The evolutionary ancestry of the modern human race became even more complicated in 2012 with the results of studies on DNA extracted from bits of 50,000-year-old bone from Siberia. The analysis confirmed that an archaic species of people called Denisovans—contemporaries of Neandertals who were unknown to science until 20120—are indeed ancestors of many people living today. See also: Denisovans; DNA unveils enigmatic Denisovans; Neandertals
In 2008 archaeologists excavating the Denisova Cave in Siberia discovered a fragment of finger bone from a young girl who had lived there 50,000 or more years ago. When Svante Pääbo and colleagues at the Max Planck Institute for Evolutionary Anthropology examined the well-preserved mitochondrial DNA in the fragment in 2010, their paleogenomics studies determined that the bone had belonged to a human group distinct from Neandertals (who had also lived in the cave) as well as from anatomically modern people. That piece of bone and a tooth with some unusual features that had been found in the cave in 2000 authenticated the existence of the Denisovans as a previously unknown species. See also: Paleogenomics
The Denisovans and the Neandertals both seem to be descended from archaic humans who first migrated out of Africa about 800,000 years ago, long before anatomically modern humans did. Those early emigrants eventually split into at least two distinct populations: the well-known Neandertals, who became Europe’s first inhabitants but also roamed across much of Asia, and the Denisovans who seem to have established themselves primarily in eastern Asia.
Many archaeologists long discounted the idea that the modern human line could have interbred at any point with their Neandertal cousins after they, too, left Africa within the past 100,000 years. Studies of the Neandertal genome by Max Planck Institute scientists showed in 2010, however, that about 4% of the DNA of non-African people is derived from Neandertals, suggesting that a significant amount of interbreeding did occur. A 2012 analysis by Pääbo’s group found evidence of that between 4 and 6% of the genomes of people ancestrally native to Melanesia, Australia, and some other parts of southeast Asia came from Denisovans. See also: Neandertal genome
Taken together, all these results are prompting archaeologists to reconsider their theories about the relatedness of fossil humans and about how early modern humans emerged. Since the 1980s, the archaeological community has generally been divided between those who favored a multiregional hypothesis for human origins—in which diverse human groups across the Old World retained the ability to interbreed and remained one species—and the out-of-Africa model in which the modern humans who emerged from Africa roughly 60,000 years ago replaced other human groups without interbreeding. The genome analysis of the Denisovans, like that of the Neandertals earlier, indicates that a more complex pattern of at least limited interbreeding may be more accurate. See also: Early modern humans; Fossil humans