Settlement of the Americas

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Map of the earliest securely dated sites showing human presence in the Americas, 24–13 ka for North America and 22–11 ka for South America.

The settlement of the Americas is widely accepted to have begun when Paleolithic hunter-gatherers entered North America from the North Asian Mammoth steppe via the Beringia land bridge, which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum. These populations expanded south of the Laurentide Ice Sheet and spread rapidly throughout both North and South America, by 14,000 years ago. The earliest populations in the Americas, before roughly 10,000 years ago, are known as Paleo-Indians.

The peopling of the Americas is a long-standing open question, and while advances in archaeology, Pleistocene geology, physical anthropology, and DNA analysis have progressively shed more light on the subject, significant questions remain unresolved. While there is general agreement that the Americas were first settled from Asia, the pattern of migration, its timing, and the place(s) of origin in Eurasia of the peoples who migrated to the Americas remain unclear.

The prevalent migration models outline different time frames for the Asian migration from the Bering Straits and subsequent dispersal of the founding population throughout the continent. Indigenous peoples of the Americas have been linked to Siberian populations by linguistic factors, the distribution of blood types, and in genetic composition as reflected by molecular data, such as DNA.

The "Clovis first theory" refers to the 1950s hypothesis that the Clovis culture represents the earliest human presence in the Americas, beginning about 13,000 years ago; evidence of pre-Clovis cultures has accumulated since 2000, pushing back the possible date of the first peopling of the Americas to 33,000 years ago. Moreover, faunal bones discovered in the Coxcatlan Cave, dated between 33,448 to 28,279 years old, indicated that arrival of humans in North America might have occurred prior to the period of the Last Glacial Maximum.

The environment during the latest glaciation

Emergence and submergence of Beringia

Figure1. Submergence of the Beringian land bridge with post-Last Glacial Maximum (LGM) rise in eustatic sea level

During the Wisconsin glaciation, the Earth's ocean water was, to varying degrees over time, stored in glacier ice. As water accumulated in glaciers, the volume of water in the oceans correspondingly decreased, resulting in lowering of global sea level. The variation of sea level over time has been reconstructed using oxygen isotope analysis of deep sea cores, the dating of marine terraces, and high resolution oxygen isotope sampling from ocean basins and modern ice caps. A drop of eustatic sea level by about 60 to 120 metres (200 to 390 ft) from present-day levels, commencing around 30,000 years BP, created Beringia, a durable and extensive geographic feature connecting Siberia with Alaska. With the rise of sea level after the Last Glacial Maximum (LGM), the Beringian land bridge was again submerged. Estimates of the final re-submergence of the Beringian land bridge based purely on present bathymetry of the Bering Strait and eustatic sea level curve place the event around 11,000 years BP (Figure 1). Ongoing research reconstructing Beringian paleogeography during deglaciation could change that estimate and possible earlier submergence could further constrain models of human migration into North America.

Glaciers

The onset of the Last Glacial Maximum after 30,000 years BP saw the expansion of alpine glaciers and continental ice sheets that blocked migration routes out of Beringia. By 21,000 years BP, and possibly thousands of years earlier, the Cordilleran and Laurentide ice sheets coalesced east of the Rocky Mountains, closing off a potential migration route into the center of North America. Alpine glaciers in the coastal ranges and the Alaskan Peninsula isolated the interior of Beringia from the Pacific coast. Coastal alpine glaciers and lobes of Cordilleran ice coalesced into piedmont glaciers that covered large stretches of the coastline as far south as Vancouver Island and formed an ice lobe across the Straits of Juan de Fuca by 15,000 ¹⁴C years BP (18,000 cal years BP). Coastal alpine glaciers started to retreat around 19,000 cal years BP while Cordilleran ice continued advancing in the Puget lowlands up to 14,000 ¹⁴C years BP (16,800 cal years BP). Even during the maximum extent of coastal ice, unglaciated refugia persisted on present-day islands, that supported terrestrial and marine mammals. As deglaciation occurred, refugia expanded until the coast became ice-free by 15,000 cal years BP. The retreat of glaciers on the Alaskan Peninsula provided access from Beringia to the Pacific coast by around 17,000 cal years BP. The ice barrier between interior Alaska and the Pacific coast broke up starting around 13,500 ¹⁴C years (16,200 cal years) BP. The ice-free corridor to the interior of North America opened between 13,000 and 12,000 cal years BP. Glaciation in eastern Siberia during the LGM was limited to alpine and valley glaciers in mountain ranges and did not block access between Siberia and Beringia.

Climate and biological environments

The paleoclimates and vegetation of eastern Siberia and Alaska during the Wisconsin glaciation have been deduced from high resolution oxygen isotope data and pollen stratigraphy. Prior to the Last Glacial Maximum, climates in eastern Siberia fluctuated between conditions approximating present day conditions and colder periods. The pre-LGM warm cycles in Arctic Siberia saw flourishes of megafaunas. The oxygen isotope record from the Greenland Ice Cap suggests that these cycles after about 45k years BP lasted anywhere from hundreds to between one and two thousand years, with greater duration of cold periods starting around 32k cal years BP. The pollen record from Elikchan Lake, north of the Sea of Okhotsk, shows a marked shift from tree and shrub pollen to herb pollen prior to 26k ¹⁴C years BP, as herb tundra replaced boreal forest and shrub steppe going into the LGM. A similar record of tree/shrub pollen being replaced with herb pollen as the LGM approached was recovered near the Kolyma River in Arctic Siberia. The abandonment of the northern regions of Siberia due to rapid cooling or the retreat of game species with the onset of the LGM has been proposed to explain the lack of archaeosites in that region dating to the LGM. The pollen record from the Alaskan side shows shifts between herb/shrub and shrub tundra prior to the LGM, suggesting less dramatic warming episodes than those that allowed forest colonization on the Siberian side. Diverse, though not necessarily plentiful, megafaunas were present in those environments. Herb tundra dominated during the LGM, due to cold and dry conditions.

Coastal environments during the Last Glacial Maximum were complex. The lowered sea level, and an isostatic bulge equilibrated with the depression beneath the Cordilleran Ice Sheet, exposed the continental shelf to form a coastal plain. While much of the coastal plain was covered with piedmont glaciers, unglaciated refugia supporting terrestrial mammals have been identified on Haida Gwaii, Prince of Wales Island, and outer islands of the Alexander Archipelago. The now-submerged coastal plain has potential for more refugia. Pollen data indicate mostly herb/shrub tundra vegetation in unglaciated areas, with some boreal forest towards the southern end of the range of Cordilleran ice. The coastal marine environment remained productive, as indicated by fossils of pinnipeds. The highly productive kelp forests over rocky marine shallows may have been a lure for coastal migration. Reconstruction of the southern Beringian coastline also suggests potential for a highly productive coastal marine environment.

Environmental changes during deglaciation

Pollen data indicate a warm period culminating between 14k and 11k ¹⁴C years BP (17k-13k cal years BP) followed by cooling between 11k-10k ¹⁴C years BP (13k-11.5k cal years BP). Coastal areas deglaciated rapidly as coastal alpine glaciers, then lobes of Cordilleran ice, retreated. The retreat was accelerated as sea levels rose and floated glacial termini. It has been estimated that the coast range was fully ice-free between 16k and 15k cal years BP. Littoral marine organisms colonized shorelines as ocean water replaced glacial meltwater. Replacement of herb/shrub tundra by coniferous forests was underway by 12.4k ¹⁴C years BP (15k cal years BP) north of Haida Gwaii. Eustatic sea level rise caused flooding, which accelerated as the rate grew more rapid.

The inland Cordilleran and Laurentide ice sheets retreated more slowly than did the coastal glaciers. Opening of an ice-free corridor did not occur until after 13k to 12k cal years BP. The early environment of the ice-free corridor was dominated by glacial outwash and meltwater, with ice-dammed lakes and periodic flooding from the release of ice-dammed meltwater. Biological productivity of the deglaciated landscape was gained slowly. The earliest possible viability of the ice-free corridor as a human migration route has been estimated at 11.5k cal years BP.

Birch forests were advancing across former herb tundra in Beringia by 14.3ka ¹⁴C years BP (17k cal years BP) in response to climatic amelioration, indicating increased productivity of the landscape.

Analyses of biomarkers and microfossils preserved in sediments from Lake E5 and Burial Lake in northern Alaska suggest early humans burned Beringian landscapes as early as 34,000 years ago. The authors of these studies suggest that fire was used as means of hunting megafauna.

Chronology, reasons for, and sources of migration

25,000 years ago Beringia during the LGM 16–14,000 years ago peopling of the Americas just after the LGM

The archaeological community is in general agreement that the ancestors of the Indigenous peoples of the Americas of historical record entered the Americas at the end of the Last Glacial Maximum (LGM), shortly after 20,000 years ago, with ascertained archaeological presence shortly after 16,000 years ago.

There remain uncertainties regarding the precise dating of individual sites and regarding conclusions drawn from population genetics studies of contemporary Native Americans. It is also an open question whether this post-LGM migration represented the first peopling of the Americas, or whether there had been an earlier, pre-LGM migration which had reached South America as early as 40,000 years ago.

Chronology

In the early 21st century, the models of the chronology of migration are divided into two general approaches.

The first is the short chronology theory, that the first migration occurred after the Last Glacial Maximum, which went into decline after about 19,000 years ago, and was then followed by successive waves of immigrants.

The second theory is the long chronology theory, which proposes that the first group of people entered the Americas at a much earlier date, possibly before 40,000 years ago, followed by a much later second wave of immigrants.

The Clovis First theory, which dominated thinking on New World anthropology for much of the 20th century, was challenged by the secure dating of archaeosites in the Americas to before 13,000 years ago in the 2000s. The "short chronology" scenario, in the light of this, refers to a peopling of the Americas shortly after 19,000 years ago, while the "long chronology" scenario permits pre-LGM presence, by around 40,000 years ago.

The archaeosites in the Americas with the oldest dates that have gained broad acceptance are all compatible with an age of about 15,000 years. This includes the Buttermilk Creek Complex in Texas, the Meadowcroft Rockshelter site in Pennsylvania and the Monte Verde site in southern Chile. Archaeological evidence of pre-Clovis people points to the South Carolina Topper Site being 16,000 years old, at a time when the glacial maximum would have theoretically allowed for lower coastlines.

It has often been suggested that an ice-free corridor, in what is now Western Canada, would have allowed migration before the beginning of the Holocene, but a 2016 study has argued against this, suggesting that the peopling of North America via such a corridor is unlikely to significantly pre-date the earliest Clovis sites. The study concludes that the ice-free corridor in what is now Alberta and British Columbia "was gradually taken over by a boreal forest dominated by spruce and pine trees" and that the "Clovis people likely came from the south, not the north, perhaps following wild animals such as bison". An alternative hypothesis for the peopling of America is coastal migration, which may have been feasible along the deglaciated (but now submerged) coastline of the Pacific Northwest from about 16,000 years ago.

Evidence for pre-LGM human presence

Figure 2. Schematic illustration of maternal (mtDNA) gene-flow in and out of Beringia (long chronology, single source model).

 

Map of Beringia showing the exposed seafloor and glaciation at 40,000 years ago and 16,000 years ago. The green arrow indicates the "interior migration" model along an ice-free corridor separating the major continental ice sheets, the red arrow indicates the "coastal migration" model, both leading to a "rapid colonization" of the Americas after c. 16,000 years ago.

Pre-Last Glacial Maximum migration across Beringia into the Americas has been proposed to explain purported pre-LGM ages of archaeosites in the Americas such as Bluefish Caves and Old Crow Flats in the Yukon Territory, and Meadowcroft Rock Shelter in Pennsylvania.

At the Old Crow Flats, mammoth bones have been found that are broken in distinctive ways indicating human butchery. The radiocarbon dates on these vary between 25,000 and 40,000 years BP. Also, stone microflakes have been found in the area indicating tool production.

Previously, the interpretations of butcher marks and the geologic association of bones at the Bluefish Cave and Old Crow Flats sites, and the related Bonnet Plume site, have been called into question.

In addition to disputed archaeological sites, support for pre-LGM human presence has been found in lake sediment records of northern Alaska. Biomarker and microfossil analyses of sediments from Lake E5 and Burial Lake in suggest human presence in eastern Beringia as early as 34,000 years ago. These analyses are indeed compelling in that they corroborate the inferences made from the Bluefish Cave and Old Crow Flats sites.

In 2020, evidence emerged for a new pre-LGM site in North-Central Mexico. Chiquihuite cave, an archaeological site in Zacatecas State, has been dated to 26,000 years BP based on numerous lithic artefacts discovered there.

Pre-LGM human presence in South America rests partly on the chronology of the controversial Pedra Furada rock shelter in Piauí, Brazil. A 2003 study dated evidence for the controlled use of fire to before 40,000 years ago. Additional evidence has been adduced from the morphology of Luzia Woman fossil, which was described as Australoid. This interpretation was challenged in a 2003 review which concluded the features in question could also have arisen by genetic drift. In November 2018, scientists of the University of São Paulo and Harvard University released a study that contradicts the alleged Australo-Melanesian origin of Luzia. Using DNA sequencing, the results showed that Luzia was entirely Amerindian, genetically.

The ages of the earliest positively identified artifacts at the Meadowcroft site are safely within the post-LGM period (13.8k–18.5k cal years BP).

Stones described as probable tools, hammerstones and anvils, have been found in southern California, at the Cerutti Mastodon site, that are associated with a mastodon skeleton which appeared to have been processed by humans. The mastodon skeleton was dated by thorium-230/uranium radiometric analysis, using diffusion–adsorption–decay dating models, to 130.7 ± 9.4 thousand years ago. No human bones were found and expert reaction was mixed; claims of tools and bone processing were called "not plausible" by Prof. Tom Dillehay.

The Yana River Rhino Horn site (RHS) has dated human occupation of eastern Arctic Siberia to 27k ¹⁴C years BP (31.3k cal years BP). That date has been interpreted by some as evidence that migration into Beringia was imminent, lending credence to occupation of Beringia during the LGM. However, the Yana RHS date is from the beginning of the cooling period that led into the LGM. But, a compilation of archaeosite dates throughout eastern Siberia suggest that the cooling period caused a retreat of humans southwards. Pre-LGM lithic evidence in Siberia indicate a settled lifestyle that was based on local resources, while post-LGM lithic evidence indicate a more migratory lifestyle.

The oldest archaeosite on the Alaskan side of Beringia date to 12k ¹⁴C years BP (14k cal years BP). It is possible that a small founder population had entered Beringia before that time. However, archaeosites that date closer to the Last Glacial Maximum on either the Siberian or the Alaskan side of Beringia are lacking. Biomarker and microfossil analyses of sediments from Lake E5 and Burial Lake in northern Alaska suggest human presence in eastern Beringia as early as 34,000 years ago. These sedimentary analyses have been suggested to be the only possibly recoverable remnants of humans living Alaska during the last Glacial period.

Genomic age estimates

Studies of Amerindian genetics have used high resolution analytical techniques applied to DNA samples from modern Native Americans and Asian populations regarded as their source populations to reconstruct the development of human Y-chromosome DNA haplogroups (yDNA haplogroups) and human mitochondrial DNA haplogroups (mtDNA haplogroups) characteristic of Native American populations. Models of molecular evolution rates were used to estimate the ages at which Native American DNA lineages branched off from their parent lineages in Asia and to deduce the ages of demographic events. One model (Tammetal 2007) based on Native American mtDNA Haplotypes (Figure 2) proposes that migration into Beringia occurred between 30k and 25k cal years BP, with migration into the Americas occurring around 10k to 15k years after isolation of the small founding population. Another model (Kitchen et al. 2008) proposes that migration into Beringia occurred approximately 36k cal years BP, followed by 20k years of isolation in Beringia. A third model (Nomatto et al. 2009) proposes that migration into Beringia occurred between 40k and 30k cal years BP, with a pre-LGM migration into the Americas followed by isolation of the northern population following closure of the ice-free corridor. Evidence of Australo-Melanesians admixture in Amazonian populations was found by Skoglund and Reich (2016).

A study of the diversification of mtDNA Haplogroups C and D from southern Siberia and eastern Asia, respectively, suggests that the parent lineage (Subhaplogroup D4h) of Subhaplogroup D4h3, a lineage found among Native Americans and Han Chinese, emerged around 20k cal years BP, constraining the emergence of D4h3 to post-LGM. Age estimates based on Y-chromosome micro-satellite diversity place origin of the American Haplogroup Q1a3a (Y-DNA) at around 10k to 15k cal years BP. Greater consistency of DNA molecular evolution rate models with each other and with archaeological data may be gained by the use of dated fossil DNA to calibrate molecular evolution rates.

Source populations

There is general agreement among anthropologists that the source populations for the migration into the Americas originated from an area somewhere east of the Yenisei River (Russian Far East). The common occurrence of the mtDNA Haplogroups A, B, C, and D among eastern Asian and Native American populations has long been recognized, along with the presence of haplogroup X. As a whole, the greatest frequency of the four Native American associated haplogroups occurs in the Altai-Baikal region of southern Siberia. Some subclades of C and D closer to the Native American subclades occur among Mongolian, Amur, Japanese, Korean, and Ainu populations.

A 2019 study suggested that Native Americans are the closest living relatives to 10,000-year-old fossils found near the Kolyma River in northeastern Siberia.

Human genomic models

The development of high-resolution genomic analysis has provided opportunities to further define Native American subclades and narrow the range of Asian subclades that may be parent or sister subclades. For example, the broad geographic range of haplogroup X has been interpreted as allowing the possibility of a western Eurasian, or even a European source population for Native Americans, as in the Solutrean hypothesis, or suggesting a pre-Last Glacial Maximum migration into the Americas. The analysis of an ancient variant of haplogroup X among aboriginals of the Altai region indicates common ancestry with the European strain rather than descent from the European strain. Further division of X subclades has allowed identification of subhaplogroup X2a, which is regarded as specific to Native Americans. With further definition of subclades related to Native American populations, the requirements for sampling Asian populations to find the most closely related subclades grow more specific. Subhaplogroups D1 and D4h3 have been regarded as Native American specific based on their absence among a large sampling of populations regarded as potential descendants of source populations, over a wide area of Asia. Among the 3764 samples, the Sakhalin – lower Amur region was represented by 61 Oroks. In another study, Subhaplogroup D1a has been identified among the Ulchis of the lower Amur River region (4 among 87 sampled, or 4.6%), along with Subhaplogroup C1a (1 among 87, or 1.1%). Subhaplogroup C1a is regarded as a close sister clade of the Native American Subhaplogroup C1b.

Subhaplogroup D1a has also been found among ancient Jōmon skeletons from Hokkaido The modern Ainu are regarded as descendants of the Jōmon. The occurrence of the Subhaplogroups D1a and C1a in the lower Amur region suggests a source population from that region distinct from the Altai-Baikal source populations, where sampling did not reveal those two particular subclades. The conclusions regarding Subhaplogroup D1 indicating potential source populations in the lower Amur and Hokkaido areas stand in contrast to the single-source migration model.

Subhaplogroup D4h3 has been identified among Han Chinese. Subhaplogroup D4h3 from China does not have the same geographic implication as Subhaplotype D1a from Amur-Hokkaido, so its implications for source models are more speculative. Its parent lineage, Subhaplotype D4h, is believed to have emerged in east Asia, rather than Siberia, around 20k cal years BP. Subhaplogroup D4h2, a sister clade of D4h3, has also been found among Jōmon skeletons from Hokkaido. D4h3 has a coastal trace in the Americas.

The contrast between the genetic profiles of the Hokkaido Jōmon skeletons and the modern Ainu illustrates another uncertainty in source models derived from modern DNA samples:

However, probably due to the small sample size or close consanguinity among the members of the site, the frequencies of the haplogroups in Funadomari skeletons were quite different from any modern populations, including Hokkaido Ainu, who have been regarded as the direct descendant of the Hokkaido Jōmon people.

The descendants of source populations with the closest relationship to the genetic profile from the time when differentiation occurred are not obvious. Source population models can be expected to become more robust as more results are compiled, the heritage of modern proxy candidates becomes better understood, and fossil DNA in the regions of interest is found and considered.

HTLV-1 genomics

The Human T cell Lymphotrophic Virus 1 (HTLV-1) is a virus transmitted through exchange of bodily fluids and from mother to child through breast milk. The mother-to-child transmission mimics a hereditary trait, although such transmission from maternal carriers is less than 100%. The HTLV virus genome has been mapped, allowing identification of four major strains and analysis of their antiquity through mutations. The highest geographic concentrations of the strain HLTV-1 are in sub-Saharan Africa and Japan. In Japan, it occurs in its highest concentration on Kyushu. It is also present among African descendants and native populations in the Caribbean region and South America. It is rare in Central America and North America. Its distribution in the Americas has been regarded as due to importation with the slave trade.

The Ainu have developed antibodies to HTLV-1, indicating its endemicity to the Ainu and its antiquity in Japan. A subtype "A" has been defined and identified among the Japanese (including Ainu), and among Caribbean and South American isolates. A subtype "B" has been identified in Japan and India. In 1995, Native Americans in coastal British Columbia were found to have both subtypes A and B. Bone marrow specimens from an Andean mummy about 1500 years old were reported to have shown the presence of the A subtype. The finding ignited controversy, with contention that the sample DNA was insufficiently complete for the conclusion and that the result reflected modern contamination. However, a re-analysis indicated that the DNA sequences were consistent with, but not definitely from, the "cosmopolitan clade" (subtype A). The presence of subtypes A and B in the Americas is suggestive of a Native American source population related to the Ainu ancestors, the Jōmon.

Physical anthropology

Paleoamerican skeletons in the Americas such as Kennewick Man (Washington State), Hoya Negro skeleton (Yucatán), Luzia Woman and other skulls from the Lagoa Santa site (Brazil), Buhl Woman (Idaho), Peñon Woman III, two skulls from the Tlapacoya site (Mexico City), and 33 skulls from Baja California have exhibited craniofacial traits distinct from most modern Native Americans, leading physical anthropologists to the opinion that some Paleoamericans were of an Australoid rather than Siberian origin. The most basic measured distinguishing trait is the dolichocephaly of the skull. Some modern isolates such as the Pericúes of Baja California and the Fuegians of Tierra del Fuego exhibit that same morphological trait. Other anthropologists advocate an alternative hypothesis that evolution of an original Beringian phenotype gave rise to a distinct morphology that was similar in all known Paleoamerican skulls, followed by later convergence towards the modern Native American phenotype. Genetic studies support an Australoid origin.

A report published in the American Journal of Physical Anthropology in January 2015 reviewed craniofacial variation focussing on differences between early and late Native Americans and explanations for these based on either skull morphology or molecular genetics. Arguments based on molecular genetics have in the main, according to the authors, accepted a single migration from Asia with a probable pause in Berengia, plus later bi-directional gene flow. Studies focusing on craniofacial morphology have argued that Paleoamerican remains have "been described as much closer to African and Australo-Melanesians populations than to the modern series of Native Americans", suggesting two entries into the Americas, an early one occurring before a distinctive East Asian morphology developed (referred to in the paper as the "Two Components Model". A third model, the "Recurrent Gene Flow" [RGF] model, attempts to reconcile the two, arguing that circumarctic gene flow after the initial migration could account for morphological changes. It specifically re-evaluates the original report on the Hoya Negro skeleton which supported the RGF model, the authors disagreed with the original conclusion which suggested that the skull shape did not match those of modern Native Americans, arguing that the "skull falls into a subregion of the morphospace occupied by both Paleoamericans and some modern Native Americans."

Stemmed points

Stemmed points are a lithic technology distinct from Beringian and Clovis types. They have a distribution ranging from coastal east Asia to the Pacific coast of South America. The emergence of stemmed points has been traced to Korea during the upper Paleolithic. The origin and distribution of stemmed points have been interpreted as a cultural marker related to a source population from coastal east Asia.

Migration routes

Interior route

Map showing the approximate location of the ice-free corridor along the Continental Divide, separating the Cordilleran and Laurentide ice sheets. Also indicated are the locations of the Clovis and Folsom Paleo-Indian sites.

Historically, theories about migration into the Americas have revolved around migration from Beringia through the interior of North America. The discovery of artifacts in association with Pleistocene faunal remains near Clovis, New Mexico in the early 1930s required extension of the timeframe for the settlement of North America to the period during which glaciers were still extensive. That led to the hypothesis of a migration route between the Laurentide and Cordilleran ice sheets to explain the early settlement. The Clovis site was host to a lithic technology characterized by spear points with an indentation, or flute, where the point was attached to the shaft. A lithic complex characterized by the Clovis Point technology was subsequently identified over much of North America and in South America. The association of Clovis complex technology with late Pleistocene faunal remains led to the theory that it marked the arrival of big game hunters that migrated out of Beringia then dispersed throughout the Americas, otherwise known as the Clovis First theory.

Recent radiocarbon dating of Clovis sites has yielded ages of 11.1k to 10.7k ¹⁴C years BP (13k to 12.6k cal years BP), somewhat later than dates derived from older techniques. The re-evaluation of earlier radiocarbon dates led to the conclusion 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. Numerical dating of Clovis sites has allowed comparison of Clovis dates with dates of other archaeosites throughout the Americas, and of the opening of the ice-free corridor. Both lead to significant challenges to the Clovis First theory. The Monte Verde site of Southern Chile has been dated at 14.8k cal years BP. The Paisley Cave site in eastern Oregon yielded a ¹⁴C date of 12.4k years (14.5k cal years) BP, on a coprolite with human DNA and ¹⁴C dates of 11.3k-11k (13.2k-12.9k cal years) BP on horizons containing western stemmed points. Artifact horizons with non-Clovis lithic assemblages and pre-Clovis ages occur in eastern North America, although the maximum ages tend to be poorly constrained.

Geological findings on the timing of the ice-free corridor also challenge the notion that Clovis and pre-Clovis human occupation of the Americas was a result of migration through that route following the Last Glacial Maximum. Pre-LGM closing of the corridor may approach 30k cal years BP and estimates of ice retreat from the corridor are in the range of 12 to 13k cal years BP. Viability of the corridor as a human migration route has been estimated at 11.5k cal years BP, later than the ages of the Clovis and pre-Clovis sites. Dated Clovis archaeosites suggest a south-to-north spread of the Clovis culture.

Pre-Last Glacial Maximum migration into the interior has been proposed to explain pre-Clovis ages for archaeosites in the Americas, although pre-Clovis sites such as Meadowcroft Rock Shelter, Monte Verde, and Paisley Cave have not yielded confirmed pre-LGM ages.

Dené–Yeniseian language family proposal

A relationship between the Na-Dené languages of North America (such as Navajo and Apache), and the Yeniseian languages of Siberia was first proposed as early as 1923, and developed further by others. A detailed study was done by Edward Vajda and published in 2010. This theory received support from many linguists, with archaeological and genetic studies providing it with further support.

The Arctic Small Tool tradition of Alaska and the Canadian Arctic may have originated in East Siberia about 5,000 years ago. This is connected with the ancient Paleo-Eskimo peoples of the Arctic, the culture that developed by 2500 BCE.

The Arctic Small Tool tradition source may have been the Syalakh-Bel’kachi-Ymyakhtakh culture sequence of East Siberia, dated to 6,500 – 2,800 calBP.

The interior route is consistent with the spread of the Na-Dene language group and subhaplogroup X2a into the Americas after the earliest paleoamerican migration.

Nevertheless, some scholars suggest that the ancestors of western North Americans speaking Na-Dene languages made a coastal migration by boat.

Pacific coastal route

The Pacific coastal migration theory proposes that people first reached the Americas via water travel, following coastlines from northeast Asia into the Americas, originally proposed in 1979 by Knute Fladmark as an alternative to the hypothetical migration through an ice-free inland corridor. This model would help to explain the rapid spread to coastal sites extremely distant from the Bering Strait region, including sites such as Monte Verde in southern Chile and Taima-Taima in western Venezuela.

The very similar marine migration hypothesis is a variant of coastal migration; essentially its only difference is that it postulates that boats were the principle means of travel. The proposed use of boats adds a measure of flexibility to the chronology of coastal migration, because a continuous ice-free coast (16–15,000 calibrated years BP) would then not be required: Migrants in boats could have easily bypassed ice barriers and settled in scattered coastal refugia, before the deglaciation of the coastal land route was complete. A maritime-competent source population in coastal east-Asia is an essential part of the marine migration hypothesis.

A 2007 article in the Journal of Island and Coastal Archaeology proposed a "kelp highway hypothesis", a variant of coastal migration based on the exploitation of kelp forests along much of the Pacific Rim from Japan to Beringia, the Pacific Northwest, and California, and as far 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 homogenous migration corridor, entirely at sea level, and essentially unobstructed. A 2016 DNA analysis of plants and animals suggest a coastal route was feasible.

Mitochondrial subhaplogroup D4h3a, a rare subclade of D4h3 occurring along the west coast of the Americas, has been identified as a clade associated with coastal migration. This haplogroup was found in a skeleton referred to as Anzick-1, found in Montana in close association with several Clovis artifacts, dated 12,500 years ago.

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 such problem is that global sea levels have risen over 120 metres (390 ft) since the end of the last glacial period, and this has submerged the ancient coastlines that 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. Strategies for finding earliest migration sites include identifying potential sites on submerged paleoshorelines, seeking sites in areas uplifted either by tectonics or isostatic rebound, and looking for riverine sites in areas that may have attracted coastal migrants. On the other hand, there is evidence of marine technologies found in the hills of the Channel Islands of California, circa 10,000 BCE. 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), but research in South America related to the possibility of early coastal migrations has been limited

Early human migrations

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https://en.wikipedia.org/wiki/Early_human_migrations 

Putative migration waves out of Africa and back migrations into the continent, as well as the locations of major ancient human remains and archeological sites (López et al.2015).

Early human migrations are the earliest migrations and expansions of archaic and modern humans across continents. They are believed to have begun approximately 2 million years ago with the early expansions out of Africa by Homo erectus. This initial migration was followed by other archaic humans including H. heidelbergensis, which lived around 500,000 years ago and was the likely ancestor of Denisovans and Neanderthals as well as modern humans. Early hominids likely "crossed land bridges that were eventually covered in water" (History Alive, pub. 2004, TCI).

Within Africa, Homo sapiens dispersed around the time of its speciation, roughly 300,000 years ago. The recent African origin paradigm suggests that the anatomically modern humans outside of Africa descend from a population of Homo sapiens migrating from East Africa roughly 70–50,000 years ago and spreading along the southern coast of Asia and to Oceania by about 50,000 years ago. Modern humans spread across Europe about 40,000 years ago.

Early Eurasian Homo sapiens fossils have been found in Israel and Greece, dated to 194,000–177,000 and 210,000 years old respectively. These fossils seem to represent failed dispersal attempts by early Homo sapiens, who were likely replaced by local Neanderthal populations.

The migrating modern human populations are known to have interbred with earlier local populations, so that contemporary human populations are descended in small part (below 10% contribution) from regional varieties of archaic humans.

After the Last Glacial Maximum, North Eurasian populations migrated to the Americas about 20,000 years ago. Northern Eurasia was peopled after 12,000 years ago, in the beginning Holocene. Arctic Canada and Greenland were reached by the Paleo-Eskimo expansion around 4,000 years ago. Finally, Polynesia was peopled within the past 2,000 years in the last wave of the Austronesian expansion.

Early humans (before Homo sapiens)

The earliest humans developed out of australopithecine ancestors after about 3 million years ago, most likely in Eastern Africa, most likely in the area of the Kenyan Rift Valley, where the oldest known stone tools were found. Stone tools recently discovered at the Shangchen site in China and dated to 2.12 million years ago are claimed to be the earliest known evidence of hominins outside Africa, surpassing Dmanisi in Georgia by 300,000 years.

Homo erectus

Between 2 and less than a million years ago, Homo spread throughout East Africa and to Southern Africa (Telanthropus capensis), but not yet to West Africa. Around 1.8 million years ago, Homo erectus migrated out of Africa via the Levantine corridor and Horn of Africa to Eurasia. This migration has been proposed as being related to the operation of the Saharan pump, around 1.9 million years ago. Homo erectus dispersed throughout most of the Old World, reaching as far as Southeast Asia. Its distribution is traced by the Oldowan lithic industry, by 1.3 million years ago extending as far north as the 40th parallel (Xiaochangliang).

Key sites for this early migration out of Africa are Riwat in Pakistan (~2 Ma?), Ubeidiya in the Levant (1.5 Ma) and Dmanisi in the Caucasus (1.81 ± 0.03 Ma, p=0.05).

China shows evidence of Erectus from 2.12 Mya in Gongwangling in Lantian county. Two Homo erectus incisors have been found near Yuanmou, south China, and are dated to 1.7 Mya, and a cranium from Lantian has been dated to 1.63 Ma. Artefacts from Majuangou III and Shangshazui in the Nihewan basin, north China, have been dated to 1.6–1.7 Ma. The archaeological site of Xihoudu (西侯渡) in Shanxi Province is the earliest recorded use of fire by Homo erectus, which is dated 1.27 million years ago.

Southeast Asia (Java) was reached about 1.7 million years ago (Meganthropus). Western Europe was first populated around 1.2 million years ago (Atapuerca).

Robert G. Bednarik has suggested that Homo erectus may have built rafts and sailed oceans, a theory that has raised some controversy.

After H. erectus

Spread of Denisovans and Neanderthals after 500,000 years ago

 

Known Neanderthal range with separate populations in Europe and the Caucasus (blue), the Near East (orange), Uzbekistan (green), and the Altai region (purple)

One million years after its dispersal, H. erectus was diverging into new species. H. erectus is a chronospecies and was never extinct, so that its "late survival" is a matter of taxonomic convention. Late forms of H. erectus are thought to have survived until after about 0.5 million ago to 143,000 years ago at the latest, with derived forms classified as H. antecessor in Europe around 800,000 years ago and H. heidelbergensis in Africa around 600,000 years ago. H. heidelbergensis in its turn spread across East Africa (H. rhodesiensis) and to Eurasia, where it gave rise to Neanderthals and Denisovans.

H. heidelbergensis, Neanderthals and Denisovans expanded north beyond the 50th parallel (Eartham Pit, Boxgrove 500kya, Swanscombe Heritage Park 400kya, Denisova Cave 50 kya). It has been suggested that late Neanderthals may even have reached the boundary of the Arctic, by c. 32,000 years ago, when they were being displaced from their earlier habitats by H. sapiens, based on 2011 excavations at the site of Byzovaya in the Urals (Komi Republic, 65.02°N 57.42°E).

Other archaic human species are assumed to have spread throughout Africa by this time, although the fossil record is sparse. Their presence is assumed based on traces of admixture with modern humans found in the genome of African populations. Homo naledi, discovered in South Africa in 2013 and tentatively dated to about 300,000 years ago, may represent fossil evidence of such an archaic human species.

Neanderthals spread across the Near East and Europe, while Denisovans appear to have spread across Central and East Asia and to Southeast Asia and Oceania. There is evidence that Denisovans interbred with Neanderthals in Central Asia where their habitats overlapped. Neanderthal evidence has also been found quite late as of 33,000 years ago at the almost 65th latitude of the Byzovaya site in the Ural Mountains. This is far outside of otherwise known habitat, during a high ice cover period, and perhaps reflects a refugia of near extinction.

Homo sapiens

Early modern human migrations based on the distribution of mitochondrial haplogroups.

Dispersal throughout Africa

Homo sapiens are believed to have emerged in Africa about 300,000 years ago, based in part on thermoluminescence dating of artefacts and remains from Jebel Irhoud, Morocco, published in 2017. The Florisbad Skull from Florisbad, South Africa, dated to about 259,000 years ago, has also been classified as early Homo sapiens. Previously, the Omo remains, excavated between 1967 and 1974 in Omo National Park, Ethiopia, and dated to 200,000 years ago, were long held to be the oldest known fossils of Homo sapiens.

In September 2019, scientists reported the computerized determination, based on 260 CT scans, of a virtual skull shape of the last common human ancestor to anatomically modern humans, representative of the earliest modern humans, and suggested that modern humans arose between 260,000 and 350,000 years ago through a merging of populations in East and South Africa.

In July 2019, anthropologists reported the discovery of 210,000 year old remains of a H. sapiens and 170,000 year old remains of a H. neanderthalensis in Apidima Cave in southern Greece, more than 150,000 years older than previous H. sapiens finds in Europe.

Early modern humans expanded to Western Eurasia and Central, Western and Southern Africa from the time of their emergence. While early expansions to Eurasia appear not to have persisted, expansions to Southern and Central Africa resulted in the deepest temporal divergence in living human populations. Early modern human expansion in sub-Saharan Africa appears to have contributed to the end of late Acheulean (Fauresmith) industries at about 130,000 years ago, although very late coexistence of archaic and early modern humans, until as late as 12,000 years ago, has been argued for West Africa in particular.

The ancestors of the modern Khoi-San expanded to Southern Africa before 150,000 years ago, possibly as early as before 260,000 years ago, so that by the beginning of the MIS 5 "megadrought", 130,000 years ago, there were two ancestral population clusters in Africa, bearers of mt-DNA haplogroup L0 in southern Africa, ancestral to the Khoi-San, and bearers of haplogroup L1-6 in central/eastern Africa, ancestral to everyone else. There was a significant back-migration of bearers of L0 towards eastern Africa between 120 and 75 kya.

Expansion to Central Africa by the ancestors of the Central African forager populations (African Pygmies) most likely took place before 130,000 years ago, and certainly before 60,000 years ago.

The situation in West Africa is difficult to interpret due to a sparsity of fossil evidence. Homo sapiens seems to have reached the western Sahelian zone by 130,000 years ago, while tropical West African sites associated with H. sapiens are known only from after 130,000 years ago. Unlike elsewhere in Africa, archaic Middle Stone Age sites appear to persist until very late, down to the Holocene boundary (12,000 years ago), pointing to the possibility of late survival of archaic humans, and late hybridization with H. sapiens in West Africa.

Early northern Africa dispersal

Populations of H. sapiens migrated to the Levant and to Europe between 130,000 and 115,000 years ago, and possibly in earlier waves as early as 185,000 years ago.

A fragment of a jawbone with eight teeth found at Misliya Cave, Israel, has been dated to around 185,000 years ago. Layers dating from between 250,000 and 140,000 years ago in the same cave contained tools of the Levallois type which could put the date of the first migration even earlier if the tools can be associated with the modern human jawbone finds.

These early migrations do not appear to have led to lasting colonisation and receded by about 80,000 years ago. There is a possibility that this first wave of expansion may have reached China (or even North America) as early as 125,000 years ago, but would have died out without leaving a trace in the genome of contemporary humans.

There is some evidence that modern humans left Africa at least 125,000 years ago using two different routes: through the Nile Valley heading to the Middle East, at least into modern Palestine (Qafzeh: 120,000–100,000 years ago); and a second route through the present-day Bab-el-Mandeb Strait on the Red Sea (at that time, with a much lower sea level and narrower extension), crossing to the Arabian Peninsula and settling in places like the present-day United Arab Emirates (125,000 years ago) and Oman (106,000 years ago), and possibly reaching the Indian Subcontinent (Jwalapuram: 75,000 years ago). Although no human remains have yet been found in these three places, the apparent similarities between the stone tools found at Jebel Faya, those from Jwalapuram and some from Africa suggest that their creators were all modern humans. These findings might give some support to the claim that modern humans from Africa arrived at southern China about 100,000 years ago (Zhiren Cave, Zhirendong, Chongzuo City: 100,000 years ago; and the Liujiang hominid (Liujiang County): controversially dated at 139,000–111,000 years ago ). Dating results of the Lunadong (Bubing Basin, Guangxi, southern China) teeth, which include a right upper second molar and a left lower second molar, indicate that the molars may be as old as 126,000 years. Since these previous exits from Africa did not leave traces in the results of genetic analyses based on the Y chromosome and on MtDNA (which represent only a small part of the human genetic material), it seems that those modern humans did not survive in large numbers and were assimilated by our major antecessors. An explanation for their extinction (or small genetic imprint) may be the Toba eruption (74,000 years ago), though some argue it scarcely impacted human population.

Coastal migration

Overview map of the peopling of the world by early humans during the Upper Paleolithic, following to the Southern Dispersal paradigm.

The so-called "recent dispersal" of modern humans has taken place after beginning about 70–50,000 years ago. It is this migration wave that led to the lasting spread of modern humans throughout the world.

A small group from a population in East Africa, bearing mitochondrial haplogroup L3 and numbering possibly fewer than 1,000 individuals, crossed the Red Sea strait at Bab el Mandib, to what is now Yemen, after around 75,000 years ago. A recent review has also shown support for the northern route through Sinai/Israel/Syria (Levant). Their descendants spread along the coastal route around Arabia and Persia to the Indian subcontinent before 55,000 years ago. Other research supports a migration out of Africa between about 65,000 and 50,000 years ago. The coastal migration between roughly 70,000 and 50,000 years ago is associated with mitochondrial haplogroups M and N, both derivative of L3.

Along the way H. sapiens interbred with Neanderthals and Denisovans, with Denisovan DNA making 0.2% of mainland Asian and Native American DNA.

Near Oceania

Migrations continued along the Asian coast to Southeast Asia and Oceania, colonising Australia by around 50,000 years ago. By reaching Australia, H. sapiens for the first time expanded its habitat beyond that of H. erectus. Denisovan ancestry is shared by Melanesians, Aboriginal Australians, and smaller scattered groups of people in Southeast Asia, such as the Mamanwa, a Negrito people in the Philippines, suggesting the interbreeding took place in Eastern Asia where the Denisovans lived. Denisovans may have crossed the Wallace Line, with Wallacea serving as their last refugium. Homo erectus had crossed the Lombok gap reaching as far as Flores, but never made it to Australia.

The map shows the probable extent of land and water at the time of the last glacial maximum, 20,000 yrs ago and when the sea level was probably more than 110m lower than today.

During this time sea level was much lower and most of Maritime Southeast Asia formed one land mass known as Sunda. Migration continued Southeast on the coastal route to the straits between Sunda and Sahul, the continental land mass of present-day Australia and New Guinea. The gaps on the Weber Line are up to 90 km wide, so the migration to Australia and New Guinea would have required seafaring skills. Migration also continued along the coast eventually turning northeast to China and finally reaching Japan before turning inland. This is evidenced by the pattern of mitochondrial haplogroups descended from haplogroup M, and in Y-chromosome haplogroup C.

Sequencing of one Aboriginal genome from an old hair sample in Western Australia revealed that the individual was descended from people who migrated into East Asia between 62,000 and 75,000 years ago. This supports the theory of a single migration into Australia and New Guinea before the arrival of Modern Asians (between 25,000 and 38,000 years ago) and their later migration into North America. This migration is believed to have happened around 50,000 years ago, before Australia and New Guinea were separated by rising sea levels approximately 8,000 years ago. This is supported by a date of 50,000–60,000 years ago for the oldest evidence of settlement in Australia, around 40,000 years ago for the oldest human remains, the earliest humans artifacts which are at least 65,000 years old and the extinction of the Australian megafauna by humans between 46,000 and 15,000 years ago argued by Tim Flannery, which is similar to what happened in the Americas. The continued use of Stone Age tools in Australia has been much debated.

Dispersal throughout Eurasia

The population brought to South Asia by coastal migration appears to have remained there for some time, during roughly 60,000 to 50,000 years ago, before spreading further throughout Eurasia. This dispersal of early humans, at the beginning of the Upper Paleolithic, gave rise to the major population groups of the Old World and the Americas.

Towards the West, Upper Paleolithic populations associated with mitochondrial haplogroup R and its derivatives, spread throughout Asia and Europe, with a back-migration of M1 to North Africa and the Horn of Africa several millennia ago.

Presence in Europe is certain after 40,000 years ago, possibly as early as 43,000 years ago, rapidly replacing the Neanderthal population. Contemporary Europeans have Neanderthal ancestry, but it seems likely that substantial interbreeding with Neanderthals ceased before 47,000 years ago, i.e. took place before modern humans entered Europe.

There is evidence from mitochondrial DNA that modern humans have passed through at least one genetic bottleneck, in which genome diversity was drastically reduced. Henry Harpending has proposed that humans spread from a geographically restricted area about 100,000 years ago, the passage through the geographic bottleneck and then with a dramatic growth amongst geographically dispersed populations about 50,000 years ago, beginning first in Africa and thence spreading elsewhere. Climatological and geological evidence suggests evidence for the bottleneck. The explosion of Toba, the largest volcanic eruption of the Quaternary, may have created a 1,000 year cold period, potentially reducing human populations to a few tropical refugia. It has been estimated that as few as 15,000 humans survived. In such circumstances genetic drift and founder effects may have been maximised. The greater diversity amongst African genomes may reflect the extent of African refugia during the Toba incident. However, a recent review highlights that the single-source hypothesis of non-African populations is less consistent with ancient DNA analysis than multiple sources with genetic mixing across Eurasia.

Europe

The recent expansion of anatomically modern humans reached Europe around 40,000 years ago from Central Asia and the Middle East, as a result of cultural adaption to big game hunting of sub-glacial steppe fauna. Neanderthals were present both in the Middle East and in Europe, and the arriving populations of anatomically modern humans (also known as "Cro-Magnon" or European early modern humans) interbred with Neanderthal populations to a limited degree. Populations of modern humans and Neanderthal overlapped in various regions such as the Iberian peninsula and the Middle East. Interbreeding may have contributed Neanderthal genes to palaeolithic and ultimately modern Eurasians and Oceanians.

An important difference between Europe and other parts of the inhabited world was the northern latitude. Archaeological evidence suggests humans, whether Neanderthal or Cro-Magnon, reached sites in Arctic Russia by 40,000 years ago.

Cro-Magnon are considered the first anatomically modern humans in Europe. They entered Eurasia by the Zagros Mountains (near present-day Iran and eastern Turkey) around 50,000 years ago, with one group rapidly settling coastal areas around the Indian Ocean and another migrating north to the steppes of Central Asia. Modern human remains dating to 43–45,000 years ago have been discovered in Italy and Britain, as well as in the European Russian Arctic from 40,000 years ago.

Humans colonised the environment west of the Urals, hunting reindeer especially, but were faced with adaptive challenges; winter temperatures averaged from −20 to −30 °C (−4 to −22 °F) with fuel and shelter scarce. They travelled on foot and relied on hunting highly mobile herds for food. These challenges were overcome through technological innovations: tailored clothing from the pelts of fur-bearing animals; construction of shelters with hearths using bones as fuel; and digging "ice cellars" into the permafrost to store meat and bones.

A mitochondrial DNA sequence of two Cro-Magnons from the Paglicci Cave in Italy, dated to 23,000 and 24,000 years old (Paglicci 52 and 12), identified the mtDNA as Haplogroup N, typical of the latter group.

Migration of modern humans into Europe, based on simulation by Currat & Excoffier (2004)
(YBP=Years before present)

 

Up to 37,500 YBP

 

Up to 35,000 YBP

 

Up to 32,500 YBP

 

Up to 30,000 YBP

The expansion of modern human population is thought to have begun 45,000 years ago, and it may have taken 15,000–20,000 years for Europe to be colonized.

During this time, the Neanderthals were slowly being displaced. Because it took so long for Europe to be occupied, it appears that humans and Neanderthals may have been constantly competing for territory. The Neanderthals had larger brains, and were larger overall, with a more robust or heavily built frame, which suggests that they were physically stronger than modern Homo sapiens. Having lived in Europe for 200,000 years, they would have been better adapted to the cold weather. The anatomically modern humans known as the Cro-Magnons, with widespread trade networks, superior technology and bodies likely better suited to running, would eventually completely displace the Neanderthals, whose last refuge was in the Iberian peninsula. After about 25,000 years ago the fossil record of the Neanderthals ends, indicating extinction. The last known population lived around a cave system on the remote south-facing coast of Gibraltar from 30,000 to 24,000 years ago.

From the extent of linkage disequilibrium, it was estimated that the last Neanderthal gene flow into early ancestors of Europeans occurred 47,000–65,000 years BP. In conjunction with archaeological and fossil evidence, interbreeding is thought to have occurred somewhere in Western Eurasia, possibly the Middle East. Studies show a higher Neanderthal admixture in East Asians than in Europeans. North African groups share a similar excess of derived alleles with Neanderthals as non-African populations, whereas Sub-Saharan African groups are the only modern human populations with no substantial Neanderthal admixture. The Neanderthal-linked haplotype B006 of the dystrophin gene has also been found among nomadic pastoralist groups in the Sahel and Horn of Africa, who are associated with northern populations. Consequently, the presence of this B006 haplotype on the northern and northeastern perimeter of Sub-Saharan Africa is attributed to gene flow from a non-African point of origin.

East and North Asia

"Tianyuan Man", an individual who lived in China c. 40,000 years ago, showed substantial Neanderthal admixture. A 2017 study of the ancient DNA of Tianyuan Man found that the individual is related to modern Asian and Native American populations. A 2013 study found Neanderthal introgression of 18 genes within the chromosome 3p21.31 region (HYAL region) of East Asians. The introgressive haplotypes were positively selected in only East Asian populations, rising steadily from 45,000 years ago until a sudden increase of growth rate around 5,000 to 3,500 years ago. They occur at very high frequencies among East Asian populations in contrast to other Eurasian populations (e.g. European and South Asian populations). The findings also suggest that this Neanderthal introgression occurred within the ancestral population shared by East Asians and Native Americans.

A 2016 study presented an analysis of the population genetics of the Ainu people of northern Japan as key to the reconstruction of the early peopling of East Asia. The Ainu were found to represent a more basal branch than the modern farming populations of East Asia, suggesting an ancient (pre-Neolithic) connection with northeast Siberians. A 2013 study associated several phenotypical traits associated with Mongoloids with a single mutation of the EDAR gene, dated to c. 35,000 years ago.

Mitochondrial haplogroups A, B and G originated about 50,000 years ago, and bearers subsequently colonized Siberia, Korea and Japan, by about 35,000 years ago. Parts of these populations migrated to North America during the Last Glacial Maximum.

Last Glacial Maximum

Eurasia

Schematic illustration of the Beringia migration based on matrilineal genetics: Arrival of Central Asian populations to the Beringian Mammoth steppe c. 25,000 years ago, followed by a "swift peoplling of the Americas" c. 15,000 years ago.

Around 20,000 years ago, approximately 5,000 years after the Neanderthal extinction, the Last Glacial Maximum forced northern hemisphere inhabitants to migrate to several shelters (refugia) until the end of this period. The resulting populations are presumed to have resided in such refuges during the LGM to ultimately reoccupy Europe, where archaic historical populations are considered their descendants. The composition of European populations was later altered by further migrations, notably the Neolithic expansion from the Middle East, and still later the Chalcolithic population movements associated with Indo-European expansion. A Paleolithic site on the Yana River, Siberia, at 71°N, lies well above the Arctic Circle and dates to 27,000 radiocarbon years before present, during glacial times. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought.

Americas

Main articles: Settlement of the Americas and Genetic history of indigenous peoples of the Americas

Paleo-Indians originated from Central Asia, crossing the Beringia land bridge between eastern Siberia and present-day Alaska. Humans lived throughout the Americas by the end of the last glacial period, or more specifically what is known as the late glacial maximum, no earlier than 23,000 years before present. Details of Paleo-Indian migration to and throughout the American continent, including the dates and the routes traveled, are subject to ongoing research and discussion.

The routes of migration are also debated. The traditional theory is that these early migrants moved when sea levels were significantly lowered due to the Quaternary glaciation, following herds of now-extinct pleistocene megafauna along ice-free corridors that stretched between the Laurentide and Cordilleran ice sheets. Another route proposed is that, either on foot or using primitive boats, they migrated down the Pacific coast to South America as far as Chile. Any archaeological evidence of coastal occupation during the last Ice Age would now have been covered by the sea level rise, up to a hundred metres since then. The recent finding of indigenous Australasian genetic markers in Amazonia supports the coastal route hypothesis.

Holocene migrations

Prehistoric migration routes for Y-chromosome Haplogroup N lineage following the retreat of ice sheets after the Last Glacial Maximum (22–18 kya).

The Holocene is taken to begin 12,000 years ago, after the end of the Last Glacial Maximum. During the Holocene climatic optimum, beginning about 9,000 years ago, human populations which had been geographically confined to refugia began to migrate. By this time, most parts of the globe had been settled by H. sapiens; however, large areas that had been covered by glaciers were now re-populated.

This period sees the transition from the Mesolithic to the Neolithic stage throughout the temperate zone. The Neolithic subsequently gives way to the Bronze Age in Old World cultures and the gradual emergence of the historical record in the Near East and China beginning around 4,000 years ago.

Large-scale migrations of the Mesolithic to Neolithic era are thought to have given rise to the pre-modern distribution of the world's major language families such as the Niger-Congo, Nilo-Saharan, Afro-Asiatic, Uralic, Sino-Tibetan or Indo-European phyla. The speculative Nostratic theory postulates the derivation of the major language families of Eurasia (excluding Sino-Tibetan) from a single proto-languages spoken at the beginning of the Holocene period.

Eurasia

Evidence published in 2014 from genome analysis of ancient human remains suggests that the modern native populations of Europe largely descend from three distinct lineages: "Western Hunter-Gatherers", derivative of the Cro-Magnon population of Europe, Early European Farmers introduced to Europe from the Near East during the Neolithic Revolution and Ancient North Eurasians which expanded to Europe in the context of the Indo-European expansion.

The Afroasiatic Urheimat has been placed in either Africa or Asia.

Sub-Saharan Africa

The Nilotic peoples are thought to be derived from an earlier undifferentiated Eastern Sudanic unity by the 3rd millennium BCE. The development of the Proto-Nilotes as a group may have been connected with their domestication of livestock. The Eastern Sudanic unity must have been considerably earlier still, perhaps around the 5th millennium BCE (while the proposed Nilo-Saharan unity would date to the Upper Paleolithic about 15kya). The original locus of the early Nilotic speakers was presumably east of the Nile in what is now South Sudan. The Proto-Nilotes of the 3rd millennium BCE were pastoralists, while their neighbors, the Proto-Central Sudanic peoples, were mostly agriculturalists.

The Niger-Congo phylum is thought to have emerged around 6,000 years ago in West or Central Africa. Its expansion may have been associated with the expansion of Sahel agriculture in the African Neolithic period, following the desiccation of the Sahara in c. 3900 BCE. The Bantu expansion has spread the Bantu languages to Central, Eastern and Southern Africa, partly replacing the indigenous populations of these regions. Beginning about 3,000 years ago, it reached South Africa about 1,700 years ago.

Some evidence (including a 2016 study by Busby et al.) suggests admixture from ancient and recent migrations from Eurasia into parts of Sub-Saharan Africa. Another study (Ramsay et al. 2018) also shows evidence that ancient Eurasians migrated into Africa and that Eurasian admixture in modern Sub-Saharan Africans ranges from 0% to 50%, varying by region and generally higher in the Horn of Africa and parts of the Sahel zone, and found to a lesser degree in certain parts of Western Africa, and Southern Africa (excluding recent immigrants).

Indo-Pacific

Chronological map of the Austronesian expansion

The first seaborne human migrations were by the Austronesian peoples originating from Taiwan known as the "Austronesian expansion". Using advanced sailing technologies like catamarans, outrigger boats, and crab claw sails, they built the first sea-going ships and rapidly colonized Island Southeast Asia at around 3000 to 1500 BCE. From the Philippines and Eastern Indonesia they colonized Micronesia by 2200 to 1000 BCE.

A branch of the Austronesians reached Island Melanesia between 1600 and 1000 BCE, establishing the Lapita culture (named after the archaeological site in Lapita, New Caledonia, where their characteristic pottery was first discovered). They are the direct ancestors of the modern Polynesians. They ventured into Remote Oceania reaching Vanuatu, New Caledonia, and Fiji by 1200 BCE, and Samoa and Tonga by around 900 to 800 BCE. This was the furthest extent of the Lapita culture expansion. During a period of around 1,500 years, they gradually lost the technology for pottery (likely due to the lack of clay deposits in the islands), replacing it with carved wooden and bamboo containers. Back-migrations from the Lapita culture also merged back Island Southeast Asia in 1500 BCE, and into Micronesia at around 200 BCE. It was not until 700 CE when they started voyaging further into the Pacific Ocean, when they colonized the Cook Islands, the Society Islands, and the Marquesas. From there, they further colonized Hawaii by 900 CE, Rapa Nui by 1000 CE, and New Zealand by 1200 CE.

In the Indian Ocean, Austronesians from Borneo also colonized Madagascar and the Comoros Islands by around 500 CE. Austronesians remain the dominant ethnolinguistic group of the islands of the Indo-Pacific, and were the first to establish a maritime trade network reaching as far west as East Africa and the Arabian peninsula. They assimilated earlier Pleistocene to early Holocene human overland migrations through Sundaland like the Papuans and the Negritos in Island Southeast Asia. The Austronesian expansion was the last and the most far-reaching Neolithic human migration event.

Caribbean

The Caribbean was one of the last places in the Americas that were settled by humans. The oldest remains are known from the Greater Antilles (Cuba and Hispaniola) dating between 4000 and 3500 BCE, and comparisons between tool-technologies suggest that these peoples moved across the Yucatán Channel from Central America. All evidence suggests that later migrants from 2000 BCE and onwards originated from South America, via the Orinoco region. The descendants of these migrants include the ancestors of the Taíno and Kalinago (Island Carib) peoples.

Arctic

The earliest inhabitants of North America's central and eastern Arctic are referred to as the Arctic small tool tradition (AST) and existed c. 2500 BCE. AST consisted of several Paleo-Eskimo cultures, including the Independence cultures and Pre-Dorset culture.

The Inuit are the descendants of the Thule culture, which emerged from western Alaska around AD 1000 and gradually displaced the Dorset culture.