What did ancient humans actually do all night?

Nobody slept eleven hours

The obvious guess is that with no lights and nothing to do, people went to bed at sunset and slept until dawn. When researchers finally measured it, the opposite turned up. In 2015 a team led by Gandhi Yetish put wrist monitors on the Hadza in Tanzania, the San in Namibia and the Tsimane in Bolivia. Across all three groups people slept 5.7 to 7.1 hours a night, less than the industrialised average, and stayed up more than three hours after the sun went down.

Four hours a night, ten years a life

Near the equator there are 11 to 12 hours of darkness, all year round. Take out seven hours of sleep and you're left with about four hours awake in the dark every night, with no book and no lamp worth the name. Across a lifetime that adds up to roughly ten years, more time than anyone spends in a classroom. We usually assume that time was wasted, just waiting for dawn. We get that wrong because none of us has ever had those hours. Electric light took them off the schedule about six generations ago.

Fire builds a room

Everything about the night ran through fire. Wonderwerk Cave in South Africa has burnt bone and plant ash 30 metres inside the entrance, in layers around a million years old. At Gesher Benot Ya'aqov in Israel, about 790,000 years ago, burnt flint clusters in the same spots level after level. By around 400,000 years ago hearths were normal across Europe and the Near East. Light was the lesser part of what a fire did. Outdoors at night there are no walls, and a fire makes a room out of nothing. In 2021 a team led by María Ángeles Medina-Alcaide rebuilt Palaeolithic lighting in a cave in northern Spain and timed it. We have the lamps themselves: a carved sandstone lamp from Lascaux, 17,000 years old, and close to 300 Palaeolithic lamps from France alone. Nobody was reading by them. The light was for seeing each other's faces.

The night changes the subject

Polly Wiessner spent decades with the Ju/'hoansi of the Kalahari. She recorded what people said in daylight and what they said after dark, then counted. Daytime talk was admin: who is going where, who owes what, who isn't pulling their weight. About a third of it was about money and work, and only around 6% was stories. At night around the fire, 81% of the talk was stories. Those stories went to places the daytime talk never did: people 200 km away, relatives dead for 40 years, spirits, journeys nobody in the circle had made. Wiessner argues that firelight talk is where humans learned to keep in mind people they couldn't see, and the video agrees with her. Healing dances, where hours of singing push a healer into trance, happen at night too.

Beds with built-in pest control

People also went to bed, and some of the beds survive. At Border Cave in South Africa, Lyn Wadley's team found grass bedding 200,000 years old, laid deliberately on top of ash. The ash dries out crawling insects, so the bed sat on a bug barrier that somebody worked out and taught to others. At Sibudu, 77,000 years ago, bedding was made partly from the leaves of Cryptocarya woodii, which are insecticidal. When it got dirty, people burned it and made new bedding. These were people making the dark comfortable, not just putting up with it.

Someone was always awake

In 2017 David Samson and colleagues monitored 33 people in a Hadza camp for 20 days. In all that time, everyone in the camp was asleep at the same moment for a total of 18 minutes. Nobody arranged this. Older people went to bed early and woke at 4am, while young adults stayed up past 1am, and between them the whole night was covered. There's a more famous idea too: the historian Roger Ekirch found more than 500 references to "first" and "second" sleep in pre-industrial Europe, and Thomas Wehr's experiments in the 1990s produced split sleep in volunteers kept in long darkness. But the Hadza, San and Tsimane sleep in one block, so split sleep might just be what northern winters do to people. As for why someone was always awake, Craig Packer's records of lion attacks in Tanzania show most of them happen between 6pm and about 10pm, and the risk rises in the ten days after a full moon, when early evenings are at their darkest. The person feeding the fire at 2am was keeping watch.

• 5.7–7.1 hof sleep a night, measured in three foraging groups
• 81%of night-time talk around the fire was stories
• 18 minwhen the whole Hadza camp slept at once, in 20 days

The hours came back unclaimed

Then came gas lighting, and in 1879 Edison's bulb, and within about six decades electric wiring reached ordinary homes. The four hours came back to us, but without the story circle and without anyone watching the tree line. Nobody decided to give up the hours humans had used for talking. It just happened, within about six generations. You still have those four hours every evening. The difference is that now you have something to look at.

Chapters

1. 0:00Everyone assumes they slept eleven hours
2. 0:54The four hours nobody counts
3. 2:18What a fire actually does
4. 4:08Eighty-one percent of it was stories
5. 5:51The beds, and the ash underneath them
6. 6:43Eighteen minutes out of twenty days
7. 7:28The famous theory that might be wrong
8. 8:45Why somebody was always awake
9. 9:50The night we switched off

Next questionHow did ancient humans survive deadly winters?