Full transcript
0:00You wake up at 3:00 a.m. some nights and
0:02you just can't fall back asleep. You
0:04blame your phone or stress or that
0:06coffee you had too late. Maybe you're a
0:08night owl instead. You feel tired all
0:10evening and then your brain suddenly
0:12switches on after midnight. Or maybe you
0:15sleep like a rock, but one small noise
0:17in the dark still has you wide awake in
0:19a second. Most of us never think twice
0:22about any of this, but the person wide
0:24awake at 3:00 a.m. may have been the
0:26most important person in the camp for
0:28most of human history. Our ancestors had
0:30no walls and no doors. They had a fire
0:33burning low and a group of people asleep
0:35around it. They slept out in the open in
0:37Africa where lions and leopards do most
0:40of their hunting after dark. So somebody
0:42had to hear them coming or the whole
0:44camp was dead. But nobody can stay awake
0:47every single night. Everyone has to
0:49sleep at some point. So who was
0:51listening while the others slept? The
0:53answer might explain why your brain
0:55switches on after midnight. Let's find
0:57out what ancient humans actually did all
0:59night. We have to start with something
1:01you probably haven't looked at in weeks,
1:04the moon. Today we have street lights,
1:06locked doors, and phones that light up
1:08the whole room. Their nights had none of
1:11that. It got dark for about 12 hours
1:13every night near the equator where our
1:15species spent most of its history. The
1:17fire and the moon were the only light.
1:20So the moon was a big deal and some
1:22nights it didn't show up at all. The
1:24Hadza of Tanzania still live through
1:26nights like that. They are one of the
1:27last groups on Earth who still live by
1:30hunting and gathering. They aren't Stone
1:31Age people. They live today, but their
1:33nights are the closest look scientists
1:35have at life without electricity. The
1:38Hadza hold their most important ritual
1:40on the darkest nights of the month when
1:42there's no moon at all. It's a dance
1:44called the Epeme. The women sing and the
1:46men take turns, one at a time. Each man
1:49puts on a head dress of feathers, ties
1:51bells to his ankles, and stomps in time
1:53to the song. The Hadza say the ancestors
1:55come out of the bush on these nights to
1:57dance with them. That sounds like the
1:58worst night to be out making noise
2:00because the dark is exactly when
2:02predators hunt people. Lion researcher
2:04Craig Packer studied nearly 500 lion
2:07attacks on people in Tanzania between
2:091988 and 2009. More than 2/3 of those
2:13people died. His team checked the date
2:15of every attack. The attacks peaked in
2:17the days just after a full moon. Most of
2:20them happened between sunset and 10:00
2:21at night. The moon rises early in the
2:24days before a full moon. So, the
2:26evenings are bright. Lions have a hard
2:28time hunting in that light. Things flip
2:30after the full moon. The moon rises a
2:32little later every night and the first
2:34few hours after sunset stay completely
2:36dark. People are still awake and moving
2:38around in those hours. Lions come out
2:40hungry at the exact moment people are
2:42easiest to catch. Packer's data comes
2:45from modern Tanzania, but lions and
2:47humans shared African nights for
2:49hundreds of thousands of years. Our
2:51ancestors most likely learned the same
2:53pattern. The moon worked like a warning
2:55calendar for them. It told them which
2:56nights to stay close to the fire. So,
2:59why would the Hadza dance on the darkest
3:01nights of all? Nobody knows for sure,
3:03but a whole camp that's awake, singing,
3:05and stomping is a lot harder for a
3:07predator to sneak up on. That dance also
3:09breaks one of the biggest myths about
3:11ancient nights. Most people imagine
3:13there was nothing to do in the dark. So,
3:15everyone just lay down and went to sleep
3:17when the sun went down. But, that's not
3:18what scientists see. A team led by
3:20Gandhi Yetish and Jerome Siegel tracked
3:23the sleep of three groups who still live
3:25without electricity. They studied the
3:27Hadza in Tanzania, the San in Namibia,
3:30and the Tsimane in Bolivia, and they
3:31published the results in 2015. These
3:34people stayed awake for more than 3
3:36hours after sunset on average. Our video
3:38on what ancient humans did all day
3:40showed what filled some of those hours.
3:42The fire was where the stories came out.
3:45Most people spent those evening hours
3:46right there, around the fire, talking.
3:49But, fire did one more thing for them.
3:51It let people carry light with them.
3:53Some of the clearest proof comes from
3:55caves in Ice Age Europe tens of
3:57thousands of years ago. There's no light
4:00at all deep inside a cave, day or night.
4:03People still walked in there again and
4:05again carrying fire in their hands. So,
4:08how long do you think that light lasted?
4:10A team of archaeologists in Spain
4:12rebuilt Stone Age lights in 2021 and
4:14tested them inside a real cave called
4:16Isuntza. A torch made of sticks and tree
4:19resin burned for about 41 minutes on
4:21average. A stone lamp burning animal fat
4:24lasted over an hour, but it only lit up
4:26a few meters around you. And a small
4:29fire on the cave floor made so much
4:31smoke that it went out after about half
4:33an hour. Now, picture it. You're deep
4:35inside a cave with a torch in your hand.
4:38The way out is far behind you. And that
4:40torch has about 40 minutes left before
4:42it burns out. People took that risk to
4:45paint the walls. Chauvet Cave in France
4:47has paintings more than 30,000 years
4:49old. And one of them is a bison with
4:52eight legs. That just looks like a
4:54mistake in daylight. But archaeologist
4:56Mark Azéma studied these paintings the
4:58way people back then would have seen
5:00them by the light of a flickering flame.
5:02The extra legs seem to run as the flame
5:05moves. Azéma thinks some artists made
5:07animals move on purpose, a bit like a
5:09flip book. That would mean people were
5:11watching the first cartoons by firelight
5:14more than 30,000 years ago. And it
5:16wasn't only adults in there. Small
5:18fingers pressed lines and swirls into
5:21the soft walls of Rouffignac Cave, also
5:23in France, about 13,000 years ago.
5:26Researchers Jess Cooney and Leslie Van
5:28Gelder measured those finger marks
5:30against modern children's hands. A few
5:32were made by kids as young as three, and
5:34some of those marks are high up on the
5:36ceiling where no three-year-old could
5:38ever reach. So, somebody, maybe a mom or
5:41a dad, lifted that child up in the dark,
5:44held them there by the light of a flame,
5:46and let them draw. The moon may have
5:48ended up on those walls, too. Ben Bacon
5:50is a furniture restorer from London, not
5:53a professional scientist. He studied
5:55hundreds of cave paintings using the
5:56British Library and the internet, and he
5:58noticed rows of dots painted next to the
6:01animals. He published a study with a
6:02team of archaeologists in 2023. His idea
6:05is that each dot counts one moon,
6:08starting from spring, and the number of
6:10dots matches the month that animal made
6:12it. That would mean people were keeping
6:13a calendar on cave walls more than
6:1520,000 years ago. Not every
6:18archaeologist agrees, but a furniture
6:20restorer might have cracked a code that
6:22sat in the dark for 20,000 years. The
6:25torches burn out eventually, and
6:27everyone has to lie down somewhere, and
6:29we still haven't found the person who
6:31stayed awake while the rest of the camp
6:32slept. We'll get there. First, let's see
6:35where they slept. Ancient people didn't
6:37sleep deep inside caves. That's another
6:40myth. People lived at cave entrances,
6:42under rock overhangs, and out in the
6:44open. The deep, dark parts of caves were
6:47places you visited with a torch, not
6:49places you lived. And they weren't
6:50sleeping on bare dirt, either.
6:52Archaeologist Lynn Wadley and her team
6:54found the remains of grass beds at
6:56Border Cave in South Africa, about
6:58200,000 years old. That's more than
7:00120,000 years older than any beds found
7:03before. And these beds had a clever
7:05trick. A layer of ash sat under the
7:08grass. Ash makes it hard for crawling
7:10insects to move through, so it may have
7:12kept bugs out of the bed. The team even
7:14found burned leaves of camphor in the
7:16bedding. And camphor is a plant people
7:18still use today to keep insects away.
7:21That means people had a mattress and bug
7:23spray 200,000 years ago, before they had
7:26anything we'd call a house. But the bugs
7:28found a way in anyway. Scientists at
7:31Virginia Tech studied the DNA of bed
7:33bugs and found that they used to live on
7:35bats in caves. One group of them
7:37switched to a new host about 60,000
7:40years ago, and that host was us. They've
7:43followed us ever since. Their numbers
7:45exploded about 12,000 years ago once
7:48people started living together in big
7:49settlements. So, the bed bugs in hotel
7:52mattresses today have a family history
7:54that goes back to a bat in a cave. Now,
7:57they've got a bed and they've got a
7:58fire. The big question is, how long they
8:01actually slept? Most people assume our
8:03ancestors slept way more than we do.
8:06They had no phones, no screens, and no
8:08job in the morning. Nine or 10 hours a
8:10night sounds about right. The 2015 sleep
8:13study on the Hadza, the San, and the
8:15Tsimane measured it. 94 people wore
8:18sleep trackers on their wrists for more
8:19than 1,100 days and nights in total. And
8:23the average night of sleep came out to
8:24about 6 and 1/2 hours. It was closer to
8:27six in summer. That's about the same as
8:29people in modern cities and sometimes
8:31even less. Jerome Siegel, one of the
8:33scientists behind the study, said, "The
8:36idea that modern life stole our sleep
8:38looks like a myth." Insomnia was so rare
8:41that the San and the Tsimane don't even
8:43have a word for it. You might have heard
8:45that people used to sleep in two shifts
8:47with an hour awake in the middle of the
8:48night. Historian Roger Ekirch found that
8:51pattern all over old European records
8:53from places with long winter nights. But
8:56the sleep trackers didn't show it in
8:57these hunter-gatherers. They mostly
8:59slept in one go and they woke up around
9:01the coldest part of the night just
9:03before dawn. So, now we have a real
9:05problem. These people slept only about 6
9:08and 1/2 hours. Out in the open next to a
9:11fire that was burning down with lions
9:13and leopards nearby. The whole camp
9:16would be in danger if everybody fell
9:17asleep at the same time. So, who was
9:20watching? Anthropologist David Samson
9:22went to Tanzania in 2017 to find out. He
9:25and his team put sleep trackers on 33
9:28Hadza men and women between 20 and 60
9:30years old and recorded their sleep for
9:3220 days. Every adult in the study was
9:35asleep at the same time for just 18
9:37minutes out of more than 220 hours of
9:40night. More than a third of the group
9:42was awake or only dozing lightly at
9:44almost any moment of the night. Nobody
9:46planned any of it. There was no schedule
9:49and nobody was waking anyone up for
9:50their turn. Age made it work. The older
9:53people in camp went to bed early and
9:55woke up early. The younger people stayed
9:57up late and slept in. Everyone else fell
9:59somewhere in between. So, the camp sleep
10:02overlapped like shifts without anyone
10:04ever deciding it. The night got covered
10:06from both ends and none of them
10:08complained about sleeping badly. Samson
10:11has a name for this. He calls it the
10:13poorly sleeping grandparent hypothesis.
10:15The idea is simple. A group with early
10:18birds and night owls mixed together is
10:20harder to sneak up on than a group where
10:22everyone sleeps on the same clock. It's
10:24still an idea and it comes from one
10:26group of people, but it fits. Now, look
10:29at your own family. There's the
10:30grandparent who's up at 5:00 a.m. making
10:32tea wondering why everyone else is still
10:35in bed. There's the teenager who can't
10:37fall asleep before 1:00 a.m. no matter
10:39what. There's the night owl whose brain
10:41switches on after midnight and the deep
10:43sleeper who still wakes up at one
10:45strange noise. Most of us never think
10:48twice about any of it, but put that same
10:50family around a fire 100,000 years ago
10:53and you've got a night watch that nobody
10:55had to organize. They still weren't
10:57alone even after they fell asleep. David
10:59Samson teamed up with sleep scientist
11:01Lampros Perogamvros in 2023 to compare
11:04people's dreams. They collected dreams
11:06from the Hadza in Tanzania and the Byaka
11:09in the Congo and compared them with
11:10dreams from people in Switzerland,
11:12Belgium, and Canada. The
11:14hunter-gatherers had scary dreams, too.
11:16They dreamed about being attacked by a
11:18buffalo or falling into a well, but
11:20their dreams often ended the same way.
11:22Someone from the camp showed up and
11:24saved them. The danger often just hung
11:27there in the Western dreams with nobody
11:29coming to help, especially for people
11:31who suffer from nightmares. The
11:32researchers think dreams like these may
11:34help people deal with fear. Someone who
11:36sleeps every night in a circle of people
11:38who would come running at a scream might
11:41learn that help will always come. Our
11:43nights look nothing like that anymore.
11:45We built walls, then doors, then locks
11:48over thousands of years. Today, most of
11:50us sleep behind a locked door in our own
11:52room with nobody else awake. The lock on
11:55your front door now does the job a
11:56grandmother by the fire used to do. Your
11:59body might still be doing its old job at
12:013:00 a.m. It just doesn't have a camp
12:03left to protect. And that's not the only
12:05old thing still running inside you.
12:07Researchers tracked the sleep of the
12:08Toba Qom, an indigenous people in
12:10northern Argentina in 2021. Some of
12:13their villages had electricity and some
12:15had none. People went to bed later and
12:17slept less in the few days before a full
12:19moon. Their sleep changed by almost an
12:22hour across the moon's cycle. The
12:23pattern was strongest in the villages
12:25without electricity, but it showed up in
12:27all of them. Then, the team checked 464
12:30college students in Seattle in the
12:32middle of a big, modern city, and the
12:34same pattern showed up there, too. You
12:36probably haven't looked at the moon in
12:38weeks, but it looks like part of you is
12:40still keeping track of it. Your
12:41ancestors watched that same moon to know
12:44when the lions would come. They stayed
12:45up for hours around the fire telling
12:48stories, and on the darkest nights, they
12:50danced. Some carried torches deep into
12:52caves, painted animals that moved in the
12:55flicker, and lifted their kids up to
12:57draw on the ceiling. They slept about 6
12:59and 1/2 hours on grass beds with bug
13:01spray underneath, and somebody in the
13:03camp was awake all night long without
13:05anyone planning it. That person was
13:07never broken. They were the reason
13:09everyone else could close their eyes.
13:11So, go easy on yourself the next time
13:13you're wide awake at 3:00 a.m. Your body
13:15might just be keeping a watch that's
13:17hundreds of thousands of years old.
13:19There's one more thing you should know
13:20before you go. You'll see a lot of other
13:23claims about ancient nights online. Some
13:25of them might even be true. We just
13:26don't have strong evidence for them yet.
13:28Some people say our ancestors went
13:30hunting at night. There's no clear proof
13:33they did it often. With lions out there,
13:35the dark was usually the time to stay
13:37close to the fire. Others say they used
13:39the stars to find their way. That's
13:40possible, but we have no direct evidence
13:43of it from that far back. Then, there's
13:45the story of the Seven Sisters. Ancient
13:47Greeks and Aboriginal Australians both
13:49tell a story about seven sisters in the
13:51night sky, where one sister goes
13:53missing. These two cultures had no
13:55contact for tens of thousands of years.
13:58Some astronomers think the story could
14:00be around 100,000 years old, from a time
14:02before people spread out of Africa. It's
14:04a beautiful idea, but it's still just an
14:07idea. And one study found that watching
14:10a crackling fire lowered people's blood
14:12pressure. A later study didn't find the
14:14same thing. So, if a campfire relaxes
14:16you, that might be something ancient, or
14:19it might just be a really nice fire. Oh,
14:21and one more thing. We just crossed
14:23100,000 subscribers, and we're really
14:26grateful for every one of you. Every
14:28view, every comment, and every share
14:31helped get us here.
14:32Thank you for supporting us. We'll keep
14:34working hard to make every video better
14:36than the last. Our video on what ancient
14:38humans did all day is right here if you
14:40haven't seen it yet. See you in the next
14:42one.