Wolves were once native to the US' Yellowstone National Park -- until hunting wiped them out. But when, in 1995, the wolves began to come back (thanks to an aggressive management program), something interesting happened: the rest of the park began to find a new, more healthful balance. In a bold thought experiment, George Monbiot imagines a wilder world in which humans work to restore the complex, lost natural food chains that once surrounded us.