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Analysis of ancient nuclear DNA, recovered from 40,000-year-old remains in the Denisova Cave, Siberia, hints at the multifaceted interaction of human populations following their migration out of Africa.

The new discipline of palaeogenetics is delivering increasing dividends, the latest news coming from Reich, Pääbo and colleagues on page 1053 of this issue. The authors' analysis of nuclear DNA of a human-like finger bone, found in Denisova Cave in southern Siberia, points towards a complex model of migration and colonization after anatomically modern humans moved out of Africa some 50,000–60,000 years ago.

Ever since 1925, when Raymond Dart's report of the first Australopithecus skull in southern Africa upended Victorian views of human origins, there has been debate over whether our species arose only once and spread throughout the world, replacing all extant species of Homo, or whether our ancestors interbred with the other populations and subspecies. The most extreme version of the 'candelabra' model of human origins — according to which human species arose multiple times independently of our Homo ergaster ancestors — has been largely discounted.

But it has been difficult to assess more nuanced models, such as the possibility of genetic exchange with some archaic populations, including Neanderthals, and now perhaps ancient Siberians. Until recently, genetic data and interpretation of the fossil record seemed to favour a complete-replacement model, in which all human species trace all of their genetic ancestry to a single origin in one or more African populations of moderate size some 200,000 years ago2, 3, 4, 5. However, the Denisovan nuclear genome sequence, along with that of Homo neanderthalensis published by some of the same authors6, suggest that the out-of-Africa population history of Homo sapiens is probably much more intertwined than previously thought, with more intertwining in some parts of the world than others.

Read more and follow discussion at Nature.

Triangles and circles respectively represent sampling locations of Neanderthal remains and of present-day human genomes. The blue arrows indicate generally accepted major migrations of anatomically modern humans, following their departure from Africa 50,000–60,000 years ago. At this time, there were two primary archaic species in Eurasia, Neanderthals and Homo erectus; Reich, Pääbo and co-workerssuggest that a third group was also present, represented by the ancient Denisovan genome. From ancient DNA, they identify additional putative events involving two episodes of limited gene flow: first, genetic admixture from Neanderthals to modern humans, shortly after the exit from Africa; second, subsequent admixture with the archaic population exemplified by the nuclear DNA extracted from the Denisova finger bone. This second event seems to affect only the ancestors of present-day Melanesians, who are thought to have colonized Papua New Guinea some 45,000 years ago. African populations, both past and present, are genetically highly diverse, as indicated by the multiple labels.

See also "New Hominin Probably Explains Distinctiveness of Melanesians"