By analyzing the older infant’s genome, Potter and his colleagues, including José Víctor Moreno Mayar and Lasse Vinner, have shown that she belonged to a previously unknown group of ancient people, who are distinct from all known Native Americans, past and present. The team have dubbed them the Ancient Beringians.

“We’d always suspected that these early genomes would have important stories to tell us about the past, and they certainly didn’t disappoint,” says Jennifer Raff from the University of Kansas, who was not involved in the study.

By comparing Xach’itee’aanenh T’eede Gaay’s genome to those of other groups, the team showed that the Ancient Beringians and other Native Americans descend from a single founding population that started to split away from other East Asians around 36,000 years ago. They became fully separated between 22,000 and 18,000 years ago, and then split into two branches themselves. One gave rise to the Ancient Beringians. The other gave rise to all other Native Americans, who expanded into the rest of the Americas. Native Americans, then, diverged into two more major lineages—a northern and a southern one—between 14,600 and 17,500 years ago.

This story unequivocally supports the so-called Beringian standstill hypothesis, “which for a long time has been the dominant explanation for how people initially peopled the Americas,” says Raff. This scenario says that the ancestors of Native Americans diverged from other East Asians at a time when ice was smothering the Northern Hemisphere. That left them stranded and isolated for millennia somewhere outside the Americas, for their eastward movements were blocked by a giant ice sheet that covered much of North America. Only when that sheet started melting, around 15,000 years ago, could they start migrating down the west coast of the Americas.

Xach’itee’aanenh T’eede Gaay’s genome anchors this narrative in time, suggesting that the millennia-long pit stop took place between 14,000 and 22,000 years ago. It doesn’t, however, say where those early peoples stood still.

In one scenario, they paused in Beringia itself and split into two lineages there. One, the Ancient Beringians, stayed put. The other eventually made it further east and south and gave rise to the other Native Americans. If that’s right, “there was just a single migration of people from Asia who peopled the New World,” says Connie Mulligan from the University of Florida. She and others have found further evidence for that idea, but “this study provides the final piece needed to prove there was only a single migration,” she says.

But Potter prefers an alternative scenario in which the standstill took place further back in northeast Asia, and the Ancient Beringians split from other Native Americans there. Both groups then independently traveled into Beringia and subsequently into the Americas, perhaps by different routes or perhaps at different times.