When Americans quote writer and naturalist Henry David Thoreau, they often reach for his assertion that “In Wildness is the preservation of the world.” This phrase elicited little response when Thoreau first read it during a lecture in 1851. A century later, however, it had become a guiding mantra for the American environmental movement, adopted by the Sierra Club as its motto and launched into the cultural stratosphere via bumper stickers, T-shirts and posters.