Out of Africa or not

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Out of Africa (or not)

• The incredibly complex and mostly true story of
  the origin and dispersal of Homo sapiens
  throughout the World.

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There are currently two competing theories of the
origin of anatomically modern Homo sapiens
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• The Replacement model, which states that there
  was a single origin for Homo sapiens (in Africa),
  and these anatomically modern humans subsequently
  radiated out from Africa and replaced other
  species of Homo as they came in contact with them
  throughout Europe and Asia.

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• The Regional Continuity model, which states that
  modern Homo sapiens developed from regional
  populations of archaic Homo sapiens populations
  that in turn evolved from regional populations of
  Homo erectus.

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• The replacement model of Christopher Stringer
  and Peter Andrews proposes that modern humans
  evolved from archaic Homo sapiens 200,000-100,000
  years ago in Africa and then some of them
  migrated into the rest of the Old World replacing
  all of the Neanderthals and other late archaic
  Homo sapiens.   If this interpretation of the
  fossil record is correct, all modern people share
  relatively modern African ancestry.  All other
  lines of humans that had descended from Homo
  erectus presumably became extinct.  From this
  view, the regional anatomical differences that we
  see among humans today are recent
  developments--evolving only in the last
  50,000-40,000 years.  This hypothesis is also
  referred to as the out of Africa and the Noah's
  ark model.

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The regional continuity (or multiregional) model
of Milford Wolpoff at the University of Michigan
proposes that modern humans evolved more or less
simultaneously in all major regions of the Old
World from local archaic Homo sapiens
populations.  For example, modern Chinese are
seen as having evolved from Chinese archaic Homo
sapiens and ultimately from Chinese Homo
erectus.  This would mean that the Chinese and
some other peoples in the Old World have great
antiquity in place.  Advocates of this model
believe that the ultimate common ancestor of all
humans was Homo erectus in Africa more than a
million years ago.  Since then, however, it is
proposed that there was sufficient gene flow
between Europe, Africa, and Asia to prevent
reproductive isolation and the subsequent
evolution of distinct regional species. 
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Regional Continuity Model
Replacement Model
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• Obviously, whether you believe in one theory or
  the other has a great impact on the question of
  early dispersal and migration of Homo sapiens.
• The replacement model necessitates long distance
  dispersal and migration and adaptation to new
  environments, and the multi-regional model
  suggests in situ development and adaptation over
  a longer period of time.

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• The following figure is a family tree for the
  phylogenetic Class Primates. Although somewhat
  out of date, it does give an idea of the
  closeness of genetic relationships among the
  different families and the approximate timing of
  their divergence from the trunk of the primate
  family tree. Although there is at least one big
  problem with this particular diagram that might
  cause a skeptic to question the veracity of the
  whole thing.
• See if you can spot the
  problem

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(Hominidea)
(Hominoidea)
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Showing Modern humans as different branches is
not accurate--were all the same species
Yikes!
12
Dispersal corridors opened out of Africa and
across the Middle East into South and East Asia
during the late Pliocene. Corridors formed
primarily along coastal land masses, the product
of expanding polar ice caps and resultant drop in
sea-level. Incipient development of the Red Sea
rift also established departure routes through
the Middle East. The drop in sea level in island
Southeast Asia would have connected Sumatra, Java
and Borneo with the mainland. Evolutionary
analysis of fossil species indicates that large
mammals dispersed along these routes sporadically
during the late Pliocene and early Pleistocene.
New fossil finds suggest that early Homo arrived
in Asia some 1.8 to 1.9 million years ago, after
departing Africa at least 100,000 years earlier.
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Hominids now known as Homo erectus  were found on
Java, Indonesia, in 1891, and at Zhoukoudian,
near Beijing, in the 1930s. As Homo erectus  was
clearly more primitive than hominid fossils known
in Europe, human beings were initially thought to
have emerged in East Asia and dispersed westward.
Since the early 1960s, numerous fossils from
African localities in the eastern Rift Valley,
Lake Malawi and South Africa have demonstrated an
African emergence for Homo . In the 1990s,
advances in dating methods and new finds at
Dmanisi (Georgia), Riwat and Pabbi Hills
(Pakistan), Sangrian and Mojokerto (Java) and
Longgupo (China) show that early Homo  had
arrived in East Asia by just after 2 million
years ago. The following map shows dispersal
corridors that would have been available due to
lowered sea level in the at the
Pliocene-Pleistocene boundary.
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• According to the Replacement Model, there is
  little question that Homo sapiens emerged in
  Africa, although the date of emergence, the
  technological associations and the dates for its
  Eurasian dispersals are debatable. Homo sapiens
  originated between 200,000 and 100,000 years ago,
  somewhere in sub-Saharan Africa. Some recent
  discoveries in Zaire of ancient and finely
  crafted tool types (such as barbed-bone harpoons)
  indicate that the technology associated with this
  emergence may have been very advanced indeed,
  resembling the much later Upper Paleolithic of
  Europe. In the Levant, where Homo sapiens is
  evident about 90,000 years ago, a more archaic
  Middle Paleolithic technology still held sway.
  Consequently, we may not yet say whether the
  European dispersal of Homo sapiens was associated
  with either its emergence or a new technology.

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Genetic Evidence for the Replacement Model

• Mitochondrial DNA
• Y chromosomal DNA

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Mitochondrial DNA

• Mitochondrial DNA offers a quick-ticking
  molecular clock and by comparing the number of
  mutations that have collected in separate
  populations, geneticists can infer when the
  populations split from each other.
• When selected sequences of mtDNA from a group of
  people representing African, Asian, Australian,
  Caucasian and New Guinean ethnic groups were
  compared, 133 variants of mtDNA were found. When
  these different mitochondrial types were arranged
  into an evolutionary tree, that tree showed a
  trunk splitting into two major branches.

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Mitochondrial DNA

• One branch consisted only of Africans, the other
  included some modern Africans and some people
  from everywhere else. The first branch represents
  the first modern humans and forms the trunk and
  longest branch of the tree. The second branch
  represents a subgroup of modern humans that left
  Africa and later spread out to the rest of the
  world.

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Mitochondrial DNA

• It was also found that all of the mtDNA (even
  from far regions of the world) was similar. This
  suggested that the molecular clock has not been
  ticking long enough to accumulate appreciable
  differences in our DNA. In other words, our
  species is young.
• But the African samples had the most mutations.
  This too implied that the African lineage is the
  oldest, that all modern humans trace their roots
  back to Africa.

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Map illustrating the timing of the migration of
anatomically modern Homo sapiens out of Africa,
based on mtDNA evidence.
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Y chromosomal DNA

• An international study of Y chromosomal DNA shows
  that East Asian populations migrated out of
  Africa and suggests that little or no
  interbreeding of Homo erectus and Homo sapiens
  occurred after the migration.The goal of the
  study was to test the hypothesis that the common
  origin of human populations is in Africa, and
  also to see if there was evidence of archaic
  admixture of Homo erectus and Homo sapiens.

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Y chromosomal DNA

• The researchers tested 12,127 male individuals
  from 163 East Asian populations. The Y chromosome
  was used because it remains the same when passed
  from father to son. The Y chromosome is was
  examined because it does not recombine, and so a
  lot more evolutionary information is available
  than is found in mitochondrial DNA. Researchers
  from China, Indonesia, England and the U.S.
  collected samples, genotyped the Y chromosomes
  and analyzed the results. They looked for
  specific mutations at three locations on the Y
  chromosome and found that every one of the 12,127
  samples typed, carried one of these three
  polymorphisms.

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Y chromosomal DNA

• These three markers can be used to test the
  completeness of the replacement of modern humans
  of African origin in East Asia, because finding a
  male not carrying one of the three polymorphisms
  would be indicative of a potential ancient origin
  and possibly leading to the rejection of complete
  replacement.This result indicates that modern
  humans of African origin completely replaced
  earlier populations in East Africa.

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• In linking the early dispersal of early Homo with
  its emergence, we are describing a hominid very
  different from the australopithecines, whose
  bipedal but still ape-like anatomy must have
  limited them to wooded locales. Thus the
  significance of an early dispersal to Asia is
  manifold. First, the climatic conditions of cool
  aridity that played a great role in the emergence
  of Homo itself also drew hominid populations out
  of Africa and into Asia. Emergence and dispersal
  are, to a great extent, a product of
  environmental change.

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• Nevertheless, early Homo emerged with a radical,
  yet still generalized, set of characteristics
  that granted it ecological hegemony across the
  subtropical Old World. An early intercontinental
  distribution signifies a hominid not adapted to
  specific territorial conditions, but adapted to
  manage many local conditions through physical
  presence, technology and flexible social
  organization. Ironically, as the first species to
  use technology, early Homo colonized much of the
  subtropical Old World without the benefit of
  language, symbolic culture or individual
  consciousness as we know it.

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Critiques of the Replacement Model

• Critics of this genetic argument say that the
  rate of mutation is not necessarily constant and
  that there were flaws in the computer program
  that was used to construct the human family
  trees for instance, the results of the study
  varied with the order in which the data were
  entered.  Further genetic studies carried out
  since the mid 1990's have both supported and
  undermined an African origin for modern humans. 
  John Relethford, of the State University of New
  York College at Oneonta, has pointed out that
  Africa could have had the greatest diversity in
  mtDNA simply because there were more people
  living there during the last several hundred
  thousand years. 

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Critiques of the Replacement Model

• Researchers from the University of Chicago and
  Yale University have discovered that variations
  in the DNA of the Y chromosome and chromosome 12
  have the greatest diversity among Africans.  This
  is consistent with the replacement model. 
  However, geneticists from Oxford University have
  found that the human betaglobin gene is widely
  distributed in Asia but not in Africa.  Since
  this gene is thought to have originated more than
  200,000 years ago, it undercuts the claim that an
  African population of Homo sapiens sapiens
  replaced East Asian archaic Homo sapiens.

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The Regional Continuity Model

• Fossil evidence is used to support the regional
  continuity model.  Its advocates claim that there
  has been a continuity of some anatomical traits
  from archaic Homo sapiens to modern humans in
  Europe and Asia.  In other words, the Asian and
  European physical characteristics have antiquity
  in these regions going back over 100,000 years. 
  They point to the fact that many Europeans have
  relatively heavy brow ridges reminiscent of
  Neandertals.  Similarly, it is claimed that
  Chinese facial characteristics can be seen in
  Asian archaic Homo sapiens dating to 200,000
  years ago.  Like Homo erectus, East Asians today
  commonly have shovel-shaped incisors while
  Africans and Europeans rarely do.  This supports
  the contention of direct genetic links between
  Asian Homo erectus and modern Asians. 

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The Regional Continuity Model

• Alan Thorne of the Australian National University
  believes that Australian aborigines share key
  skeletal and dental traits with people who
  inhabited Indonesia at least 100,000 years ago. 
  The implication is that there was no replacement
  by modern humans from Africa 60,000-50,000 years
  ago.  However, the evidence does not rule out
  gene flow from African populations to Europe and
  Asia at that time and before.  David Frayer of
  the University of Kansas believes that a number
  of European fossils from the last 50,000 years
  have characteristics that are the result of
  archaic and modern Homo sapiens interbreeding.

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The Regional Continuity Model

• Part of the mitochondrial DNA was extracted
  recently from the bones of a 60,000 year old
  modern Homo sapiens skeleton found in 1974 on the
  shores of Lake Mungo in Southeastern Australia. 
  This is the oldest DNA that has been extracted
  from a human so far.  Comparison of this DNA with
  that of nine other ancient Australian skeletons,
  2 Neanderthals, and 3,453 contemporary people
  from around the world indicates that "Mungo Man"
  had a unique genetic marker.  This indicates that
  a now lost genetic line of modern Homo sapiens
  existed in Australia prior to the arrival of
  later Australian Aborigines.  This evidence
  provides significant support for rejecting the
  "out of Africa" complete replacement model of
  modern Homo sapiens evolution.

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The Regional Continuity Model

• Alan Templeton, a geneticist at Washington
  University, has reported that a new computer
  based analysis of 10 different human DNA
  sequences indicate that there has been
  interbreeding between people living in Asia,
  Europe, and Africa for at least 600,000 years. 
  These data suggest that the complete replacement
  model of Homo sapiens origin is incorrect. 
  According to Templeton, "humans expanded again
  and again out of Africa, but these expansions
  resulted in interbreeding, not replacement, and
  thereby strengthened the genetic ties between
  human populations throughout the world."  This
  view is gaining support among paleoanthropologists
  , but critics say that Templeton's sample is
  still too small to be conclusive.

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Expansion Out of the Old World 
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Expansion Out of the Old World 
The world population of modern Homo sapiens began
to grow rapidly after 50,000-40,000 years ago. 
It was around this time they expanded their
territory by migrating into new regions.   Their
movement into northern areas coincided with the
end of a long cold period that had begun about
75,000 years ago.  By 60,000 years ago, modern
humans apparently moved into Australia for the
first time.  Around 35,000-30,000 years ago, they
moved into Northeastern Siberia. 
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Expansion Out of the Old World 
Possibly as early as 30,000 years ago and
certainly by 11,500 years ago, they migrated into
North America via the Bering Land Bridge (or
Beringia ).  That intercontinental land
connection appeared between Siberia and Alaska as
a result of sea levels dropping more than 300
feet during the last ice age.  Until that time,
all human evolution had occurred in the Old
World.  The rate of human population growth has
continued to accelerate until now.  The current
world population is over six billion and
intercontinental migration and gene flow are at
higher levels than ever before.
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Expansion Out of the Old World 
A tragic consequence of human migrations into new
regions of the world has been the extinction of
many animal species indigenous to those areas. 
By 11,000 years ago, human hunters in the New
World apparently had wiped out 135 species of
mammals, including 3/4 of the larger ones.  Most
of these extinctions apparently occurred within a
few hundred years.  It is likely that the
changing climate at the end of the last ice age
was also a contributing factor. 
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Expansion Out of the Old World 
However, the same cannot be said for the animal
extinctions that occurred following the arrival
of aboriginal people in Australia and Polynesians
in New Zealand.  In both cases, humans were
instrumental in wiping out easily hunted
species.  Vulnerable marsupials were the main
victims in Australia.  In New Zealand, it was
mostly large flightless birds that were driven to
extinction by hunters. 
The Moa, a very large and apparently quite tasty
flightless bird. It became extinct within
centuries of the Polynesian arrival in New Zealand
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Of course, the ultimate destruction of all giant
flightless birds in New Zealand made this island
nation safe for naked bungee jumping.
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The Peopling of the New World
Early theories regarding the peopling of the New
World were based on the concept of Clovis
First, which stated that the first culture to
enter the New World were big game hunters of the
Clovis tradition, which first appears in the
archaeological record in North America in the
last part of the Pleistocene at around 11,600
years ago. Clovis hunters were thought to have
crossed into North America from northeast Asia
across a land bridge, which was a broad area of
land up to a thousand miles wide that connected
Siberia and Alaska. This land bridge, called
Beringia, was exposed when sea levels were lower
during the last glacial period of the Pleistocene
and the shallow floor of the Bering sea was
exposed.
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The Peopling of the New World
According to the this theory, groups of people
that were culturally adaptated to the cold
environments of northeast Asia would have
followed the herds of the large mammals (like
mammoth) that they relied on for the majority of
their subsistence. As these herds moved across
Beringia, groups of hunters and their families
would have followed them into the New World.
This was a slow process that could have taken
generations to accomplish. The migration to the
New World was not a conscious decision, but a
natural consequence of subsistence.
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Studies of pollen, fossil insects and peat from
cores taken from the floor of the Bering Sea
indicate that Beringia was covered with tundra
similar to that found in the arctic areas of
modern Alaska, and dates from peat indicate that
at least parts of the bridge were above water as
recently as 11,000 years ago.
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Archaeologists excavating the remains of a
mammoth bone hut in the Ukraine. Huts of this
sort have been found in eastern Europe and Asia
and predate the Clovis culture, but they are a
good example of the sorts of cold environment
adaptations that Clovis ancestors would have
possessed.
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The superstructure of bones would have been
covered with mammoth hide.
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The Peopling of the New World
Once across Beringia, the ancestors of the Clovis
hunters could occupy an ice-free area in what is
now Alaska. How did these people get down into
the lower part of North America? Geological
evidence suggests that as the glaciers began to
recede at the end of the Pleistocene, an ice-free
corridor opened up between the Laurentide ice
sheet on the east and the Cordilleran ice sheet
on the west. This corridor is supposedly how the
Clovis people migrated south.
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Map of Beringia showing the ice free area of
Alaska and the migration route (in red) through
the ice-free corridor between the Laurentide and
Cordilleran ice sheets in North America. The
exposed continental shelf is in light green.
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The Peopling of the New World
The journey through the ice-free corridor was
possible, though, only before 21,000 years ago
and after 12,000 years ago. At about 21,000 to
19,000 years ago the Cordilleran Ice Sheet and
Laurentide Ice Sheet coalesced thereby blocking
the corridor and preventing passage. Although
glacial ice retreated and the corridor re-opened
about 18,000 years ago, the landscape was
forbidding, a cold, semi-arid steppe with scant
precipitation and only 10-25 percent of the land
bearing sparse grass and sagebrush. Until about
12,000 years ago, such harsh climate, sparse
vegetation, and minimal fauna probably would not
have sustained human population.
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The Peopling of the New World
An alternative to the ice-free corridor was first
suggested by archaeologist Knut Fladmark.
Fladmark hypothesized that travel would have been
much more rapid by boat along the coast of the
exposed continental shelf. Confirmation of this
hypothesis is difficult, because the
archaeological sites that would document the
journey are now under 80 meters or more of water.
However, there are other pieces of evidence that
may support this model. For instance, the
distribution of native American languages had
their greatest clustering and distinctiveness
along the West Coast, suggesting a longer period
of time to diversify, compared to languages in
the interior.
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The Peopling of the New World
The coastal resources of northeastern Asia are
very similar to those of northwest North America,
and once people had adapted to hunting and
gathering these resources, moving along that
coastline would have been easy. It would not
require much invention of new technologies or
adaptation to drastically different climates,
even in the course of a migration of thousands of
kilometers. The possibility that the colonizers
used boats during their entry into the New World
has also been proposed.
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The Peopling of the New World
It would have been much easier and safer for
sizable groups of migrating people, including
children, pregnant women and the elderly, to move
along the coast by boat. Also, the environment
along the coast would have provided many more
resources (i.e.. shellfish) that could have been
gathered by all members of the group. By
contrast, inland groups slogging across the
tundra through the ice-free corridor would be
dependent on the few adult, male big-game hunters
in their band. During the best of times
resources other than large game would not have
been abundant.
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The Peopling of the New World
Using boats would have aided greatly in the speed
and safety of the coastal journey. Early use of
boats has been demonstrated--boats would have
been necessary for the colonization of
Australia,which occurred 60,000 years ago, and
there is also evidence of possible Homo erectus
use of some sort of water craft to colonize
islands that would not have been otherwise
accessible. So it isnt a stretch to suppose
that the technology was available to the
colonizers of the New World. Colonization by
boat has another advantage as a mode of
colonization. It does not require an ice-free
corridor or a completely ice free continental
shelf, and so could have occurred any time over
the last 60,000 years.
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Strong yet flexible skin boats that could carry
more than 40 people is a technology found among
the ancient, northern sea peoples of Europe, Asia
and North America.
Eskimo skin boats
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The Peopling of the New World
It has also been proposed, based on technological
similarities in lithic technology that the origin
of the Clovis culture is due to settlement in
North America by people of the Upper Paleolithic
Solutrean culture (21,000-16,500 B.P.) of
southern France and the Iberian Peninsula. These
first settlers were participating in a
hypothesized Paleo-Arctic Maritime Tradition,
whose economy was based on the hunting of large
marine mammals and fishing from hide covered
boats along the glacial ice margin in the north
Atlantic.
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A comparison of Solutrean and Clovis flaking
techniques- the outre passé flake. .
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The Peopling of the New World
Some of these sailors eventually worked their way
over to the New World and settled in what is now
the southeastern U.S., where the concentration
of Clovis sites is greatest and where the oldest
Clovis sites are located. Needless to say, there
is contentious debate associated with this theory.
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Other Evidence for the Colonization of the New
World

• Dental Morphology
• Linguistics
• Mitochondrial DNA
• Other Genetic Data

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Other Evidence

• Synthesis of linguistic, dental and genetic data
  suggest three migrations from Asia to America,
  with each wave leading to a separate linguistic
  group. Dental variation is greater in the north,
  and that there are three Native American dental
  (and parallel linguistic) clusters, Na-Dene,
  Aleut-Eskimo, and Amerind (Paleoamericans). The
  Aleut-Eskimo is the most recent, the Na-Dene
  (Athabaskan) the next oldest, and the Amerind the
  oldest.

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Other Evidence

• There are limitations to mtDNA studies, such as
  the fact that molecular divergence can precede
  population divergence. When molecules in the
  mtDNA chain diverge, it only reflects when a
  populations genetic composition diverges, but
  does not necessarily coincide with when a
  population became genetically isolated. Mutations
  evidenced today may predate divergence, and
  statistical change may be due more to population
  dynamics than temporal depth.

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Other Evidence

• That said, most of the statistical measures
  based on models for mtDNA mutation rate
  assumptions suggest that the Amerindian
  colonization of the New World occurred between
  nineteen and seventy-eight thousand years ago.
  This by itself should suggest that the Clovis
  First theory for the peopling of the New World
  doesnt hold water. But when the growing body of
  archaeological evidence indicating greater time
  depth of occupation is added to the mix, then
  debate of whether the New World was occupied
  during pre-Clovis times becomes moot.

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Antiquity of New World Archaeological Sites

• Pedra Furada, Brazil 32,000 B.P.
• Meadowcroft Rockshelter, Pennsylvania 16,200
  B.P.
• Topper, South Carolina 16,000 B.P.
• Cactus Hill, Virginia 15,070 B.P.
• Monte Verde, Chile 14,500 B.P.

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Monte Verde projectile points and a wood foreshaft
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Human footprint from the 14,500 B.P. level at the
Monte Verde site
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Until 1997 no site was widely accepted as
pre-dating the Clovis culture (11,000 to 11,500
radiocarbon years before present). That year, a
blue-ribbon commission of Paleoindian specialists
visited Monte Verde, a site in Chile with dates
averaging 12,500, and declared it to be valid.
Other possible pre-Clovis sites include Hebior
and Schaefer, Cactus Hill, and Topper.
Meadowcroft and Pedra Furada have also been
proposed as pre-Clovis. Additional early sites
include Taima-Taima, Pedra Pintada, Santa Barbara
in the Channel Islands, Quebrada Tacahuay, and
Quebrada Jaguay. (Map by Joe LeMonnier).
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Other Evidence

• By various measurements of genetic distance, New
  World populations have more similarities to east
  Asian populations that they do to other
  populations around the world (no real surprise).
  However, there are some intriguing differences
  between the populations. Native Siberians lack
  one peculiar mtDNA mutation that appeared in the
  Amerinds 6,000 to 10,000 years ago. This
  particular mutation pattern is also found in
  aboriginal populations in Southeast Asia and in
  the islands of Melanesia and Polynesia. This
  suggests contact between these populations, but
  how? The route by which this gene found its way
  into the population is unknown. It either came
  across the Pacific to Central and South America
  or up the east coast of Asia and across the
  northern Pacific to Alaska and Canada.

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Other Evidence

• There are also genetic similarities between New
  World populations and the indigenous Ainu of
  Japan, which exhibit more genetic similarities to
  European populations than to other Japanese or
  mainland Asian populations (shades of Kenniwick
  Man). These similarities have been interpreted
  variously as either representing a common origin
  for these two populations (more likely) or a
  Jomon fishing boat that was blown off course (not
  so much).
• There are even some investigators that have
  suggested contact with Africa, based on the
  cranial morphology of a skeletal population from
  an archaeological site in Brazil (!).

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Other Evidence

• The one thing that should become obvious from
  the above discussion, is that deducing the timing
  and nature of migration and diffusion is never a
  clean cut process. The theories about the origin
  of Homo sapiens and the subsequent radiation of
  the species is still a topic that is debated, and
  as the above evidence demonstrates, it is
  unlikely that any long-term migration is the
  product of a unilinear process. Several
  different groups have colonized the The New World
  over time and contributed their genes to the
  populations that lived here, and it is just as
  likely that many other groups arrived over time
  and perished without contributing to the genetic
  makeup of the population.

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Hypothesized prehistoric migration routes into
the New World, including the ice-free corridor,
the coastal route, the Solutrean entry, and the
Polynesian and Australian mariners.
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Weve looked at human migration at a global
scale, lets examine a case of human migration on
a smaller scale.
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So, What Happened Once People Arrived in the New
World?

• Well, they didnt just spread out, settle down
  and stay put for the next 15,000 years, THATS
  for sure.

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A Late Prehistoric Example of Migration in North
AmericaThe Numic Expansion
Which offers problems no less complex or less
hotly debated than those cited for the migration
scenarios discussed above.
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The Numic Expansion
The Numa are several groups of people that speak
related languages of the Uto-Aztecan Family,
which arrived in the southern Sierra
Nevada-Mohave Desert area from northern Mexico
approximately 5000 years ago. This area
(southwestern or central Great Basin) is
considered to be the ancestral Numic homeland. It
is from here that the Numic groups expanded north
and east into the Rocky Mountains, Basin and
Range and Northern Plains regions.
The Great Basin
77
The Numic Expansion
The Numa can be divided into three groups based
on language the western group consisting of the
Mono and Northern Paiute, the Central group that
contains the Panamint, Western, Northern and
Eastern Shoshone, and the Southern group, which
consists of the Kawaiisu, Chemehuevi, Southern
Paiute and Ute. The environment of the Numa
homeland is particularly arid and harsh, and
traditional economies have always been based on
highly mobile hunting and gathering.
78
Traditional Paiute and Shoshone lifeways in the
Great Basin.
79
The modern distribution of Numic-speaking peoples
in western North America
80
There has been considerable debate in the
archaeological community concerning the place of
origin and timing of the migration of the Numa
throughout the West. Most archaeologists (but
not all) agree that the likely Numa homeland was
in either the southwestern or central Great
Basin. There are also several schools of thought
regarding the timing of the expansion out of this
homeland. These can be roughly divided into the
early and late schools. There is less agreement
on why the expansion occurred and who the people
were that the Numa replaced as they expanded.
81
Some archaeologists believe that the expansion
out of the Numic homeland occurred soon after the
arrival of the Uto-Aztecans from Mexico. This
would have occurred just after a mid-Holocene
climatic arid episode formerly known as the
Altithermal.
82
Numic speakers would have come into contact with
other hunter-gatherer groups, and it is unknown
if they replaced these peoples or intermixed with
them. Regardless, in this scenario the Middle
and Late Archaic populations throughout the
Intermountain West would have been Numic in
makeup.
83
Other archaeologists believe that the expansion
occurred much later, at around 1000 B.P. This
would have been well into the Late Prehistoric
period, and it would have brought the Numa into
contact with sedentary Horticultural cultures.
84
This later expansion has some support from
archaeological data, especially in the
documentation of the entry of the Ute and
southern Paiute in the southern area. This later
expansion makes sense for several reasons.
85

• The big question is, how did the Numa expand
  relatively rapidly into an area that was already
  inhabited? There are theories that invoke an
  adaptation that was more efficient than that
  possessed by the native populations that were
  replaced, but they do not address the problem of
  differences in population density. As was
  pointed out above, the Mohave Desert and the
  Great Basin as a whole are harsh environments,
  and historically supported native population
  densities lower than anywhere in North America
  other than the Arctic.
• How could a relatively small population with low
  density push into areas with larger, denser
  populations?

86

• Data suggest that there were significant and
  precipitous decreases in population throughout
  western North America starting approximately A.D.
  850 and continuing through the Anasazi
  abandonment of the Four Corners region in the
  late 13th century. This depopulation may have
  been associated with climatic deterioration and
  increased frequency of drought prior to A.D.
  1200, and elsewhere has been correlated with the
  Medieval Climatic Anomaly. Depopulation would
  have set the scene for a rapid radiation of a
  relatively small group of people that were
  pre-adapted to harsh environments.
• Now that we have examined the nature of
  population dynamics on very large and moderately
  large scales, lets examine the nature of
  population dynamics on a smaller regional scale.

87
Population Dynamics of Prehistoric
HunterGatherer Groups in Eastern Colorado
88
Recognition of a Regional PatternPeaks in Late
Prehistoric Radiocarbon Age Frequency

• Platte River Basin (1300-1200 BP).
• Arkansas River Basin (1100-1000 BP).
• Northern Colorado River Basin ( 1300-1200 BP).
• Wyoming (1200-1000 BP).

89
From Gilmore et. al. (1999)
90
Platte Basin Radiocarbon Ages
Adapted from Gilmore et. al. (1999)
91
Arkansas Basin Radiocarbon Ages
Adapted from Zier and Kalasz 1999
92
Northern Colorado River Basin
From Reed and Metcalf (1999)
93
Wyoming
From Frison (1993)
94
Platte Basin Curve Peaks 1300-1200 B.P.
Arkansas Basin Curve Peaks 1100-1000 B.P.
95
The Data Set
96
Distribution of archaeological sites and
isolated finds in the Platte and Arkansas River
Basins (N17,812)
97
Distribution of sites with radiocarbon ages
between 3000 and 100 BP
98
Distribution of archaeological sites with
associated radiocarbon ages 3000-100 BP C-14
ages n621 Components n534
99

• If changes in the number of radiocarbon dates
  are accepted as representing changes in relative
  population, then it is also reasonable to assume
  that changes in the spatial distribution of these
  dated occupations represents changes in the
  spatial distribution of population.

100
Geographic Mean Centers for Archaeological Sites
by Cultural Period
This shows the progress south and east of the
geographic mean centers of sites assigned to
cultural periods by temporally diagnostic
artifacts.
Middle Archaic (5000-3000 BP)
Early Ceramic (1850-800 BP)
Middle Ceramic ( 800-400 BP)
Late Archaic (3000-1850 BP)
All Middle Ceramic Cultures
Apishapa Phase (900-500 BP)
101
Geographic Mean Centers for Archaeological Sites
by Century, 2500100 BP
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Period of Relative Stability
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Population shifts south
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128
Significance?

• Difference of means tests comparing the locations
  (UTM northings and eastings) of the set of all
  stable sites (2400-1200 BP) to the locations of
  the set of all sites falling within the
  hypothesized period of population movement south
  (1200-500 BP)
• are significant at p.05

129
Significance?

• Not only is the movement south significant, but
  the movement from west to east is also
  significant.
• What does this mean?

130
Are we looking at Population Movement, or
Differential Rates of Natural Increase?
131
Probably Some of Both
132

• As the climate gradually became warmer and wetter
  between A.D. 1 and 900, two things apparently
  happened. The Plains became more productive
  plants were more abundant and more productive,
  and so animals were also more abundant. People
  spent more of their time at lower elevations,
  because the resources that the mountains could
  provide were not as critical as they had been.
  And human population increased.

133

• As you can see from the following radiocarbon
  frequency curves, population apparently began to
  decrease first in the mountains between about
  1600 to 1300 BP (top), followed by the Foothills
  at 1300 (middle), and then finally on the Plains
  at 850 BP. Based on the slope of the respective
  curves, the drop in population was more gradual
  in the mountains (900 years), more rapid in the
  Foothills (500 years), and precipitous on the
  Plains (300 years). This may indicate a
  relatively rapid out migration from the Plains,
  where the more gradual drops in the mountains and
  Foothills suggests a decrease in the frequency
  and duration of visits.

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135

• After about A.D. 900, population begins to drop
  precipitously, perhaps in response to a return to
  more arid conditions. Instead of returning to a
  pattern where the resources in the mountains
  became more important relative to decreasing
  resources on the Plains, population also
  decreases in the mountains. This is a pattern
  that is apparently reflected across much of the
  west.

136

• One possible explanation is that this dry period
  was not hot and dry, but cold and dry. This
  might explain why both the plains and the
  mountains were apparently abandoned at the same
  time. It was too dry on the Plains, which which
  resulted in decreased resource availability, and
  in the mountains it was too cold, which also
  resulted in decreased resources.
• There wasnt anywhere to go that was productive
  enough to support the population that had
  increased in size and density over the past 900
  years.

137

• A measure of the relative mobility of
  prehistoric people called the the Component
  Complexity Index (CCI) can help to determine if
  there was movement from the Platte basin to the
  Arkansas basin as a response to climate change.
• A higher aggregate CCI for all the sites in a
  region during a particular century suggests a
  combination of longer occupations, and/or
  increased frequency of visits and/or more people
  occupying sites during occupations dated to that
  century.

138

• In contrast, a lower aggregate Component
  Complexity Index for a region during a particular
  time is indicative of greater residential
  mobility and possibly smaller populations and/or
  lower population densities.

139
Component Complexity Index
140

• Although the peaks in the component curves are
  offset by 200 years between the Platte and
  Arkansas basins, the Component Complexity Index
  curves are concordant, suggesting that even
  though population was fluctuating, the relative
  mobility of the populations in both places was
  following the same trends at the same time.

141

• There is a trough in both CCI curves between 1250
  and 950 BP, which corresponds to the period
  between the peak in radiocarbon frequency in the
  Platte basin at 1300-1200 BP and the peak in the
  Arkansas at 1100-1000 BP. This indication of
  greater mobility in both basins during a period
  of decreasing population in the Platte and
  increasing population in the Arkansas could
  represent migration from north to south.

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143
The peaks and subsequent decreases in radiocarbon
age frequency occur hundreds of years prior to
the onset of the Pacific climatic episode
(850-400 BP), which is thought to have
contributed to dry conditions in eastern
Colorado. The Pacific episode would have been a
likely culprit for contributing to population
movement and decline.
144
In fact, the peaks and subsequent decline in both
basins occurs in the middle of the Neo-Atlantic
episode (1260-850), which is hypothesized to have
been a period of greater summer precipitation and
higher carrying capacity.
145
Component Frequency Curves and Paleoclimatic
Episodes
146

• The drop in population in both the Platte and
  Arkansas basins does, however, correspond to the
  onset of the Medieval Climate Anomaly (remember?)
  mentioned above. The decrease in population in
  eastern Colorado also correlates to the drop in
  populations throughout the region and west into
  the Colorado Plateau, the Great Basin and
  California.

147

• Introduction of new technologies such as the bow
  and arrow and ceramics to the prehistoric
  inhabitants of eastern Colorado in the first few
  centuries A.D. may have enhanced already
  established trends in prehistoric population
  growth by contributing to the more efficient
  exploitation of food resources.

148

• The onset of dryer conditions associated with the
  Pacific paleoclimatic episode that occurred after
  850 BP almost certainly contributed to already
  established trends of population decrease. The
  introduction of epidemic disease by Europeans
  some five to seven hundred years after population
  begins to decrease also undoubtedly contributed
  significantly to further decline in population.

149

• Changes in subsistence, technology, economy and
  climate all contributed to prehistoric population
  dynamics during the past 3000 years
• But

150

• The mechanisms providing the initial impetus
  that resulted in almost exponential growth in
  proxy population starting at around 2200 BP and
  the equally precipitous decrease in population
  that occurred after about 1200-1000 BP in eastern
  Colorado still remain a mystery.

151
Conclusions
152

• If the radiocarbon age and component frequency
  curves are accepted as a proxy for general
  population trends, and the spatial distributions
  of radiocarbon ages represent the spatial
  distributions of prehistoric people, what are the
  implications?

153

• There is a dramatic increase in population in
  the region and beyond starting at approximately
  2200 BP and peaking at approximately 1200-1000
  BP.

154

• There is an equally dramatic decrease in
  population in the region that begins at
  approximately 1000 BP, or 500 years prior to
  European contact and the introduction of epidemic
  European diseases.

155

• There is evidence that prehistoric population
  change in eastern Colorado can be partially
  explained by migration.

156
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