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http://www.newscientist.com/ns/981017/americans.html
[Archive: 17 October 1998]
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Young Americans
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Illustration: John Millar
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Europeans may have roamed the New World thousands of years before the Santa
Maria made land. Roger Lewin describes a radical rethink of how the
Americas were settled. WHEN Colombus "discovered" the Americas half a
millennium ago, it was a profound shock for European intellectuals. As well
as redrawing their maps of the world, they were forced to reassess their
place in it. And native Americans were equally stunned by the unexpected
arrival of people from unknown shores. Both groups struggled to adapt their
world view to incorporate the other's existence, often through wild
speculation and mythology. This century, anthropologists wondering when and
how the first humans set foot on the vast continent, came up with a more
prosaic explanation. Diverse as Native Americans are, they all seemed to
originate from eastern Asia. Their pioneering ancestors supposedly arrived
in the New World little more than 11 300 years ago on foot, in three waves
of migration over the Bering land bridge that used to link Siberia with
Alaska. Evidence for this view started accumulating in the 1920s and went
unchallenged for decades. But anthropologists have now been forced to
reassess their ideas. "We are in the middle of a paradigm in the process of
shifting," says Richard Jantz, an anthropologist at the University of
Tennessee at Knoxville. Driving this shift is a confection of evidence,
including powerful new genetic data and dogged analysis of a once highly
controversial palaeoindian settlement in South America. And there are
tantalising hints in the anatomy of a 9300-year-old skeleton that was found
in Oregon two years ago. "We are looking at a much more complex scenario
emerging," says Jantz. The picture is of the first settlers reaching the
Americas at least 25 000 years ago. It seems likely that people arrived by
boat as well as on foot, and, most intriguing of all, east Asians may have
had European companions on the virgin continent. Early this century,
anthropological dogma had it that the New World had been inhabited for only
a short time, perhaps a couple of millennia, and by technologically naive
foragers. But a discovery in 1927 at Folsom, New Mexico, exploded that view.
A stone projectile point was found embedded between the ribs of a bison that
had become extinct at the end of the last ice age, 10 000 years ago. Five
years later, archaeologists working in a gravel pit near the town of Clovis,
again in New Mexico, unearthed more primitive stone points, this time
alongside the bones of mammoths. The image of the first Americans as simple
foragers quickly gave way to one of a people who were big game hunters par
excellence, sweeping down from Alaska to the far reaches of South America,
leaving a trail of carnage as they went. When radiocarbon dating showed that
these colonisers arrived more than 11 000 years ago, when the Earth was
still in the frigid grip of an ice age, the image of a heroic, pioneering
people was further enhanced. A way through the ice As it has turned out,
big game hunting was only one of the ways that palaeoindians got by. Some
were simple foragers. However, they did indeed have to struggle with the
challenge of making their way from the Old World to the New while much of
North America was buried under ice sheets almost two kilometres thick. For
periods from 75 000 to 10 000 years ago, during the last throes of the
Pleistocene ice age, the oceans were at least 50 metres lower than they are
today, low enough to expose the Bering land bridge. Nevertheless, this
wasn't a continuous green light for entry into the Americas, because the
fluctuating size of the eastern and western ice sheets of North America left
only two windows of opportunity for safe passage through an ice-free
corridor between them: before 20 000 and after 12 000 years ago. The age of
the many Clovis sites--all clustering around 11 000 years--encouraged the
widespread conviction that the first Americans had entered through the
second window. And the paradigm for the event was "Clovis first". However,
this paradigm did not discourage a blizzard of claims for archaeological
sites predating Clovis, some by as much as 200 000 years. But, as David
Meltzer, of Southern Methodist University, Dallas, pointed out recently, "Of
the scores of pre-Clovis archaeological finds made in the last sixty years,
none so far has withstood the harsh glare of critical scrutiny." The claims
have been rejected on various grounds including erroneously old dates and
naturally shaped stones mistaken as human handiwork. "So many pre-Clovis
claims have failed that the archaeological community grew sceptical of any
and all pre-Clovis claims," says Meltzer. Until Monte Verde, that is.
Between 1977 and 1985, Thomas Dillehay of the University of Kentucky led an
excavation of a palaeoindian site at Monte Verde in southern Chile. His team
found that about thirty people had lived on the sandy bank of a small creek,
where they erected hide shelters and lived mainly by foraging. They ate
roots, stems, fruits and nuts, many of which are still used by the local
Mapuche people today, as food, drink and medicine. Animal bones large and
small, including those of mastodons, testify to the Monte Verde group's
taste for meat. Stone points and grinding stones, digging sticks and bola
stones (still used by technologically primitive people today to disable
small animals) yield a hint of the settlers' technology. Most poignant of
all is the print of a child's foot near a hearth. The Monte Verde site is
well preserved because soon after its people left, the site was covered by
water and fibrous peat which kept out oxygen and so slowed decay. The
richness of the site makes Monte Verde important enough, but more astounding
is the age of more than 30 samples of charcoal, wood and ivory. Radiocarbon
dating sets the time at 12 500 years, more than a thousand years earlier
than Clovis. If true, this would undermine the dominant Clovis paradigm. No
wonder Dillehay had such a hard time persuading his fellow archaeologists to
take him seriously, even after a decade of meticulously recording and
analysing the material recovered from Monte Verde. Finally, he effectively
said: "Come and see for yourself." In January last year, a team of nine
archaeologists--staunch sceptics among them--did just that, spending a week
poring over the site. Convinced by what they saw, they admitted collectively
that their scepticism had been misplaced. Dennis Stanford, an archaeologist
at the Smithsonian Institution and a member of the team, said, "It totally
changes how we think of the prehistory of America. Our models clearly are
not right." Vance Haynes of the University of Arizona, who has made it his
business to keep pre-Clovis claims honest, described Monte Verde as a
"paradigm buster". The site had clearly met the three criteria that
archaeologists demanded for accepting a pre-Clovis claim: the tools are
undeniably made by humans; the setting is undisturbed, as the occupants had
left it; and the dating is beyond criticism. Vindicated, Dillehay said, "I
knew if they would only come to the site and look at the setting and see the
artefacts they would agree that Monte Verde was pre-Clovis." Off the radar
screen So, the Clovis people were not the first Americans. Although some
researchers stick doggedly to the old theory, the widespread acceptance of
Monte Verde has led to a scramble for new scenarios. Ryk Ward, a geneticist
at the University of Oxford, warns that this enthusiasm is leading to less
than exacting standards of assessment of some of the data and to premature
conclusions. "We need to be rolling up our sleeves and collecting new data,
and be more rigorous about our analysis of existing data," he says.
Theories about the peopling of the Americas will, no doubt, get much more
complex before consensus is reached. One problem is the lack of
archaeological evidence. If the dates for the ice-free corridor are correct,
then people must have entered the Americas at least 25 000 years ago. So
where are all the signs of occupation before 11 300 years ago? Aside from a
rock shelter site near Pittsburgh, known as Meadowcroft and claimed--but not
universally accepted--to be at least 14 500 years old, there is precious
little else on the archaeological radar screen that is older than Clovis.
"It's a question of archaeological visibility," suggests Meltzer. "People
entered a virgin land, rich in resources and space, and so they probably
didn't stay in any one place very long, which is what you need to create
archaeological visible sites." It could easily have taken 10 000 years or
more before populations reached a level that would start to be detected on
the radar screen, he speculates. With the Clovis bulwark fallen, what of
the mode of entry to this new land? A little more than a decade ago,
archaeologists were all abuzz over the so-called Greenberg hypothesis. It
was named after the Stanford University linguist Joseph Greenberg, who
argued that people had entered the Americas in three waves beginning around
12 000 years ago, each giving rise to a distinct linguistic group. Two of
the linguistic groups, the Na-Dene in the northwest coastal region (with a
pocket in the southwest, the Apache and Navajo), and the Eskimo-Aleut in the
northeast coastal region, are accepted by most scholars. But Greenberg's
proposed third group, the Amerind in the rest of the continent, raised
American linguists' collective eyebrows. The languages in this putative
group are too diverse to be part of a single family, they insisted.
Greenberg stuck to his guns, as he has many times in his distinguished but
often controversial career. Then, in 1992, Douglas Wallace and his
colleagues at Emory University in Atlanta announced the results of their
analysis of mitochondrial DNA from living Native Americans. Mitochondria are
the cells' energy factories and contain many copies of a circular piece of
DNA. Using enzymes to cut the DNA at certain specific sequence sites, the
researchers found four distinct types, or lineages, of mitochondrial DNA,
which they called A, B, C and D. These lineages are also found in Asian
populations, but not in Europeans or Africans, thus supporting the theory of
native Americans having an ancestral link to Asia. Moreover, Wallace and
his colleagues found that all four lineages exist in populations of
Amerindian people, but in the Na-Dene only A is present, while in the
Eskimo-Aleut people only A and D appear. This distribution of mitochondrial
lineages is consistent with Greenberg's proposal of three waves of
migration. By counting the differences in sequences between Asian and
American lineages, and using a generally accepted rate at which mutations
accumulate, the Emory team came up with times of entry for the three groups:
25 000 years for the Amerind and about 12 000 years for the Na-Dene and the
Eskimo-Aleut. Linguistic clues The Emory dates fit nicely with the
estimated times of the two ice-free corridors, but for the Amerind,
Wallace's date was roughly twice as early as Greenberg proposed. Just
recently, another linguist, Johanna Nichols at the University of California,
Berkeley, calculated that the time of first entry must be as ancient as
Wallace says, based on the estimated amount of time required to produce the
diversity of languages present in the Americas, a technique known as
glottochronology. Greenberg disagrees, and sticks with his original
calculation. However, with the acceptance of Monte Verde's age there is now
no theoretical block to the earlier dates. This relatively simple picture
has grown more complicated over the past few years, as more data on
mitochondrial DNA have flowed in from genetics laboratories in the US and
Europe. More mitochondrial lineages have turned up, and all four major
types--A, B, C and D--have been found in people from all three linguistic
groups, although lineages B, C and D are rare in the Na-Dene as are B and C
in the Eskimo-Aleut. Andrew Merriwether of the University of Michigan
interprets these new data as indicating a single migration, rather than
three. According to Merriwether, a single wave of genetically diverse
people entered Alaska about 25 000 years ago, probably as "a trickle of
people over a period of a thousand years or so". Some of these people headed
south, forming what Greenberg calls the Amerind family, while others
remained in isolated patches in the north. This latter group must have been
living in a gruelling environment surrounded by glaciers, Merriwether
suggests. As a result, their numbers shrank. However, isolated populations
persisted for thousands of years, finally bouncing back and migrating to
(mainly) northern regions. Their reduced genetic diversity would have
produced the skewed distribution of their mitochondrial lineages. Wallace
disagrees. He suggests that the existence of low frequencies of lineages B,
C and D in the Na-Dene, and B and C in the Eskimo-Aleut, are the result of
the later interbreeding of these people with Amerinds. One line of evidence
he invokes to support this view is that lineage A in the Na-Dene is only
9500 years old while in the Amerind population it is close to 30 000 years.
"If the Na-Dene and the Amerind people descended from the same population,
the A lineages would be the same age," he says. The latest mitochondrial
DNA data from the Emory team, to be published later this year, has produced
the biggest surprise: a putative link between Native Americans and
Europeans. A few years ago Wallace and his colleagues found a new
mitochondrial lineage in Amerindians in the Central Great Lakes region in
North America, which they called X. The same lineage is present, at low
frequency, in European populations, but is absent in Asian populations.
"Initially we thought X was present in Native Americans as a result of
interbreeding between them and Europeans, post-Columbus," says Wallace. "But
that turned out not to be the case." If such interbreeding had occurred
then other European lineages should be present, not just X. But data from
Wallace's own lab and from that of Antoni Torroni at the University of Rome
showed that there were no other European lineages, which implies that X has
been present in Native Americans from the beginning. That implication was
strengthened last year when Anne Stone of the University of Arizona found
lineage X in the tooth enamel of people in a pre-Columbian burial in
Illinois. The lineage therefore cannot have been introduced by interbreeding
after Europeans arrived in the Americas and so must have come over during an
earlier migration. Disputed bones "It looks as if a European population
moved up through Asia and was part of the wave of east Asian people who
moved across the Bering land bridge," says Wallace. This population movement
must have been occurred than 30 000 years ago if the early date for entry
into the Americas is correct. And these people evidently did not interbreed
with populations in Asia, or at least not to any great extent. There are
alternative explanations for the absence of the X lineage in Asia, such as
the possibility that it was once there but has been lost through genetic
drift. Wallace believes his interpretation is the most parsimonious,
however. A European link with Native Americans has been made before, in the
1960s, based on purported similarities between certain stone tool
technologies in France and the Clovis fluted points. Modern archaeologists
are not persuaded by this argument. The new mitochondrial data, however, are
much more persuasive. And they may cast light on the interpretation of a
skeleton found in Oregon a little more than two years ago. Known as
Kennewick Man, the skeleton was initially thought to be very modern. James
Chatters, an independent anthropologist, suggested the skeleton belonged to
a European settler from the 19th century, based on what he described as
Caucasoid features. These include a narrow skull, a light-boned face and a
receding forehead. But when the bones of Kennewick Man were dated to 9300
years ago, it was obvious that he wasn't European but a Native American. As
soon as the skeleton's age was known, it became embroiled in a political
mire that has effectively removed it from the gaze of any immediate detailed
study. The Umatilla tribe in Oregon claimed Kennewick Man to be one of their
ancestors and, under the 1990 Native American Graves Protection and
Repatriation Act, sought to rebury him. Anthropologists have been pressing
the courts to let them have an opportunity to study the skeleton before it
goes back into the ground. Last month a judge ordered that the skeleton be
moved to the Burke Museum at the University of Washington, thus brightening
the hopes that one day it will be available for study. Could Kennewick
Man's purported Caucasoid features be an anatomical manifestation of the
genetic message encoded in the mitochondrial DNA of some Native Americans?
"That's an interesting speculation," says Wallace, "but unless we can get a
small piece of tooth enamel for genetic analysis, we can never be sure."
Jantz, who has seen a cast of the skeleton, agrees that it could signal the
presence of European blood in the earliest Americans, but is cautious, as
are most anthropologists, principally because the skeleton has had so little
scientific scrutiny. One thing Jantz is certain of, however, is that
Kennewick Man underscores the high degree of anatomical variation that
existed among the earliest Americans. That variation tells you that the
settlers of the New World came from many diverse populations in the Old
World, he says. It also could include people who arrived by boat rather than
on foot. Evidence suggesting a maritime route for at least some of the first
Americans was published last month in Science, in the form of archaeological
findings from a coastal settlement in southern Peru where the people were
evidently skilled fisherfolk as much as 13 000 years ago. Their presence and
their dedication to a maritime way of life suggests that these people might
have been seafarers for a long time, rather than originally being
landlubbers who later took to the sea in search of food. But whatever this
group's history, their existence is yet another piece of evidence all
supporting the same theory: that the New World is a lot older--and its
origins more diverse--than we've been led to believe. Although this
diversity decreased over time as a result of interbreeding and extinction of
local populations, the pioneering Americans came from many homelands and not
all at one time. "All the evidence suggests that the peopling of the
Americas was much more complicated than just a few people walking across the
Bering Strait," says Jantz. Further reading: "Monte Verde and the
Pleistocene Peopling of the Americas" by David Meltzer,Science, vol 276, p
754 (1997) "Kennewick Man's Trials Continue" by Virginia Morell, Science,
vol 280, p 190 (1998) "Quebra Jaguay: early American maritimeadaptations"
by Daniel Sansweiss and others,Science, vol 281, p 1830 (1998) Graphics:
map, 63K <map1.html> map, 70K <map2.html> From New Scientist, 17 October
1998
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