Genetic
analysis of a baby girl who died at the end of the last ice age shows she
belonged to a previously unknown ancient group of Native Americans
An illustration
of the Upward Sun River camp in what is now Interior Alaska. Illustration:
Illustration by Eric S. Carlson in collaboration with Ben A. Potter
Ian
Sample Science editor
Wed 3 Jan
‘18 18.00 GMT Last modified on Thu 4 Jan ‘18 00.10 GMT
A baby
girl who lived and died in what is now Alaska at the end of the last ice age
belonged to a previously unknown group of ancient Native Americans, according to DNA recovered from
her bones.
The
child, a mere six weeks old when she died, was found in a burial pit next to
the remains of a stillborn baby, perhaps a first cousin, during excavations of
an 11,500-year-old residential camp in Tanana River Valley in Central Alaska.
The remains were discovered in 2013, but a full genetic analysis has not been
possible until now.
Researchers
tried to recover ancient DNA from both of the infants but succeeded only in the
case of the larger individual. They had expected her genetic material to
resemble modern northern or southern lineages of Native Americans, but found
instead that she had a distinct genetic makeup that made her a member of a
separate population.
The
newly-discovered group, named “ancient Beringians”, appears to have split off
from the founding population of Native Americans about 20,000 years ago. While
the ancestors of other Native Americans pushed south into the continent as the
ice caps thawed, the ancient Beringians remained in the north until they
eventually died out.
“This is
a new population of Native Americans,” said Eske Willerslev, an evolutionary
geneticist at the University of Copenhagen, whose team recovered the girl’s DNA
from a dense part of her skull known as the petrous bone. Details of the work
are published in Nature.
Working
with scientists at the University of Alaska and elsewhere, Willerslev compared
the genetic makeup of the baby, named Xach’itee’aanenh t’eede gaay or
“sunrise child-girl” by the local community, with genomes from other ancient
and modern people. They found that nearly half of the girl’s DNA came from the
ancient north Eurasians who lived in what is now Siberia. The rest of her
genetic makeup was a roughly even mix of DNA now carried by the northern and
southern Native Americans.
Using
evolutionary models, the researchers showed that the ancestors of the first
Native Americans started to emerge as a distinct population about 35,000 years
ago, probably in north-east Asia. About 25,000 years ago, this group mixed and
bred with ancient north Eurasians in the region, the descendants of whom went
on to become the first Native Americans to settle the New World.
During
the last ice age, so much water was locked up in the ice caps that a land bridge reached from Asia to North America across
what is now the Bering Strait. Willerslev believes the ancestors of Native
Americans travelled to the continent in a single wave of migration more than
20,000 years ago. Those who settled in the north became the isolated ancient
Beringians, he said, while those who moved south, around or through the ice
sheets, split into the north and south Native Americans about 15,700 years ago.
But there
is another possibility. Ben Potter, an archaeologist on the team from the
University of Alaska in Fairbanks, suspects that the Beringians split from the
ancestors of other Native Americans in Asia before both groups made their way
across the land bridge to North America in separate migrations. “The support
for this scenario is pretty strong,” he said. “We have no evidence of people in
the Beringia region 20,000 years ago.”
The
families who lived at the ancient camp may have spent months there, Potter
said. Excavations at the site, known as Upward Sun River, have revealed at
least three tent structures that would have provided shelter. The two babies
were found in a burial pit beneath a hearth where families cooked salmon caught
in the local river. The cremated remains of a third child, who died at
the age of three, were found on top of the hearth at the abandoned camp.
Connie
Mulligan, an anthropologist at the University of Florida, said the findings
pointed to a single migration of people from Asia to the New World, but said
other questions remained. “How did people move so quickly to the southernmost
point of South America and settle two continents that span a huge climatic and
geographic range?” she said.
David
Reich, a geneticist at Harvard University, said the work boosted the case for a
single migration into Alaska, but did not rule out alternatives involving
multiple waves of migration. He added that he was unconvinced that the ancient
Beringian group split from the ancestors of other Native Americans 20,000 years
ago, because even tiny errors in scientists’ data can lead to radically
different split times for evolutionary lineages. “While the 19,000-21,000 year
date would have important implications if true and may very well be right, I am
not convinced that there is compelling evidence that the initial split date is that
old,” he said.
Source:
theguardian
No comments:
Post a Comment