The findings, published in the journal Scientific Reports, help to explain why native North Africans today are genetically related to people from Europe and Asia, in addition to other Africans. It also offers strong evidence that "Out of Africa" was not a one-way trip for some human lineages that traveled back to North Africa starting around 45,000 years ago.
At the center of it all is a prehistoric individual named the Pestera Muierii Woman, or PM-1 for short. Her skull, dated to 35,000 years ago, was unearthed in the Pestera Muierii cave of Romania.
Her "mosaic of modern human and archaic Neanderthal morphological (physical) features may be the result of Neanderthal interbreeding," senior author Concepcion de-la-Rúa of the University of the Basque Country's Department of Genetics told Discovery News.
de-la-Rúa and her colleagues extracted DNA from two of the woman's teeth and determined the ancient female's mitochondrial genome (mitogenome), i.e., a complete set of particular genes that are passed down from mothers to their daughters. The researchers noted that one component of this set, named "U6 basal," had not previously been identified in any ancient or existent humans.
Investigating the U6 mystery further, the scientists discovered that an evolved version of U6 does indeed exist today.
"U6 is found predominantly in present-day North African populations," de-la-Rúa said, adding that the form in Pestera Muierii Woman dates to a much earlier time and therefore is "basal," or at the root of U6's emergence.
Putting the clues together, the researchers believe that the woman's Homo sapiens ancestors migrated out of Africa and, at some point, mated with one or more Neanderthals, since she appears to have been part Neanderthal. This is actually true of all people of Asian and European heritage today, who retain Neanderthal DNA in their genomes.
The woman then "represents an offshoot to South-East Europe, i.e. Romania, of this back migration starting in the Early Upper Paleolithic period about 40–45,000 years ago," de-la-Rúa said.
As for why Romanians today do not have U6 basal, the researchers think this early form of U6 could have gone extinct hundreds or even thousands of years after the woman lived. de-la-Rúa explained that "mitochondrial lineages may disappear when a woman does not have children or if she only has male descendants."
The "Out of Africa" migrants clearly went to a lot of trouble to travel to Asia and then to Europe, so why would many of their not-too-distant later relatives have been so eager to return to Africa? The researchers offered a two-word answer: a "difficult climate."
De-la-Rúa explained that "between 50,000–20,000 years ago, it was (often) very cold due to climatic fluctuations" in Europe.
Vicente Cabrera, professor at the University of La Laguna in Tenerife, Spain, said that "a migration from Eurasia is the best explanation for the radiation of U6 in Africa."
Read more at Discovery News
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