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From seabirds to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Currently, scientists propose that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were intimately acquainted. Among previous studies, researchers have discovered humans and their Neanderthal relatives possessed the same mouth microbe for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were kissing," the researcher noted, adding that the idea aligned with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genome, revealing genetic mixing was at play.

Intimate Interpretation

"This offers a different spin on ancient interactions," the lead researcher said.

Writing in the journal a scientific periodical, Brindle and her team detail how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how people smooch.

Describing Kissing

"Previously there were some previous attempts to define a kiss, but it's largely focused on humans, which implies that essentially non-human species do not engage in this. Now we understand that they probably do, it might just not look from what human kissing looks like," explained the evolutionary biologist.

However, she noted some actions that looked like intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", seen in aquatic species called certain marine animals.

Consequently the research group developed a description of kissing based on friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but absence of nutrition.

Study Methods

The lead researcher explained they concentrated on accounts of intimate behavior in non-human species from the African continent and Asian regions, including primates, apes and great apes, and employed digital recordings to verify the observations.

Scientists then integrated this data with information on the genetic connections between extant and ancient species of such animals.

Historical Timeline

The team say the findings indicate intimate contact developed approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of Neanderthals on this family tree means it is likely they, too, engaged in a intimate act, the researchers say. But the activity may not have been confined to their specific group.

"Reality that humans engage intimately, the fact that we now have shown that ancient relatives very likely kissed, indicates that the two [species] are also likely to have engage," Brindle noted.

Biological Importance

Although the scientific reasoning is discussed, Brindle explained kissing could be used in reproductive situations to possibly enhance reproductive success or help choose between mates, while it could assist strengthen connections when used in a platonic way.

A separate researcher in the behavior of primates commented that as kissing behavior was seen in a broad spectrum of primates it was logical its roots lie deep in our evolutionary past, and an examination of various types of kissing among a broader range of species might push its origins back even earlier still.

"Behaviors that we think of as signatures of human life, like kissing, are not exclusive to us if we examine carefully at different species," the expert noted.

Social Elements

Another professor explained that intimate contact had a cultural element as it was not universal to all human groups.

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging trust and intimacy will have been significant for millions of years," the professor stated. "This could represent an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and even Neanderthals and our own species collectively – engaged intimately."