by EWEN CALLAWAY
IMAGE/Dant/Getty Images/iStockphoto Thinkstock Images (MARS)
A 4,500-year-old skeleton from a cave in Ethiopia has produced Africa’s first ancient human genome. The man’s DNA suggests that Middle Eastern farmers migrated into Africa several thousand years ago, leaving traces of their Eurasian ancestry in the genomes of many modern-day Africans.
Modern humans, Homo sapiens, emerged in Africa around 200,000 years ago, before populating nearly every corner of the planet. Proof of these travels is written in the genomes of people living today. DNA gleaned from ancient remains found in Europe, Asia and the Americas in recent years has added new twists to the human evolutionary story. Yet Africa has missed out on this DNA-based revolution, in part because genetic material degrades quickly in the hot temperatures of the continent.
Ethiopian discovery
In 2011, archaeologists working with Gamo tribesman in the highlands of southwest Ethiopia discovered Mota Cave, 14 metres wide and 9 metres high, overlooking a nearby river. A year later, they excavated a burial of an adult male, his body extended and hands folded below his chin. Radiocarbon dating suggested that the man died around 4,500 years ago—before the proposed time of the Eurasian migrations and the advent of agriculture in eastern Africa.
Advances in ancient DNA technology allow researchers to reap DNA from ever older bones, and the cool, constant temperatures of caves are kind to the molecule. So a team co-led by Ron Pinhasi, an archaeologist at University College Dublin, tested the Mota man’s bones for intact DNA and found enough to sequence his genome 12 times over.
The man’s genome is, unsurprisingly, 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. But further genetic studies show that the Ari also descend from people that lived outside Africa, which chimes with a previous study that discovered a ‘backflow’ of humans into Africa from Eurasia around 3,000 years ago. (Humans first migrated from Africa some 60,000 to 100,000 years ago.)
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