Have you ever noticed that you seem to get tired or hungry at about the same time each day? That’s no coincidence. It’s your circadian rhythm at work.
No, circadian rhythm isn’t the latest dance craze from the makers of Now That’s What I Call Music Vol. 1,240. The circadian rhythm is a 24-hour cycle that all living things — including plants, bacteria, and other animals — experience. The first modern scientific study of the circadian rhythm occurred in 1729, when Jean-Jacques d’Ortous de Mairan, a French astronomer, noticed that his plants opened and closed at the same time every day. Curious about this behavior, he then placed all his plants in total darkness and observed that they continued to open and close at the same time despite the absence of light.