This may seem like an obvious point however civilization as we know could not have developed without a system of written transmission of knowledge from one generation to the next. There was probably a few nomadic cultures in existence not so long ago who may not have fully utilized writing but passed on their cultural heritage through oral tradition, cultural artificats or the medium of language itself. In ancient Egypt it's probable the majority of the population were illiterate (if such a term could apply) however via the medium of monuments cultural information could be passed down many generations. Perhaps only an elite priestly caste understood fully the system of symbolic written encoding of information. The breakthrough of a formal use of writing to easily transmit knowledge from one generation to the next cannot be underestimated.
