Some 200,000 years ago, Homo sapiens arose in Africa, and began spreading across the globe some 100 to 150 thousand years later. Naturally, Africa should be one of the most-studied continents in regards to tracing our genetic history, but no one has been able to reconstruct ancient African DNA—until now, as researchers across the United Kingdom and Ireland have managed to do just that.
The main problem has been the climate: Scientists were able to compile DNA fragments from European Neanderthals, prehistoric Asian herders, and Paleoindians from the Americas, but the heat and humidity of Africa degraded DNA to the point where too little was left to compose a genome.
Researchers were able to sequence the degraded DNA from a 4,500 year-old skeleton and detailed their findings in the journal Science. The researchers applied an interesting theory to extract the DNA found in the Ethiopian Mota Cave: Some bones, being more contained, are better able to protect DNA from a harsh environment and ravaging bacteria.
The best bone, it seemed, was the petrous bone of the inner ear—it has been used successfully before with ancient skeletons, but never in African skeletons. Indeed, the skeleton (now called Mota, after the cave) had DNA within this bone—enough to fully sequence Mota’s genome.
Researchers were able to sequence each individual DNA base over 12.5 times on average, leading to a very high-quality genome. From this DNA, the researchers have discovered that he had brown eyes and dark skin, along with genes linked to high-altitude adaptations.
Shifts in the world population
Besides the enormous breakthrough in ability to sequence ancient African DNA, the team also made a fascinating discovery about migrations into Africa. Usually, we tend to think of the African populations expanding elsewhere, but a common theory is that some populations of the Near East returned some 3,000 years ago.
So Mota’s 4,500-year-old genome was compared to genomes of modern Ethiopians from the same region, the Ari—who are the most genetically related to him—along with 39 other African populations and 81 European populations. It now appears that Mota lacks between 4% and 7% of the DNA found in the Ari and other African populations.
This 4% to 7% of new DNA is actually closest to that of modern Sardinians and a prehistoric farmer found in Germany, and Mota helps to pinpoint when this new genetic information entered into the populations—sometime after 4,500 years ago.
This could mean that Sardinians immigrated to Africa around that time, but co-author and population geneticist Andrea Manica of the University of Cambridge has a different idea.
It’s more likely, according to her, that such European farmers and Africans got this new DNA from the same source—a population in the Middle East, perhaps from Anatolia or Mesopotamia. Around 3,000 to 3,500 years ago, farmers from those regions migrated into Eastern Africa, a notion that fits with archeological evidence: Traces of Middle Eastern grains of the same age have been found in Africa.
But this new DNA didn’t just stay in the east; it spread all throughout the continent, even to extremely isolated groups. For example, the Mbuti Pygmies of the Congo share it.
“It must have been lots of people coming in or maybe they had new crops that were very successful,” Manica said in a press release.
Of course, Mota may have belonged to an extremely isolated group, and thus never added the new DNA to his genome, but many are leaning towards a migration 3,500 years ago. And regardless of migration patterns, this advance is an enormous game-changer for geneticists and antropologists alike.
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