Wilco48,

It's a great question. I suspect there has been a lot of work on this from the social and psychological end that I'm not familiar with. From the physiological end, though, I would argue that the evidence is that the voice came first, at least for music as we understand it. Our ears look for equal-spaced spectra, and our voices produce equal-spaced spectra. However, our voices produce sound via driven oscillations, and are really quite committed to the equal-spacing in a fundamental way. I am not so sure our ears absolutely have to respond to equal-spaced spectra in the same way, though I really need to find enough information to work this out. But given that, I suspect that on this one fundamental point (what we perceive as a musical sound) our ears evolved to fit the sorts of sounds the voice must make. It's just speculation, but I think it is a good one.

Once the basic physical mechanism is in place, of course, the can affect each other and co-evolve under whatever social pressures may arise.

Dustin