The human mind and body have a built-in circadian system, a coordinated assembly motivated to perform certain tasks, what we might call the macrobiological clock. At the molecular level there is a circadian oscillator, specific cell groups that work together, like the mechanism of a clock, to cause a larger system of mind and body to function in a daily rhythm. In the early 1980s Jeffrey Hall and Michael Rosbash, along with Rosbach’s graduate student Paul Hardin at Brandeis, discovered such a circadian oscillator in the fruit fly, an insect that has timekeeping gene qualities associated with clock genes in humans. Hall and Rosbash won the 2017 Nobel Prize in Physiology or Medicine for their discoveries of the molecular processes that control circadian rhythms.
— Read on m.nautil.us/issue/83/intelligence/how-your-body-knows-what-time-it-is