AFRICAN DNA STUDY DETECTS MYSTERIOUS HUMAN SPECIES

WASHINGTON—SCIENTISTS examining the genomes of West Africans have detected signs that a mysterious extinct human species interbred with our own species tens of thousands of years ago in Africa, the latest evidence of humankind’s complicated genetic ancestry.

The study indicated that present-day West Africans trace a substantial proportion, some 2 to 19 percent, of their genetic ancestry to an extinct human species—what the researchers called a “ghost population.”

“We estimate interbreeding occurred approximately 43,000 years ago, with large intervals of uncertainty,” said University of California, Los Angeles human genetics and computer science professor Sriram Sankararaman, who led the study.

Homo sapiens first appeared more than 300,000 years ago in Africa and spread worldwide, interbreeding with other human species in Eurasia that have since gone extinct including the Neanderthals and the lesser-known Denisovans.

But while there is an ample fossil record of the Neanderthals and a few fossils of Denisovans, the newly identified “ghost population” is more enigmatic.

Asked what details are known about this population, Sankararaman said, “Not much at this stage.”

“We don’t know where this population might have lived, whether it corresponds to known fossils, and what its ultimate fate was,” Sankararaman added.

Sankararaman said this extinct species seems to have diverged roughly 650,000 years ago from the evolutionary line that led to Homo sapiens.

The researchers found DNA segments in the West Africans that could best be explained by ancestral interbreeding with an unknown member of the human family tree that led to what is called genetic “introgression.”