Why Do Some People Prefer ‘Morning People’ and Others Are Night Owls?

Some people wake up easily, while others need more time to get going. Imagine your body has a clock inside it that tells you when it's time to be awake or sleepy. Some clocks are set for early mornings, like birds that sing at dawn, they're called morning larks. Others have clocks that say, 'Why wake up now? I'm still having fun!', these people are called night owls.