Originally Posted by: Whune

i don't really know much about it;

but it looks to me like first we had

classical where it's these themed parts, that just flow into each other

then with blues we have just a single pattern repeated over and over again

(12 bars)

and with pop (i'm including "rock, R&B, country; etc in this)

we have alternating parts like Verse, chorus, etc...

This is the sort of topic that require books on music history to answer. :) Wiki is a good place to get a brief overview.

https://en.wikipedia.org/wiki/Music#History

Music likely developed first as a utilitarian function. A means of communicating about the danger or safety of the area, preparation for hunting or gathering. Eventually, it gradually became more of a free time luxury activity.

In the same way language got more complex & nuanced in order to identify & communicate a wider range of ideas, objects, actions, music also got more complex as people wanted to express more thoughts & emotions by means of auditory art.

Historically, the melodic & harmonic component developed as more subdivisions of the octave were discovered & used. So, first the octave, fifth, major third, following the order of the natural overtone series. You can see evidence of this in prehistoric flutes, for example. Eventually, the diatonic scales & then chromaticism in the Renaissance.

By the time of the Greeks music was very developed compared to prehistoric times & they integrated into their other arts. It was typically used in dramatic plays to augment the story.

This is an important point also, because it mirrors the overall development of the arts in general. As story telling got more complex, so did epic poems, dramatic plays, and music!

Think about how the structure of plays eventually as grew to have sections called acts, how epic poetry had subdivisions. Likewise music developed complexity & in order to provide more depth & more variety artists added multiple sections to songs.

Eventually, in Renaissance Europe & China (1500s) equal temperament tunings made it possible to write music in increasingly complex patterns!

Baroque & classical music of the Enlightenment era was when Western music developed into it's full stature with the music of Bach & Beethoven, the old masters.

Your question specifically mentions sections. This is about overall structure or form. Form is the manner in which all the sections (or melodies if more than one) are structured in what particular order. In classical music, the gold standard of structural form was Sonata-Allegro. In the widest sense this consisted of:

1. Exposition (statement of themes 1 & 2, or more)

2. Development (variation on themes)

3. Recapitulation (restatement of themes 1 & 2, more).

The form was highly plastic, though, allowing many different possibilities for variation & alterations. There were other forms: Rondo, Minuet & Trio, etc. Larger forms were the symphony, the concerto, etc.

Modern Western music (pop, rock, blues, jazz) all follow the basic structural forms established by the classical masters. For example, standard pop song’s structure:

1. Verse & chorus

2. Optional bridge/solo

3. Repeat verse & chorus

On a much smaller scale this is just an exact replica of sonata-allegro form. Larger forms that muliple songs fit into are albums & stage musicals.

The reason this protean form is so often used is that it serves a great way to provide a story arc. A song, piece of music should have a beginning, a middle in which it "goes somewhere", then has a conclusion. Often the ending echoes or bookends the beginning by resolving the original conflict.

Even a simple blues or folk song typically has more than one section even if it's just the same verse or chorus repeated over & again. Sometimes the means of variation is in the storytelling of the lyrics, in which case the music is just serving in an accompaniment, background role.

There's a brief history of music & musical composition. For a more in depth approach I'd recommend a good book. For example:

https://www.amazon.com/Music-History-Prehistoric-Classical-Electronic/dp/1542523095/

Hope this helps!