147. Drift, noun/verb. Traceable to the Proto-Indo-European root dhreibh, “to drive; to push.” A small, ordinary word that expresses many big scientific ideas about gradual effects.
The matter—rocks and sediment—that glaciers and their melting waters leave behind them as they move is known as drift; so is any randomly-driven—as opposed to adaptive—change in the commonness of a particular gene variant in a population as generations pass. A laboratory animal (or a human being) that reverts to its natural behaviors over time, even if these behaviors contradict a conditioned response, is said to be manifesting instinctual drift. Geologists don’t tend to use the term “continental drift” very much anymore, but there’s still no better way to describe the slow, inexorable wandering of the pieces of the surface of the earth that we now call plates.
There’s an impressive drift on the side of your tent, says K. on the second day of the blizzard, kicking crystals off her boots as she opens the door of the weatherport. I grab my gloves and hat and run outside to look. I feel, taking this picture, an inexplicable pride. There is snow everywhere—but not all of it has gathered into something more than powder, something like a form. It is my drift, I think: my stray, stochastic accumulation.