Circadian Rhythm

The drowsiness that arrives every October has more to do with light than temperature, and the warm room may be doing more harm than the cold outside.

Plants that fold their leaves at night aren't wilting or sleeping — they're running an evolved, energy-spending routine called nyctinasty.

Seventy percent of people are biologically wired for a sleep schedule the workweek doesn't respect. Social jet lag is what happens when body clock and calendar keep disagreeing.