Among the most exciting questions in human evolution is how modern humans spread from Africa to the rest of the world. What routes did they take? When did the migration occur? And what behavioral adaptations facilitated the expansion? One theory suggests the migration moved northward along the Nile River toward the Mediterranean. Another suggests that the route wound eastward from the Horn of Africa, across or along the Red Sea, and around or across the Arabian peninsula. John Kappelman's latest fossil finds add details on humans living along the upper Blue Nile tributaries on the lowland slope of Ethiopia's northwestern plateau. The data suggest that these people kept close to waterholes and rivers where they could find food and water a journey along what he calls the "blue highways."