It lifts all boats, but not by equal amounts. : Mr. Edsall contributes a weekly column from Washington, D.C., on politics, demographics and inequality. There is an ongoing debate over what kinds of investment in human capital — roughly the knowledge, skills, habits, abilities, experience, intelligence, training, judgment, creativity and wisdom possessed by an individual — contribute most to productivity and life satisfaction. Is education no longer “a great equalizer of the conditions of men,” as Horace Mann declared in 1848, but instead a great divider?