This is Hidden Brain, I'm Shankar Vedantam.

Last week on the show, we featured the story of Randy Gardner, a San Diego man who went

11 days without sleeping, breaking a world record.

You don't need sleep.

That was the thinking back in the 60s and that's the thinking that I had.

Of course, as it turns out, that was absolutely wrong.

Randy's exploit would come back to hunt him later on in life in the form of crippling

insomnia.

This week on the show, we continue to look at sleep and explore one of the greatest mysteries

in human behavior.

Nature has endowed us with an amazing brain.

So why in the world would nature have that very same brain put itself to sleep for one

third of our lives?

If we didn't need 8 hours of sleep and we could survive on 6, Mother Nature would have

done away with 25% of our sleep time millions of years ago.

Because when you think about it, sleep is an idiotic thing to do.

If sleep does not provide a remarkable set of benefits, then it's the biggest mistake

the evolutionary process has ever made.

Matthew Walker is a professor of neuroscience and psychology at the University of California

at Berkeley.

He studies sleep and he's the author of the book Why We Sleep?

I started our conversation by asking him to tell me a story he describes in his book.

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