Chrono‐colloquium: On the origin of circadian rhythms

Abstract

The common view that circadian rhythms evolved as an adaptation to the exogenous daily cycle is questioned regarding early eukaryotic unicellulars. An alternative explanation of their origin is presented: circadian ‐ and other endogenous ‐ rhythms made available a temporal coordination mechanism to those intracellular symbioses which developed into eukaryotic cells. For the functioning of such associations a synchronization between host cells and endosymbionts has to be considered essential. It may have been achieved by the coupling of cellular activities to endogenous rhythms.