Primary takeaway: simple, visible theories are rarely completely correct, especially when they're formulated in response to primitive data.

Commentary: "Species" is a wrong idea, and much of the start is uninteresting discussion of whether or not neanderthals were a "separate species." Taboo species, and everything becomes clear: they had a separate evolutionary history than the strain of homo sapiens that originated in Africa, but they could and did interbreed with that strain, and so current humans have genes from at least one of the African, Neanderthal, and Denisovan varieties.