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. 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...