We all are Africans. Or, more precisely, we all are descendants of some undocumented immigrants from Africa. Or, to make this statement scientifically and perhaps politically correct we all humans descended from Homo species originated in sub-Saharan Africa.

Until recently it was generally accepted that all 7.6 billion humans currently living on Earth descended from a single group of early modern people, aka Cro-Magnons who left Africa around 60 thousand years ago in one large wave and then gradually settled the whole planet. But now tracing back our ancestry may become a bit more complicated.

According to the article recently published in Science, an international group of scientists from the Max Planck Institute for Evolutionary Anthropology in Germany and the University of Hawaii in Manoa came to the conclusion that the ancient Homo Sapiens left Africa in several waves and gradually mixed with other, earlier hominids.

The authors, Christopher J. Bae, Katerina Douka and Michael D. Petraglia, have a view that the established definition of the hypothesis "man from Africa," according to which the ancestors of all modern people moved from the Black continent 60,000 years ago in a single wave of migration and then drove out the indigenous inhabitants of Eurasia, can no longer be considered valid. Their conclusions were made in the light of new data obtained when archaic DNA extracted from ancient Homo Sapiens fossils found in South-East Asia was analysed.

In one of the examples, the remains of a man discovered in South Central China and estimated to be 70 -120 thousand years old yielded a DNA sample which researchers were able to compare two genomes of various people from across the globe. The results of these genetic studies have shown that in the case of aboriginal people of Papua New Guinea up to two percent of their modern genome is inherited from ancestors who left Africa earlier than 60 thousand years ago.

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The new paleontological findings make it necessary to rethink the classical framework of the hypothesis of the African origin of the modern humans.

Heading North: smaller groups of migrants may have preceded major exodus

The "Out of Africa" theory, or simply OOA is accepted as the dominant model of the geographic origin and early migration of anatomically modern humans. According to this hypothesis, all modern people evolved on the Black Continent from where they settled on the planet. From the results of the complete decoding of ancient and modern peoples genomes is known that all modern non-African human populations separated from the ancestors living on the Black Continent during the late Pleistocene epoch, or roughly in the last million of years.

As opposed to the recent single-origin hypothesis (RSOH), replacement hypothesis, or recent African origin model (RAO), scientists now believe that even before the main wave of migration, which indeed occurred 60 thousand years ago, people moved from Africa to Eurasia and farther as part of smaller dispersed groups.

There these early immigrants mixed with other ancient hominids, such as Neanderthals and Denisovans, the latter named after a cave in south-western Siberia where their remains were found in 2010, as well as with other Homo species which are yet to be identified. Thanks to this mixing, the genome of almost all modern non-Africans include one to four percent of Neanderthal DNA, while Melanesians have up to five percent of DNA inherited from the Denisovans.

According to the latest data, the intermarrying could have begun within the time interval spanning from 40 to about 200 thousand years ago. Thus the revised model sees modern humans evolved in East Africa between 400,000 and 200,000 years ago, from where they began to disperse throughout the world roughly 70,000 to 135,000 years ago. And, in a striking similarity to the fate of more recent groups of migrants trying to cross Mediterranean, their way was perilous and their destination inhospitable. The first migration wave from northern Africa took place between 130,000–115,000 years ago, and these people appear to have mostly died out or retreated to their homeland. The second dispersal wave via the so-called Southern Route ran along the southern coastline of Asia was more successful. It eventually led to the lasting settlement of Australia by around 65,000-50,000 years ago, about the same time as Europe was populated by early arrivals from the Near East.