I have a had a theory about this very subject for several minutes now. Here it is.

The first person who saw something worth retelling. It probably wasn't a song but a cave painting that carried the tale. The need to pass on history surely predated spoken language.

The importance of passing along a human experience to other members of the family or tribe could have been critical to survival. The cave paintings in France and Germany not only show that they killed bison and bear but how they were killed as well. The need to sing must have followed the need to speak by particles of seconds. The discovery of rhythym, meter, and rhymn made the stories easier to remember and pass along.

Anyone care to expand on this.

Don