Inequality is at an all-time high in America. Since the 2008 crash, recent IRS figures show, the wealth of the top 1 percent grew 31 percent while the rest of American incomes grew by less than 1 percent. But although it might appear that income disparities affect only the poor and have primarily an economic impact, dozens of studies now link extreme inequality with poor health and shorter lives, across the entire socioeconomic spectrum.