When this hoot owl is just heading out for the night to do some hunting, you’re dropping off to sleep. And in the morning, when you get up and stretch and head for the shower, well that owl will be tucking himself in for a long day’s rest. We creatures aren’t all on the same schedule, but we’re all listening to the ticking of our biological clocks. Im Jim Metzner, and this is the Pulse of the Planet, presented by DuPont.

“Biological clocks are a fundamental characteristic of almost all living organisms.”

Vince Cassone is professor of biology at Texas A & M University.

“They time everything. They make us wake up in the morning and they contribute to making us go to sleep. They make us become hungry at certain times of the day and they control almost all of our biological processes.”

These biological clocks are at work in everything from bread mold to Monarch butterflies to humans. They’re what makes the corn grow higher in summer, geese fly south in the winter and your cat’s fur start getting thicker before the weather turns cold. In animals, the core of the biological clock is in the brain. And in humans, scientists have determined exactly where it’s located.

“It’s actually, literally at the base of the brain. Just really right between our eyes.”

And that makes sense, because in humans, and most organisms, the biological clock is primarily triggered by light. A part of your brain gets light messages from the retina, and then tells your body what it needs.

“The hormones involved in digestion can be marshaled before you have to have a meal, and we can marshal up metabolic enzymes and glucose before we’re ready to wake up.”

And it’s your biological clock that tells your body to start pumping sleep hormones, when it’s time to call it a day. There’s a lot more to biological clocks, on our next program. Pulse of the Planet is presented by DuPont, bringing you the miracles of science. With additional support provided by the National Science Foundation. I’m Jim Metzner