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From Galápagos albatrosses to polar bears, primates to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers propose that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance experts have proposed ancient relatives and early modern humans were intimately acquainted. In previous studies, researchers have discovered modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, implying they swapped saliva.

"Probably they were engaging in intimate contact," she said, explaining that the concept chimed with research that has found people of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating interbreeding was occurring.

Intimate Interpretation

"It certainly puts a more romantic perspective on ancient interactions," Brindle commented.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues report how, to investigate the historical roots of kissing, they first had to come up with a description that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's very much been focused on humans, which implies that basically non-human species don't kiss. Now we understand that they probably do, it might just not look from what our intimate contact looks like," said Brindle.

However, she said some actions that looked like intimate contact were something rather different – such as the chewing and food sharing, or "mouth contact", observed in fish known as French grunts.

Consequently the team developed a description of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but no transfer of nutrition.

Study Approach

Brindle said they focused on reports of kissing in non-human species from Africa and Asian regions, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

The researchers then integrated this information with details on the genetic connections between extant and extinct types of such animals.

Evolutionary Timeline

Researchers say the findings indicate intimate contact evolved somewhere between 21.5m and 16.9 million years ago in the ancestors of the great primates.

Placement of ancient hominins on this family tree suggests it is probable they, too, indulged in a intimate act, the researchers say. But the behavior may not have been limited to their own species.

"The fact that humans engage intimately, the reality that we currently have demonstrated that Neanderthals probably engaged, suggests that the both groups are probably did engage," Brindle added.

Evolutionary Importance

While the evolutionary explanation is debated, the expert said intimate contact could be used in sexual contexts to possibly enhance mating outcomes or assist in selecting between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as intimate contact was seen in a broad spectrum of primates it made sense its origins lie deep in our ancient history, and an examination of various types of kissing among a broader range of species might extend its origins back even earlier still.

"Things that we consider as characteristics of human life, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Cultural Elements

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

"Nonetheless, as humans we thrive or fail on the strength of our emotional bonds, and methods of promoting confidence and closeness will have been significant for eons," the professor stated. "It might be an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but really it should be expected that ancient hominins – and even Neanderthals and our own species together – kissed."