Why people sleep less than their primate relatives

The San hunter-gatherers of Namibia have no electric lights or new Netflix releases that keep them awake. Yet, they don't sleep more than the typical Western city-dweller who stays up doom-scrolling on their smartphone.

• Research shows that people in non-industrial societies average less than seven hours a night.
• Chimps sleep around 9.5 hours out of 24. Three-striped night monkeys sleep for 17 hours a day. 

The various ways that human sleep is unusual. We spend fewer hours asleep than our nearest relatives, and more of our night sleep is spent in the rapid eye movement or REM phase.

To learn about how ancient humans slept, anthropologists study contemporary non-industrial societies, such as the Hadza hunter-gatherers of Tanzania and various groups in Madagascar, Guatemala, and elsewhere. Sleep across all three groups averages around 5.7 - 7.1 hours, which is much less than primates.

Evolutionary anthropologist David Samson thinks the evolution of human sleep is a story about safety in numbers when humans began sleeping on the ground and napping often.