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    Out of Africa's midlife crisis

    It is hard to find vocal critics of the Out of Africa theory today as it is deemed racist. Here is a good article that questions the theory.

    Out of Africa's midlife crisis



    Here is how the groups break down:
    1. [COLOR=var(--print_on_web_bg_color, #1a1a1a)]Scarcely half a million of us are very-diverse.[/COLOR]
    2. [COLOR=var(--print_on_web_bg_color, #1a1a1a)]1.14 billion of us are not-very-diverse. [/COLOR]
    3. [COLOR=var(--print_on_web_bg_color, #1a1a1a)]6.42 billion of us are very-not-diverse. [/COLOR]

    Alone on our planet today, those maybe half a million very-diverse souls hint at our species’ one-time amazing levels of genetic diversity. In our DNA, we all contain multitudes. But once, we all contained mega-multitudes. Only the very-diverse retain much of it today.




    What we thought we knew

    In 2014, Richard Dawkins tweeted a picture of himself in a t-shirt that read “We Are All Africans.” Beside lending fertile basis for a meme (fitting, given the source), it is rooted in a central truth that genetics and paleoanthropology both have converged upon over the past 40 years: Homo sapiens is a “young” species with origins within the last few hundred thousand years on the continent of Africa.
    In 1987, Allan Wilson’s group published a blockbuster result in Nature that gave rise to the popular conception of Mitochondrial Eve, the “mother of us all." Spun into a Nova documentary, Mitochondrial Eve reflected the discovery that all women could be shown to descend from a common ancestress around 200,000 years ago. This owed to the fact that all direct maternal lineages (recorded in our mitochondrial DNA (mtDNA) which passes from mother to daughter) can be traced back to a common genetic ancestor. Because most of the branches of the family tree of Eve wend their way back into Africa, the continent with the greatest mtDNA diversity, the team was able to conclude that our last common maternal ancestor was an ancient African.
    From a paleontological finding of the earliest anatomically modern human in Ethiopia, the theory was further refined to have Eve living in East Africa. And from there, all of us, her descendants, were imagined to have spread to every corner of the globe. This, in turn, was followed and seemed substantiated by “Y-chromosomal Adam.” As with the mtDNA, the Y phylogeny’s deepest lineages lie within Africa.


    Mitochondrial Eve was such a mainstay of our culture that it was featured in the series finale of Battlestar Galactica. But around this same time, in 2010, scientists discovered that Neanderthals, and a new human lineage in East Asia called “Denisovans”, contributed enduringly to the ancestry of all humans outside of Africa. The technological revolution of the Human Genome Project also yielded the complication that there seem to be wide differences in the magnitude and nature of the bottlenecks that had impacted different human populations.


    Rather than a single punctuated event, where moderns suddenly became equipped to expand, replacing Neanderthals and overrunning other humans in a lone explosive pulse, the development of modern humanity was clearly more complex and multifocal. It occurred over hundreds of thousands of years of evolution within Africa, and later involved interbreeding with archaic hominins outside of Africa.


    In short, the classic model was coming closest to fitting convincingly for non-Africans, while the complex situation within the mother continent still defied our simplifying impulses. Basically, our models for Africa remain more provisional.
    But even as we home ever closer in on some clarity, we are still left with a host of unsolved mysteries. Why were the ancestors of non-Africans isolated for so long? Were they trapped on the other side of the Sahara from their African kin? If not there, where then? Arabia is another spot we can’t rule out. And why did they begin expanding explosively 60,000 years ago from a very small population? We still don’t know.

    Below I answer some reader questions (Thanks for submitting these. Feel free to send along more.):


    To what extent can we still describe Out of Africa as the basically correct account of humanity’s origins?


    93-98.5% of the ancestry of humans outside of Sub-Saharan Africa (among those with no recent Sub-Saharan African ancestry, obviously) derives from a breeding population of 1,000 to 10,000, which expanded rapidly 60,000 years ago (reaching Australia and Europe around 45,000 and 50,000 years ago, accordingly).


    So the simple “Out of Africa” narrative of a population crash and explosion across the world holds for North Africans, Eurasians, Oceanians, and Amerindians, some six and a half billion of us. But the origins of modern populations south of the Sahara are clearly more complex. Any bottleneck’s effects were much weaker within Africa, and multiple proto-modern populations seem to have been separating into distinct lineages as early as 200,000 years ago.


    Additionally, Africa’s small populations of hunter-gatherers (that scant half-million people from above) are very different from agriculturalists (the other 1.14 billion Sub-Saharan Africans), the latter of whom are genetically closer to all the rest of humanity than to the hunter-gatherers near them on their same continent. We don’t have an exhaustive and comprehensive model to account for all these disparate facts. At least yet.


    How does the newly defined Nesher Ramla Homo fit the picture?


    We don’t know. The Nesher Ramla humans seem to have resembled European Neanderthals. If this surmise ends up holding, it is quite possible that the Neanderthal ancestry outside of Africa derives from this group.


    Neanderthals occupied Europe, but they were also present as far east as western Mongolia. There are Neanderthal remains in Denisova cave, and a mixed Neanderthal-Denisovan girl was even discovered there. But Neanderthals were also present in West Asia, most famously in Shanidar Cave in Iraq. The Neanderthal ancestry in modern humans seems to be from a single group, and is present in all modern human populations from Europe to Australia. The most likely scenario is an admixture event in the Middle East then, as the nascent migration out of Africa ran into another human lineage and promptly absorbed it. If “Dragon Man” hadn’t randomly dropped at the same time, we’d probably be talking more about these possible Neanderthal ancestors of modern humans in Israel.


    What is the status of the hypothesis that ancestors of Neanderthals and Denisovans developed outside Africa? (i.e. the scenario in Reich, page 69.). Any new evidence in the last few years?
    Is Out of Asia still possible in the development of sapiens?

    Possible? Yes, I think so. But it would be a complex scenario, and seems to be improbable, though the possibility is greater than we’d have thought twenty years ago when modern human origins were defined by an exceedingly simple model. The old Out of Africa model, where humans expanded less than 100,000 years ago from a small tribe in East Africa, populated all of Africa, and then exited the continent to settle the rest of the world, excluded this scenario in totality. The newer models may have more room for the possibility, remote as it is.
    Read the entire article at the link.
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    Admiral Ackbar (07-17-2021),Chris (07-17-2021)

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    This is interesting. Things are never as simple as we want them to be.
    "Don't piss down my back and tell me it's raining"----Fletcher in The Outlaw Josey Wales

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    Quote Originally Posted by Admiral Ackbar View Post
    This is interesting. Things are never as simple as we want them to be.
    I did appreciate how the article mentioned Battlestar Galactica (the remake). The last show of the last episode was the crew of Galactica settling in East Africa and planning on genetically engineering the humaniods (homo-erectus) that they were observing- to make them like them, homo sapiens. At least that is what I took from the episode.
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