Summer 2012

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Keeping Time

INTERNAL TIME:
Chronotypes, Social Jet Lag, and Why You’re So Tired.
By Till Roenneberg.
Harvard Univ. Press. 272 pp. $26.95

It’s late, and, as always, I have lots of things I’d like to do before I go to bed. I don’t sleep much. I enjoy being awake. My dreams are quiet, but my days are full of things to explore, the treasures of ordinary life. So when I began to read Till Roenneberg’s Internal Time, a book whose dust jacket mentions sleep and biological clocks, I was hoping to find a passage clearly stating that those who sleep less are happier and wiser, and live longer, or at least are more interesting to talk to at parties. I didn’t find it, but the book was fascinating, and so I read on, and now, at 11 p.m., I have begun to write.

The story of the daily rhythms of our bodies begins with the study of the skies. In 1729, French astronomer Jean Jacques d’Ortous de Mairan found himself wondering how the Earth’s spin affected the species around him. He kept a mimosa, one of his favorite plants, on a windowsill near his desk. Leaves furled, it slept even when he could not, and so he decided to stay up a little longer and study how it knew what to do during the day and night. De Mairan put his plant in the cupboard. There it did as it had always done, opening all of its leaves simultaneously at daybreak and closing them at night. Somehow the plant knew what was going on outside the cabinet. That was the end of de Mairan’s experiment; he left the rhythm of mimosas observed but unexplained.

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