If Michael Apted's Up series of documentaries plays like the older, more relaxed brother of reality TV, it's because that's basically what it is. Launched in 1964 as a one-off special of interviews with 7-year-olds in Seven Up by director Paul Almond, the film surveyed 14 kids of various economic backgrounds to explore England's class system (it was based on the repeatedly invoked Jesuit motto "Give me a child until he is seven and I will give you the man"). Apted, who helped cast that film, then took over and has returned to its subjects every seven years to document their lives over time. Though the films are still inherently political, what emerged was less of an economic survey and more one of humanity. Reality TV is often referred to as a sociological experiment, but the Up series is as bona fide of a longitudinal study as pop culture has ever offered.

56 Up, the series' eighth film and most recent entry, features all but one of the people interviewed in the first film. It aired last year in England and opened last week in America. While you feel the project's prescience – our cultural ideal that, as Apted put it to me last week in the First Run Features office, "every life is worth sharing" – the film plays vastly different than what you'd expect from reality TV. It's almost two and a half hours of soft-spoken, 56-year-old British people describing their quiet existences which, in most cases, seek to avoid drama as opposed to reveling in it. Take Jackie, who describes a string of familial deaths she's endured since 49 Up, and whose mother and ex-husband have since been diagnosed with cancer. She is without a partner, suffering from rheumatoid arthritis and her benefits have been taken away, forcing her to rely on her sons for support. And yet the tone of her segment is as upbeat as the rest. She likes her life, she says. We see her meeting men. She is, in fact, here to make friends.

The pacing of all of these films is perhaps the sharpest contrast with modern reality's sensibility. Each subject gets a little over 10 minutes to update us on what would be mostly unremarkable lives were they not being remarked on by one of the greatest undertakings in the history of documentary filmmaking. Most of them are, at this point, settled into gentle domesticity. There is no underlining music or apparent sensationalizing, and the segments' effects can be as soothing and banal sitting with your mom's kindly older neighbors. Up's deliberateness runs counter to the short-attention-span baiting that is de rigueur in today's pop culture.

"Whenever I do one of these, there's always new management at [the films' production company] Granada Television and they say, ‘You have to put music on it, you've gotta do this,' and I say no," said Apted, who's also directed more traditional Hollywood fare like Gorillas in the Mist and the 1999 Bond entry The World Is Not Enough. "I've always been a square about it because of the big thing I've got, which is to be able to counterpoint the generations — my big card was always that people's faces changing over the decades would be the shocker. When you get to eight, which is where I am now, there's got to be such a straightforward style to it. I'm giving the audience enough to worry about – figuring out where the fuck we are – without having them worry about new styles. I've always kept the rhythm and style the same so I can meld them all together."

I asked Apted if he felt at all responsible for reality TV, and while he conceded that you can see its roots in the manner that the Up series has "celebrated ordinary life," he says he thinks reality "would have happened anyway," especially as so much of its presence is based on economics (reality shows are, in short, cheap to put up). But the functions of his medium and reality TV are also at odds.

"Reality puts [its subjects] in situations they aren't used to and see how they respond to it, which can be illuminating but it can also be very cruel," he explained. "Whereas with a documentary, what you're trying to do is express as truthfully as you can, the moments that you're meeting with, the situations people are in. You're trying to express their frame of reference, not extract it from them."

Some extraction is palpable, though – unlike the talking-head, "confessional" segments of reality TV that seem driven by the ids and wills of its subjects but are the results of interviews with producers, Apted's guiding hand is never less than apparent. You hear him conversing with his subjects, giving his films what he refers to as a "transparency" that conflicts with the "spontaneity" of reality TV (which itself is often guided, at least to a point).

The transparency extends to the treatment of the production. Whereas referring to "this show" is a general no-no in reality TV, Apted includes footage of his subjects discussing the impact of appearing in a series of documentaries all of their lives. They are often critical of the Up series. Suzy, one of the most naturally eccentric personalities who has matured into a lovely and pleasant woman, says in 56 Up that she "hates" the films and likens showing up to participate every seven years to "seeing through a bad book." We watch Nick balking at his portrayal, saying what is seen in the documentaries is "not an absolute accurate picture of me, but it's a picture of somebody."

"I think they make good points," says Apted on including critiques of his movies within his movies. "They're answerable points, but they're good points…[The subjects are] not so angry that they fuck off and never come back."

I wondered why they come back, when so many of them (probably around half in 56 Up) voice disdain for their participation.

"I think we're all in this together and they see some value in it," Apted told me. "It is well received. It's not brain surgery, but in the spectrum of television documentaries, it's well regarded and they're part of it. The older they get, the more they realize it and they have a certain respect for it."

Also, he has started paying them. He won't say how much, but he described the fee as "not bad." It was enough that I knew they wouldn't want to turn it down," he added.

Subject Tony, a former aspiring jockey turned cab driver, was also in town last week and he told me he saw the value in the series as a document.

"I've often said that when I'm gone, it will be a testament to my life," he said. "My kids can press the video recorder button and see their dad, their grandfather, their great-grandfather."

Tony is one of the ones who likes the films, unlike the aforementioned Nick, who in addition to criticizing the films in 56 Up, told The Independent last year, "I've learnt that the stupider the thing I say, the more likely it is to get in. You're asked to discuss every intimate part of your life. You feel like you're just a specimen pinned on the board. It's totally dehumanizing." Apted told me the article left him "gobsmacked." I wondered, if Nick's comments, especially the "picture of somebody" one, underlined the impossibility of Apted's task.

"Any time you're condensing a life, you know it's going to be some version of life," he said. "Some immense distillation of life. And then it's just down to me and my sense of taste and responsibility. It's so self-evident that it's not life that it's not even worth thinking about. It's a view of a tiny part of life. It's a snapshot of when I visit them every seven years. God knows what happens in the other 6 years and 363 days when I'm not with them. If you break it down to what it is, it's sort of ridiculous, but that doesn't make it irrelevant, unimportant or trivial. It's what anyone has to do when they're communicating anything about other people."