In 1873, Charles Darwin was stumped by a puzzle that had nothing to do with finches: how do humans and animals navigate vast featureless spaces by dead reckoning? The evidence he cited came from the journals of a Russian explorer who admitted, remarkably for a decorated imperial officer, that his state-of-the-art instruments had been useless on the shifting Siberian sea ice while his indigenous companions always knew exactly where they were.

This episode follows Baron Ferdinand von Wrangel from 46 days on dog sledges over hummocky ice, where he learned to read wind, snowdrifts, and ice texture from the Yakut, to his years as governor of Russian America, where he planted potatoes to stabilize a fur colony. It ends with his most elegant feat: deducing the existence of an island he never saw from the flight paths of migrating birds, an island  ...