Recent African origin of modern humans

In paleoanthropology, the recent African origin of modern humans is the mainstream model describing the origin and early dispersal of anatomically modern humans, Homo sapiens sapiens. The theory is known popularly as the (Recent) Out-of-Africa model, and academically also as the recent single-origin hypothesis (RSOH), Replacement Hypothesis or Recent African Origin (RAO) model. The hypothesis originated in the 19th century, with Darwin's Descent of Man, but remained speculative until the 1980s when it was corroborated based on a study of present-day mitochondrial DNA, combined with evidence based on physical anthropology of archaic specimens.

According to both genetic and fossil evidence, archaic Homo sapiens evolved to anatomically modern humans solely in Africa, between 200,000 and 100,000 years ago, with members of one branch leaving Africa by 60,000 years ago and over time replacing earlier human populations such as Neanderthals and Homo erectus. According to this theory around the above time frame one of the African subpopulations went through a process of speciation prohibiting gene flow between African and Eurasian Human populations. The recent single origin of modern humans in East Africa is currently the near consensus position held within the scientific community.

The competing hypothesis is the multiregional origin of modern humans. Some push back the original "out of Africa" migration - in this case, by Homo erectus, not by Homo sapiens - to two million years ago.

History of the theory

Charles Darwin was one of the first to suggest that all humans had a common ancestor who lived in Africa. In the Descent of Man he writes:

The prediction was highly insightful because at the time, in 1871, there were hardly any human fossils of ancient hominids available. Almost fifty years later Darwin was vindicated, as anthropologists began finding numerous fossils of ancient hominids all over Africa (list of hominina fossils).

In 19th century anthropology, "monogenism" was opposed by "polygenism", the idea that the various human races had evolved independently out of archaic hominids. Polygenism was largely obsolete by the mid 20th century, although there were isolated proponents in the later 20th century such as Carleton Coon who hypothesized as late as 1962 that Homo sapiens arose five separate times from Homo erectus in five separate places. The Recent African origin of modern humans means "single origin" - monogenism and has been used in various contexts as an antonym to polygenism .

With the advent of archaeogenetics in the 1990s, it became possible to date the "out of Africa" migration with some confidence until 2000 when mtDNA sequence of Mungo Man was published. This work was later questioned and explained by of W. James Peacock leader of team who sequenced mungo man ancient mtdna.

The question whether there inheritance of other typological (not de facto) Homo subspecies into Homo sapiens genetic pool remains under debate.

Early Homo sapiens

Archaic Homo sapiens originated in Africa about 250,000 years ago. The trend in cranial expansion and the acheulean elaboration of stone tool technologies which occurred between 400,000 years ago and the second interglacial period in the Middle Pleistocene (around 250,000 years ago) provide evidence for a transition from H. erectus to H. sapiens. In the RAO scenario, migration within and out of Africa eventually replaced the earlier dispersed H. erectus.

Homo sapiens idaltu, found at site Middle Awash in Ethiopia, lived about 160,000 years ago. It is the oldest known anatomically modern human and classified as extinct subspecies. Fossils of modern humans were found in Qafzeh cave in Israel and have been dated to 100,000 years ago. However these humans seem to have either gone extinct or retreated back to Africa 70,000 to 80,000 years ago, possibly replaced by south bound Neanderthals escaping the colder regions of ice age Europe. Hua Liu & al. analyzing autosomal microsatellite markers dates to 56,063±5,678 years ago mtDNA evidence. The paleontological fossil of early modern human from Qafzeh cave dated at 80,000–100,000 Liu interpret as isolated early offshoot that retracted back to Africa.

All other fossils of fully modern humans outside of Africa have been dated to more recent times(80,000–100,000 year ago). The next oldest fossil of modern humans outside of Africa are those of Mungo Man found in Australia and have been dated to about 42,000 years ago.

Beginning about 100,000 years ago evidence of more sophisticated technology and artwork begins to emerge and by 50,000 years ago fully modern behaviour becomes more prominent. By this time the ritual burying of the dead is noted. Stone tools show regular patterns that are reproduced or duplicated with more precision. Tools made of bone and antler appear for the first time.

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