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From Galápagos albatrosses to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Now, researchers suggest that ancient hominins did it too – and possibly exchanged kisses with modern humans.

Common Oral Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. In earlier research, scientists have discovered modern people and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," she said, adding that the concept chimed with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was occurring.

Intimate Interpretation

"This offers a more romantic spin on ancient interactions," Brindle commented.

Publishing in the journal Evolution and Human Behavior, the researcher and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not limited to how people kiss.

Describing Intimate Contact

"Previously there were some efforts to define a intimate act, but it's very much been human-centric, which means that basically other animals don't kiss. Currently we know that they likely engage, it might just not look from what our intimate contact looks like," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "kiss-fighting", observed in aquatic species called French grunts.

As a result the team came up with a definition of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a member of the same species, with some motion of the oral area but absence of food.

Research Approach

The lead researcher said they focused on accounts of kissing in non-human species from the African continent and Asia, including primates, apes and great apes, and employed digital recordings to confirm the reports.

Scientists then combined this information with details on the genetic connections between extant and extinct types of such primates.

Evolutionary Timeline

The team say the results suggest intimate contact evolved somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers say. But the activity might not have been limited to their specific group.

"The fact that modern people kiss, the fact that we currently have shown that Neanderthals very likely engaged, indicates that the two [species] are probably did kissed," the researcher added.

Evolutionary Importance

While the scientific reasoning is discussed, the expert said intimate contact could be used in reproductive situations to potentially increase mating outcomes or help choose between mates, while it could assist reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of primates commented that as intimate contact was observed in a wide range of apes it was logical its origins extend far into our ancient history, and an analysis of various types of intimate behavior among a wider variety of species might extend its beginnings back even earlier still.

"Behaviors that we think of as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Social Aspects

Another professor explained that kissing had a social component as it was not universal to all societies.

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and ways of promoting confidence and intimacy will have been important for millions of years," she said. "It might be an image that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be no surprise that ancient hominins – and including Neanderthals and our human ancestors together – engaged intimately."