A 4,500-year-old skeleton from a cave in Ethiopia has produced Africa’s first ancient human genome, with DNA suggesting that Middle Eastern farmers migrated into Africa 4,500 years ago, leaving traces of their Eurasian ancestry in the genomes of many modern-day Africans, according to Nature.com.
The sequenced genes of the Mota skeleton — named for the cave where it was found –are helping define a wave of Eurasian migration back into Africa that now appears twice as large as previously believed, TheSmithsonian reports.
No one knows why the Eurasians migrated back to Africa, but a study by the University of Cambridge suggests they brought new crops to the continent such as wheat, barley and lentils.
“This back migration of Western Eurasians to Africa was a very large, one-off event, it seems,” says study coauthor Marcos Gallego Llorente of the University of Cambridge. “Its genetic signature got to every corner of Africa.”
Homo sapiens — modern humans — emerged in Africa about 200,000 years ago and migrated off the continent 60,000-to-100,000 years ago, populating almost every corner of the planet.
Proof of these ancient migrations is found in the genomes of living people, according to Nature. DNA from ancient remains found in the Americas, Europe and Asia add to the human evolutionary story but Africa has missed out on the DNA-based revolution until now, partly because genetic material degrades fast in hot temperatures.
Modern Africans have a surprisingly large percentage of Eurasian ancestry due to the Eurasian backflow — a previously known reverse migration from the Near East and Anatolia into the Horn of Africa, according to Smithsonian.
Without ancient African genomes, scientists had to work backward with modern genes to produce a genetic baseline.
Mota man’s genes provide the best African baseline to date. They show that modern African populations, thought to be basically unmixed, actually have significant Eurasian ancestry.
The Mota man’s genome is more closely related to present-day Ethiopian highlanders known as the Ari than to any other population the team examined, suggesting a clear line of descent for the Ari from ancient human populations living in the area, Nature reports. But further genetic studies show that the Ari also descend from people that lived outside Africa.
Even in the Congo, for example, the Mbuti people now show as much as 6 percent of their genome being West Eurasian, according to the study, Smithsonian reports.
“What we find is that even West and Southern African populations started showing 6 or 7 percent of their genomes to be West Eurasian,” Gallego Llorente said. “And populations with more Eurasian ancestry like Ethiopians also rise accordingly, so this basically means the backflow migration was larger than we thought.”
Events like the backflow migration, along with later population movements around Africa, scrambled genetics across the continent.
The Mota skeleton was preserved in dry air at 6,560-feet in the Ethiopian Highlands, which helped preserve DNA in the skull’s thick petrous bone, according to a study published this week in the Science journal.
Harvard geneticist David Reich said what he found particularly interesting in the study was the claim that all sub-Saharan Africans today have a substantial amount of ancestry from back-to-Africa migrations. “This is a surprising claim given previous studies, so I am still not 100-percent convinced, but the analyses seem thorough and I am eager to get a look at the data,” he said, according to Smithsonian.
The genome sequencing doesn’t answer the question or solve the mystery of why so many humans decided to move back to Africa. The study’s authors estimate that the migration may have included as much as 25 percent of the people then living in West Eurasia. There’s no evidence of a climatic change or other major event that would have spurred them to undertake the journey.
