The nights are drawing in, and with them for many people a sense of darkness and of discontent. The rhythm of day and night affects our health, and our cognitive functioning. When it is disturbed, we are. But our sense of upset, or even jet lag, is just a minute part of the whole living world’s adaptation to the alternation of day and night: animals, insects, plants and even plankton show a cyclical pattern of behaviour as the Earth turns. This is built into their DNA. But to get beyond that statement of the obvious, and to ask what is encoded, and how it might work, has been the labour of decades. The three American scientists who have just been awarded the Nobel prize in physiology or medicine have unpicked a complicated feedback loop whereby a gene encodes the protein that will shut its own operations down and then decay to let the gene start work again. It’s not that simple in practice but the principle is a beautifully clear example of the way in which biological clocks were built by evolution a billion years or more before humans could build mechanical ones. Some of our cleverest moments as a species come when we understand how much cleverer than us nature can be.