Abstract
Living on earth has made us use the sun as reference and the 24-hour succession of light and darkness is probably the most pervasive epigenetic influence in the evolution from a single cell organism to man. This periodic succession of light and darkness provided the base for relative timing of biological processes over the 24 hours of a day. Because energy supply is the limiting parameter for survival, a system for optimal timing of energy expenditure and uptake developed. The mechanism of this system took the shape of a cycle reflecting the recurrence of sunrise and sunset, and is termed a " circadian clock"–a clock with a period of about one day (latin: circa diem). The internalization of environmental time within the organism not only allows organization of biological processes along the 24-hour time scale but also prediction of recurring events, such as availability of food and emergence of predators. Therefore it is not surprising that alterations in the genetic machinery of the circadian clock leads to alterations in biochemical and physiological processes.Data illustrating the influence of the Per2 gene on adaptation to changing lighting conditions, addiction, the aging process and food anticipation will be presented. [J Physiol Sci. 2006;56 Suppl:S16]
