Protein may help the eyes tell time
By John Travis
The light-sensitive skin cells of the African horned frog may have resolved a lingering mystery about the internal biological clock that all mammals possess, suggests a new study.
This physiological timepiece, whose period is almost exactly a day, governs many bodily rhythms. To synchronize with the day-night cycle of the outside world, the mammalian biological clock adjusts itself daily by sensing sunlight and other stimuli.
How the clock detects illumination has long puzzled scientists. They know that human eyes perceive illumination and convey a signal to the portion of the brain where the clock resides.