Buddhism: it took hundreds of years after Siddhartha Gautama died before his orally-transmitted teachings were written down. Homer's epics: hundreds of years, maybe thousands. The Old Testament: definitely thousands of years of survival by word of mouth only, and then finally written down. Once written, the words are available for all to learn and experience, right? No; one must also know how to read, which the vast majority of humanity did not know how to do until fairly recently. And even then, one could only read what was written in a language known by the reader, and the written copies of texts were not plentiful.
How much observation, insight, knowledge, and wisdom was lost over the course of the 1st 10,000 years or more of "civilization" because the observer or holder of the insight/wisdom couldn't write down their thoughts and were not able to successfully pass them on orally? That, to me, is the single most influential differentiator between the "advanced" cultures of the Old World as compared to the New World. Although individual brilliance can and does pop up anywhere, anytime, in any culture, a people can only accomplish so much without a writing system that enables them to refer to and build on existing knowledge. The minuscule number of "geniuses" throughout the ages is almost certainly several orders of magnitude larger than we know, but we have no record of their brilliance which died with them. The explosion of invention, creativity, knowledge, and all else which springs from the mind of humanity that has taken place over the last few hundred years is, I believe, due to nothing more than the widespread ability to read, write, translate, and mass produce copies of writings into languages and onto media that can be consumed by the whole human race, allowing all Mankind to stand on the shoulders of giants.