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Nature Reviews Molecular Cell Biology 6, 965–971 (1 December 2005) | doi:10.1038/nrm1766

Circadian clocks |[mdash]| the fall and rise of physiology

Till Roenneberg & Martha Merrow

Circadian clocks control the daily life of most light-sensitive organisms — from cyanobacteria to humans. Molecular processes generate cellular rhythmicity, and cellular clocks in animals coordinate rhythms through interaction (known as coupling). This hierarchy of clocks generates a complex, |[sim]|24-hour temporal programme that is synchronized with the rotation of the Earth. The circadian system ensures anticipation and adaptation to daily environmental changes, and functions on different levels — from gene expression to behaviour. Circadian research is a remarkable example of interdisciplinarity, unravelling the complex mechanisms that underlie a ubiquitous biological programme. Insights from this research will help to optimize medical diagnostics and therapy, as well as adjust social and biological timing on the individual level.