The act of kissing is something we only really associate with our own species, but the practice has been observed in many modern primates; chimpanzees, macaques, baboons, and more have all been documented planting kisses on others of their kind.
This observation inspired a team of researchers from the University of Oxford, University College London, and Florida Institute of Technology to conduct a study into the origin of kissing, not only to find out when our ancestors started kissing, but who were the first to do it.
What animal was the first to kiss?
Prior to their investigation, the team had to determine a definition of ‘kissing’, specifically one that could be distinguished from animals simply smacking their lips together during other, less intimate interactions, such as kiss-fighting in fish and the mouth-to-mouth transfer of fluids between ants and other social insects, known as trophallaxis.
They ultimately concluded that kissing is “a non-agonistic interaction involving directed, intraspecific (between the same species), oral-oral contact with some movement of the lips/mouthparts and no food transfer.”
Using this as a definition, the team collected lots of observational data from a series of modern primate studies and plugged it into a model that allowed them to reconstruct the evolutionary history of kissing.
They found the act of kissing can be traced all the way back to the last common ancestor of humans and other great apes, which lived roughly 21.5 to 16.9 million years ago. They also found Neanderthals, our closest extinct relatives, probably kissed too.
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This particular finding backs up a study from 2017 that suggested Neanderthals and Homo sapiens may have kissed one another. The study compared microbes preserved in the dental plaque of a Neanderthal who lived 48,000 years ago with those found in the mouths of humans and found some startling similarities.
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It’s also reasonable to assume Neanderthals and Homo sapiens ‘made out’ during the mating sessions they’re known to have engaged in.
Interestingly, the team found Eastern gorillas, unlike Western gorillas and all other great apes, don’t practice kissing. They also found the ancestors of macaques and baboons didn’t kiss, suggesting the act evolved separately in these groups.
It’s unclear exactly why our ancestors started kissing. Some suggest it strengthens social bonds, increases reproductive success, and maybe even boosts immunity via the exchange of microbes. However, others have warned of its serious downsides, such as the spread of potentially deadly diseases.
The researchers involved with this latest study think kissing may have evolved from the practice of premastication, an act of feeding where a parent will pre-chew food before transferring it to an expecting infant, usually via mouth-to-mouth contact. This behaviour may have, over the course of many generations, evolved into the act of kissing.
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