The Unfolding of Language: An evolutionary tour of mankind's greatest invention, 2: Perpetual Motion, 71

The most important discovery we have made so far is that language is in a state of constant flux. While no one in particular seems to be going about changing it, a few deep-rooted motives that drive all of us (economy, expressiveness, analogy) create powerful forces of change and ensures that sounds, meanings and even structures are always on the move. And while our capacity to accommodate synchronic variation means that we are often hardly aware that one form is usurping another, changes can proceed so quickly that after just a few centuries a language can hardly recognize itself when leafing through the old family albums.