单选题   Para. 1 ①Modem humans evolved somewhere in Africa roughly 200,000 years ago. ②But how did our species go on to populate the rest of the globe? ③Did humans flood out of Africa in a single diaspora, or did we trickle from the continent in waves spread out over tens of thousands of years? @The question, one of the biggest in human evolution, has plagued scientists for decades.
    Para. 2 Now they may have found an answer.
    Para. 3 In a series of unprecedented genetic analyses published on Wednesday in the journal Nature, three separate teams of researchers conclude that all non-Africans today trace their ancestry to a single population emerging from Africa between 50,000 and 80,000 years ago.
    Para. 4 ①Each team of researchers used sets of genomes to tackle different questions about our origins, such as how people spread across Africa and how others populated Australia. ②But all aimed to settle the question of human expansion from Africa.
    Para. 5 ①In the 1980s, a group of paleoanthropologists and geneticists began championing a hypothesis that modem humans emerged only once from Africa, roughly 50,000 years ago. ②Skeletons and tools discovered at archaeological sites clearly indicated the existence of modem humans in Europe, Asia and Australia.
    Para. 6 ①Early studies of bits of DNA also supported this scenario. ②Yet there are also clues that at least some modem humans lived outside Africa well before 50,000 years ago, perhaps part of an earlier wave Of migration.
    Para. 7 In 2011 Eske Willerslev, a renowned geneticist at the University of Copenhagen, and his colleagues reported evidence that some living people descended from this early wave.
    Para. 8 ①Willerslev and his colleagues reconstructed the genome of an aboriginal Australian from a century-old lock of hair kept in a museum—the first reconstruction of its kind. ②The DNA held a number of peculiar variants not found in Europeans or Asians.
    Para. 9 ①He concluded that the ancestors of Aboriginals split off from other non-Africans and moved eastward, eventually arriving in East Asia 62,000—75,000 years ago. ②Tens of thousands of years later, a separate population of Africans spread into Europe and Asia.
    Para. 10 ①It was big conclusion to draw from a single fragile genome, so Willerslev decided to contact living Aboriginals to see if they would participate in a new genetic study. ②He joined David Lambert, a geneticist at Griffith University in Australia, who was already meeting with aboriginal communities about beginning such a study.
    Para. 11 ①Their new paper also includes DNA from people in Papua New Guinea. ②All told, the scientists were able to sequence 83 genomes from aboriginal Australians and 25 from people in Papua New Guinea.
    Para. 12 ①Meanwhile, Mait Metspalu of the Estonian Biocentre was leading a team of 98 scientists on another genome-gathering project. ②They picked out 148 populations to sample, mostly in Europe and Asia, with a few genomes from Africa and Australia. ③They sequenced 483 genomes at high resolution.
    Para. 13 ①David Reich, a geneticist at Harvard Medical School, and his colleagues assembled a third database of genomes from all five continents. ②The Simons Genome Diversity Project, sponsored by the Simons Foundation and the National Science Foundation, contains 300 high-quality genomes from 142 populations.
    Para. 14 ①Reich and his colleagues probed their data for the oldest evidence of human groups genetically separating from one another. ②They found that the ancestors of the KhoiSan, hunter-gatherers riving today in southern Africa, began to split off from other riving humans about 200,000 years ago and were hilly isolated by 100,000 years ago.