Harvard University’s Faculty of Arts and Sciences now formally bans sexual relationships between professors and undergraduate students.

That’s not because they think there’s all kinds of professor-student dating on campus: The professor who led the panel that wrote the policy said she has never heard of it happening, in years of studying and teaching at Harvard. The new policy is there just to clarify that it would not be okay.

“We’re using this opportunity to reaffirm our priorities as teachers,” said Alison Johnson, a Harvard history professor, “and to imagine what we’re seeing when we’re looking at these students, and what we’re not seeing. We’re not seeing potential romantic partners. We are seeing students.”

A small but growing number of colleges, including Yale and the University of Connecticut, now have written policies banning such relationships, Bloomberg reported.

The new policy comes at a time when sex and gender issues — all the ways that people define themselves, their sexuality, their relationships, and how they interact with one another — are relentlessly discussed on college campuses.

Billie Dziech, a professor at the University of Cincinnati who has studied and written about relationships between professors and students, said policies about such relationships are evolving.

“Originally, there were no policies,” she said. “Institutions wouldn’t go near it, just wanted to avoid pushback from faculty. We’ve come a long way from that time. There are many institutions that have what I personally would describe as very weak policies. There are policies that don’t mention it at all. What Harvard and an increasingly long list of universities has done is to have prohibitionist policies.”

Dziech said some policies have earned complaints from students who would say, “‘Oh, we’re grownups, we can choose with whom we have sex.'” She said Harvard’s decision was courageous.

“It sends a message: You don’t sleep with other people’s children — whether they agree to do it or not — because you’re abusing your power,” Dziech said.

The American Association of University Professors stopped short of recommending a ban on relationships, but it sounded a similar warning, saying that professor-student romantic relationships can make voluntary consent by a student suspect because of the power dynamic. In a statement, the organization also said that sexual relationships can later make the faculty member and the institution vulnerable to allegations of sexual harassment.

“Sexual relations between students and faculty members with whom they also have an academic or evaluative relationship are fraught with the potential for exploitation,” the AAUP said in a statement. “In their relationships with students, members of the faculty are expected to be aware of their professional responsibilities and to avoid apparent or actual conflict of interest, favoritism, or bias. When a sexual relationship exists, effective steps should be taken to ensure unbiased evaluation or supervision of the student.”

In some ways, it’s easier for schools to ban such relationships so they’re not forced into taking sides — or acting as judge and jury — in cases where a student or faculty member complains about harassment, or worse, Dziech said.

Scores of universities are under scrutiny from the federal government for its handling of sexual assault cases, as the Obama administration uses Title IX legislation, which bars discrimination based on gender, to pressure colleges on the issue. Under a settlement with the Education Department’s Office of Civil Rights, Harvard University and its law school promised to revise sexual harassment and assault policies to ensure a safe campus.

The committee had meetings all fall with students, faculty and staff who eagerly participated and asked tough questions, Johnson said. They got some pushback from faculty questioning where to draw the line between protecting people from unequal relationships and unnecessarily interfering in people’s personal lives, she said.

The rule about professors and undergrads is the only blanket ban. The new policy doesn’t ban sexual and romantic relationships between all people who teach and all people who are students. They included contextual prohibitions, she said; “Professors can’t have sex with graduate students if they are teaching or supervising or evaluating them in some way. Graduate students can’t have sex with undergraduates if they are teaching them or grading them in some way.

“We want to be careful not to become overly paternalistic or interfere with the choices in their lives, even choices we may think are unwise choices.”

But the idea of banning romantic relationships between professors and undergraduates was not controversial, Johnson said.

If anything, it surprised people that there wasn’t already such a ban, she said.

“It just seemed commonsensical. It made sense to me as a teacher. It made sense to me as former student. It made sense to me as a parent. It just made sense.”

“Nobody said, ‘You’re treating me like a child, trampling on my civil rights, I’ll have sex with whomever I please. That would be the only argument against it — that it’s paternalistic,” Johnson said. “I like to think of it not as telling students who they may not have sex with,” she added, “but telling faculty who they may not have sex with.”

She pointed out that the college’s student population, while diverse in many ways, is decidedly not diverse in age; there aren’t a lot of older students, as there are at other schools. It would be more difficult to do at a place such as George Mason, she said; “it would be strange.” Harvard’s undergraduates are mostly in their late teens and early 20s.

Because sexual harassment so often comes down to power dynamics, Johnson said, they wanted to be very clear in a case where those are as stark as an undergraduate’s interactions with a faculty member.

They also wanted to make the policy easy to find. When Johnson went to familiarize herself with the existing rules, because Harvard is such a decentralized place, she said she had to look in about 11 different places. They want to be sure the school isn’t making it more difficult for people concerned about sexual harassment to address the problem.

Harvard provided a brief and decidedly unsexy statement: “As part of a formal process to review Harvard University’s Title IX policy, the Faculty of Arts and Sciences Committee on Sexual Misconduct Policy and Procedures, led by Professor Alison Johnson, determined that the existing language on relationships of unequal status did not explicitly reflect the faculty’s expectations of what constituted an appropriate relationship between undergraduate students and faculty members. Therefore, the Committee revised the policy to include a clear prohibition to better accord with these expectations.”

Or, as Johnson said, “it wasn’t some kind of crazy hippie commune where professors and undergraduate students were having sex with each other three weeks ago.”