Experts in evolution determined decades ago that the human species arose in Africa. Fossil bones found there are far more ancient than human remains found anywhere else. But when and why our ancestors first ventured away from the mother continent to take up residence in other parts of the world have been matters of debate. The conventional wisdom had long held that Homo erectus, the immediate ancestor of Homo sapiens, made the exodus about 1 million years ago, after developing relatively sophisticated stone tools that enabled him to gather food more efficiently during his wanderings.
But that wisdom was upset in...