MathOverflow will be down for maintenance for approximately 3 hours, starting Monday evening (06/24/2013) at approximately 9:00 PM Eastern time (UTC-4).
show/hide this revision's text 1 [made Community Wiki]

The invention of numbers beyond "one", "two", and "many" probably had more impact than any other development in mathematics. You need to be able to count your livestock! Modern civilization would never have gotten started without the key insight that you can memorize an ordered list of words, and put objects in bijective correspondence with them.