In this review we present facts and comments on the evolution of the timing systems ("biological clocks") in humans. In the Introduction we define basic concepts of Chronobiology which will be used along the paper. In the four following sections we discuss landmarks which characterize biological rhythmicity in distinct moments of ontogeny: infants, adolescents, adults and elderly. We close the review with an invitation to consider the perspectives now open in this new area of knowledge.
Chronobiology; Human development; Biological rhythms; Sleep wake cycle