The general reaction left me mystified, because "Evolution" is pretty mediocre fare. Clearly patterned after "Ghostbusters," which was also directed by hit-and-miss filmmaker Ivan Reitman, the sci-fi comedy pits wisecracking academics against bizarre creatures and petty government officials, but the similarities between the films end there. "Ghostbusters" was a true original, while "Evolution" is, at best, a moderately entertaining variation on a theme.

Set in Glen Canyon, Arizona, "Evolution" opens with would-be fire fighter Wayne Green (Seann "what's the deal with that extra 'n'?" William Scott) practicing rescue techniques in the desert when a meteor screams down from the sky, wrecking his car before it crash-lands in a cavern. Two local college professors come to study the rock: geologist/volleyball coach Harry Block (Orlando Jones) and biologist Ira Kane (David Duchovny).

They discover that the meteor is teeming with one-celled alien organisms with the ability to reproduce and adapt at amazing speed. When Ira leads a field trip to the site, he learns that the evolution is happening even faster than he and Harry believed; the ground is covered with extraterrestrial flatworms.

Soon, the government takes over the crash site, with a snide general (Ted Levine) banning the locals. Working alongside the general is Dr. Allison Reed (Julianne Moore) from the Centers for Disease Control. Ira and the comely doc initially butt heads, but quicker than you can say "formula flick" she hooks up with the good guys.

Just in time, too, as the little alien critters are multiplying and mutating like crazy. One mosquito-like creature invades Harry's body, throwing the geologist into panic mode as an examining physician states "It's headed toward his testicles!" Note: In the trailers for the film, the destination is changed to "crotch," while "bottom" is used in the TV ads. Hmmm. Regardless, the whole thing builds to an anal rescue scene that had the audience in hysterics.

Initially, the aliens die as soon as they are exposed to our atmosphere, but they quickly adapt and grow even more aggressive. A sad-eyed creature absurdly misidentified as a dog (wow - just like in "Ghostbusters." What a coincidence!) demonstrates its jaw power in front of a group of housewives. A winged lizard swoops through a mall with a shoplifter in its talons. Ira, Harry, Allison and Wayne team up to stop the invasion, leading to the obligatory battle royale. In this case, the insipid finale involves yet another anal procedure, coupled with one of the most blatant product placements in movie history.

While "Evolution" is mildly entertaining, its lazy screenplay (which began as a drama) insures that the movie will never rise above tepid. There are a number of good one-liners (Duchovny gets off a nice joke based on his former "X-Files" persona), but for the most part, the filmmakers simply lean on the special effects, which are not all that special. Sorry, boys, but a parade of monsters isn't enough anymore.

The cast is saddled with characters as unimaginative as the script. Seann William Scott, Stifler from "American Pie," says "Wow!" a lot, Orlando Jones, best known as the star of a dreadful series of 7-Up ads, makes black jokes, Julianne Moore stumbles over everything and David Duchovny does his usual deadpan shtick. Oh, and he moons the general. Speaking of the general, you might remember Ted Levine from "The Silence of the Lambs," where he played Buffalo Bill, the serial-killing lunatic. I kept hoping Levine would turn up in front of the aliens nude, with his genitals tucked behind his legs, saying "It doesn't come to Earth without an invitation."

But that would have been nervy, and "Evolution" isn't about taking chances. About two-thirds of the way through the story, some of the aliens evolve into quasi-human form. What if they had evolved further? They could have developed language skills and negotiated with the government for citizenship. Or they could have done to us what we did to the Native Americans, dumping our heroes into low-income housing on a Human Reservation. At the very least, they should have developed their writing skills and turned out a better screenplay than this one.