http://www.bbc.com/earth/story/20150929-why-are-we-the-only-human-species-still-alive Interesting piece. Two million years ago in Africa, several species of human-like creatures roamed the landscape. Some looked surprisingly similar to each other, while others had distinct, defining features. In September 2015, another species was added to the list. Hundreds of bones discovered in a South African cave are now believed to belong to a new species, known as Homo naledi. There may well be many more extinct hominin species waiting to be uncovered. Our own species appeared around 200,000 years ago, at a time when several others existed. Yet today, only we remain. Why did we manage to survive when all of our closest relatives have died out? (...)
exactly right - the only "pure" humans without neanderthal DNA are those whose ancestors never left Africa. The human genome experiment pretty much proves this, or is at least heads & shoulders above any other theories.
Having had my DNA analysed, I happen to know that I'm 2.8% Neanderthal (all non-Africans are somewhere between 0 and 4 it seems). There are plenty of theories about what happened to the poor buggers, for whom I have a soft spot. But nobody knows for sure. To a small degree, they live on in us.
Game show host: "And Homo sapiens continues its improbable winning streak, moving on to the final elimination round!"