antiquity and prehistory of the Americas, study of the origins of the aboriginal peoples of the Americas. Archaeologists believe humans had entered and occupied much of the Americas by the end of the Pleistocene epoch, but the date of their original entry into the Americas is unresolved. The term "Paleo-Indians" is generally used to refer to early Native Americans up through the end of the Ice Age (c.8000 BC). Most authorities believe they entered North America from Siberia as small bands of migratory hunters. Such a journey could have been made by means of a now submerged plain, known as Beringia, which emerged several times during the Pleistocene and would have formed a land bridge between Asia and the Americas. More recent theories, based in part on DNA evidence, suggest that the Paleo-Indians were isolated for 10,000 to 15,000 years in Beringia before the melting of the North American ice permitted their movement into the Americas. The migration of the ancestors of the Eskimo (or Inuit) into and across N North America is believed to have occurred more recently, around 1,000 years ago; they displaced the genetically unrelated Paleo-Eskimos, who had first migrated into the region about 6,000 years ago.

The Asian derivation of the Native Americans is supported by the physical similarity of the native populations of East Asia and the Americas; studies indicate that the DNA patterns of modern Native Americans are very similar to those of Asian populations. All human skeletal remains from the Americas, including the very oldest, have been found in geologically recent contexts and belong to anatomically modern human beings. While recent analyses of the early skeletal material from the Americas indicate these populations exhibited considerable variability, and had dental and cranial characteristics rather different from those of modern Native American populations, such differences probably resulted from a process of gradual physical evolution after one or more Asian-derived groups had reached the Americas. DNA evidence suggests that the majority of modern Native American populations, mainly in Central and South America, descend from one group of migrants, that many North American Native Americans have a mixed, or separate but related, descent that involves a somewhat later migration, and that the Eskimo-Aleut descended from much later migrants.

The best known Paleo-Indian culture is that of the fluted-point hunters (see Clovis culture and Folsom culture), found throughout much of North America and dating to c.10,000–8000 BC; they were specialized big-game hunters adapted to an open, temperate, terrestrial environment. For many years, most authorities believed these fluted-point hunters were the oldest Paleo-Indians in the Americas, but since the 1970s new archaeological evidence from a number of sites as well as genetic studies has indicated a date of settlement that is at least 3,000 years earlier. Paleo-Indians had definitely reached the southern tip of South America by 9000–8500 BC, and evidence at Monte Verde, Chile, indicates Paleo-Indians were in S South America some 1,500 years earlier.

During the Pleistocene, glaciers covered much of North America, and the growth and contraction of these giant ice sheets may have played a crucial role in the timing of human migration into the Americas. During the height of the Wisconsin Glaciation (c.17,000–13,000 BC)—and perhaps several thousand years before and afterward as well—the ice formed a continuous sheet across N North America, preventing any overland migration from Alaska into the Great Plains of North America. For much of the 20th century, most Americanists held that the first Paleo-Indians entered lower North America only after the height of the Wisconsin Glaciation, when an ice-free corridor had emerged between the continental ice sheets in Canada. This development may have taken place as recently as 10,000 BC Then, according to this theory, the first Paleo-Indians moved rapidly southwards into North and South America, the speed of their migration being conditioned by the great abundance of game animals and the absence of human competitors in this virgin territory. These first inhabitants of North America were identified as the Clovis and Folsom fluted-point hunters.

A minority of archaeologists always opposed this theory and argued for the existence of an earlier, pre-Clovis occupation of the Americas. The presence of humans at the southern tip of South America by 9000—8500 BC suggested to some investigators that the fluted-point hunters were not the first migrants into the Americas, as this would have necessitated a very rapid rate of migration by these hunters. However, the absence of clearly convincing pre-Clovis sites frustrated the development of alternative models for the original human migration into the Americas. Some supposedly pre-Clovis sites contained very crude stone artifacts that had almost certainly been produced by natural processes. Other sites, such as the Meadowcroft Rock shelter near Pittsburgh, Wilson Butte Cave in Idaho, and Buttermilk Creek in Texas are more convincing (the last is dated to around 13,000 BC), but many archaeologists remain skeptical and believe these and other early sites to have been misdated.

Two early South American sites have now won broad acceptance among archaeologists, giving impetus to the proponents of the pre-Clovis hypothesis. Monte Verde, near Puerto Montt in S Chile (c.10,500 BC), is a remarkable pre-Clovis site in a moist peat bog with preserved perishable wooden and bone material. A large variety of plant remains were recovered at the site, along with mastodon meat, indicating its inhabitants practiced a hunting-and-gathering economy in a cool temperate rain forest. Pedra Pintada, near Monte Alegre in the lower Amazon (c.9,000–8,200 BC), is essentially contemporary with Clovis and represents a previously unknown Paleo-Indian subsistence pattern based on fishing, foraging, and limited hunting in the tropical rain forest. These early sites have shattered the archaeological consensus that the fluted-point hunters were the first Native Americans. While still earlier radiocarbon dates have been reported from some South American sites, including Monte Verde—reaching back to 30,000 BC—most dates earlier than 12,000 BC have been questioned by many Americanists.

Given the presence of the great North American glaciers throughout most of the late Pleistocene, the presence of humans in South America in the pre-Clovis era represents a puzzle. No new consensus on the problem of the antiquity of humans in the Americas has yet emerged. DNA evidence does suggest that the peopling of the Americas, once it began, occurred relatively rapidly, and it is possible that the original southward migration into the Americas occurred along the Pacific coast by groups who possessed boats. There is currently no direct evidence for such a migration along the Pacific Coast of North America, but this is not surprising, as rising sea levels during the Holocene would have concealed or destroyed early coastal settlements there. Recently, two pre-Clovis coastal sites, Quebrada Jaguay and Quebrada Tacahuay, have been reported in S Peru. They both date to c.10,000 BC and, along with Monte Verde, provide possible evidence for such a coastal migration. Another possibility is that the first Paleo-Indians migrated into lower North America over land prior to the formation of the continental ice sheet across Canada. Many experts believe the continental ice sheets presented an insurmountable barrier to terrestrial migrations after c.20,000 BC

After c.8000 BC the Pleistocene ended. Changing environmental conditions and the extinction of Pleistocene megafauna forced human groups to diversify their economic strategies and become more reliant on foraging and capturing small game. Known collectively as Archaic adaptations, these new subsistence strategies were highly specialized responses to local environmental conditions and actually emerged in different times in different places. In some regions, such as the Great Plains of North America, human reliance on big-game hunting continued until historic times. In contrast, the early South American sites described above indicate that a subsistence strategy based on plant foraging, the hunting of small game, and fishing actually emerged during the Pleistocene, thereby permitting an early colonization of a diversity of environments. In some areas of the New World, most notably the Andean region, the Amazon basin, Mesoamerica, the SW United States, and the Mississippi Basin and Eastern Woodlands, Archaic Native Americans evolved into sedentary agricultural societies, generally beginning about 2000 BC, although recent radiocarbon dating of Caral, in Peru's Supe valley, indicates that a city of several thousand arose there c.2600 BC

See also Natives, North American, Natives, Middle American, and Natives, South American.

See J. D. Jennings, Prehistory of North America (3d ed. 1989); S. J. Fiedel, Prehistory of the Americas (2d ed. 1992); C. C. Mann, 1491: New Revelations of the Americas before Columbus (2005).