“The World in Six Songs: How the Musical Brain Created Human Nature” (Dutton. 336 pages. $25.95), by Daniel J. Levitin: Why do humans act the way we do? Evolutionary biologists often give the simplified answer: Because we're driven by the instincts that helped our ancestors survive.

This reasoning has been used to explain everything from why babies are so cute to why a martyr sacrifices himself or herself to save others.

But it doesn't work so well in “The World in Six Songs.” Author Daniel J. Levitin repeatedly evokes that theory to explain why music has become a vital part of every human culture. But his logic is often unconvincing, leading to a book that offers plenty of interesting anecdotes but fails to deliver on its scientific promise.

Levitin is a former record producer and professional musician who now studies musical perception at McGill University in Canada. He doesn't say what his scientific credentials are, so his arguments of evolutionary biology come across only as educated speculation.

That can still be a convincing form of argument, as long as the speculation makes intuitive sense. But Levitin's arguments often don't.

For example, he says the reason it feels good to make and listen to music is because those of our ancestors who happened to feel good during musical activities were the ones who survived to pass on the gene that leads to those feelings.

The rationale isn't clear. After all, a curmudgeonly caveman who was always telling his neighbors to keep their cave music down might still have survived long enough to find a mate. The link between music appreciation and survival isn't immediately obvious.

Levitin uses a similar argument to explain why we prefer listening to music in stereo over mono. Our ancestors, whose brains were better at processing sounds from multiple sources, were better at detecting and avoiding predators, Levitin says, and were hence more likely to survive.

That argument makes a little more sense but a reader could also speculate we prefer stereo because it's richer and just sounds better. Eventually, Levitin's assertions become tiresome when he repeatedly offers nothing to back them up.

The book's main strength comes from the author's flair for the anecdote. Levitin sprinkles the chapters liberally with fascinating nuggets of human nature.

The book's title comes from his claim that human nature has been shaped by six types of songs: those expressing friendship, joy, comfort, knowledge, religion and love. He describes each genre in detail, and here's where those nuggets shine.

For example, he provides a biological explanation for why we might tap our feet or bob our heads in time with a favorite song. He also discusses how singing might soothe a baby and how music emboldens soldiers or athletes preparing for conflict.

To Levitin's credit, “Six Songs” is an easy read and provides plenty of interesting fodder for conversation. But a reader looking for convincing science might come away disappointed.