In the last century, the linguist George Zipf noticed that the second most common word in English ("of") was used about half as often as the most common word ("the"), the third most common word ("and") occurred about one-third as often, and so on. This curious behavior, that the frequency of any word is inversely proportional to its ranking in the list of words, became known as Zipf's Law. Others had noticed the same behavior for the populations of cities, namely, that the second most populous city had roughly half the population of the most populous city, the third most populous city had one-third the population, and so on. Scientists studying the detection of faint signals in a background of noise also began to notice a similar effect, with most systems having a component of noise whose intensity varied inversely with the frequency, so-called "one-over-f" noise. Theoretical statistical analyses have found many other cases in which Zipf's Law, or close approximations to it, could result from quasi-random distributions of the element being considered, whether words or cities. There are many slight deviations, however, and no consensus exists on the origin of Zipf's Law.
"Zipf's Law from Scale-Free Geometry," Henry W. Lin and Abraham Loeb, Phys. Rev. E 93, 032306, 2006.