28 FEBRUARY 2014 VOL 343 SCIENCE www.sciencemag.org 962
32,000 years BP
Swift peopling of the Americas
14,400 years BP
and isolation until about
15,000 years BP
12,600 years BP
Coastline during last glacial
of miles away. Back in 2007, for example,
researchers led by molecular anthropologist Erika Tamm of the Estonian Biocentre
in Tartu analyzed mitochondrial DNA from
601 Native Americans and 3764 Asians
from geographically diverse populations.
The team identified three subclades—C1b,
C1c, and C1d—that were widely distributed in Native American groups, but absent
in Asians. This pattern, plus a chronology
based on mutation rates, strongly suggested
that the ancestors of the first Americans
were isolated from their Asian kin some
25,000 years ago, diversifying into the
C subclades before they entered the Americas some 15,000 years ago.
After analyzing how the genetic signals are distributed geographically, Tamm
and her colleagues concluded that the most
likely place for this isolation was Beringia.
If the ancestors of the Native Americans
toughed it out there during the LGM, they
would have been well positioned to swiftly
people the New World when the cold period
ended. Several other analyses of mitochondrial and nuclear DNA have supported this
“Beringian standstill” model.
Archaeological evidence for this
scenario remains scarce, but some clues
come from the Yana RHS locality at 71°N
latitude in Beringia’s far west in Siberia.
This locality, the earliest known in Beringia
at 32,000 years old, brimmed with carved
ivory ornaments and bone tools such as sewing needles (Science, 2 January 2004, p. 52),
suggesting a culture well adapted to life in
the Arctic interior. Yana’s broad-based hunters and foragers appear to have brought down
diverse game including steppe bison, reindeer, horses, polar foxes, and birds.
After Yana, the
archaeological record in
Given the spotty archaeological record,
most archaeologists remained skeptical that
people occupied northern Beringia throughout the brutally cold LGM. Most of the region
escaped glaciation because of its largely arid
climate, but winters averaged about 8°C
colder than today. “Beringia seemed the last
place on Earth that you would put a large population during one of the coldest periods in
history,” says archaeologist John Hoffecker of
the University of Colorado, Boulder.
In search of new clues, a team led by
molecular biologists Meirav Meiri of Tel Aviv
University and Ian Barnes of the Natural His-
tory Museum in London examined another
Asian immigrant that passed through Berin-
gia on its way to the New World: the elk, or
wapiti (Cervus elaphus canadensis). Previ-
ous studies had suggested that these temper-
ate and boreal forest dwellers first appeared
in Alaska about 15,000 years ago, roughly the
same time that humans seem to have arrived.
Meiri and Barnes hypothesized that as tem-
peratures rose, the elk swiftly barreled across
Beringia and into the Americas.
To test the idea, they collected 113 bone,
antler, and teeth samples from ancient elk in
museums and 74 specimens from modern elk
across North America and Asia. After dat-
ing and sequencing most of the samples, they
found what Barnes calls an “astonishing”
picture, very different from what they had
expected, as reported in the 7 February issue
of the Proceedings of the Royal Society B.
The radiocarbon dates and locality data
indicate that elk had pushed into northwest-
ern Beringia by at least 50,000 years ago,
but didn’t advance into North America until
15,200 years ago. Barnes and colleagues
were so surprised that they analyzed
hydrogen and oxygen isotopes from
the Siberian specimens to double-
check the locality data supplied by
the museums. (The water and food the
elk ingested influenced the isotopes in
their bones, and can be used to trace
the latitude where the animals lived.)
The results confirmed the samples’
Arctic origins. The researchers also
used DNA data to estimate elk popu-
lation size, which apparently declined
during the LGM. But there was no
sign that the population had been
wiped out and later replaced.
If the elk stood still in Beringia, perhaps
humans did, too. The elk data suggest that
humans could have been present in north-
western Beringia “much earlier and longer
than we thought,” Barnes says. Elk and
humans may have migrated into the Americas
together, he adds. Some of the oldest known
artifacts in North America—13,000-year-
old rods buried with Clovis tools and human
Light my fire. Woody plants in Beringia’s shrub tundra may
have supplied firewood and tools for humans.
Standing still. One model suggests that people and
game were isolated in Beringia for thousands of years
before migrating to the Americas.