A few days ago Spencer and I recorded a “predictions for 2020s” episode for The Insight, before we go back to “regularly scheduled programs.” One of the topics (of ten) we discussed is that the old “Out of Africa” model is going to be marginalized/complicated.
What did we mean by this? Some of the hints are already present in David Reich’s Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past. If you look at and analyze genome-wide data, especially ancient data, there are just too many strange results to be accounted for by our current consensus understandings. There are new things we’ll learn. And some of the old things will be wrong. We just don’t know what.
In the 1980s and 1990s, and into the 2000s, the “Out of Africa” narrative was one that the “community” of paleoanthropology went hard into (and to a lesser extent human geneticists). Perhaps too hard. Not only is there “archaic” admixture outside of Africa, but there is “deep structure” within Africa. At some point, there are too many epicycles, and there needs to be a major model revision.
Over ten years ago Dienekes Pontikos presented what I thought at the time was a “crazy” paradigm of back-to-Africa migration. Though I’m still not sure of that particular model, I think there is a high likelihood of reciprocal gene-flow between Africa, and Eurasia, especially Western Eurasia, within the last few hundred thousand years. The debates around Y haplogroup E, which is modal within Africa, but also present with deep lineages in Eurasia, shed light I think on some of the complexity.
Instead of a single “Out of Africa” movement 50-60,000 years ago, there seems to have been a sequence of events 50-100,000 years ago which resulted in the population genetic patterning that we see around us. Some of it is the classic wave expansion from a small founder group for non-Africans, but within Africa it seems there were also expansions and admixtures, albeit more complicated, continuous, and long-standing. Some of the deepest branches within African population history go back hundreds of thousands of years, but much of it dates to expansions with closer affinities to non-Africans 50-100,000 years ago.
Sometimes it can be exciting to say that the question is the answer….
@Razib: In that context, why did you up to recently propose that the majority of modern humans date to a 50.000 years expansion out of Africa and why do you still use the 100.000 years time frame as fixed boundary?
You know more than most about the genetic background, more than me for sure, but I think the factual justification for any such limitations is and always was pretty thin. But it even got much thinner recently.
For a start the time for the differentiation between the various human forms shortly after the supposed expansive explosion appears to be much too short.
The distribution of archaic admixture and anatomically early moderns outside of Africa too doesnt fit the narrative.
There were, in all likelihood, more than one migration out and into Africa at much earlier dates and they were not lost. And what’s Africa supposed to mean, its a huge continent with very different habitats. But moderns seem to have been living mostly in territories which were climatically closer to the Near East than in the tropical parts.
Anyway, so you still think “the 50.000 event” is THE thing and the timing of 50.000-100.000 will hold?
What are the compelling arguments to stick with it and what could change your mind?
I really think the Near East is not done yet (especially the South of the Arabian peninsula). More like an intuitive assertion, but nobody can say its done yet. There will be a massive back migration being proven and the Near East will be closer to North East Africa and vice versa than North East Africa to the rest of the continent even before that.
Ancient DNA samples from 60-120 kya would be useful.
Asian BT1, B0 and E0 type Y lineages, anyone?
Just as an example, what happened with these bones:
“A single human finger bone discovered in 2016 at an ancient lake site in Saudi Arabia called Al Wusta has now been dated to approximately 88,000 years ago, according to a new study in the journal Nature Ecology and Evolution.”
https://www.nationalgeographic.com/news/2018/04/saudi-arabia-finger-human-migration-homo/
Not that this is the earlist date to expect. Did a team try to analyse it? Proteins at least?
@Razib: In that context, why did you up to recently propose that the majority of modern humans date to a 50.000 years expansion out of Africa and why do you still use the 100.000 years time frame as fixed boundary?
outside of africa the archaeological turnover is pretty intense around 50K. more relevant re: genetics, it’s pretty clear that the neanderthal mix is around that period, and everyone has it. everyone outside of africa seems to have gone through an intense bottleneck too. so genetically
1) neanderthal is 50K, everyone has it (outside of africa)
2) everyone went through same bottleneck (outside of africa)
so single population + 50K seems the point of admixture which is relatively even.
@Razib
>outside of africa the archaeological turnover is pretty intense around 50K. more relevant re: genetics, it’s pretty clear that the neanderthal mix is around that period, and everyone has it
Everyone other than Basal/crown Eurasians, or has that notion been changed to simply low Neanderthal in place of no Neanderthal?
My current perspective is, please correct me if I’m off by what you know, that we have much earlier, still more archaic Homo sapiens expansions taking place, which might even have been producing “Denisovans” with Homo erectus in Asia and surviving in low percentages (highest in Australo-Melanesian and AASI-Negrito related populations).
Modern Homo sapiens entered the scene from Northern and North-Eastern Africa, founding a large population which included the Southern Near East (so Al Wusta should be part of this meta-population).
This modern Homo sapiens, with an established presence outside of Africa, began indeed to expand in all directions, let’s say between 70.000-50.000 years ago and the Northern group interbred with Neandertals, resulting in what you mean. Whereas the Southern group, with less or even no Neandertal admixture (unlikely imo), would be the equivalent to “Basal Eurasians”. An early expansion moved down to West and South Africa, founding the modern Subsaharans by mixing with local archaic populations which were not part of the modern meta-population before.
The archaeologial turnover might even been caused by the contact and admixture with Neandertals actually, because the modern Homo sapiens was ahead, but Homo neanderthalensis might just have added the genetic and cultural input needed to break the “cold winter barrier” with more ease and get rid of the cultural limitations present before.
These fully modern and more advanced Homo sapiens displaced all other Homo groups in Eurasia, among which were Neandertals, Denisovans/mixed Homo erectus and the earlier, more archaic Homo sapiens. But not fully so, as we know by now. The assumption the earlier Homo sapiens disappeared completely is wrong imho. We just don’t have the necessary reference samples, as we lack good reference for the older layers of Subsaharan Africans. Because even the oldest we have (Mota), dates to a period, when, going after the constant backflow-expansion model, at least one major wave from the modern metapopulation had moved down to Africa from the North.
Where the modern Homo sapiens metapopulation had its demographic and developmental center before the large expansions and mixture with Neandertals took place is open to debate. I guess there are mainly two viable candidates, North Eastern Africa and/or the Southern Near East (again Al Wusta and similar finds might prove to be crucial!). Most likely forming one large metapopulation with constant gene flow between the local groups of people.
@DaThang: I never bought that “no Neandertal in Subsaharans” and I’m still not convinved, even less so than before. I guess there were more than one admixture events and its just that the first, lower case (= Basal Eurasian like) moved mainly into Africa and mixed there with archaic groups with no Neandertal, further reducing Neandertal proper. If we ever get earlier, probably even archaic Homo samples, like the ones from Iwo Eleru.
We will see that everything was very complicated in Subsaharan Africa and that all moderns have at least some Neandertal admixture.
obs, not crazy. here is my short summary
1) ‘amh’ spread few times btwn 200 and 50K bp
2) vast majority of signal in modern nonafricans outside of basal eurasian is from the 50K expansion (some researchers have detected possible older stuff in papuans etc. but it’s not certain and that whole pop is really complex)
3) not sure about ‘basal eurasian’. let’s see when the newest lazaridis paper comes out (no idea when myself)
@Obs
>I never bought that “no Neandertal in Subsaharans” and I’m still not convinved, even less so than before. I guess there were more than one admixture events and its just that the first, lower case (= Basal Eurasian like) moved mainly into Africa and mixed there with archaic groups with no Neandertal, further reducing Neandertal proper. If we ever get earlier, probably even archaic Homo samples, like the ones from Iwo Eleru.
I am not sure how the basal ancestry is inferred, but as you can see here, there is a general negative correlation between basal Eurasian ancestry and Neanderthal ancestry.
https://dash.harvard.edu/bitstream/handle/1/31731830/5003663.pdf
Still, theoretical 100% basal wouldn’t be 0% Neanderthal, but it would be close enough. Perhaps the Neanderthal admixture in Basals is independent of the primary Neanderthal admixture in west and east Eurasians.
On top of this, there are probably 2 very different kinds of ‘basal Eurasians’. I don’t just mean 2 sub-groups, but 2 different completely different groups that have been referred to as basal: one being ANA (separate from all Eurasians) and the other being a hypothetical 3rd branch within Eurasia. I have seen people theorizing about it on twitter with one example being: DE was the original heavily Neanderthal admixed population living in the Levant while CF moved through the south of Arabia (remaining largely uncontacted by Neanderthals for tens of thousands of years) and some CF subgroups later mixed with the northern Levantine DE groups.
Since everyone is throwing shots in the dark, I might as well add one myself:
The Skhul and Qafzeh hominins were probably not meaningless or even trivial to the ancestry of the later humans who moved through the Levant in the beginning of the upper paleolithic.
@DaThang: “Perhaps the Neanderthal admixture in Basals is independent of the primary Neanderthal admixture in west and east Eurasians.”
That’s exactly what I meant. The possibility of at least two major admixture events, “one for all” Eurasians/moderns, one for “crown Eurasians” exclusively, probably through backflow from a more mixed group.
Definitely more samples from Near East and Africa needed.
@Obs
What are your current guesses about the different admixture details? Like which Neanderthal populations do you suspect contributed to basal, east and west Eurasians respectively?
I think that east and west Eurasians got most of their Neanderthal from the general western range indirectly through Skhul and Qafzeh hominins, while east Eurasians got a little extra from the Altai-Denisovan hybrid, and basals got their tiny bit entirely from the Shanidar population.
I think that east and west Eurasians got most of their Neanderthal from the general western range indirectly through Skhul and Qafzeh hominins, while east Eurasians got a little extra from the Altai-Denisovan hybrid, and basals got their tiny bit entirely from the Shanidar population.
the segment length too long in 40K genomes i think for it to be that old.
@Razib
Okay, so maybe a direct western range Neanderthal input in west and east Eurasians, with a separate mixture of pre-basals with Shanidar or in general some southern Neanderthal group, is that compatible with the current information?
Formation of BT and B seems to coincide with the beginning and end respectively of the Abbassia Pluvial. E forms shortly before an extremely dry phase. So climate-wise, an early OoA with back migrations works. Now we need genetic evidence.
“Out of Africa” was a reasonable idea, but it was pushed particularly hard by the anti-racist left in academia. ‘See – the ‘Aryans’ are just an insignificant side branch of human evolution. Africa is the motherland, and We are Family!’ I’m old enough to remember the sociological snark that was usually included in the O-o-A propaganda.
Razib,
I know the Neanderthal introgression in Ust-Ishm is usually dated to around 10,000 years or so before he lived (based on the IBD lengths of the introgressed segments as you mentioned above), so the primordial admixture event between Neans and proto-Eurasians (sans Basal, whatever that turns out to be) was roughly 55,000 years ago, which is a pretty solid piece of evidence supporting the conventional OoA time frame of 50-60,000 ybp. However, is there a chance that this date might biased downwards, if there were in fact multiple, small scale admixture events with Neans over a longer stretch of time (say starting 80,000 years ago and ending with a final admixture around 55,000 ybp)? I know with RollOff or ALDER (or both), I’ve seen people say that those programs only capture the most recent episode of admixture between populations, and so can obscure longer-term episodes of admixture. And I remember last year, Pontus Skoglund tweeting about a paper that had a data point in it about the Nean + Eurasian admixture being significantly older than the conventional dating inferred from Ust-Ishm, something like 80,000 years ago or what have you.
It seems beyond any doubt that there was Nean+Eurasian admixture, but I’m wondering if the conventional dating and nature of the event (was it really a one-off pulse, or were there multiple episodes over time) is really so air-tight.
i need to read the papers again (tianyun is pretty old too). but it’s not outside realm of possibility….
That’s exactly the point, a lot of things are completely open. We know Neandertal admixture took place around 50.000, but who can say for sure there was no earlier or later admixture?
Even more, the Near Eastern Neandertals were more sapiens like and might have mixed with archaic sapiens at a much older date. We have no genetic profile of archaic sapiens or Near Eastern Neandertals to compare with.
Actually some of the proven admixed sapiens lineages (like Romanian) seem to have died off. The exact time and place, even of the most recent-influential admixture event is not known!
Too many open ends, but so many hints for the early modern sapiens presence outside of Africa.
I think because the classic narrative is just so deeply entrenched and ideologically burdened, most scholars hesitate to come forward with completely new concepts until its bullet proven.
Even the findings of Al Wusta, with anatomical comparisons making its sapiens characteristics clear, were not just met with positive attitudes and comments.
But getting a real DNA profile from those finger bones seems to be almost impossible with the current methods.
The title reminded me of Dierdre McCloskey’s epigram, “All theories are metaphors, and all metaphors are lies” (but some are useful).