Who you gonna call? Not Ivan

What's your favourite film? The question often comes up. I can't restrict myself to one. I can give you five at a push – a Fassbinder, a Buñuel, maybe The Palm Beach Story if I'm trying to persuade you I'm a fun guy and you really should come out to dinner with me.

But always in my mind are those unkempt children in the back row, messing up the nice, neat school photograph with their unwashed faces and nose-picking. Your secrets will find you out. In other words, I could bore the legs off you talking about Renoir or Eisenstein, but the fact remains that my recall of the topless mud-wrestling scene in Stripes is as impeccable as my memory of anything in La Regle du Jeu or Battleship Potemkin. You have no more control over the films to which you gravitate in your youth than you do over your parents' hairstyles. Face it. You're a Breakfast Club person. That woman over there is a Blue Lagoon. I'm a Stripes.

I would like to find a non-ingratiating way of saying this to Ivan Reitman, who directed Meatballs (1979) and Stripes (1981) as well as Ghostbusters (1984) and its 1989 sequel, but when I meet him the atmosphere is slightly stiff. Still, I tell him I was brought up on his movies. He gives a little snort. "Whenever people say that to me, I'm not sure how to take it," he says with palpable discomfort. Great. I was all set to reel off some of that Stripes dialogue to prove I wasn't bluffing – maybe Bill Murray's charmless attempt to get his girlfriend to stay ("You can't leave! All the plants are gonna die!"). Now it seems we'll just have to talk about Reitman's new movie. Ho-hum.

Evolution is a science-fiction comedy with David Duchovny leading the fight against an alien invasion. And if the graft of gross-out humour on to science fiction never quite takes, this could be because Evolution began life as a straight-arrow thriller. Reitman bought the script, saw the funny side and stuck his oar in. "I was especially drawn to the original script's idea of an alien invasion that's on organic, biological terms. It was an interesting idea that I hadn't seen before."

That's not strictly true: Reitman produced Shivers (1975) and Rabid (1977), early works by his fellow Torontonian, David Cronenberg, which were based on that very idea. "I hadn't thought of that," he laughs, sounding genuinely surprised. "That whole organic thing is very Cronenbergian, isn't it? Having said that, I think Evolution is much funnier than David's films." Oh dear. How could I tell him I laughed more during Crash than Evolution?

After parting company with Cronenberg, Reitman went on to produce a stage revue brimming with performers who would later define American film comedy – Bill Murray, John Belushi, Gilda Radner, Harold Ramis. Despite the success of the movies that sprung from this – including National Lampoon's Animal House (1978), which Reitman produced – he evidently feels as though he has been written out of the history of American comedy, and is keen, perhaps too keen, to set the record straight.

"With comedy, people tend to think that you just get some funny guys in a room, turn the camera on and 'boom!' whereas I like to think that I had something to do with it. It's more than just organisation, you know. It's a perspective and a tone that I applied judiciously."

He claims that his only goal was to "create a good time". Fair enough. But he must know that he has not yet generated in his own work the complexities and ambiguities that his old chums Murray and Ramis went on to unearth in Groundhog Day (1993). "I just make the kind of movies I would like to see," he shrugs. "What I'm proud of in my work when I look back on it is the continuity – a recognisable style where people thought there was none."

Style is perhaps the wrong word, but there are undoubtedly prevailing concerns in his work. The movies are languid, with a counter-cultural bias best epitomised by the slobs who become heroes on their own terms in Stripes. And there are standard Reitman preoccupations that surface again in Evolution, including: fat people are inherently funny. And: bureaucracy is bad (the villain in Ghostbusters was the environmental health department, while an Ordinary Joe triumphed over White House fuddy-duddies in Dave, the 1993 comedy, which is Reitman's most subtle work).

Throughout our meeting I sense a hazardous area around which I am tiptoeing. It's known as Ivan Reitman's recent work. Admittedly, I do raise the subject of Arnold Schwarzenegger, with whom Reitman toiled on a trio of successively more disheartening films – Twins (1988), Kindergarten Cop (1990) and Junior (1994). Those movies were calculated stabs at diversification from a star who had predicted and feared his own dimming. You have only to hear the story of Reitman's first meeting with Schwarzenegger – the actor approached him with the words: "You're that Ghostbusters guy. I could be a Ghostbuster" – to experience again the naked desperation of that misguided trilogy.

Reitman may be on to something with his assessment of why Junior, in which Schwarzenegger had a bun in the oven, was not quite a hit. "Young men were pissed off that I had taken this macho icon and turned him on his head. I had crossed the line." Put like that, the picture sounds subversive. In reality, it marked the beginning of a mediocre stretch during which Reitman was clawing at the air, hoping to chance upon a handful of his old irreverence. But he found only Six Days, Seven Nights (1998), a laborious romantic comedy, and the jaundiced farce Father's Day (1997). There was fatigue in every frame of those movies, and when Reitman talks now about how the film industry has changed, the frustration and weariness come at you in waves; you hear a man for whom goofing around just isn't a breeze anymore.

"Audiences have become jaded. Everyone is interested in grosses now. Then there are the internet people. Do you know that Evolution had its script reviewed while we were shooting? All this insider yapping creates intense moviegoers, but it also creates disdain for the whole creative process. Then there's the fact that few film-makers preside over studios anymore, they're all run by big corporations, the movies are more expensive." So much for evolution.