According to the theory of evolution, life itself - as well as its countless permutations - derives from a series of fortuitous accidents. Billions of years ago, a well-partnered group of proteins embarked upon a chain reaction we now know as procreation. The chemistry was right, so things took off from there.

On Sunday, June 10th, a swarm of theatre people proved that artistic creativity follows a similar path - only they sped it up, like time-lapse photography of flowers blooming or storms brewing.

Fledgeling theatre company "Semper Fi", in association with the Project Arts Centre, Dublin, didn't so much put together Within 24 Hours as create the conditions in which this risky and exciting scheme could take place.

The result, after literally 24 hours and innumerable random combinations, was an evening of theatre that had both its shining and rougher moments, all incandescent with energy.

Actor Karl Sheils, one of the three founding members of Semper Fi (an expression from Latin, meaning "always faithful"), prepared this project for, oh, nearly an entire month.

He got the idea from something similar in San Francisco - but the company there always used the same actors, writers and directors. "We wanted to keep everything open," Sheils says.

"We called everybody. We didn't want it to be too cliquy or too cosy. We know what it's like to hear about something and not be part of it. Anyone could put their name forward.

"So we had 30 to 40 actors, and pulled 20 out of a hat (their names, not them) - 10 male and 10 female. Nobody was hand-picked. We're big into the game of chance."

On Friday morning, June 8th, the writers' and directors' names were similarly pulled out of a hat - four of each, two male, two female.

The countdown started on Saturday night, when they, along with the 20 actors, met up at 11 p.m. to get their brief and vote on a theme. From three concepts - including "hell on earth" and "blood and water" - they chose "love and games" with which to work.

The writers - Alice Barry, Deirdre Kinahan, Eugene O'Brien and Michael West - were chauffeured home at midnight to begin their overnight vigil of work. In six hours, according to various stipulations (no gender bias, no monologues, anything from two to five characters), four plays had to issue from their brains.

"I never had such a short interval between getting something and doing it," says West.

"I thought I wasn't doing it, so I went out on Friday and got drunk, and only found out at lunchtime on Saturday that I was doing it. It was like being at school: the next day you've got the big exam, and you haven't done any revision. By the time I got home to write, my fingertips were sweating. It was the shortest night of my life."

But he was ready for 6.30 next morning when the chauffeur returned - not for them but for their finished plays, which all of them had produced. Collected, photocopied, collated - the Semper Fi people now knew how many actors they needed.

More names were pulled from hats to choose the actors and assign the directors - Charlie Bonner, Veronica Coburn, Maureen Collender and Jim Culleton - their plays and casts. The actors, who had been told to keep their mobiles switched on, were summoned.

Having only eight to 10 hours to memorise and rehearse, polish and prop their individual plays, everyone went right at it. At lunch, drinking what is probably too much coffee, Paschal Friel, a partner with Shiels and David Pearse in Semper Fi and co-producer of 24 Hours, says they are "not worried. We don't have the time to be worried". He takes another gulp, and continues: "They're all professionals." He had his part of the programme to attend to as well - "We're rehearsing the dice men".

Siobhan Colgan, press officer of the Project, interrupts briefly to draw our attention out the window: one of the actors was sitting on the footpath opposite, rehearsing his lines in the sunshine. All he needed was a hat with a few coppers planted in it, and he could have made the day pay for him as well - everyone involved in 24 Hours had volunteered.

Surprisingly, lunch is a relatively placid affair. Nobody appears nervous, at any rate. Culleton, who is directing O'Brien's play, Weekends, says he got his script "at about 8.30 this morning. I had half an hour to read it - and by then I had the four actors. We read through it a few times and swapped round parts to get a feel for it." He got involved in Within 24 Hours because "it sounded like fun. It's all done by the lottery system, so it's interesting to see how relationships are created."

While a group of young assistant stag-managers, culled from the Gaiety school of acting, answers questions, Karl Sheils plunges into the conversation. "Has anyone got a copy of The Blue Danube?" Blank silence. "The Blue Danube. By Strauss. On CD." Someone does, and she is asked to fetch it - after finishing lunch, of course.

Rehearsals continue throughout the afternoon. Catherine Fay moves from one group to another to organise costumes. Luckily, the writers have been realistic here, and "most of them could nearly wear their own clothes", Fay says. By the evening, they have all progressed to the point - because they have to have progressed to this point - to work out a stage-lighting scheme with lighting designer Paul Keoghan. Audience members are turning up early for drinks and their crack at the casino.

Even ticket price is arbitrary. As people arrive at the Project, they are met by Las Vegas-type hustlers in red sequinned jackets and presented with dice. Their roll determines the price of their ticket - anywhere between £2 and £12. The dice men have rehearsed their parts well. (The more timid theatre-goers could step discreetly aside and pay for tickets by credit card which, priced at £6, represented the only mathematical certainty of the day.)

The audience is summoned into the Space Upstairs; somehow viewers too become a part of the intuitive processes going on all day, and silence falls seconds before the lights dim. Staging and props are skeletal. As in workshops, the actors have just enough of what they need to convey the message of the play. They know their lines. If they don't, their improvisation is convincing. And the atmosphere in the theatre is electric. Everyone - actors, writers, directors, stage people, audience - is here for the excitement of the unknown. The "love and games" theme proves to be the most appropriate for the Darwinistic selections of the past 24 hours - the plays are all about the random selections and couplings of men and women, and the extraordinary results that emerge.

At the end, Karl Sheils gets on the stage, delivering kudos all round between bursts of applause. "We created Semper Fi so we wouldn't have to be out of work," he says quite bluntly. "And theatre here needs a boost."

Earlier in the evening, before the curtain went up, Kinahan said she got involved in Within 24 Hours because, "I liked the danger of it". She paused briefly.

"And isn't theatre always dangerous? There's always an element of risk, or working against the clock. You have to have an element of that in your personality if you want to do something like this. That's where the creativity comes from."