Even your houseplants keep time

In 1729, the French astronomer Jean-Jacques d’Ortous de Mairan put a mimosa plant in a dark cupboard. Its leaves kept opening and closing on a daily schedule, with no sun to guide them.

That was one of the first hints of an internal clock. The plant was not only reacting to daylight. It was anticipating it.

Nearly every living thing on this planet carries such a clock, from bacteria to trees to us. Life evolved on a spinning planet, and it learned to plan ahead.