I think that as humans evolved they used art to communicate or document their lives and beliefs. Some of the pieces created served a more functional purpose such as the early ceramic bowls that were used in ceremonies. Other pieces were used to pay homage to their ancestors and their beliefs as evident in the houses in ÇATALHÖYÜK. Early cave paintings that depict hunting could have been used to tell a story or help teach future generations of the traditions used when hunting.
In response to Bob Hook’s posting. I agree with your caution on interpretations of early art given human nature to disagree. The contrast you pointed out on each piece was very thoughtful. As for the thought that caves could have been the first art museums, I would more likely suspect they were just the most stable structures that humans could inhabit/defend at the time.