How did our ancestors sleep?

Episode Summary

Executive Summary: CrowdScience asks whether people sleep better now than in the past. Sleep researcher Russell Foster argues that artificial light and modern schedules have compressed sleep and disrupted our biological rhythms; historically, people may have slept in two or more periods. Reports from the Arctic and archaeological evidence add context, while research links poor sleep with health risks. Foster recommends individualized, practical habits that protect sleep.

Main Topics: Historical patterns of segmented sleep: Russell Foster describes evidence that under natural 12-hour light-dark conditions, sleep can include a first sleep, a waking period, and a second sleep. Medieval writing also refers to first and second sleeps. Modern expectations of one uninterrupted block may not reflect older patterns. Artificial light, modern schedules, and circadian rhythms: Electric lighting and packed work and social schedules have allowed people to extend activity into the night. Erin Flynn Evans explains that daily light exposure resets the circadian clock, and light or darkness at inappropriate times can misalign it. Sleep in Arctic conditions and traditional lifestyles: In Tromsø, students use bright full-spectrum lamps during the polar night to support daily rhythms. Sami reindeer herder Ken Evan Berg describes a lifestyle shaped by seasons and animals rather than fixed clock times, with reindeer alternating between eating and sleeping. Sleep among ancient human ancestors: Archaeologist Rebecca Wragg Sykes suggests that early humans faced nighttime predator risks and may have slept lightly in sheltered places. Neanderthals had controlled fire, organized living spaces around hearths, and were skilled hunters, potentially making them safer at night. Sleep, health, and practical advice: Foster says sleep supports memory and problem-solving and discusses evidence linking disrupted or insufficient sleep with negative mood, dementia-related protein accumulation, stroke survival, cancer risks, obesity, and diabetes. His advice includes reducing evening light and stimulation and making the bedroom cool, dark, and comfortable.

Key Arguments: A consolidated seven- to eight-hour sleep block may not be the only natural human pattern: under long periods of darkness, people can experience two sleep bouts separated by a waking interval. Artificial light and modern demands encourage people to extend activity into nighttime, narrowing the sleep window and potentially working against an ancient circadian system. Sleep needs and patterns vary between individuals, so advice should be tailored rather than treated as a single universal prescription. Sleep is important for more than next-day alertness: it supports memory and problem-solving, and research discussed by Foster connects disrupted sleep with multiple long-term health concerns. Traditional and environmental examples show that sleep timing is shaped by light, seasons, work, and other living beings, not just personal preference.

Data Points: Light-dark exposure in the lab example: 12 hours of light and 12 hours of darkness - Foster says this schedule can produce a sleep pattern resembling that of societies without electric light. Sleep and transition durations in the described biphasic pattern: About 2-hour transitions, two sleep periods of about 4 hours each, and an intervening wake period of 30 minutes or more - Foster outlines a pattern of settling into sleep, waking between bouts, then sleeping again. Widespread use of electric light: From the 1950s - Foster identifies widespread lighting as a factor in changing sleep patterns, while noting that effective light developed earlier. Polar-night lamp recommendation: 45 minutes to an hour daily for about two weeks; around 10 minutes for an energy boost - A university counsellor in Tromsø describes suggested use of full-spectrum lamps. Reindeer activity pattern: They alternate between sleeping and eating roughly every two hours - Ken Evan Berg describes the animals' rhythms as a major influence on herding life. Herding schedule example: Waking around 8 a.m. and going to bed around 2–3 a.m. - Berg gives an example of his schedule while working, amounting to about six hours of sleep. Evolutionary timescale cited: 500–600 million years - Foster uses this timescale to emphasize the deep evolutionary roots of the sleep-wake system.

Pivotal Quotes: "We've invaded the night because we can." — Russell Foster: He argues that modern life and artificial light have encouraged people to push activity later and compress sleep. "An internal sleep-wake cycle, an internal biological clock is embedded right at the heart of all of us. And we really ignore it at our peril." — Russell Foster: Foster stresses that human biology remains governed by circadian rhythms despite modern habits. "It's all about shoe size. You know, one size doesn't fit all. Find the shoe that fits your foot best." — Russell Foster: He advises listeners to find sleep practices that work for their individual needs instead of becoming anxious about rigid rules.

Implications: Listeners may benefit from protecting a regular sleep opportunity, limiting evening light and stimulation, and making bedrooms comfortable. Waking during the night is not automatically abnormal, but persistent problems or health concerns warrant individualized professional advice.