A new early modern human genome from Siberia28 Mar 2014
Ann Gibbons reports from a recent conference in Spain about new work that has sequenced a whole genome from a 45,000-year-old femur from Siberia: “Oldest Homo sapiens Genome Pinpoints Neandertal Input”. The femur as yet is a context-free find from a riverbank, so it isn’t correct to call it an “Upper Paleolithic” specimen, though its radiocarbon date puts it into that time frame in this region of the world. The overall genome of the specimen is similar to living people rather than Neandertals, and the investigators (led by Svante Pääbo) are calling it the earliest modern human specimen to produce a whole genome so far.
Because it is a report on a conference presentation, there are very few useful details. This is the most interesting of the results reported:
Because all living people in Europe and Asia carry roughly the same amount of Neandertal DNA, Pääbo's team thought that the interbreeding probably took place in the Middle East, as moderns first made their way out of Africa. Middle Eastern Neandertal sites are close to Skhul and Qafzeh, so some researchers suspected that those populations were the ones that mingled. But the team's analysis favors a more recent rendezvous. The femur belonged to an H. sapiens man who had slightly more Neandertal DNA, distributed in different parts of his genome, than do living Europeans and Asians. His Neandertal DNA is also concentrated into longer chunks than in living people, Pääbo reported. That indicates that the sequences were recently introduced: With each passing generation, any new segment of DNA gets broken up into shorter chunks as chromosomes from each parent cross over and exchange DNA. Both features of the Neandertal DNA in the femur suggest that the Ust-Ishim man lived soon after the interbreeding, which Pääbo estimated at 50,000 to 60,000 years ago.
Without details, there’s not much I can say. There are a lot of controls I’d like to see, but as described here it is not an unexpected result. A slight increase in the representation of the Neandertal DNA coupled with more resolution on the timeline of introgression.
I will point out that the methods used to detect chunks of Neandertal DNA work better with longer chunks. So the result described here is a rather tricky one. Much here seems to depend on the assumption that there was only one time that Neandertals contributed DNA to later populations.
That’s not the assumption I would start with.