Magazine article Science News

Origins of Native Americans Debated: Views Differ on What DNA Says about Ancestral Populations

Magazine article Science News

Origins of Native Americans Debated: Views Differ on What DNA Says about Ancestral Populations

Article excerpt

A previously hidden genetic link between native peoples in Australia and the Amazon has inspired two different research teams 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.

One team, reporting online 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 Medical School. He and colleagues say that data indicate that two ancestral groups populated the New World. And one of these groups, which they call Population Y, was also related to the ancestors of people who settled Australia and Melanesia.

Signs of a South America-Australia link are also present in the second team's data, reported online 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 began migrating from Asia into the New World about 23,000 years ago. Aleutian Islanders or some of their ancestors may have later migrated along the Pacific coast and mixed with those in South America sometime after the original peopling of the Americas, bringing in the mysterious genetic signal.

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 Ice Age, so the ancestral population must have been a complex mix of people, Schurr says. Skoglund and colleagues' 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. …

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