Circadian Rhythmicity: Is the “Biological Clock” Hardware or Software?

Abstract

Awareness of the influence of external rhythms such as seasons, Tides and the solar day on organisms, Plants and animals including humans, dates back to the early advent of human culture (Waterhouse 2001). One of the earliest demonstrations of an intrinsic or endogenous free-running daily rhythm in organisms is often acknowledged to be that of the nyctinastic day/night movements of the pinnulae of leaves of the higher plant Mimosa by (1729). Pioneers of higher-plant chronobiology are Wilhelm Pfeffer (1845–1920) and Erwin Bünning (1906–1990). Notwithstanding much work producing a wealth of evidence, even in the latter half of the twentieth century, It often occurred — as occasionally mentioned by Erwin Bünning—that the notion of a “biological clock” was associated with parascience. As recently as 1989 one could still read that biorhythmicity and the “biological clock” belonged to the field of parabiology together with fire-walking, The divining rod, And the like (Resch 1989). Conversely, International societies and journals of chronobiology were founded, And indeed occurrence of endogenous “daily” rhythmicity in organisms including green organisms such as the prokaryotic cyanobacteria, Eukaryotic unicellular and multicellular algae and higher plants is now a solid fact.