> I think the reason we sleep so long has a bit to do with our lack of predation. It might be more of an evolutionary accident than a necessity. I don't think

> I think the reason we sleep so long has a bit to do with our lack of predation. It might be more of an evolutionary accident than a necessity. I don't think that's backed up by evidence. Elephants, which have very few predators and are really only preyed on when sick, old, or young, sleep only a few hours a day. It's strange because they're highly intelligent and have big, complex brains. Even cats, who sleep a lot everyday, have more predators in the wild, even the big cats. Cats don't sleep long because of lack of predation. They sleep long because they expend huge amounts of energy while awake (i.e., hunting). They require large amounts of energy stored for rabid bursts of expenditure. Sloths sleep a ton, mainly because they're low energy animals. https://faculty.washington.edu/chudler/chasleep.html https://faculty.washington.edu/chudler/chasleep.html There are plenty of animals on that list that contradict the conjecture that sleep duration is correlated with predation. > Aquatic creatures have shorter sleep cycles because the dangerous environment requires being alert at all times. Apex predators resort to strategies like sharks, who switch half their brain asleep while the other is awake, or whales, who sleep for only up to 30 minutes to maintain breath. That again isn't correct. Dolphins have more predators than sperm whales, yet dolphins sleep much longer per day than sperm whales. Most larger whales don't sleep longer than 30 minutes because they need to be awake and more active to keep their body temperature up. It isn't due to needing to breath as most whales consciously breath just fine while sleeping with the side of the brain that stays awake. Sperm whales don't do this because they can hold their breath for long amounts of time (and sleep vertically, which is quite eery looking). Whales, which includes dolphins, mainly adopted the unihemispherical sleeping primarily because they are conscious breathers. > I think you're on to something about energy. I don't think that's much of a revelation. Sleep is all about energy and restoration.