According to Ch.12, why did writing spread to some societies and not others?
Writing developed in one of two ways, and seems to have arisen independently in both Mesopotamia and Mesoamerica. Developing writing was a matter of assigning symbols to spoken words, and later to sounds, syllables, and abstract concepts. These early writing systems were very complex and hard to master, which made them slow to spread. Additionally, the vast majority of people in a society did not need writing in their daily lives. Because of this fact and its complexity, it was largely limited only to a small group of scribes and other bureaucrats who used it for record-keeping, either for economic or religious purposes. It spread only among settled agricultural societies, who had a need to keep such records, and not to hunter-gathering societies, who had no need for them.