November 20, 2013 - New genome sequences from two extinct human
relatives suggest that these 'archaic' groups bred with humans and with each other more extensively than was previously known.
The ancient genomes, one from a Neanderthal
and one from a different archaic human group, the Denisovans, were presented on 18 November at a meeting at the Royal Society in London. They suggest that interbreeding went on between the members of several ancient human-like groups living in Europe and Asia
more than 30,000 years ago, including an as-yet unknown human ancestor from Asia.
"What it begins to suggest is that we're looking at a 'Lord of the Rings'-type world - that there were many hominid populations," says Mark Thomas, an evolutionary geneticist at University College London who was at the meeting but was not involved in the work.
The first Neanderthal1 and the Denisovan2 genome sequences revolutionized the study of ancient human history, not least because they showed that these groups interbred with anatomically modern humans, contributing to the genetic diversity of many people alive today.
All humans whose ancestry originates outside of Africa owe about 2% of their genome to Neanderthals; and certain populations living in Oceania, such as Papua New Guineans and Australian Aboriginals, got about 4% of their DNA from interbreeding between their ancestors and Denisovans, who are named after the cave in Siberia's Altai Mountains where they were discovered. The cave contains remains deposited there between 30,000 and 50,000 years ago.
Those conclusions however were based on low-quality genome sequences, riddled with errors and full of gaps, David Reich, an evolutionary geneticist at Harvard Medical School
in Boston, Massachusetts said at the meeting. His team, in collaboration with Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology
in Leipzig, Germany, have now produced much more complete versions of the Denisovan and Neanderthal
genomes - matching the quality of contemporary human genomes. The high-quality Denisovan genome data and new Neanderthal
genome both come from bones recovered from Denisova Cave.
The new Denisovan genome indicates that this enigmatic population got around: Reich said at the meeting that they interbred with Neanderthals and with the ancestors of human populations that now live in China and other parts of East Asia, in addition to Oceanic populations, as his team previously reported. Most surprisingly, Reich said, the new genomes indicate that Denisovans interbred with another extinct population of archaic humans that lived in Asia more than 30,000 years ago, which is neither human nor Neanderthal.
The meeting was abuzz with conjecture about the identity of this potentially new population of humans. "We don't have the faintest idea," says Chris Stringer, a paleoanthropologist at the London Natural History Museum, who was not involved in the work. He speculates that the population could be related to Homo heidelbergensis, a species that left Africa around half a million years ago and later gave rise to Neanderthals in Europe. "Perhaps it lived on in Asia as well," Stringer says.
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Meyer, M. Science 338, 222 - 226 (2012)