November 19, 2025
3 minute read
Kissing may have originated 21.5 million years ago
Humans and their ancestors have probably been kissing for a very long time.
Photo by Stefano Bianchetti/Getty Images; Illustration Scientific American
For humans, kissing has important cultural significance, accompanying declarations of romantic love, religious rituals of veneration and even betrayal, a la The Godfather Part Two“kiss of death”
A new study suggests that kissing likely predates humanity, originating between 16.9 and 21.5 million years ago, after ancestor of great apes separated from the lower apes or gibbons. There is even evidence that Neanderthals kissed.
“Kissing is really interesting because people seem to take it for granted,” says study lead author Matilda Brindle, an evolutionary biologist at the University of Oxford. Surprisingly, romantic kissing has been documented. in only 46 percent of human culturesshe says. “But for those who kiss, this everyday act also has enormous cultural significance.”
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Brindle and her colleagues, Catherine Talbot of the Florida Institute of Technology and Stuart West of Oxford, wanted to evaluate kissing from an evolutionary perspective. So they searched past research for contemporary examples of primate kissing, defined rather unromantically as “a non-agonistic interaction involving directed, intraspecific, oral-oral contact with some lip/oral movement and no food transfer.” They found that, like humans, apes kiss for a variety of reasons, from conveying sexual desire to expressing friendly, affectionate feelings.
“When chimpanzees fight,” she says, “they often go and literally kiss and then make up.”
The researchers also found messages about kisses in all great apes, from humans to chimpanzees and orangutans, with the exception of the eastern gorilla. There have been no observations of gibbons kissing. Based on this taxonomy, researchers estimate that kissing evolved after apes split from the great apes. This means that Neanderthals and other human ancestors probably kissed. This idea is supported by preliminary data on DNA in ancient dental plaques, showing that Neanderthals and humans shared oral bacteria to 112,000 years ago, hinting that they may have kissed each other.
However, observations of primate kissing have been too fragmentary to reveal much about how and why kissing evolved. Species that kiss tend to have mating systems in which females mate with multiple males, researchers report in a new study published in the journal. Evolution and human behavior. According to Brindle, every species that kisses also engages in pre-chewing, or chewing, of food before passing it to another individual, which may be a precursor to kissing. However, data on pre-chewing in non-kissing species is sparse, making the association tenuous.
It's also unclear whether platonic and sexual kissing have the same roots, says Zanna Clay, a comparative psychologist at Durham University in England who studies primate behavior but was not involved in the study. Kissing during mating is observed less frequently than affectionate kissing in the wild, Clay says: “This study works with a relatively limited data set.”
Primate researchers haven't paid much attention to primate kissing, Brindle agrees, saying the paper is a “call” for researchers to collect more data. “It's really interesting that we traced the evolutionary history of kissing back to 21.5 million years ago,” she says, “but we could do a lot more if we had more data.”
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