Nineteenth-century philosophers proposed that God was a clockmaker who created the world and then let it run. Modern biologists might in part agree, for it's clear that evolution has carefully crafted clocks that allow almost all organisms to follow the rhythm of the sun. Now that they better understand the cellular clock, scientists can begin to manipulate it, with applications from curing jet lag to brightening winter depression.
Clock genes glow in the cells of a fruit fly.
JEFF HALL Clocks made the Runner-Up list in 1997 too, after researchers identified the first two mammalian clock genes, Clock and per . This year a prodigious amount of work from the clock research community filled out the story dramatically. These two proteins eventually shut down their own genes. But to keep the proteins on a 24-hour cycle, PER and TIM's turnoff must be delayed. Discovering all this in one organism would be breakthrough enough, but researchers found the same proteins or close variants playing the same roles in mice, too.