For example, plant leaves opening and closing at different times of the day or the sleep-wake schedule of animals can all include circadian rhythms.
[5] At this time, one of Alexander's generals, Androsthenes, wrote that the tamarind tree would open its leaves during the day and close them at nightfall.
[3] In 1729, Jean-Jacques d'Ortous de Mairan demonstrated that the rhythms of a plant opening and closing its leaves continued even when placed somewhere where sunlight could not reach it.
In 1923, Ingeborg Beling published her paper "Über das Zeitgedächtnis der Bienen" ("On the Time Memory of Bees") which extended oscillations to animals, specifically bees[6] In 1971, Ronald Konopka and Seymour Benzer discovered that mutations of the PERIOD gene caused changes in the circadian rhythm of flies under constant conditions.
[7] Paul Hardin, Jeffrey Hall, and Michael Rosbash demonstrated that relationship by discovering that within the PERIOD gene, there was a feedback mechanism that controlled the oscillation.
[12] In addition to these feedback loops, post-translational modifications also play a role in changing the characteristics of the circadian clock, such as its period.