Click on the graphs and all will be revealed!
Thanks to:-
Jean-Baptiste Michel*, Yuan Kui Shen, Aviva Presser Aiden, Adrian Veres, Matthew K. Gray, The Google Books Team, Joseph P. Pickett, Dale Hoiberg, Dan Clancy, Peter Norvig, Jon Orwant, Steven Pinker, Martin A. Nowak, and Erez Lieberman Aiden*. Quantitative analysis of culture using millions of digitized books. Science. Published Online Ahead of Print: 12/16/2010.