Current understanding of human migration to and throughout the Americas derives from advances in four interrelated disciplines: archeology, physical anthropology, DNA analysis and linguistics. While there is general agreement that America was first settled from Asia by people who migrated across Beringia, the pattern of migration, its timing, and the place of origin in Asia of the peoples who migrated to the Americas remains unclear.
In recent years researchers have sought to use familiar tools to validate or reject established theories like Clovis first. As new discoveries come to light, past hypotheses are reevaluated and new theories constructed. The archeological evidence suggests that Paleo-Indians' first "widespread" habitation of the Americas occurred during the end of the last glacial period, or more specifically what is known as the late glacial maximum, around 16,500–13,000 years ago.
Understanding the debate
The chronology of migration models is currently divided into two general approaches. The first is the short chronology theory with the first movement beyond Alaska into the New World occurring no earlier than 15,000 – 17,000 years ago, followed by successive waves of immigrants. The second belief is the long chronology theory, which proposes that the first group of people entered the hemisphere at a much earlier date, possibly 21,000–40,000 years ago, with a much later mass secondary wave of immigrants.
One factor fueling the debate is the discontinuity of archaeological evidence between North and South America Paleo-Indian sites. A roughly uniform techno-complex pattern known as Clovis appears in North and Central American sites from at least 13,500 years ago onwards. South American sites of equal antiquity do not share the same consistency and exhibit more diverse cultural patterns. Thus, archaeologists conclude that the "Clovis-first", and Paleo-Indian time frame do not adequately explain complex lithic stage tools appearing in South America. Some theorists seek to develop a colonization model that integrates both North and South American archaeological records.
Availability of unobstructed routes for human migration southward from Beringia during the ice age (summarized)
Dates BCE Beringia "Land Bridge" Coastal Route Mackenzie Corridor
38,000-34,000 accessible (open) open closed
34,000-30,000 submerged (closed) open open
30,000-22,000 accessible (open) closed open
22,000-15,000 accessible (open) open closed
15,000 - today submerged (closed) open open
Indigenous Amerindian genetic studies indicate that the "colonizing founders" of the Americas emerged from a single-source ancestral population that evolved in isolation, likely in Beringia. Age estimates based on Y-chromosome micro-satellite place diversity of the American Haplogroup Q1a3a (Y-DNA) at around 10,000 to 15,000 years ago. This does not address if there were any previous failed colonization attempts by other genetic groups, as genetic testing can only address current population ancestral heritage.
Migrants from northeastern Asia could have walked to Alaska with relative ease when Beringia was above sea level. But traveling south from Alaska to the rest of North America may have posed significant challenges. The two main possible routes proposed south for human migration are: down the Pacific coast or by way of an interior passage (Mackenzie Corridor) along the eastern flank of the Rocky Mountains. When the Laurentide and Cordilleran ice sheets were at their maximum extent, both routes were likely impassable. The Cordilleran sheet reached across to the Pacific shore in the west, and its eastern edge abutted the Laurentide, near the present border between British Columbia and Alberta. Geological evidence suggests the Pacific coastal route was open for overland travel before 23,000 years ago and after 15,000 years ago. During the coldest millennia of the last ice age, roughly 23,000 to 19,000 years ago, lobes of glaciers hundreds of kilometers wide flowed down to the sea. Deep crevasses scarred their surfaces, making travel across them dangerous. Even if people traveled by boat—a claim for which there is currently no direct archaeological evidence as sea level rise has hidden the old coastline — the journey would have been difficult with abundant icebergs in the water. Around 15,000 to 13,000 years ago the coast was presumed ice-free. Additionally, by this time the climate had warmed, and lands were covered in grass and trees. Early Paleo-Indian groups could have readily replenished their food supplies, repaired clothing and tents, and replaced broken or lost tools.
Coastal or watercraft theories have broad implications: one being that Paleo-Indians in North America may not have been purely terrestrial big-game hunters, but instead were already adapted to maritime or semi-maritime lifestyles. Additionally, it is possible that "Beringian" (western Alaskan) groups migrated into the northern interior and coastlines only to meet their demise during the last glacial maximum, approximately 20,000 years ago,[20] leaving evidence of occupation in specific localized areas. However, they would not be considered a founding population, unless they had managed to migrate south, populate and survive the coldest part of the last ice age.
Timeline of selected archaeological, geological and genetic evidence
40,000 B.C. – 25,000 B.C.
Paleolithic people move into Beringia across the Bering Land Bridge into western Alaska.
Bison (buffalo), mammoths, and mastodons are thought to have migrated from Asia to America about this time. This would imply a land bridge between the continents that would have had a food supply.
30,000–20,000 years ago:
Mammoth bones, believed to have been chipped by humans, are found at the Yukon's Bluefish Caves and Old Crow Flats sites investigated in the 1970s and 1980s by archeologist Jacques Cinq-Mars and his team.
In 2004, Albert Goodyear of the South Carolina Institute of Archaeology and Anthropology announced that radiocarbon dating of a bit of charcoal found in the Topper Site near Allendale County, South Carolina. However, these deposits may have been made by forest fires.
(Note: The dates given for the Old Crow and Topper digs have not been completely accepted by the archaeology community.)
Ice-free corridor running north and south through Alberta and the continental glacier called Laurentide ice sheet. Introduced by geologists in the 1950s when stone tools were found in the Grimshaw, Bow River and in Lethbridge Alberta, under glacial sand and gravel are believed to be pre-glacial and therefore may indicate nomadic humans occupied the area. A child's skull found in 1961 near Taber, Alberta is believed to be one of the oldest inhabitants discovered in Alberta.
(Note: The conclusions reached in Alberta on dates have not been accepted by the entire archaeology community.)
Cambridge DNA Services estimates around 25,000 years ago humans entered the Americas. Other geneticists have variously estimated that peoples of Asia and the Americas were part of the same population from about 21,000 to 42,000 years ago.
Siberian mammoth hunters believed to have penetrated far into the Arctic where ice-free corridors north during the time are believed found. Theory first introduced by geologists in the late 1970s when core samples indicate the ice is no older than 17,000 years old.
23,000–16,500 years ago:
The Ice Age entombs the northern hemisphere in glaciers, cutting off routes from Siberia to the south.
2002 the presence of the X haplogroup was found in a small percentage of modern indigenous Americans that is known to exist in a few locations in Europe and the Middle East. Subsequent research indicated that this DNA was not the result of genetic mixing after Columbus. However, the time estimates on haplogroup X entering Americas is around 15,000 to 20,000 years ago.
Genetic evidence (2007–2009) suggests the Beringia population's first genetic diversification from Asian populations occurred. An article in the American Journal of Human Genetics states "Here we show, by using 86 complete mitochondrial genomes, that all Native American haplogroups, including haplogroup X, were part of a single founding population.
16,500–13,000 years ago:
Receding glaciers reopened an ice-free corridor through Canada between Alaska and the rest of the Americas. Massive flooding would have created large lakes covering vast areas of north America with glacial waters.
Age estimates based on Y-chromosome micro-satellite place diversity of the so called "American Haplo" Q1a3a1 at around 10,000 to 15,000 years ago
Mass extinction of large fauna begins due to climate change and perhaps hunting. The Dire Wolf, Smilodon, Cave Lion, Giant beaver, Ground sloth, Mammoth, American Mastodon, American Camel, American Equine, and American lion all become extinct by 11,000 years ago
Pre-Clovis sites uncovered from 1973 to 1978 Meadowcroft Rockshelter in Pennsylvania site indicated occupancy as early as 16,000 years ago and possibly as long as 19,000 years ago. Dates in excess of 19,000 years have been claimed for the deepest occupation layer uncovered.
pre-Clovis sites found in Monte Verde, located along Chinchihuapi Creek, in Chile. A crew of eighty people, led by Tom Dillehay of the University of Kentucky, excavated the site from 1977 to 1985. A coastal migration could explain how people arrived in Monte Verde.
2000, archaeologists say people were living at Cactus Hill, Virginia where stone tools and charcoal from a fire pit are found.
15,000–13,000 years ago:
The Taima Taima mastodon kill/butchering site in Falcon, Venezuela was first excavated by J.M. Cruxent in the 1960s and 1970s. It is one of the earliest archaeological sites that is pre-Clovis. In 1976 a broken El Jobo point (red arrow) was found inside the pubic cavity of a partially disarticulated and butchered young mastodon whose bones had been cut, with a jasper flake found near the left ulna of the animal.
Peñon women found by an ancient lake bed near Mexico City in 1959.
El Abra sites located in the valley east of the city of Zipaquirá, Colombia. First excavated by Gonzalo Correal and associates in the late 1970s and early 1980s. 3,072 pieces found indicate it was inhabited continuously for over 7,000 years.
At Paisley Caves in the Cascade Range of Oregon, archaeologists find a scattering of human coprolites, or fossil feces in 2003. The mitochondrial DNA extracted from coprolites linked the cave dwellers to two genetic groups of early Americans that arose 14,000 to 18,000 years ago. These two genetic groups were the founding Paleo-Indians and later Na-Dené migration.
13,500 – 12,000 years ago:
The Ice Age is ending, melting glaciers have raised sea levels 120 meters and submerged the land bridge between Alaska and Siberia. Geologic evidence indicates that by 11,500 years ago, the Cordilleran and Laurentide ice sheets had retreated far enough to open a habitable ice-free corridor between them. The exposed land was dry and probably restored enough to support plants and animals, which the migrating hunter-gatherer followed.
Clovis theory – People were living near Clovis, New Mexico where tools from this era were found in the 1930s. This find gave rise to the widely held "Clovis First" theory that people spread through the Americas only after the Ice Age. The Clovis culture was believed replaced by several more localized regional cultures, such as the Folsom tradition, from the time of the Younger Dryas cold climate period.
Peru coastal region inhabitants fished with nets and bone hooks, collecting seafood such as crabs and sea urchins.
12,000–10,000 years ago:
Ice age over, climate similar to present temperatures. Old migration theories believe first widespread migration in South America and subsequently a dramatic rise in population all over the Americas, introduced in the 1930s.
The Maritimes of Canada are settled by Paleo-Indians. Sites in and around Belmont, Nova Scotia have evidence indicating small seasonal hunting camps, perhaps re-visited over many generations.
Luzia Woman's skull and other bones excavated in the Lagoa Santa, Brazil area by French archaeologist Annette Laming-Emperaire in the 1970s.[52] By 2006, Lagoa Santa sites had produced no fewer than 75 well-preserved ancient skulls.
1994, University of California, Riverside anthropologist R. Erv Taylor examined seventeen of the Spirit Cave artifacts near Fallon, Nevada from the 1940s using mass spectrometry. The results indicated that a mummy was approximately 9,400–10,200 years old — older than any previously known North American mummy.
Unique markers found in DNA recovered from an Alaskan tooth were found in specific coastal tribes, and were rare in any of the other indigenous peoples in the Americas. This finding lends substantial credence to a migration theory that at least one set of early peoples moved south along the west coast of the Americas in boats.
9,000–8,000 years ago:
Remains, known as Kennewick Man, are found in 1996 on the Columbia River near Kennewick, Washington. A skull and more than 300 bones and bone fragments were found at the site, making up among the oldest, best preserved, and most complete human remains ever found in North America. Initial radiocarbon dating indicated the remains were between 7,000 and 9,500 years old. A leaf-shaped projectile found on the body was long, broad and had serrated edges, all fitting the definition of a Cascade point. This type of point is a feature of the Cascade phase, occurring in the archaeological record from roughly 6,000 to over 8,500 years ago.
1930s-1990s no major Central American archaeological sites that go back more than 9,000 years have been found. Isolated finds of stone tools in Belize, Nicaragua and Costa Rica indicates that such sites almost certainly exist. Lack of funding for exploration in the areas has postponed likely finds.
Tehuacan Valley of Mexico – people are living in rock shelters and using stone cooking pots, which were left in the center of the hearth. Maize was to be used in the same valley between 7,000–6,000 years ago.
Genetics and blood type
For more details on this topic, see Genetic history of indigenous peoples of the Americas.
Schematic illustration of maternal (mtDNA) gene-flow in and out of Beringia.
By the 1920s studies indicated that blood type O was predominated in pre-Columbian populations, with a small admixture of type A in the north. Further blood studies combining statistics and genetic research were pioneered by Luigi Cavalli-Sforza and applied to population migrations predating historical records. This led Jacob Bronowski to assert in 1973 (in The Ascent of Man) that there were at least two separate migrations: "I can see no sensible way of interpreting that but to believe that a first migration of a small, related kinship group (all of blood group O) came into America, multiplied, and spread right to the South. Then a second migration, again of small groups, this time containing either A alone or both A and O, followed them only as far as North America."
Modern Amerindian genetics studies focus primarily on Human Y-chromosome DNA haplogroups and Human mitochondrial DNA haplogroups. The genetic pattern emerging shows two very distinctive genetic episodes occurred, first with the initial peopling of the Americas, and secondly with European colonization of the Americas. The former is the determinant factor for the number of gene lineages, zygosity mutations and founding haplotypes present in today's indigenous Amerindian populations.
Genetics and blood studies indicate human settlement of the New World occurred in stages from the Bering sea coastline, with an initial layover on Beringia for the small founding population. The micro-satellite diversity and distributions of the Y lineage specific to South America indicates that certain Amerindian populations have been isolated since the initial colonization of the region. The Na-Dené, Inuit and Indigenous Alaskan populations exhibit haplogroup Q (Y-DNA) mutations, but are distinct from other indigenous Amerindians with various mtDNA and atDNA mutations. This suggests that the earliest migrants into the northern extremes of North America and Greenland derived from later migrant populations.
Land bridge theory
Shrinking of the Bering land bridge
Also known as the Bering Strait Theory or Beringia theory, the Land Bridge theory has been widely accepted since the 1930s. This model of migration into the New World proposes that people migrated from Siberia into Alaska, tracking big game animal herds. They were able to cross between the two continents by a land bridge called the Bering Land Bridge, which spanned what is now the Bering Strait, during the Wisconsin glaciation, the last major stage of the Pleistocene beginning 50,000 years ago and ending some 10,000 years ago, when ocean levels were 60 metres (200 ft) lower than today. This information is gathered using oxygen isotope records from deep-sea cores. An exposed land bridge that was at least 1,000 miles wide existed between Siberia and the western coast of Alaska. In the "short chronology" version, from the archaeological evidence gathered, it was concluded that this culture of big game hunters crossed the Bering Strait at least 12,000 years ago and could have eventually reached the southern tip of South America by 11,000 years ago.
Synopsis
At some point during the last Ice Age, about 17,000 years ago, as the ice sheets advanced and sea levels fell, people first migrated from the Eurasian landmass to the Americas. These nomadic hunters were following game herds from Siberia across what is today the Bering Strait into Alaska, and then gradually spread southward. Based upon the distribution of Amerind languages and language families, a movement of tribes along the Rocky Mountain foothills and eastward across the Great Plains to the Atlantic seaboard is assumed to have occurred at least some 13,000 to 10,000 years ago.
Clovis culture
Clovis culture and Clovis point
Map showing the approximate location of the ice-free corridor and specific Paleoindian sites (Clovis theory).
This big game-hunting culture has been labeled the Clovis culture, and is primarily identified with fluted projectile points. The culture received its name from artifacts found near Clovis, New Mexico, the first evidence of this tool complex, excavated in 1932. The Clovis culture ranged over much of North America and appeared in South America. The culture is identified by distinctive "Clovis point", a flaked flint spear-point with a notched flute by which it was inserted into a shaft; it could then be removed from the shaft for traveling. This flute is one characteristic that defines the Clovis point complex.
Dating of Clovis materials has been by association with animal bones and by the use of carbon dating methods. Recent reexaminations of Clovis materials using improved carbon-dating methods produced results of 11,050 and 10,800 radiocarbon years B.P. (before present). This evidence suggests that the culture flowered somewhat later and for a shorter period of time than previously believed. Michael R. Waters of Texas A&M University in College Station and Thomas W. Stafford Jr., proprietor of a private-sector laboratory in Lafayette, Colorado and an expert in radiocarbon dating attempted to determine the dates of the Clovis period. The heyday of Clovis technology has typically been set between 11,500 and 10,900 radiocarbon years B.P. (The radiocarbon calibration is disputed for this period, but the widely used IntCal04 calibration puts the dates at 13,300 to 12,800 calendar years B.P.). In a controversial move, Waters and Stafford conclude that no fewer than 11 of the 22 Clovis sites with radiocarbon dates are "problematic" and should be disregarded—including the type site in Clovis, New Mexico. They argue that the datable samples could have been contaminated by earlier material. This contention was received as highly controversial by many in the archaeological community.
Clovis-type artifacts seem to disappear from the archaeological record after the hypothesized Younger Dryas impact event roughly 12,900 years before the present. The effects of the event possibly caused a decline in post-Clovis human populations and shifts in culture and behavior patterns.
Problems with Clovis migration models
Significant problems arise with the Clovis migration model. If Clovis people radiated south after entering the New World and eventually reached the southern tip of South America by 11,000 years ago, this leaves only a short time span to populate the entire hemisphere.[citation needed] Another complication for the Clovis-only theory arose in 1997, when a panel of authorities inspected the Monte Verde site in Chile, concluding that the radiocarbon evidence predates Clovis sites in the North American Midwest by at least 1,000 years. This supports the theory of a primary coastal migration route that moved south along the coastline faster than those that migrated inland into the central areas of the Americas. Many excavations have uncovered evidence that subsistence patterns of early Americans included foods such as turtles, shellfish, and tubers. This is quite a change of diet from the big game mammoths, long-horn bison, horse, and camels that early Clovis hunters apparently followed east into the New World.
At the Topper archaeological site (located along the banks of the Savannah River near Allendale, South Carolina) investigated by University of South Carolina archaeologist Dr. Albert Goodyear, charcoal material recovered in association with purported human artifacts returned radiocarbon dates of up to 50,000 years BP. This would indicate the presence of humans well before the last glacial period. Nevertheless, considerable doubt over the validity of these findings has been raised by many other researchers, and the pre-Clovis Topper dates remain controversial. Charcoal could have originated from forest fires and the crude stone artifacts can actually be misinterpreted geofacts.
Pre-Clovis dates have been claimed for several sites in South America, but these early dates have yet to be verified unequivocally.
Recent discoveries of human coprolites (fossilized feces) found deeply buried in an Oregon cave indicate the presence of humans in North America as much as 1,200 years prior to the Clovis culture.
Watercraft migration theories
Earlier finds have led to a pre-Clovis culture theory encompassing different migration models with an expanded chronology to supersede the "Clovis-first" theory.
Pacific coastal models
Pacific models propose that people reached the Americas via water travel, following coastlines from northeast Asia into the Americas. Coastlines are unusually productive environments because they provide humans with access to a diverse array of plants and animals from both terrestrial and marine ecosystems. While not exclusive of land-based migrations, the Pacific 'coastal migration theory' helps explain how early colonists reached areas extremely distant from the Bering Strait region, including sites such as Monte Verde in southern Chile and Taima-Taima in western Venezuela. Two cultural components were discovered at Monte Verde near the Pacific Coast of Chile. The youngest layer is radiocarbon dated at 12,500 radiocarbon years (~14,000 cal BP) and has produced the remains of several types of seaweeds collected from coastal habitats. The older and more controversial component may date back as far as 33,000 years, but few scholars currently accept this very early component.
Other coastal models, dealing specifically with the peopling of the Pacific Northwest and California coasts, have been advocated by archaeologists Knut Fladmark, Roy Carlson, James Dixon, Jon Erlandson, Ruth Gruhn, and Daryl Fedje. In a 2007 article in the Journal of Island and Coastal Archaeology, Erlandson and his colleagues proposed a corollary to the coastal migration theory—the kelp highway hypothesis—arguing that productive kelp forests supporting similar suites of plants and animals would have existed near the end of the Pleistocene around much of the Pacific Rim from Japan to Beringia, the Pacific Northwest, and California, as well as the Andean Coast of South America. Once the coastlines of Alaska and British Columbia had deglaciated about 16,000 years ago, these kelp forest (along with estuarine, mangrove, and coral reef) habitats would have provided an ecologically similar migration corridor, entirely at sea level, and essentially unobstructed.
Southeast Asians: Paleoindians of the Coast
The boat-builders from Southeast Asia may have been one of the earliest groups to reach the shores of North America. One theory suggests people in boats followed the coastline from the Kurile Islands to Alaska down the coasts of North and South America as far as Chile [2 62; 7 54, 57]. The Haida nation on the Queen Charlotte Islands off the coast of British Columbia may have originated from these early Asian mariners between 25,000 and 12,000. Early watercraft migration would also explain the habitation of coastal sites in South America such as Pikimachay Cave in Peru by 20,000 years ago and Monte Verde in Chile by 13,000 years ago [6 30; 8 383].
"'There was boat use in Japan 20,000 years ago,' says Jon Erlandson, a University of Oregon anthropologist. 'The Kurile Islands (north of Japan) are like stepping stones to Beringia,' the then continuous land bridging the Bering Strait. Migrants, he said, could have then skirted the tidewater glaciers in Canada right on down the coast." [7 64]'
Atlantic coastal model
Archaeologists Dennis Stanford and Bruce Bradley champion the coastal Atlantic route. Their Solutrean Hypothesis is also based on evidence from the Clovis complex, but instead traces the origins of the Clovis toolmaking style to the Solutrean culture of Ice Age Western Europe. The theory suggests that early European people (or peoples) may have been among the earliest settlers of the Americas. Citing evidence that the Solutrean culture of prehistoric Europe may have provided the basis for the tool-making of the Clovis culture in the Americas, the theory suggests that Ice Age Europeans migrated to North America by using skills similar to those possessed by the modern Inuit peoples and followed the edge of the ice sheet that spanned the Atlantic. The hypothesis rests upon particular similarities in Solutrean and Clovis technology that have no known counterparts in Eastern Asia, Siberia or Beringia, areas from which, or through which, early Americans are known to have migrated. The theory is largely discounted by most professionals for a variety of reasons, including the fact that the differences between the two tool making traditions far outweigh the similarities, the several thousand miles of the Atlantic Ocean and the 5000 year span that separate the two different cultures. Genetic studies of Native American populations have also shown the Solutrean theory to be unlikely, showing instead that the 5 main mtDNA haplogroups found in the Americas were all part of one gene pool migration from Asia.
Problems with evaluating coastal migration models
The coastal migration models provide a different perspective on migration to the New World, but they are not without their own problems. One of the biggest problems is that global sea levels have risen over 100 metres since the end of the last glacial period, and this has submerged the ancient coastlines which maritime people would have followed into the Americas. Finding sites associated with early coastal migrations is extremely difficult—and systematic excavation of any sites found in deeper waters is challenging and expensive. If there was an early pre-Clovis coastal migration, there is always the possibility of a "failed colonization." Another problem that arises is the lack of hard evidence found for a "long chronology" theory. No sites have yet produced a consistent chronology older than about 12,500 radiocarbon years (~14,500 calendar years)[citation needed], but South America has still seen only limited research on the possibility of early coastal migrations.
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