The ability to acquire and use language represents a dramatic evolutionary development. No individual or people discovered or created language. The human language faculty appears to be biologically and genetically determined.
This is not true of the written form of human languages. Children learn to speak naturally through exposure to language, without formal teaching. To become literate, to learn to read and write, one must make a conscious effort and receive instruction.
Before the invention of writing, useful knowledge had to be memorized. Messengers carried information in their heads. Crucial lore passed from the older to the newer generation through speaking. Even in today’s world many spoken languages lack a writing system, and oral literature still abounds. However, human memory is short lived, and the brain’s storage capacity is limited.
Writing overcomes such problems and allows communication across space and through time. Writing permits a society to permanently record its literature, its history and science, and its technology. The creation and development of writing systems is therefore one of the greatest of human achievements.
~ An Introduction to Language 6th ed. by Victoria Fromkin and Robert Rodman.