But genes cannot explain the extraordinary rigor of Knight’s renunciation. Finkel plumbs the history of hermits for a similar case, considering Lao-tzu, the anchorites of the Middle Ages, the tomb-dwelling Saint Anthony, and India’s estimated 4 million sadhus, many of whom file their own death certificate before commencing a life of monastic bliss. He does not mention Christopher McCandless, the subject of Jon Krakauer’s Into the Wild, who lasted less than four months after disappearing into the Alaskan taiga, but McCandless had no cabins to break into. Finkel concludes as he begins, with the theory that Knight entered the forest because there was no place for him in modern society. “I wasn’t content,” Knight says. Before he left he was shy, socially inept, anxious. After, he says, “I was lord of the woods.”

Knight’s hermitage was not entirely pure—he stole processed food and a twin-size mattress, listened to talk radio (a lot of Rush Limbaugh), played handheld video games, and even watched a miniature Panasonic black-and-white television, charged with stolen car batteries (an admission that draws into question his claim that he did not know what decade it was). And it was not easy—he had to endure Maine winters when temperatures sank to –20° F, pacing across his site at two in the morning to fend off frostbite. But the forest granted him freedom, privacy, and serenity. And it transformed his brain. He developed photographic recall, a proclivity for deep contemplation, a limitless attention span. One of his favorite pastimes was hiking before dawn to a rise and watching the fog gather in the valley.

Finkel quotes a handful of recent scientific studies to argue that Knight’s camp “may have been the ideal setting to encourage maximal brain function.” In her new book, The Nature Fix, about the growing field of environmental-health research, the journalist Florence Williams reports on dozens of studies that find that exposure to nature is “good for civilization.” A few days in nature yields a 50 percent improvement in creativity, increases attention span, and lessens hyperactivity and aggression. Proximity to the ocean correlates with one’s happiness, and mortality rates drop in greener neighborhoods, while traffic noise increases the strain on one’s heart. Put another way, our growing alienation from nature is killing us.