— Jalal ad-Din Mohammed Balkhi (Rumi)

On a clear day on flat ground—in a landscape, say, like the bone-yellow floor of the Great Rift Valley of northern Ethiopia that surrounds me now—it is possible to see 60 miles. This is a three-day walking radius. For the next seven years of my life, as I retrace, on foot, the pathways of the first anatomically modern humans who rambled out Africa, this distance will represent for me, as it was for our ancestors, my tangible universe, my limiting horizon.

I’ll be cheating a bit, of course: The communications kit I’m lugging on my back to share this journey will fling open digital infinitudes that our nomadic forebears could scarcely imagine. Yet the experience of pacing off the continents, one yard at a time through 2020, will still expose, I believe, an inescapable biological reality. We’re built to walk. We’ve been wired by natural selection to absorb meaning from our days at the loose-limbed gait of three miles an hour. And whether we count ourselves cursed or lucky to be standing on the Earth at this frenetic moment in our history—I, for one, would choose no other time to be alive—reasonable arguments abound to slow down. To pause in our tracks, the way a local Afar pastoralist named Idoli Mohamed does, arms folded akimbo atop hand-greased acacia sticks. To watch. To listen. To glance over our shoulders, seeking older compass bearings. Those first bands of Homo sapienswho blazed the trail to our becoming a planetary species—hunter-gatherers we know oddly little about and who may have numbered, researchers say, a paltry few thousand individuals—have valuable lessons to impart. They were, after all, consummate survivors. This is the premise of the Out of Eden walk.

Idoli Mohamed, an Afar herder who lives in the Herto Bouri area at the start of the walk. Photograph by Paul Salopek

The template for my long trek—the first global human dispersal out of Africa—is fairly well plotted by science.

Fossils and DNA markers found in modern populations suggest that people began trickling north of our archaeological “Eden” in Africa’s Rift Valley sometime between 50,000 and 70,000 years ago. Pushed by population pressure or lured on by favorable climate shifts, some early wayfarers plodded west into Europe and probably wiped out the Neanderthals. Others turned right into Eurasia. That will be my route. (I don’t have sufficient knee longevity to add Europe to the schedule. As for Oceania, which humans reached by boat 50,000 years ago: I can barely dog paddle.) From the Middle East I’ll follow the ghostly tracks of ancient migrations through Central Asia to China, then angle northward into Arctic Siberia, from where I’ll take passage by ship to Alaska. (So fabulously rich was the American fauna encountered by the first Americans that one archaeologist, Ofer Bar Yosef, suggested I should rename this project Into Eden.) Finally, I’ll hike down the length of the Americas to Tierra del Fuego, the gale-whipped tip of South America where we at last ran out of continents, and where a callow 23-year-old named Charles Darwin began igniting this entire chain of rediscovery in the 1830s.

Retracing on foot the path our ancient ancestors traveled as they migrated across the world.

A few weeks ago, before coming to Africa, I flew to Isla Navariño in Chilean Tierra del Fuego.

Cristina Calderon, 84, the last full-blooded Yaghan speaker. She lives in Tierra del Fuego, Chile, at the end of the walk. Photograph by Paul Salopek

I wanted to preview the finish line of a project that will consume a seventh of my life. An old woman there, Cristina Calderón, 84, greeted me at her cabin door. She is the last full-blooded speaker of Yaghán—the culturally extinct indigenous group that Darwin gaped at as they fished naked on the icy beaches of the Beagle Channel. I expect and hope to meet Calderón once again, when I walk up to her shoreline porch years from now, in another hemisphere. But I also wanted to carry her words with me across the world. Her people had scanned one of humankind’s last virgin, 60-mile viewsheds about 7,000 years ago. I explained this in Spanish. She sat at her window, knotting her fingers, peering out at the inky chop, enunciating objects and animals in a dying a language that sounded more like lapping water than something human—words that are sinuous and supple and sheer. She was trying to remember.