Music hasn't really changed

Music has been around for a really long time. Ever since man "came" to the planet we have been combining noises, that we call music. In the beggining you probably had cave men hitting different sized rocks on stones or something of that sort, and as our civilization has progressed so the sounds of our music. Changing now from rocks and sticks to guitars and drums. In all though we have not really changed much in how our music is composed. Yes we have added new tones and new instruments but we have not really changed how it is done. We have tons of different kinds of music out there now- country, rock, etc... -but just about everything is the same thing. A perfect example of this would be AC/DC. Have you heard their music? They have 12 cd's and they all sound exactly the same, there is maybe a little variety when you include Back in Black or Highway to Hell but aside from that they sound exactly the same. So in conclusion, we have been on the earth for a very long time and yet our music sounds just about the same.