Google Ngram Viewer - Some interesting examples

Researchers from Google analysed a series of million books and came up with frequencies of Ngrams (phrases with N words) in those books up to N=5. One can form a query (e.g. ask for the frequency of a word in a subset of books based on geographical origin and a subset of time) and then visualise the results using their tool. In this post, I have included some queries of my own. 

Philosophers in Literature - Query: http://goo.gl/Kb39l

The 3 Greek philosophers (Socrates, Plato and Aristotle) correlate very well and maintain the same frequency over the years. Marx's breakthrough and fall are also quite obvious.

Political Systems in Literature - Query: http://goo.gl/7vrns

Interestingly the frequency of Monarchy is stable, Democracy was not popular before 1820 and after World War II Communism overtook Democracy and Socialism (until mid 70's).

Sciences in Literature - Query: http://goo.gl/f4MFp

Well, one would expect Philosophy to be the most popular in literature. The interesting thing here is that Physics and Mathematics correlate really well and together with Biology and Chemistry are being kept within the same range of frequencies.

Penis vs Vagina - Query: http://goo.gl/MoVzt

On the fun part, mid 20's must have been the decade when:
a) books started to target females as a potential buyer
b) females started to write/publish books
c) homosexuals (gays mainly) started to feel comfortable
d) ... ?