Few elements of the living world are as ubiquitous as the circadian rhythm. Derived from Latin (circa = approximately; diem = day), the circadian rhythm is a roughly 24-hour intrinsic cycle that is the direct result of evolving on a planet with a 24-hour day–night period. The clock is found in animals, plants, fungi, and even unicellular organisms, allowing for the living world to be physiologically, metabolically, and behaviorally in tune with the external environment.1 

In humans, the reaches of the 24-hour cycle are far greater than many realize. The most well-known function of the circadian rhythm is to provide an alerting signal that waxes and wanes in a predictable fashion throughout the day. Perhaps not as well known is that organ systems and even individual cells display a 24-hour periodicity, all of which are kept in sync by the suprachiasmatic nucleus within the hypothalamus.

But what happens when...

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