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Why do we kiss? It's an evolutionary conundrum

NPR | By Emily Kwong,

Hannah Chinn, Rebecca Ramirez

Published February 13, 2026 at 9:46 AM EST

A pair of chimpanzees kiss. Modern primates have been observed kissing in both platonic and sexual contexts ... but what does that tell scientists about how kissing might have evolved?

The evolutionary purpose of kissing has long eluded scientists. Smooching is risky, given things like pointy teeth, and inherently gross, given an estimated 80 million bacteria are transferred in a 10 second kiss. And yet, from polar bears to humans, albatrosses and prairie dogs, many animals kiss. So, what gives? Evolutionary biologist Matilda Brindle tells us the sordid details driving this behavior, what distinguishes different kinds of kissing and whether culture has anything to do with why people kiss.

Interested in more of the science behind love and connection? Email us your question at shortwave@npr.org.

Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.

The evolutionary purpose of kissing has long baffled scientists.

Smooching is risky (teeth) and inherently gross (80 million bacteria are estimated to be transferred in a 10 second kiss). And yet, many animals kiss, from polar bears to albatrosses to prairie dogs.

What gives?

We speak with evolutionary biologist Matilda Brindle at the University of Oxford on what may drive this behavior, what distinguishes different kinds of kissing, and whether culture has anything to do with it.

For more on how Matilda traced kissing through the primate family tree, check out this episode.

Interested in more of the science behind love and connection? Email us your question at shortwave@npr.org.

Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.

Listen to Short Wave on Spotify and Apple Podcasts.

This episode was produced by Hannah Chinn. It was edited by Rebecca Ramirez. Tyler Jones checked the facts. The audio engineer was Robert Rodriguez.