Paley was voluble and earthy, a French Zorba. He was joining me for a rare foot crossing of Afghanistan's Wakhan corridor, a forgotten redoubt tucked high behind the mountain walls of the Hindu Kush. In the mornings he performed yoga on the road to soothe a tricky back. Expanded font settings on my laptop were my own concessions to middle age. But I didn't feel old. Not at all. Walking the Earth makes you a child again. By the time I eventually reach Tierra del Fuego, my destination six or seven years away, I will be newborn.

Paley was doing a Wakhi dance now -- paddling his arms and shimmying his hips along the desolate banks of the Panj. Across the glacial currents in Afghanistan, a few delighted Wakhi shepherds in dirt-brown shalwar kameezes gathered to mimic his moves. Everyone dances in Afghanistan. During the war, in the early 2000s, I had danced into Kabul with a column of Northern Alliance troops, two-stepping behind a T-55 tank to avoid land mines: a combat conga line. I remember how one fighter broke ranks to pillage a farmhouse. A booby trap blew off his feet with a dull pop. This was a long time ago. It was before I began truly to walk, back when I was a million or more years old.