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The purpose of sleep? To forget, scientists say

Over the years, scientists have come up with a lot of ideas about why we sleep.

Some have argued that it’s a way to save energy. Others have suggested that slumber provides an opportunity to clear away the brain’s cellular waste. Still others have proposed that sleep simply forces animals to lie still, letting them hide from predators.

A pair of papers published recently in the journal Science offer evidence for another notion: We sleep to forget some of the things we learn each day.

Carl Zimmer in The New York Times.