Adaptive cycles: Their significance for defining environmental hazards

Abstract

Among the great variety of biological rhythms with frequencies from less than 1/msec up to 1/several years,there are four rhythms which represent adaptations to time structures of the environment. These are the tidal, the diurnal, the lunar, and the seasonal rhythms. Using the diurnal or "circadian" rhythm as the most extensively studied example, the paper describes: (a) the properties of biological, self-sustained oscillators under constant conditions as well as under the influence of a synchronizing environmental rhythm; (b) the multiplicity of rhythmic functions in an organism, especially those of sensitivity to external stimuli, and (c) cases of internal desynchronization in man. After a brief outlook to rhythms with lower frequencies (weekly and seasonal rhythms), the final discussion deals with the problem of defining environmental hazards with regard to temporal organization in the environment as well as in the organism.