Department of Chronobiology

There are owls and there are larks.
Owls only wake up in the morning when larks have been active for a long time. But, in the evening, owls are in top form, when larks are barely able to stay awake from fatigue.

Everyone knows this, because everyone has their own chronotype (chronos: "the time").
What determines the chronotype?
What controls sleeping and waking behavior?
What happens when it gets out of balance?

These are questions to which the interdisciplinary subject of chronobiology seeks answers.