Listen," he says, frowning, "there are these things called clock genes.

It is extremely likely that in humans too there is a clock gene, probably on chromosome 4.

This result provides further evidence that the clock gene has a profound impact on metabolic processes in mice.

And there are other clues, like a clock gene associated with fruit flies that has recently been identified in humans.

What researchers hope to determine is where the clock genes might fit in among the major theories of aging.

Dr. Hekimi thinks the clock genes tie into the second theory.

The specific clock genes are not conserved across distant species, but the underlying mechanism is the same.

Mutations in some of these shared clock genes can cause sleep disorders in people.

This negative feedback mechanism gives a 24-hour rhythm in the expression of the clock genes.

IN another step toward understanding the daily rhythms of life, scientists have identified the first biological clock gene in plants.