Our Human Journey: Migration
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Institute of Human Origins
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Early humans (before Homo sapiens) Homo erectus migrated from out of Africa via the Levantine corridor and Horn of Africa to Eurasia around 1.9 to 2 million years ago, possibly as a result of climate change caused by the ice ages in the Northern Hemisphere. 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 discovered in Eastern Africa. Key sites for this early migration out of Africa are Riwat in Pakistan (approximately 2 MYA), Ubeidiya in the Middle Eastern region known as the Levant (1.5 MYA), and Dmanisi in the mountainous region between the Black Sea and the Caspian Sea called the Caucasus (1.81MYA). 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. 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. 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 50,000 years ago. The evolutionary ancestor of Denisovans is likely to be shared with H. sapiens and H. neanderthalensis 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.
Within Africa The most recent common ancestor shared by all living human beings, dubbed Mitochondrial Eve, probably lived roughly 120–150 millennia ago, probably in East Africa. 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)
Exodus from Africa 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. Nonetheless, in July 2017, evidence suggests that Homo sapiens may have migrated from Africa as early as 270,000 years ago, much earlier than the 70,000 years ago thought previously.
South Asia and AustraliaNOTE: A haplogroup is a genetic population group of people who share a common ancestor on the patriline or the matriline . Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations. Dating of teeth from China provides evidence of an early migration of modern humans from Africa into Southeast Asia before 80,000 - 120,000 years ago. A 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 people in the Philippines, suggesting the interbreeding took place in Eastern Asia where the Denisovans lived. Denisovans may have made it as far as the islands of Indonesia. Homo erectus crossed as far as the Indonesian island of Flores, but never arrived in Australia During this time sea level was much lower and most of Maritime Southeast Asia formed one land mass known as Sunda. Homo sapiens migration continued Southeast on the coastal route to the straits between Sunda and the continental land mass of present-day Australia and New Guinea (called Sahul). The gaps, however, may have been 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, and around 40,000 years ago for the oldest human remains. The earliest human artefacts are at least 65,000 years old and the extinction of large Australian animals (megafauna) by humans between 46,000 and 15,000 years ago advocated by Tim Flannery, an event similar to what happened in the Americas.
Migration of the Cro-Magnons into Europe 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 colonized 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. 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. Some scientists estimate that the last Neanderthal gene flow into early ancestors of Europeans occurred 47,000–65,000 years ago. 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 similar amounts of Neanderthal DNA as do non-African populations, whereas Sub-Saharan African groups are the only modern human populations that generally did not experience Neanderthal admixture.
Three-part origin of modern Europeans 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 Caspian Sea nomads who contributed DNA (and Indo-European languages) to a wide range of modern humans including native Americans.
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. 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 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. Current estimates range from 40,000 to around 16,500 years ago. 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.
© Adapted from: https://en.wikipedia.org/wiki/Early_human_migrations and numerous other sources cited at the beginning.