Kissing did not begin with tragically infatuated human couples, but with the primate ancestors of great apes around 20 million years ago, a recent study shows.
Researchers from the University of Oxford and the Florida Institute of Technology wanted to examine when kissing began, given that, from an evolutionary point of view, it has no obvious survival benefit and can spread disease.
However, humans, chimpanzees, bonobos, orangutans and gorillas all kiss, strongly suggesting that the habit was inherited from a common ancestor. In the study, scientists combined observations of primate behavior with data on evolutionary relationships to "turn back the clock" and try to date the first kiss, Reuters reports.
"Using these two key types of data, we applied modeling that allowed us to simulate different evolutionary scenarios," said lead author Matilda Brindle from the Department of Biology at the University of Oxford.
Running the model millions of times placed that first kiss between 21,5 and 16,9 million years ago.
The results were published in the journal Evolution and Human Behavior.
Scientists have defined kissing rather unromantically as "non-aggressive, mouth-to-mouth contact that does not involve the exchange of food." This includes sexual kissing, but also platonic kisses, such as those between family members or in friendly greetings. How kissing originated remains a matter of debate, as does why it has persisted.
"Some suggest that sexual kissing is a useful way to assess the quality or suitability of a partner," Brindle said. "Alternatively, kissing may be a form of foreplay, which heightens sexual arousal and increases the chance of fertilization."
Platonic kisses are thought to be used to navigate complex social relationships or strengthen attachments, she said.
The study argues that Neanderthals and humans probably also kissed, given evidence that they interbred and shared an oral microbe – a sign that they exchanged saliva – long after the two species split 450.000–750.000 years ago.
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