Most animals that we know of sleep. Sleep is very important for a healthy brain and our brains are important in regulating sleep. Interestingly, recent studies have shown that the cerebrospinal fluid actually washes out toxins from the brain when we get enough sleep at night. That “rinse cycle” so to speak is the brain’s way of staying healthy and is thought to prevent neurodegenerative diseases like Alzheimer’s.
You may be surprised to learn that animals without a brain also need their beauty sleep. Hydra are little freshwater animals that do not have brains. Yet, these animals still enter cyclical sleep-like states. Similarly, jellyfish do not have a centralized brain but they too show signs of sleeping. What is unique is that the hormones that regulate sleep in hydra are the same as those that regulate sleep in humans and other animals (melatonin and the neurotransmitter GABA). Whereas jellyfish do not share these mechanisms. What was also interesting is that the hydras showed signs of sleep deprivation if they were disturbed during their sleep cycles. These findings suggest that the need for sleep likely evolved before the evolution of brains.
NE Fultz, G Bonmassar, K Setsompop, RA Stickgold, BR Rosen, JR Polimeni, LD Lewis. Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science. 366(6465): 628-631, 2019.