Fact
People living without electricity don't sleep more than we do
In three pre-industrial societies with no electricity (the Hadza of Tanzania, the San of Namibia and the Tsimane of Bolivia), wrist actigraphy put average sleep at 5.7 to 7.1 hours a night across 10 recording groups (6.4 h on average), with sleep periods of 6.9 to 8.5 hours.
Confidence: DebatedCredible evidence on more than one side; read the context.Show the data as a table
| label | Sleep time per night |
|---|---|
| Hadza, May 2013 | 6.3 h |
| Tsimane, Aug 2013 (winter) | 6.6 h |
| Tsimane, Sep 2013 (winter–spring) | 6.4 h |
| Tsimane, early Oct 2013 (spring) | 6.4 h |
| Tsimane, mid Oct 2013 (spring) | 6.5 h |
| Tsimane, late Oct 2013 (spring) | 5.9 h |
| Tsimane, Nov 2013 (summer) | 5.7 h |
| San, May 2014 (fall–winter) | 7.1 h |
| San, Aug 2014 (winter) | 6.9 h |
| San, Jan 2015 (summer) | 6.2 h |
"SLEEP TIME h" column of Table S2 ("Information about participant groups") in the paper's Supplemental Information. The published paper has no Table 1; the per-group numbers are only in this supplementary table. Overall average (6.4 h) and totals (94 participants, 1,165 days) are from the same table.
These are not sleep-deprived people catching up on rest. Across all three groups, sleep onset came on average 3.3 hours after sunset, people usually woke before sunrise, and they slept 53 to 56 minutes longer in winter than in summer. The authors say the totals sit "near the low end" of industrial societies, but that comparison is the contested part. Fourteen sleep researchers led by de la Iglesia and Roenneberg replied that the Toba/Qom of Argentina, who also still partly hunt and gather, slept longer (7.0 to 8.5 h) and lost up to an hour when they got electricity. They called the conclusion that sleep has not changed over human history "a strong over-interpretation." Other caveats: this is 94 people measured by wrist actigraphy, which estimates sleep from movement rather than measuring brain activity. The groups are tropical or subtropical, the Tsimane farm as well as forage, and the San are no longer nomadic.
Source and method
- Yetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current BiologySample: 94 adults (47 women, 47 men), 1,165 participant-days of actigraphy
- de la Iglesia HO, Moreno C, Lowden A, et al. (2016). Ancestral sleep (correspondence). Current Biology
Adults in each group wore an Actiwatch-2 wrist actigraph (movement plus light sensor) for 6 to 28 days, and sleep was scored with the Actogram program. Sleep period is the time from sleep onset to offset; sleep time is that period minus wake after sleep onset (WASO). The Hadza (fully hunting and gathering) were recorded for 8 days in May 2013 (10 people). The Tsimane (hunter-horticulturalists) were recorded as six separate groups of 7 to 12 people between August and November 2013. The Ju/'hoansi San (formerly nomadic hunter-gatherers, now settled in a village) were recorded in May and August 2014 and again in January 2015. All three groups live south of the equator, so January is summer. Some San recordings also used temperature loggers on the fingers, the abdomen and the sleeping site.
Published October 14, 2026.
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