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 can trace a substantial proportion, about 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, published this week in the journal Science Advances.