Biologic Rhythms from Biblical to Modern Times. A Preface

Abstract

The origins of chronobiology go back to the very beginning of life on this planet. Living matter and the evolving organisms were exposed to the earth’s revolution around the sun with its periodicity of day and night, of light and darkness, with the periodic changes in the length of the daily light and dark span and with the climatic changes of the seasons. In addition some aquatic forms of life especially were exposed to the periodic input provided by the cycles of the moon with its influence on ocean tides. Adaptation to the periodically changing environment on our planet was a necessity for the earliest and all later forms of life. The related periodic functions — originally in response to the environmental stimuli — seem to have impressed themselves on the genetic makeup of living matter. Periodic variations, many but not all of which follow the frequencies of the periodic environmental input, are found in the most primitive and ancient forms of life presently available for study. Many other periodic functions, however, ranging in the length of their cycle from milliseconds (as in the activity of single neurons) to seconds (such as the heart and respiration rate) and to months (such as the menstrual cycle in sexually mature women) have no known environmental counterpart. Some biochemical and biophysical mechanisms creating or maintaining periodic functions at the cellular level are related to the genetic material in nuclear DNA, while others are apparently functioning apart from nuclear material in relation to membranes or to metabolic processes in the cytoplasm (Edmunds, this volume; Lakatua, this volume).