[msluyter]

I once asked an ethnomusicologist if any common factors existed across all musical cultures and he said that about all he could point to was: a) some concept of a tonal center and b) the interval of the 5th remained fairly constant, despite whatever scales/tunings might exist.

So, I'd grant that much, but beyond that, I don't see much evidence for the diatonic scale as being somehow inherently inevitable. The harmonic series isn't much help, since you get to the flat-7 or flat-five before various other diatonic notes (plus, it's not particularly in tune at the higher partials).

And the circle of fifths rationale seems to be a just so story: http://en.wikipedia.org/wiki/Just-so_story (why stop at 7 notes? why not include G# or even C#? why not just C-G-D-A-E? (incidentally, a pentatonic scale) etc...?)

But this debate could go on ad infinitum, because the issue lacks empirical grounding. Which is to say, how could one falsify either the nature or culture thesis?

[jerf]

I answered a slightly different question than I think you think I did. You said "Well, IMHO this is a purely arbitrary cultural artifact resulting from the evolution of the keyboard (first in pipe organs). Since the octave is divided into 12 chromatic tones, you could in theory devise a keyboard with alternating white/black keys." I gave you a plausible non-arbitrary answer for why that particular pattern was chosen. Not why equal temprement is inevitable or why "7" notes in a scale are special, just why the white keys are ABCDEFG as we know them and not some other pattern. You can put more or fewer notes in your scales in stuff we still would call "Western" music without anybody caring or even noticing. (Much good Western music uses all 12 tones pretty freely.)

As for whether it's a Just So story, sometimes that's all you get. However, if it is just coincidence it's a mighty coincidence.