
Contents
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Sleep and Its Stages Sleep and Its Stages
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Sleep Stages Sleep Stages
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Stage 0 (W, or Wakefulness) Stage 0 (W, or Wakefulness)
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Stage 1 (N1) Stage 1 (N1)
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Stage 2 (N2) Stage 2 (N2)
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Stage 3 and Stage 4 (N3) Stage 3 and Stage 4 (N3)
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REM (R) REM (R)
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Major Theories of Why Organisms Sleep Major Theories of Why Organisms Sleep
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Reduced Energy Demands Reduced Energy Demands
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The Facilitation of Learning and Memory by Sleep The Facilitation of Learning and Memory by Sleep
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Sleep and the Synaptic Homeostasis Hypothesis Sleep and the Synaptic Homeostasis Hypothesis
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Priming Priming
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Creativity Creativity
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An Empirical Test of Sleep Insight and Creativity An Empirical Test of Sleep Insight and Creativity
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Sleep and Homo erectus Revisited Sleep and Homo erectus Revisited
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Cognitive Repercussions Cognitive Repercussions
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Archaeological Evidence for More Complex Thinking in Homo erectus Archaeological Evidence for More Complex Thinking in Homo erectus
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Preliminary Summary Preliminary Summary
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Summary Summary
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9 The Evolution of Sleep and Dreams
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Published:January 2020
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Abstract
Primitive sleep states developed from earth’s rotational cycle, where activities were constrained by alternating periods of light and dark. Extant reptiles, birds, mammals, and primates exhibit slow-wave sleep (SWS) and rapid eye movement (REM) sleep, which suggests an early evolutionary development dating to at least 300 million years ago or earlier. There may have been no single purpose of sleep, however, multiple reasons for its evolution and different sleep stages have been suggested, including reduced energy demands, facilitation of learning and memory, removal of waste metabolites, priming for subsequently successful waking activities, and aiding creativity. When Homo erectus appeared about 1.9 million years ago, it made a full transition to terrestrial life, including sleeping on the ground instead of in nests in trees. Ground sleep resulted in a single integrated sleep period, which had many positive cognitive repercussions. The design for the Acheulean handaxe, attributed to Homo erectus, may have come to a stone knapper in a dream. Some handaxes, beginning about 500,000 years ago, had aesthetic qualities and may have been used as a means of sexual selection.
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