Researchers mapped non-aggressive, food-free mouth-to-mouth contact across primates and used evolutionary modelling to estimate that kissing likely originated in a large ape ancestor about 21.5–16.9 million years ago. The behaviour appears retained in most great apes and may have been practised by Neanderthals. Although biologically ancient, kissing is documented in only about 46% of human cultures, highlighting an interplay between evolutionary roots and cultural variation.
Study Suggests Romantic Kissing Originated in a Common Great-Ape Ancestor ~21 Million Years Ago
Researchers mapped non-aggressive, food-free mouth-to-mouth contact across primates and used evolutionary modelling to estimate that kissing likely originated in a large ape ancestor about 21.5–16.9 million years ago. The behaviour appears retained in most great apes and may have been practised by Neanderthals. Although biologically ancient, kissing is documented in only about 46% of human cultures, highlighting an interplay between evolutionary roots and cultural variation.
04:18 PM, 11/19/2025Science
Researchers reconstructed the evolutionary history of kissing and found evidence that mouth-to-mouth contact likely first appeared in a large ape ancestor roughly 21.5–16.9 million years ago. The team — led by evolutionary biologist Matilda Brindle and colleagues — mapped non-aggressive, food-free mouth-to-mouth contact across primate species and used computer simulations on a primate family tree to estimate when the behaviour first evolved.
Observations of kiss-like behaviours exist across a range of animals, from chimpanzees, bonobos and gorillas to some reports in dogs, cats and dolphins. To focus on the origins of human kissing, the researchers compiled verified observations of primates (particularly African, European and Asian monkeys and apes such as chimpanzees, bonobos and orangutans) engaging in non-aggressive mouth-to-mouth contact that did not involve food exchange.
The team then mapped this trait onto a primate phylogeny and ran simulations to estimate the likelihood that ancestral lineages displayed the behaviour. Their models indicate a high probability that the trait emerged in a prehistoric large ape lineage about 21.5 million years ago and was retained in most descendant great apes, including gorillas and humans. The analysis was published in the journal Evolution and Human Behaviour.
"This is the first time anyone has taken a broad evolutionary lens to examine kissing," said Matilda Brindle, lead author and evolutionary biologist. "Our findings add to evidence of the remarkable diversity of social and sexual behaviours across primates."
The study also suggests Neanderthals probably engaged in similar mouth-to-mouth contact. Supporting this, analyses of oral bacteria from early humans and Neanderthals indicate patterns consistent with saliva exchange between the species, which could reflect direct mouth-to-mouth contact.
Authors defined a kiss operationally as non-aggressive mouth-to-mouth contact without transfer of food. They emphasize that while the behaviour appears to be evolutionarily old, cultural expression varies: previous surveys report that only about 46% of human cultures document romantic kissing. That variation raises important questions about how biological tendencies and cultural practices interact.
The authors note limitations: observational gaps for many species, possible reporting bias, and the difficulty of distinguishing affectionate kissing from other mouth-related behaviours. They call for more systematic observations across under-studied primates and further investigation of microbial evidence to refine the evolutionary picture.
Implications: The study provides a framework to explore whether romantic kissing reflects an inherited social behaviour that was retained in some lineages and modified by culture, or whether culture plays the dominant role in shaping how mouth-to-mouth contact is expressed among humans today.