In this Feb. 20, 1962 file photo, an elder warrior with a stone axe over his shoulder stands over the Baliem Valley in the central mountain range of Papua New Guinea. New research published Wednesday, Sept. 21, 2016 suggests that the genetic ancestry of people living outside Africa can be traced almost completely to a single exodus of humans from that continent long ago. But some native islanders of Papua New Guinea may also carry a tiny legacy from an earlier exit. (AP Photo)