Abstract:
Behavioural and physiological mechanisms have evolved to adapt to the cyclic variations in the environment and adjust to the temporal sequence of events present on earth (Moore-Ede and Sulzman 1981) (Sharma 2003) (Vaze and Sharma 2013). Four geophysical cycles i.e. tidal, daily, lunar and annual cycles are considered to synchronize corresponding biological rhythms that are known to persist even under constant environmental conditions (Aschoff, 1967). The daily or Circadian rhythms (term coined by Franz Halberg (Pittendrigh 1965)), are endogenously driven (Aschoff, 1958) near-24 hour rhythms found in almost all life forms examined. They are generated by internal time keeping systems - circadian clocks, and are capable of perceiving local time as well as estimating the progression of time. After the first suggestion by DeMairan (de Mairan 1729) of an internal timing mechanism, many studies aimed to establish the endogenous origins of the same (Kleinhoonte 1929) (Bunning and Stern, 1930, referred in Hamner, 1963) (Pittendrigh 1965) and others). In addition, crossing experiments between individuals with different clock periods established that heritable factors encode an internal clock (Bunning 1932) (Bunning 1973).
