By now, social scientists once predicted, the gender gap in wages should have been as thin as a Roosevelt dime. More and more highly educated women were entering and staying in the workforce – many in lucrative occupations where formerly only men were found.

So why has the gap between men and women’s hourly pay stopped shrinking?

Men’s “overwork” has a lot to do with it, according to Kim Weeden, Cornell professor of sociology. She says employers are paying more per hour to workers who put in exceptionally long workweeks.

“Women – even highly educated women – still spend far more time than men on housework and child care,” says Weeden, co-author, with Indiana University’s Youngjoo Cha (Cornell Ph.D. 2010), of “Overwork and Slow Convergence in the Gender Gap in Wages,” to be published in a forthcoming issue of American Sociological Review. (“Overwork” is defined as 50 or more hours a week at a single job.)

The Cornell sociologist concedes, “Today’s men are spending more time with their children than their fathers did. But the gender gap in core housework – cooking, cleaning, other day-to-day tasks – hasn’t changed much in the past 25 years. These dynamics in the household carry over into a gender gap in who puts in long work hours.”

The sociologists’ article says 21st century overworkers are concentrated in the so-called “greedy occupations,” such as doctors, lawyers, even academics. In these occupations, Weeden says, “employers often expect undivided attention, loyalty and time commitments from their employees. In some cases, employees compete over who can put in the most hours.

“Just as college students boast about pulling all-nighters,” the Cornell professor observes, “employees in greedy occupations may boast about putting in long hours.”

Yet not all workers today can overwork, even if they want to. People who work long hours at a single job, Weeden observes, are less common in today’s workforce than people who would like to work more hours at their main jobs but don’t have the opportunity.

“With the decline of manufacturing, the growth of the service sector, and the waning power of unions,” Weeden says, “there are fewer opportunities for lower-skilled workers to earn overtime or a living wage at just one job.” Low wage workers – particularly service workers, the majority of whom are women – have to “cobble together multiple part-time or full-time low-paying jobs, and work longer hours overall, to have the same inflation-adjusted income as workers of a bygone era.”