New signs of massive human migration
Study reveals unknown group that split off from other Native Americans just after — or before — they arrived in North America
The girl was just six weeks old when she died. Her body was buried on a bed of antler points and red ocher, and she lay undisturbed for 11,500 years. Archaeologists discovered her in an ancient burial pit in Alaska in 2010, and on Wednesday an international team of scientists reported they had retrieved the child’s genome from her remains. The second-oldest human genome ever found in North America, it sheds new light on how people — among them the ancestors of living Native Americans — first arrived in the Western Hemisphere.
The analysis, published in the journal Nature, shows that the child belonged to a hitherto unknown human lineage, a group that split off from other Native Americans just after — or perhaps just before — they arrived in North America.
“It’s the earliest branch in the Americas that we know of so far,” said Eske Willerslev of the University of Copenhagen, a co-author of the new study. As far as he and other scientists can tell, these early settlers endured for thousands of years before disappearing.
The study strongly supports the idea that the Americas were settled by migrants from Siberia, and experts hailed the genetic evidence as a milestone. “There has never been any ancient Native American DNA like it before,” said David Reich, a geneticist at Harvard Medical School who was not involved in the study.
The girl’s remains were unearthed at the Upward Sun River archaeological site in the Tanana River Valley in central Alaska. Ben Potter, an archaeologist at the University of Alaska, discovered the site in 2006.
It was apparently home to short-lived settlements that appeared and disappeared over thousands of years. Every now and then, people arrived to build tent-like structures, fish for salmon, and hunt for hare and other small game.
In 2010, Potter and his colleagues discovered human bones at Upward Sun River. Atop a hearth dating back 11,500 years were the cremated bones of a 3-year-old child. Digging into the hearth itself, archaeologists discovered the remains of two infants.
The two infants were given names: The baby girl is Xach’itee’aanenh T’eede Gaay (“sunrise girl-child,” in Middle Tanana, the dialect of the local community), and the remains of the other infant, or perhaps a fetus, is Yelkaanenh T’eede Gaay (“dawn twilight girl-child”).
The Healy Lake Village Council and the Tanana Chiefs Conference agreed to let scientists search the remains for genetic material. Eventually, they discovered mitochondrial DNA, which is passed only from mother to child, suggesting each had different mothers. Moreover, each infant had a type of mitochondrial DNA found also in living Native Americans.
That finding prompted Potter and his colleagues to begin a more ambitious search. They began collaborating with Willerslev, whose team of geneticists has built an impressive record of recovering DNA from ancient Native American bones.
Among them are the 12,700-year-old Anzick Child, the oldest genome ever found in the Americas, and the Kennewick Man, a 8,500-yearold skeleton discovered in a river bank in Washington state. Questions over his lineage provoked a decadelong legal dispute between scientists, Native American tribes and the Army Corps of Engineers.
Living Native Americans descend from two major ancestral groups. The northern branch includes a number of communities in Canada, such as the Athabascans, along with some tribes in the United States like the Navajo and Apache.
The southern branch includes the other tribes in the United States, as well as all indigenous people in Central America and South America. Both the Anzick Child and Kennewick Man belonged to the southern branch, Willerslev and his colleagues have found.
So he was eager to see how the people of Upward Sun River might be related. But the remains found there represented a huge scientific challenge.
The search for DNA in the cremated bones ended in failure, and Willerslev and his colleagues managed to retrieve only fragments from the remains of Yelkaanenh T’eede Gaay, the youngest of the infants.
But the researchers had better luck with Xach’itee’aanenh T’eede Gaay. Eventually, they managed to put together an accurate reconstruction of her entire genome. To analyze it, Willerslev and Potter collaborated with a number of geneticists and anthropologists.