The historical record does seem to indicate, at least to my reading, that illiterate people are at a significant disadvantage when it comes to engaging in high-level rational thought.
Writing things down doesn't just store and transmit information, it forces an author to crystallize and review their arguments. Writing certainly makes me more rational.
Those societies that never developed writing did have oral traditions with lots of "human knowledge and culture" but neither of these things are rational thought. Most oral traditions are rich with culture, but shot through with extreme irrationalism, exaggeration, fabuluism. This applies as much to a tribal society as to the stories your friends tell at the bar.
What exactly are you counting as high-level rational thought? If it's the ability to clamp down on "extreme irrationalism, exaggeration, and fabuluism", and Western societies are better at this, then I'd think Fox News wouldn't be a thing. ;)
Writing things down doesn't just store and transmit information, it forces an author to crystallize and review their arguments. Writing certainly makes me more rational.
Those societies that never developed writing did have oral traditions with lots of "human knowledge and culture" but neither of these things are rational thought. Most oral traditions are rich with culture, but shot through with extreme irrationalism, exaggeration, fabuluism. This applies as much to a tribal society as to the stories your friends tell at the bar.