@Lugia: thank’s for these precisions, we can indeed travel very far in time and space.
By the way, originally, we all have an old relative called 'Homo habilis' who lived in Tanzania 2 million years ago. Under the milky lights of full moon nights, he probably sang strange and wonderful kind of drones, like 'plainsongs' mingling with those of other animals in the plain. (Etymologically, 'plain' comes from the Latin 'planus' which can be found in 'cantus planus', in French 'plain-chant'). Today, I think that we don’t do anything else with our drones: we still question ‘The Great Mystery’...
For my part, I prefer to focus on the History of Western music; starting with the Gothic Period, it's already a long way :)
@troux : thanks, I'll read it with pleasure.
'On ne devrait jamais quitter Montauban' (Fernand Naudin).