The whole thing is about a power struggle over the head of a tribe during a time before civilization. Everyone's nearly naked. There are wild beasts, strange desert and mountain landscapes to be endured. Hey, someone has to be head honcho.
The movie is damn quiet making it a pretty difficult watch. The entire movie is nearly mute with the exception of some animal growls. In that perhaps it's somewhat innovative for Hammer. This was the only movie they shot that fit this mold, silent-ish and caveman. I suppose you can consider it somewhat of an experiment. Since they didn't reproduce it ad nauseum, I'm pretty sure it wasn't successful upon it's 1970 release which is why they took everyone's clothes off in all their later vampire films.
You can pick up Creatures the World Forgot now.