Ancient infant helps scientists unravel America's genetic history
PARIS - AFP
A baby girl who died in Alaska some 11,500 years ago belonged to a formerly-unknown population group whose discovery has shed light on the peopling of the Americas, a study of her genome revealed on Jan. 3.
By decoding the child's genetic fingerprint, scientists could look back on the history of the first people to conquer the New World, and conclude they likely arrived from Siberia some 20,000 years ago.
"The study provides the first direct genomic evidence that all Native American ancestry can be traced back to the same source population during the last Ice Age," researcher Ben Potter of the University of Alaska said.
Potter and a team analyzed the DNA of an infant whose remains were unearthed at the Upward Sun River archaeological site in Alaska in 2013.
She was named Xach'itee'aanenh T'eede Gaay (Sunrise Girlchild) by the indigenous community, and her genome "provided an unprecedented window into the history of her people", said Potter. The team had expected the girl's genetic profile to match that of known Native American groups. Instead, it showed she belonged to a completely new group, which they named Ancient Beringians.
"Prior to this study, we did not know that this Ancient Beringian population existed," said Potter.
Critically, the girl's genome also revealed the identity of a common ancestor her people shared with Native Americans.
This common forebear or "source population," which the team dubbed Ancestral Native Americans, emerged some 36,000 years ago in what is Russia today, splitting from East Asians, whose progeny include the Han Chinese.
The common ancestor stuck around on the Asian continent for several thousand years, with genetic evidence that it interbred with its East Asian cousins.
This likely stopped due to "brutal changes in the climate" at the height of the last Ice Age, which may have isolated the ancestral group.
Around 20,000 years ago, it split into two groups, one of them the Ancient Beringians, the gene data showed.
This was about the same time that the first people started moving into America via the so-called Bering Land Bridge -- then an expanse of dry land between Alaska and Siberia which was submerged at the end of the last Ice Age, some 18,000 years ago, when glaciers melted and sea levels rose.
What is still not sure is whether the common ancestor group was the first to make the crossing, splitting only thereafter, or whether the Beringians and their cousins' group made the journey to America together.
But the study does narrow the timeframe for the great migration, and said it was unlikely to have happened in several waves.
"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," said study leader Eske Willerslev of the University of Cambridge.
"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."
While Ancient Beringians appear to have stayed in the north of the Americas, its cousin group split into two Native American sub-groups between 17,000 and 14,000 years ago and spread throughout the continent, the scientists found.
These were the ancestors of most of the indigenous populations of the Americas.