Circadian rhythms appear to be simply one type of component within a biogeosolunar rhythmic complex. The complex includes in addition to the solar-day ones, lunar-day (tidal), monthly, and annual rhythms which, like the circadian, may persist in constancy of all obvious environmental factors and display complete or nearly complete apparent temperature- and drug-independence. Steadily accumulating evidence suggests that this complex is widespread among plants and animals, perhaps omnipresent. Especially over the past 15 years, a number of kinds of newer observations on circadian rhythms have demanded for their explanation that information, including timing from the fluctuating external environment, be continuously available to the organisms exhibiting rhythmicity in the previously presumed shielded experimental conditions. An intensive investigation of the nature of this information has disclosed that organisms possess an extraordinarily specialized, receptive capacity for the natural geoelectromagnetic fields. Responsiveness to these fields has been demonstrated to be related to all the organismic geosolunar rhythmic components. Responses to such overt environmental factors as light and temperature have been shown, furthermore, to interact with the subtle geophysical responses in manners suggesting significance for biological clocks and compasses. Several of the properties of the subtle geophysical responses which have been uncovered, collectively now permit a rational explanation for the timing of circadian and other geosolunar rhythms without the classically postulated independent, intraorganismic "durational" timers for these periods. Organisms have been demonstrated to possess exactly that composite of capacities needed to enable them to use exogenous "coordinate" timing of circadian and other rhythmic physiological patterns.