I have read Pinker's "Language Instinct" and several other of his books as well.  We agree, it's a great book and so well written, but I don't recall anything like what I mention above included in any of them, although, it's been five or six years or so since I read them.  You are also right, Pinker is a well-regarded scientist, and my source is, well, a well-regarded author, but no scientist.  My reference is a human interest, light-hearted story on National Public Radio (NPR) last week which can be found at this URL: http://www.npr.org/2011/02/07/133571685/Our-Love-Affair-With-Euphemisms.  In it Ralph Keyes, author of "Euphemania: Our Love Affair with Euphemisms" answers a question with this comment, "It's well-known that some people who suffer certain kinds of stroke lose their ability to speak, but they don't lose their ability to curse. And this has led linguistic researchers to conclude that swearing comes from a very primitive part of our brain and almost as not language at all. It's closer, say, to a dog's barking than to actual sophisticated conversation."  There is more, but this is the core of the idea.