"Where is the proof? How old was the bones of the oldest caucasian dug up in Africa? And, what happened to the neanderthals? What happened to those hairybacks that once roamed across northern europe?"

When I said all humans have common origins in Africa, I didn't mean they all looked the same as they do now when they were in Africa. The ancestors of Caucasians and Mongoloids came originally from Africa, but they weren't Caucasian or Mongoloid when they were in Africa. They BECAME Caucasion or Mongoloid AFTER they left Africa. The ancestors of Caucasians and Mongoloids were probably black when they were in Africa (otherwise they would have been decimated by skin cancer). Hence, white people (and all other "races") are descended from black people.
As for the neanderthals, they came from a different (but related) line to modern humans, though for a time they co-existed. Prevailing evidence suggests that the neanderthals died out because they couldn't compete for food with modern humans who were the more successful hunters. But even the ancestors of the neanderthals (and all other hominid species) came originally from Africa. Check out the following web page.