In this August 2013 photo provided by the University of Alaska, excavators work at the Upward Sun River discovery site in Alaska. According to a report released on Wednesday, Jan. 3, 2018, DNA from an infant who died in Alaska some 11,500 years ago, found at this site, is giving scientists the best look yet at the genetics of the ancestors of today’s native peoples of the Americas. (Ben Potter/University of Alaska via AP)

The two infants were buried at Upward Sun River in what we now call Alaska some 11,500 years ago.

One of the little skeletons, of a baby girl, held DNA for millennia that has now pointed to a new understanding of how the Americas were settled. Those genes show a single human population who crossed the Bering Strait around 20,000 years ago, and then gradually settled southward across the entirety of the Western Hemisphere, reports a team led by the University of Cambridge in the journal Nature.

“Our findings support a long-term genetic structure in ancestral Native Americans, consistent with the Beringian ‘standstill model,’” the study authors write. “Our findings further suggest that the far-northern North American presence of northern Native Americans is from a back migration that replaced or absorbed the initial founding population of Ancient Beringians.”

That little girl – who was unearthed in 2013 and has been dubbed Xach’itee’aanenh t’eede gay (Sunrise Girl Child) – showed that shew as part of a population heretofore unknown in the prehistoric annals within native genes.

That other native population has now been called the Ancient Beringians, a group that did not venture far into the Western Hemisphere, unlike other groups, which have generally been split into “northern” and “southern” lineages.

But all three – the Ancient Beringians, northern and southern peoples – all share a common ancestor who first traveled to Alaska over the frozen Bering Strait in the late Pleistocene, the analysis shows.

“Using demographic modeling, we infer that the Ancient Beringian population and ancestors of other Native Americans descended from a single founding population that initially split from East Asians around (36,000 years ago), with gene flow persisting until around (25,000) years ago,” the authors write.

The infant’s DNA seems to triangulate a common history that explains the branches of the peoples who would cover America for millennia before the conquest by Europeans, they add.

“We were able to show that people probably entered Alaska before 20,000 years ago,” said Eske Willerslev, leader of the team, from Cambridge and the University of Copenhagen. “It’s the first time that we have had direct genomic evidence that all Native Americans can be traced back to one source population, via a single-founding migration event.”

"It would be difficult to overstate the importance of this newly revealed people to our understanding of how ancient populations came to inhabit the Americas," said Ben Potter, anthropologist at the at the University of Alaska Fairbanks, and one of the authors. "This new information will allow us a more accurate picture of Native American prehistory. It is markedly more complex than we thought."

The findings further elucidate theories by other scientific teams. For instance, a University of Utah study of both of the child skeletons from Upward Sun River found that there were descendants common in many groups like the Navajo, the Pima, Zuni, Anasazi, and even the extinct Tainos of Puerto Rico, as described in a paper in the Proceedings of the National Academy of Sciences. But another paper in Nature in July 2015 by David Reich and a team at Harvard found that there were multiple migrations from Asia.