I just finished the last chapter in "This Is Your Brain On Music" called The Music Instinct.  This is, in my opinion, one of the most interesting chapters in the book.  It talks about the origins of music and how and why it might have been created.  One of the main topics discussed is the reason that music has lasted so long throughout human existence and evolution.

 Levitin discusses evolution and other theories of what scientists believe to be the origin of music.  One of the theories that was brought up was that music is a by-product of human's ability of language and communicating emotion.  It explains that most traits and behaviors are evolutionary adaptions and have clear evolutionary purposes, and then, found very rarely, there are attributes or traits that have no clear purpose or basis, such as the ability of musical creation or musical talent.  Levitin says that the adaption of such a trait "occurs when evolutionary forces propagate an adaption for a particular reason, and something else comes along for the ride, what Stephen Jay Gould called a spandrel, borrowing the term from architecture."

I thought considering music a spandrel, a mistake, or a by-product of human existence is an interesting theory.  An analogy that is made is that "birds evolved feathers to keep warm, but they coopted the feathers for another purpose - flying.  This is a spandrel."