I have reread a bit about the physiology of the ear. The hair cells of the inner ear do not differ between people from different cultures to the best of the present knowledge. What can be modified by cultural influence, that is musical experience, are the synaptic connections in higher regions of the brain.

Those who stress the physical limitations do not at all deny that there are big cultural differences in the scales used. But they point to the fact that of all theoretically possible scales only a small subset is used (still alowing for many differences) and that there are physical reasons for that.

Now, lets make the step from physics to physiology. If a tone of a certain frequency is heard the hair cells in the inner ear at a certain place 'fire' more than with the base rate of firing that is they are active. Each cell that is active adapts to the stimulation that is it fires less per time unit with prolonged stimulation. If a new tone comes another subset of the hair cells is active and fires along. Now the picture that only at one single place the cells fire with one tone is not entirely correct. Also cells at other places fire and therefore adapt. When a new tone comes that is an octave from the other tone, the two subsets of hair cells that fire are quite similar that is the total firing of cells, the sum of neural activity, is minimal in comparison to other intervals.

And so it goes on. The intervals which are in a physical sense simpler lead to less neural firing. The same goes for chords. The 'agreeable' chords are linked to a minimum of neural activity.

Intervals or chords that lead to a high level of activity are arousing and often 'unpleasant'. They are very good as warning signals. Any mother or father in any human culture soothing the child or singing it to sleep uses without conscious decision those intervals that keep the neural activity of the child at a low. There is a lot of freedom within the constraints of physics and physiology allowing for different cultures to find their own musical expressions. But each culture keeps its individual rule of music making within the natural constraints. One of these constraints is that what is close to a minimum in neural activity in the hair cells is found usually more pleasant.

Wolfgang