In today’s unsurprising news, a new study has found that women in academia perform more unpaid labor than men. Researchers writing in the journal Research in Higher Education say female professors are more likely—and more expected—to give their time to students, while their better-compensated male colleagues use those same hours to publish, conduct research, and advance their careers.

Education experts culled data from the 2014 Faculty Survey of Student Engagement (FSSE), which asked nearly 19,000 faculty members at 143 colleges about their interactions with their students. They also dug into detailed faculty activity reports at two institutions.

The results showed a significant difference in the way academic men and women spent their time. Female respondents to the FSSE spent an average of 30 minutes more per week on service tasks like advising students, serving on committees, and leading extracurricular activities. Even among full professors, women devoted significantly more time to service activities than their male counterparts. This was true even after the researchers controlled for variables like race, academic department, and university.

The paper’s authors couldn’t pinpoint the root cause (or causes) of this disparity, but there are plenty of theories. Journalism professor Amy Quinn of Rowan University says gender stereotypes may have something to do with it. “[Women are] the ones students usually talk to about their personal crises,” she told Newsweek. “They tend to come to the women for the ‘mom things.’”

The gender breakdown is likely not the result of any conscious decisions, but rather of differing cultural expectations and career opportunities. “Women are less conditioned to saying no to things,” Sara Thompson of the University of Maryland said in Newsweek, “and having to work harder than men for the same opportunities since they’re sometimes seen as starting at a lower point.”

The unfortunate reality is that saying “yes” to mentoring students means saying “no” to something else that may be more likely to lead to tenure or a higher salary. This phenomenon is, of course, not unique to academia, but can be seen across many major career fields, from finance to medicine.

On average, women are paid less than men for the same work. They’re also less likely to get high-paying jobs or work in more financially lucrative fields.

But the operative word there is “average.” When the numbers are broken out to focus on women of color, overweight women, and LGBT people, the inequalities are even greater.

Paper author Cassandra M. Guarino of UC-Riverside said recognizing the issue is a good first step.

“There’s no woman who loves [unpaid labor] more than men,” she told Inside Higher Ed. “But until we see evidence and we can really help women say no, it’s just going to keep happening.”