The Peopling of the American Continents
(revised 7 April 2001; see also early theories)

The date of entry of human beings into the American continents remains controversial. While dates as early as 35,000 years ago have been suggested, there was clearly a major wave around 11,000. A reentry into North America from South America around that time is currently being considered; finally, evidence from Brazil suggests early populations were anatomically varied.

The Clovis hypothesis top

The idea that the original Americans had somehow migrated from Siberia many thousands of years ago was first proposed in 1589, by José de Acosta, a Jesuit missionary to South America. It was subsequently elaborated in the Clovis hypothesis, for which a considerable body of evidence was assembled in the early decades of the twentieth century.

The paleoanthropologist Peter Frost <> notes that according to the Clovis hypothesis, humans colonized Beringia at some point before 11,000 B.P., possibly as early as 20,000 B.P., but were unable to go any further because of the glaciation covering most of what is now Canada.  At around 11,000 B.P., a corridor opened up between the Cordilleran ice sheet and the Laurentian ice sheet (through what is now the Mackenzie valley and Alberta), allowing the Clovis people to move down from Beringia and spread out onto the Great Plains. The Clovis people were successful big-game hunters that rapidly settled large areas.

Paleoindian cultural complexes
Paleoindian cultural complexes and approximate time periods.

A very large number of large animals became extinct in the Americas around 12,000 years ago. This appears to be strong evidence for a major influx of humans into North America at this time, and thus for the Clovis hypothesis.

For a detailed defense of the Clovis framework as still the most convincing story of the human settling of the Americas, see James Q. Jacobs (2001). "The Paleoamericans: Issues and Evidence Relating to the Peopling of the New World," available at

Megafauna extinctions top

The Arctoduspaleozoologist Valerius Geist <> speaks about "the predator hell hole which was Pleistocene North America" and argues that it was uninhabitable to human beings until around 15,000 years ago. In addition to the still surviving Black Bear, "there were three short-faced bear species, all larger, two specialized as super carnivores (one about 7-8 feet at the shoulder [the Arctodus simus, see painting]), and one as a super vegetarian convergent with Europe's cave bear. Nasty customers all. In addition there were true lions, only twice the mass of African specimen, two species of large sabre toothed cats, jaguars, large cheetah-like running cats and big dire wolves." Grizzly bears came later, across the Bering land bridge, along with humans. Remains of some of the mammals and birds present in the Los Angeles valley between 10,000 and 40,000 years ago -- including thousands of sabre-toothed cats -- can be seen at the La Brea Tarpits (external).

Large-scale extinction of big animals generally coincided with the arrival of early modern humans in places where they had never been (see details). This did not happen in Africa, presumably because people and other animals evolved there together. African animals were therefore not naïve about humans -- and they were resistant to their diseases. One of the most rapid extinctions was in North America, where a sudden wave of mammal extinctions swept through around 12,000 years ago. Not only big plant-eaters but also the predators that depended on them -- including saber-toothed cats, short-faced bears, cheetahs, maned lions and bigger versions of today's wolves -- are believed to have vanished in perhaps 400 years. Three possible causes have been advanced for this extinction episode.

  1. Humans swept across the continent from Siberia in a "killing front" that moved perhaps 100 miles in a decade (e.g. Daniel Fisher at UMich argues mammuth were hunted to extinction)
  2. Ross MacPhee of the American Museum of Natural History argues the culprit was extremely virulent disease, which humans -- and their dogs -- helped transport as they migrated into the New World (see 2 Jan 01 interview, external, and Feb 2001 Scientific American).

  3. Rapid climate change played the critical role.

MacPhee argues that the disease hypothesis is more plausible than the others. Even the most intensive hunting could not have caused the extinction of upward of 130 species in a time period of maybe half a millennium or less, and dramatic climate variations took place on a regular basis. Humans may, however, have introduced a new set of pathogens into the New World.

In contrast, Leigh Dayton notes in Science 292. 5523 (June 2001): 1819 that new evidence from Australia and North America points to Homo sapiens as the culprit behind the mass extinctions of many species of big, exotic mammals and flightless birds in the late Pleistocene era, 11,000 to 50,000 years ago. If these findings are confirmed, humans are guilty of two counts of serial mass murder, 35,000 years apart, and rival suspects such as climate change are off the hook (full text, external; summary in New Scientist, external).

The megafauna extinction dates suggest there may have been a major influx of people around 11,000 years ago. However, it does not rule out the presence of human beings in the Americas at an earlier date. They may have arrived by sea rather than by land.

The Coastal entry hypothesis

The possibility that the early settlers of the Americas arrived in boats is looking increasingly likely; see Drowned land holds clue to first Americans, Science News 5 Feb 2000 (external). Knut Fladmark, a professor of archaeology at Simon Fraser University in Burnaby, B.C., first put forward the hypothesis in the 1970s and remains an advocate of a coastal entry into the Americas.

The coastal entry hypothesis opens for an earlier date for the spread of human beings into the Americas, as this mode of settlement would not require an ice-free land corridor. The Arlington Springs Woman, found on Santa Rosa Island, has recently been carbondated to 13,000 years. Her presence on the island at this early date is consistent with the hypothesis that migrations into the new world took place by sea. Such coastal migration also opens up for a new set of possible routes and entry times.

The Solutrean Hypothesis

That Native Americans today are descendants of peoples who migrated from eastern Asia is firmly established and no longer controversial (Daniel Defoe once argued they were descendants of the Carthagenians; see early theories of the origin of the indiginous peoples of the Americas). Recently, further evidence confirming this turned up in a surprising corner. It appears that human beings all over the world play host to a small virus, dubbed JC, that changes very slowly. It can be used to trace ancient migration patterns; cf. David Brown's Microbe's Map Of Migration.

However, this evidence does not automatically rule out the presence of other groups of people with a different ancestry at earlier times. Dennis Stanford at the Smithsonian has argued that the Clovis culture may not be of Asian origin but may have come from Southern Europe; cf. interview (external), Cyclone Covey's The Solutrean Connection (external), and a report from digs in Kenosha (external). This entails a scenario where European peoples skirted the ice sheets of the Atlantic in boats and came down to the South-Eastern US, where the earliest Clovis cultures are found. Genetic testing of hair on Clovis sites may be enough to clear this up; the possibility must be considered highly speculative. The discovery in the Americas of human remains from around 10,000 years ago that lack typical mongoloid features (cf. Kennewick Man, external, and updates in Archaeology), and that have been characterized as 'caucasoid' is not evidence clearly in favor of Stanford's European hypothesis. Pleistocene skull data is varied and suggests complex patterns of small and mobile groups. The oldest known population of Japan, the Ainu, are loosely European in appearance (cf. the Ainu, also Ainu exhibit, both external).

If the European hypothesis has found little to support it, there is an increasing body of evidence suggesting a pre-Clovis entry.

Pre-Clovis evidence top

1. Archaeological evidence

Monte Verde. Contrasting with the Clovis hypothesis, the excavations at the Monte Verde site in southern Chile dug by Tom Dillehay and colleagues suggest a much earlier date. The older component, Monte Verde I, has several dates which cluster around 33,000 years B.P. Preliminary investigations suggest that this cultural material is crude but clearly present; the stratiography appears to be solid. Dillehay is going back in January 2001 to dig this component, which is only barely touched at present. The main component at the site, Monte Verde II, has dates ranging from 11,800 to 13,500. Dillehay notes it shows no evidence of Clovis or typical Paleoindian technology, suggesting that this is a pre-Clovis phenomenon.

Adovasio, J.M. & D.R. Pedler. Monte Verde and the antiquity of humankind in the Americas

Chilean Field Yields New Clues to Peopling of Americas, New York Times, August 1998.

Dillehay, Tom D. (1989). Monte Verde: A Late Pleistocene Settlement in Chile. Volume I: Palaeoenvironment and Site Context. Smithsonian Press.

Dillehay, Tom D. (2000). The Settlement of the Americas. Basic Books.

Meadowcroft in Pennsylvania. James Adovasio, an archaeologist at Mercyhurst College, has spent almost 30 years excavating Meadowcroft Rockshelter southwest of Pittsburgh, where early settlers set up camp at least 12,900 years ago. If these peoples came through the ice-free Canadian corridor, it is unclear how they reached the Eastern parts of North America at such an early date.

Cactus Hill in Virginia (there is also a possibly pre-Clovis site at Topper Site in South Carolina). Cactus Hill has some short, stubby, unfluted Clovisoid tools that appear to be a precursor of Clovis; tentative dates range from 13 to 19 thousand. See Tool Time on Cactus Hill (external) Scientific American 1998. Firmer dates are now available; see the April 2000 followup (external), with confirmed dates from 15 to 17,000 years before the present: "The lower layer dating back to 15,000 years roughly matches in age the controversial Meadowcroft rockshelter site in southwestern Pennsylvania. Cactus Hill and Meadowcroft so far are the only sites with extensive evidence of a culture that existed prior to the Clovis culture."

Mexico. Skulls found in Mexico have recently been dated to 13,000 years ago; see BBC report (external, 3 December 2002). They are dolichocephalic, or long and narrow-headed. More recent skulls from the same area were short and broad, like those from native American remains.

In general, the variety of morphological characteristics of the early skulls indicates that the New World was already populated by the time the Clovis culture entered, possibly by several, likely smaller groups..

2. Genetic evidence

Geneticists, including Theodore Schurr of the Southwest Foundation for Biomedical Research in San Antonio, Tex., and Douglas Wallace of Emory University, present an argument for a pre-Clovis entry based on genetic diversity. By comparing several DNA markers found in modern Native Americans and modern Siberians, Schurr and Wallace estimate that the ancestors of the former left Siberia for the New World at least 30,000 years ago." From Who were the first Americans?

3. Linguistic evidence

Linguist Johanna Nichols of the University of California at Berkeley argues that the amazing diversity of languages among Native Americans could have arisen only after humans had been in the New World for at least 20,000 years--possibly even 30,000.

The South American reentry hypothesis

This evidence of very ancient pre-Clovis cultures in South America and more recent pre-Clovis settlements in North America has led some researchers to suggest that the first wave of settlements took place prior to the most recent ice age. These first peoples may have entered as early as 35,000 years ago either overland or (perhaps more likely) by boats along the coast and up the rivers. (In comparison, current evidence suggests Australia may have been settled using boats as early as 60,000 years ago.) They would have been able to reach the warmer regions of Central and South America before the climate cooled. As the northern continent became covered in ice once again around 25,000 years ago, settlements would have been located primarily in the southern continent. As the ice receded around 11,000 years ago, they would have trekked north, at the same time as new peoples from Eastern Asia descended from Beringia.

If this hypothesis is correct, the archaelogical record should show two distinct cultural patterns: one coming in from the north and other from the south, both entering North America around 11,000 or a little earlier. Much older cultural remains in South and Central America should be continuous with the more recent remains in the Southern US.

The African Hypothesis

Recent evidence presented by Walter A. Neves of the University of São Paulo suggests early immigrants to South America may have come from Africa. Neves and and coworkers excavated the skeletal remains of at least 40 individuals in 28 separate graves at Santana do Riacho 1, the largest known prehistoric burial site in the Americas. Radiocarbon analyses indicated that the burials occurred over a 3,000-year span, beginning about 11,000 years ago.

The Santana do Riacho 1 skulls exhibit considerable variation in shape. However, Neves argues they share several traits with Africans and aboriginal Australians. These characteristics include a long, narrow brain case and eye sockets set relatively low on the face.

Richard L. Jantz of the University of Tennessee in Knoxville comments that if ancient Brazilian settlers exhibited a large amount of anatomical variability, it may be a coincidence that Neves found a few who show African similarities (see Science News report, external).

General References (external links) top

For the individual topics, see references within each section above.

Agriculture in the New World (local)

Center for the Study of the First Americans at Texas A&M University.

Clovis and Beyond, material presented by Scientific American from a conference in October 99.

Nemecek, Sasha (2000). "Who were the first Americans?" Scientific American. September 2000. Full text.

Smithsonian web site has the material on the recent rethinking of the peopling of the New World.

For an overview, see The peopling of the New World (external) and Who were the first Americans in the September 2000 issue of SciAm (external).



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