The dawn of man: a Neanderthal wallops the guy in the cave next door for no reason at all. Underdeveloped humans laugh for the first time. Yep, that's how slapstick was invented.
Jump forward a couple of million years and you'll think hardly anything's changed when you see "Jackass: The Movie".
Men stupidly hurt each other for the amusement of their peers. And it's filthy, hilarious stuff that keeps going one better in both laughs and stunts.
Johnny Knoxville's gang of sado-masochists move from the TV to the movies, wisely dispensing with a narrative. Instead, like the hit MTV show it's based on, you get a series of OTT set-pieces that are now bleep-free but only marginally more violent and extreme.
Bizarrely, they succeed in being entertaining - if you're of a certain mindset. Clamping baby alligators to your nipples or trampolining into ceiling fans isn't for everyone, but the gleeful egging-on the performers give each other - together with their giggling winces as each new disgrace is perpetrated - eventually becomes infectious.
The purile comedy is particularly fine when the team creep onto a golf course and sound an air-horn just as wealthy WASP-types are tee-ing off. To see the golfers' rage at being (gasp!) put off their game becomes even funnier when they drive the ball straight at Knoxville and co., completely missing the point that such a response is the object of the stunt.
It's sure to be lambasted as irresponsible and perverse, but you'll see nothing here that's worse than in the acclaimed documentary "Sick: The Life & Death of Bob Flanagan, Supermasochist" of a few years ago. Sadly, it's likely "Jackass" will get it in the neck because it's about having a laugh.
As brainless as the movie incarnations of both South Park and Beavis and Butt-head, "Jackass" is just as funny as both - and better than many of the so-called comedies Hollywood produces.