system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Are musical scales integrated into our brains? Are we born liking only certain combinations of notes, or do we learn them early on? What's so special about those combinations?
gpt
The short answer is that it's a combination of nature and nurture.

There are certain harmonies that all humans seem to naturally find pleasing. They have some nice mathematical properties, like if you play any note, and then another note with a frequency that's exactly a 3:2 ratio, or a 4:3 ratio, or a 5:4 ratio, it sounds harmonious.

Those ratios are found throughout music from all around the world.

Why? Our best guess is that our brains are hard-wired to listen for sounds, and also to look for patterns. Music tickles our brains in ways that exploit the thing our brains naturally evolved to do well for survival.

Musical scales, like the major and minor scales, or the 12 notes in the full chromatic scale in western music, are like generalizations of those basic ratios. They start with those basic ones and add a few others in-between to make it possible to create melodies.

That second part is more arbitrary / learned. Most of us grew up hearing the 12-tone Western music scale so that's what sounds normal to us, but there are plenty of other scales that would also work equally well.

However, there are no scales found that don't contain lots of those fundamental ratios in them, and no scales that have more than about 24 notes, because that's about the limit that the human ear can easily distinguish.