Saturday, June 04, 2005

Circadian rhythms

Since last I posted, I've flown the Atlantic and settled myself for the summer in Ireland. I've reset my watch, turned the small hand ahead five hours. Reset the clock in my laptop. There's one clock I can't reset so quickly -- the one inside my body, the tick-tocking proteins that tell my body when to wake and sleep.

Eventually, my body clock will reset itself in response to signals from specialized photoreceptors on the retinas of my eyes. The clock will change its rate of ticking until it is again in synch with light and dark.

Mosquitoes, morning-glories, even bread molds possess biological timekeepers; only the most primitive single-cell organisms appear to be without internal clocks.

"We live in an old chaos of the sun, or old dependency of day and night," wrote poet Wallace Stevens. The Earth spins and carries all living things into light and shadow. Anthropologists tell us that the primary myth of human culture is the story of the luminous hero who goes into darkness and returns triumphant. Our bodies hum with the solar rhythms. All complex plants and animals have innate biochemical metronomes beating in time with the spinning Earth.