I'd expect something things like Chinese Writing to be a big upstream dependency, but here it's a terminus. Detecting a western-bias in the sourcing.
why are they separate?
If you include all of the Latin-script characters, Cyrillic, Greek, accent symbols and ligatures, you'd have over 300 characters, and that is a very conservative estimate
This is vastly overstated. This was a widely popularized idea in the west but has largely been debunked by more recent scholarship that is less interested in demonstrating the superiority of the west.
History research is typically published in books rather than papers, so it isn't content I can link to directly.