“What watch?... such much!” Complexity and evolution of circadian clocks

This review uses three examples to summarise our knowledge about the complexity and the evolution of circadian systems. The first example describes the ecology of unicellular algae, which use their circadian system to optimise the daily exploitation of resources that are spatially separated. The second example looks at the role of clocks in tissues and cells within a complex organism, and the third speculates on how the circadian system may have evolved.