ABC’s “Cougar Town” was pitched on a lark.

“The reason this show is so horribly titled is because it started as a gag on the modern way of selling a television show,” says “Cougar Town” creator Bill Lawrence. “We had always joked that if you had Courteney Cox or someone like her, you could just walk in to a pitch meeting and say you had a show about an older woman chasing younger guys and call it ‘Cougar Town.’ It’s a funny idea when you are being a snarky comedy writer. It’s not so funny when you’ve actually sold the concept and now you have to come up with a show.”

“Cougar Town” exemplifies how a show’s very core mission can evolve after it premieres. While the show’s pilot and early episodes did feature Cox’s character — Jules Cobb, a recent divorcee — dating younger men, the show quickly became about something else entirely.

“I think it’s a show about adult friendship and how we while away the time,” says Lawrence. “But I can’t sell that show. It would be interesting to go back and time and see if we could get the same commitment from the network if we pitched them the show that’s on the air today.”

Almost every showrunner will say the show that he or she is producing today isn’t the show he or she first planned.

“We jettisoned the ‘cougar’ thing early on, but unfortunately the shitty title still represents something the show is no longer about,” says Lawrence. “We’re just wearing it like a badge of courage now.”

A show’s lead actor is often the catalyst for deep change. Much of the “Cougar Town” evolution happened because of Cox, recalls Lawrence.

“Courteney found that she was jealous of all the other actors who got to have scenes together while she was off dating,” he says. “Early on, the ensemble scenes were the only scenes she really loved. She was really the driving force in those changes.”

A show that has gotten funnier with each passing episode is NBC’s third-year sitcom “Parks and Recreation.” The center always has been Amy Poehler, but it took the show’s writers a while to figure out how best to use TV’s most versatile comic actress.

“You can have everything happen in exactly the way that you imagined, and still realize that it doesn’t work,” says exec producer Mike Schur. “That’s what happened a bit with Amy’s character, Leslie Knope. The way that the audience received her wasn’t the way that we wrote it. We always wanted her to be optimistic and forward-thinking, but she came off as naive and ditsy. Leslie is a person who doesn’t have a ton of game but is very smart.”

So Schur, Greg Daniels and their writing staff started making little tweaks to alter the perception of Leslie’s character, such as having her date a policeman, played by Louis C.K., and finding ways to show that her staff liked and respected her.

“Leslie’s relentless rallying of the troops is infectious,” Schur says, “and she would lay herself in front of a train to save the jobs and careers of everyone in the office.”

Of course, some major evolutions start before a series premieres. Showtime’s “Nurse Jackie” started life as a graphic novel, in which all of these fantastical things happened to an emergency room nurse. Showtime had a pilot script based on that concept written by Evan Dunsky.

At the same time, Showtime’s then-president of entertainment, Robert Greenblatt, had an “internal quest,” to secure Edie Falco’s services for Showtime.

“Greenblatt told us that ‘if I can get Edie Falco’s face on a billboard for Showtime, I will have done my job,’ ” says “Nurse” exec producer Liz Brixius.

Greenblatt asked Falco what project might interest her, and she immediately took to the idea of being an ER nurse in New York, where Falco wanted to work. Greenblatt brought in Brixius and her writing partner Linda Wallem to rework Dunsky’s fantastical pilot around Falco.

While the story of Jackie — a married emergency room nurse and mother who is under the spell of prescription drugs — remains the show’s focus, the supporting characters have evolved drastically.

“In the first season, everyone was there simply to be in orbit around Jackie,” says Brixius. The audience response to first-year nurse Zoe (Merritt Wever) and hospital administrator Gloria Akalitus (Anna Deavere Smith) “was so enormous. I don’t think they have changed so much as grown as characters. They now take up more real estate than they used to.”

In the end, actors can certainly influence a show’s direction.

“People say it starts with a script, but it really starts with an actor,” says Brixius. “People don’t tune in to hear the words of Aaron Sorkin. They tune in to see an actor that they like.”

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