When Paul Salopek was twenty-three, his motorcycle broke down on a lonely road in the sand near Roswell, New Mexico. He was on his way to find work at a fishery to eventually pay for a graduate degree in environmental biology; instead, he got a job at a local paper and became a journalist.

Salopek has always understood that journalism is a physical trade. He spent his late teens roving between manual labor jobs from Alaska to Australia: he was a farmhand, a commercial fisher, a gold miner. Reporting became its own kind of itinerant work. He often worked alongside his subjects—as a gas station clerk, for example, while writing a story for The Chicago Tribune that traced the US oil supply chain. While at the Tribune, he won two Pulitzer Prizes, the first for a series on the Human Genome Diversity Project and the second for his work as a foreign correspondent in Africa, in particular his coverage of Congo’s civil war. His body of work shows not a dedication to particular beats so much as the development of a long-view perspective through which one sees the percolating effects of global systems, the spooling and unraveling of power over time, and humanity’s shared history.

I first encountered Salopek in Chicago in 2012, when he was already done with foreign reporting. I had biked down from the neighborhood where I lived to Hyde Park to attend a talk he was giving at the University of Chicago. The auditorium was hot and the acoustics were poor, but Salopek’s words were captivating. He explained that he had become dissatisfied with the standard method of international reporting, for which correspondents helicoptered into countries with little notice, reported, filed, and helicoptered out. Storytelling, he said, requires the writer to come in at ground level with the subject. His solution to this problem was to walk. He indicated a world map projected on the wall behind him, with a route traced out in a squiggly line—it was a footpath. He would start in Herto Bouri, Ethiopia, and proceed twenty-four thousand miles to Tierra del Fuego, at the tip of South America. The project would be called the Out of Eden Walk, since the route followed the migratory path of our human ancestors, and Salopek would publish regular stories on the project through National Geographic.

A year later, I started working part-time for the Out of Eden Walk’s nonprofit team. I am still with them, which means I have closely followed almost all of Salopek’s journey. People on social media often describe the Out of Eden Walk as “inspiring” and “beautiful.” I think what they...