A new study reconstructs the evolutionary origins of kissing, arguing the behavior evolved more than 21 million years ago and was likely present in the common ancestor of humans and other great apes.

Lead author Dr. Matilda Brindle frames the work as applying an evolutionary lens to a behavior rarely fossilized, underscoring primate diversity in sexual behaviors.

The authors call for more observational data from wild and captive populations to test competing hypotheses about kissing’s adaptive benefits across species and contexts.

The research is published in Evolution and Human Behavior in 2025, with DOI 10.1016/j.evolhumbehav.2025.106788.

The article stresses the need for richer context in documentation—such as whether kisses are romantic or platonic, who participates, and timing with feeding or mating—to refine evolutionary interpretations.

The paper provides a standardized framework for primatologists to record kissing in nonhuman animals and outlines a path for future cross-species behavioral research.

Positioned as the first broad evolutionary analysis of kissing, the work offers a framework for future cross-species inquiry into this behavior.

Acknowledging sparse data outside large apes, the study advocates a standardized recording framework to aid future research on kissing in nonhuman species.

Co-author Prof. Stuart West notes that integrating evolutionary biology with behavioral data enables inferences about traits that do not fossilize, like kissing.

Researchers define kissing as non-aggressive mouth-to-mouth contact without food transfer to ensure cross-species comparability.

While its exact function remains debated, hypotheses include mate assessment, foreplay to boost fertilisation chances, and platonic bonding to navigate social relationships.

The study notes limitations such as reliance on recorded behaviors and simulations rather than direct observation, with sparse data beyond great apes and results sensitive to model assumptions.