For decades, scientists could describe the peopling of the Americas only in broad strokes, leaving plenty of mysteries about when and how people spread across the continents. Now, state-of-the-art ancient DNA methods, applied to scores of new samples from around the Americas, are filling in the picture. Two independent studies, published in Cell and online in Science, find that
ancient populations expanded rapidly across the Americas about 13,000 years ago. They also emphasize that the story continued in the thousands of years since, revealing previously undocumented, large-scale movements between North and South America.
The data include 64 newly sequenced ancient DNA samples from Alaska to Patagonia, spanning more than 10,000 years of genetic history. "The numbers [of samples] are just extraordinary," says Ben Potter, an archaeologist at the University of Alaska in Fairbanks. Prior to these studies, only six genomes older than 6000 years from the Americas had been sequenced. As a result, says Jennifer Raff, an anthropological geneticist at the University of Kansas in Lawrence, "The [genetic] models that we've been using to explain the peopling of the Americas have always been oversimplified."
Eske Willerslev, an evolutionary geneticist at the University of Copenhagen who led the Science team, worked closely with the Fallon Paiute-Shoshone Tribe in Nevada to gain access to some of the new samples. The tribe had been fighting to repatriate 10,700-year-old remains found in Nevada's Spirit Cave and had resisted destructive genetic testing. But when Willerslev visited the tribe in person and vowed to do the work only with their permission, the tribe agreed, hoping the result would bolster their case for repatriation.
It did. Willerslev found that the remains from Spirit Cave are most closely related to living Native Americans. That strengthened the Fallon Paiute-Shoshone Tribe's claim to the bones, which were returned to them in 2016 and reburied. Willerslev's study validates that "this is our homeland, these are our ancestors," says Rochanne Downs, the tribe's cultural coordinator.
Willerslev added the Spirit Cave data to 14 other new whole genomes from sites scattered from Alaska to Chile and ranging from 10,700 to 500 years old. His data join an even bigger trove published in Cell by a team led by population geneticist David Reich of Harvard Medical School in Boston. They analyzed DNA from 49 new samples from Central and South America dating from 10,900 to 700 years old, at more than 1.2 million positions across the genome. All told, the data decisively dispel suggestions, based on the distinctive skull shape of a few ancient remains, that early populations had a different ancestry from today's Native Americans. "Native Americans truly did originate in the Americas, as a genetically and culturally distinctive group. They are absolutely indigenous to this continent," Raff says.
