“When I say that for more than seventy years... American Gothic has represented the nation, I mean that, like the American flag, the bald eagle, and the Statue of Liberty (perhaps the only national symbols that continue to surpass it in circulation), it has not only reflected but helped create American identity.” In American Gothic: A Life of America’s Most Famous Painting (W. W. Norton, 160 pages, $21.95), Stephen Biel traces the fluctuating career of Grant Wood’s stolid farmer and his wife (or daughter? This is a debate of more than 50 years’ standing). The couple was first seen as a satire on small-town narrowness, but the intervening years wore the humor away, and in time they evolved to represent granitic national virtues through the same mysterious process by which the Midwest came to embody all that is wholesome in America. Biel’s account of this Iowa apotheosis is shrewd, lively, and highly entertaining.