Cocooned inside a bubble of loud noise and a tonnage of steel, members of the internal combustion tribe tend to adopt ownership of all consumable space. They roar too close. They squint with curiosity out of the privacy of their cars as if they themselves were invisible. In Saudi Arabia, this sometimes meant a total loss of privacy as Bedouins in pickups, soldiers in S.U.V.’s and curiosity seekers in sedans circled my desert camps as if visiting an open-air zoo, gaping at the novelty of a man on foot with two cargo camels. Other motorists steered next to my elbow for hundreds of yards, interrogating me through a rolled-down car window. (Not to pick on Saudi Arabia, which is no worse than any other Car Brain society, but exactly one driver in 700 miles of walking in the kingdom bothered to park and stroll along for a while.)

More striking than a Car Brain’s impaired road etiquette, though, are the slow pleasures it misses in life.

The Car Brain will never know the ceremony of authentic departures and arrivals. Towns and villages that were mere smears of speed along busy superhighways were celebratory events savored by my Saudi walking partners and me. Our step lightened with anticipation as we wandered into the outskirts. We laughed. We felt good: flushed with accomplishment. Similarly, packing our camel bags and walking out of a town was a special moment — an embarkation that signaled a tangible advance through space and time, and not the commuter’s inconvenience of simply “getting there.”

Car Brains have lost all knowledge of human interactions on foot. People stiffen when they see a pedestrian approaching from a distance. But they relax and smile as they hear your voice, see your empty (unarmed) hands. In Africa and in the remnant pastoral communities of Arabia you must stand dozens of yards away from huts and homes, waiting politely to be noticed, before exchanging greetings. A lovely courtliness marks these bipedal encounters.

AND then there is simply the act of traveling through the world at three miles per hour — the speed at which we were biologically designed to move. There is something mesmerizing about this pace that I still can’t adequately describe. While roaming the old pilgrim roads in Saudi Arabia, I came to understand how the journey to Mecca — the hajj — in the pre-airline days was perhaps as important as reaching Islam’s holiest city. Watching the Red Sea slide by my left shoulder as I walked north, seeing the white desert coast dance with ink-blue waters as one bay after another scalloped by, put me in a meditative trance that must be primordial.

These are natural, limbic connections that reach back to the basement of time — ones that Car Brains rarely experience. I must continually remind motorists that what I am doing is not extreme. Anthropologists have strapped G.P.S. devices to the Hadza people of Tanzania, among the last hunter-gatherers left on earth, and discovered that the men walk on average seven miles a day in pursuit of game. (Women a little less.) This adds up to 2,500 miles annually, or tramping from New York to Los Angeles every year. Given that this ancient economy is one that dominated 95 percent of human history, walking that distance is our norm. Sitting down is what’s radical.