What a hilarious time the cast of "Quest for Fire" must have had, all dressed up as pre- historic folks with beetle brows and matted hair, grunting away -- the entire dialogue of the film is in grunts, of which the author is Anthony Burgess -- and performing ingeniously uncouth novelties, the contribution of Desmond Morris.

Merrily, the characters pick insects from the air or from one another's hair and pop them in their mouths, scramble up trees to avoid lions and make peace overtures to woolly mammoths. During the course of the film, we witness the invention, or at least the very first example in (pre)history, of such civilized treats as: The bow and arrow. The live porno show. The clay pot. Frontal sex. The joke. Home-started fire. Romance. The gift of gab.

Any one of these is a sketch, of course, for an actor. Imagine having your face modeled into brutishness with extensions of the forehead and mouthpieces to make the lips protrude, and having the assignment of showing a dawning realization that a rock falling on another's head can be a new experience, called humor. Or that a woman is not just something to leap on from behind or beat off with a stick, but to be rotated frontwards and taken on as a partner.

The question is whether the good time exextends to the audience; to those in the right mood, all primed for silliness, it should. Backward sci-fi is even funnier than the frontward kind.

But the difference between this and, for example, the first act of Thornton Wilder's "The Skin of Our Teeth," when papa telegraphs home from the city that he has just invented the wheel and the dinosauers whimper to come indoors because the Ice Age is rapidly approaching the porch, is that "Quest of Fire" has some simplistic thinking behind the antics.

Its theme is the survival of the most moral. Among the tribes at various stages of development, from the near-apes to the decadent voyeurs, the folks we're supposed to root for earn our sympathy by a distaste for cannibalism, compassion for their own wounded, openness to recognizing the rights of women, community spirit and family orientation. If those aren't the very qualities you need as a hedge against extinction, what are?

QUEST FOR FIRE -- At the Springfield Mall in 35 mm and the Uptown in 70 mm and Dolby Stereo.