In the original script, the cavemen make peace with the time travellers after Ian shows them how to make fire.
The original title for this episode was The Dawn of Knowledge.
The serial was originally going to end with the TARDIS materialising near a Frank Lloyd Wright-style house floating in the air. This was to lead into The Masters of Luxor, a story that was unmade.
This episode takes place in 100,000 BC.
Howard Lang (Horg) is the only Credited Actor to never make a reappearance in Doctor Who at any time, and curiously died a few days after the Series concluded in 1989.