How “old” does this make sleep? Worms emerged during the Cambrian explosion: at least 500 million years ago. That is, worms (and sleep by association) predate all vertebrate life. This includes dinosaurs, which, by inference, are likely to have slept. Imagine diplodocuses and triceratopses all comfortably settling in for a night of full repose! Regress evolutionary time still further and we have discovered that even some of the very simplest forms of unicellular organisms, such as bacteria, have active and passive phases that correspond to the light-dark cycle of our planet. It is a pattern
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