Reading James Herriot's wonderful stories about his life as a vet, I came across an interesting phrase, hybrid vigor. In short, hybrid vigor means "the improved...quality in a hybrid offspring (Wikipedia)". For example, a mixed breed dog is usually healthier than purebred dogs. But how does all this relate to music?
If you think about it, it becomes obvious that the best composers and the most succesful compositions really are results of some kind of hybrid vigor. J.S.Bach is a great example. In his music, he combined influences from German, French and Italian music of the time, as well as folk music of his region and liturgical music of the Lutheran church. It cannot be denied that the resulting "mixed breed" music of J.S. Bach is supremely vigorous!
How about popular music? I don't think there's any need to think of any examples—it goes without saying that all popular music is the offspring of several, highly varied sources, from the traditional music of the african slaves to the various musical idioms of european immigrants.
Turning to guitar now. For me at least, the best classical guitar compositions are results of combining several musical traditions or styles. Classical guitar music has always been an island apart from the mainstream. All through the history of music, guitar has had a close relationship with the popular music of the times. That close relationship has perhaps relegated guitar to a niche among classical music, but it has also been a great thing for the repertoire. Think about Villa-Lobos! Rodrigo, Albéniz (although he had to write for the piano, not being a guitarist :), Tárrega, Barrios—it seems that all the greats have had folk music close at heart. Brouwer! The list goes on. I'm not saying that more mainstream classical composers have not been influenced by folk and popular music, but guitar composers really are a different breed in this respect!
I think this is a good thing for me as well. As I've said many times, my compositions for classical guitar combine influences from classical music, pop, film music, folk music and so on. I hope that my music also has some of that magical and empowering hybrid vigor I've written about in this article! I guess time will tell.