Why are we the only human species left?

Did you know that the Neanderthals were not the only other human species that lived? At one time we shared this planet with about 5 other "homo" species and we believe our human ancestry was made up of at least 14 other human species. This week Peter and Russell will take a look at our ancestral family tree and find out what other hominins lived before and while we were around. What did we share with them? What did we learn from them? and most important of all What happened to them and why are we the only one's left?