The earliest recorded account of a circadian process dates to the 4th century BC. Theophrastus described a tree with many leaves like the rose that closes at night and opens at sunrise. He noted that natives said this plant goes to sleep during the evening hours. This observation came from Androsthenes, a ship's captain serving under Alexander the Great. Later botanists identified the tree as the tamarind species. Chinese medical texts from around the 13th century mentioned circadian processes in humans. These documents included the Noon and Midnight Manual and the Mnemonic Rhyme to Aid in the Selection of Acu-points According to the Diurnal Cycle.
Experiments In Constant Darkness
Jean-Jacques d'Ortous de Mairan conducted his first experiment in 1729. He observed 24-hour patterns in the movement of Mimosa pudica leaves. The plants persisted in their rhythm even when kept in constant darkness. Patrick and Gilbert reported similar findings in 1896 regarding sleep deprivation periods. J. S. Szymanski showed animals maintained 24-hour activity patterns without external cues by 1918. Colin Pittendrigh demonstrated eclosion rhythms in Drosophila pseudoobscura in 1954. Temperature changes delayed but did not stop these biological cycles. Auguste Forel, Ingeborg Beling, and Oskar Wahl studied rhythmic feeding times in bees during the early 20th century.Genetic Clocks And Feedback Loops
Ron Konopka and Seymour Benzer identified the first clock mutation in Drosophila in 1971. They named the gene period or per. Michael W. Young's team discovered the gene covers a 7.1-kilobase interval on the X chromosome. Jeffrey Hall, Michael Roshbash, and Young received the Nobel Prize in Physiology or Medicine 2017 for this work. Joseph Takahashi found the first mammalian circadian clock mutation using mice in 1994. Chris Jones identified the first human clock mutation in an extended Utah family. Ying-Hui Fu and Louis Ptacek characterized this mutation as a single amino acid change in the PER2 protein. The molecular mechanism involves interlocked feedback loops of gene products creating periodic fluctuations.