Laughter: We do it spontaneously, we do it forcefully, we do it with each other and by ourselves. But why did we evolve to giggle in the first place?

Emily and Regina explore the evolutionary underpinnings of laughter — from chimpanzees to modern-day humans — and the ways it unites us.

Keep laughing with us on Twitter — we're at @NPRShortWave — or email the show at shortwave@npr.org.

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