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From seabirds to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Oral Evidence

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were closely connected. In earlier research, researchers have discovered modern people and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the idea aligned with research that has found people of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"It certainly puts a different spin on ancient interactions," the lead researcher commented.

Publishing in the journal a scientific periodical, the researcher and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a description that was not limited to how humans smooch.

Defining Intimate Contact

"There have been some efforts to define a kiss, but it's largely human-centric, which means that basically non-human species do not engage in this. Currently we understand that they likely engage, it might just not look from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she noted some behaviors that resembled kissing were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species called French grunts.

As a result the research group came up with a description of intimate contact based on social behaviors involving intentional oral interaction with a member of the identical group, with some motion of the mouth but no transfer of food.

Research Approach

The lead researcher explained they focused on accounts of kissing in primates from the African continent and Asian regions, including primates, apes and orangutans, and used digital recordings to confirm the observations.

Scientists then combined this information with information on the evolutionary relationships between living and ancient types of such primates.

Evolutionary Timeline

The team propose the results indicate kissing developed approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists conclude. But the activity might not have been confined to their specific group.

"Reality that modern people engage intimately, the reality that we now have demonstrated that ancient relatives very likely engaged, indicates that the two [species] are probably did engage," the researcher added.

Evolutionary Significance

While the evolutionary explanation is discussed, Brindle said kissing could be used in sexual contexts to potentially enhance mating outcomes or assist in selecting between partners, while it could assist strengthen connections when used in a platonic way.

A separate researcher in the activities of great apes said that as intimate contact was observed in a broad spectrum of primates it was logical its roots lie deep in our ancient history, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back further still.

"Things that we think of as characteristics of human life, like kissing, are not unique to us if we look closely at different species," he said.

Cultural Aspects

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

"However, as people we thrive or fail on the strength of our relationships, and methods of encouraging trust and intimacy will have been important for eons," she said. "This could represent an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be no surprise that Neanderthals – and even Neanderthals and our human ancestors collectively – engaged intimately."