[Evolution of the circadian organization (author's transl)].
The evolution of cicadian rhythmicity was possible by selection and mutation. Rhythms which strongly deviate from the circadian rhythms are still existent in case no selective pressure has occurred. An evoluution regressive to those strongly deviating rhythmus can be observed in case the selective pressure has disappeared. The circadian rhythmicity in the various cells and organs of multicellular organisms has not got lost during the evolution. But certain organs have grown important for maintaining the circadian organization within the body and for allowing the synchronization with the light-dark cycles. In addition, contrary to lower organisms, certain processes, e. e. photoreception, are coupled to the circadian rhythm only in specially differentiated organs. The high precision in the clock's running within higher organisms becomes possible by mutual synchronization within the multioscillator system.