Without sleep we'll surely die yet it's unclear as to why we even need to sleep. What's your theory?

I'm not really sure. It was probably originally just a way to conserve energy in the hours of the day when an animal wouldn't have been hunting anyway (night for day creatures, day for night creatures) and gradually took on a number of other roles, until at some point the biology of the creatures shaped itself around sleep in a way that made it indispensable for life.

I think things might be very different for us if we evolved on a planet that was tidally locked to it's star (one side of the earth facing the sun, continually bathed in daylight.) There are many animals that don't fully sleep - the cetaceans, for example. If they did, they'd drown. They have the happy knack of shutting down half their brain. A skill I often see displayed in this forum.

i think we need sleep because our brain is a computer and once in a while you have to shut it down (well most of the conscious regions anyway). In a way it also gives our bodies a schedule, we sleep, we wake, we work, we sleep. If we did not sleep we would be in perpetual working mode, sounds depressing to me. Not to mention sleep also helps people comprehend abstract ideas, as the conscious mind is constantly overwhelmed by data to process.

I think it deals with personality. Scientists still don't know much about it, and ours is more advanced than that of most animals. I think it is the part that gets burnt out, and it is more necessary to *human* life than some suggest.

My best guess is that mental activity is the most taxing brain function.

Maybe sleep is like a recharge for your brain. Just like your phone

Weird Darryl doesn't know much about religion. Interpretation of dreams was a pretty big deal in the OT. Abrahamic faiths make up a huge chunk of the worlds religious population. Therefore, questions about sleep have some bearing here. Anyhoo - I was taught years ago, that sleep is the brains way of rebooting itself, so to speak. It starts to misfire when sleep deprived....that's when you get all weird and cranky and deranged or slap happy from staying up too long. Chronically sleep deprived individuals get pretty crazy. The human brain needs down time to process and store information.

I don't know why people would die without of sleep deprivation, but I know that thoughts are organized during sleep. Have you ever had an exam, you study and study and you think nothing sticks in your mind, you get some sleep and the next morning, you can remember everything quite well. And people who think you're brain is resting during the time you're asleep are totally wrong. Mental activity never stops, that's how you have dreams. In fact, dreams help you organize your everyday experiences.

My theory is, let's go with what scientists say. Specifically "I dunno, we don't understand this well enough to confidently come to a conclusion." It probably served some purpose very early on, around the time the earliest lifeforms were dividing into separate kingdoms (which would explain why it's present in all animals). It may be that something about the operation of an animal body inherently requires these intermittent rest periods, but I'm just speculating at this point.