I’ve been trying to find this quote for some time now and finally have located it. It’s from the Prologue of William Rosen’s The Most Powerful Idea in the World (Random House, 2010):
“Once humanity was tethered to the ground where its food grew, settled societies developed; and in them, hierarchies. The weakest members of those hierarchies depended upon the goodwill of the strongest, who learned to operate the world’s longest-lasting protection racket.”