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Biological clock is a popular name given to a mysterious timing system that operates in plants and animals. It keeps accurate time of days, weeks, months, and even years. It also times the activities of living things to keep them in harmony with the regular changes of their surroundings. Birds migrate, fish spawn, and flowers blossom on schedules set by their built-in clocks. The biological clock in human beings times our periods of sleep and wakefulness and many body activities.

No one knows where this biological clock is located, or how it works. Some scientists believe that every living thing has its own built-in timing system that operates independently. Others believe that the clocks are set by the natural rhythms of the earth’s electromagnetic or gravitational forces. Still others suggest that forces both inside and outside the body are necessary to keep the clocks accurate. Scientists hope that experiments with plants and animals in outer space, far from the earth’s natural rhythms, may provide more information about how biological clock works.

Biological clocks keep track of rhythmic changes in the environment, including day and night, movements of the ocean tides, phases of the moon, and seasons of the year. Many, and possibly all, living things seem to have internal cycles – called biorhythms – that respond to these external rhythmic changes. The biorhythms of each particular species seem to be timed to enable the organism to take advantage of the changes in its environment. Biorhythms continue on schedule even in laboratories where the plant or animal is shielded from all evidence of passing time and of outside change. But the biorhythms can be shifted – and the biological clock reset – by changing the time at which the plant or animal gets light.

Biological clocks in people work on schedules essential to life and health. Many vital body processes are programmed for 24-hour biorhythms. The functions of cells, glands, kidneys, liver, and nervous system are all coordinated with each other and with the day-night rhythm of the environment. Each is timed to operate when it can do the greatest good for the entire body.