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Among seabirds to polar bears, primates to great apes, certain species appear to kiss. Now, scientists suggest that ancient hominins did it too – and possibly locked lips with modern humans.

Shared Microbial Evidence

It is not the first time experts have suggested Neanderthals and Homo sapiens were closely connected. In previous studies, researchers have discovered modern people and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were kissing," she said, explaining that the idea chimed with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genome, revealing interbreeding was occurring.

Romantic Spin

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

Publishing in the publication Evolution and Human Behavior, the researcher and her team detail how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not limited to how humans smooch.

Describing Intimate Contact

"Previously there were some efforts to define a kiss, but it's largely human-centric, which means that basically non-human species don't kiss. Currently we understand that they probably do, it may appear different from what human kissing resembles," explained Brindle.

However, she noted some actions that resembled intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

Consequently the research group came up with a definition of kissing based on friendly interactions involving intentional oral interaction with a individual of the same species, with some movement of the mouth but absence of food.

Research Approach

Brindle explained they focused on accounts of kissing in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and used digital recordings to confirm the reports.

The researchers then combined this information with details on the evolutionary relationships between extant and extinct species of such animals.

Historical Timeline

The team propose the results suggest kissing developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this family tree means it is probable they, too, indulged in a kiss, the researchers conclude. But the activity might not have been limited to their own species.

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

Evolutionary Significance

While the scientific reasoning is discussed, the expert explained kissing could be employed in sexual contexts to possibly increase reproductive success or assist in selecting between partners, while it might help reinforce bonding when used in a platonic way.

Another expert in the activities of great apes 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 examination of different forms of kissing among a broader range of species might push its origins back further still.

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

Social Aspects

Another professor explained that kissing had a cultural element as it was not common to all societies.

"Nonetheless, as humans we thrive or fail on the strength of our emotional bonds, and ways of promoting confidence and intimacy will have been significant for eons," she said. "It might be an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be no surprise that ancient hominins – and including them and our human ancestors together – engaged intimately."