(CN) – Genetic evidence from recently analyzed fossils reveals how and when people who were among the first to arrive in North America came to the continent.
The report, published Wednesday in the journal Nature, offers insight into the migration of the continent’s earliest settlers, which has been the subject of extensive debate among scientists.
The findings suggest that Native Americans entered North America in a single migratory wave perhaps more than 20,000 years ago.
For the study, researchers sequenced the entire genome of an infant named Xach’itee’aanenh t’eede gay, or Sunrise Child-girl, whose remains were discovered at the Upward Sun River archaeological site in Alaska in 2013.
The team was surprised to find that despite living around 11,500 years ago, the child’s genetic information did not match either of the two known populations of early Native Americans called Northern and Southern. Instead, she appears to have been part of a distinct Native American population that academics have named the “Ancient Beringians.”
Further examination then showed the Ancient Beringians were an offshoot of the same lineage as the Northern and Southern Native American groups. The newly discovered group separated from that population earlier in its history.
This timeline enabled the researchers to develop a framework of how and when the continent might have been settled by a common population of ancestral Native Americans that gradually separated into these sub-groupings.
“The Ancient Beringians diversified from other Native Americans before any ancient or living Native American population sequenced to date,” said lead author Eske Willerslev, an evolutionary geneticist at the University of Copenhagen in Denmark. “It's basically a relict population of an ancestral group which was common to all Native Americans, so the sequenced genetic data gave us enormous potential in terms of answering questions relating to the early peopling of the Americas.
“We were able to show that people probably entered Alaska before 20,000 years ago. 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.”
The researchers compared data from the Sunrise Child-girl’s remains with ancient genomes and those of several present-day populations. This allowed the team to determine that the Ancient Beringians were more closely related to early Native Americans than their Asian and Eurasian ancestors, and established the exact nature of that relationship and how they separated into distinct populations over time.
The existence of the Northern and Southern branches of early Native Americans has previously sparked debate over how the continent was first populated: whether the groups split after humans arrived in Alaska or whether they represent different migrations.
The Upward Sun River genome reveals Ancient Beringians were isolated from the common Native American population before the Northern and Southern divide and after the ancestral source group separated from others in Asia. The team believes this shows there was likely only one wave of migration into the Americas, with population subdivisions developing thereafter.
"One significant aspect of this research is that some people have claimed the presence of humans in the Americas dates back earlier – to 30,000 years, 40,000 years, or even more," Willerslev added.
"We cannot prove that those claims are not true, but what we are saying, is that if they are correct, they could not possibly have been the direct ancestors to contemporary Native Americans."
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