Chapter 01 of 5
Why We Sleep at All
We spend a third of our lives asleep. Here's what it's for.
- Scale
A third of your life
Most people spend roughly a third of their lives asleep. Evolution wouldn't keep something that costly without good reason.
- Everywhere
Animals sleep too
Every animal scientists have studied closely shows some form of sleep, from mammals and birds to fruit flies.
- Surprise
Even jellyfish rest
In 2017, researchers found that a species of jellyfish with no brain at all shows a sleep-like state at night.
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Could you answer this?
Which chemical builds up while you're awake, and has its effects blocked by caffeine?
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😴 The Science of Sleep
- 01Why We Sleep at AllWe spend a third of our lives asleep. Here's what it's for.
- 02Inside a NightSleep cycles, REM and the strange world of dreams.
- 03The Body's ClockThe inner timekeeper that runs your days — and the Nobel Prize that explained it.
- 0411 Days AwakeThe teenager who stayed awake for 264 hours — and what sleep loss does.
- 05Owls, Larks and Jet LagMorning people, night owls, and working with your own clock.