Our story-teller was using comparisons to let his audience identify more closely with his experience. He discovered the simile, one of the basics of poetry. In time, all he needed to say was "thundering " and everyone knew he was telling of a herd of great beasts running over the plain. He now had metaphor, the sky-noise standing in place of the hooves-noise. The tribe liked the way this one told stories, but they wanted to hear them again and again.
To help him remember what came where, he developed a pattern of sounds in the telling - rhyme and then other patterns. He developed a rhythm so his cousin could beat that pattern on a drum and help him out, especially when the stories became more intricate or when he began to make up some that hadn't happened but he had only imagined.This way of passing on history and imagination became not just popular but necessary since there was no other way to let the younger ones know what the elders had done. Poetry became the history, the record, the expression of the life of the tribe.
And then came painting scenes on the cave walls. Nice, but unlike poetry and stories, you couldn't take it with you when you moved.