By now it is common knowledge that professionals are more likely to marry and less likely to divorce than are less educated workers. Among 20- to 49-year-old men in 2013, 56 percent of professional, managerial and technical workers were married, compared with 31 percent of service workers, according to the American Community Survey of the Census Bureau. Some people argue that the gap is largely a result of a decline in traditional values among working-class men, particularly whites who constitute the majority of them. Supposedly they are not as industrious in seeking employment as were their fathers and grandfathers and so fail to secure the steady jobs needed for marriage.

But some digging into historical census records shows that social class differences in marriage have been tied to the extent of income inequality among white Americans for at least 130 years. They also suggest that commentators who insist that the marriage gap is wholly a matter of values are almost surely wrong.

Census records, which have been compiled into the Integrated Public Use Microdata Series by demographers at the University of Minnesota, tell us that the current era is not the first time that the nation has experienced a large marriage gap; it is at least the second. Another instance occurred in the late 19th century. What these two eras have in common, according to the economists Claudia Goldin, Lawrence F. Katz and Robert A. Margo, is that economic inequality was high and rising during both of them.