Rhythmic and Temporal Processes in Biology

Abstract

We are ruled by time and we need to know the time to tell us what to do. But the clocks that instruct us to wake, eat, and go to bed are unnatural. In our modern world, we are being driven by the energy states of an electron in the cesium atom and use machines to hack our day into hours, minutes, and seconds. Yet, despite the atomic clock, our bodies answer to another more persistent beat that probably started to tick shortly after life evolved. Embedded within the genes of us, and almost all life on earth, are the instructions for a biological clock that marks the passage of approximately 24 h. Biological clocks drive or alter our sleep patterns, alertness, mood, physical strength, blood pressure, and every other aspect of our physiology and behavior. Under normal conditions, we experience a 24-h pattern of light and dark, and our clock uses this signal to align biological time to the day and night. The clock is then used to anticipate the differing demands of the 24-h day and “fine-tune” physiology and behavior in advance of the changing conditions. Body temperature drops, blood pressure decreases, and tiredness increases in anticipation of going to bed. While, before dawn, metabolism is geared up in anticipation of increased activity when we wake. The past decade has witnessed remarkable progress in the understanding of circadian rhythms in many different organisms. Much of what we know of the molecules that make up our biological clockwork has been learnt from the fruit fly ( Drosophila ) and mouse. It is remarkable that species separated by hundreds of millions of years of evolutionary history are united by the ways in which they generate biological time. The understanding of the molecular basis of circadian rhythms is one of the first success stories arising from the genome sequencing projects, and is currently one of the best examples we have of how genes and their protein products give rise to complex behaviors.