Temporal Coordination of Physiologic Function

The organism, as well as its parts, usually does not function at a constant rate along a 24-hour scale; many of its diverse, discrete changes do not recur at purely chance intervals. More often than might be expected from classical physiologic knowledge, we encounter circadian (circa, dies; 1–3) repetitive sequences of events; this organization in time has apparently evolved through genetic adaptation of body metabolism to a terrestrial environment (for references see 1).