The genes that rewrite American pre-history
Ancient DNA reveals how the first humans arrived on the continent in one wave more than 25,000 years ago and then split into three ancestral Native American groups
The DNA of a six-week-old Native American infant who died 11,500 years ago has rewritten the history of the Americas. The young girl's genes reveal the first humans arrived on the continent 25,000 years ago - much earlier than some studies claim - before splitting into three Native American groups. This is the first time that direct genetic traces of the earliest Native Americans have been identified.
The girl belonged to a previously unknown population of ancient people in North America known as the 'Ancient Beringians.' This small Native American group resided in Alaska and died out around 6,000 years ago, researchers claim.
It is widely accepted that the earliest settlers crossed from what is now Russia into Alaska via an ancient land bridge spanning the Bering Strait which was submerged at the end of the last Ice Age.
Issues such as whether there was one founding group or several, when they arrived, and what happened next have been the subject of extensive debate. Some scientists previously hypothesised about multiple migratory waves over the land bridge as recent as 14,000 years ago. But the new study shows that this migration occurred in one wave, with sub-divisions of Native American groups forming later on. It also shows that a previously undiscovered group named the 'Ancient Beringians' formed as part of this split, taking the known number of ancestral Native American groups from two to three.
'We didn't know this population existed,' said study coauthor Professor Ben Potter, an anthropologist at the University of Alaska Fairbanks. 'These data also provide the first direct evidence of the initial founding Native American population, which sheds new light on how these early populations were migrating and settling throughout North America.'
The international team of researchers, led by scientists from the Universities of Cambridge and Copenhagen, studied the full genome of an ancient Native American infant. Named Xach'itee'aanenh t'eede gay, or Sunrise Child-girl, by the local Native community, the young girl's remains were found at the Upward Sun River archaeological site in Alaska in 2013. Although the child had lived around 11,500 years ago, long after people first arrived in the region, her genetic information did not match either of the two recognised branches of early Native Americans.
These are referred to as Northern, residing mostly in what is now Alaska and Canada, and Southern, residing mostly in what is now the United States. The girl appeared to have belonged to an entirely distinct Native American population, which they called Ancient Beringians. Further analyses showed the group were separated from the same founding population as the Northern and Southern Native American groups, but that they separated from that population earlier in its his tory.
'The Ancient Beringians diversified from other Native Americans before any ancient or living Native American population sequenced to date,' said study lead author Professor Eske Willerslev, from the University of Cambridge. '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 study compared data from the Upward Sun River remains with both ancient genomes, and those of numerous present-day populations. According to the researchers' timeline, the ancestral Native American population first emerged as a separate group around 36,000 years ago in northeast Asia.
Constant contact with Asian populations continued until around 25,000 years ago, when the gene flow between the two groups ceased. This cessation was probably caused by brutal changes in the climate, which isolated the Native American ancestors. At this point the group likely began crossing to Alaska via an ancient land bridge spanning the Bering Strait which was submerged at the end of the last Ice Age.
Then, about 20,000 years ago, that group split into two lineages: The Ancient Beringians and the ancestors of all other Native Americans. The newly discovered group continued to breed with their Native American cousins at least until the Upward Sun River girl was born in Alaska around 8,500 years later. (© Daily Mail, London)