QI | Why Do We Sleep?

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michael Longford : Sleep was invented to cure being knackered.

Timothy McLean : Why do we sleep? Because we get sleepy. Why do we get sleepy? ...We're working on that.

Patrick Headland : David's wearing his special travel dressing gown!!

Stevie Cole : This is a perfect video for someone perusing YouTube at ungodly hours of the morning

Jacob Seager : Awww Alan got that fact at the start from a previous episode from Stephen

New Message : Sleep is a conspiracy to disable the population for 7 - 9 hours a day, perpetrated by the De-Illuminati.

Victor Dalloz : To anyone interested in the topic, I highly recommend the book "Why we sleep" by Matthew Walker (former Harvard professor, currently at UC Berkley). It's really a fascinating read.

Arctic IceFox : The description still says Stephen Fry lol

Rosalie MYFHC : I'm a simple girl, I see Noel, I click

r0bw00d : Oh no, I need my alarm clock. I went an entire summer vacation without using one and wound up staying up later and sleeping later until I was keeping vampiric hours. Then I spent a week using my alarm clock to get myself back on schedule in time for school.

Widdekuu91 : A better question; Why aren't I sleeping? The answer; This video, I'm watching it.

Zake Budek : ...perchance to dream - ay, there's the rub, for in this sleep what dreams may come...

angelstouch92 : A study I read recently showed that during the day things build up in the brain that essentially intoxicates you and sleeping helps clear it away. It's why if you don't sleep you show signs like being drunk.

Ben Blackburne : I’ve always imagined that it might have been a way for our ancestors to get through the night, as it was so dark they couldn’t get much done so sleep would essentially they could sleep and then wake up when it’s morning. I’m not saying that this is the reason for sleep as it’s obviously not the main reason, but I’ve always been fascinated as to how sleep seems to be a time machine to the morning time. You can’t feel yourself sleeping, you just sort of wake up and it feels instant to when you went to sleep but really 8 or 9 hours may have passed. I’ve just always found that quite cool

Hubert Cumberdale : Noel's starting to look like a tired old woman.

Combicon : Was honestly expecting this to be a 'Nobody Knows' answer.

Doctor Witten : The answer's a bit misleading. There's a rather popular book published recently by neuroscientist Matthew Walker, that's literally called Why We Sleep. It talks about how studies have indicated sleep's important role in improving mental functions like learning and memory; maintaining the health of your immune system ; and even helping reduce/prevent serious illnesses like dementia and cancer.

M Standenberg : Can’t even answer the question “does our consciousness continuity break during sleep, in which case, do we effectively die and our bodies generate a new ego as we wake?”

MrWombatty : The weirdest dreams are 'wanting-to-wee' dreams, especially those where I'm searching for a toilet but can't find one anywhere!

The Winspear : 2:34 My brain can't be cleaned because I'm dirty minded.

bookashkin : From immortal Bill Hicks: I need my sleep. I need about 8 hours a day... And 10 at night, and then I am good.

sed8me69 : Regenerating, Hence we all wake up with that taste that's like fish fingers and custard 🤣

Get the Joke! : My dentist said to me, that my gum has to come out.

Lena Oxton : Your brain cells don't grow back either, and that's both a blessing and a curse. On the downside, you have terrible degenerative neural disorders you can never recover from, but on the upside, you won't have to go every two years for a new skull fitting for that big growing brain of yours!

Veronica Bean : I've had my gums trimmed...

MeFirst please : I kinda didn’t want this to end

cloudsRniceC0M3 : Havent slept in month I can see smells Feel colours Touch sound

WuXiit : Wasn't this a question back when Stephen Fry was hosting? I seem to remember brain cleaning being the answer then.

FutureChaosTV : "gum dresser" ;-)

youcometome9 : Why do we sleep ? Cuz U don't got to be WOKE all the time !

Neil Bevan : Why do we sleep? It's the only legitimate excuse a person has to mentally get away from their partner.

Alagass : Boosh

Yj k : We evolved the ability to sleep as an easy excuse to get out of work

Chriscom28 : I had almost the exact same sleep analogy. Sleep is when our bodies undergo maintenance and repair and is best done while the body is less active.

nriab23 : That blond woman on the panal just isn't funny, I don't believe her jokes are supposed to funny rather her presentation of them, but even at that. I don't find either funny

Ras Putin : When we were a kid we don't like to sleep, now that we're adult we want to sleep all day!

Madam Satan : Why do we sleep? To avoid people

Cloeren Jackson : I don't understand why this is a question. OK, so I think they mean they can't explain it scientifically. But surely it can explained in simple terms even if science doesn't understand the specific mechanism? First off, you can just as easily ask: What would be the point in staying awake all the time? From an evolutionary standpoint, the only things you need to do is carry on living, and to continue existing evolve as a species you have to have offspring. So basically, eating and having babies is the extent of your role from a survival standpoint. Secondly, conditions are very different at night that make hunting and mate finding more difficult. First off, it's probably easier to evolve into a species which specialises in taking advantage of either day time or night time conditions, and not both. Secondly, I expect there's some processing happening: During the day 100% of your time is spent surviving, while asleep you get to run different processes. Processing the events of the day while not engaged in distracting activity may be one. I expect though the reason is similar to why you need to recharge your phone. They say it isn't energy conservation, I don't think it is that, I think it's energy transference. For the purposes of surviving it seems reasonable for energy to work better if you consume food and then release it all in a powerful day long swoop to maximinise ones own effectiveness at hunting. Like releasing a rocket, it works better to just dump the whole thing out in activity in one big thrust. But since the body is essentially chemical, it's likely that chemical storage gets thrown into muscle and work energy and gradually expires. Sleeping gives the body a chance to push that boulder of chemicals back to the top of the hill again ready to release it in another big food and mate hinting expedition the following day. You also reduce the risk of injury by sleeping. The paralysis helps to further reduce the chance of injury. You find somewhere, lay still and enjoy some regenerative rest and time to heal. Surely that's what sleep is about? It compartmentalises life into two basic stages of activity and recuperation. Isn't it obviously that ultimately, we sleep for exactly the reason we think we do? To basically recharge for the next daylight stretch of activity? After which we reach exhaustion, just like anything in motion does. Why can't it be just exactly what it obviously is?

L1am21 : 3:55 jump scare

Dan Ryder : What about tattoos

Audun Paudun : We probably sleep to avoid predators at night. Our ancestors were probably the ones smart enough to stay hidden during night time, when predators where out hunting.

Dan Ryder : The kit kat thing was the wrong way round. You can have a kitkat if you stay up all night.

Orrenman : Saying Rochester is in New York is like saying Belfast is in Ireland. You're in the right ball park but you're not the ones people came to see.

Matthew Burch : Nobody has lasted past I think 216 hours. People have tried to go longer, but it's like the 4 minute mile, our bodies just aren't capable.

Christian Buczko : This cannot be correct about energy saved when sleeping. It only works if you compare sleeping to lying down awake. If your highly active, you will burn far more energy than if lying down awake. So compared that to being asleep, your saving far more. You also sleep to allow your brain to sort out the accumulated crap, its like refreshing the cash memory on a computer. It fills up while awake, until your mentally exhausted, then you sleep. It's not physical, its mental. To refresh physically you eat, to resupply the energy used. I've tested this, and often go 3 days no sleep. If you don't exercise much, its your brains thinking which suffers, but you don't get physically tired. I've also gone without food, mentally you can handle it, but physically you become exhausted....

Tom Lees : I swear Alan is a Time Lord

Bri A. : "I went along with him and now I'm frightened!" David Mitchell, QI

B uppy : It is my understanding that the body repairs itself during this downtime. Anecdotally, In one of the James Herriott stories he talks about getting ready to put down an ailing sheep, of which he could do nothing for. He had given it the painkiller/sleeping agent and was ready to give it the lethal injection, when he was called away. He'd came back a few days later to find the same sheep was alive and well, and frolicking, and not needing of euthanasia. We also tend to sleep more when we are ailing, additionally we do receive injuries to ourselves during the day that might overwhelm the body without the extra repair time of sleep. There also seems to be the time spent dreaming resolving issues. Dreams are powerful in their ability to encapsulize conceptually the problems/issues we experience during wakefulness and give us a different way of resolving them.

FortisConscius : I like Daniel C. Dennet's take on "why do we sleep?" The real question is "why do we wake?" - plants are a profoundly successful organism and they spend their whole lives asleep - seems a perfectly viable evolutionary strategy. (Waking is vastly overcomplicated by comparison. We wake because it gives us a competative advantage - moving where we need to be, not where we're drifting to. I.e. Outmanouevring predators and prey, etc. It's costly in development and maintenance but an advantage overall. No need to be awake all the time though - that's a good way to go crazy with information overload. The so-called Brain Cleaning seems apt alongside that line of reasoning.)

Bob Lawblawblaw : It's 5.35am and I'm bog eyed.