CU study – Bering Land Bridge long-term habitat for earliest Americans
Feb. 27, 2014
John Hoffecker
A new study led by CU-Boulder strengthens the theory that the first
Americans, believed to have migrated over the Bering Land Bridge from Asia,
may have settled in the region instead of quickly migrating into the Americas
as other theories have suggested.
The theory, known as the “Beringian Standstill,” was first proposed in
1997 and refined in 2007 by a team led by the University of Illinois who
sampled mitochondrial DNA from more than 600 Native Americans.
According to CU-Boulder Research Associate John Hoffecker, lead
author of the study, they found that mutations in the DNA indicated a group
of their direct ancestors from Siberia was likely isolated for thousands of years
in the land bridge region.
CUT 1 “What the genetics show is that most Native Americans, other than the
most recent arrivals that live in North America such as the Eskimo, the Inuit,
the Aleuts and Athabaskans, diverged from their Asian source populations at
a much earlier time than we had thought based on the age of the earliest
archaeological sites in North and South America. (:23) Therefore it becomes
important to explain this genetic divergence through this ‘Beringia Standstill’
model.” (:30)
Beringia was a large landmass that stretched between present day
Alaska and Siberia during the last ice age around 20,000 to 30,000 years ago
when oceans were 400 feet lower due to water frozen in massive glaciers and
ice sheets.
Hoffecker says for years archaeologists never considered that region as
a place where humans could have survived the last ice age -- that is until they
started to pay attention to studies conducted by ecologists and geneticists
indicating the climate there was much more habitable than they thought.
CUT 2 “It seemed to us that Beringia would be the last place on Earth where
you would have a large population surviving during the coldest period of the
last glacial. (:08) What has happened here is that a geneticist, an archaeologist
and an ecologist got together and came to the conclusion that the ecological
data fit this hypothesis very nicely. The environment in central Beringia seems
to have been much wetter, characterized by more tundra-type communities of
vegetation. It probably included some woody shrubs and also a few trees.
And wood may have been the key to human survival.” (:35)
The key to survival because prehistoric people living in northern
regions during the last ice age burned large mammal bones for fuel and they
needed wood to create fires hot enough to ignite the bones.
CUT 3 “We know from experimental studies that bone burns very hot and fast
and if you are going to be burning a lot of bone, in order to make practical
as a fuel, you need to supplement it with at least a little wood. (13) And sure
enough when we look at the archaeology of people’s living in areas where
wood was scarce we find heavy use of bone but always find a little wood in
there.” (:22)
It is believed that the population of the group numbered a few
thousand and that they were very diverse by the time they migrated south
from Beringia into the Americas.
CUT 4 “The geneticists are telling us that the population was fairly large.
We’re talking about at least a few thousand people here. And it was a
population that was doing quite well. (:10) And the genetics show that the
genetic diversity of the population was actually increasing during this period
of isolation. And we now have 16 identified mitochondrial maternal DNA
maternal lineages coming out of Beringia at the time people began dispersing
into North and South America.” (:28)
Hoffecker says a good example of how divergent this group had
become was the discovery of a the remains of a prehistoric man in the 1990s
called the “Kennewick Man,” found on a bank of the Columbia River in
Kennewick, Washington. Bone tests date the remains from 7300 to 7600 B.C.
CUT 5 “A few years ago we recovered some skeletal remains -- the Kennewick
Man remains. And it was noted they don’t look like modern Asians -- the
remains of a modern Asian. They look quite different. They are more sort of
generic. And I think that the ‘Beringia Standstill’ hypothesis helps explain this
apparent dilemma. (:19) The Kennewick man makes perfect sense as the
descendant of a group of people who diverged over 30,000 years ago from
the then inhabitants of Northeast Asia and not, say, 12,000 years ago.” (:32)
13,000 years ago temperatures warmed and glaciers covering much of
North America receded creating ice-free corridors that the Beringian people
used to migrated south into the Americas.
Hoffecker is a researcher with INSTARR, the Institute of Arctic and
Alpine Research at CU-Boulder.
-CU-