It is well worth noting that many animals use the two halves of their brains in sequence rather than in parallel: one half of their brain sleeps at a time, meaning that they don’t need as much “true sleep” because they are often half asleep in a very literal way.
Sharks don’t truly sleep at all and cats can sleep up to twenty hours a day. The amount of sleep one needs is different between species due to behavioral and metabolic differences that have evolved over millennium to suit an ecological niche.
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