Circadian clock

Their work began in the nineteen eighties when they isolated the period gene in fruit flies and showed that the protein it encodes oscillates in concentration over a twenty-four-hour cycle.

The discovery that the same clock genes exist in organisms ranging from fruit flies to fungi to humans demonstrated that the circadian clock is an ancient evolutionary innovation shared across the tree of life.

Even cyanobacteria, single-celled organisms that evolved billions of years ago, have circadian clocks that regulate their metabolism in response to the daily cycle of light and dark.

The cyanobacterial clock uses a completely different set of proteins than the animal circadian clock, suggesting that biological timekeeping may have evolved independently more than once.

The universality of circadian rhythms in living things suggests that the ability to anticipate the daily rotation of the Earth provided such a strong survival advantage that it was maintained across billions of years of evolution.

Plants also have circadian clocks that control when they open and close their leaves, and this was actually one of the first circadian rhythms ever documented scientifically.

In seventeen twenty-nine, the French astronomer Jean-Jacques d'Ortous de Mairan placed a mimosa plant in constant darkness and observed that its leaves continued to open and close on a roughly twenty-four-hour cycle, even without sunlight.

De Mairan's experiment is generally considered the first scientific demonstration that a living organism has an internal clock, rather than simply responding to external cues.