Another aspect to this, which I found interesting is that one of the authors of one of the above books reported that a musicologist who had worked with African master drummers came to the conclusion that, where "western" musicians think in terms of 1/4 notes, the African drummers thought more in terms of 1/8 notes, and were able to play very subtle variations in timing. One author wrote that very complicated polyrhythms of African music had pretty much disappeared by the swing era, when written arrangements were the prevailing form for big bands. That rhythmic sophistication returned with bebop. I've been reading too much to give you page #s for this! And, as always, there are exceptions.