The DNA of a Siberian boy who died 24,000 years ago has revealed that he is closely related to modern Native Americans, but that his ancestors lived in Europe or western Asia.
The consensus view was that the ancestors of Native Americans mainly originated in East Asia. As the ice sheets covering the Northern Hemisphere began to retreat around 16,000 years ago, some migrated by navigating the coastlines from East Asia into the Americas. Others came via the Beringia land bridge which, exposed by lower sea levels, joined present-day Siberia and Alaska and stretched for several hundred miles into both the East Asian and North American continents.
Previous DNA studies of living Native Americans have strongly supported their East Asian ancestry. It had been generally assumed that where admixed western Eurasian genetic signatures did exist, they come from colonial times when European settlers mixed with the indigenous population.
However, ancient DNA from the arm bone of a 4 year-old boy who lived by Siberia’s BelayaRiver is causing a re-think. His grave was discovered by Russian archaeologists near the village of Mal’ta in the 1920s, and was found adorned with flint tools, pendants, and a sprinkling of ochre. Geneticist Eske Willerslev of the University of Copenhagen radiocarbon dated the bone sample and used it to sequence the boy’s genome – the oldest complete genome of a modern human sequenced to date.
Willerslev’s team found that a portion of the boy’s genome is shared only by modern Native Americans and no other groups. In fact, nearly all indigenous people from North and South America were equally related to the Mal’ta boy, indicating that he represented very deep Native American roots. Yet his Y chromosome belongs to haplogroup R and his mitochondrial DNA to haplogroup U, found almost exclusively in populations living west of the Altai Mountains. The boy’s genome showed no connection to modern East Asians.
“This was kind of puzzling at first,” said Willerslev, but could be explained by a simple scenario: some time before 24,000 years ago, the ancestors of Native Americans and the ancestors of today’s East Asians split into distinct groups. The Mal’ta boy was part of a population of Native American ancestors who moved into Siberia from Europe or west Asia. Some time after the Mal’ta boy died, his population mixed with the East Asians. This admixed population then made its way to the Americas.
Consequently, said Willerslev, “his DNA shows close ties to those of today’s Native Americans – yet he apparently descended not from East Asians, but from people who had lived in Europe or western Asia. The finding suggests that about a third of the ancestry of today’s Native Americans can be traced to western Eurasia. The west Eurasian signatures that we very often find in today’s Native Americans don’t all come from postcolonial admixture. Some of them are ancient.”
Willerslev said his team will now concentrate on sequencing the genomes of ancient skeletons “further west.”
Source: Science Magazine