Human sleep is evolutionarily distinct from other primates, characterized by shorter total durations but a disproportionately high percentage of REM sleep. While most primates spend roughly 9% of their sleep in the REM stage, humans dedicate 20-25% to this dreaming phase. This shift occurred as *Homo erectus* transitioned from precarious arboreal sleeping in trees to terrestrial sleeping on the ground. Tree-dwelling ancestors faced the risk of fatal falls due to the muscle paralysis inherent in REM sleep, which naturally constrained the duration of this stage. The mastery of fire provided the safety and pest control necessary for ground sleeping, allowing for a doubling of REM sleep. This neurological re-engineering fueled the development of heightened emotional intelligence and creative problem-solving, providing the cognitive foundation for uniquely human achievements like advanced technology and complex social structures.
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