I studied musicology with a focus on perception of sound. As far as I understand it, we evolved to be able to perceive distinct colors because it's relevant to

I studied musicology with a focus on perception of sound. As far as I understand it, we evolved to be able to perceive distinct colors because it's relevant to distinguish surfaces from another visually. For auditory sensations on the other hand rough pitch estimations sufficed but relations between pitches (think of hearing 2 pitches. you probably won't know the exact note or frequency but have learned to recognize patterns in the relations between them - e.g. musical intervals) which comes down to periodicities in the signal turned out to be a lot more relevant or helpful. As to why we needed to be able to relate pitches to one another: Without looking up literature on the topic I hypothezise that it might be a byproduct of the way we calculate a single perceived pitch out of a harmonic frequency spectrum. When hearing a note that is not a sinus wave in the frequency spectrum there are at least parts of the multiples of the base frequency. Since we do something like frequency analysis by detecting periodicities our brain tries to determine a single pitch for the signal, which it does by calculating the base frequency of harmonic spectrum (this works even of only part of the harmonics are availabe.). In order to do that the processing needs to treat the base frequency differently than the overtones. Since overtones roughly correlate with western musical intervals and we needed the processing to get extract them. We might have gotten relative pitch perception and part od what is music as a byproduct. Anecdata for this: Try determining the existence and intervals of notes when the higher note is an octave or an octave and a fifth above the first one (1st and 2nd overtone). Depending on the instrument this can be quite hard. Disclaimer: These are my interpretations / theories, but since I'm not working in this field, the literature might tell a different story.