Something very scary happened in western Iran around 5000 years ago. People started using a writing system for their bookkeeping, used and developed it for a few centuries, and then stopped writing.
The system they used is called proto-Elamite script, it is obviously inspired by Mesopotamian cuneiform but has mostly developed its own symbols, which aren't completely decoded yet. Decoding it further may help to explain how and why people fell back to illiteracy.
I interviewed the leading researcher specialising in this script, who happens to be based in Oxford, and wrote a feature which is out in Current Biology today. And, writing for biologists, I've given the story a bit of a biological spin, hence the title:
The evolution of writing
Current Biology, Volume 22, Issue 23, R981-R984, 4 December 2012 doi:10.1016/j.cub.2012.11.032
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Photo of a proto-Elamite tablet from the Louvre, Paris © Marie-Lan Nguyen / Wikimedia Commons