“Each generation thinks it invented sex,” science fiction author Robert Heinlein famously claimed.

A corollary to that oft-quoted maxim is each generation assumes the subsequent one is having raucous sexual encounters with lots of attractive, sweaty strangers in unimaginable ways.

Case in point: millennials—those born between 1982 -1999 (including yours truly)—have been branded the hook-up generation.

Ever since the pesky media got whiff of our supposed, rainbow parties non-Millennials have assumed Generation Y has been racking up sexual partners like new versions of iPhones.

In all fairness, how could they think otherwise? Millennials have access to a seemingly infinite array of dating apps, which, yes, can and do double as hook-up apps.

American adults are getting married at an older age and few of us are bothering to even do so. All of this leaves more time to add a few notches above the bedpost.

And yet, we’re the ones keeping our legs crossed—sort of.

A new report published Tuesday in the Archives of Sexual Behavior shows that millennials will have sex with fewer people than the immediately previous generations.

“Number of sexual partners increased steadily between the G.I.s [born 1901-1924) and 1960s-born GenX’er and then dipped among millennials,” the study notes. Take this for a contrast: Americans born in the 1950s had sex with 11.68 people on average during a lifetime while millennials will average 8.26.

Jean M. Twenge of San Diego State University and author of Generation Me, a book examining the millennial generation, crunched four decades of sexual data gathered from 1972 to 2012 through the General Social Survey. (Ryne A. Sherman of Florida Atlantic University and Brooke E. Wells of Hunter College of the City of New York co-authored the report.)

They weren’t just focused on what people were doing between the sheets, but how they felt about it. They were able to control for age, meaning they could compare how a 25-year-old in 1972 felt about sexual issues with a 25-year-old in 2010 [in effect, getting rid of any notion that liberal sexual views and behaviors were merely a result of being 25 as opposed to 55].

Among Boomers surveyed in the early 1970s, 47 percent said premarital sex was “not wrong at all.” Sixty-two percent of millennials said it is “not wrong at all.”

Unsurprisingly, millennials are also far more accepting of same-sex relations, with 56 percent voicing unqualified approval, compared to 26 percent of GenX’ers in the early 1990s and 21 percent of Boomers in the early 1970s.

The big conclusion: even though millennials are more the most sexually tolerant generation, the number of people they have sex with does not match a free love mentality—at least in the most black-and-white view.

However, it is by no means clear that millennials are more restrained in their sexual behavior.

One of the first complicators: millennials are more likely to participate in casual sex, perhaps partially proving the penchant for hook-ups.

“This data indicates that millennials are more likely to report having casual sex than earlier generations, jumping from 25 to 38 percent having ever engaged in casual sex,” Wells tells the Daily Beast.

Specifically, among 18-29 year olds who reported having sex outside of a monogamous relationship in the year prior to being surveyed, “35 percent of GenX’ers in the late 1980s had sex with a casual date or pickup compared to 45 percent of millennials in 2010,” the study notes.

So, more casual sex but fewer partners. How are millennials pulling of this sexual mathematics?

Perhaps, with a little help from their friends.

“I think ‘friends with benefits’ is considered in that casual sex number,” Wells says. “Is it an ongoing sexual relationship with a non-romantic partner versus going to a bar and picking someone up? We need a more fine-grain distinction.”

“The survey doesn’t ask how they feel about casual sex, and I think culturally norms around casual sex are constantly evolving,” she says. “There’s talk about how millennials are less willing to put labels on relationships. It may be a sign of the changing definition of them.”

Twenge points out that among American adults who say they have had casual sex in the past year, the percent who said they had “sex with an acquaintance” in the last year jumped from 30.7 percent in data collected 2005-2009 to 41.2 percent in data collected 2010-2012.

American adults who had sex with a friend jumped from 54.2 percent in the 1995-1999 cohort to 70.8 percent in the 2000-2004 cohort (and has held steady around 68 percent since).

“It could be that instead of having non-committed sex with lots of partners, they could be having non-committed sex with a shorter list. That could be due to ‘friends with benefits,’” says Twenge. However, she adds that based on this specific set of data “it looks more like acquaintances with benefits.”

Another element that may obscure the millennial sexual landscape is how we define “sex.” The General Social Survey asks how many partners respondents had sex with, but the generation that grew up with the Lewinsky scandal blasting into our living rooms knows the answer to that question isn’t so simple.

“It doesn’t specify what kind of sex. It’s the Bill Clinton question,” Twenge says with a bit of a laugh. “For most people, that [the question] probably includes anal and vaginal sex. It may not include oral sex.”

“In our culture, there was a time when the president suggested that oral sex wasn’t sex, and that is still with us, to some degree,” psychologist Geoffrey Michaelson told ABC News in 2012.

Could fellatio and cunnilingus blow (sorry) the numbers off?

“That is possible. We certainly can’t rule it out,” says Twenge.

But she ultimately believes that millennials may be reining in the number of sexual partners. After all, millennials have come of age increasingly aware of AIDS and other STIs.

Twenge argues that in general, millennials were also raised in an atmosphere of greater caution than previous generations.

“This is a generation that was raised very protectively by their parents. It was the first generation in which car seats were mandatory and playgrounds were made safer. They may continue those attitudes into adulthood,” says Twenge.

She also suggests that the generation that has been accused of being narcissistic, self-entitled, and overly confident, may simply be using that bravado to brush off outside sexual pressure. They wouldn’t get swept up in a “free love” movement because they do not care enough about what others think of them. “I’m going to do my own thing. I’m going to make my own choices,” is how Twenge characterizes the millennial attitude.

Personally, as a millennial, I think Twenge might be giving us too much credit by mistaking our laziness for individualism. My generation may simply prefer staying home in sweat pants and red wine—and yes, if we’re so inclined, with a ‘friend with benefits.’ Older generations may think this sounds lame, but we simply don’t care.