1- Script evolution changes in time, and here are the reasons: 1- Geography, language, existing culture and cultural influences from the outside and finally, history (whether war, annexation, colonization, etc).
2- Old Roman & Trajan becomes Rustica (no papyri or vellum yet) around the 5th century. Why? Nobody really knows. Why are Latin peoples more boisterous than the Nordic? Climate? Food? Language? ALL OF THE ABOVE.
I made the point to compare Romanic vs. Gothic. The south is more rounded, that's it.
3- With the advent of papyri and vellum we get: NEW ROMAN CURSIVE (miniscules). It was used from approximately the 3rd-7th century, and uses letter forms that are more recognizable to modern readers; "a", "b", "d", and "e" have taken a more familiar shape, and the other letters are proportionate to each other rather than varying wildly in size and placement on a line.
4- We also get UNCIALS (majuscules), this is the lettering of power, church, aristocracy, royalty. Uncials move all over, west, east, north. Greeks loved uncials! Byzantium loved uncials! This is around 7th-9th centuries Carolingian in the west, Byzantium in the east.
5- Then we get half-uncials. What do they do? They allow for serifs! That's tghe beginning of ascenders and descenders (remember half-uncials have nothing to do with uncials, all it means is that it's a church letter! Hymns, psalters, etc).
6- Now the half-uncial goes insular (British Isles). Actually Ireland!
Merovingian, basically Carolingian miniscule
and Beneventan, basically derivation of Carolingian miniscule
In time you get this beauty. The Gothic Textura!
Mature Gothic is already the Humanist style.
Bastarda, Chancery, secretary, etc, and the rest are just variations of these styles.