The Circadian Clock

Volume 12 of the series Protein Reviews pp 1-35


A History of Chronobiological Concepts

  • Serge DaanAffiliated withUnit of Chronobiology, University of Groningen Email author 

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The perpetual alternation of night and day could not escape being noticed by the earliest humans. It must have marked to them the passage of time. Tilling their fertile soil, the early Sumerians needed precise knowledge of time. When should the wheat be sown, when be harvested? How many days to wait till the great floods in spring? How allocate their stores of grain such that daily rations would last till the new harvest? Scores of practical questions. The Sumerians went to their temples to seek the answers. Much more than the nomads’ opportunistic way of life, early agricultural civilisation relied on planning, on anticipation, on keeping track of time. There was a growing caste of those who assembled the information: the priests. They noticed the rigid patterns of annual change in the sun’s position. They started to observe the movements of other celestial bodies. They constructed their temples almost as astronomical observatories, with the major axes aligned to the stellar constellation on days of importance. The priests in Sumer were the first, but not the last in this respect. Most of the Mesopotamian temples, such as the Ziggurath in Babylon had a long East–West axis. In Egypt, temples were often oriented towards the direction where the sun rises on the longest day. Once per year, at dawn of the summer solstice, the first rays would illuminate the god-statue at the end of a narrow pillar gallery. Much later, the Incas in South-, the Anasazi in North America again dramatized special days in the annual cycle by the architecture and orientation of their places of worship. It was the place where priests engaged both in scientific observation and in religious duties. It also became the great storage room of past observations and events, of accumulating knowledge. The observation of stellar constellations as a means of measuring time became the first scientific activity in most early settlements, long before the cause of their movements was evident.