Circadian clocks

The biological world is not static: organisms inhabit environments which change predictably over the course of the day and night. There will therefore be selective advantage to any individuals able to anticipate these changes and attune their physiology and behaviour accordingly. Anticipation of daily cycles is conferred by endogenous timers, biological clocks with an intrinsic period of approximately one day (hence circadian). It is now widely accepted that circadian timing is a fundamental property of life, and the ubiquitous expression of circadian rhythms has provided the biologist with many ways of looking at the clock. As a result, circadian timing now stands out as a paradigm for the explanation of how apparently complex patterns of behaviour and physiology might arise from the properties of a relatively small number of gene products, acting in single cells.