Do all human beings have a single oldest ancestor (a man and a woman), or were there were many ancestors at the same time at different places on earth? This article sheds some light. Is there another authoritative report released more recently?
You are talking about the mitochondrial eve and the chromosome Y adam. At some point there must be just one pair, though historically the evidence can be lost if there is a near complete extinction event. Current evidence for eve points to SE Africa.