"Year One" is more or less indefensible, but I'll gladly defend parts of it. It's the knockabout biblical lark Mel Brooks never got around to making, with Jack Black and Michael Cera playing Zed and Oh, outcast members of a Paleolithic tribal village whose wanderings bring them into contact with Cain and Abel and Abraham and Isaac and Sodom and Gomorrah and poop jokes and pee jokes and some pretty funny circumcision jokes. "What's with all the genital mutilation--" asks Oh, a sensitive gatherer (as opposed to hunter), upon hearing the circumcision action plan put forth by Hank Azaria's Abraham. Don't worry, the bearded one says. "It's a very sleek look."

The director and co-writer is Harold Ramis. "Year One," to be clear, won't join his list of essential comedies, the ones Ramis helped create as writer, director, performer or combination thereof. At this point we needn't re-emphasize the hardy, very different glories of "Animal House" and "Groundhog Day," but let us not forget the easygoing service-comedy appeal of "Stripes," which holds up mysteriously well. Or Ramis' weirdest characterizations on the old, deathless "SCTV." Or his Zen-like turn in "Knocked Up."

Ramis' challenge in "Year One," which he wrote with Gene Stupnitsky and Lee Eisenberg, is to keep the vibe loose while delivering the laughs. They come in fits and starts. Much of the film takes place in Sodom, which means plenty of gags about sodomy. In what might be called the P.J. Soles and Sean Young "Stripes Goes to Sodom" roles, June Raphael and Juno Temple play a couple of the boys' fellow villagers, now slaves, who need rescuing. Oliver Platt minces through the role of a high priest with copious chest hair and an eye for the young men. David Cross, whom I have yet to find funny in a movie, takes up an undue amount of screen time as Cain, dispatcher of Paul Rudd's Abel and the best frenemy Zed and Oh could ever have.

Hit and miss doesn't begin to describe it. Cera's deft, improvisatory underplaying is an asset, however, as is Azaria's George C. Scott impression. "Year One" feels anachronistic in many different ways (it'll bring back hazy memories of everything from "Life of Brian" on the higher end, to "Wholly Moses!" on the lower). A lot of it's wince-worthy. And then, just when you're about to give up on it, Ramis and company toss off some stupid, stupid joke and, against the Lord's wishes, you laugh.