Every so often the New Yorker gives readers their first glimpse of a classic of American fiction. Indeed, all the other apparent functions of that organ are peripheral. What must it have been like to open up the magazine and get hit between the eyes with “The Secret Life of Walter Mitty” or “The Lottery” or In Cold Blood or Maus? Today, my friends, you get to find out. “Trailhead” is a free-standing excerpt from the forthcoming first novel by the naturalist E.O. Wilson.