4000 years ago isn’t very far back—more recent than the Great Pyramids, probably more recent than Stonehenge, far younger than the cave paintings in Spain and France as well as some in Indonesia.
Didn't you read even the FIRST sentence of the excerpt?
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.
Regards,