The exchange theory of marriage has been adopted to understand both homogamy and heterogamy. While marriage choice is often characterized by homogamy, where individuals with equivalent resources form unions to double the total utility, departures from it can be conceptualized as maximizing utility through exchange of different desirable assets. The classic example for the latter pattern is the class-caste exchange between well-educated black men and white women as the most common type of black-white intermarriage in the U.S. (Davis 1941; Merton 1941). A later study by Schoen and Wooldredge (1989) found exchanges between men‟s higher education and women‟s younger age.