DNA extracted from the skull of a man buried facedown 4,500 years ago in the Ethiopian highlands is again forcing scientists to rethink how populations poured into the Horn of Africa.
The DNA, which was preserved in Ethiopia's cold Mota Cave, provided for the first sequencing of an ancient human genome from Africa. Instead of having to work back through the genomes of current populations, the DNA gave researchers a look at life before one of two massive African migrations.
It was possible that the region incubated the genetic diversity that spilled across the whole continent when about a quarter of the population dispersed, the researchers from the University College Dublin and the University of Cambridge found. Their findings were published in the journal Science.
The researchers compared the genome to DNA from modern Africans, leading them to conclude that up to 25 percent of the modern population in East Africa contain Eurasian ancestry from a migration event back into Africa known as the "Eurasian backflow." Modern populations to the west and to the south would have about 5 percent of their genome traceable to this Eurasian migration.
"Genomes from this migration seeped right across the continent, way beyond East Africa, from the Yoruba on the western coast to the Mbuti in the heart of the Congo - who show as much as 7 percent and 6 percent of their genomes respectively to be West Eurasian," says study author Marcos Gallego Llorente, of Cambridge's Zoology Department.
That backflow event is one of two early African migration events that had been puzzling researchers. The DNA found in Mota Cave predates the Eurasian backflow, which occurred about three millienia ago.
"Africa is a total melting pot," said Llorente. "We know that the last 3,000 years saw a complete scrambling of population genetics in Africa. So being able to get a snapshot from before these migration events occurred is a big step."
Researchers still are unsure why populations migrated into Europe before flowing back to Africa. What researchers are more sure of is that Eurasian migrants directly descended from, or alongside, the Early Neolithic farmers that brought Near East agriculture into West Eurasia about 7,000 years ago and then when back to Africa about 4,000 years later.
While researchers continue to work out exactly why populations came back to Africa with agriculture, there's a more modern example of something similar occurring, according to Trinity College Dublin's Eppie Jones, a geneticist that led the lab work in sequencing the genome from the skull's DNA.
The Sardinians can be compared to the Neolithic migrants, because the Isle of Sardinia sits in isolation, said Jones.
"The farmers found their way to Sardinia and created a bit of a time capsule," Jones explained. "Sardinian ancestry is closest to the ancient Near East."
Photo: Rod Waddington | Flickr