Why Are We The Only Humans Left?

In part 2 of our special series on human ancestry, we ask why we are the only surviving branch on the human evolutionary tree. Just 50,000-100,000 years ago, Earth was home to three or four separate human species, including our most famous cousins: the Neanderthals. New research has shown that Neanderthals were not the brutish, unintelligent cavemen that cartoons make them out to be.