Early human migrations

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Map of early human migrations according to mitochondrial population genetics (numbers are millennia before present) (accuracy disputed).

Evolution of the genus Homo took place in Africa. First Homo erectus migrated out of Africa across Eurasia, beginning about 2 million years ago.

The expansion of Homo erectus was followed by that of Homo sapiens. H. sapiens reached the Near East around 70 millennia ago. From the Near East, these populations spread east to South Asia by 50 millennia ago, and on to Australia by 40 millennia ago (for the first time Homo sapiens reached territory never reached by Homo erectus). Europe was reached by Homo sapiens some 40 millennia ago. East Asia was reached by 30 millennia ago. The date of migration to North America is disputed; it may have taken place around 30 millennia ago, or only considerably later, around 14 millennia ago.

The Pacific islands of Polynesia were not colonized until the 1st millennium CE.

[edit] Early humans (before Homo sapiens)

A reconstruction of Homo erectus. Anthropologists believe that H. erectus was the first hominid to control fire.

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,^[1] as early as 1.66 Mya based on stone artefacts found in the Nihewan Basin.^[2] Stone tools found at Xiaochangliang site were dated to 1.36 million years ago.^[3] The archaeological site of Xihoudu (西侯渡) in Shanxi Province is the earliest recorded of use of fire by Homo erectus, which is dated 1.27 million years ago.^[1]

Southeast Asia (Java) was reached about 1.7 million years ago (Meganthropus).

West Europe was populated since c. 1.2 million ago (Atapuerca).^[4]

Bruce Bower has suggested that Homo erectus may have built rafts and sailed oceans, a theory that has raised some controversy.^[5]

It should be noted that Homo was not the first Hominid to colonize Asia: Pongo had arrived in Southeast Asia some 15 million years earlier (see Sivapithecus).

[edit] Homo sapiens migrations

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[edit] 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.^[6]

Around 100-80 millennia ago, three main lines of Homo sapiens diverged, bearers of mitochondrial haplogroup L1 (mtDNA) / A (Y-DNA) colonizing Southern Africa (the ancestors of the Khoisan (Capoid) peoples), bearers of haplogroup L2 (mtDNA) / B (Y-DNA) settling Central and West Africa (the ancestors of Niger-Congo and Nilo-Saharan speaking peoples and of the Mbuti pygmies), while the bearers of haplogroup L3 remained in East Africa.

[edit] Exodus from Africa

Red sea crossing

According to the Recent African Origin hypothesis a small group of the L3 bearers living in East Africa migrated north east, possibly searching for food or escaping climate changes, crossing the Red Sea about 70 millennia ago, and in the process going on to populate the rest of the world.

Around 50,000 years ago the world was entering the last ice age and sea levels were much lower as water was trapped in the polar ice caps. 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 meters lower. Though the straits were never completely closed, there may have been islands in between which could be reached using simple rafts. Shell middens 125,000 years old have been found in Eritrea indicating the diet of early humans was sea food obtained by beachcombing. This is perceived to be evidence that humans may have crossed the Red Sea in search of new food sources available on uninhabited beaches.

[edit] 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^[7] 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.

The map shows the probable extent of land and water at the time of the last glacial maximum and when the sea level was probably more than 150m lower than today

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 channel between Sunda and Sahul, the continental land mass that was made up of present-day Australia and New Guinea. This channel is also known as the Wallace Line. The channel was 90 km wide, indicating that settlers had knowledge of seafaring skills. Archaic humans such as Homo erectus never reached Australia.

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 about 46,000 years ago, all large mammals weighing more than 100 kg suddenly became extinct. The 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. The land bridge connecting New Guinea and Australia became submerged approximately 8,000 years ago, thus isolating the populations of the two land masses^[8][9].

[edit] Europe

Europe is thought to have been colonized by northwest bound migrants from Central Asia and the Middle East. The expansion is thought to have begun 45,000 years ago and may have taken up to 15,000 years for Europe to be fully colonized.^[7][10] During this time the Neanderthals were slowly being displaced. Because it took so long for Europe to be overrun, 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, however, 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 humans from Africa. 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.^[11] Some scientists continue to search autosomal DNA for traces of Neanderthal admixture.^[12] 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. However in the absence of autosomal DNA from a Neanderthal, the scientists conclude that this hypothesis is entirely speculative^[13].

Some archaeologists doubt that Neanderthals and Homo sapiens were 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.^[14]

[edit] 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.

[edit] The Americas

Beringia

The Americas were occupied by Asian people who crossed from Siberia into Alaska. At the time sea levels were lower and a land bridge of the lost continent of Beringia connected North America to Eurasia. It is likely they used the southern route that may have been much warmer.

There is considerable controversy over when the Americas were first colonized and how many migrations there were. Controversial findings in Chile at Monte Verde may indicate a human presence in the Americas by up to 33,000 years ago. The oldest indisputable evidence of human presence in the Americas are, however, findings related to the Clovis culture, which have been dated to about 11,000 years ago. The findings of Clovis points indicate the early settlers hunted large animals. About the same time as the arrival of the clovis culture many large animals such as Mammoths became extinct (as in Australia, possibly due to hunting).

Linguist Joseph Greenberg controversially classified American languages into three major families: Eskimo-Aleut, spoken by the Inuit peoples; Na-Dené, comprising 32 languages spoken only in North America by the Apache, Navajo, and tribes in Alaska and Canada; and Amerind, comprising more than 500 languages spoken in North and South America. Greenberg suggested that these three languages families represented three separate migrations that filled the Americas in the order they arrived.

[edit] See also

• Historical migration
• Middle Paleolithic
• Upper Paleolithic

[edit] References