Before caves or Callas or Nick Cave we lived in trees. Two important principles about sleeping in trees....don't fall and be quiet. So late arriving member of the troop arrives at the tree house and makes a low sound of some sort not to alarm his fellow limb dwellers. One or two respond in a rhythm or cadence unintended and music is born! Next day on a long slog to a better tree the previous night's melodic episode is picked up by the ordered march and repeated by the group to the great effect of mitigating drudgery.
Then that night around the fire a stick is introduced to a log, the music repeated, and someone sways, dances, and gets laid. No stopping this train now. Well Prog Rock is trying.