Why Do We Kiss? (Most Cultures Don't)

Why do we kiss? It feels like the most natural thing in the world, yet fewer than half of the world's cultures kiss romantically. In the early 2000s, a psychologist counted which way couples turned their heads at airports, and what he found pointed to the months before any of them were born. In this episode: kissing chimps and bonobos, a 20-million-year-old habit, Neanderthal mouth microbes, your brain's touch map, three competing theories, the "first kiss test", the germs a single kiss swaps, and why the direction of a kiss may be settled in the womb. Subscribe to Why Theory for animated answers to the questions you never thought to ask. Chapters 0:00 Counting kisses at the airport 0:31 Why do humans kiss at all? 0:47 Most cultures don't 1:13 Apes, Neanderthals and 20 million years 1:52 Ancient and optional 2:00 The lips and the brain's touch map 2:27 Feeding, smell or grooming? 3:05 The first-kiss test 3:26 The cost: germs 3:54 Back to the airport: two out of three turn right 4:17 I choose you Sources Güntürkün, O. (2003). Adult persistence of head-turning asymmetry. Nature. https://doi.org/10.1038/421711a Jankowiak, W. et al. (2015). Is the romantic-sexual kiss a near human universal? American Anthropologist. https://doi.org/10.1111/aman.12286 University of Oxford (2025). Ape ancestors and Neanderthals likely kissed. https://www.ox.ac.uk/news/2025-11-19-... Weyrich, L. S. et al. (2017). Neanderthal behaviour, diet, and disease inferred from ancient DNA in dental calculus. Nature. https://doi.org/10.1038/nature21674 Wedekind, C. et al. (1995). MHC-dependent mate preferences in humans. Proc. R. Soc. B. https://doi.org/10.1098/rspb.1995.0087 Hughes, S. M. et al. (2007). Sex differences in romantic kissing among college students. Evolutionary Psychology. https://www.semanticscholar.org/paper... Kort, R. et al. (2014). Shaping the oral microbiota through intimate kissing. Microbiome. https://doi.org/10.1186/2049-2618-2-41 Arbøll, T. P. & Rasmussen, S. L. (2023). The ancient history of kissing. Science. https://doi.org/10.1126/science.adf0512 #science #psychology #evolution