From 2K Elizabeth at the 2K site.
"Currently, the histograph shows the first 7 historical events in your Civilization, which could be military or domestic (winning a city or spawning a Great Person.) As many of you have been confused by these markings, in patch 1.30 well be taking them out and leaving only the graph which represents each Civilizations score throughout the game, which is derived on a number of factors including how many cities you have, how many settlers you produce, your attack and defensive power, and many other markers that indicate how strong and prosperous your Civilization is in relation to your opponents."
Well, months and months later we finally have an answer. I think you'd be pretty dimwitted not to realize this answer doesn't match what is displayed, time line wise. Further evidence that the game was rushed(no legend), and released with known errors(time line). They dropped the ball, and keep fumbling the pick up.