Several expansions of populations of archaic humans (genus Homo) out of Africa and throughout Eurasia took place in the course of the Lower Paleolithic, and into the beginning Middle Paleolithic, between about 2.1 million and 0.2 million years ago (Ma). These expansions are collectively known as Out of Africa I, in contrast to the expansion of anatomically modern humans (Homo sapiens) into Eurasia, which may have begun shortly after 0.2 million years ago (known in this context as "Out of Africa II").The term "Out of Africa I" is informal and somewhat rare. The phrase Out of Africa used on its own generally refers to "Out of Africa II", the expansion of anatomically modern humans into Eurasia. "Out of Africa I" is used in 2004, in Marco Langbroek, 'Out of Africa': an investigation into the earliest occupation of the Old World, p. 61, and as the title of a collection of essays, J. G. Fleagle et al. (eds.), Out of Africa I: The First Hominin Colonization of Eurasia (2010). see also: ;
The earliest presence of Homo (or indeed any hominin) outside of Africa dates to close to 2 million years ago. A 2018 study identified possible hominin presence at Shangchen, central China, as early as 2.12 Ma based on magnetostratigraphic dating of the lowest layer containing what may possibly be stone artefacts."Eight major magnetozones are recorded in the Shangchen section, four of which have normal polarity (N1 to N4) and four of which have reversed polarity (R1 to R4). By comparison with the geomagnetic polarity timescale [...] magnetozone N4 corresponds to the Réunion excursion (2.13–2.15 Ma) in L28." The oldest known human skeletal remains outside of Africa are from Dmanisi, Georgia (Dmanisi skull 4), and are dated to 1.8 Ma. These remains are classified as Homo erectus georgicus.
Later waves of expansion are proposed around 1.4 Ma (early Acheulean industries), associated with Homo antecessor and 0.8 Ma (cleaver-producing Acheulean groups), associated with Homo heidelbergensis.
Until the early 1980s, early humans were thought to have been restricted to the African continent in the Early Pleistocene, or until about 0.8 Ma; Hominin migrations outside East Africa were apparently rare in the Early Pleistocene, leaving a fragmentary record of events.
Early dispersals
Pre-Homo hominin expansion out of Africa is suggested by the presence of Graecopithecus and Ouranopithecus, found in Greece and Anatolia and dated to c. 8 million years ago, but these are probably Homininae but not Hominini. Possibly related are the Trachilos footprints found in Crete, dated to close to 6 million years ago; the age of the footprints was later reestimated to be 6.05 million years ago, 0.35 million years older than previous estimations. Another reestimation by Willem Jan Zachariasse and Lucas Lourens interpret the purported footprints to have originated 3 million years ago and doubt if they were footprints or the hominins had made the footprints because of the shallow marine setting and the separation of Crete from mainland Greece and Turkey in the Late Pliocene by the South Aegean Basin.
Australopithecina emerged about 5.6 million years ago, in East Africa (Afar Depression). Gracile australopithecines (Australopithecus afarensis) emerged in the same region, around 4 million years ago. The earliest known retouched tools were found in Lomekwi, Kenya, and date back to 3.3 Ma, in the late Pliocene. They might be the product of Australopithecus garhi or Paranthropus aethiopicus, the two known hominins contemporary with the tools. Genus Homo is assumed to have emerged by around 2.8 million years ago, with Homo habilis being found at Lake Turkana, Kenya. The delineation of the "human" genus, Homo, from Australopithecus is somewhat contentious, for which reason the superordinate term "hominin" is often used to include both. "Hominin" technically includes chimpanzees as well as pre-human species as old as 10 million years old (the separation of Homininae into Hominini and Gorillini).
The earliest known hominin presence outside of Africa dates to close to 2 million years ago. A 2018 study claims evidence for human presence at Shangchen, central China, as early as 2.12 Ma based on magnetostratigraphic dating of the lowest layer containing stone artefacts.
It has been suggested that Homo floresiensis was descended from such an early expansion. It is not clear whether these earliest hominins leaving Africa should be considered Homo habilis, or a form of early Homo or late Australopithecus closely related to Homo habilis, or a very early form of Homo erectus. In any case, the morphology of H. floresiensis has been found to show greatest similarity with Australopithecus sediba, Homo habilis and Dmanisi Man, raising the possibility that the ancestors of H. floresiensis left Africa before the appearance of H. erectus. A phylogenetic analysis published in 2017 suggests that H. floresiensis was descended from a species (presumably Australopithecine) ancestral to Homo habilis, making it a "sister species" either to H. habilis or to a minimally habilis-erectus-ergaster-sapiens clade, and its line is older than H. erectus itself. On the basis of this classification, H. floresiensis is hypothesized to represent a hitherto unknown and very early migration out of Africa, dating to before 2.1 million years ago. A similar conclusion is suggested by the date of 2.1 Ma for the oldest Shangchen artefacts.
Homo erectus
Homo erectus emerges just after 2 million years ago. Early H. erectus would have lived face to face with H. habilis in East Africa for nearly half a million years. The oldest Homo erectus fossils appear almost contemporaneously, shortly after two million years ago, both in Africa and in the Caucasus.
Dmanisi and social complexity The earliest documented Eurasian H. erectus were the Dmanisi hominins near the city of Dmanisi, Georgia, securely dated to 1.8 Ma.1.85-1.78 Ma 95% CI. One specimen (composite skull D 3444/D 3900) excavated at Dmanisi has been framed as evidence for human social care of the elderly or disabled, a social adaptation likely important for success in diverse and novel ecosystems. The specimen shows signs of advanced age and severe periodontal disease based on extensive bone loss in the maxilla and mandible from resorption of the tooth alveoli, something very commonly seen in elderly humans and appearing as a loss of height in the upper lip and an increased gonial angle. It has been cited as the earliest edentulous human skull, a term which refers to long-term lifespan and pathophysiological effects of tooth loss rather than an specimen where simply no teeth remains, such as from a traumatic injury. In the publication first describing the remains, David Lordkipanidze and colleagues suggested that this individual likely could not have survived without supportive care and perhaps preparation of pulverized food, in addition to other assistance likely needed for survival at very advanced age in a Lower Paleolithic context. It has been suggested that this type of social complexity would have been necessary for the successful adaptation of H. erectus and descendant groups to the wide variety of ecosystems they eventually inhabited.
Expansion The earliest known evidence for African H. erectus, dubbed Homo ergaster, is a single occipital bone (KNM-ER 2598), described as "H. erectus-like", and dated to about 1.9 Ma (contemporary with Homo rudolfensis). This is followed by a fossil gap, the next available fossil being KNM-ER 3733, a skull dated to 1.6 Ma. Early Pleistocene sites in North Africa, the geographical intermediate of East Africa and Georgia, are in poor stratigraphic context. The earliest of the dated is Ain Hanech in northern Algeria (c. 1.8 – 1.2 Ma), an Oldowan grade layer. These sites attest that early Homo erectus have crossed the North African tracts, which are usually hot and dry. There is little time between Homo erectus''' apparent arrival in South Caucasus around 1.8 Ma, and its probable arrival in East and Southeast Asia. There is evidence of H. erectus in Yuanmou, China, dating to 1.7 Ma and in Sangiran, on Java, Indonesia, from 1.66 Ma.
Ferring et al. (2011) suggest that it was still Homo habilis that reached West Asia, and that early H. erectus developed there. H. erectus would then have dispersed from West Asia, to East Asia (Peking Man) Southeast Asia (Java Man), back to Africa (Homo ergaster), and to Europe (Tautavel Man).
It appears H. erectus took longer to move into Europe, the earliest site being Barranco León in southeastern Spain dated to 1.4 Ma, associated with Homo antecessor, and a controversial Pirro Nord in Southern Italy, allegedly from 1.7 – 1.3 Ma. The paleobiogeography of early human dispersals in western Eurasia characterizes H. ex gr. erectus as a temperature sensitive stenobiont, that failed to disperse north of the Alpide Belt. The geographically restricted earliest human presence in the Iberian Peninsula should be regarded as evidence of a sustainable presence of human population in this isolated area. The Pannonian plain, situated south-west of the Carpathian Mountains, was apparently characterized by a comparatively warm climate similar to that of the Mediterranean Area, while the climate of the western European paleobiogeographic area was mitigated by Gulf Stream influence and could support the episodic hominin dispersals toward the Iberian Peninsula. Apparently, the faunal exchanges between southeastern Europe and the Near East and southern Asia were controlled by the complex interaction of such geographic obstacles as the Bosporus and the Manych Strait, the climate barrier from the north of the Greater Caucasus range, and the 41 kyr glacial Milankovitch cycles that repeatedly closed the Bosporus and thus triggered the two-way faunal exchange between southeastern Europe and the Near East, and, apparently, the further westward dispersal of the archaic hominins in Eurasia.
By 1 Ma, Homo erectus had spread across Eurasia (mostly restricted to latitudes south of the 50th parallel norththe northernmost known Middle Pleistocene site is Whithlingham, at 52.6° N. Mourre, V., Implications culturelles de la technologie des hachereaux, doctoral thesis, Université de Paris X – Nanterre (2003) Fig. 48 (p. 115).). It is hard to say, however, whether settlement was continuous in Western Europe, or if successive waves repopulated the territory in glacial interludes. Early Acheulean tools at Ubeidiya from 1.4 Ma is some evidence for a continuous settlement in the West, as successive waves out of Africa after then would likely have brought Acheulean technology to Western Europe.
He has reproduced a primitive dirigible (steerable) raft to demonstrate the feasibility of faring across the Lombok Strait on such a device, which he believes to have been done before 850 ka. The strait has maintained a width of at least 20 km for the whole of the Pleistocene.
Homo heidelbergensis Archaic humans in Europe beginning about 0.8 Ma (cleaver-producing Acheulean groups) are classified as a separate, erectus-derived species, known as Homo heidelbergensis. H. heidelbergensis from about 0.4 Ma develops its own characteristic industry, known as Clactonian.H. heidelbergensis is closely related to Homo rhodesiensis (also identified as Homo heidelbergensis sensu lato or African H. heidelbergensis), known to be present in southern Africa by 0.3 Ma.Homo sapiens emerges in Africa before about 0.3 Ma from a lineage closely related to early H. heidelbergensis. The first wave of "Out of Africa II and "earliest presence of H. sapiens in West Asia, may date to between .3 and 0.2 Ma, and ascertained for 0.13 Ma. Genetic research also indicates that a later migration wave of H. sapiens (from .07-.05 Ma) from Africa is responsible for all to most of the ancestry of current non-African populations.
Routes out of Africa