Why did sleep evolve?

Scientists disagree as to why sleep evolved. It seems peculiar that we should spend so much of our lives sleeping when it’s at this time that our vigilance is at its lowest and we’re at our most vulnerable. It’s also a time when we don’t typically eat, drink, or reproduce. There are a plethora of theories as to why sleep evolved, including the idea that sleep allows us to save or optimise our energy use and keep us alert to danger. Sleep also allows us to clean toxins from our brains and consolidate memories, and it’s increasingly clear that it helps in many aspects of our waking lives, from controlling our weight and regulating our emotions, to bolstering our immune systems.