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In paleoanthropology, the single-origin hypothesis (or Out-of-Africa model) is one of two accounts of the origin of anatomically modern humans, Homo sapiens. (The other theory is the multiregional hypothesis.)

Because of the scarcity of fossils and the discovery of important new finds every few years, researchers disagree about the details and sometimes even basic elements of human evolutionary history. While they have revised this history several times over the last decades, researchers currently agree that the oldest named species of the genus Homo, Homo habilis, evolved in Africa around two million years ago, and that members of the genus migrated "out of Africa" somewhat later. The descendants of these ancient migrants, which probably included Homo erectus, have become known through fossils uncovered far from Africa, such as those of "Peking man" and "Java man". The Homo neanderthalensis is also considered a descendant of early migrants.

According to the single-origin model, however, every species of the genus Homo but one, Homo sapiens, was driven extinct. This species had evolved in eastern Africa between 100,000 and 200,000 years ago and, some time afterwards, in a relatively recent exodus, began colonizing the rest of the world. According to the single-origin model, these more recent migrants did not interbreed with the scattered descendants of earlier exoduses. For this reason, the model is sometimes called the "replacement scenario". In support of it, advocates have drawn from both fossil and DNA evidence, in particular from mitochondrial and Y-chromosome DNA sequences. Research on the X chromosome claims to be the first genetic evidence against Out of Africa.

Assuming only relatively recent migrants from Africa gave rise to today's non-African humans, was there more than one migration that left descendants? (for example, one each via the north and south ends of the Red Sea)

* John Hawks in Playing games with dates criticizes current presentations of the idea

The opponents of a single origin argue that interbreeding indeed occurred, and that the characteristics of modern humans, including those that have been and still are perceived by some to distinguish races, could only be the result of genetic contributions from several earlier lineages that evolved semi-independently in different parts of the world. This is the "multiregional hypothesis".

Mitochondrial Eve is the name given by researchers to the woman who is the matrilineal common ancestor of all living humans. Eve was a member of a population of humans around 150,000 years ago in Africa. We know about Eve because of mitochondria organelles that are only passed from mother to offspring. Each mitochondrion contains Mitochondrial DNA, and the comparison of DNA sequences from Mt DNA reveals a phylogeny. Based on the molecular clock technique of correlating elapsed time with observed genetic drift, Eve is believed to have lived about 150,000 years ago.

Although Mitochondrial Eve was named after Eve of the Genesis creation myth, this has led to some misunderstandings amongst the general public. A common misconception is that Mitochondrial Eve was the only living female of her time -- she was not thought to be. It is thought that there wer many women alive at the same time as Mitochondrial Eve, but only Mitochondrial Eve produced an unbroken line of daughters that persists today -- each of the other matrilineal lineages was broken when a woman had no children or only sons.

The smaller a population, the more quickly matrilineal lineages converge.

We know about Eve because of mitochondria organelles that are only passed from mother to offspring. Each mitochondrion contains Mitochondrial DNA (MtDNA), and the comparison of DNA sequences from MtDNA reveals a molecular phylogeny. Because of recombination, genes in nuclear DNA become mixed and therefore we can be is statistically less certain about their origins. Mutations that reveal, and thus diversity is magnified in mitochondrial DNA. Population bottlenecks are particularly magnified (Wilson et al 1985).

As mitochondria are inherited matrilineally, Y-chromosomes are inherited patrilineally. Thus it is possible to apply the same principles outlined above to men. The common patrilineal ancestor of all humans alive today has been dubbed Y-chromosomal Adam. Importantly, he was not alive at the same time as Mitochondrial Eve but much more recently, and certainly was not her husband.

Allan Wilson, Rebecca Cann, Steven Carr, M. George Jr., U. B. Gyllensten, K. Helm-Bychowski, R. G. Higuchi, Stephen Palumbi, E. M. Prager, R. D. Sage, and Mark Stoneking laid out the theoretical background for the analysis of mitochondrial DNA in 1985 paper. Cann, Wilson and Stoneking then proposed the concept of Mitochondrial Eve in a 1987 paper in Nature. Cann et al used restriction mapping on 147 persons from five separate populations to derive their data. Gradually mitochondrial DNA sequence data from more people around the world were collected, giving a better picture.

Mitochondrial Eve is sometimes referred to as African Eve, an ancestor who has been hypothesized on the grounds of fossil as well as DNA evidence. According to the most common interpretation of the mitochondrial DNA data, the titles belong to the same hypothetical woman. Family trees (or "phylogenies") constructed on the basis of mitochondrial DNA comparisons show that the living humans whose mitochondrial lineages branched earliest from the tree are indigenous Africans, whereas the lineages of indigenous peoples on other continents all branch off from African lines. Researchers therefore reason that all living humans descend from Africans, some of whom migrated out of Africa to populate the rest of the world. If the mitochondrial analysis is correct, then because mitochondrial Eve represents the root of the mitochondrial family tree, she must have predated the exodus and lived in Africa. Therefore many researchers take the mitochondrial evidence as support for the "single-origin" or Out-of-Africa model.

The construction of family trees from DNA data is an inexact science, however. Critics of the "African genesis" model argue that the mitochondrial evidence can be explained as well or better by trees that associate Eve most closely to the indigenous peoples of Asia. As of 2003, however, following advances in computing power and in methods of tree determination, these criticisms have diminished. In any event, the strongest support that mitochondrial DNA offers for the African-origin hypothesis may not depend on trees. One finding not subject to interpretation is that the greatest diversity of mitochondrial DNA sequences exists among Africans. This diversity would not have accumulated, researchers argue, if humans had not been living longer in Africa than anywhere else. Analysis of Y chromosome sequences have corroborated the evidence that mitochondrial DNA has provided for an African origin for hominids.

Bryan Sykes has written a popular science book entitled The Seven Daughters of Eve.

The Discovery Channel has produced a documentary entitled The Real Eve.

In human genetics, Y-chromosomal Adam (Y-mrca) is the male counterpart to mitochondrial Eve: the last male ancestor from whom all male human Y chromosomes are descended. Unlike other genes, those of the Y chromosome are passed exclusively from father to sons, just as mitochondrial DNA is passed to all children only by their mothers.