TIME MATTERS: Biological Clockworks

Introduction

The period of twenty-four hours formed by the regular revolution of our Earth...is apparent in all diseases... It is, as it were, the unit of our natural chronology.
— Christopher William Hufeland, 1796

We live in a clockwork universe — regulated by astronomical forces like the movements of planets and forces like gravity. The spinning of the Earth imposes a 24-hour cycle of night and day on its inhabitants and most have adapted by evolving their own internal timepieces tuned to a 24-hour day. These internal timing mechanisms, or biological clocks, are in many ways analogous to mechanical clocks. They run at a reasonably accurate rate. They can be "reset." And they keep accurate time despite fluctuations in temperature. At the heart of any mechanical or biological clock is a mechanism that can produce a reliable oscillation — a repetitive motion or occurrence that can be used to measure time accurately.

The existence of biological clocks has been suspected for centuries, but for most of human history little was known about how they worked. In the last few decades — with enormous advances in molecular biology and genetics — the detailed chemical workings of biological clocks have begun to be understood. This exhibit explores the inputs, outputs, and mechanisms of biological clocks with a primary focus on circadian rhythms — circadian being a term that biologists use to describe biological mechanisms on the scale of a day, from the Latin meaning "about a day."