Sleep Purpose Biological Mystery

Scientists know sleep is essential, but they still do not fully know why living brains require it in the first place. Over decades of research, they have linked sleep to memory, metabolism, immune function, tissue repair, and brain housekeeping, yet no single explanation fully accounts for why sleep became such a universal biological requirement. Sleep researcher William Dement once summed up the mystery with a blunt line after roughly 50 years in the field: the only really solid reason we need sleep is that we get sleepy.

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