Trying to understand income inequality, the most profound change in American society in your lifetime. - By Timothy Noah - Slate Magazine: In the late 1970s, a half-century trend toward growing income equality reversed itself. Ever since, U.S. incomes have grown more unequal. Middle-class incomes stagnated while the top 1 percent's share of national income climbed to 24 percent. Middle-income workers no longer benefit from productivity increases, and upward mobility, long the saving grace of the American economy, has faltered. Why is this happening? In the following 10-part series, Slate's Timothy Noah weighs eight possible causes of what Princeton economist Paul Krugman has labeled the Great Divergence. This 30-year trend "may represent the most significant change in American society in your lifetime," Noah writes, "and it's not a change for the better."