The lost 50,000 years of non-African humanity

The figure above is from Efficiently inferring the demographic history of many populations with allele count data. This preprint came out a few months ago, but I was prompted to revisit it after reading Spectrum of Neandertal introgression across modern-day humans indicates multiple episodes of human-Neandertal interbreeding.

The latter paper indicates that there were multiple waves to Neanderthal admixture into both Europeans and East Asians. The motivation to do the analysis is that East Asians are about ~12 percent more Neanderthal than Europeans. The authors don’t reject the idea that there was ‘dilution’ of Neanderthal through selection and especially admixture with a “Basal Eurasian” group which didn’t have Neanderthal ancestry. I don’t want to get into the details of the results except for one thing: the preprint confirms a consistent finding over the past eight years that the Neanderthal contribution to the modern human genome is from a single population.

Perhaps it was a small population. Or perhaps it was a large population that had gone through a bottleneck and was genetically not very differentiated. But unlike Denisovans it seems that it was a particular Neanderthal lineage that interacted with modern humans.

Moving back to the “Basal Eurasians,” notice some details of the schematic above. The divergence of Basal Eurasians from other non-Africans was ~80,000 years ago, across an interval of 70 to 100 thousand years ago. The admixture of Basal Eurasians into the proto-LBK population occurred ~30,000 years ago, across an interval of 11 to 41 thousand years ago. Ancient DNA from North Africa indicates that Basal Eurasians were already well admixed well before 11 thousand years ago.

The other dates make sense. 50,000 years for Europeans-Han Chinese, 96,000 years for Mbuti-Eurasians, and 696,000 years for Neanderthal-modern humans.

Ancient modern humans were highly structured. We know this from within Africa. But it seems clear that modern humans who had crossed over the other side of the Sahara also exhibited the same tendency. Basal Eurasians did not mix with Neanderthal populations. I suspect that that might be due to the fact that they were in Northeast Africa. At some point in the Pleistocene a mixing event occurred. This may have been precipitated by drier conditions and human retreat into only a few habitable areas, and the original Basal Eurasian populations may have mixed into other Near Eastern groups, which were part of the broader Neanderthal-mixed populations.

8 thoughts on “The lost 50,000 years of non-African humanity

  1. Any remains in the pipeline for being tested from Egypt and Arabia which could be largely unmixed Basal Eurasians? Nothing?

  2. In your prediction post below, you talked about Basal Eurasians being in southern Arabia. Which do you think is more likely, there or northeastern Africa?

  3. Any remains in the pipeline for being tested from Egypt and Arabia which could be largely unmixed Basal Eurasians? Nothing?

    they have been trying to get stuff out of qafzeh skhul. that’s before BEu, but who knows?

    In your prediction post below, you talked about Basal Eurasians being in southern Arabia. Which do you think is more likely, there or northeastern Africa?

    i go back and forth. i need to read more paleoclimatology.

  4. But isnt Qafzeh likely to harbour Neandertal admixture. So there is really not too much. This means the BEA might be unsolved for years. Too bad, really want to know.

  5. > Aeon: Would the child have a protruding chin and a globular skull (defining characteristics of modern humans), plus pronounced brow ridges and a rounded occipital bun at the back of the skull (traits associated with Neanderthals)?

    “””There are still some human populations which often exhibit occipital buns. A greater proportion of early modern Europeans had them, but prominent occipital buns in modern populations are now relatively infrequent.”””

    The wikipedia has removed previous assertion that the occipital bun is common in Scandinavian. It seems that anything that exclude certain group of people is taboo and refutations along certain lines do not need any citations. The Swedish call the occipital bun “Geniknol”, lump of genius,
    Despite the assertion from wikipedia, an informal self reported survey on out of 178 responses, 157/178= 88.20% reported to have prominant occipital bun or ridge. From the country of origin identified by the IP address or self identified ancestry, the percentages that have occipital bun or ridge,

    %Occi Nocci Ethnic
    93.55 29/31 UK
    81.82 27/33 US
    86.36 19/22 DE
    82.61 19/23 SW
    100.00 7/ 7 IE
    100.00 6/ 6 FI
    100.00 5/ 5 DK
    100.00 4/ 4 EE
    100.00 3/ 3 NL
    100.00 2/ 2 CN
    60.00 3/ 5 CA
    50.00 1/ 2 NO ??
    33.33 1/ 3 RU

    I must have too much free time to tally that.

  6. Youre mixing things up. Its not about a prominent, rounded occiput per se, but a specific, peaked version of it. Shapes most similar to Neandertals I saw most often in Southern and South Eastern Africans for whatever reason.
    A well rounded occiput is the opposite shape.

  7. The preprint referenced in this link shows a bottleneck for all non-Africans from ca. 125 kya to 40 kya, so far tens of thousands of years leading up to the Upper Paleolithic.

    It seems to support something analogous to the Berginian standstill hypothesis, the non-Africans got out of Africa, hung out for a long time in a limited range, and then expanded again out of there intermediate “holding area”, which probably consisted of SW Asia, West Asia and South Asia. We have archaeology pointing to modern humans in Arabia to about 125 kya and to modern humans in Southern Indian pre-75 kya.

    But, we only have evidence of modern humans in Europe ca. 45 kya and only have evidence of modern humans anywhere on the coastal route from Bangladesh to Australia and Papua New Guinea post-75 kya (i.e. post-Toba). Major volcanic activity was a plausible contributor to both weakening Neanderthals as a force keeping modern humans out of Europe, and to somehow opening up Burma and beyond to Southeast Asia.

    Given the heavy presence of Neanderthals in SW Asia until the Upper Paleolithic, coexisting with modern humans for much of that time period, where we have a pretty strong documented bottleneck genetically (when a little introgression would have the most effect), it also does make quite a bit of sense to conceptualize Basal Eurasians as probable Northeast Africans as you suggest.

    Of course, then there are the old, seemingly non-H. Erectus hominins of East Asia and the Philippines, ca. 100 kya. They could either be Northern route first wave modern humans or Denisovans or something else. The possibility that Denisovans replaced H. Erectus in the Middle Paleolithic, only to be supplanted by modern humans in the Upper Paleolithic (possibly due to disruption in the local hominin population and ecology in SE Asia by the Toba eruption), seems pretty plausible to me.

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