‘Ghost’ Ancestor Detected in DNA of Today’s West Africans

An unknown hominin made a substantial contribution to the genome of modern West Africans, a new study has demonstrated. The genetic signal of this unknown ancestral species has been identified in four groups of West Africans, report Arun Durvasula and Sriram Sankararaman of the University of California, Los Angeles.

In fact, you may have a trace of this unknown archaic human as well. “Our study shows that some of this ancestry is also present in non-African populations,” Sankararaman tells Haaretz – it’s just less pronounced than in the West African groups.

He and Durvasula are in the process of testing other populations around Africa for the signal, he shares.

The interbreeding event in West Africa may have been quite recent in evolutionary terms, even though this new unknown species split off from the Homo line well over half a million years ago, before the split between Neanderthals and Homo sapiens, they reported Wednesday in Science Advances.

Yoruba Obatala priests in their temple in Ife Dierk Lange, Wikimedia Commons

Specifically, by comparing the genomes of 405 West Africans with Neanderthal and Denisovan genomes and applying computer modeling, Durvasula and Sankararaman have discovered that contemporary Yoruba and Mende people derive between 2 to 19 percent of their genomes from this mysterious archaic hominin. In terms of averages, 6.6 percent of the Yoruba and 7 percent of Mende genome sequences are archaic, they calculate.

Their revelation comes years after the discovery that non-Africans contain genetic signals from Neanderthals and Denisovans. But in this case, the authors demonstrate by statistical methods that these sequences cannot have originated in Neanderthals, Denisovans or African populations such as the southern African Khoisan or central African pygmies.

Asked if Neanderthals might have had it too, Sankararaman explains that we can’t know at this stage. “Our methods require substantial sample sizes to detect this ghost population,” he says – and there is very little Neanderthal DNA around to work with, which is a challenge.