History of Mystery
This pretty little plant looks unexceptional, but it belongs to a mystery dating to the eighteenth century. At that time, French scientist Jean-Jacques d’Ortous de Mairan noticed that the plant had a quirk. As night fell, its leaves would fold inward and close up, while at dawn, the process would reverse. De Marain assumed the plant was reacting to the daily changes of light and dark, but when he tested his explanation by enclosing the plant in a light-tight box, he discovered that the plant continued its 24-hour routine in total darkness.
Did the plant have an internal clock to dictate when to open up, and then close, its leaves? And if Mimosa pudica had such a clock, did other plants and animals have a secret inner mechanism too? And how about people? Might people be governed, in some way, by an internal clock of which they were unaware? This thought may have unnerved de Marain, or he may have wondered whether other factors accounted for the plant’s behavior. At any rate, he did not publish his work. Today we only know of his observations because a colleague published his study for him.
Many other experiments belong to the history of mystery surrounding circadian rhythms, including two by other Frenchmen. One involved a researcher who trained bees to show up for sugar water during a two-hour period each evening. Then, one night, the man flew his bees from France to New York. The bees continued to show up for sugar water just as before–on French time!
The other experiment featured Michel Siffre, 23, as a 24-hour guinea pig seven days a week for two months. During that time, Siffre lived in a dark cave completely cut off from the world: no mail, no television, no phone calls. And, since this was 1962, no texting.
What did Siffre do in the cave besides freeze? He conscientiously sent signals to his colleagues on the surface of the earth, so they could track his patterns of sleeping and waking to find out what happened when a person was enclosed in a light-tight situation, just as Mimosa pudica had been. But Siffre’s internal cycle of waking and sleeping was not 24 hours long: it turned out to be 24 1/2 hours long. Consequently, without the cues of the dawn and dusk, or the guidance of an alarm clock to keep Siffre in synch with the calendar, real, 24-hour days marched on faster than Siffre’s 24 1/2-hour approximations.
When it was time for Siffre’s friends to rescue him from his self-imposed exile, Siffre thought they were joking. To him, it was August 20–not September 14!
These experiments suggest that a variety of organisms may live by an internal clock, but it may not be exactly a 24-hour clock. In addition, this glimpse of the tip of the iceberg of research on circadian rhythms shows that internal clocks can drift without external cues, especially the powerful sun.
Elizabeth Saenger, PhD