The origins of sleep across different animals

Sleep is a fundamentally ancient process that may predate neurons.

• The evolutionary purpose of sleep remains largely unexplained in the animal kingdom.
• Circadian rhythms are closely linked to sleep and may have influenced its evolution.
• Evidence suggests sleep exists in species without a centralized nervous system.
• Molecular oscillators and conserved sleep signaling molecules may have evolved before neurons.
• A comparative physiology approach reveals the complexity of sleep behavior across species.

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