A previously hidden genetic link between native peoples in Australia and the Amazon has inspired two different teams of researchers to reach competing conclusions about the origins of Native Americans.
One team analyzing modern genetic data finds evidence that at least two ancestral populations gave rise to Native Americans. Another team, analyzing DNA from present-day and ancient Americans, reports that Native Americans came from a single ancestral population.
Both teams agree that Native American roots stem from Asia. Both also say the other group has strong data and has analyzed it superbly. They just don’t see eye-to-eye on the interpretation of the information.
One team, reporting July 21 in Nature, found that about 1 to 2 percent of DNA in some native peoples in South America is shared with native Australians and Melanesians.
“It’s a small but distinct signal,” says study coauthor Pontus Skoglund, a population geneticist at Harvard University. He and colleagues say their data indicate that one of two ancestral groups, which they call Population Y, comprised some of the first people in the New World. Population Y was also related to ancestors of people who settled Australia and Melanesia.
Signs of an Amazon-Australia link are also present in the second team’s data, reported July 21 in Science. But those researchers explain the finding differently. “We see a bit, a hint, just a taste of the same signal in the Aleutian Islanders,” says study coauthor Rasmus Nielsen, a computational biologist at the University of California, Berkeley.
His team concludes that a single ancestral population of Native Americans from Asia began migrating into the New World about 23,000 years ago. Aleutian Islanders or some of their ancestors may have migrated along the Pacific coast and mixed with native South Americans sometime after the original peopling of the Americas, bringing in the mysterious genetic signal, Nielsen says.
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Native American origins have been a matter of contention for decades, says Theodore Schurr, an anthropological geneticist at the University of Pennsylvania who wasn’t involved in either study. Native Americans share ancestry but are genetically and culturally diverse, speaking hundreds of different languages. Seeds of that diversity germinated from the founding populations that moved across the Bering land bridge at the end of the last Ice Age, so the ancestral population must have been a complex mix of people, Schurr says. Skoglund and colleagues’ two-population argument that more than one group contributed to Native Americans’ genetic heritage is consistent with that view.
Connie Mulligan, a molecular anthropologist at the University of Florida in Gainesville, sees it differently. Much of the variation among native peoples in the Americas may have arisen after they reached the Western Hemisphere, she says. Australians and Amazonians may randomly have developed the same genetic patterns through a process known as genetic drift, she says.
Once in the Americas, native people did go their own way. Data from Nielsen’s one-population team point to a genetic split between northern and southern Native Americans that happened about 13,000 years ago. That’s about the same time a culture known as Clovis began to dominate North America. Researchers have recently discovered that an ancient child known as Anzick-1 who was part of the Clovis culture is an ancestor to all Native Americans (SN: 3/22/14, p. 6).
This isn’t the first time a connection between Australia and the Americas has been proposed. Researchers had previously noticed that skulls of ancient Americans resembled those of native Australians and Melanesians. Some people thought a group called Paleoamericans originated in Asia and gave rise to both the earliest settlers of the Americas and to present-day native Australians and Melanesians. Paleoamericans were replaced by a wave of people crossing the Bering land bridge later.
Skoglund and colleagues conclude in Nature that more data, particularly from ancient DNA, is needed to address the question. In the Science one-population study, Nielsen and colleagues did just that; they examined DNA from 17 ancient people from Mexico, Chile and Argentina who had the characteristic Paleoamerican skull shape. Despite their skull shape, the ancient people didn’t genetically resemble Australians. Instead, they were clearly related to other Native Americans.
It’s clear that the genetic signal isn’t from ancient Australians migrating directly to South America, says Jennifer Raff, an anthropological geneticist at the University of Texas at Austin. She agrees that the pattern may represent a subgroup of people who lived along the Bering land bridge, a now underwater region known as Beringia, for thousands of years before crossing into the Americas. The two research groups’ findings can be reconciled, she says. Both papers are exciting because they give researchers hints about the first Americans.