Recent African Origin of Modern Humans - History of The Theory

History of The Theory

Further information: Timeline of human evolution

With the development of anthropology in the early 19th century, scholars disagreed vigorously about different theories of human development. Those such as Johann Friedrich Blumenbach and James Cowles Prichard held that since the creation, the various human races had developed as different varieties sharing descent from one people (monogenism). Their opponents, such as Louis Agassiz and Josiah C. Nott, argued for polygenism, or the separate development of human races as separate species or had developed as separate species through transmutation of species from apes, with no common ancestor.

Charles Darwin was one of the first to propose common descent of living organisms, and among the first to suggest that all humans had in common ancestors who lived in Africa. Darwin first suggested the "Out of Africa" hypothesis after studying the behaviour of African apes, one of which was displayed at the London Zoo. The anatomist Thomas Huxley had also supported the hypothesis and suggested that African apes have a close evolutionary relationship with humans. These views were however opposed by Ernst Haeckel the German biologist who was a proponent of the Out of Asia theory. Haeckel argued that humans were more closely related to the primates of Southeast Asia and rejected Darwin’s hypothesis of Africa.

In the Descent of Man, Darwin speculated that humans had descended from apes which still had small brains but walked upright, freeing their hands for uses which favoured intelligence. Further, he thought such apes were African:

In each great region of the world the living mammals are closely related to the extinct species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere. But it is useless to speculate on this subject, for an ape nearly as large as a man, namely the Dryopithecus of Lartet, which was closely allied to the anthropomorphous Hylobates, existed in Europe during the Upper Miocene period; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale. —Charles Darwin, Descent of Man

The prediction was insightful, because in 1871 there were hardly any human fossils of ancient hominids available. Almost fifty years later, Darwin's speculation was supported when anthropologists began finding numerous fossils of ancient small-brained hominids in several areas of Africa (list of hominina fossils).

The debate in anthropology had swung in favour of monogenism by the mid-20th century. Isolated proponents of polygenism held forth in the mid-20th century, such as Carleton Coon, who hypothesized as late as 1962 that Homo sapiens arose five times from Homo erectus in five places. The "Recent African origin" of modern humans means "single origin" (monogenism) and has been used in various contexts as an antonym to polygenism.

In the 1980s Allan Wilson together with Rebecca Cann and Mark Stoneking worked on the so-called "Mitochondrial Eve" hypothesis. In his efforts to identify informative genetic markers for tracking human evolutionary history, he started to focus on mitochondrial DNA (mtDNA) — genes that sit in the cell, but not in the nucleus, and are passed from mother to child. This DNA material is important because it mutates quickly, thus making it easy to plot changes over relatively short time spans. By comparing differences in the mtDNA Wilson believed it was possible to estimate the time, and the place, modern humans first evolved. With his discovery that human mtDNA is genetically much less diverse than chimpanzee mtDNA, he concluded that modern human races had diverged recently from a single population while older human species such as Neandertals and Homo erectus had become extinct. He and his team compared mtDNA in people of different racial backgrounds and concluded that all modern humans evolved from one 'lucky mother' in Africa about 150,000 years ago. With the advent of archaeogenetics in the 1990s, scientists were able to date the "out of Africa" migration with some confidence.

In 2000, the mitochondrial DNA (mtDNA) sequence of "Mungo Man 3" (LM3) of ancient Australia was published indicating that Mungo Man was an extinct subspecies that diverged before the most recent common ancestor of contemporary humans. The results, if correct, supports the multiregional origin of modern humans hypothesis. This work was later questioned and explained by W. James Peacock, leader of the team who sequenced Mungo man's ancient mtdna.

The question of whether there was inheritance of other typological (not de facto) Homo subspecies into the Homo sapiens genetic pool is debated.