Did Ancient Humans Really Sleep Twice a Night?

You wake up at 3:07 a.m. and think something is wrong with you. But what if waking in the middle of the night was never a sleep problem at all? In this video, we test the famous "two sleeps" idea against the evidence: old diaries, a darkness experiment, a camping study and the Hadza of Tanzania. The answer is more interesting than "yes" or "no." In this video: 0:00 The 3:07 a.m. wake-up 1:18 The old records: "first sleep" and "second sleep" 2:36 The darkness experiment 4:02 Segmented Sleep 4:31 No Separate Bed Rooms 4:50 The 18 minutes: who was actually asleep? 5:42 The camping experiment 7:25 So what was the real pattern? The short version: two-part sleep is real in old records, in a lab, and in some communities. But the evidence does not show it was the universal human pattern. Human sleep bends with light, season and the people around you. SOURCES ▸ Pre-industrial two-phase sleep: Ekirch, 2001, American Historical Review, "Sleep We Have Lost: Pre-Industrial Slumber in the British Isles." Expanded in "At Day's Close: Night in Times Past" (2005). ▸ Darkness experiment: Wehr, 1992, Journal of Sleep Research, "In short photoperiods, human sleep is biphasic." ▸ Camping resets the body clock: Wright et al., 2013, Current Biology, "Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle." ▸ Hadza and the 18 minutes: Samson et al., 2017, Proceedings of the Royal Society B, "Chronotype variation drives night-time sentinel-like behaviour in hunter-gatherers." ▸ Sleep in pre-industrial societies: Yetish et al., 2015, Current Biology, "Natural Sleep and Its Seasonal Variations in Three Pre-Industrial Societies." ▸ Segmented sleep in Madagascar: Samson et al., 2017, American Journal of Human Biology (check the exact title and year before publishing). Note: the Hadza result does not prove ancient humans took turns guarding the group. That is an interpretation, not a demonstrated fact. What time do you usually wake up in the night? Tell me in the comments. Next video: What Did Ancient Humans Actually Do in the Dark? #TwoSleeps #AncientHumans #HumanHistory #Prehistory #HumanHistory #Anthropology #Sleep #StoneAge #History