A number of factors have probably contributed to this, including: (1) Circadian rhythms are not essential in the lab, although they presumably do contribute to survival in the wild.

The ensuing 35В years of circadian biology have made circadian rhythms the best understood behaviour at the molecular level. But Konopka and Benzer succeeded in identifying the first three clock mutants, all in the period (per) gene: a null allele ( per 01) that led to a complete loss of rhythmic behaviour, and two alleles that left rhythms intact but gave flies either short-period (19В h) or long-period (27В h) rhythms in DD. When Konopka and Benzer initially screened mutant flies for disrupted circadian rhythms, others were sceptical that mutating a single gene would have much effect on a complex behaviour. More recently, this molecular understanding has been used to move towards an understanding of the neural circuits driving circadian behaviour. However, the mechanisms underlying temperature compensation remain mysterious. It was the identification of the first clock gene mutants by Konopka and Benzer in Drosophila that opened a door which ultimately led to a detailed molecular understanding of how intracellular clocks tick and how they are reset by light. This last feature of molecular clocks is important not just for cold-blooded animals like Drosophila, but also for mammals given the daily fluctuations in body temperature, and especially for hibernating animals. In one classic paper, Colin Pittendrigh demonstrated that the clock that drives rhythms in eclosion (hatching of adults from their pupal case) free-runs with a circadian rhythm in constant darkness, can be reset by light delivered during darkness and runs with an в€ј24 h period over a 10вЊ temperature range-a phenomenon known as temperature compensation. Many of the pioneering experiments on circadian rhythms were performed in Drosophila. Since these rhythms run with an approximately 24 h repeating period under constant conditions, they are termed circadian-вЂabout a dayвЂ™. He found that leaves continued to show daily cycles of opening and closing even in constant darkness (DD), indicating the existence of an internal clock.

Having observed a daily cycle of leaf opening and closing in heliotrope plants, he asked what would happen to this rhythm in the absence of environmental cues by moving the plants to his dark wine cellar. The existence of an endogenous clock was first reported by French geophysicist Jean-Jacques dвЂ™Ortous de Mairan in 1729. In contrast, reindeer that live in the Arctic abandon daily activity rhythms during summers of constant light and winters of constant darkness since an endogenous circadian clock is apparently unnecessary without daily environmental changes to anticipate.

In other words, circadian rhythms are very important for the normal well-being of an animal because they enable an organism to anticipate and respond to environmental changes before they happen. Circadian rhythm disruptions can lead to depression, obesity and higher incidences of cancer and have even been implicated in the sensitivity of an organism to drugs of abuse. In addition to controlling the timing of sleep/wake cycles and thus influencing alertness, circadian clocks in mammals have been shown to control rates of drug detoxification, bone growth, liver regeneration and cell division. This small, yet statistically significant effect, as recorded from 1991вЂ“1993, may even have accounted for the Atlanta Braves winning their division by one game from their West Coast rivals in 19. This effect decreases as the visiting team acclimatizes during the course of a three- or four-game series. In Major League Baseball, the effect of jet lag on West Coast teams that travel to the East Coast (but not vice versa) increases the chance of East Coast teams winning home games. The roles of these internal clocks in our lives can perhaps most clearly be understood by seeing what happens when our clocks become desynchronized from the environment.

Yet virtually all organisms from Cyanobacteria to humans have an internal circadian clock that allows them to anticipate daily environmental changes and to alter their behaviour and physiology accordingly. Intuitively, an organism could optimize its behaviour and physiology by responding to daily and seasonal changes in the environment.

Dclock date font size