Early human migrations
Early human migrations began when Homo erectus first migrated out of Africa over the Levantine corridor and Horn of Africa to Eurasia about 1.8 million years ago. The expansion of H. erectus out of Africa was followed by that of Homo antecessor into Europe around 800,000 years ago, followed by Homo heidelbergensis around 600,000 years ago, where they probably evolved to become the Neanderthals.
Modern humans, Homo sapiens, evolved in Africa up to 200,000 years ago and reached the Near East around 125,000 years ago. From the Near East, these populations spread east to South Asia by 50,000 years ago, and on to Australia by 40,000 years ago, 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. East Asia was reached by 30,000 years ago.
The date of migration to North America is disputed; it may have taken place around 30 millennia ago, or considerably later, around 14 millennia ago. Colonisation of the Pacific islands of Polynesia began around 1300 BC, and was completed by 900 AD. The ancestors of Polynesians left Taiwan around 5,200 years ago.
The study of early human migrations since the 1980s has developed significantly due to advances in archaeogenetics.
Early humans (before Homo sapiens) 
Early members of the Homo genus, i.e. Homo ergaster, Homo erectus and Homo heidelbergensis, migrated from Africa during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 1.9 million years ago, and 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 the associated first emergence of full bipedalism, 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 (1.9 Mya), Ubeidiya in the Levant (1.5 Mya) and Dmanisi in the Caucasus (1.7 Mya).
China was populated more than a million years ago, as early as 1.66 Mya based on stone artifacts found in the Nihewan Basin. Stone tools found at Xiaochangliang site were dated to 1.36 million years ago. 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.
Homo sapiens migrations 
Homo sapiens are supposed to have appeared in East Africa around 200,000 years ago. The oldest individuals found left their marks in the Omo remains (195,000 years ago) and the Homo sapiens idaltu (160,000 years ago), that was found at the Middle Awash site in Ethiopia. Recent claims of remains of anatomically modern humans from 400,000 years ago, found at Qesem Cave (Israel), are controversial. Some authors argue that these remains are from Neanderthals or their ancestors.
From there they spread around the world. An exodus from Africa over the Arabian Peninsula around 125,000 years ago brought modern humans to Eurasia, with one group rapidly settling coastal areas around the Indian Ocean and one group migrating north to steppes of Central Asia.
Within Africa 
The matrilinear 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 (Capoid) 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)
Exodus from Africa 
There is some evidence for the argument that modern humans left Africa at least 125,000 years before present (BP) using two different routes: the Nile Valley heading to the Middle East, at least into modern Israel (Qafzeh: 120,000–100,000 years BP); 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 BP) and Oman (106,000 years BP) and then possibly going into the Indian Subcontinent (Jwalapuram: 75,000 years BP). 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 BP (Zhiren Cave, Zhirendong, Chongzuo City: 100,000 years BP; and the Liujiang hominid: controversially dated at 139,000–111,000 years BP ).
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, responsible for a determinant posterior exit. An explanation for their extinction (or small genetic imprint) may be the Toba catastrophe theory (74,000 years BP). 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. According to some authors, based in the fact that only descents of L3 are found outside Africa, only a few people left Africa in a single migration to a settlement in the Arabian peninsula. From that settlement, some others point to the possibility of several waves of expansion close in time. For example, Wells says that the early travelers followed the southern coastline of Asia, crossed about 250 kilometers [155 miles] of sea (probably by simple boats or rafts), and colonized Australia by around 50,000 years ago. The Aborigines of Australia, Wells says, are the descendants of the first wave of migration out of Africa.
Around 50,000 years ago the world was entering the last ice age and water was trapped in the polar ice caps, so sea levels were much lower. Today at the Gate of Grief the Red Sea is about 12 miles (20 kilometres) wide but 50,000 years ago it was much narrower and sea levels were 70 metres lower. Though the straits were never completely closed, there may have been islands in between which could be reached by simple rafts. Shell middens 125,000 years old indicate that the diet of early humans in Eritrea included sea food obtained by beachcombing. This has been seen as evidence that humans may have crossed the Red Sea in search of food sources on new beaches.
South Asia and Australia 
Some genetic evidence points to migrations out of Africa along two routes. However, other studies suggest that a single migration occurred, followed by rapid northern migration of a subset of the group. Once in West Asia, the people who remained south (or took the southern route) spread generation by generation around the coast of Arabia and Persia until they reached India. One of the groups that went north (east Asians were the second group) ventured inland and radiated to Europe, eventually displacing the Neanderthals. They also radiated to India from Central Asia. The former group headed along the southeast coast of Asia, reaching Australia between 55,000 and 30,000 years ago, with most estimates placing it about 46,000 to 41,000 years ago.
During that time, sea level was much lower and most of Maritime Southeast Asia was one land mass known as the lost continent of Sunda. The settlers probably continued on the coastal route southeast until they reached the series of straits between Sunda and Sahul, the continental land mass that was made up of present-day Australia and New Guinea. The widest gaps are on the Weber Line and are at least 90 km wide, indicating that settlers had knowledge of seafaring skills. Archaic humans such as Homo erectus never reached Australia, although they crossed the Lombok gap reaching as far as Flores.
If these dates are correct, Australia was populated up to 10,000 years before Europe. This is possible because humans avoided the colder regions of the North favoring the warmer tropical regions to which they were adapted given their African homeland. Another piece of evidence favoring human occupation in Australia is that beginning about 46,000 years ago, all megafauna weighing more than 100 kg became extinct. Tim Flannery and others argue new settlers were likely to be responsible for this extinction. Many of the animals may have been accustomed to living without predators and become docile and vulnerable to attack (as occurred later in the Americas).
While some settlers crossed into Australia, others may have continued eastwards along the coast of Sunda eventually turning northeast to China and finally reaching Japan, leaving a trail of coastal settlements. This coastal migration leaves its trail in the mitochondrial haplogroups descended from haplogroup M, and in Y-chromosome haplogroup C. Thereafter, it may have become necessary to venture inland possibly bringing modern humans into contact with archaic humans such as H. erectus. Recent genetic studies suggest that Australia and New Guinea were populated by one single migration from Asia as opposed to several waves,in these single migration a population which had split from the ancestral Eurasian population, before Asians and Europeans split each other, reach Australia and Melanesia between 62.000 and 75.000 years before present, the descendants of the earlier migration became assimilated or replaced by the later dispersing populations from the next migration waves, with a few exceptions that include Aboriginals Australians and other related populations like Papuans.  2 The land bridge connecting New Guinea and Australia became submerged approximately 8,000 years ago, thus isolating the populations of the two land masses.
Europe is thought to have been colonized by northwest bound migrants from Central Asia and the Middle East. When the first anatomically modern humans entered Europe, Neanderthals were already settled there. Debate exists whether modern human populations interbred with Neanderthal populations, most of the evidence suggesting that it happened to a small degree rather than complete absorption. Populations of modern man and Neanderthal overlapped in various regions such as in Iberian peninsula and in the Middle East and that 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 BC, 10,000 years after the Neanderthal extinction, the Last Glacial Maximum took place forcing northern hemisphere inhabitants to migrate to several shelters (known as refugia) until the end of this period. The resulting populations, whether interbred with Neanderthals or not, are then presumed to have resided in those hypothetical refuges during the LGM to ultimately reoccupy Europe where archaic historical populations are considered their descendents. An alternate view is that modern European populations have descended from Neolithic populations in the Middle East that have been well documented in this area. The debate surrounding the origin of Europeans has been worded in terms of cultural diffusion versus demic diffusion. Archeological evidence and genetic evidence strongly support demic diffusion, that a population spread from the Middle East over the last 12,000 years. A scientific genetic concept called the Time to Most Recent Common Ancestor or TMRCA has been used to refute the demic diffusion in favour of cultural diffusion.
Migration of the Cro-Magnons into Europe 
Cro-Magnon are considered the first anatomically modern humans in Europe. They entered Eurasia by the Arabian Peninsula 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.
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 some around 45,000 years ago, probably along the Danubian corridor. By 20,000 years ago, the whole of Continental Europe (except Scandinavia), which was not covered under the Ice sheets, had been settled. The first complete human remains that have been preserved is the mummy Ötzi, from 3300 BC, belonging to the K1 MitDNA.
Migration of modern humans into Europe, based on simulation by Currat & Excoffier (2004)
(YBP=Years before present)
Competition with Neanderthals 
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 were larger and had a more robust or heavy built frame which may suggest 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 superior technology and language would eventually completely displace the Neanderthals, whose last refuge was in the Iberian peninsula. After about 30,000 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.
Proponents of the multiregional hypothesis have long believed that Europeans were descended from Neanderthals and not from this Homo sapiens migration. Others believed the Neanderthals had interbred with modern humans. In 1997 researchers managed to extract mitochondrial DNA from a 40,000 year old specimen of a Neanderthal. On comparison with human DNA, its sequences differed significantly, indicating that based on the mitochondrial DNA, modern Europeans are not descended from the Neanderthals and that no interbreeding took place. Some scientists continue to search autosomal DNA for traces of Neanderthal admixture. A few alleles of some autosomal genes such as the H2 allele of the MAPT gene have been suggested, since they were only found among Europeans. In the absence of autosomal DNA from a Neanderthal, the scientists conclude that this hypothesis is speculative.
Some archaeologists suspect that Neanderthals and Homo sapiens were not interfertile. This is because Neanderthals and Europeans shared the same habitat for up to 20,000 years, yet no undisputed skeletal fossils have been found that show intermediate properties between the two species.
Current (as of 2010) genetic evidence suggests interbreeding took place with Homo sapiens sapiens (anatomically modern humans) between roughly 80,000 to 50,000 years ago in the Middle East, resulting in non-ethnic sub-Saharan Africans having no Neanderthal DNA and Caucasians and Asians having between 1% and 4% Neanderthal DNA.
Central and Northern Asia 
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.
Paleo-Indians are agreed to have 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, around 16,000 — 13,000 years before present. The 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 Northwest 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 meters since then.
See also 
- Historical migration
- Human migrations
- List of countries and islands by first human settlement
- Middle Paleolithic
- Timeline of human evolution
- Upper Paleolithic
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