To make the cave a little brighter and a little warmer. And to bring the food in.
Yes. Besides the hide being used for warmth/shelter (I think some tribes made teepees from them), buffaloes were and are used for food. My husband had a buffalo steak when we went out to eat a couple of weeks ago.
And if I may add on a bit to making the cave a little brighter, a corollary result is the dispelling of the shadows. We also have an innate distrust of deep shadowy places, wherein we cannot see what danger may lie... (Ooh, the very word 'shadowy' gives me the shivers!)
The drive evinces itself in many different ways of course. Were you thinking of any in particular?