By the close of 2002, there were at least three contenders for the title of “earliest known human.” There was the 7 million year old Sahelanthropus tchadensis from the Djurab Desert, the 6 million year old Orrorin tugenensis from Kenya, and the 5.6 million year old Ardipithecus kadabba from northeastern Ethiopia’s Afar region. Though very different from each other, each species appeared to fit somewhere near the base of the human family tree, not long after our split with the ancestors of chimpanzees. But which of these species were truly our ancestors, and how can we be sure that we are properly reading their bones?

Separating fossil ancestors