• One good book deserves another, and I’m sorry to say that Daniel J. Levitin, the author of This Is Your Brain on Music: The Science of a Human Obsession, has not quite lived up to expectations the second time around.

This Is Your Brain on Music, which I reviewed in this space last year, is that rarity of rarities, a lively and informative book written in a clear, straightforward style by a specialist in a field notable for its technical complexity. It was and still is the best introductory discussion of the psychology of musical perception and cognition ever to see print. But Levitin, a musician and record producer turned neuroscientist, has since succumbed to the urge to simplify and theorize, and The World in Six Songs: How the Musical Brain Created Human Nature (Dutton, 333 pp., $25.95), while full of good things, doesn’t add up to a persuasive whole.

Part of the problem-most of it, really-is that The World in Six Songs makes a promise that it fails to keep. “I have come to believe,” Levitin writes, “that there are basically six kinds of songs, six ways that we use music in our lives, six broad categories of music. . . . They are songs of friendship, joy, comfort, knowledge, religion, and love.” This sentence is breathtakingly broad in its implications, and the book appears at first glance to be organized in such a way as to prove the point, though no more than a moment’s thought will leave most readers suspecting that the world of music is rather more complicated than Levitin suggests. What about songs of sorrow? Or story-driven ballads whose subject matter is not romantic love? Into which of his six pigeonholes would Levitin stuff, say, Irving Berlin’s “Top Hat, White Tie and Tails,” the Beatles’ “Paperback Writer,” or Donald Fagen’s “Morph the Cat”? And his decision to disregard instrumental music is so cavalier as to require far more justification than he offers:

The evolution of mind and music is easiest to follow in music that involves lyrics, because the meaning of the musical expression is less debatable. . . . Because music wasn’t recorded until about a hundred years ago, nor even accurately notated until a few hundred years before that, the historic record of music is substantially lyrics. For these two reasons, music with lyrics will be the predominant focus of The World in Six Songs.

That near-exclusive focus, alas, negates much of the explanatory power of The World in Six Songs, for it is impossible to take seriously any account of “the impact music has had on the course of our social history” that completely ignores the culture-shaping power of abstract instrumental music.

Fortunately, a closer look at Levitin’s book reveals that its purpose is not nearly so sweeping as the title suggests. In fact, the real subject matter of The World in Six Songs turns out to be “the evolution of music and brains over tens of thousands of years and across the six inhabited continents.” According to Levitin, music is “a core element of our identity as a species, an activity that paved the way for more complex behaviors such as language, large-scale cooperative undertakings, and the passing down of important information from one generation to the next.” Thus his six categories of song turn out not to be all-encompassing, but merely to represent the principal ways in which music “influenced the eveolution of human emotion, reason, and spirit.”

That I’ll buy, necessarily conjectural though it is. What I still find hard to accept is the loose organization of The World in Six Songs, which is less a well-structured book than a bagful of factual goodies into which the reader reaches more or less blindly to see which one comes out next. To be sure, I learned a lot from The World in Six Songs, but Levitin’s style is so discursive, anecdote-driven and gratuitously autobiographical (at one point he interrupts the narrative for an eight-page account of the development of his pacifist views) that I found much of the book needlessly difficult to follow. If you read it with patience, you’ll come away knowing more than when you started, but I wouldn’t blame you for giving up well before the halfway point.