Circadian rhythms and the circadian organization of living systems.

The writing of this paper has been influenced by strongly held convictions. This does not concern the validity of the theoretical scheme it offers; it concerns the need at this juncture in the study of “daily” rhythms for bold and explicit theory formation. We are beset rather than blessed with an enormous number of observations about a great diversity of organisms that range from unicellulars through African violets to man. Moreover, the fact that a majority of these observations is highly fascinating is itself a danger-the common danger threatening the biologist of mistaking acquisition of more fascinating facts, and more concrete detail, for analytic progress. To make progress analyzing circadian rhythms we must perceive what the problems are-or rather state what we take them to be-and proceed with accumulation of new information only as it tests, and alas probably eliminates, theory. The low life-expectancy of any detailed explanatory scheme in this field is no reason to eschew theory formation altogether. On the contrary, I take it there is an infinity of facts, relatively few of which are necessary for an understanding of general principles; and that the function of theory is not only, or even principally, to state one’s best estimate of those principles as to minimize the error in improving that estimate through discovery of new fact. The applied mathematicians and physicists from whom we are seeking models and analogs wish to know not all the facts but the significant facts. And one can rebut the likely objection that which are significant is something known only in retrospect by insisting that present judgment on the matter is necessary to proceed. Theory formation, then, involves judgments-especially in a loosely defined field; judgment on what the problems are; and judgments on which are the most pertinent of all the available observations. It is, in brief, a tool for what remains to be done. At any rate it is in this spirit that the present essay has been written; I have chosen for emphasis those facts I think are significant. I have discussed everything in this paper so many times with my colleague, Victor Bruce, that I am uncertain where many ideas came from; several I know came from him. This, however, is not to imply that he condones all my interpretive ventures. I am indebted also to Ewald Pauming and Dorothy Minis; to my students Drs. Burchard, Roberts, and Menaker, and Messrs . Swade, Plumlee, Weiss, Tobin, and Golden-they have all contributed to the experimental results used here. And finally I take pleasure in expressing deep gratitude to Professors Aschoff and Bunning in whose laboratories I recently spent several profitable months while enjoying a Guggenheim Fellowship. I owe a special debt to Mr. Swade for permission to reproduce and interpret some unpublished records of his on arctic mammals; it goes without saying that he cannot be held to my views of their meaning. His work and all the other experimental results from our laboratory reported here were made possible by funds from several sources; from the Eugene Higgins Trust; the National Science Foundation; the Office of Naval Research; and the Air Force Office of Scientific Research.