Clocklike properties of limit-cycle oscillations in cells and complex organisms

The lecture is a general review of biological phenomena regulated by cellular oscillators whose period (day, month, year) is an evolved match to the major periodicities in the physical environment. These oscillators function as clocks, timing diverse events to "appropriate" times of day, month or year. Emphasis is given to oscillator properties that are not trivial analytic necessities, but rather are, evolved refinements enhancing the oscillators\´ capacity (1) to identify local time and (2) measure lapses of time. Hints at the still obscure physical nature of the oscillator are also reviewed.