Scholars were not concerned about the origins of native groups found in North America until they realized that the "New World" was not part of Asia, as Columbus and others had originally assumed. Once the continent's separation from Eurasia was clear, however, philosophers and scientists struggled to reconcile the diversity of groups found in the Americas with biblical accounts of a single human creation. The most insightful of these early speculations was proposed in the late sixteenth century by the Jesuit missionary José de Acosta, who theorized that the Americas were originally settled before the birth of Christ by groups of hunters and their families who inadvertently passed overland from Asia to the Americas while following the animal herds they hunted.
The discovery of the Bering Strait in 1728 made a prehistoric overland migration from Siberia to North America seem improbable in spite of the evidence of similarities between Eurasian and North American mammalian populations. As geologists of the last century deciphered the traces of massive prehistoric glaciers on exposed rock, the concept of periodic Ice Ages began to develop. Then, in the early twentieth century, it was proposed that Siberia and North America had been connected by a land bridge when increasing coldness and the formation of continental glaciers lowered sea levels worldwide. Evidence now shows that the last time this bridge—the Bering Land Bridge—was in existence was between 25,000 and 14,000 years ago, near the end of the Ice Age. Anthropologists call this land bridge, together with the adjacent unglaciated areas of North America and Asia, Beringia. Less than 14,000 years ago melting glaciers and higher sea levels submerged the land bridge. Since then migration from Siberia has required boats or, in winter, a walk over sea ice.
Currently, anthropologists, biological anthropologists, and historical linguists agree with de Acosta that Native Americans are descended from northeastern Asians, but there is heated debate over whether the first people arrived in America more than or less than 15,000 years ago. Beringian climatic and ecological conditions, the route or routes taken, and the number of prehistoric migration events are also in dispute.
Archaeologists who argue for an initial colonization less than 15,000 years ago note that the late-Ice Age animal bones found in Beringia are predominantly those of grazing animals such as bison, horses, mammoths, camels, and caribou. Beringia was part of the route from America to Asia used by horses and camels during the Ice Age. During this time mammoths, elk, moose, and caribou also used the land bridge to cross from Asia into the Americas. Therefore, less than 25,000 years ago, human groups culturally adapted to a severely cold climate could have seasonally occupied the Bering Land Bridge and followed grazing herds into the Alaskan and Canadian areas of eastern Beringia. These groups could not have moved farther south at this time because an ice sheet formed by the merging of two huge glaciers separated eastern Beringia from the rest of North America. This ice sheet stretched from the Pacific Ocean to the Atlantic Coast, creating a barrier five hundred miles long between Beringia and Alberta to the south. Less than 14,000 years ago rising sea levels prevented human groups and the animals they preyed on in eastern Beringia from crossing back to the rest of Beringia. It is at this time that melting glaciers created an ice-free corridor that allowed migration southward to the middle latitudes of North America.
Archaeological investigations into the thousands of square miles that represent the remaining Siberian and Alaskan regions of Beringia that were not submerged by rising sea levels have been limited to a few settled areas. The incomplete evidence these surveys have generated indicates that the first human settlement of eastern Siberia dates to around 18,000 years ago. By 14,000 years ago microblades and wedge-shaped cores similar to those of eastern Siberia had spread to wide areas of northeastern Siberia, perhaps as an adaptation to caribou hunting. The archaeological evidence for the earliest prehistoric settlement of eastern Beringia, as represented by modern Alaska and the Yukon, begins around 12,000 years ago with the Nenana complex of central Alaska. The earliest well-defined evidence of human occupation of North America south of where the glaciers of the Ice Age reached comes from the Clovis culture of the Paleo-Indian tradition, which begins 11,200 years ago. While this evidence supports the argument that the first human occupation of the New World occurred less than 15,000 years ago, it has not convinced all archaeologists.
Some of the archaeologists who argue for an earlier date for the initial colonization interpret the late-Ice Age pollen record of inland Beringia as indicative of a sparse tundra, or a polar desert environment, unable to sustain the large animal populations needed to support human groups. They suggest that the southern Beringian coast was more temperate and that groups subsisting on maritime resources moved along this unglaciated coastline to the west coast of the Americas sometime less than 25,000 years ago. Subsequent flooding of the land bridge and the continental shelf forced groups inland, south of the merged glaciers.
Currently there is no evidence to support this scenario, other than a few isolated and controversial North American sites dated to more than 15,000 years ago. What is needed is proof for the existence of ice-free areas south of Beringia large enough to have supported human groups, evidence of boats in this region more than 8,000 years ago, and evidence of archaeological sites on the drowned continental shelves of western North America and northeastern Asia. Unfortunately, most archaeological surveys on the inundated continental shelf areas of North America have been restricted to more temperate localities, such as Florida and the Gulf of Mexico. When the northwest coastal areas are adequately researched, evidence to confirm the hypothesis of an early coastal migration may be found.
Anthropologists who specialize in historical linguistics have tried to determine the date of the initial colonization, and the number of subsequent migrations, by organizing the more than one thousand known Native American languages into families and establishing the degree of diversity both within and between these groups. One such system suggests that most North American and South American languages, which form what scholars call the Amerind language group, are descended from the first migration, which is thought to have taken place more than 11,000 years ago. A second migration is represented by the Na-Dene family of languages found in the American Northwest and among the Navajos and Apaches of the Southwest. Inuit and Aleut language groups of the Arctic are considered to be the third, and most recent, language family. This theory of three discrete migration events has remained a minority view among anthropological linguists. The majority of linguists explain language diversity among modern Native American groups as the result of many more episodes of migration.
Some biological anthropologists have attempted to establish the number of migration events and their timing through studies of Native American dental and blood-group traits. Most of these studies confirm a late date for initial settlement and superficially agree with the linguistic data of a tripartite division among modern Native Americans. For example, dental variation between modern American Indian populations has been interpreted to suggest that members of the Amerind language family share similar dental traits and that they probably represent the descendants of an original Paleo-Indian colonization that occurred less than 15,000 years ago. These dental traits separate this group from a second group, the Na-Dene speakers of northwestern North America. This group is thought to have migrated from Siberia no later than 9,000 years ago. The third group, the Inuits and Aleuts of the Arctic, probably entered the Americas no later than about 8,000 years ago.
Blood-group studies of modern Native American populations generally support this dental and linguistic evidence. On the other hand, analyses of mitochondrial DNA (mtDNA) of modern Native American groups suggest that there are four lineages in this population. Thus the three proposed population groups do not explain all the genetic variation found in modern Native American populations. Other researchers have noted that Native Americans are about as genetically varied as any other population group. This suggests that the prehistoric peopling of the Americas was not the result of discrete migrations of a few genetically homogeneous people, as suggested by the linguistic, dental, mtDNA, and blood-group studies. It has been proposed that the genetic variation evidenced among modern Native Americans is instead the result of inadvertent migrations from western Beringia to the Americas by thousands of individuals over many thousands of years.
Other biological anthropologists have attempted to establish when the colonization of the Americas occurred by estimating the amount of time that has elapsed since Native American populations descended from a common Asian ancestor. This has been done by comparing Native American mtDNA with the mtDNA of northeastern Asian populations. The time since separation can then be determined by examining the amount of variation evidenced between these groups. This technique has proved to be problematic for two reasons. First, estimates of mtDNA evolutionary rates range, depending on the time allowed for variation to evolve, from more than 20,000 years ago to less than 15,000 years ago. Consequently, this DNA research has been inconclusive in determining whether colonization occurred more than or less than 15,000 years ago. Second, the mtDNA research assumes that the modern groups studied derive from a small, genetically similar founding population. Genetic variation in the original population would increase the estimated time of separation. Therefore, the dates generated are difficult to interpret without better demographic information on the groups ancestral to migrant populations. Further archaeological research is needed to provide this information.
See also
Origins: Native American Perspectives.
E. James Dixon, Quest for the Origins of the First Americans (Albuquerque: University of New Mexico Press, 1993); Brian M. Fagan, The Great Journey: The Peopling of Ancient America (New York: Thames and Hudson, 1987).
John A. K. Willis
Northwestern University
