The earliest migrations and expansions of archaic and modern humans across continents began 2 million years ago with the migration out of Africa of Homo erectus. This was followed by the migrations of other pre-modern humans including H. heidelbergensis, the likely ancestor of both anatomically modern humans and Neanderthals. Finally, the recent African origin paradigm suggests that Homo sapiens migrated out of Africa around 100,000 years ago, spread across Asia approximately 60,000 years ago, and subsequently populated other continents and islands.
Knowledge of early human migrations, a major topic of archeology, has been achieved by the study of human fossils, occasionally by stone-age artifacts and more recently has been assisted by archaeogenetics. Cultural and ethnic migrations are estimated by combining archaeogenetics and comparative linguistics.
Homo erectus migrated from out of Africa via the Levantine corridor and Horn of Africa to Eurasia during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 1.9 million years ago. They dispersed throughout most of the Old World, reaching as far as Southeast Asia. The date of original dispersal beyond Africa virtually coincides with the appearance of Homo ergaster in the fossil record, and about half a million years after the appearance of the Homo genus itself and the first stone tools of the Oldowan industry. 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 was populated as early as 1.66 Mya based on stone artifacts found in the Nihewan Basin. The archaeological site of Xihoudu () in Shanxi Province is the earliest recorded use of fire by Homo erectus, which is dated 1.27 million years ago.
Robert G. Bednarik has suggested that Homo erectus may have built rafts and sailed oceans, a theory that has raised some controversy.
The expansion of H. erectus was followed by the arrival of H. antecessor in Europe around 800,000 years ago, which was in turn followed by migration from Africa to Europe of H. heidelbergensis, the likely ancestor of both modern humans and Neanderthals, around 600,000 years ago. The presence of a third homo species, h. denisova (Denisovans) in Siberia (via archeological evidence) and East/South East Asia (via DNA evidence) is now well accepted. Denisovans interbred with Neanderthals and modern humans (including ancestors of Papuans, Melanesians and Australian aboriginals) as recently as 50,000ya. The evolutionary ancestor of Denisovans is likely to be shared with h.sapiens and h.neandertal by way of h.heidlebergensis, though the scant archaeological evidence makes a history of Denisovans largely a matter of assumptions based on DNA data.
Neanderthal gene flow has also been observed among various populations in Africa. Additionally, among certain groups below the Sahara, there is DNA evidence of archaic admixture from hominins that broke away from the modern human lineage around 700,000 years ago. This genetic introgression has been estimated to date to 35-40,000 years before present.
Ethiopia is considered one of the earliest sites of the emergence of anatomically modern humans, Homo sapiens. The oldest of these local fossil finds, the Omo remains, were excavated in the southwestern Omo Kibish area and have been dated to the Middle Paleolithic, around 200,000 years ago. Additionally, skeletons of Homo sapiens idaltu were found at a site in the Middle Awash valley. Dated to approximately 160,000 years ago, they may represent an extinct subspecies of Homo sapiens, or the immediate ancestors of anatomically modern humans. Fossils excavated at the Jebel Irhoud site in Morocco have since been dated to an earlier period, about 300,000 years ago.
Current dating of human fossils indicates that modern humans migrating Out of Africa between 125 - 18 kya (thousand years ago) moved into lands occupied by at least four known homo species. These are (species/place/most recent date alive): h.erectus, Eurasia, 27kya; h.neanderthalensis, Europe 30kya/Central Asia 40kya; h.sp.altai (or Denisovans), Siberia/Asia/SE Asia, 30kya), h. floresiensis (or 'Hobbits', note controversy whether this is a homo species), SE Asia, 18kya. There is genetic evidence from Melanesian and Australian Aboriginal DNA, of another unidentified homo species from around 400kya to a time when interbreeding with modern humans migrating OoA could have occurred (70-30kya?). Plus, early humans could have interacted with any number of hybrid groups that became extinct, as indicated by examples such as: Lapedo Child, Europe, 24kya; Red Deer Cave People, China, 11kya; h.tsaichangensis, Taiwan, 10kya.
When modern humans reached the Near East or Levantine corridor 125,000 years ago, evidence suggests they were forced out, as their settlements were replaced by Neanderthals between 80-47kys . This same reference shows support for the probability that multiple Out of Africa (OoA) migrations occurred from as early as 125kya to as far as China, but "died out" and did not contribute to the DNA of living modern humans. One well supported view is that the first modern humans that contributed to the DNA of living modern humans, spread east across Asia from Africa about 75,000 years ago across the Southern Route of Bab el Mandib connecting Ethiopia and Yemen. A recent review has shown support for both the Northern Route through Sinai/Israel/Syria (Levant), and, that both routes may have been used. From the Near East, some of these people went east to South Asia by 50,000 years ago, and on to Australia by 46,000 years ago at the latest, when for the first time H. sapiens reached territory never reached by H. erectus. H. sapiens reached Europe around 43,000 years ago, eventually replacing the Neanderthal population by 40,000 years ago East Asia was reached by 30,000 years ago. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover. The date of migration to North America, and whether humans had previously inhabited the Americas is disputed; it may have taken place around 130 thousand years ago, or considerably later, around 14 thousand years ago. The oldest radiocarbon dated carbonized plant remains were determined to be 50,300 years old and were discovered at the Topper site in Allendale South Carolina in May 2004 alongside stone tools similar to those of pre-Clovis era humans. The oldest DNA evidence of human habitation in North America however, has been radiocarbon dated to 14,300 years ago, and was found in fossilized human coprolites uncovered in the Paisley Five Mile Point Caves in south-central Oregon. Colonization of the Pacific islands of Polynesia began around 1300 BC, and was completed by 1280 AD (New Zealand). The ancestors of Polynesians left Taiwan around 5,200 years ago.
More recent migrations of language and culture groups within the modern species are also studied and hypothetised. The African Epipaleolithic Kebaran culture is believed to have reached Eurasia about 18,000 years ago, introducing the bow and arrow to the Middle East, and may have been responsible for the spread of the Nostratic languages. The people of the Afro-Asiatic language family seem to have reached Africa in 6,200 BC, introducing the Semitic languages to the Middle East.
From there they spread around the world. An initial venture out of Africa 125,000 years ago was followed by a flood out of Africa via the Arabian Peninsula into Eurasia around 60,000 years ago, with one group rapidly settling coastal areas around the Indian Ocean and one group migrating north to steppes of Central Asia.
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 Lake Toba created a 1,000 year cold period, as a result of the largest volcanic eruption of the Quaternary, 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 be in part due to the greater prevalence of African refugia during the Toba incident. However, a recent review highlights that the single-source hypothesis of non-African populations is less supported by ancient DNA analysis than multiple sources plus genetic mixing across Eurasia.
The most recent common ancestor shared by all living human beings, dubbed Mitochondrial Eve, probably lived roughly 120-150 millennia ago, the time of Homo sapiens idaltu, probably in East Africa.
The broad study of African genetic diversity headed by Dr. Sarah Tishkoff found the San people to express the greatest genetic diversity among the 113 distinct populations sampled, making them one of 14 "ancestral population clusters." The research also located the origin of modern human migration in south-western Africa, near the coastal border of Namibia and Angola.
Around 100,000-80,000 years ago, three main lines of Homo sapiens diverged. Bearers of mitochondrial haplogroup L0 (mtDNA) / A (Y-DNA) colonized Southern Africa (the ancestors of the Khoisan ( peoples), bearers of haplogroup L1 (mtDNA) / B (Y-DNA) settled Central and West Africa (the ancestors of western pygmies), and bearers of haplogroups L2, L3, and others mtDNA remained in East Africa (the ancestors of Niger-Congo- and Nilo-Saharan-speaking peoples). (see L-mtDNA)
There is some evidence for the argument that modern humans left Africa at least 125,000 years ago using two different routes: the Nile Valley heading to the Middle East, at least into modern Israel (Qafzeh: 120,000-100,000 years ago); and a second one 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 it into the Arabian Peninsula, settling in places like the present-day United Arab Emirates (125,000 years ago) and Oman (106,000 years ago) and then possibly going into the Indian Subcontinent (Jwalapuram: 75,000 years ago). Despite the fact that no human remains have yet been found in these three places, the apparent similarities between the stone tools found at Jebel Faya, the ones from Jwalapuram and some African ones 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 or survived in small numbers and were assimilated by our major antecessors. An explanation for their extinction (or small genetic imprint) may be the Toba catastrophe theory (74,000 years ago). However, some argue that its impact on human population was not dramatic.
According to the Recent African Origin theory a small group of the L3 haplogroup bearers living in East Africa migrated north east, possibly searching for food or escaping adverse conditions, crossing the Red Sea about 70 millennia ago, and in the process going on to populate the rest of the world. This event may have originated as a single crossing from the Horn of Africa to the Arabian peninsula, or from several waves of migration in close proximity.
The later major migration from Africa traveled along the coast of Arabia and Persia to India and the rest of South Asia. Along the way H. sapiens interbred with Neanderthals and Denisovans, with Denisovan DNA making 0.2% of mainland Asian and Native American DNA. David Reich of Harvard University and Mark Stoneking of the Planck Institute team, found genetic evidence that Denisovan ancestry is shared by Melanesians, Australian Aborigines, 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 crossed the Lombok gap reaching as far as Flores, but never made it to Australia.
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 to 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 artefacts are at least 65,000 years old and the extinction of the Australian megafauna by humans between 46,000 and 15,000 years ago advocated 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.
The recent expansion of anatomically modern humans reached Europe around 40,000 years ago, from 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) have interbred with Neanderthal populations to a limited degree. Populations of modern humans and Neanderthal overlapped in various regions such as in Iberian peninsula and in 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.
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 (known as refugia) until the end of this period. The resulting populations are then 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.
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 one group migrating north to steppes of Central Asia. Modern human remains dating to 43-45,000 years ago have been discovered in Italy and Britain, with the remains found of those that reached the European Russian Arctic 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) while fuel and shelter were scarce. They travelled on foot and relied on hunting highly mobile herds for food. These challenges were overcome through technological innovations: production of tailored clothing from the pelts of fur-bearing animals; construction of shelters with hearths using bones as fuel; and digging of "ice cellars" into the permafrost for storing 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. The inland group is the founder of both North- and East Asians, Caucasoids and large sections of the Middle East population. Migration from the Black Sea area into Europe started sometime around 45,000 years ago, probably across the Bosphorus and along the Danubian corridor. By 20,000 years ago, the whole of Continental Europe had been settled.
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 that they had become extinct. 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, the gene flow is thought likely 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 do non-African populations, whereas Sub-Saharan African groups are the only modern human populations that generally did not experience Neanderthal admixture. The Neanderthal-linked haplotype B006 of the dystrophin gene has also been found among nomad 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.
Evidence published in 2014 from genome analysis of ancient human remains suggests that the modern native populations of Europe largely descend from three distinct lines: Hunter-gatherers who lived 45,000 years ago and most probably originated in the second human migration out of Africa into Europe, early agriculturists who moved into Europe about 9,000 years ago and mixed in, and finally a population of pontic-caspian steppe nomads who contributed DNA (and Indo-European languages) to a wide range of modern humans including 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.
East Asian genetics shows a number of concentrated alleles suggestive of selection pressures since their separation from Caucasoids. This concerns the genes EDAR, ADH1B, ABCC1, and ALDH2 in particular. The East Asian types of ADH1B are associated with rice domestication and would thus have arisen after the c. 11,000 years ago. 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. 
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 suggests that this Neanderthal introgression occurred within the ancestral population shared by East Asians and Native Americans. "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 closely related to modern East Asian populations, but not a direct ancestor.
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.
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.
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 Australoid genetic markers in Amazonia supports the coastal route hypothesis.
We found that North African populations have a significant excess of derived alleles shared with Neandertals, when compared to sub-Saharan Africans. This excess is similar to that found in non-African humans, a fact that can be interpreted as a sign of Neandertal admixture. Furthermore, the Neandertal's genetic signal is higher in populations with a local, pre-Neolithic North African ancestry. Therefore, the detected ancient admixture is not due to recent Near Eastern or European migrations. Sub-Saharan populations are the only ones not affected by the admixture event with Neandertals.
Of 1,420 sub-Saharan chromosomes, only one copy of B006 was observed in Ethiopia, and five in Burkina Faso, one among the Rimaibe and four among the Fulani and Tuareg, nomad-pastoralists known for having contacts with northern populations (supplementary table S1, Supplementary Material online). B006 only occurrence at the northern and northeastern outskirts of sub-Saharan Africa is thus likely to be a result of gene flow from a non-African source.
Canada's oldest known home is a cave in Yukon occupied not 12,000 years ago like the U.S. sites, but at least 20,000 years ago
However, despite the lack of conclusive or widespread evidence, there are suggestions of human occupation in the northern Yukon about 24,000 years ago, and hints of the presence of humans in the Old Crow Basin as far back as about 40,000 years ago.