The recent African origin of modern humans or the "Out of Africa" theory (OOA) holds that present-day humans outside Africa descend mainly from a single expansion of anatomically modern humans (Homo sapiens) from Africa about 70,000–50,000 years ago. It is the most widely accepted paleo-anthropological model of the geographic origin and early migration of the human species.
This expansion follows the earlier expansions of hominins out of Africa, accomplished by Homo erectus and then Homo neanderthalensis.
The model proposes a "single origin" of Homo sapiens in the taxonomic sense, precluding parallel evolution in other regions of traits considered anatomically modern, but not precluding multiple admixture between H. sapiens and archaic humans in Europe and Asia. H. sapiens most likely developed in Africa between 300,000 and 200,000 years ago, with one hypothesis arguing that diverse morphological features of H. sapiens appeared locally in different parts of Africa and converged due to gene flow between different populations within the same period. The "recent African origin" model proposes that all modern non-African populations are substantially descended from populations of H. sapiens that left Africa after that time.
There were at least several "out-of-Africa" dispersals of modern humans, possibly beginning as early as 270,000 years ago, certainly via North Africa and the Arabian Peninsula about 130,000 to 115,000 years ago at least. There is evidence that modern humans had reached China around 80,000 years ago..See also Modern humans in China ~80,000 years ago (?), Dieneks' Anthropology Blog. Practically all of these early waves seem to have gone extinct or retreated back, and present-day humans outside Africa descend mainly from a single expansion about 70,000–50,000 years ago, via the so-called "Southern Route". These humans spread rapidly along the coast of Asia and reached Australia by around 65,000–50,000 years ago, (though some researchers question the earlier Australian dates and place the arrival of humans there at 50,000 years ago at earliest, while others have suggested that these first settlers of Australia may represent an older wave before the more significant out of Africa migration and thus not necessarily be ancestral to the region's later inhabitants) while Europe was populated by an early offshoot which settled the Near East and Europe less than 55,000 years ago...See also
In the 2010s, studies in population genetics uncovered evidence of interbreeding that occurred between H. sapiens and archaic humans in Eurasia, Oceania and Africa, indicating that modern population groups, while mostly derived from early H. sapiens, are to a lesser extent also descended from regional variants of archaic humans.
Proposed waves
"Recent African origin", or Out of Africa II, refers to the migration of anatomically modern humans (Homo sapiens) out of Africa after their emergence at c. 300,000 to 200,000 years ago, in contrast to "Out of Africa I", which refers to the migration of archaic humans from Africa to Eurasia from before 1.8 and up to 0.5 million years ago. Omo-Kibish I (Omo I) from southern Ethiopia is the oldest anatomically modern Homo sapiens skeleton currently known (around 233,000 years old). There are even older Homo sapiens fossils from Jebel Irhoud in Morocco which exhibit a mixture of modern and archaic features at around 315,000 years old.
Since the beginning of the 21st century, the picture of "recent single-origin" migrations has become significantly more complex, due to the discovery of modern-archaic admixture and the increasing evidence that the "recent out-of-Africa" migration took place in waves over a long time. As of 2010, there were two main accepted dispersal routes for the out-of-Africa migration of early anatomically modern humans, the "Northern Route" (via Nile Valley and Sinai) and the "Southern Route" via the Bab-el-Mandeb strait.
Posth et al. (2017) suggest that early Homo sapiens, or "another species in Africa closely related to us", might have first migrated out of Africa around 270,000 years ago based on the closer affinity within Neanderthals' mitochondrial genomes to Homo sapiens than Denisovans.; see also . An interpretation, with as of yet limited recognition, of a skull fragment coming from Apidima Cave in Greece dated at 210,000 years ago as a Homo sapiens specimen may also points to an early Homo sapiens migration. Finds at Misliya cave, which include a partial jawbone with eight teeth, that may belong to a Homo sapiens specimen, have 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. An eastward dispersal from Northeast Africa to Arabia 150,000–130,000 years ago is based on the stone tools finds at Jebel Faya dated to 127,000 years ago (discovered in 2011), although fossil evidence in the area is significantly later at 85,000 years ago. Possibly related to this wave are the finds from Zhirendong cave, Southern China, dated to more than 100,000 years ago. Other evidence of modern human presence in China has been dated to 80,000 years ago. The most significant out of Africa dispersal took place around 50,000–70,000 years ago via the so-called Southern Route, either before or after the Toba event, which happened between 69,000 and 77,000 years ago. This dispersal followed the southern coastline of Asia and reached Australia around 65,000–50,000 years ago or according to some research, by 50,000 years ago at earliest. Western Asia was "re-occupied" by a different derivation from this wave around 50,000 years ago and Europe was populated from Western Asia beginning around 43,000 years ago. describes an additional wave of migration after the southern coastal route, a northern migration into Europe about 45,000 years ago. This possibility is ruled out by and , who argue for a single coastal dispersal, with an early offshoot into Europe.
Northern Route dispersal
Beginning 135,000 years ago, tropical Africa experienced megadroughts which drove humans from the land and towards the sea shores, and forced them to cross over to other continents.
Paleontological fossils of early Homo sapiens were found in Qafzeh and Es-Skhul Caves in Israel and have been dated to 80,000 to 120,000 years ago. These humans seem to have either become extinct or retreated back to Africa 70,000 to 80,000 years ago, possibly replaced by southbound Neanderthals escaping the colder regions of ice-age Europe. Based on analyses of autosomal microsatellite markers, Hua Liu et al. date the expansion of modern human to about 56,000 years ago, suggesting that the older fossils may represent an isolated early offshoot that died out.
The discovery of stone tools in the United Arab Emirates in 2011 at the Faya-1 site in Mleiha, Sharjah, indicated the presence of modern humans at least 125,000 years ago, leading to a resurgence of the "long-neglected" North African route. This new understanding of the role of the Arabian dispersal began to change following results from archaeological and genetic studies stressing the importance of southern Arabia as a corridor for human expansions out of Africa.
In Oman, a site was discovered by Bien Joven in 2011 containing more than 100 surface scatters of stone tools belonging to the late Nubian Complex, known previously only from archaeological excavations in the Sudan. Two optically stimulated luminescence age estimates placed the Arabian Nubian Complex at approximately 106,000 years old. This provides evidence for a distinct Stone Age technocomplex in southern Arabia, around the earlier part of the Marine Isotope Stage 5.
According to Kuhlwilm and his co-authors, Neanderthals contributed genetically to modern humans then living outside of Africa around 100,000 years ago: humans which had already split off from other modern humans around 200,000 years ago, and this early wave of modern humans outside Africa also contributed genetically to the Altai Neanderthals..See also Ancestors of Eastern Neandertals admixed with modern humans 100 thousand years ago, Dienekes'Anthropology Blog. They found that "the ancestors of Neanderthals from the Altai Mountains and early modern humans met and interbred, possibly in the Near East, many thousands of years earlier than previously thought". According to co-author Ilan Gronau, "This actually complements archaeological evidence of the presence of early modern humans out of Africa around and before 100,000 years ago by providing the first genetic evidence of such populations." Similar genetic admixture events have been noted in other regions as well.
Southern Route dispersal
Coastal route
By some 50–70,000 years ago, a subset of the bearers of mitochondrial haplogroup L3 migrated from East Africa into the Near East. It has been estimated that from a population of 2,000 to 5,000 individuals in Africa, only a small group, possibly as few as 150 to 1,000 people, crossed the Red Sea. The group that crossed the Red Sea travelled along the coastal route around Arabia and the Persian Plateau to India, which appears to have been the first major settling point. argued for the route along the southern coastline of Asia, across about , reaching Australia by around 50,000 years ago.
Today at the Bab-el-Mandeb straits, the Red Sea is about wide, but 50,000 years ago sea levels were lower (owing to glaciation) and the water channel was much narrower. Though the straits were never completely closed, they were narrow enough to have enabled crossing using simple rafts, and there may have been islands in between. Shell middens 125,000 years old have been found in Eritrea, indicating that the diet of early humans included seafood obtained by beachcombing.
Toba eruption
The dating of the Southern Dispersal is a matter of dispute. It may have happened either pre- or post-Toba, a catastrophic volcanic eruption that took place between 69,000 and 77,000 years ago at the site of present-day Lake Toba in Sumatra, Indonesia. Stone tools discovered below the layers of ash deposited in India may point to a pre-Toba dispersal but the source of the tools is disputed. An indication for post-Toba is haplo-group L3, that originated before the dispersal of humans out of Africa and can be dated to 60,000–70,000 years ago, "suggesting that humanity left Africa a few thousand years after Toba". Some research showing slower than expected genetic mutations in human DNA was published in 2012, indicating a revised dating for the migration to between 90,000 and 130,000 years ago. Some more recent research suggests a migration out-of-Africa of around 50,000-75,000 years ago of the ancestors of modern non-African populations, similar to most previous estimates.
West Asia Following the fossils dating 80,000 to 120,000 years ago from Qafzeh and Es-Skhul Caves in Israel there are no H. sapiens fossils in the Levant until the Manot 1 fossil from Manot Cave in Israel, dated to 54,700 years ago,See also though the dating was questioned by . The lack of fossils and stone tool industries that can be safely associated with modern humans in the Levant has been taken to suggest that modern humans were outcompeted by Neanderthals until around 55,000 years ago, who would have placed a barrier on modern human dispersal out of Africa through the Northern Route. Climate reconstructions also support a Southern Route dispersal of modern humans as the Bab-el-Mandeb strait experienced a climate more conductive to human migration than the northern landbridge to the Levant during the major human dispersal out of Africa.