Researchers at the University of Oxford, Oxford, England, traced the evolutionary origins of kissing and described their work on Evolution and Human Behavior as the first attempt to reconstruct its history across species.

The researchers compiled evidence of kissing behavior across primates using their scientific definition of a kiss as a “nonagonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips/mouthparts and no food transfer.”

The researchers then compiled a list of animal species in which such kisses were observed. Humans kiss (even if the practice of kissing is not shared by all civilizations).

Other great ape species, such as chimpanzees, gorillas, and orangutans kiss, with chimpanzees and bonobos being the most adept at this type of contact, not hesitating to use their tongues.

Researchers have observed that apes can kiss platonically, sexually, or as a gesture of reconciliation. Two male gorillas were seen interrupting their mating to kiss, while chimpanzees may kiss on the mouth to end an argument.

Furthermore, tailed monkeys from Africa and Asia, such as rhesus macaques, Macaca fascicularis, and baboons, have also been observed kissing. Surprisingly, primatologists indicated that these embraces were primarily observed during sexual relations between animals of the same sex proving that same-gender attraction is not unnatural.

In nonhuman primates, kissing has been observed in most large apes and some Afro-Eurasian monkeys. Similar behaviors that are sometimes termed kissing, but which do not meet all the criteria from the definition, have been observed in a diversity of other organisms including mammals, birds, fish and even insects.

According to the lead author Matilda Brindle, PhD from the Department of Biology, University of Oxford, Life and Mind Building, Oxford, kissing has persisted throughout evolution and is still present in most great apes. Our findings add to the growing body of research highlighting the remarkable diversity of sexual behavior observed in our primate cousins.

The analysis also examined extinct species. Using Bayesian interpolation, the authors noted that kissing occurs in most extant large apes, and occurred in Neanderthals (Homo neanderthalensis), first evolving in the ancestor to this group approximately 21.5-16.9 million years ago.

This interpretation aligns with earlier research showing that modern humans and Neanderthals shared “commensal oral microbes,” a pattern consistent with close oral contact, although parental feeding or food sharing could also contribute.

“We hope that our results provide a useful starting point for further research into the adaptive function of kissing that highlights hypothesis generation and testing within a phylogenetic framework,” the authors concluded.

This story was translated and adapted from JIM, part of the Medscape Professional Network.