http://msnvideo.msn.com/?videoid=d2d4a1 ... epermalink (http://msnvideo.msn.com/?videoid=d2d4a128-39f0-4605-ad94-9a85e41fea1e&src=v5:share:sharepermalink:uuids&from=sharepermalink) Solitary
I guess since we became behaviourally modern.
Human nature. Beats and Rhythms are all a natural occurrences in our mental and physical being. Like your heart beat. We're biologically rhythmic.