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What makes us tick?

Q: I can wake up at a desired time (plus or minus 15 minutes). Over the years I have become proficient. My friends declaim my ability and attribute my skill to other causes. Can you explain this ability please? --"Wake us up", Huntsville, Texas

A: You share an ability with creatures large and small. Bats wake up to hunt because their clock tells them it's dusk--summer or winter, no matter. A white-crowned sparrow fattens for weeks ahead of migration time because his clock triggers. A honeybee knows the exact time to visit a particular flower--when that flower is making nectar. Her "alarm" goes off and she flies to that flower to sip the sweet liquid.

[Corel] A bio clock ticks deep in our brains

Biological clocks exist and you have one. Why you can set your alarm clock and wake up when you want takes us to the frontiers of knowledge. We barely understand how the clock works. According to experts, no study has rigorously investigated your question. So, I cannot answer your question completely but I can explain how bio clocks work and discuss an alarm system that bees "learn". Perhaps your alarm system evolved from a similar need.

Worker bees have no daily rhythm when they first emerge from their cocoons as adults. They work in the hive tending the queen, keeping house, and caring for the brood: tasks that busy them around the clock. Later, they emerge from the hive and forage for food.

Forager bees live or die by the clock. They must know when a flower opens shop and offers its nectar. They "learn" to use a clock. Out a bee goes. When she finds a flower that's open and she gathers its nectar, she records the place and time: say, 11 a.m. The next day at 11 a.m., a nerve synapse sends a message to the bee's brain and the bee returns to that flower and gets its nectar. Otherwise, if the bee gets no nectar from a flower, she makes no entry in her brain. In this fashion, the new forager gradually builds a flower diary and makes her daily rounds accordingly.

Animals use their clocks so many ways it's difficult to see how they could survive without such a mechanism. Our common clock reflects either a common evolutionary ancestor or a clock that arose from the same overpowering need but along several evolutionary paths.

Whatever the source, almost all animals have bio clocks and they work much in the same way. In humans, the clock is a system with three primary elements: a clump of brain cells (called the SCN), light receptors in the eye that talk to the SCN, and a gland that makes hormones when the SCN says to. Next week I'll explain how these elements tell time.

(Answered Aug. 2, 2002)

Further Surfing:

PBS, Nature: how a bee's brain senses time

Moore D, Siegfried D, Wilson R, and Rankin MA (1989) The influence of time of day on the foraging behavior of the honeybee, Apis mellifera. Journal of Biological Rhythms 4: 305- 325.