by Greg Mayer
One of the most exciting recent developments in paleoanthropology has been the discovery, based on just a few bones, of a previously unsuspected type of human called Denisovans (named for the cave where they were found in Siberia). Because of the paucity of skeletal evidence, our knowledge of them is based almost entirely on DNA extracted from the bones. Both Jerry and I have been following developments in these genetic studies here at WEIT (here, here, and here), and so the release of a new paper in Science by Matthias Meyer and a cast of thousands (well, 33, actually) (abstract only) is of great interest, presenting a high quality full genomic sequence of Denisova Woman.
The paper’s results are well summarized in the above figure: in comparison with 11 geographically diverse modern Homo sapiens genomes, the Denisovan genome is distinctive, but shows evidence of interbreeding with Papuans, such that 6% of the Papuan genome derives from the Denisovans. Based on genetic evidence, they date the modern-Denisovan split at about 800,000 years ago (this would also be the date of the modern-Neanderthal split, since Neanderthals and Denisovans split from each other after the moderns split off), and date the Denisovans themselves to about 80,000 years ago.
This essentially confirms what had been found by Reich et al. (2010) in an earlier study (of which Meyer was a coauthor) of the same material, which had not achieved as high quality a determination of the Denisovan genome. The new study is also noteworthy for its technical advances in the genome sequencing of ancient DNA. Interestingly, modern humans from Asia (through which the ancestors of the Papuans had to pass on their way to Papua), do not show a Denisovan genetic influence, so the history of migration through Asia must involve at least two migration events (one in which the Papuans’ ancestors encountered and interbred with Denisovans, and another in which the ancestors of modern Asians did not).
The current work tends to confirm the conclusion that archaic humans (Neanderthals and Denisovans) were part of a group of interbreeding populations in nature that included the immediate ancestors of modern humans, and thus were members of the species Homo sapiens. This was a conclusion that Jerry, I, and, independently, John Hawks, the University of Wisconsin paleoanthroplogist, had reached. Hawks has a very interesting and detailed take on the new paper which is well worth reading.
In another recent paper (may be abstract only), Anders Eriksson and Andrea Manica argue that the shared components of the modern and archaic genomes may result from the retention of variation from an ancestral African population, and not from interbreeding outside of Africa; John Hawks finds their conclusion unlikely.
Eriksson, A. and A. Manica. 2012. Effect of ancient population structure on the degree of polymorphism shared between modern human populations and ancient hominins. Proceedings of the National Academy of Sciences (USA) 109:13956-13960.
Meyer, M., et al. 2012. A high-coverage genome sequence from an archaic Denisovan individual. Science in press. [This is presumably a MS in press, but Science in the past has released preprints whose subsequent publication history has been murky- think arsenic based life.]
Reich, D., et al. 2010. Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature 468:1053-1060.