The basic idea, in one sentence, is that our preferences in art are a result of our ancestral environment.
He cover various ways in which both natural and sexual selection pressures have shaped how we appreciate various artistic products and how we create them. He explores aesthetics from Aristotle to post-modernism and looks, from the Darwinian perspective he's formulated, why we regard forgeries and modern art "readymades" the way we do.
Daniel Levitin has also written a book (This is Your Brain On Music) that explains recent interesting discoveries dealing specifically with sound and music cognition. Awfully interesting stuff.