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| Scientists Trace an Ancient Connection Between Amazonians and Australasians | |
| (34 minutes later) | |
| Some people in the Brazilian Amazon are very distant relations of indigenous Australians, New Guineans and other Australasians, two groups of scientists who conducted detailed genetic analyses reported Tuesday. But the researchers disagree on the source of that ancestry. | Some people in the Brazilian Amazon are very distant relations of indigenous Australians, New Guineans and other Australasians, two groups of scientists who conducted detailed genetic analyses reported Tuesday. But the researchers disagree on the source of that ancestry. |
| The connection is ancient, all agree, and attributable to Eurasian migrants to the Americas who had some Australasian ancestry, the scientists said. | The connection is ancient, all agree, and attributable to Eurasian migrants to the Americas who had some Australasian ancestry, the scientists said. |
| But one group said the evidence is clear that two different populations came from Siberia to settle the Americas 15,000 or more years ago. The other scientific team says there was only one founding population from which all indigenous Americans, except for the Inuit, descended and the Australasian DNA came later, and not through a full-scale migration. For instance, genes could have flowed through a kind of chain of intermarriage and mixing between groups living in the Aleutian Islands and down the Pacific Coast. | But one group said the evidence is clear that two different populations came from Siberia to settle the Americas 15,000 or more years ago. The other scientific team says there was only one founding population from which all indigenous Americans, except for the Inuit, descended and the Australasian DNA came later, and not through a full-scale migration. For instance, genes could have flowed through a kind of chain of intermarriage and mixing between groups living in the Aleutian Islands and down the Pacific Coast. |
| Both papers were based on comparisons of patterns in the genomes of many living individuals from different genetic groups and geographic regions, and of ancient skeletons. | Both papers were based on comparisons of patterns in the genomes of many living individuals from different genetic groups and geographic regions, and of ancient skeletons. |
| David Reich of Harvard, the senior author of a paper published Tuesday in the journal Nature, said the DNA pattern was “surprising and unexpected, and we weren’t really looking for it.” | David Reich of Harvard, the senior author of a paper published Tuesday in the journal Nature, said the DNA pattern was “surprising and unexpected, and we weren’t really looking for it.” |
| Pontus Skoglund, a researcher working with Dr. Reich who was investigating data gathered for previous research, found the pattern, or signal, as he described it. He and Dr. Reich and their colleagues used numerous forms of analysis, comparing different groups to see how distant they were genetically, to determine if there was some mistake. | Pontus Skoglund, a researcher working with Dr. Reich who was investigating data gathered for previous research, found the pattern, or signal, as he described it. He and Dr. Reich and their colleagues used numerous forms of analysis, comparing different groups to see how distant they were genetically, to determine if there was some mistake. |
| But, Dr. Skoglund said, “we can’t make it go away.” | But, Dr. Skoglund said, “we can’t make it go away.” |
| Dr. Reich reported in 2012, based on some of the same evidence, that a group he called the First Americans came from Siberia 15,000 or more years ago, and were the ancestors of most Native Americans on both continents. There was a second and later migration, he said, that gave rise to a group of Indians including the Chipewyan, Apache and Navajo, who speak similar languages. The Inuit are generally agreed to have made a separate, later migration. | Dr. Reich reported in 2012, based on some of the same evidence, that a group he called the First Americans came from Siberia 15,000 or more years ago, and were the ancestors of most Native Americans on both continents. There was a second and later migration, he said, that gave rise to a group of Indians including the Chipewyan, Apache and Navajo, who speak similar languages. The Inuit are generally agreed to have made a separate, later migration. |
| Now, based on new evidence and much deeper analysis, he and Dr. Skoglund and colleagues concluded that the first migration, which began 15,000 or more years ago, consisted not only of the group he identified as the First Americans, but of a second group that he calls Population Y. They could have come before, after or around the same time as the First Americans. But Population Y, he writes, “carried ancestry more closely related to indigenous Australians, New Guineans and Andaman Islanders than to any present-day Eurasians or Native Americans.” | Now, based on new evidence and much deeper analysis, he and Dr. Skoglund and colleagues concluded that the first migration, which began 15,000 or more years ago, consisted not only of the group he identified as the First Americans, but of a second group that he calls Population Y. They could have come before, after or around the same time as the First Americans. But Population Y, he writes, “carried ancestry more closely related to indigenous Australians, New Guineans and Andaman Islanders than to any present-day Eurasians or Native Americans.” |
| Population Y comes from Ypykuéra, a word meaning ancestor in a language spoken by the two Amazonian groups, the Surui and Karitiana, that show the strongest genetic connection to Australasians. | Population Y comes from Ypykuéra, a word meaning ancestor in a language spoken by the two Amazonian groups, the Surui and Karitiana, that show the strongest genetic connection to Australasians. |
| The other paper, published in the journal Science, originated in the lab of Eske Willerslev, a noted detective of ancient DNA at the University of Copenhagen and the Center for Geogenetics. It came to involve 101 authors around the globe over several years of work. The goal, said Maanasa Raghavan, a molecular biologist in Copenhagen who was one of the main scientists on the project, was to bring together genomic, archaeological and other research on modern and ancient peoples of the Americas to come up with a clearer picture of how the continents were populated. | The other paper, published in the journal Science, originated in the lab of Eske Willerslev, a noted detective of ancient DNA at the University of Copenhagen and the Center for Geogenetics. It came to involve 101 authors around the globe over several years of work. The goal, said Maanasa Raghavan, a molecular biologist in Copenhagen who was one of the main scientists on the project, was to bring together genomic, archaeological and other research on modern and ancient peoples of the Americas to come up with a clearer picture of how the continents were populated. |
| They concluded that Native Americans diverged genetically from Eurasians about 23,000 years ago. They also concluded, in contrast to the Harvard group, that all indigenous Americans except the Inuit came from one founding population. | They concluded that Native Americans diverged genetically from Eurasians about 23,000 years ago. They also concluded, in contrast to the Harvard group, that all indigenous Americans except the Inuit came from one founding population. |
| But they, too, found the trace of Australasian ancestry in some South American natives, although it was not as strong as that reported by Harvard. | But they, too, found the trace of Australasian ancestry in some South American natives, although it was not as strong as that reported by Harvard. |
| Dr. Raghavan said the raw evidence in both papers of an Australasian genetic signal was consistent. | Dr. Raghavan said the raw evidence in both papers of an Australasian genetic signal was consistent. |
| “What is different is how we think that the signal got here,” she said. | “What is different is how we think that the signal got here,” she said. |
| Neither group supported an existing theory, based on the shape of ancient skulls in South America, that a group called PaleoAmericans, who were very similar to Australasians, came to the Americas before the ancestors of most Native Americans did. The Science paper specifically rejected that idea, saying that both gene studies and a re-examination of the shape of some historical skulls contradicted that theory. | Neither group supported an existing theory, based on the shape of ancient skulls in South America, that a group called PaleoAmericans, who were very similar to Australasians, came to the Americas before the ancestors of most Native Americans did. The Science paper specifically rejected that idea, saying that both gene studies and a re-examination of the shape of some historical skulls contradicted that theory. |
| Rasmus Nielsen, a computational geneticist at the University of California, Berkeley, and one of the senior authors of the Science paper, said he saw no conflict in the raw data used in the two studies. | Rasmus Nielsen, a computational geneticist at the University of California, Berkeley, and one of the senior authors of the Science paper, said he saw no conflict in the raw data used in the two studies. |
| David Meltzer, an anthropologist and archaeologist at Southern Methodist University and another author of the Science paper, said the difference in interpretation between the two groups was “not an irresolvable problem.” More analysis of ancient DNA or the discovery of a new skeleton could provide an answer. | David Meltzer, an anthropologist and archaeologist at Southern Methodist University and another author of the Science paper, said the difference in interpretation between the two groups was “not an irresolvable problem.” More analysis of ancient DNA or the discovery of a new skeleton could provide an answer. |
| Dr. Reich, of Harvard, agreed that the papers were not in disagreement, but said his team had delved far deeper in its analysis of the Australasian trace. | Dr. Reich, of Harvard, agreed that the papers were not in disagreement, but said his team had delved far deeper in its analysis of the Australasian trace. |
| “We have overwhelming evidence of two founding populations in the Americas,” he said. | “We have overwhelming evidence of two founding populations in the Americas,” he said. |