A 7-year, 21,000 mile journey for a Pulitzer-winning journalist.

ON THE GULF OF AQABA, Jordan — I AM walking across the world. In January I set out on foot from Herto Bouri, an early site of Homo sapiens fossils in the Rift Valley of Ethiopia, to retrace the pathways of the first anatomically modern humans who colonized the planet at least 60,000 years ago.