Also, I have a suspicion the complexity depends on the civilization's needs -- take so-called Ebonics, or Black American English, which has developed in parallel to standard AmE, but partly independently of it -- and it ends up that functioning in North America in modern times, even when segregated from white society, Blacks ended up needing all of the verb tenses and other structures AmE had -- not the same ones, but equivalent ones, and even more forms of the present tense. You can't get people who earn a salary or hourly wages to collapse their numbering system to the Yanomami "one, two, many" when they have a need to express things like "40,000 a year." I think you get the idea. [Edit: Spelling is another matter, and I'm in favour of modernizing it to some degree -- gaol?]