We could offer you our own one-line plot description for "Year One," a high-concept comedy set in biblical times, but we prefer star Jack Black's pithy take: "Just two dudes wandering through early civilization."
The dudes in question are Black and Michael Cera, two buddies living in an ancient hunter/gatherer society, trying to hit on ladies and prove their manliness to the tough guys in the village. Neither of these pursuits are working out too well, and after Zed bites into some forbidden fruit and accidently burns everyone's huts down, the two friends set out on an epic journey through time, the Bible and the very limits of PG-13 comedy.