Sleep Is Older Than Brains

Sleep or sleep-like rest appears across virtually every animal group scientists have studied, including insects, fish, birds, reptiles, and mammals. Even simple animals show quiet states that look like primitive sleep.

That means sleep is ancient. It likely evolved early because nervous systems need recurring maintenance, not because modern mammals happen to like beds.

Skipping sleep hits fast. Stay awake for 24 hours and your reaction time and judgment sink to the level of someone who is legally drunk.

Push further and it gets strange. People kept awake for days start to hallucinate and lose track of memory. Lab rats kept from sleeping entirely die within a few weeks — in classic experiments, the total loss of sleep proved about as deadly as the total loss of food.