It may or may not be a coincidence that the considerable increase in the use of the word “rape” coincides with the very rapid rise in the use of “feminism” in the 1970’s. Whole books have been written on the basis of such slender associations, though admittedly mostly in the behavioural sciences.
As previously discussed, behavioural scientists are under no compunction to choose their variables according to established principles, after sustained perusal of a century of published literature, or Delphic consultation with knowledgeable colleagues. The best researchers attempt one or all of those preliminary steps, but they are not compulsory.
So, to examine what may be a chance correlation of frequency patterns it is wise to try other possible words. A reader has kindly suggested “virile” but as my reply (below) shows, this does not work. Neither do the following words, chosen by a most distinguished person, to whom I had described the problem over breakfast. “Nuclear” “culture” “ethnic” “political” “economic” “black power” and “terrorist” all fail to show the same pattern, although they undoubtedly were frequent words at the time (much more frequent than our words in question).
One word shows a clear association, though as a mirror image: “intelligent”. As it goes down and down, rape goes up, until the two words, the formerly common “intelligent” and the formerly rare “rape” touch each other in 1997. The conclusion is clear and irrefutable (I am using behavioural science talk ironically): as we ceased to regard people as being intelligent there was a rise in rape, and feminism. Perhaps we were all too aware of dysgenic trends and, looking at people’s behaviour, the word did not spring to mind so easily.