I think we killed off the Neanderthals, in much the same way we have committed genocide against Native Americans,made slaves of Africans, colonized Africa, South America & Asia. Homo Sapiens Sapiens are killers. But just not us, carnivore mammals, reptiles, birds, bacteria, viruses, even plants are all killers too, that's one of the basic facts of evolution. As far as the false claim that neanderthals weren't very bright, what nonsense! They had a brain slightly larger than ours, survived multiple ice ages, hunted woolly rhinos, killed the cave bear, saber-tooth cats, lions larger than today's lions, burried their dead & took care of their old & disabled. As far as the dna evidence that all non-African people have over 2+% Neanderthal dna, so what. We know most African Americans have some White dna, a holdover from slavery, when the choice was submit or die. We killed them, probably because we had better weapons.