This story appears in the December 2013 issue of National Geographic magazine.

Walking is falling forward.

Each step we take is an arrested plunge, a collapse averted, a disaster braked. In this way, to walk becomes an act of faith. We perform it daily: a two-beat miracle—an iambic teetering, a holding on and letting go. For the next seven years I will plummet across the world.

I am on a journey. I am in pursuit of an idea, a story, a chimera, perhaps a folly. I am chasing ghosts. Starting in humanity’s birthplace in the Great Rift Valley of East Africa, I am retracing, on foot, the pathways of the ancestors who first discovered the Earth at least 60,000 years ago. This remains by far our greatest voyage. Not because it delivered us the planet. No. But because the early Homo sapiens who first roamed beyond the mother continent—these pioneer nomads numbered, in total, as few as a couple of hundred people—also bequeathed us the subtlest qualities we now associate with being fully human: complex language, abstract thinking, a compulsion to make art, a genius for technological innovation, and the continuum of today’s many races. We know so little about them. They straddled the strait called Bab el Mandeb—the “gate of grief” that cleaves Africa from Arabia—and then exploded, in just 2,500 generations, a geological heartbeat, to the remotest habitable fringe of the globe.

Millennia behind, I follow.

Using fossil evidence and the burgeoning science of “genography”—a field that sifts the DNA of living populations for mutations useful in tracking ancient diasporas—I will walk north from Africa into the Middle East. From there my antique route leads eastward across the vast gravel plains of Asia to China, then north again into the mint blue shadows of Siberia. From Russia I will hop a ship to Alaska and inch down the western coast of the New World to wind-smeared Tierra del Fuego, our species’ last new continental horizon. I will walk 21,000 miles.

Step by Step Follow Paul Salopek during the first leg of his walk around the world.

If you ask, I will tell you that I have embarked on this project, which I’m calling the Out of Eden Walk, for many reasons: to relearn the contours of our planet at the human pace of three miles an hour. To slow down. To think. To write. To render current events as a form of pilgrimage. I hope to repair certain important connections burned through by artificial speed, by inattentiveness. I walk, as everyone does, to see what lies ahead. I walk to remember.

The trails scuffed through the Ethiopian desert are possibly the oldest human marks in the world. People walk them still: the hungry, the poor, the climate stricken, men and women sleepwalking away from war. Nearly a billion people are on the move today across the Earth. We are living through the greatest mass migration our species has ever known. As always, the final destination remains unclear. In Djibouti city, the African migrants stood waving cell phones on trash-strewed beaches at night. They were capturing a cheap signal from neighboring Somalia. I heard them murmur: Oslo, Melbourne, Minnesota. It was eerie and sad and strangely beautiful. After 600 centuries we were still seeking guidance, even rescue, from those who had walked before.

Herto Bouri, Ethiopia

“Where are you walking?” the Afar pastoralists ask.

“North. To Djibouti.” (We do not say Tierra del Fuego. It is much too far—it is meaningless.)

“Are you crazy? Are you sick?”

In reply, Mohamed Elema Hessan—wiry and energetic, the ultimate go-to man, a charming rogue, my guide and protector through the blistering Afar Triangle—doubles over and laughs. He leads our micro-caravan: two skinny camels. I have listened to his guffaw many times already. This project is, to him, a punch line—a cosmic joke. To walk for seven years! Across three continents! Enduring hardship, loneliness, uncertainty, fear, exhaustion, confusion—all for a rucksack’s worth of ideas, palaver, scientific and literary conceits. He enjoys the absurdity of it. This is fitting. Especially given our ridiculous launch.

I awoke before dawn and saw snow: thick, dense, choking, blinding. Like plankton suspended at the bottom of a sunless sea, swirling white in the beam of my headlamp. It was the dust. Hundreds of animals in Elema’s village had churned up a cloud as fine as talc. Goats, sheep, and camels—but, sadly, not our camels.

The cargo animals I had requisitioned months before (a key arrangement in a project that has consumed thousands of hours of planning) were nowhere to be found. Their drivers, two nomads named Mohamed Aidahis and Kader Yarri, were absent too. They never showed up. So we sat in the dust, waiting. The sun rose. It began to grow hot. Flies buzzed. To the east, across the Rift, our first border, Djibouti, was receding at the rate of three-quarters of an inch every year—the speed at which Arabia is drifting away from Africa.

Are you crazy? Are you sick? Yes? No? Maybe?

The Afar Triangle in northeast Ethiopia is dreaded as a waterless moonscape. Temperatures of 120°F. Salt pans so bright they burn out the eyes. Yet today it rained. Elema and I have no waterproof tents. We have an Ethiopian flag, which Elema wraps himself in as he walks. We have found and rented two camels. We plod across an acacia plain darkened to the color of chocolate by the warm raindrops. We tread on a photographic negative: The camels’ moccasin-like feet pull up the frail crust of moisture, leaving behind ellipses of pale dust.

After a dozen miles, Elema already asks to turn back.

He forgot his new walking shoes from America. And his flashlight. And his hat—and the cell phone. So he hitches a ride from our first camp to his village to retrieve these vital items. And now he has jogged all the way back to catch up. He complains, laughing, of crotch rash.

This absentmindedness is understandable. It is impossible to remember every detail on a walk of this scope. I have forgotten things myself—nylon stuff sacks, for instance. Because of this, I begin my trek out of Africa with airplane luggage, a city slicker’s rig with plastic rollers and collapsible handle, strapped to a camel’s back.

It is the scientists of the Middle Awash research project who invited us to begin walking at Herto Bouri, our symbolic mile zero in the Ethiopian Rift—one of the richest human boneyards in the world. This is the famous site where some of the world’s oldest human fossils have been found. Homo sapiens idaltu. Gone for 160,000 years. A big-boned ancestor—a dawn version of us.

The Middle Awash Project researchers, a team led by Tim White, Berhane Asfaw, and Giday WoldeGabriel, have uncovered in Ethiopia many of the most important hominin fossils of our day, including Ardipithecus ramidus, a 4.4-million-year-old biped. My unpredictable Afar guide, Elema, is their veteran fossil hunter.

Raised in a nomad culture feared for its tough warriors, Elema speaks three languages—Afar, Amharic, and a profane English patois gleaned from the Middle Awash scientists. He is a paleontologist in his own right. He exclaims “Wow” and “Crazy, man” and “Jeezus” while identifying the Rift’s key geological strata. (Me he calls, not without endearment, White Asshole; I return the compliment with equal fondness, dubbing him and his perennial rash, Burned Asshole.) He is the balabat,or traditional leader, of the Bouri-Modaitu clan of the Afar. His cell phone holds the numbers of Ethiopian grandees and French academics. Educated to the eighth grade in schools of the Emperor Haile Selassie, he bridges more cultures than a Malinowski. He holds more time warps inside his head than an Einstein. He is a phenomenon.

We are camped at Aduma when the Middle Awash scientists find us. They have come to show us a Middle Stone Age site.

“These tools are still a little early for the people you’re following,” says Yonatan Sahle, an Ethiopian researcher based in the Human Evolution Research Center at the University of California, Berkeley. “But their technology was basically as advanced. They made throwing weapons that allowed them to outcompete the other hominins they encountered outside Africa.”

We lean over a delicate stone point, a work of art that lies where its maker dropped it 80,000 to 100,000 years ago. In the distance we hear screaming. We look up.

An Afar woman strides in from the desert, waving her arms wildly. Where did she come from? Is she warning us off her hill? Is she mad? No. She marches up to a man dozing nearby on the ground. She gives him a sharp kick. She hefts a stone—a Middle Stone Age tool, perhaps—and threatens to brain him. Is it the collection of a debt? A matter of the heart?

I hear the victim laughing. I know this maniacal laugh. It is the man who will guide me to Djibouti, to the Gulf of Aden.

Dalifagi, Ethiopia

Water is gold in the Afar Triangle of Ethiopia.

No surprise. This is one of the hottest deserts in the world. Walking for three days near the western scarp of the Rift, Elema and I find only one miraculous pool of muddy rainwater to ease our camels’ thirst. But we stumble across a new type of water hole a day later—a coveted oasis of electrons, the village of Dalifagi.

The immense salt scapes that shroud the borders of Ethiopia, Djibouti, and Eritrea weren’t even mapped until the 1920s. For centuries the martial Afar pastoralists who ruled the area resisted all incursions by the outside world. Today, though, besides their usual armament of pointy daggers and Kalashnikov rifles, they carry cell phones. They embrace the tool of instant communication with a vengeance. “It has given them power,” says Mulukan Ayalu, 23, an Ethiopian government technician who maintains the tiny power plant at Dalifagi. “They can call different goat traders. They can choose their selling prices.”

The diesel generator at Dalifagi chugs out a 220-volt current for six hours a day. Ayalu plugs in the nomads’ cell batteries for a few cents each. On Mondays—market day—grizzled Afars line up at his office door. The folds of their sarong-like skirts bulge with dead cell phones of faraway neighbors. The nomads are addicted to the devices. “Hallow? Hallow?” Elema bellows into his phone on the trail, with an accent that sounds, to my ear, straight out of Brooklyn. But he is asking directions to some ancient well. Or exchanging news of the dreaded Issa, armed raiders from a rival nomad group.

The electronic oasis at Dalifagi would never draw tourists, much less inspire the verse of caravan poets. But it is the real story today in sub-Saharan Africa. Nine hundred million people. A headlong sprint into the digital age. Exploding aspirations. Consequences unknown.

Near the Talalak River, Ethiopia

Footwear is a hallmark of modern identity. How best to glimpse an individual’s core values at the start of the 21st century? Look down at people’s feet—not into their eyes.

In the affluent “global north,” where fashion caters to every whim and vanity, shoes announce their wearer’s class, hipness, career choice, sexual availability, even politics (the clog versus the cowboy boot). It is disorienting, then, to be walking through a landscape where human beings—millions upon millions of women, men, and children—slip on identical-style footwear every morning: the cheap, democratic, versatile plastic sandal of Ethiopia. Poverty drives demand. The only brand is necessity.

Available in a limited palette of chemical hues—black, red, brown, green, blue—the humble rubbery shoes are a triumph of local invention. They cost a pittance to manufacture. Any pair can be had for the equivalent of a day’s field labor. (Perhaps two dollars.) They are cool—permitting the air to circulate about the feet on the desert’s scalding surface. The ubiquitous sandals of rural Ethiopia weigh nothing. They are recyclable. And home repair is universal: Owners melt and mend the molded-plastic straps over wood fires.

Our binary camel caravan—our two beasts are named A’urta, or Traded for a Cow, and Suma’atuli, Branded on the Ear—has been joined at last by its two long-lost cameleers, Mohamed Aidahis and Kader Yarri. These men caught up with us from our departure point at Herto Bouri, crossing miles of gravel pans and rumpled badlands during days of quickstep walking. In the manner of life here, no explanation was asked or given regarding the nature of their weeklong delay. They were late. Now they were with us. Each wore a pair of the region’s signature plastic sandals. Color: lime green.

The dust of the Rift Valley is a palimpsest stamped by such footwear. Yet if Ethiopia’s populist sandals are mass-produced, their wearers are not. One man might drag his left heel. A woman might mar her right shoe’s sole by stepping on an ember.

Elema knelt the other day on the trail, examining this endless mutation of impressions.

“La’ad Howeni will be waiting for us in Dalifagi,” he said. He pointed to a single sandal track. La’ad was waiting in Dalifagi.

Near Hadar, Ethiopia

We are walking in the direction of Warenso.

The world changes when you are thirsty. It shrinks. It loses depth. The horizon draws close. (In northern Ethiopia the Earth butts against the sky, hard and smooth as the surface of a skull.) The desert tightens around you like a noose. This is the thirsty brain compressing the distances of the Rift, sucking in the miles through the eyes, magnifying them, probing them for any hint of water. Little else matters.

Elema and I have trudged more than 20 miles through the crushing heat. We have separated from the cargo camels to visit an archaeological site folded into a wrinkled draw: Gona, the location of the oldest known stone tools in the world. (Age: 2.6 million years.) Our water bottles are empty. We are uncomfortable, anxious. We speak little. (What can be said? Why dry the tongue?) The sun’s rays corkscrew into our heads. An Afar proverb: It is best, when you are lost or thirsty, to keep walking under the sun, because eventually someone will see you. To be tempted into shade, to drop under one of 10,000 thornbushes, means death: No one will find you. So we stagger on into the blinding afternoon—until we hear the faint bleating of goats. Then we smile. We can begin to relax. Goats mean people.

Our hosts: an Afar family camped on a hill. Two strong, smiling young women. Eight children in thin rags that once may have been articles of clothing. And a very old woman—she doesn’t know her age—who hunches like a gnome in the shade of a reed mat. Her name is Hasna. She has been sitting there, weaving with spidery fingers, since the beginning of time. She invites us to join her, to rest our bones, to remove our shoes. From a battered jerrican she pours us water—chalky and warm, so salty, so alkaline, it oozes down the throat like soap, but precious nonetheless. She offers us a fistful of yellow berries from a wild tree that grows in wadis. She is our mother.

When our ancestors wandered out of Africa 60,000 or more years ago, they encountered other species of hominins. The world was crowded then with strange cousins: Homo neanderthalensis, Homo floresiensis, the Denisovans, and perhaps other varieties of people who weren’t quite us.

When we met them, perhaps like this, on some remote hilltop, did we share water, or even interbreed peacefully, as some geneticists suggest? (Outside Africa, modern human populations seem to contain as much as 2.5 percent of Neanderthal DNA.) Or did we rape and kill, launching our species’ long and terrible history of genocides? (In a cave occupied by modern humans, Fernando Ramirez Rozzi, of Paris’s Centre National de la Recherche Scientifique, has identified a Neanderthal jawbone mutilated by the cut marks of butchery, perhaps cannibalism.) Scientists still debate this puzzle. All that is certain is that we alone survived to claim the Earth. We won the planet. But at a cost: We are without close family. We are a species racked by survivor’s guilt. We are a lonely ape.

Hasna’s gentle voice lulls me to sleep.

When I awake, Elema is hunkered in low conversation with the men of the nomad camp. They have returned from tending their flocks. We shake hands. We thank them. We leave packets of crackers for grinning Hasna, and walk on. We are hurrying to meet the camels, walking toward Warenso. That night, while sipping our gift of salty water around a red fire that saws back and forth in the wind, Elema tells me the men of Hasna’s camp had threatened him. He was not of their clan. He nearly hit them over the head with his walking stick.

Dubti, Ethiopia

Moving north and then east, we abandon the desert and stub our toes on the Anthropocene—the age of modern humans.

Asphalt appears: the Djibouti-Ethiopia road, throbbing with trucks. We drift through a series of gritty towns. Dust and diesel. Bars. Shops with raw plank counters. Garlands of tin cups clink in the wind outside their doors.

Then, near Dubti: a sea (no, a wall) of sugarcane. Miles of industrial irrigation. Canals. Diversion dams. Bulldozed fields. Levees crawling with dump trucks. Elema becomes lost. Night envelops us. We end up pulling the weary camels in a gigantic circle. “Wow, man!” Elema says angrily. “No way! Too much change!”

This is the multimillion-dollar Tendaho sugar plantation, an Ethiopian-Indian project that is making the Afar Triangle bloom. Fifty thousand migrant workers will soon toil here, tending 120,000 acres of desert that have been scraped, shaped, molded, and flooded by the Awash River to sweeten the world’s coffee, its tea. Eventually, it could make Ethiopia the sixth largest sugar producer in the world. It will help break the country’s dependence on foreign aid—a good thing.

But the benefits of economic progress are rarely shared equally with all involved. There are winners and losers in every improvement scheme. Here, one of the losers is a bright young Afar woman—a girl, really, though her poise makes her seem old beyond her years. She is wrapped in a red dress. She stands by a new levee. She is collecting water from what used to be the Awash River.

“The company moved us off our land,” she tells us, waving her arm at the sheets of cane. “We get a little work, we Afars, but it is always the lowest work. Watchmen. Shovel work.”

A typical sugar plantation salary: $20 a month. The girl says police came to expel the Afar diehards who refused to move. Shots were exchanged. Blood flowed on both sides.

How old is this story? It is one of the oldest stories in the world.

What are the individual names of the Sioux forced from the Black Hills of the Dakota Territory by gold miners? Who remembers this anymore? Who are the millions of people who surrender their livelihoods today—Irish farmers in the European Union, Mexican ranchers shunted aside by highways—for some abstract common cause? It is impossible to keep track. Humanity remakes the world in an accelerating cycle of change that strips away our stories as well as the topsoil. Our era’s breathtaking changes flatten collective memory, blur precedence, sever lines of responsibility. (What disconcerts us about suburbia? Not just its sameness, but its absence of time. We crave a past in our landscapes.)

Dubti is a busy green frontier. Ethiopians are flocking there, bringing new hopes, tastes, ambitions, voices, a new future—a new history.

In Dishoto, another truck stop town, I recharge my laptop at a police station. The officers are all outsiders, non-Afar, from the highlands, from the south. They are friendly, curious, generous. They ply Elema and me with tea. (It is dense with sugar.) Our conversation is interrupted by government ads. The policemen watch these nation-building commercials intently: music played over video loops of strip mining, roadbuilding, workers in medical labs. We thank them. We walk on.

Milan Kundera, the Czech novelist, once wrote that the struggle of man against power is the struggle of memory against forgetting.

The Afar girl’s name is Dahara. She is 15.

Near the Ethiopia-Djibouti border

We camp on the flank of Fatuma mountain, a basalt sentinel overlooking the caravan trails that braid eastward to the old coastal sultanate of Tadjoura. The tiny Republic of Djibouti sprawls below: a scalded plain, hotter and drier than the Ethiopian desert, with dry lake beds of blinding white salt, scarps of gunmetal gray, and doubtless, huddled somewhere in the shade of a doom palm, more Afar nomads—herders cleaved from their Ethiopian brethren by a colonial border, speaking in halting French.

This is where I begin to say goodbye to the Afar camel men from Herto Bouri.

Elema, Yarri, and Aidahis declare themselves ready to push on. They wish to walk with me to the beaches of the Gulf of Aden. But this is impossible. Two of them have no passports, no documents, no scraps of paper attesting to their existence. (“This is all Afar land!” they say.) And besides, Elema is sick. He issues his camel-loading orders lying down, from under his shire, his sarong, which he drapes over his head like a sheet. In a few hours we will part ways in the ugly border town of Howle.

What is it like to walk through the world?

It is mornings like these: Opening your eyes to nothing but seamless sky for day after day; a pale, numinous void that for one fleeting instant, when you first awake, seems to suck you upward, out of your body, out of yourself. It is the clarity of hunger, a transparency that seems blown through by the wind, the way a hollow pipe is blown to make it whistle. (We trekked 18 miles yesterday on short rations, on a single bowl of noodles and a handful of biscuits each. My wedding ring, once tight, jiggles loosely along my finger.) It is learning to read landscape with your whole body, your skin, not merely your eyes—sensing camel fodder in a thorn scratch, the coming dust in the smell of the wind, and of course, precious water in the fold of the land: a limbic memory of great power. It is watching the eternity of Africa slip by at a walking pace, and coming to realize dimly that, even at three miles an hour, you are still moving too fast. It is the journey shared.

Mohamed Aidahis: a powerful ant-stomping gait. Kader Yarri: the marionette looseness of a skinny man’s step. Mohamed Elema: the spring-loaded step of a square dancer. On our best days we four ramblers recognize our immense good luck. We ricochet down steep mountain trails, almost running, with the desert of Ethiopia shining at our feet. We bounce our voices off the walls of black-rock canyons in whooping contests. Then we catch each other’s eye, three Afars and a man from the opposite longitude of the Earth, and grin like children. The cameleers catch the spark, and sing.

What is it like to walk through the world?

It is like this. It is like serious play. I will miss these men.

Ardoukoba lava field, Djibouti

The dead appear on the 42nd day of the walk.

There are five, six, seven of them—women and men sprawled faceup, facedown, on the black lava plain as if dropped from the sky. Most are naked. They have stripped off their clothes in a final spasm of madness. Sandals, trousers, brassieres, cheap nylon backpacks—their belongings lie scattered, faded, washed out, bleached by the sun to the pale gray of undersea things. The skin of the dead is parched a deep burned yellow. The little wild dogs that come in the night have taken their hands, taken their feet. They might have been Ethiopians. Or Somalis. A few, probably, were Eritreans. They were walking east. This is what unites them now in the mineral silences of the desert: They were making for the Gulf of Aden—for the open boats of the Yemenis who smuggle destitute Africans to peons’ jobs in the Middle East. How many such migrants die in the Afar Triangle? Nobody knows. At least 100,000 attempt the crossing to the Arabian Peninsula each year, according to the UN. Police chase them. They become lost. Thirst kills them.

“A crime!” Houssain Mohamed Houssain shouts back at me. “A disgrace!”

Houssain is my guide in Djibouti. He is a decent man. He is angry and perhaps ashamed. He strides far ahead, shaking his walking stick at the stone white sky. I lag behind. I wipe the sweat from my eye sockets and study the dead.

A demographer calculates that 93 percent of all the human beings who ever existed on Earth—more than 100 billion people—have vanished before us. Most of humanity is gone. The bulk of our heartaches and triumphs lie behind us. We abandon them daily in the wasteland of the past. Rightly so. Because even though I have told you that I am walking to remember, this isn’t completely true. As we reenact the discovery of the Earth over and over again, to keep going—to endure, to not sit down—we must embark also on journeys of forgetting. Houssain appears to know this. He never looks back.

One day later we reach the Gulf of Aden.

A beach of gray cobbles. Waves of hammered silver. We shake hands. We laugh. Houssain opens a sack of hoarded dates. It is a celebration. We stand on the rim of Africa. The sea is walking—it falls endlessly forward into Africa and then rolls forever back, pulling away to the east … toward Yemen and the Tihamah Coast, toward the lupine valleys of the Himalaya, toward ice, toward sunrise, toward the hearts of unknown people. I am happy. I write this down in my journal: I am happy.