Unexpected discovery
European arrival to América about 24,000 years ago
Oldest human genome
reveals less of an East Asian ancestry than thought.
Native Americans may
have a more complicated heritage than previously believed.
Nearly one-third of
Native American genes come from west Eurasian people linked to the Middle East
and Europe, rather than entirely from East Asians as previously thought,
according to a newly sequenced genome.
Based on the arm bone
of a 24,000-year-old Siberian youth, the research could uncover new origins for
America's indigenous peoples, as well as stir up fresh debate on Native
American identities, experts say.
The study authors
believe the new study could also help resolve some long-standing puzzles on the
peopling of the New World, which include genetic oddities and archaeological
inconsistencies. (Explore an atlas
of the human journey.)
"These results
were a great surprise to us," said study co-author and ancient-DNA
specialistEske
Willerslev, of the University of Copenhagen, Denmark.
"I hadn't expected
anything like this. A genome related to present-day western Eurasian
populations and modern Native Americans as well was really puzzling in the
beginning. How could this happen?"
So what's new?
The arm bone of a
three-year-old boy from the Mal'ta site near the shores of Lake
Baikal in south-central Siberia (map) yielded what may be the oldest
genome of modern humans ever sequenced.
DNA from the remains
revealed genes found today in western Eurasians in the Middle East and Europe,
as well as other aspects unique to Native Americans, but no evidence of any
relation to modern East Asians. (Related: "Is
This Russian Landscape the Birthplace of Native Americans?")
A second individual
genome sequenced from material found at the site and dated to 17,000 years ago
revealed a similar genetic structure.
It also provided
evidence that humans occupied this region of Siberia throughout the entire
brutally cold period of the Last Glacial Maximum, which ended about 13,000
years ago.
Why is it important?
Prevailing theories
suggest that Native Americans are descended from a group of East Asians who
crossed the Bering Sea via a land bridge perhaps 16,500 years ago, though some
sites may evidence an earlier arrival. (See "Siberian,
Native American Languages Linked—A First [2008].")
"This study
changes this idea because it shows that a significant minority of Native
American ancestry actually derives not from East Asia but from a people related
to present-day western Eurasians," Willerslev said.
"It's approximately
one-third of the genome, and that is a lot," he added. "So in that
regard I think it's changing quite a bit of the history."
While the land bridge
still formed the gateway to America, the study now portrays Native Americans as
a group derived from the meeting of two different populations, one ancestral to
East Asians and the other related to western Eurasians, explained Willerslev,
whose research was published in the November 20 edition of the journal Nature.
"The meeting of
those two groups is what formed Native Americans as we know them." (Learn
more about National Geographic's Genographic Project.)
What does this mean?
Willerslev believes the
discovery provides simpler and more likely explanations to long-standing
controversies related to the peopling of the Americas.
"Although we know
that North Americans are related to East Asians, it's striking that no
contemporary East Asian populations really resemble Native Americans," he
said.
"It's not like you
can say that they are really closely related to Japanese, Chinese, or Koreans,
so there seems to be something missing. But this result makes a lot of sense
regarding why they don't fit so well genetically with contemporary East
Asians—because one-third of their genome is derived from another
population."
The findings could also
allow reinterpretation of archaeological and anthropological evidence, like the
famed Kennewick Man,
whose remains don't look much like modern-day Native American or East Asian
populations, according to some interpretations.
"Maybe, if he
looks like something else, it's because a third of his ancestry isn't coming
from East Asia but from something like the western Eurasians." (Read about
history's greatmigration
mysteries.)
What's next?
Many questions remain
unanswered, including where and when the mixing of west Eurasian and East Asian
populations occurred.
"It could have
been somewhere in Siberia or potentially in the New World," Willerslev
said.
"I think it's much
more likely that it occurred in the Old World. But the only way to address that
question would be to sequence more ancient skeletons of Native Americans and
also Siberians."
Intriguing questions
also exist about the nature of the advanced Upper Paleolithic Mal'ta society
that now appears to figure in Native American genomes.
The Siberian child
"was found buried with all kinds of cultural items, including Venus
figurines, which have been found from Lake Baikal west all the way to Europe.
"So now we know
that the individual represented with this culture is a western Eurasian, even
though he was found very far east. It's an interesting question how closely
related this individual might have been to the individuals carving these
figurines at the same time in Europe and elsewhere."
By Brian Handwerk
National Geographic
22/11/2013
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