by EWEN CALLAWAY
This rocky area in Mota cave held bones that yielded the first ancient African genome PHOTO/Kathryn and John Arthur
Finding that much of Africa has Eurasian ancestry was mistaken.
An error has forced researchers to go back on their claim that humans across the whole of Africa carry DNA inherited from Eurasian immigrants.
This week the authors issued a note explaining the mistake in their October 2015 Science paper on the genome of a 4,500-year-old man from Ethiopia1 — the first complete ancient human genome from Africa. The man was named after Mota Cave, where his remains were found.
Although the first humans left Africa some 100,000 years ago, a study published in 2013 found that some came back again around 3,000 years ago; this reverse migration has left its trace in African genomes.
In the Science paper, researchers confirmed this finding. The paper also suggested that populations across the continent still harbour significant ancestry from the Middle Eastern farmers who were behind the back-migration. Populations in East Africa, including Ethiopian highlanders who live near Mota Cave, carried the highest levels of Eurasian ancestry. But the team also found vestiges of the ‘backflow’ migration in West Africans and in a pygmy group in Central Africa, the Mbuti.
Andrea Manica, a population geneticist at the University of Cambridge, UK, who co-led the study, says the team made a mistake in its conclusion that the backflow reached western and central Africa. “The movement 3,000 years ago, or thereabouts, was limited to eastern Africa,” he says.
Incompatible software
Manica says that the error occurred when his team compared genetic variants in the ancient Ethiopian man with those in the reference human genome. Incompatibility between the two software packages used caused some variants that the Ethiopian man shared with Europeans (whose DNA forms a large chunk of the human reference sequence) to be removed from the analysis. This made Mota man seem less closely related to modern European populations than he actually was — and in turn made contemporary African populations appear more closely related to Europeans. The researchers did have a script that they could have run to harmonize the two software packages, says Manica, but someone forgot to run it.
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