Humans, like all living organisms, have an internal biological clock. Referred to as the Circadian Rhythms (from the Latin “circa dies/diem” meaning “about a day”), ours is actually around 10 to 20 minutes longer than our standard 24 hour day. However, the clock resets itself at the beginning of the day when we see morning light to match the natural Earth Day. Which is handy, because if that didn’t happen, jet lag would be a LOT worse than it is already for some people. This internal timer controls things such as body temperature, blood pressure, oxygen consumption and metabolism during different times throughout the day as well as when we feel sleepy or awake. When the genes that control our biological clocks mutate, they can cause disruptions to the normal sleep cycle and if scientists can learn more about them they may be able to treat sleeping disorders such as narcolepsy.
Many circadian rhythms are observed at the same time as external changes – for an obvious example, we feel the need to sleep when it is night and there is no natural light. A similar thing appears to be the case with migrating birds – the shorter daylight hours in the fall trigger something internally that cause them to move. Plants also have internal systems that operate according to the light cycle of their environments. Some animals that live in arctic environments where the sunrise and sunset cycle only occurs in parts of the year have circadian rhythms only when there is change in the light and not through constant light or darkness.
The cool thing about biological clocks is that the external factors are not always necessary. Fiddler crabs are naturally darker in the morning and lighter in the evening (like a reserve tan!) but studies have shown that even when exposed to constant environmental conditions the rhythm of the colour changing continues. Additionally, completely blind animals (such as the blind mole rat) also maintain circadian rhythms despite the obvious lack of light as a trigger. Remember about the arctic animals that only had circadian rhythms when there was change in light? Yeah, well, a different study showed that some animals (ground squirrels and porcupines) maintained their circadian rhythms through 82 straight “days” of sunlight.
And now my biological clock is screaming “sleeeeep!” The wikipedia article for this is super awesome, so I recommend you check that one out, down in the info-links.
~ Darcie Rae