The first ancient human genome from Africa to be sequenced has revealed that a wave of migration back into Africa from Western Eurasia around 3,000 years ago was up to twice as significant as previously thought, and affected the genetic make-up of populations across the entire African continent. 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. Previously, ancient genome analysis has been limited to samples from northern and arctic regions. 

The latest study is the first time an ancient human genome has been recovered and sequenced from Africa, the source of all human genetic diversity. The findings are published today in the journal Science.

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 ancient 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 have been able to show that not only do East African populations today have as much as 25% 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% of their genome traceable to the Eurasian migration. 

Researchers 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. 

"Roughly speaking, the wave of West Eurasian migration back into the Horn of Africa could have been as much as 30% of the population that already lived there - and that, to me, is mind-blowing. The question is: what got them moving all of a sudden?" said Dr Andrea Manica, senior author of the study from the University of Cambridge's Department of Zoology.