It's not prehistoric, it's just pre-Christ. It's like an old, biblical tale. Cane and Abel type of stuff. Just two dudes wandering through early civilization," Black explained. "It's kind of like 'The Meaning of Life' or 'Life of Brian' — a funny look at biblical tales."MTV also have a video of Black discussing the film, but unfortunately, it's not available to view outside of the US.
"A lot of the humor comes from that — the fact that it's an adventure," Cera added. "We're walking across these mountains, and I think it's gonna look really cool. Hopefully it'll be kind of epic."
Peter Chattaway has also highlighted a third Hollywood Reporter article article on the film (here's one and two) which claims that June Diane Raphael will play the Jack Black's love interest, who also gets "involved" with "another man in her village".
It's difficult to work out whether this film will actually be "biblical" in any sense other than its setting, and, even then, the timing of these events might not coincide (strictly) with biblical times. There's obviously a bit of a contradiction between the film's title Year One and Black's description as "pre-Christ", but it might even fit into that inter-testamental period. So it will be interesting to see whether this film re-works some (or even just one) of the biblical narratives, or whether it's just comedy in funny costumes.