The Time of Your Life
Everyone has a clock in their brain that organizes daily life. This clock, a pinhead-sized cluster of nerve cells, makes you feel more alert or more sleepy at some times of day than at others.
Your body clock also directs manual dexterity, ups and down in reaction time, and the the rise and fall of body temperature and blood pressure over the day. It sparks hunger pangs before your usual meal times, controls how fast medications work, and directs the timing of hundreds of functions that make your body run smoothly.
Your body clock ticks in sync with the earth's light/dark cycle, and daily exposure to sunlight anchors your inner clock to a 24-hour schedule. Cut off from sunlight, the clock runs on a schedule that is close-to, though not exactly, 24 hours long.
Daily life on earth conforms to our planet’s light/dark cycle. Living things stay most active when they can find food most easily. For humans, that's the daytime.
The discovery of fire, and the invention of electric lights a little more than a century ago, made it possible for people to work and engage in other activities any time of day or night. Nevertheless, people still function better in the daytime, and sleep more soundly and longer at night.
Even if they sleep in the daytime, and work at night, people still experience bouts of sleepiness, typically between about 4 AM and 6 AM. On days off, most people—regardless of their work hours—prefer to stay awake in the day, and sleep at night.
Some people feel and function better early in their waking day. They are morning people, or larks. Others feel and function better later in their waking day. They are evening people, or owls. Most people do not have a strong morning or evening preference. They can get up early or stay up late without discomfort when necessary. As people grow older, many become more larkish, and find it easier to adapt to early morning shifts. Paying attention to your lark or owl tendencies may help you organize your day.