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From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Currently, researchers suggest that ancient hominins did it too – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. In earlier research, scientists have found modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, explaining that the concept aligned with research that has revealed people of non-African ancestry have bits of Neanderthal DNA in their genome, revealing interbreeding was at play.

Romantic Spin

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

Writing in the publication Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not restricted by how people smooch.

Describing Kissing

"There have been some efforts 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 know that they likely engage, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish called certain marine animals.

As a result the team developed a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but no transfer of nutrition.

Research Methods

The lead researcher explained they concentrated on reports of intimate behavior in non-human species from Africa and Asian regions, including bonobos, apes and orangutans, and used digital recordings to confirm the reports.

The researchers then combined this data with information on the evolutionary relationships between living and extinct types of such animals.

Historical Timeline

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

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a kiss, the scientists conclude. But the activity might not have been confined to their own species.

"The fact that humans kiss, the reality that we now have demonstrated that Neanderthals very likely engaged, suggests that the two [species] are probably did engage," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert explained intimate contact could be used in sexual contexts to possibly increase reproductive success or assist in selecting between mates, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of primates commented that as intimate contact was observed in a broad spectrum of primates it made sense its origins lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a wider variety of animals might push its origins back even earlier still.

"Things that we think of as signatures of our species, like intimate contact, are not unique to us if we examine carefully at different species," the expert noted.

Cultural Aspects

An archaeology expert explained that kissing had a social component as it was not common to all societies.

"Nonetheless, as people we thrive or fail on the quality of our relationships, and ways of promoting trust and intimacy will have been significant for eons," the professor stated. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but really it should be expected that Neanderthals – and even Neanderthals and our own species together – kissed."