Short Wave Why do we kiss? It's an evolutionary conundrum
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Feb 13, 2026 
Matilda Brindle, an evolutionary biologist at Oxford who studies primate social and sexual behaviour, explores why mouth-to-mouth contact evolved. She covers surprising kissing across animals. She traces deep primate origins. She contrasts platonic and sexual kissing and considers mate assessment, microbiome sharing, bonding and cultural learning.
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Kissing Is Evolutionarily Puzzling
- Kissing transfers huge amounts of bacteria and feels unhygienic, making it an evolutionary puzzle.
- Matilda Brindle highlights ~80 million bacteria exchanged in a 10-second kiss as surprising evidence.
Polar Bears' Frothy 'Kisses'
- Matilda Brindle describes polar bears engaging in frothy mouth-to-mouth contact that looks like kissing.
- She warns it's unsettling footage and recommends watching it away from meals.
A Broad Scientific Definition Of Kissing
- Kissing is defined broadly as non-agonistic, intraspecific oral contact with lip or mouth movement and no food transfer.
- This wide definition lets researchers compare kissing across species that lack human-like lips.