scientificamerican.com/article/humans-are-all-more-closely-related-than-we-commonly-think/
https://en.wikipedia.org/wiki/Identical_ancestors_point
https://phys.org/news/2013-08-dna-earth.html

[–] Quasimodo (16388) 2 years ago

Does this theory include the population ( and its descendants ) that stayed behind in Africa ? Chew on that one for a while...

[–] jriley555 (8551) 2 years ago

Yes. And China, etc. Anywhere where non-zero gene flow occurs. An evolutionary biologist acquaintance explained it thusly regarding Australia. Any truly relict populations would have to be excluded it seems, but that is evidently quite rare :

Current evidence suggest that while there was limited gene flow, they were probably not completely isolated and received intermittent admixture from the Indian subcontinent (e.g., Pugh et al. 2013; Malaspinas et al. 2016; Nielson et al. 2017). The only way the current estimates from Rohde et al.'s model to be inaccurate would be if Australians were completely isolated with zero gene flow (side note, it's a famous result from founder of the Modern Synthesis, Sewall Wright, that even 1 migrate per generation is sufficient to prevent differentiation!). Rohde et al. note that the best candidate for pushing the date back would be the Tasmanians, assuming they were completely isolated after the flooding of the Bass Strait ~10,000 years ago. But it's uncertain if the cessation of gene flow was absolute, even in their case.

[–] Quasimodo (16388) 2 years ago

Yes but none of that addresses the question I asked. Just for some context I am sceptical about the current trend in insisting that we are all "tremendously" closely related. It seems to me to be driven by a Woke mindset as it supports the Globalist agenda.

[–] jriley555 (8551) 2 years ago

I'm more skeptical of the plausibility of 'putting over fables' by a scientific gestapo of some sort. The biggest thumb on the scale on actually important questions bearing upon national policy comes from big capital (e.g.: AGW is a socialist one-world-government boondoggle).

I think anyone would agree that these findings defy 'common sense'. That doesn't make them wrong. There is mathematical & genetic sampling vigor behind all this.

Sometimes our evolving notions about things run up against a paradigm shift, such as Darwin's natural selection, Einstein's curved space, Born/Heisenberg's quantum theory, the discovery of dark matter & energy. This is, on a smaller scale, such a one - to me, anyway. I'm still wrapping my brain around it.

The main sticking point for me is that even miniscule gene-flow can yield to the observed effect. Perhaps there will be refinement. Science does tend to correct its misperceptions.

[–] Quasimodo (16388) 2 years ago

I can see how the people descended from the people who left Africa according to the "Out of Africa" theory may be reasonably closely related, particularly if there was only a small number of them. But the "Stayed in Africa" population should have been reasonably genetically diverse because there was a continent "full" of them. In that sense they and the "Out of Africa" lot are separate populations.

Even the "Out of Africa" population and its descendants then had a number of ( Neanderthal, Denisovan and who knows how many other ) interbreeding episodes so that would have to be taken into account as well. Could this population have become so diverse in appearance ( White North Western Europeans compared to Australian Aborigines for example ) in 70,000 years ?

And the interbreeding in Africa between various hominins would be even more extensive and it would go back further in time.

[–] jriley555 (8551) 2 years ago

Most of that makes sense, but it is fairly-well established that Australians did not reach the continent until circa 50-70K years ago, so their divergence must date from that era

I'm met Indians who were dead ringers for Australians.

Sapients likely began diverging from Heidelbergensis (the progenitor of Neanders & Denisovans) circa 800K years ago, subsequent inter-breeding events aside.

The process of raciation is evidence of isolation, but not evidently total isolation, according to the theory, observations.

[–] Quasimodo (16388) 2 years ago

I'm met Indians who were dead ringers for Australians.

Yes this one keeps coming up one way or another. I remember there was an announcement a while back that scientists had discovered evidence of an Indian genetic influx into the Australian Aboriginal population about 4,000 years ago ( about the same time the Dingo turned up in Australia so they said ).

This was backed up by a linguistic change at around that time as well where a "new" language seemed to have superseded many older Aboriginal languages. I remember hearing Indians speaking their native tongue and being struck by how much it sounded like the Aboriginal speech I had heard.

And I heard an Indian fellow saying after seeing a group of "traditional" Aboriginal women sitting on the ground in a circle to talk. " Never mind what they look like these are Indian women. How on earth did they get here !? " So I guess village Indian women do the same thing.

Here is a photo of an Aboriginal man and you can see the very prominent brow ridge reminiscent of Neanderthals or probably in his case Denisovans as Aboriginals have as much as 6% Denisovan DNA so the scientists say.

https://www.artistwd.com/joyzine/australia/dreaming/images/wise_man.jpg

[–] jriley555 (8551) 2 years ago

A lot of good information there. The brow ridge could be either or combination of early modern human and/or denisovan traits. That was clearly selected out in Eurasia.

Paleolithic humans

Pronounced brow ridges were a common feature among paleolithic humans. Early modern people such as those from the finds from Jebel Irhoud and Skhul and Qafzeh had thick, large brow ridges, but they differ from those of archaic humans like Neanderthals by having a supraorbital foramen or notch, forming a groove through the ridge above each eye, although there were exceptions, such as Skhul 2 in which the ridge was unbroken, unlike other members of her tribe.[17][18] This splits the ridge into central parts and distal parts. In current humans, almost always only the central sections of the ridge are preserved (if preserved at all). This contrasts with many archaic and early modern humans, where the brow ridge is pronounced and unbroken.[19]
https://en.wikipedia.org/wiki/Brow_ridge

Don't care what anyone says, I love wiki.

[–] CrabgrassWilly (1616) 2 years ago

You're like 3% away from being a chimp, so this ain't such a stretch.

[–] Quasimodo (16388) 2 years ago

Actually humans and chimpanzees share very close to 99% of their DNA so the scientists say. And yet the Woke Folk don't walk around saying " We are all chimpanzees ! "

It turns out that in genetics small differences are big differences. There are 3 billion base pairs in the human genome so even if all humans share 99.9% of their DNA that still means that 3 million base pairs are different.

[–] TimeTunnel (4769) 2 years ago

For centuries, scientists ruled out that modern humans interbred with Neanderthals.
Until Neanderthal genes were found in modern humans...Uppsala. 🥸
Then there was the interesting book The Seven Daughters of Eve. 🧍‍♀️🧍‍♀️🧍‍♀️🧍‍♀️🧍‍♀️🧍‍♀️🧍‍♀️

Anyhow, our mother's crazy theory is still the best:
A special white (!) worm crawled out of the North Sea and was the progenitor of her family. 🌊 🪱 🌊

[–] McQualude (4231) 2 years ago

It's weird the first time you hear about it but it's simple mathematics anyone can do themselves. Inbreeding certainly happened but that is generally understood to be close relatives having children. Endogamy is more common, and is very common in certain groups, Jews, Amish, all island, early Americans, Native Americans. I have the same man on 2 branches of my family tree but the family isn't inbred. One son went one way, another son moved somewhere else, and 300 years later two of their descendants married but by that point they shared no DNA. Only 90% of 3rd cousins share any DNA. Only 45% of 4th cousins share any DNA. It recombines pretty quickly.

[–] jriley555 (8551) 2 years ago

Good point. There is that distinction between geneological relation and genetic relation. Recombination rapidly diminishes the contribution of antecedents generation by generation. An individual may have virtually no genetic component even from one of their grandparents. Its a random mixing, every generation.