Late in the third trimester of Judd Apatow's magnificent new comedy, Knocked Up, Seth Rogen makes a distressed phone call to his father, looking for advice about how to salvage the disintegrating romance he has fashioned with the woman he has accidentally, well, put in the family way. His dad is stymied: "What do you want me to tell you?" he asks. "Just tell me what to do," Rogen pleads. He repeats the command, more quietly, as a helpless supplication: "Just tell me what to do."

It seems telling that the man on the other end of the line, the parent who does not have the first notion what to do, is played by Harold Ramis. In a period spanning the late 1970s through the mid-1980s, Ramis was the linchpin in turning improvisational comedy into a staple of feature films. There's no question that his work in movies like National Lampoon's Animal House and Caddyshack was a formative influence for Apatow, who has perfected a similarly chaotic humor in The 40 Year-Old Virgin and this latest directing effort. But as Tad Friend convincingly argued in a 2004 New Yorker profile, Ramis accomplished another cultural feat: He made the anti-establishment values of the 1960s palatable to mainstream audiences. After Bluto and Otter took the piss out of Dean Wormer, rebellion wasn't a countercultural act; rebellion was the culture.

The onscreen result was a generation of comedies reveling in perpetual—and often literal—adolescence. Away from the cinema, a generation of parents was finding it impossible to tell their sons that fat, drunk and stupid is no way to go through life. And for the preponderance of my generation—people now between 20 and 30—the result has not been decadence but confusion: fumbling, blustering confusion. What makes Judd Apatow's movies so remarkable is that they dramatize, and milk every ounce of humor from, that uncertain feeling.

In Knocked Up, that bewilderment finds a face in Seth Rogen. He's that teddy bear who's been hulking in the corner of Apatow's frames since television's Freaks and Geeks, and here he takes top billing as Ben, a 23-year-old layabout who isn't too sure he's cut out to be a leading man. He bumps into Allison (Grey's Anatomy's Katherine Heigl) at a club where they're both celebrating the blessings of pop culture: She's been promoted to stand in front of the camera at E!, and he's feeling a surge of ethnic honor from rewatching Munich ("The Jews didn't just kick ass...we took names!"). He takes her name at the bar, they both take a few too many shots, she takes him home, he doesn't take proper care with the condom. Eight weeks later, the pregnancy tests have smiley faces on them. Allison does not.

As he did in The 40 Year-Old Virgin, Apatow is basing a lot of laughs on an obvious joke. Steve Carell was a singularly unlikely candidate to get laid; Rogen is just as dubious as a dad. Ben is still living off the proceeds of an injury settlement with the Postal Service, working on a softcore website he doesn't know is an imitation of, and living with a collection of buddies (including Apatow staples Martin Starr, Jay Baruchel and Jason Segel) whose life aspirations mostly revolve around pingpong and cannabis. When he discovers that his boys have swum, Ben is prepared to do the honorable thing, but he isn't prepared in any other way—and he isn't aided by a glimpse into the hostile marriage of Allison's sister Debbie (Leslie Mann) and her husband, Pete (Paul Rudd).

Virgin first gained attention for its raunch, and Knocked Up is likely to achieve the same notoriety. The verbal ripostes ("If this were our second date, what would you do?" "I was hoping for a BJ.") are transcendently vulgar, and drug use is unbridled—Rogen and Rudd endure a Vegas trip on mushrooms that is as funny as anything in the movies this decade. But the picture is a sex comedy in the same way that most people's lives are sex comedies: Nobody's getting any. Ben and Allison's congress is a freak occurrence, Ben's pals are without prospects, and Pete's escape from his frozen union is a fantasy baseball league. What's more, Knocked Up is patently dealing with the results of sex, and the life choices that don't come with instruction manuals. (Babies do come with manuals—shelves of them—but Ben has to decide whether to read them.)

Which is why Judd Apatow, for all the seeming anarchy of his films, is actually creating a counterrevolution to Harold Ramis, his artistic father. His movies aren't about "family values"—the hollow pettifogging that accompanies every election cycle—but the values required for growing up and starting a family. He makes responsibility and commitment funny; no mean feat. Knocked Up calls to mind a line from another moral humorist, the writer Kingsley Amis: "It wasn't so much doing what you wanted to do that was important, I ruminated, as wanting to do what you did." Apatow is no frowning parent, but by demonstrating how to embrace the fruit of our actions, he does tell us what to do.

Knocked Up

is rated R and opens Friday, June 1.