Scientists Reveal the Origin of Kissing

It seems that kissing is an age-old practice, spanning back 21 million years. This is the finding of University of Oxford and Florida Institute of Technology (FIT) researchers who have unearthed evidence that kissing evolved in the shared ancestors of humans and large apes around this time. In fact, they say, it seems likely that our cousins the Neanderthals liked a smooch, too. The practice of kissing can be observed across the animal kingdom, but exactly how it arose, the team explained, presents something of an “evolutionary puzzle, since the fitness benefits are unclear.” “While kissing may seem like an ordinary or universal behavior, it is only documented in 46 percent of human cultures,” said study author Catherine Talbot, psychology professor at FIT, in a statement. “The social norms and context vary widely across societies, raising the question of whether kissing is an evolved behavior or cultural invention. This is the first step in addressing that question.” Orangutan kissing another orangutan. | Getty Images/olga_gl “This is the first time anyone has taken a broad evolutionary lens to examine kissing. Our findings add to a growing body of work highlighting the remarkable diversity of sexual behaviors exhibited by our primate cousins,” added study author and evolutionary biologist Matilda Brindle of Oxford in a statement. The team used a cross-species approach based on the primate family tree, defining kissing as “non-aggressive, mouth-to-mouth contact that did not involve food transfer.” They deterimined that kissing is an ancient trait in the large apes, evolving in an ancestor of that group 21.5–16.9 million years ago. It was retained over time and is still present in most of the large apes. The researchers also found the Neanderthals—archaic humans that went extinct around 40,000 years ago—were likely to have engaged in kissing, adding to previous evidence that humans and Neanderthals shared oral microbes (via saliva transfer) and genetic material (via interbreeding). In their study, the team collected data on modern primate species that had been observed kissing, focusing on the group of monkeys and apes that evolved in Africa, Europe and Asia. This included chimpanzees, bonobos and orangutans. Further analysis included treating kissing as a ‘trait,’ mapping this to the family tree of primates and using a statistical approach to simulate different evolution scenarios to estimate whether ancestors also engaged in kissing. This was run 10 million times to give “robust statistical estimates,” the team reported. “By integrating evolutionary biology with behavioral data, we’re able to make informed inferences about traits that don’t fossilise—like kissing. This lets us study social behavior in both modern and extinct species,” said study author Stuart West, professor of evolutionary biology at Oxford. The researchers acknowledge that existing data are limited—particularly outside the large apes—but added the study offers a framework for future work including a consistent kissing definition for primatologists to record these behaviors in nonhuman animals. Newsweek has reached out to the researchers for additional comment. Do you have a tip on a science story that Newsweek should be covering? Do you have a question about kissing evolution? Let us know via science@newsweek.com. Bergström, A., Stringer, C., Hajdinjak, M., Scerri, E. M. L., & Skoglund, P. (2021). Origins of modern human ancestry. Nature, 590(7845), 229–237. https://doi.org/10.1038/s41586-021-03244-5 Brindle, M., Talbot, C. F., & West, S. (2025). A comparative approach to the evolution of kissing. Evolution and Human Behavior, Advance online publication. https://doi.org/10.1016/j.evolhumbehav.2025.106788 Weyrich, L. S., Duchene, S., Soubrier, J., Arriola, L., Llamas, B., Breen, J., Morris, A. G., Alt, K. W., Caramelli, D., Dresely, V., Farrell, M., Farrer, A. G., Francken, M., Gully, N., Haak, W., Hardy, K., Harvati, K., Held, P., Holmes, E. C., … Cooper, A. (2017). Neanderthal behaviour, diet, and disease inferred from ancient DNA in dental calculus. Nature, 544(7650), 357–361. https://doi.org/10.1038/nature21674