Here is an interesting article from the New York Times website about the history of our Genus, Homo:
Recent fossil evidence shows that there was likely to be at least two other species of the Homo genus living at the same time as Homo erectus in east africa (about 2 million years ago). This is good evidence towards the view that the evolution of the homo genus is not so simple and straightforward as previously thought by some, but that there are multiple lines of evolution within our genus. I find it interesting how there is relatively little consensus between scientists as to our origins. It just goes to show that it is not easy to figure out what happened in the past.