As mentioned in a previouspost, there were many research article published last month. Today's post looks into one (not peer reviewed) published on March 23 in Biorxiv, that states that two different superarchaic populations admixed with the ancestors of modern humans, within Africa, and with the ancestors of both Denisovans and Neanderthals. Then, the Denisovans received another superarchaic introgression. The H. sapiens branch also mated with Neanderthals.
This is the article on, yes, another introgression: Alan R. Rogers, Md Touhidul Islam, Colin M. Brand, Timothy H. Webster, (2026). Human Ancestors Interbred with Two Distinct Populations of Distant Relatives. bioRxiv 2026.03.22.713509; doi: https://doi.org/10.64898/2026.03.22.713509
The paper's abstract reads: "Ancient DNA has shown that a distantly-related “superarchaic” population interbred first with the ancestors of Neanderthals and Denisovans and later with Denisovans themselves. Other work has shown that a superarchaic population interbred with the African ancestors of all modern humans. But it is not yet clear whether these events involved the same superarchaic population. Here, we use the distribution of derived alleles among populations to evaluate hypotheses about superarchaics and their relationship to other hominins of the Pleistocene and Holocene. We find evidence for at least two distinct superarchaic populations. The one contributing to archaic Eurasian populations (Denisovans and Neanderthal-Denisovan ancestors) diverged earlier from the human lineage than did the one contributing to early moderns in Africa. These findings reveal previously unrecognized structure among hominin populations of the Pleistocene."
The authors argue that some archaic lineage, which they don't identify, called Z shared genes (ζ) with the lineage of ancestors that, after the split of Neanderthals and Denisovans, lead to H. sapiens (XY). In a previous paper (Rogers, A. R., Harris, N. S. & Achenbach, A. A. (2020). Neanderthal-Denisovan Ancestors Interbred with a Distantly-Related Hominin. Science Advances 6, eaay5483.) they had suggested that a superarchaic popultion called S admixed (δ) with the branch that had split from the ancestors of modern humans, and lead to Neanderthals and Denisovans (ND). The S superarchaics later admixed (β) with Denisovans (D), while Neanderthals (N) received an archaic modern Human (XY) genetic input (γ). Neanderthals injected (α) genes into Eurasian modern humans (Y) but not into Africans (X).
This is the explanation provided by tha authors for these interactions:
"To make sense of this, we pointed out that the first wave of emigration out of Africa happened early in the Pleistocene, when Homo erectus spread across Eurasia. Later, during the Middle Pleistocene, humans evolved larger brains and began making Acheulean tools. Both of these innovations appear in Africa before Eurasia, suggesting a second wave of emigration out of Africa. We proposed that this second wave interbred with the Eurasian descendants of the first, during what we refer to as the δ episode of admixture. It seemed plausible that, before this contact, the two populations had remained largely isolated because of the difficulty of traveling between Africa and Eurasia. (At least during the Upper Pleistocene, human contact between these continents was largely restricted to relatively brief periods when the Sahara was humid.)
Now we have evidence of a second superarchaic population, Z, which diverged after the first and later interbred with the ancestors of modern humans. This contact presumably occurred in Africa, because it happened before moderns spread into Eurasia. We considered the possibility that this second superarchaic population was the same as the first—see model... Thus, there were two superarchaic populations, and it seems likely that the second (population Z) was African.
This is puzzling, because it implies that two African populations—population Z and the ancestors of moderns, Neanderthals, and Denisovans—remained essentially isolated across roughly a million years. What kept them apart? Africa has no mountain barriers as large as the Himalayas or the Alps. There are deserts, but these were not continuously arid. The results of Ragsdale et al. (see above) suggest that these populations may not have been isolated after all—perhaps there was a continuous trickle of gene flow between them. Yet somehow (as discussed above) population Z acquired many mutations that show up in modern humans but not in Neanderthals and Denisovans. If there was gene flow between these populations, it must have been weak."
Comments
This is an interesting hypothesis, that needs to be polished a little. It could also be expanded by imagining even later admixture events (μ) from Z into the African group X that added to its diversity during the past 50 ky. However, it does not break the Out of Africa paradigm as it suggests that after H. erectus left Africa heading into Eurasia (are they , humans in Africa developed Acehulean tools (typical of H. erectus) and left Africa in a 2nd migration. However, this does not seem to be reflected in the trees of the paper, so I am a bit confused.
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