The paper published by Alan R. Rogers, Nathan S. Harris and Alan A. Achenbach (Neanderthal-Denisovan ancestors interbred with a distantly-related hominin June 14, 2019 biorxiv.org) finds evidence to support three human migrations out of Africa, the first one took place 1.9 Million years ago. The second wave happened 700,000 years ago and involved the ancestors of the Nenderthals and Denisovans (which they call "neandersovans". The last wave was that of modern humans. The oldest migration into Eurasia resulted in a population which they call "superarchaic".
They add: "..the large effective size of the superarchaic population hints that it comprised at least two deeply-divided subpopulations, of which one mixed with neandersovans and another with Denisovans."
They mention their molecular clock, which provided a date (95% confidence interval) of 1.9 to 2.5 Million years ago for the split between "superarhcaic" and the other trunk of mankind.
And coment that: "The lower end of this interval hardly differs from the 1.85 mya date of the earliest Eurasian archaeological remains at Dmanisi. It is possible that superarchaics separated from an African population 1.9 mya, expanded into Eurasia, and left those remains at Dmanisi. If so, then superarchaics descend from the earliest human dispersal into Eurasia. On the other hand, some authors prefer a higher mutation rate of 0.5 × 10−9 per year. Under this clock, the lower end of our confidence interval would be 1.7 mya. Thus, our results are also consistent with the view that superarchaics entered Eurasia after the earliest remains at Dmanisi."
They also find that the molecular clock calibrations used to calculate a Denisovan - Neanderthal split some 381,000 years ago by M. Meyer, et al., (Nature 531, 504, 2016) are too recent. They calculate the date of the split was almost twice that figure: 731,000 years ago.
This older date is in line with the 750 kya that we mention in our post Neanderthal and Denisovans split around 750 Kya (May 11, 2018), citing a paper by Ryan J. Bohlender and Chad D. Huff.
Although the paper does not name them, it is possible that the unknown super-archaic hominin population was in fact Homo erectus; they appeared around 2 million years ago which coincides with the split date between superarchaics and the other hominins calculated by Rogers et al.
This is in line with something we posted back in Dec. 2013 (Denisovans interbred with Homo Erectus), when we commented on a paper by Prüfer et al., that hinted at interbreeding between Denisovans and H. erectus.
Mendez, F. L., Watkins, J. C., Hammer, M. F., 2012. Global genetic variation at OAS1 provides evidence of archaic admixture in Melanesian populations. Molecular Biology and Evolution 29 (6),1513–1520.) also suggested an ancient admixture event between Denisovans and H. erectus: "These observations present the intriguing possibility that this deeply diverged region of OAS1 may have introgressed into the common ancestor of Denisova and Melanesians via admixture with an unsampled hominin group, such as Homo erectus. In fact, the introgression of a more archaic form into the ancestors of Denisova was also considered by Reich et al. (2010) to explain some archaic morphological features of the Denisova molar."
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Yes, all good points. And regarding the two older waves, there isn't enough fossil evidence to determine conclusively where they originated. They could have been from Africa, but not necessarily.
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