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  • If you follow me on Instagram, you probably know I went to the North Pole recently, and

  • this time of year the sun never sets. It was crazy. Why is it so hard to sleep when it's light out?

  • Hey light sleepers, Trace here. This is DNews. Everything sleeps or has some kind of active

  • and inactive cycle, but not everything sleeps at night, like we do.

  • Regular DNews watchers will know about the circadian rhythm, the pattern of sleep and wakefulness connected to the amount of light entering the eye.

  • When we perceive daylight, our brains lessen the release of melatonin,

  • making us more wakeful. And at night, more melatonin, more sleepy.

  • But, it's not just about sleepiness.

  • Even self-proclaimed night owls need darkness to sleep.

  • We evolved to sleep in the dark, and we know this because when it's dark our hormone levels fluctuate causing widespread changes in our physiology.

  • It's built-in. Melatonin lowers blood pressure, sugar levels, and body temperature.

  • Leptin makes us less hungry.

  • (Both of these) prepping us for rest.

  • When we're sleeping, the levels of cortisol, a stress hormone, drop, and our immune function improves.

  • Even though this explains why we sleep at night, it doesn't tell us why we evolved this way.

  • Sleeping at night is actually kinda weird. Only 20 percent of mammals sleep at night.

  • Most mammals are nocturnal, spending their days tucked away for sleepy time.

  • A study of fossils from the last 100 million years found nocturnal species evolved way before mammals even appeared.

  • Primates don't have a specific pattern of day-night cycling.

  • In fact, a study in the American Journal of Physical Anthropology looked at fossils of primates

  • and found species can be either diurnal (day active) or nocturnal (night active).

  • But because we sleep at night, modern humans must have evolved from a diurnal group of ancient primates.

  • And this is supported by scientists who study pre-industrial societies before the electric light.

  • They've found humans went to sleep just after sunset for a while, woke up, were active in the middle of the night (in the dark),

  • and then slept again -- that's our second sleep, by the way. That's awesome. That's our natural order,

  • sleeping twice, of course, in the dark.

  • But now, even a little light can mess up our sleep schedules because we have electricity. Because our brain is just watching,

  • always watching. and it gets confused when any light is present

  • because it didn't evolve to have light at night. Even when your eyes are closed your brain sees light through your eyelids,

  • and lowers melatonin release, making you more awake. You're affected by glowing electronics,

  • digital clocks, and lights from other rooms or the street that shine onto you. A study with rats

  • found they slept in different positions and had different sleep behaviors when exposed only to dim twilight sleep,

  • and a study with hamsters found signs of depression when they slept with a light at the equivalent of a glowing TV screen in their room.

  • Studies have correlated

  • excess light at night with breast cancer, and darkness at night with better performance of a breast cancer drug,

  • and even connected lessened tumor growth with more sleep.

  • Not to mention all the normal immune, obesity, depressive and other health effects associated with having too much or too little sleep.

  • So, while we don't know exactly why we evolved to sleep in the dark, we know our eyes and

  • our brains have adapted to work better during the daytime and put us to sleep at night.

  • Thus, we should sleep in a dark room, regardless of the actual time of day.

  • And this is supported by research in, of course, National Sleep Foundation, so... *yawn* maybe… I should… (have a nap). Give me that pillow.

  • Have a nap!

  • *yawn again* Why is it that yawning makes you want to yawn? Why do we even YAWN!?

  • Check out this old video, opens it wide, and checks in on this weird universal behavior.

  • The act itself is usually associated with being tired.

  • Of course a symbol of boredom in humans

  • But in animals, yawning could be associated with sexual arousal, fear, uncertainty,

  • mating rituals, and even as a warning sign on other animals .

  • Perhaps a it's a way to passively show large teeth to the enemy.

  • Do you sleep in PURE DARKNESS? Or you are more of a...... "I'll sleep anywhere" person

  • Subscribe so you get more DNews.Thanks for watching and let us know down on the comments.

If you follow me on Instagram, you probably know I went to the North Pole recently, and

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B1 US sleep yawn melatonin nocturnal evolved dark

Why Aren’t Humans Naturally Nocturnal?

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    Richard Wei posted on 2016/07/15
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