A new study suggests that a mysterious human species mated with our own species tens of thousands of years ago in Africa. Researchers say the study provides evidence that present-day West Africans can link about 2 to 19 percent of their genetic ancestry to an extinct human species. The study describes the species as a “ghost population.” Scientists involved in the research estimated that mating between the two species happened about 43,000 years ago. Homo sapiens the species of human that exists today - first appeared more than 300,000 years ago in Africa. The species later spread worldwide. Earlier genetic research has shown that our species mated with two early human species, the Neanderthals and the Denisovans. The species have been extinct for thousands of years, but modern human populations outside Africa still carry DNA from both.