Mota cave, where the ancient human was found. (Kathryn and John Arthur)

Africa is considered to be the birthplace of humankind -- the cradle of humanity. But because its climate is poorly suited for DNA preservation, all of the ancient genomes to be analyzed have been from Europe, Asia, and the Americas. That changed on Thursday, when researchers published a paper in Science documenting the genetic code of a man who died 4,500 years ago in what's now Ethiopia.

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Scientists know that after the great migration from Africa, where all early humans originated -- treks that took place about 60,000 years ago -- some of the Eurasians who had developed agriculture made their way back into Africa. 

That's what makes the newly sequenced man, named Mota by scientists, so interesting. Mota lived in Africa before this second, backwards migration. Unsurprisingly, Mota lacked the Eurasian DNA that seems to have proliferated across the region about 1,500 years after his death.

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By comparing his DNA -- extracted from a resilient inner ear bone, which has become the technique of choice for getting DNA in a tricky climate -- to that of modern Africans, scientists were able to estimate how large the Eurasian influx had been. 

"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?" Andrea Manica, senior author of the study from the University of Cambridge's Department of Zoology, said in a statement.

Today, Manica and his colleagues report, East Africans can attribute as much as 25 percent of their DNA to this Eurasian back flow. Even in far western and southern areas, at least 5 percent of the genome is Eurasian in origin.

The authors of the study have no idea what caused such a massive migration. And with just one skull to go on, they can't write this genetic history in stone quite yet. But as the techniques for extracting and analyzing the ancient DNA of Africa improve, we'll have more and more studies like this one to fill in the gaps of humanity's origin story.

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