While working the busy promotional circuit for The 40-Year- Old Virgin, Apatow would send himself emails on his BlackBerry with vague, unformed ideas for some kind of movie that would filter his observations and experiences through a comedy lens. “A couple gets pregnant on the first date,” he wrote in an email with the subject line “Pregnancy” on August 7, 2005. “The idea of being forced into a relationship for life is the main conflict. A relationship in reverse. A baby, then get to know one another.”
Not all of Apatow’s ideas from his hastily typed BlackBerry emails made the cut—there is no scene in which Ben, the protagonist of Knocked Up, is so nervous to meet Alison’s family that he accidentally leans in to kiss her brother, or a smash cut that leads to “suddenly huge boobs which squirt milk”—but much of what shows up in the final cut of Knocked Up can be traced back to those notes. Apatow even gives his protagonist a name that none-too-subtly revealed his intended star: Seth. (Later drafts changed it to Ben.)
With Rogen set to star, the next challenge was finding the female lead. Leslie Mann, a Knocked Up supporting player, once said Apatow wrote the part with Matchstick Men’s Alison Lohman in mind (which might be why the character is named Alison). Rogen, eager to prove himself as a leading man, read opposite every actress who auditioned, which gave him the chance to hone his character, and gave Apatow the chance to look for the chemistry he felt Knocked Up would require. Finding the comedy wasn’t always easy. “Great actresses would come in, and they would say ‘I’m pregnant,’ and it made you want to cry,” says Apatow. (Rogen, for his part, came up with Ben’s incredulous reply to the revelation: “Fuck off.” Apatow was delighted. “I never would have thought to write that,” he says.)
After a flurry of auditions, Apatow was convinced he had found his star: Anne Hathaway, who had been professionally acting since she was seventeen but had just had her major Hollywood breakthrough in Dave Frankel’s The Devil Wears Prada. Hathaway was cast, but quickly decided to quit the role, due in part to a brief shot during the climactic birth sequence of a baby crowning that—while not depicting Hathaway’s own vagina—would have been cut to give audiences the impression it was hers. “She didn’t want to allow us to use real footage of a woman giving birth to create the illusion that she is giving birth,” explained Apatow at the time. Hathaway later elaborated: “My issue with it was that having not experienced motherhood myself, I didn’t know how I was gonna feel on the other side about giving birth. And by the way, I could pop a kid out and think, Oh, well, I really should have done that movie.”
Next on the list was Katherine Heigl. She, too, had started her career early—first as a child model, and then as an adolescent performer in ’90s junk like My Father the Hero and Under Siege 2: Dark Territory before she finally landed a lead role in the WB teen sci-fi drama Roswell. By 2007, she was emerging as a breakout star in the ABC medical drama Grey’s Anatomy—a standout in a very crowded ensemble. It was the ideal time for Knocked Up to catch such a promising rising star, and they got her at the bargain salary of $300,000.