> the amount of detailed information that can be included on a couple sheets of paper

The Iliad / Odyssey was a purely oral story for a long time. Oral traditions definitely included techniques that would allow any person to memorize vastly more than just a couple sheets worth. For that matter, we still have Hafiz around -- people who memorize the entire Koran and can recite it word for word. Or in non-verbal data, London cabbies with The Knowledge.

Not really quibbling with the point that literacy and writing is important, but the human brain is mutable enough that statements about what the average person "can't" do are suspect.