His actions were so stealthy, and his bounty so niggling, that for decades residents believed that the North Pond hermit was a myth. There was willful ignorance on both sides. Knight did not learn the name of the pond he haunted until he was arrested, or the name of the nearest town (Rome). He claims to have been ignorant of the year and even the decade. He kept time like Onwas does. “The moon was the minute hand,” he tells Finkel, “the seasons the hour hand.”

What kind of man does a thing like this? What kind of man talks like this? An autodidact, for starters, with the attendant traits: overly formal speech (asked about his survival methods, Knight replies, “I have woodscraft”), narcissism (“You’re my Boswell,” he tells Finkel), and quaking insecurity (in a conversation about literature, he defiantly tells Finkel that he refuses “to be intellectually bullied into finishing” Ulysses, despite the fact that he has not encountered an intellectual or a bully in 27 years). One can have a genetic predisposition to solitude, Finkel notes, and Knight came from a family of loners; he tells Finkel that he had missed “some” of his family “to a certain degree.”

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.

W. W. Norton

Most people intuit that it’s healthy to exercise outside, to visit a park, to walk in a forest. Poets and artists have preached these values for millennia, as have planners since at least Frederick Law Olmsted, as Williams acknowledges. But intuition is not enough for the scientists she interviews. “We have to validate the ideas scientifically through stress physiology,” a Harvard lecturer says, “or we’re still at Walden Pond.” Williams agrees. “I was feeling pretty mellow,” she writes after walking through a national park in Japan, “and scientific tests would soon validate this.”