I came across an interesting paper: Guy S. Jacobs, Georgi Hudjashov, Lauri Saag, et. al., (2019), Multiple Deeply Divergent Denisovan Ancestries in Papuans, Cell,Volume 177, Issue 4,2019, pp. 1010-1021.e32, ISSN 0092-8674, https://doi.org/10.1016/j.cell.2019.02.035.
It explores three different Denisovan introgressions into the people that live in Papua New Guinea, and the relationship between the three Denisovan groups that admixed over a period of tens of thousands of years, in separate events (Modern humans met and shared genes with Denisovans several times).
I found it quite interesting:
Variety of Denisovans
"Here, we use a statistical approach on new genomes from ISEA and Papua to identify two new Denisovan groups (D1 and D2) and describe the relationships between these archaic hominins long before they first interacted with anatomically modern humans. Both groups branched off early from the Altai Denisovan clade at 283 and 363 kya and were reproductively isolated from the individuals at Denisova cave in Siberia and from each other. Yet both groups bred with modern humans, contributing around 4% of the genomes of Papuans, including over 400 gene variants enriched for traits involving immunity and diet. Some of this introgression is restricted to modern New Guinea and its surrounding islands and may have occurred as late as the very end of the Pleistocene, making the admixing D1 Denisovan population among the last surviving archaic hominins in the world."
Ancient Mariners
The Denisovans had a wide geographic range and had evolved in Asia for hundreds of thousands of years. They had split and differentiated in Siberia, Melanesia and Southeast Asia. Could they have moved northwards, into Beringia and crossed it into America?
The paper highlights the mobility and abilities of Denisovans in dealing with the sea (underline is mine:
"The genetic diversity within the Denisovan clade is consistent with their deep divergence and separation into at least three geographically disparate branches, with one contributing an introgression signal in Oceania and to a lesser extent across Asia (D2), another apparently restricted to New Guinea and nearby islands (D1), and a third in East Asia and Siberia (D0). This suggests that Denisovans were capable of crossing major geographical barriers, including the persistent sea lanes that separated Asia from Wallacea and New Guinea. They therefore spanned an incredible diversity of environments, from temperate continental steppes to tropical equatorial islands. The emerging picture suggests that far from moving into sparsely inhabited country, modern humans experienced repeated and persistent interactions as they expanded out of Africa into this highly structured archaic landscape across Eurasia. This genetic contact yielded a rich legacy, including hundreds of gene variants that continue to contribute to the adaptive success of anatomically modern humans today."
The paper explicitly mentions their seafaring capabilities, and also, that they survived until quite recently, far longer than the Neanderthals:
" this would imply that at least some Denisovan populations had the ability to cross large bodies of water, such as the one represented by the Wallace Line. This idea does not seem implausible given archaeological evidence of archaic hominin dispersals—notably, the discovery of stone tools in the Philippines dating to 700 kya (Ingicco et al., 2018) and the related finding of H. floresiensis on the island of Flores (Brown et al., 2004), both across substantial water boundaries that persisted throughout the Pleistocene. Such geographical barriers would limit gene flow and might help to explain the extent of divergence between the D1 Denisovan population and other Denisovan groups. Second, the late date for the D1 introgression and geographic structure in modern populations suggests that Denisovans survived until 30 kya, and perhaps as recently as 14.5 kya. This is longer than Neanderthals, who died out around 40 kya."
Capabilities that could have taken them along the eastern shores of Asia, into America.
Clearly, a complex pattern is being pieced together in Asia, with the Denisovans appearing to have been well established there long before the "Out of Africa" event.
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