There is great variety in ways to write human languages. Yet humans have only invented writing systems independently of prior knowledge of writing a few times. The variety comes from successive adaptations of the original writing systems.
One area where writing is known to have been invented "from scratch" is Mesoamerica. There is conflicting evidence about which Mesoamerican people were the inventors and which were the adaptors. Evidence found in just the last fifteen years suggests that either the Maya or the Olmec may have been the inventors. We may never know definitively which Mesoamerican people invented writing but we do know that the Maya had the most comprehensive writing system in ancient Mesoamerica.
We cannot estimate how prevalent literacy would have been among the Maya but it was probably reserved for the more elite classes such as nobility, priests, astronomers and possibly merchants. The Maya writing system itself came to be understood only in the past few decades — at least 2,300 years after it was invented. The story of how that happened is fascinating and is told in the book and TV documentary, Cracking the Maya Code.
It is surprising that the Maya writing system was deciphered at all considering not only how complex it is, but also that most Maya writing was destroyed by the Spanish soon after they arrived in the area. They did not realize that it was writing and instead misinterpreted it to be a form of devil worship — which would no doubt be a hindrance in converting the Maya to Roman Catholicism. (Unlike Spanish, which is written in the Latin alphabet, Maya writing used a system much more complex than an alphabet.) By the time the Spanish were invading the highlands of Guatemala, Q'umarkaj was a major city and the new capital of the K'iche' Maya people. The Spanish sacked and burnt it and then used its ruins to construct a new, colonial city, Santa Cruz del Quiché. That city still exists today and it was there that I photographed this K'iche' woman reading a Spanish-language newspaper. She is very likely descended from the original inhabitants of Q'umarkaj. Had the course of history been different, she might instead be reading a publication in her own language and its original writing system.
Without understanding their writing, our beliefs about the ancient Maya and their culture would be (and once were) very different from today. But perhaps the greatest benefit to come from cracking the Maya code is not an academic one but a humanitarian one. Today in Mesoamerica modern Maya peoples are learning the writing system of their ancestors. They are reclaiming their heritage and de-colonializing themselves. For the first time in a millennium it is possible for literacy to be as widespread among the Maya as it might have ended up becoming had their civilization continued to flourish.
The K'iche' Maya are featured in our documentary, Peoples of the World: The Maya.