Researchers have mapped the first ancient African genome from a 4,500-year-old Ethiopian and found that a "mysterious" wave of migration back into Africa from Western Eurasia around 3,000 years ago was much larger and more widespread then previously thought.
The genome was taken from the skull of a man buried face-down 4,500 years ago in a cave called Mota in the highlands of Ethiopia - a cave cool and dry enough to preserve his DNA for thousands of years.
The ancient genome predates a mysterious migratory event which occurred roughly 3,000 years ago, known as the 'Eurasian backflow', when people from regions of Western Eurasia such as the Near East and Anatolia suddenly flooded back into the Horn of Africa.
The genome enabled researchers to run a millennia-spanning genetic comparison and determine that these Western Eurasians were closely related to the Early Neolithic farmers who had brought agriculture to Europe 4,000 years earlier.
By comparing the ancient genome to DNA from modern Africans, the team has been able to show that not only do East African populations today have as much as 25 per cent Eurasian ancestry from this event, but that African populations in all corners of the continent - from the far West to the South - have at least 5 per cent of their genome traceable to the Eurasian migration.
Researchers at the University of Cambridge describe the findings as evidence that the 'backflow' event was of far greater size and influence than previously thought.
The massive wave of migration was perhaps equivalent to over a quarter of the then population of the Horn of Africa, which hit the area and then dispersed genetically across the whole continent.
The cause of the West Eurasian migration back into Africa is currently a mystery, with no obvious climatic reasons.
The researchers said it's clear that the Eurasian migrants were direct descendants of, or a very close population to, the Neolithic farmers that had brought agriculture from the Near East into West Eurasia around 7,000 years ago, and then migrated into the Horn of Africa some 4,000 years later.
The ancient Mota genome allows researchers to jump to before another major African migration: the Bantu expansion, when speakers of an early Bantu language flowed out of West Africa and into central and southern areas around 3,000 years ago.
Researchers said the Bantu expansion may well have helped carry the Eurasian genomes to the continent's furthest corners.
The genome also helped researchers identify genetic adaptations for living at altitude, and a lack of genes for lactose tolerance - all genetic traits shared by the current populations of the Ethiopian highlands.
The findings are published in the journal Science.
