First there was no language, now there is. At one time our ancestors did did not speak and now we do. Somehow creatures who did not speak came up with words and eventually started scribbling them. Since people who had no language invented it, you could say that illiterates invented language.No surprise. We see a version of language invention every generation. Kids, especially from middle school through high school, introduce rafts of new words. Go back to that period in your life and try to recall the vocabulary you and your group invented. Every few years someone writes a blog or an article listing and defining the latest neologisms. Currently hip hop gives us our greatest supply of new words.