THE BIOLOGICAL CLOCK AT THE SOUTH POLE

Journal/Book: Reprinted from Nature Vol. 195 No. 4840 pp. 476-480 . August 4 1962. 1962;

Abstract: By PROF. K. C. HAMNER J. C. FINN JUN. * G. S. SIROHI T. HOSHIZAKI and B. H. CARPENTER Department of Botany University of California Los Angeles *Present address: North American Aviation Inc. Space and Information Systems Division Downey California. Present address: Space Biology Laboratory Department of Anatomy University of California Los Angeles Medical Center. FOR many years biologists have known that plants and animals possess a mechanism - the biological clock - which permits accurate measurement of time. The twenty-fifth Symposium of Quantitative Biology at Cold Spring Harbor1 was devoted entirely to the subject of biological clocks. Since in many cases periodic oscillations in metabolic or physical activities have been shown to persist even when an organism is placed under conditions of constant temperature and constant light or darkness they have been regarded as manifestations of endogenous rhythms. Diurnal endogenous rhythms have been designated 'circadian rhythms' because their periods axe not exactly 24 hr. in duration. The use of biological clocks in compensating for the Sun's apparent motion has been well demonstrated' in experiments which show that bees birds and many other animals navigate to a particular goal by utilizing the Sun for orientation. It has also been shown that certain birds navigate apparently by 'sighting' on the stars and using their internal clocks much as a ship's captain uses a chronometer2 3. Photoperiodic responses of plants and animals appear to be dependent on biological clocks1. Organisms which are situated a sufficient distance from the equator are thus afforded an accurate estimate of the calendar day. Hence biological clocks serve as a key factor in survival of many species. One of the basic questions raised by students of biological clocks has been whether organisms growing under supposedly constant conditions actually may be receiving information from their environment. F. A. Brown jun.4 has pointed out that there are diurnal fluctuations in the air pressure and slight periodic fluctuations in gravity associated with the rotation of the Earth in relation to the Sun and Moon. Brown claims correlation between certain rhythms which he has been measuring and cosmic-ray intensity. However no one has definitely shown that the clock mechanism present in many organisms perhaps in all is guided by any particular factor of the external environment. Since Brown has been the chief proponent of the hypothesis that external factors over which the experimenter has no control even under so-called constant conditions are influencing the clock it seems worth while to quote briefly from two of his recent reviews. ... ___MH

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