Culture Shock: Heard the one about the Catholic, the Protestant and the sitcom?

When I was a child my favourite sitcoms often featured scenarios like this: a bucket of water is balanced on a door jamb. Characters wander in, around and near the bucket, in a sort of teasing dance. Eventually the bucket falls on a hapless head, and everyone in my sitting room cracks up. “I knew that was going to happen,” I say, chuckling happily. The character says a catchphrase. “I knew he was going to say that,” I add.

The conventions of the studio sitcom were formalised back in the 1950s and 1960s, and for a long time they didn’t change. Shot with multiple cameras on limited sets in front of a studio audience, they were filled with wacky neighbours, stuffy authority figures, unlikely misunderstandings, dysfunctional families, long-suffering spouses and laugh tracks (from studio audiences or from Charlie Douglass’s patented, Mellotron-like Laff Box).

Predictable doesn't mean bad. Funniness often comes not from punchlines but from how the punchline arrives – a dark comedic art known as "timing". The best sitcoms dealt with their genre's restrictions in creative ways. Fawlty Towers saw Basil Fawlty running full tilt into the artificiality of sitcom situations; The Young Ones just smashed them to bits. M*A*S*H would veer towards drama and shed its laugh track in poignant episodes. Cheers made it a matter of pride that throughout the first season its characters never left the bar. Frasier reframed sitcom formulas as a theatrical comedy of manners. Only Fools and Horses just did it all really, really well.

Thematic trends came and went: the family sitcom was supplanted by the work-based sitcom, then by pseudo-families of twentysomethings hanging out, then by the family sitcom again.

In the past few decades sitcoms have seen a Cambrian explosion of style and content. It started with a simple split: as well as set-based offerings with studio audience (Friends, Father Ted), there were suddenly many single-camera productions, filmed on location, like movies, and without laugh tracks (such as The Office, 30 Rock and It's Always Sunny in Philadelphia). The latter often tended to mix "I knew that was going to happen" moments with "I didn't see that coming" ones.

The proliferation of this approach was liberating for writers and loved by critics. Without set restrictions and a studio audience laughing along, it was easier to play in the spaces between laughter and other emotions (embarrassment, sadness, boredom or anger). It was also easier to delve into realism, often using a mock-documentary format. What made The Office, Ricky Gervais's comedy of embarrassment, so hilariously excruciating were the realistically shaky cameras and authentically awkward silences. Even former creators of classic studio sitcoms moved into single-camera territory. (For example, Larry David, cowriter of Seinfeld, became the writer-star of Curb Your Enthusiasm.)

Loosening the rules allowed for genre ambiguity. The dramedy was born. There was a spate of darkly comic programmes, such as The Big C, Weeds and Nurse Jackie, which had dramatic scenarios at their core: cancer, drug dealing, addiction.

There followed a number of excellent dramas founded on sitcom scenarios, with dark comedy creeping in at the edges: Breaking Bad (chemistry teacher makes meth), Being Human (ghost, werewolf and vampire share a house) and Life on Mars (policeman goes back in time to the 1970s).

Eventually all the shaky cameras, mock-documentary formats (Parks and Recreation, Twenty Twelve, Modern Family), celebrities playing themselves (Don't Trust the B– in Apt 23, Curb Your Enthusiasm, Episodes) and satirical shows within shows (Episodes, Extras) made the single-camera sitcom look as rule-bound as its forebears. So more recently there has been a new batch of brilliant outliers, such as Louie (from Louis CK, formerly creator of a failed studio sitcom, Lucky Louie), Broad City and High Maintenance, which borrow their aesthetics and meandering structures from indie cinema. Often beautifully filmed, they wander unpredictably between comedy and pathos, and feel fresh and new.

That's the evolution of the sitcom. But, to paraphrase Darwin denialists, if we came from monkeys, why are there still monkeys? The Big Bang Theory, an old-fashioned sitcom, filmed in front of a studio audience and awash with pratfalls, catchphrases and (more unusually) science jokes, is the biggest show on the planet. Its stars recently lobbied for $1 million each an episode. Mrs Brown's Boys is also quite popular, I believe.

Why do the old-fashioned sitcoms thrive amid all the newer forms? Here's a theory: the single-camera comedies, with their personalised plots and sophisticated close-ups, are an intimate experience based on an almost Protestant belief that your laughter is between you and your own comedy god. With the studio sitcom your laughter is mediated by a studio audience, and the situations, even when subverted, have the familiarity of ritual. It's basically Catholicism. It's why millions still tune in to watch Sheldon on The Big Bang Theory say "Bazinga". They knew he was going to say that. They can practically join in.

Fintan O’Toole is on leave