Laura Bonetta | Feb 3, 2002 | 10 min read
Circadian clocks—the biological timekeepers that operate on a daily cycle—keep virtually every living creature in tune with its environment. These internal clocks regulate a wide range of fundamental biological processes, including movement, smell, sleep, mating, and feeding. A true circadian clock is endogenous; that is, it keeps time even in the absence of external cues. The clock can, however, be reset, or entrained, by daylight, allowing the synchronization of circadian rhythms t